Exploiting the Pyrazole-Carboxylate Mixed Ligand System in theCrystal Engineering of Coordination PolymersPublished as part of the Crystal Growth & Design virtual special issue IYCr 2014 - Celebrating the InternationalYear of Crystallography

Chris S. Hawes,†,‡ Boujemaa Moubaraki,† Keith S. Murray,† Paul E. Kruger,*,‡ David R. Turner,*,†

and Stuart R. Batten*,†,§

†School of Chemistry, Monash University, Clayton, VIC 3800, Australia‡MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Canterbury, Private Bag4800, Christchurch 8140, New Zealand§Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah 22254, Saudi Arabia

*S Supporting Information

ABSTRACT: The utility of the pyrazole-carboxylate mixedligand system has been probed with the synthesis of five newcoordination polymers, derived from bis-pyrazole ligand 4,4′-methylenebis(3,5-dimethyl-1H-pyrazole) H2L1, large semirigiddicarboxylate coligands, and the deliberately designed andsynthesized ligand para-((3,5-dimethyl-1H-pyrazol-4-yl)-methylene)benzoic acid H2L4. Complex poly-[Co(H2L1)-(L2)(OH2)]·1/2H2O 1 features the coligand (S,S)-1,4,5,8-naphthalenetetracarboxylic diimide-N,N′-bis(2-propionate)L2, and comprises chiral two-dimensional sheets, associatingvia substantial π−π stacking interactions. Complexes 2 and 3contain the coligand 1,4-bis((3-carboxyphenyl)methyl)-piperazine L3. Complex poly-[Co(H2L1)2(L3)] 2 is a two-dimensional polymer containing octahedral Co(II) ions, whereasmodifying the synthesis conditions gave complex poly-[Co2(HL1)2(L3)] 3, a three-dimensional α-Po structure containingpyrazolate-bridged dimers of tetrahedral Co(II) ions, displaying weak antiferromagnetic coupling. Magnetic data for complex 3fitted well to a S = 3/2 Heisenberg (−2JS1.S2) dimer model with J = −3.2 cm−1 and g = 2.25. We then prepared the newheteroditopic ligand para-((3,5-dimethyl-1H-pyrazol-4-yl)methylene)-benzoic acid H2L4, and the complexes poly-[Co(HL4)2]·H2O 4 and poly-[Cu(HL4)2]·2MeOH 5, which demonstrate for the first time the tendency of flexible pyrazole-carboxylatecoordination polymers with perfectly commensurate linker dimensions to lead to low-dimensional assemblies. These results givefresh insight into the structural properties of flexible bispyrazole-carboxylic acid systems as a function of coligand dimensions, andprovide new directions for designed polymeric cluster compounds.

■ INTRODUCTION

The notion of predictability has long posed a challenge in thefield of structural chemistry.1 The myriad of weak interactionswhich comprise a crystalline material can be extremely difficultto predict, and great effort has been devoted to ab initioprediction of crystal structures, particularly relevant in the fieldof pharmaceuticals.2−4 Supramolecular chemistry, and coordi-nation polymer chemistry especially, views this problem from aslightly different angle. Prediction of supramolecular structuresis of substantial importance in the construction of extendedcoordination architectures, particularly where properties such asgas sorption or separation are required, which are heavilydependent on the extended solid-state structure of a materi-al.5−7 The design of such systems has been greatly aided by thediscovery of reproducible multicomponent structural motifs,sometimes referred to as secondary building units (SBUs),

which impart well-defined geometrical features to a coordina-tion assembly and greatly simplify the prediction of the networkas a whole.8 The most well-known example of this approachcame from the use of the basic zinc acetate [Zn4O(RCOO)6]motif as a node in coordination polymer construction, leadingto a series of porous coordination polymers displayingisoreticular extended structures.9

As the study of coordination polymer materials continues togrow, the need to continuously explore new ligand classes hasalso expanded. In particular, many of the early carboxylate-based materials suffer from poor hydrolytic stability, a crucialshortcoming for most applications currently in development,

Received: July 4, 2014Revised: September 15, 2014

Article

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© XXXX American Chemical Society A dx.doi.org/10.1021/cg501004u | Cryst. Growth Des. XXXX, XXX, XXX−XXX

leading several studies to suggest that nitrogen heterocycles or amixed-ligand approach may lead to more robust materials.10−14

Pyrazoles in particular have recently enjoyed substantialpopularity as ligands in coordination polymer chemistry, inboth homotopic and heterotopic ligand environments.15−18 Aswell as demonstrating excellent stability when coordinated totransition metal ions, pyrazole possesses great potential forsynthetic functionalization, providing an intriguing basis forcontinued research.19−21

In 2009, extending upon their earlier work, Mondal andcolleagues reported the discovery of a reproducible structuralmotif in a series of pyrazole-carboxylate coordination polymersbased on Zn(II), and later extended to Co(II), consisting of asingle tetrahedral metal ion coordinated by two pyrazolesthrough a nitrogen atom and two carboxylates through anoxygen atom in which N−H···O hydrogen bonds form aroundthe periphery of the coordination sphere (Figure 1).22,23

Subsequent works have cemented the pyrazole-carboxylatemixed ligand system as a useful synthon in coordinationpolymer synthesis, where hydrogen bonding interactions haveplayed a pivotal role in determining the local and extended

structure.24−28 The flexible bis-pyrazole ligand 4,4′-methylenebis(3,5-dimethyl-1H-pyrazole) H2L1 (Figure 2) hasbeen used to great effect in these studies, and the influence of aflexible sp3 methylene bridge between the coordinating groupshas been shown to exert a strong influence on the resultingextended structures. Herein we expand upon current knowl-edge of these systems in two ways: first, three new coordinationarchitectures containing H2L1 are presented, in whichuncommon carboxylate coligands H2L2 and H2L3 (Figure 2)have been used, each containing a long backbone, with flexiblegroups commensurate with that found in H2L1 itself, andrevealing previously unknown structural behavior of the H2L1ligand. Further, we report the synthesis of a new, deliberatelydesigned flexible heterotopic pyrazole-carboxylate ligand, H2L4,which contains the key structural features identified incarboxylate-containing complexes of H2L1, and present twoexamples of H2L4-derived coordination polymers.

■ EXPERIMENTAL SECTIONGeneral Considerations. All reagents, solvents, and starting

materials were purchased from Sigma-Aldrich, Alfa Aesar, or Merckand were used as received. 4,4′-Methylenebis(3,5-dimethyl-1H-pyrazole) H2L1,

29 ethyl 4-bromomethyl benzoate,30 (S,S)-1,4,5,8-naphthalenetetracarboxylic diimide-N,N′-bis(2-propionic acid)H2L2,

31 and 1,4-bis((3-cyanophenyl)methyl) piperazine32 wereprepared according to published procedures. NMR spectra wererecorded on a Bruker AVANCE spectrometer operating at 400 MHzfor 1H and 100 MHz for 13C nuclei (H2L3) or a Varian INOVAinstrument operating at 500 MHz for 1H and 126 MHz for 13C (H2L4and precursors). Melting points were recorded in air on anElectrothermal melting point apparatus, and are uncorrected. Massspectrometry was carried out using a Micromass Platform II ESI-MSinstrument (H2L3) or a Bruker MaXiS 3G UHR-TOF instrument(H2L4 and precursors). Microanalysis was performed by CampbellMicroanalytical Laboratory, University of Otago, New Zealand.Infrared spectra were obtained using an Agilent Cary 630 spectrometerequipped with an attenuated total reflectance (ATR) sampler(complexes 1−3 and 5, H2L3) or a PerkinElmer Spectrum OneFTIR instrument operating in diffuse reflectance mode with samplesdiluted in powdered KBr (complex 4, H2L4, and precursors). Bulkphase purity of all crystalline materials was confirmed with X-raypowder diffraction patterns recorded with a Bruker X8 Focus powderdiffractometer operating at Cu Kα wavelength (1.5418 Å), withsamples mounted on a zero-background silicon single crystal stage.Scans were performed at room temperature in the 2θ range 5−55° andcompared with predicted patterns based on low temperature singlecrystal data (Supporting Information). Thermogravimetric analyseswere carried out with a Mettler-Toledo STARe TGA/DSC instrument(complexes 1 and 5) or a TA Instruments Q600 DSC/TGAinstrument (complex 4). The magnetic susceptibility measurementswere carried out using a Quantum Design SQUID magnetometer

Figure 1. Representative structure of the [M(RCOO)2(HPz)2] motif.Hydrogen atoms not involved in hydrogen bonding omitted for clarity.

Figure 2. Structures of H2L1, H2L2, H2L3, and H2L4 with hydrogen atom numbering scheme for H2L3 and H2L4.

Crystal Growth & Design Article

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MPMS-XL 7 operating between 1.8 and 300 K. Crystalline sampleswere dispersed in Vaseline to avoid torquing of the crystallites. Thesample mulls were contained in a calibrated gelatin capsule held at thecenter of a drinking straw that was fixed at the end of the sample rod.Synthesis of 1,4-Bis((3-carboxyphenyl)methyl)piperazine

H2L3. 1,4-Bis((3-cyanophenyl)methyl)piperazine (450 mg, 1.4mmol) was dissolved in 10 mL of 37% hydrochloric acid solutionand heated to reflux in air for 48 h. On cooling, the white solid wasfiltered and washed with water. This solid was added to 20 mL of 2 Mpotassium hydroxide solution and refluxed for 24 h. The resulting paleyellow solution was diluted to 50 mL with water, and 3 mL of glacialacetic acid was added. After standing for 2 h, colorless crystals of theproduct were isolated by filtration, washed with water and dried invacuo. Yield 219 mg (44%). Microanalysis suggested some associationof atmospheric water with the solid on extended standing in air. mp>300 °C; Found C, 66.65; H, 6.30; N, 7.68; calculated forC20H22N2O4·1/3H2O C, 66.65; H, 6.34; N, 7.77%; δH(400 MHz, d6-DMSO) 2.39 (br s, 8H, H1), 3.52 (s, 4H, H2), 7.43 (t, 2H, J = 7.5 Hz,H5), 7.52 (d, 2H, J = 7.5 Hz, H6), 7.81 (d, 2H, J = 7.7 Hz, H4), 7.87(s, 2H, H3); δC(100 MHz, d6-DMSO) 52.54, 61.52, 127.88, 128.38,129.52, 130.83, 133.15, 138.78, 167.35; m/z (ESMS) 355.1 ([M+H+]100%, calculated for C20H23N2O4 355.2); υmax(ATR)cm

−1 2834m,1672s br, 1590w, 1326m, 1274s sh, 1219m, 1117m, 979m, 746s, 688s.Synthesis of Ethyl-para-((2,4-pentanedion-3-yl)methylene)-

benzoate EtL4acac. Ethyl 4-bromomethyl benzoate (4.86 g, 20mmol) was combined with anhydrous [Co(acac)2] (2.4 g, 10 mmol)in 25 mL chloroform, and the mixture stirred until homogeneous. Thesolution was immersed in an oil bath at 120 °C and the chloroformallowed to evaporate with stirring. The remaining mixture was allowedto stir while maintaining the temperature until a dark green color wasobserved (ca. 30 min), at which time the mixture was cooled andexhaustively extracted with a water/diethyl ether mixture. The organiclayers were combined, washed with dilute hydrochloric acid solution,dried, and evaporated to dryness to give a dark brown oil. The oil waspurified by flash chromatography (5:1 DCM/hexanes) to give a yellowliquid which was found, by comparing the relative peak integrals in the

1H NMR spectra, to comprise both the diketo and keto−enoltautomers in approximately an 8:7 ratio. Yield 2.45 g (47%). δH(500MHz, CDCl3) 1.35−1.39 (overlapping triplets, 6H, J1 = J2 = 7.1 Hz,H1 + H8), 2.03 (s, 6H, H13), 2.12 (s, 6H, H7), 3.17 (d, 2H, J = 7.7 Hz,H5), 3.69 (s, 2H, H12), 4.03 (t, 1H, J = 7.7 Hz, H6), 4.32−4.38(overlapping quartets, 4H, J1 = J2 = 7.1 Hz, H2 + H9), 7.20−7.22(overlapping doublets, 4H, J1 = J2 = 8.3 Hz, H4 + H11), 7.95(overlapping doublets, 4H, J1 = J2 = 8.3 Hz, H3 + H10), 16.83 (s, 1H,H14); δC(125 MHz, CDCl3) 14.53, 23.47, 29.99, 33.22, 34.20, 61.08,61.12, 69.55, 107.94, 127.63, 128.92, 129.00, 129.29, 130.15, 130.18,143.65, 145.35, 166.45, 166.55, 192.15, 203.22; m/z (HR-ESMS)263.1292 ([M+H+], calculated for C15H19O4 263.1283); υmax(KBr)-cm−1 2982m sh, 1718s, 1610m, 1278m, 1106s, 1021s, 943m, 736s.

Synthesis of Ethyl-para-((3,5-dimethyl-1H-pyrazol-4-yl)-methylene)-benzoate EtHL4. Ethyl-para-((2,4-pentanedion-3-yl)-methylene)benzoate (1.80 g, 6.9 mmol) was dissolved in 40 mLmethanol with stirring. To this mixture was added dropwise a solutionof hydrazine hydrate (450 μL, 9 mmol) in 5 mL of methanol. Thesolution was heated at reflux for 24 h, before cooling and evaporatingunder reduced pressure, to give the title compound as a pale yellowsolid. Yield 1.43 g (80%). mp 104−109 °C; δH(500 MHz, CDCl3)1.36 (t, 3H, J = 7.1 Hz, H1), 2.13 (s, 6H, H6), 3.77 (s, 2H, H5), 4.34(q, 2H, J = 7.1 Hz, H2), 7.15 (d, 2H, J = 8.3 Hz, H4), 7.92 (d, 2H, J =8.3 Hz, H3); δC(500 MHz, CDCl3) 11.03, 14.50, 29.19, 61.04, 113.55,128.24, 128.45, 129.89, 142.71, 146.27, 166.82; m/z (HR-ESMS)259.1443 ([M+H+], calculated for C15H19N2O2 259.1447); υmax(KBr)-cm−1 2986s, 1930m, 1720s, 1611m, 1414m, 1277s, 1177s, 1105s,1023m, 854m, 736s.

Synthesis of para-((3,5-Dimethyl-1H-pyrazol-4-yl)-methylene)-benzoic acid H2L4. Ethyl-para-((3,5-dimethyl-1H-pyrazol-4-yl)methylene)-benzoate (1.0 g, 3.8 mmol) was dissolved in40 mL tetrahydrofuran with stirring. To this mixture was added asolution of lithium hydroxide (5 g, 210 mmol) dissolved in 20 mLwater. The resulting suspension was heated at reflux for 24 h, cooled,and concentrated under reduced pressure to remove tetrahydrofuran.

Table 1. Crystallographic Data for Compounds 1−5, H2L3, and H2L4

compound reference 1 2 3 4 5 H2L3 H2L4

Chemical formula C62H60Co2N12O18·H2O

C42H52CoN10O4 C21H25CoN5O2 C26H26CoN4O4·H2O

C26H26CuN4O4·2(CH4O)

C20H22N2O4 C13H14N2O2

Formula Mass 1397.10 819.87 438.39 535.45 586.13 354.40 230.26Crystal System Orthorhombic Monoclinic Monoclinic Monoclinic Triclinic Monoclinic Orthorhombica/Å 15.0516(6) 26.6804(14) 10.954(2) 33.0036(8) 8.0390(16) 9.8442(11) 16.9424(5)b/Å 21.3252(7) 9.0407(5) 13.013(3) 8.55033(11) 9.2100(18) 11.2855(16) 7.4436(2)c/Å 9.1395(3) 17.7821(10) 14.968(3) 21.3589(4) 11.042(2) 7.5036(12) 18.1452(6)α/° 90.00 90.00 90.00 90.00 76.54(3) 90.00 90.00β/° 90.00 107.089(3) 104.00(3) 124.052(3) 72.17(3) 90.709(3) 90.00γ/° 90.00 90.00 90.00 90.00 67.29(3) 90.00 90.00Unit cell volume/Å3 2933.58(18) 4099.8(4) 2070.2(7) 4993.79(17) 711.8(2) 833.6(2) 2288.34(12)Temperature/K 123(2) 123(2) 100(2) 120.0(2) 100(2) 123(2) 123(2)Space group P21212 C2/c P21/n C2/c P1 P21/c PbcaZ 2 4 4 8 1 2 8Radiation source Mo Kα Mo Kα Synchrotron Cu Kα Synchrotron Mo Kα Mo KαReflections measured 111189 13771 38473 27263 11733 6979 47235Independent reflections 8630 4745 5852 5213 3378 2453 2643Observed Reflections((I > 2σ(I))

7533 3163 4318 4528 2797 1281 1863

Rint 0.0635 0.0507 0.0813 0.0365 0.0993 0.0932 0.0605Final R1 values (obs.data)

0.0395 0.0478 0.0505 0.0456 0.0465 0.0598 0.0363

Final wR(F2) values(obs. data)

0.0885 0.0940 0.1144 0.1030 0.1132 0.1119 0.0919

Final R1 values (alldata)

0.0500 0.0916 0.0775 0.0566 0.0591 0.1320 0.0585

Final wR(F2) values (alldata)

0.0945 0.1091 0.1275 0.1106 0.1209 0.1396 0.0996

CCDC Number 1010718 1010719 1010720 1010721 1010722 1010723 1010724

Crystal Growth & Design Article

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The residue was added to 100 mL water and filtered, and the filtrateacidified to pH 3.0 with dilute hydrochloric acid solution, at whichpoint the product precipitated as a white solid, which was filtered anddried in air at 70 °C. Yield 670 mg (76%). mp 242−244 °C; Found C,67.47; H, 6.14; N, 12.10; Calculated for C13H14N2O2 C, 67.81; H,6.13; N, 12.17%; δH(500 MHz, d6-DMSO) 2.04 (s, 6H, H4), 3.72 (s,2H, H3), 7.21 (d, 2H, J = 8.3 Hz, H2), 7.84 (d, 2H, J = 8.3 Hz, H1);δC(125 MHz, d6-DMSO) 10.64, 28.48, 112.61, 128.17, 128.27, 129.42,140.99, 146.80, 167.27; m/z (HR-ESMS) 307.0260 ([M − H+ + 2K+],calculated for C13H13N2O2K2 307.0251); υmax(KBr)cm

−1 3287s, 1682s,1313m, 1291s, 743s, 515s.Synthesis of poly-[Co(H2L1)(L2)(OH2)]·1/2H2O 1. To a 45 mL

Telfon-lined autoclave was added H2L1 (5 mg, 25 μmol), H2L2 (10mg, 24 μmol), and cobalt sulfate heptahydrate (30 mg, 100 μmol)dispersed in 2 mL of water. The autoclave was sealed and heated to130 °C and allowed to dwell at that temperature for 36 h, followed bycooling to room temperature over 6 h. The red crystals of 1 formedwere isolated by filtration and dried in air. Yield 8.6 mg (48%). mp>300 °C; Found C, 53.34; H, 4.54; N, 11.91; Calculated forC31H31N6O9.5Co1 C, 53.30; H, 4.47; N, 12.03%; υmax(ATR)cm

−1

3324w br, 1706m, 1658s, 1576s, 1432w, 1333m, 1247s, 1093w,890m, 770s.Synthesis of poly-[Co(H2L1)2(L3)] 2. A mixture of H2L1 (16 mg,

79 μmol), H2L3 (10 mg, 28 μmol), and cobalt sulfate heptahydrate(20 mg, 71 μmol) suspended in 2 mL of 20 mM sodium hydroxidesolution was added to a 45 mL Telfon-lined autoclave, which washeated to 130 °C and allowed to dwell for 36 h. Following this time,the reaction vessel was cooled to room temperature over a 6 h period,and the pink crystals of the product were isolated by filtration, washedwith water, and dried in air. Yield 18.6 mg (81%). mp >300 °C; FoundC, 61.83; H, 6.47; N, 17.10; Calculated for C42H52N10O4Co C, 61.53;H, 6.39; N, 17.08%; υmax(ATR)cm

−1 3240w, 2802m sh, 1605m, 1555s,1430m, 1378s, 1365s, 1338s, 1273w, 1161m, 1000m, 888s, 789s, 753s,674s.Synthesis of poly-[Co2(HL1)2(L3)] 3. A mixture of H2L1 (16 mg,

79 μmol), H2L3 (10 mg, 28 μmol) and cobalt sulfate heptahydrate (40mg, 140 μmol) suspended in 2 mL of 40 mM sodium hydroxidesolution was added to a 45 mL Teflon-lined autoclave. The reactionvessel was heated to 130 °C and held at that temperature for 36 h, andthen cooled to room temperature over 6 h. The resulting dark purplecrystals were isolated by filtration, washed with water and dried in air.Yield 5.3 mg (43%). mp >300 °C; Found C, 57.78; H, 5.87; N, 16.23;Calculated for C42H50N10O4Co2 C, 57.54; H, 5.75; M, 15.98%;υmax(ATR)cm

−1 2970m br, 1611w, 1546m, 1500m, 1388m sh, 1338m,1296m, 1203m, 1009s, 796s, 756s sh, 680s.Synthesis of poly-[Co(HL4)2]·H2O 4. A mixture of H2L4 (10 mg,

44 μmol) and cobalt sulfate heptahydrate (20 mg, 71 μmol) wereadded to 2 mL of water in a 45 mL Teflon-lined autoclave, to whichwas added one drop of 2,4,6-collidine. The vessel was sealed andheated to 80 °C, and then slowly heated to 120 °C at a rate of 1.5 °C/h, followed by cooling to room temperature at 8 °C/h. The purplecrystalline product was isolated by filtration and dried in air. Yield 4.1mg (35%). mp >300 °C; Found C, 58.29; H, 5.33; N, 10.29; calculatedfor C26H28N4O5Co C, 58.32; H, 5.27; N, 10.46%; υmax(ATR)cm

−1

3450 w br, 2926s br, 1657w, 1595s, 1544s, 1412m, 1388m, 1371s,1300m, 1176m, 1059m, 1018m, 856s, 792w, 747s.Synthesis of poly-[Cu(HL4)2]·2MeOH 5. A slurry of H2L4 (20

mg, 44 μmol) in 5 mL of methanol was added to a solution of coppersulfate pentahydrate (6 mg, 24 μmol) in 14 mL of methanol. Theresulting green turbid mixture was allowed to stand for 1 week,yielding a pure phase of pale purple crystals which were found to losecrystallinity and uptake water on prolonged standing in air. Yield 6.3mg. mp >300 °C; Found C, 53.71; H, 5.32; N, 9.05; calculated forC26H26N4O4Cu·0.75MeOH·3H2O C, 53.53; H, 5.88; N, 9.34%;υmax(ATR)cm

−1 2924m br, 1595s, 1556s, 1355s, 1299m, 1197w,1174m, 1098m, 1065m, 1016m, 911w, 851m, 805w, 769s, 736s.X-ray Crystallography. Crystallographic and refinement data are

presented in Table 1. Data collection for H2L3, H2L4, and complexes1 and 2 was performed on a Bruker APEX-II diffractometer, usinggraphite-monochromated Mo Kα (λ = 0.71073 Å) radiation, while the

diffraction data for complex 4 were collected using an AgilentSuperNova instrument with an Atlas area detector using mirrormonochromated, focused microsource Cu Kα (λ = 1.54184 Å)radiation. Diffraction data for complexes 3 and 5 were collected at theAustralian Synchrotron on the MX1 beamline, operating at 17.4 keV(λ = 0.7108 Å) with data collections conducted using BluIce controlsoftware.33 Data for compounds 3 and 5 were collected with a 360°scan in Φ, and the crystal of complex 5 was remounted in a differentorientation and a second 360° scan in Φ was collected, and the datamerged to provide sufficient completeness. Corrected anomalousdispersion values were calculated where necessary using Brennan andCowan data.34 Diffraction data for H2L3, H2L4, and complexes 1 and2 were processed using the Bruker SAINT suite of programs,35 withmultiscan absorption correction carried out with SADABS,36 while thediffraction data for compound 4 were processed with the CrysAlis Prosoftware suite,37 with multiscan absorption correction carried out withthe SCALE3 ABSPACK algorithm. The remaining diffraction datawere processed, reduced, and corrected with the XDS software suite.38

All structures were solved using direct methods with SHELXS39 andrefined on F2 using all data by full matrix least-squares procedures withSHELXL-9740 within OLEX-2.41 Non-hydrogen atoms were refinedwith anisotropic displacement parameters. Hydrogen atoms weremanually located from residual Fourier difference peaks and restrainedwith D−A distance restraints where appropriate, and otherwise wereincluded in calculated positions. In both cases, hydrogen atomisotropic displacement parameters were fixed at 1.2 or 1.5 times theisotropic equivalent of their carrier atoms dependent on chemicalenvironment. The functions minimized were Σw(F2o − F2c), with w =[σ2(F2o) + aP2 + bP]−1, where P = [max(Fo)

2 + 2F2c]/3. CCDC1010718−1010724.

■ RESULTSSynthesis and Structure of H2L3. Ligand H2L3 was

prepared by hydrolysis of the previously reported dinitrilecompound,32 by heating at reflux for 48 h in concentratedhydrochloric acid, followed by a further 24 h reflux in 2 mol L−1

potassium hydroxide solution. Acidification of the resultingsolution with glacial acetic acid gave a turbid solution whichdeposited colorless crystals within several hours. The diffractiondata obtained were solved and refined in the monoclinic spacegroup P21/c, and the asymmetric unit was found to contain halfof one molecule of H2L3, with the remainder generated by aninversion center located within the piperazine ring. Thestructure shows the expected chair conformation of thepiperazine ring with the benzyl substituent occupying anequatorial position from the ring nitrogen atom (Figure 3).The extended structure of H2L3 is dominated by a strong

hydrogen bonding interaction between the carboxylic acid andpiperazine nitrogen atom of adjacent molecules, with O···Ndistance 2.644(2) Å. The hydrogen atom involved in thisinteraction gave the best crystallographic fit when modeled asbonded to the carboxylic acid oxygen, rather than in azwitterionic form, although pKa considerations would implythat in the solution or gas phase this proton would most likelybe primarily bonded to the piperazine nitrogen atom. Whenallowed to freely refine, the position of hydrogen atom H1converged at an O−H distance of 1.10 Å, and in the final modelthe O−H distance was loosely restrained and converged to anO−H distance of 0.87 Å. Two such interactions occur betweeneach pair of H2L3 units, and extend the structure into a one-dimensional chain running parallel to the crystallographic aaxis. These chains also associate via intermolecular π−πinteractions between pairs of parallel phenyl rings (meaninterplanar distance 3.32 Å), while a number of weak C−H···Ointeractions originating from the piperazine and benzylmethylene groups also permeate the structure.

Crystal Growth & Design Article

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Synthesis and Structure of poly-[Co(H2L1)(L2)(OH2)]·1/2H2O 1. Single crystals of complex 1 were isolated from thereaction between cobalt sulfate heptahydrate, H2L1 and H2L2,under hydrothermal conditions. The red block crystals weresubjected to single crystal X-ray diffraction, and the data weresolved and refined in the chiral orthorhombic space groupP21212. The asymmetric unit of poly-[Co(H2L1)(L2)(OH2)]·1/2H2O 1 contains one Co(II) ion, one molecule of H2L1,which remains protonated in its neutral form, and one moleculeof L2, with both carboxylate groups deprotonated. Thegeometry of the Co(II) ion is best described as distortedoctahedral, coordinated by two pyrazole nitrogen atoms, oneaqua ligand, and two carboxylates, with one each inmonodentate and bidentate chelate coordination modes(Figure 4). Both the H2L1 and L2 linkers join two Co(II)ions each, to give a 2D polymeric assembly. The asymmetricunit also contains one noncoordinating water moleculedisordered across two symmetry-equivalent orientations.Not unexpectedly, the structure of 1 contains extensive

hydrogen bonding interactions. The aqua ligand acts as ahydrogen bond donor in two distinct interactions, forming aseven-membered R1

1(7) hydrogen bonding ring with theadjacent carboxylate ligand through the noncoordinatingcarboxylate oxygen O19, and forming a nine-memberedR11(9) ring by forming a hydrogen bond with the imide oxygen

atom O41 from the other adjacent L2 species.42 In a markeddeparture from the expected behavior, neither of the twopyrazole rings forms a hydrogen bonding interaction withanother ligand attached to the same metal ion. Instead, onepyrazole N−H group forms a hydrogen bond with non-coordinating carboxylate oxygen atom O19 from a nearby metalcenter, while the other pyrazole N−H group donates ahydrogen bond toward the disordered lattice water molecule.This water molecule was modeled as disordered across twosites straddling a twofold rotation axis, participating in threehydrogen bonding interactions and their symmetry equivalents,accepting a hydrogen bond from pyrazole nitrogen atom N3

and donating hydrogen bonds to carboxylate oxygen atom O45and imide oxygen atom O40. The hydrogen bondinginteractions within 1 are shown in Figures S1 and S2(Supporting Information).When extended through the H2L1 and L2 links, the structure

is revealed as a two-dimensional sheet running parallel to the acplane. The (4,4) sheet is defined by one-dimensional zigzagchains of H2L1-linked metal ions passing parallel to the c axis,which are linked and surrounded by helical chains of L2-linkedmetal ions which form the outer layers of each sheet. Thechirality of the structure, originating from the chiral L2 ligand,enforces a left-handed directionality for these helicesthroughout the crystal. The helical chains display a pitch ofapproximately 15 Å, and a diameter of approximately 7 Å,which defines the thickness of the two-dimensional sheetstructure within which the zigzag H2L1 chains propagate(Figure 5). Naphthalene diimides (NDIs) are well-known fortheir propensity to undergo π−π stacking interactions,43−47 andthe structure of 1 is no exception. The flat faces of thepolymeric sheets of 1 associate with one another through aseries of offset face-to-face π−π interactions, where the NDIplanes are offset by 3.7° to one another, and with a minimuminteratomic distance of 3.30 Å. No substantial π−π interactionsare observed within each sheet, with such interactionspresumably restricted by the small π-system of the pyrazolerings and steric bulk of the attached methyl substituents.

Synthesis and Structure of poly-[Co(H2L1)2(L3)] 2.Complex 2 was prepared by reacting H2L1 and H2L3 withcobalt sulfate heptahydrate in 20 mM NaOH solution undersolvothermal conditions. The pink crystals were analyzed bysingle crystal X-ray diffraction, and a structural model wasgenerated in the monoclinic space group C2/c. The asymmetricunit of poly-[Co(H2L1)2(L3)] 2 contains one Co(II) ionresiding coincident to a crystallographic twofold rotationelement, one molecule of H2L1 in the neutral protonationstate, and half of one molecule of L3 with a crystallographicinversion center located within the piperazine ring. The cobaltion displays an octahedral coordination mode, where theequatorial positions are occupied by pyrazole nitrogen atoms

Figure 3. (Top) Structure of H2L3 with heteroatom labeling scheme.C−H hydrogen atoms omitted for clarity. (Bottom) O−H···Nhydrogen bonding within the structure of H2L3 giving rise to a one-dimensional chain. Hydrogen atoms not involved in hydrogen bondingomitted for clarity.

Figure 4. Metal and ligand environments in the structure of 1.Hydrogen atoms and disordered lattice water molecule omitted forclarity.

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and the axial positions are filled by monodentate carboxylateoxygen atoms, shown in Figure 6. The pyrazole rings adopt astaggered propeller-type arrangement in order to accommodatethe steric demands of coordination around the equatorial plane.The Co−O bonds, with length 2.150(2) Å, are of a comparablelength to the equatorial Co−N bonds (2.133(2) and 2.182(2)Å). Although less common that the tetrahedral [M-(HPz)2(RCOO)2] coordination mode, similar trans-[M-(HPz)4(RCOO)2] coordination environments incorporating

the H2L1 ligand have been reported previously, for M = Ni orCd.24,25

The four N−H hydrogen bond donors in the vicinity of themetal site instigate two types of hydrogen bonding interactions,both directed toward the carboxylate groups of L3. Oneinteraction resembles the typical N−H···O interactionfrequently observed in pyrazole-carboxylate complexes betweenthe pyrazole N−H group and the noncoordinating carboxylateoxygen atom, forming a 7-membered ring. The remainingpyrazole N−H groups donate hydrogen bonds to thecoordinating carboxylate oxygen atoms, forming five-memberedrings. Although the latter interaction displays a much shorterD···A distance (2.646(3) Å vs 2.714(2) Å), the seven-membered hydrogen bonding ring displays a much morefavorable geometry, leading to an N−H···O angle of 174(2)°,cf. 133(2)° for the less favorable 5-membered ring. No solventmolecules were observed in the asymmetric unit to lendadditional hydrogen bonding interactions to the structure.Both the H2L1 and L3 ligands coordinate to two equivalent

cobalt ions, leading to a 2D polymeric network. Extension ofthe structure through H2L1 linkages gives rise to a 1-dimensional chain running parallel to the b axis comprisingCo2(H2L1)2 loops, as shown in Figure 7. These chains arelinked into a second dimension by L3 linkages parallel to the[1,0,1] vector, giving a two-dimensional sheet with (4,4)topology. Despite the presence of several aromatic groupswithin the structure, no substantial π−π interactions wereobserved either within or between the polymeric sheets, with

Figure 5. (Top) Structure of a single sheet within complex 1. H2L1ligands colored red, L2 ligands colored yellow. (Bottom) Interactionof adjacent sheets in the structure of 1 viewed parallel to the H2L1linkages, showing π−π interactions between naphthalene diimideunits. Hydrogen atoms are omitted for clarity.

Figure 6. Coordination geometry and hydrogen bonding environmentin the structure of 2. Ligand molecules truncated and hydrogen atomsnot involved in hydrogen bonding omitted for clarity. Symmetry codesused to generate equivalent atoms: 1:1 − x, +y, 1/2 − z; 2: +x, 1 + y,+z; 3:1 − x, 1 + y, 1/2 − z.

Figure 7. (Top) Structure of the Co2(H2L1)2 loops which form partof the extended structure of 2. (Bottom) Extended structure of 2viewed perpendicular to the two-dimensional sheets. Hydrogen atomsare omitted for clarity.

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the exception of a reciprocated C−H···π interaction betweenpyrazole methyl group C8 and an adjacent pyrazole ring, withcarbon−ring centroid distance 3.25 Å. As expected, thermalanalysis of 2 showed no substantial mass losses before a slowsingle-step decomposition process initiated at approximately270 °C. We found that the synthesis of compound 2 could alsobe carried out in a 10-fold scale-up by linearly scaling thequantities of solvent and reactants, albeit at a slightly lowerpercentage yield (113 mg, 61%).Synthesis and Structure of poly-[Co2(HL1)2(L3)] 3.

Crystals of 3 were prepared by a similar method to 2, except theconcentration of aqueous sodium hydroxide was increased to40 mM and a larger excess of cobalt sulfate was used, givingdark purple crystals as a pure phase. The structure of poly-[Co2(HL1)2(L3)] 3 was solved and refined in the monoclinicspace group P21/n and, similar to 2, the asymmetric unit wasfound to contain one Co(II) ion, one molecule of HL1, andhalf of one molecule of L3, with a crystallographic inversioncenter located within the piperazine ring. The coordinationgeometry of the Co(II) ion is best described as regulartetrahedral, with a coordination sphere consisting of onecarboxylate oxygen atom and three pyrazole nitrogen atoms.Ligand HL1 is present in a singly deprotonated, monoanionicstate, while both carboxylate groups on L3 are deprotonated.One pyrazole group of HL1 coordinates in a neutralmonodentate binding mode, while the deprotonated ringbridges two equivalent cobalt ions in a μ2-κN:κN′ coordinationmode. The resulting dinuclear Co2 node is overall coordinatedby two bridging pyrazolates, two monodentate pyrazoles andtwo carboxylates, connecting four HL1 ligands and two L3ligands, as shown in Figure 8. The neutral pyrazole group of

HL1 is involved in hydrogen bonding with the noncoordinatingcarboxylate oxygen atom of an adjacent L3 ligand, forming thefrequently observed seven-membered hydrogen-bonded ringaround the metal center (Figure 1). The 3-connected, singlydeprotonated coordination of the HL1 ligand represents ahitherto unknown coordination mode for methylenebis-pyrazole ligands, falling between the doubly deprotonated 4-connecting mode observed by Kruger et al. in 200029 and thecommonly observed neutral 2-connected behavior.22,23 The[M2(μ2-pz)2(Hpz)2(RCOO)2] cluster has been occasionallyobserved in discrete systems, most often with zinc;48,49

however, no polymeric examples have been reported to date.The bimetallic cobalt clusters within compound 3 are linked

into an extended three-dimensional network by bridgingthrough both HL1 and L3 ligands. Considering only theHL1 bridges and taking the cobalt clusters as nodes, a two-

dimensional sheet results, which is linked into a three-dimensional array by bridging through the two connecting L3ligands. The topological description of the overall structurematches that of the primitive cubic α-Po network, albeit withsignificant distortion to the internodal distances by therelatively long bridging distance of the L3 species of ca. 15 Å,compared with 10.5 Å for the HL1 bridging distances. Similarto that seen in compound 2, the S-shaped conformation of theL3 ligand compensates for the geometric distortion of thebimetallic node to provide a relatively regular geometry to theoverall network (Figure 9). The steric bulk of the two ligands

completely fills the space between nodes, and no solventmolecules or void space was observed within the structure.Similar to compound 2, few substantial π−π interactions areobserved in the extended structure of 3, which consist largely ofC−H···π or edge-to-face π−π interactions. The mostsubstantial interaction of this type occurs between a C−Hgroup from the piperazine phenyl ring and the deprotonatedpyrazole ring, with C···C distance 3.66 Å and C−H···C angle172°. Thermal analysis of compound 3 showed no substantialmass loss across the entire temperature range of the experiment(25−400 °C), and the sample was visually unchanged by thisheating cycle, demonstrating particularly good thermal stabilityfor the material. A 10-fold linear scale-up on compound 3resulted in an improvement of the isolated yield (118 mg,94%).

Figure 8. Metal coordination environment and hydrogen bondinginteractions in the structure of 3. Ligands truncated and hydrogenatoms not involved in hydrogen bonding omitted for clarity.

Figure 9. Extended structure of compound 3, showing linkagesbetween Co2 dimers through HL1 ligands (Top) and L3 linkages(Middle), and representation of a single α-Po unit of 3 (dashed lines)with chemical linkages shown for two edges (Bottom).

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Magnetic Properties of poly-[Co2(HL1)2(L3)] 3. Moti-vated by the presence of a closely bridged dinuclear CoII

environment, we pursued magnetic susceptibility measurementson compound 3 with the expectation of observing couplingbehavior between the two CoII nuclei. Magnetic susceptibilitymeasurements of 3 show that χMT decreases gradually from 2.3cm3 mol−1 K, per Co, at 300 K (μeff = 4.29 μB) to ∼2.0 cm3

mol−1 K at ∼70 K, then more rapidly to reach ∼0.1 cm3 mol−1

K at 2 K (Figure 10). The corresponding χM plot shows a

maximum at 18 K indicative of intracluster antiferromagneticcoupling, while below ∼5 K there is a small increase in χM dueto traces of monomer impurity. The data were fitted extremelywell to a simple −2JS1.S2 Heisenberg Hamiltonian, for a S = 3/2 dimer model. This is appropriate to tetrahedral Co(II)

centers with orbitally nondegenerate 4A2 ground states. Theparameter values are g = 2.25, J = −3.2 cm−1, with a θ value(from T − θ) of −0.01 K possibly indicative of very weakinterdinuclear interactions, the latter expected to be very weakin view of the long L3 and HL1 bridging distances (vide supra).The susceptibility plot is of very similar shape to that obtainedfor [CoII(3,5-dimethylpyrazolate)2(3,5-dimethylpyrazole)]2, adinuclear complex containing tetrahedral Co(II) centersbridged by two pyrazolates, and the J value in that work wasalso very similar, viz., −3.0 cm−1.50

Synthesis and Structure of para-((3,5-dimethyl-1H-pyrazol-4-yl)methylene)-benzoic acid H2L4. Observingthe metal coordination geometry and extended structures of1−3, as well as those previously reported with H2L1 andvarious other, more well-known aromatic dicarboxylates,22−28 itseems likely that one reason for the diversity in the extendedstructures regularly observed is the mismatch in flexibility and/or length of the carboxylate coligands employed in comparisonto that of H2L1. With only one flexible sp3 linker, two aromaticrings, and a typical donor−donor distance of 5−7 Å, it isnontrivial to envisage a dicarboxylate coligand containingcomplementary structural features with which to test thishypothesis. With this in mind, we devised the flexible ligandpara-((3,5-dimethyl-1H-pyrazol-4-yl)methylene)-benzoic acidH2L4, in order to test the effect of a perfectly complementaryligand set on the extended structure of a pyrazole-carboxylatecoordination polymer. The synthesis of H2L4 was achieved in 3steps from ethyl 4-(bromomethyl)benzoate, utilizing a radicalreaction between the alkyl halide and [Co(acac)2] first reportedby Marquet51 to generate the diketone precursor, which wascyclized and the carboxylic acid deprotected to give the productH2L4 in 29% overall yield. The synthesis of H2L4 is outlined inScheme 1.

Figure 10. Plots of magnetic susceptibility vs T for compound 3; χM(per Co, open squares), and χMT (per Co, open circles). The solidlines are the values calculated for best fit using a S = 3/2 dimerHeisenberg model and the parameters given in the text.

Scheme 1. Synthesis of H2L4 with Hydrogen Atom Labeling Scheme for H2L4 and Precursor Speciesa

aReagents and conditions: (i) [Co(acac)2], CHCl3, 120 °C; (ii) H2NNH2·H2O, MeOH, reflux 24 h; (iii) LiOH, THF/H2O, reflux 24 h, thenHCl(aq).

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Single crystals of H2L4 for structural analysis were preparedby heating 10 mg of the material to 100 °C in 5 mL of water inan acid digestion bomb, followed by cooling to roomtemperature. The diffraction data were solved and refined inthe orthorhombic space group Pbca, with one molecule ofH2L4 in the asymmetric unit. Geometrically, the molecule bearssome resemblance to H2L1, with two aromatic rings at aninterplanar angle of 69° linked by a methylene bridge, albeitwith greater distance between the sets of possible donor atomsof approximately 8 Å. The structure of H2L4 is shown in Figure11.

The extended structure of H2L4 is largely defined byhydrogen bonding interactions between the pyrazole andcarboxylic acid groups. As would be expected, two types ofinteractions are observed, of the type N−H···O and O−H···N,connecting each H2L4 molecule to four others. Extending theseinteractions from each molecule gives rise to an undulating two-dimensional (4,4) hydrogen-bonded sheet parallel to the bcplane. No other substantial intermolecular interactions wereobserved within each plane; however, adjacent planes associateby way of parallel offset face-to-face π−π interactions betweenphenyl rings at a mean interplanar distance 3.40 Å (SupportingInformation, Figure S3).Synthesis and Structure of poly-[Co(HL4)2]·H2O 4.

Compound 4 was prepared by reacting H2L4 with cobaltsulfate heptahydrate under hydrothermal conditions in thepresence of the weak organic base 2,4,6-collidine. The purplecrystals obtained were subjected to single crystal X-raydiffraction analysis, and the data obtained were solved andthe structure model refined in the monoclinic space group C2/c. The asymmetric unit of 4 was found to contain one Co(II)ion, two nonequivalent HL4 ligands, and one water molecule(Figure 12). Interestingly, while the coordination around the

metal ion is the tetrahedral N2−O2 motif seen previously, onlyone hydrogen bond between the pyrazole N−H hydrogenatoms and deprotonated carboxylate groups was observed. Theprotonated pyrazole nitrogen atom N3 instead acts as ahydrogen bond donor to the lattice water molecule O36, whichitself acts as a hydrogen bond donor to noncoordinating oxygenatoms O18 and O35, the latter of which also accepts ahydrogen bond from pyrazole nitrogen atom N20. Thehydrogen bonding environment of 4 is shown in Figure 13.Topologically, 4 possesses a one-dimensional polymeric

chain structure, with Co(II) atoms linked by zigzag loops ofHL4 molecules parallel to the c axis. However, whenconsidering hydrogen bonding connections, the network mustbe considered binodal 3,5-connected, where water moleculesare 3-connected nodes, and [Co(HPz)2(COO)2] moietiesbecome 5-connected nodes, owing to their connectivity to twoother such moieties through coordination bonds and threewater molecules through hydrogen bonds. The resultingnetwork adopts a (42·67·8)(42·6) topology, forming a double-layered two-dimensional sheet parallel to the bc plane. Aschematic diagram is shown in Figure 13. Aside from thesehydrogen bonding interactions, the structure of 4 contains fewsignificant intermolecular interactions, with only very weakpartial π−π overlap between sheets, and no other significantinteractions within each sheet. Thermogravimetric analysis of 4showed a gradual mass loss of 3.4% from 100−250 °C,consistent with the loss of the lattice water molecule (calculated3.5% mass), leading directly into a gradual decomposition.

Synthesis and Structure of poly-[Cu(HL4)2]·2MeOH 5.Following the unexpected outcome of the reaction of H2L4with Co(II) under hydrothermal conditions, the possibility offorming coordination networks of H2L4 with other metal ionswas explored, with the expectation of variable ligand behaviorbased on different metal ion geometries and sizes. To this end,the high reactivity and low probability of a stable tetrahedralcoordination sphere from CuII made it an excellent candidatefor structural studies. Reaction of H2L4 with 1 equiv of coppersulfate pentahydrate in methanol at room temperature gave agreen turbid suspension which, over the course of 1 week,deposited pale purple crystals. The crystals were analyzed bysingle crystal X-ray diffraction, and the data were solved and

Figure 11. (Top) Structure of H2L4 with heteroatom labeling scheme.Selected hydrogen atoms omitted for clarity. (Bottom) Extendedhydrogen-bonded structure of H2L4 viewed perpendicular to a two-dimensional hydrogen-bonded sheet.

Figure 12. (Top) Metal and ligand environments in compound 4 withpartial heteroatom labeling scheme. (Bottom) Extended one-dimen-sional polymeric structure of 4. Hydrogen atoms not involved inhydrogen bonding omitted for clarity.

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refined in the triclinic space group P1 . The asymmetric unit ofpoly-[Cu(HL4)2]·2MeOH 5 contains one HL4 ligand, with thecarboxylate group deprotonated, one Cu(II) ion residing on acrystallographic inversion center, and a noncoordinatingmethanol molecule. As expected from the purple color of thecomplex, the copper ion is coordinated in a square planarmanner, with the coordination sphere occupied by two pyrazolenitrogen atoms and two carboxylate oxygen atoms in a transdisposition, shown in Figure 14. The geometry of the liganditself is essentially equivalent to one of the two HL4 fragmentsin the structure of 4, and differs to the other fragment by arotation of the phenyl ring and carboxylate group (SupportingInformation, Figures S4 and S5).When extended through the coordination bonds at each end

of the HL4 molecule, a one-dimensional chain is observed inthe structure of 5. The structure is reminiscent of that seen in4; however, due to the difference in metal coordinationgeometry and the symmetry relationship of each molecule ofHL4, the loops adopt a slightly different conformation. The

metal−metal distance of 11.04 Å compares reasonably well tothat observed in 4 of 10.81 Å. The chains interact with oneanother through hydrogen bonding interactions between thenoncoordinating pyrazole N−H groups and lattice methanoloxygen atoms. The lattice methanol molecules also engage inhydrogen bonding interactions with the noncoordinatingcarboxylate oxygen atoms from a separate chain (Figure 15).

This series of interactions is reciprocated between chains ateach metal ion, forming a series of R4

4(18) hydrogen bondingrings incorporating two metal ions from adjacent chains.Extension of these interactions parallel to the a axis bridges thecoordination chains into a two-dimensional (4,4) hydrogenbonded sheet.The methanol molecules within the lattice are aligned in

linear arrangements running parallel to the c axis, which wouldbe expected to facilitate ready solvent loss. Indeed, crystals of 5were observed to lose crystallinity rapidly on standing in air,evidenced by peak broadening and the emergence of anamorphous region in the X-ray powder diffraction pattern

Figure 13. (Top) Hydrogen bonding environment in the structure of4 showing the linkage of four otherwise nonconnected chains, withhydrogen bond donors and acceptors labeled. Symmetry codes used togenerate equivalent atoms: 1: +x, 1 − y, 1/2 − z; 2: +x, 1 − y, 1/2 + z;3: +x, −y, 1/2 + z; 4: 3/2 − x, 1/2 − y, 2 − z; 5: 3/2 − x, −1/2 + y,2− z; 6: 3/2 − x, −1/2 + y, 3/2 − z; 7: 3/2 − x, 1/2 + y, 3/2 − z.(Bottom) Topological representation of the resulting double-layersheet structure. Red spheres represent water molecules, and bluespheres represent metal ions, while blue bonds represent linkagesthrough HL4 and red/blue bonds represent hydrogen bonds.

Figure 14. Metal and ligand environments in the structure of 5.Hydrogen atoms not involved in hydrogen bonding omitted for clarity.Symmetry codes used to generate equivalent atoms: 1: 1 − x, 1 − y, 1− z; 2: 1 − x, 1 − y, −z; 3: +x, +y, −1 + z.

Figure 15. (Top) Hydrogen bonding behavior in the structure of 5showing R4

4(18) hydrogen-bonded rings linking chains. (Bottom)Extended structure of 5, showing linkages of polymeric [Co(HL4)2]chains by columns of methanol molecules.

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(Supporting Information). Infrared spectroscopy and micro-analysis suggest that this process is accompanied by uptake ofatmospheric water, suggesting a solvation for the air-driedmaterial of poly-[Cu(HL4)2]·0.75(MeOH)·3(H2O). This for-mula is corroborated by thermogravimetric analysis on the air-dried material (Supporting Information), which showed a two-step mass loss with onset at room temperature, consisting of arapid 5% loss up to 60 °C, followed by gradual loss of a further9% mass up to 250 °C. These values are in agreement with theexpected loss of methanol (calculated 4%) followed by water(calculated 9%).

■ DISCUSSIONExamination of the structures of 1−3 provides several newinsights into the coordination behavior of the H2L1/HL1ligand when present in conjunction with carboxylate coligands.Largely as expected, the geometry of the bis-pyrazole specieswas consistent between the three structures, and coligands L2and L3 acted to provide additional structure direction andhydrogen bond acceptor functionality. The clip-like synconformation of the L2 ligand in complex 1 most likelycontributed to the overall two-dimensional structure observedby conveniently bridging between [CoH2L1] chains, while the[Co(H2L1)2] looped chains in compound 2 were readilybridged into two-dimensional structures by the relativelyslender nature of the L3 coligand. Surprisingly, none of thestructures 1−5 contained the well-known doubly hydrogen-bonded tetrahedral [M(HPz)2(RCOO)2] coordination geom-etry frequently seen in other systems.22,23 The coordinationgeometry observed in 1 is most likely rationalized by the largesteric bulk and backbone rigidity of L2, which may enforce theless sterically demanding geometry on the cobalt ion within thestructure and allow for additional hydrogen bondinginteractions. For compounds 2 and 3, this discrepancy is tobe expected, given the altered reaction stoichiometries in whichan excess of H2L1 was employed. Despite our attempts, wewere unable to isolate and crystallographically characterize anycompounds of the formula poly-[Co(H2L1)(L3)] by alteringthe reaction stoichiometry.The presence of a pyrazolate-bridged dinuclear node in 3

provided an additional and unexpected outcome in thisstructural investigation, and represents a rare example of amagnetically active cluster species in an L1-carboxylatecoordination polymer. Although the coupling interactionsobserved in 3 are typical of weak antiferromagnetic couplingbehavior in an isolated dimer-type system, the magneticallyactive [M2(HPz)2(μ-Pz)2(RCOO)2] system represents apromising area for future research. It is expected that usingshorter and fully conjugated carboxylate bridges to link suchclusters in HL1 systems may generate a new range ofmagnetically interesting coordination polymers, extending onthe design principles which have already been established forflexible bispyrazole-carboxylate coordination polymers.The structures of 4 and 5 display remarkably similar

attributes, especially considering the differences in metal iongeometry and synthesis conditions. In these instances, theformation of a low-dimensionality assembly was most likelydirected by the self-complementarity of the ligand sphere.Within each complex, all four coordinated ligands possessidentical bridging distances and degrees of flexibility, and aretherefore uniquely capable of forming homotopic one-dimen-sional chains. This flexibility was also sufficient to overcome thegeometric differences caused by the change in coordination

geometry from tetrahedral Co(II) to square planar Cu(II).Both compounds contain N−H hydrogen bond donorsdirected outward from the metal center, allowing theincorporation of hydrogen-bonded solvent molecules whichextend the structures into two-dimensional arrays.

■ CONCLUSIONWe have prepared and characterized three new pyrazole-carboxylate coordination polymers derived from the ditopicligand 4,4′-methylenebis(3,5-dimethyl-1H-pyrazole) H2L1, pre-pared by reaction with Co(II) and coligands (S,S)-1,4,5,8-naphthalenetetracarboxylic diimide-N,N′-bis(2-propionic acid)H2L2 and 1,4-bis((3-carboxyphenyl)methyl) piperazine H2L3.Compound 1, a chiral two-dimensional sheet containingstrongly π−π stacking outer layers, and compound 2, a denselypacked two-dimensional sheet, displayed the typical neutral bis-monodentate coordination behavior for H2L1, albeit withuncommon metal coordination geometries and hydrogenbonding modes. The emergence of previously unknowncoordination behavior for the HL1 ligand in complex 3, athree-dimensional α-Po type structure containing pyrazolate-bridged Co2 clusters, revealed the potential for the incorpo-ration of coordination clusters and magnetic couplinginteractions into materials based on mixed bis-pyrazole-carboxylate ligands. Finally, we have prepared a new flexibleheteroditopic ligand ((3,5-dimethyl-1H-pyrazol-4-yl)-methylene)-benzoic acid H2L4 and shown in one-dimensionalpolymers 4 and 5 the tendency for homotopic chain formation.This behavior is likely driven by the self-complementarydimensions provided by a homotopic ligand sphere, whichnonetheless retains the potential for intramolecular hydrogenbonding interactions in the vicinity of the metal site.

■ ASSOCIATED CONTENT*S Supporting InformationThermogravimetric analysis for all coordination compounds, X-ray powder diffraction patterns for all compounds, additionalfigures and ellipsoid plots, table of hydrogen bondingparameters. This material is available free of charge via theInternet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Authors*E-mail: stuart.batten@monash.edu.*E-mail: david.turner@monash.edu.*E-mail: paul.kruger@canterbury.ac.nz.

Author ContributionsThe manuscript was written through contributions of allauthors. All authors have given approval to the final version ofthe manuscript.

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis work is supported by the Science and IndustryEndowment Fund. Part of this research was undertaken onthe MX1 Macromolecular Crystallography beamline at theAustralian Synchrotron, Victoria, Australia. S.R.B. and D.R.T.acknowledge the Australian Research Council for fellowships.K.S.M. thanks the Australian Research Council for a Discoverygrant. C.S.H. acknowledges the University of Canterbury for a

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dx.doi.org/10.1021/cg501004u | Cryst. Growth Des. XXXX, XXX, XXX−XXXK

PhD Scholarship. C.S.H. and P.E.K. acknowledge the RoyalSociety of New Zealand Marsden Fund for financial support.

■ REFERENCES(1) Gavezzotti, A. Acc. Chem. Res. 1994, 27, 309−314.(2) Day, G. M. Crystallogr. Rev. 2011, 17, 3−52.(3) Price, S. L. Adv. Drug. Delivery Rev. 2004, 56, 301−319.(4) Datta, S.; Grant, D. J. W. Nat. Rev. Drug Discovery 2004, 3, 42−57.(5) Wilmer, C. E.; Leaf, M.; Lee, C. Y.; Farha, O. K.; Hauser, B. G.;Hupp, J. T.; Snurr, R. Q. Nat. Chem. 2012, 4, 83−89.(6) Mellot-Draznieks, C.; Dutour, J.; Ferey, G. Angew. Chem., Int. Ed.2004, 43, 6290−6296.(7) Zhang, M.; Bosch, M.; Gentle, T., III; Zhou, H.-C.CrystEngComm 2014, 16, 4069−4083.(8) Kim, J.; Chen, B.; Reineke, T. M.; Li, H.; Eddaoudi, M.; Moler,D. B.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2001, 123, 8239−8247.(9) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.;Eddaoudi, M.; Kim, J. Nature 2003, 423, 705−714.(10) Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M. Proc. Natl. Acad.Sci. U. S. A. 2006, 103, 10186−10191.(11) Phan, A.; Doonan, C. J.; Uribe-Romo, F. J.; Knobler, C. B.;O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2010, 43, 58−67.(12) Du, M.; Li, C.-P.; Liu, C.-S.; Fang, S.-M. Coord. Chem. Rev.2013, 257, 1282−1305.(13) Hawes, C. S.; Babarao, R.; Hill, M. R.; White, K. F.; Abrahams,B. F.; Kruger, P. E. Chem. Commun. 2012, 48, 11558−11560.(14) Colombo, V.; Galli, S.; Choi, H. J.; Han, G. D.; Maspero, A.;Palmisano, G.; Masciocchi, N.; Long, J. R. Chem. Sci. 2011, 2, 1311−1319.(15) Hou, L.; Lin, Y.-Y.; Chen, X.-M. Inorg. Chem. 2008, 47, 1346−1351.(16) Choi, H. J.; Dinca, M.; Long, J. R. J. Am. Chem. Soc. 2008, 130,7848−7850.(17) Zhang, J.-P.; Kitagawa, S. J. Am. Chem. Soc. 2008, 130, 907−917.(18) Hunger, J.; Krautscheid, H.; Sieler, J. Cryst. Growth Des. 2009, 9,4613−4625.(19) Yang, T.-H.; Silva, A. R.; Shi, F.-N. Dalton Trans. 2013, 42,13997−14005.(20) Zhang, J.-X.; He, J.; Yin, Y.-G.; Hu, M.-H.; Li, D.; Huang, X.-C.Inorg. Chem. 2008, 47, 3471−3473.(21) He, C.-T.; Tian, J.-Y.; Liu, S.-Y.; Ouyang, G.; Zhang, J.-P.; Chen,X.-M. Chem. Sci. 2013, 4, 351−356.(22) Basu, T.; Sparkes, H. A.; Bhunia, M. K.; Mondal, R. Cryst.Growth Des. 2009, 9, 3488−3496.(23) Mondal, R.; Bhunia, M. K.; Dhara, K. CrystEngComm 2008, 10,1167−1174.(24) Goswami, A.; Sengupta, S.; Mondal, R. CrystEngComm 2012, 14,561−572.(25) Guo, X.-G.; Yang, W.-B.; Wu, X.-Y.; Zhang, Q.-K.; Lin, L.; Yu,R.; Lu, C.-Z. CrystEngComm 2013, 15, 3654−3663.(26) Hawes, C. S.; Fitchett, C. M.; Batten, S. R.; Kruger, P. E. Inorg.Chim. Acta 2012, 389, 112−117.(27) Lin, L.; Yu, R.; Wu, X.-Y.; Yang, W.-B.; Zhang, J.; Guo, X.-G.;Lin, Z.-J.; Lu, C.-Z. Inorg. Chem. 2014, 53, 4794−4796.(28) Goswami, A.; Bala, S.; Pachfule, P.; Mondal, R. Cryst. GrowthDes. 2013, 13, 5487−5498.(29) Kruger, P. E.; Moubaraki, B.; Fallon, G. D.; Murray, K. S. J.Chem. Soc., Dalton Trans. 2000, 713−718.(30) Rajakumar, P.; Selvam, S.; Shanmugaiah, V.; Mathivanan, N.Bioorg. Med. Chem. Lett. 2007, 17, 5270−5273.(31) McCormick, L. J.; Turner, D. R. CrystEngComm 2013, 15,8234−8236.(32) Beeching, L. J.; Hawes, C. S.; Turner, D. R.; Batten, S. R.CrystEngComm 2014, 16, 6459−6468.(33) McPhillips, T. M.; McPhillips, S. E.; Chiu, H.-J.; Cohen, A. E.;Deacon, A. M.; Ellis, P. J.; Garman, E.; Gonzalez, A.; Sauter, N. K.;

Phizackerly, R. P.; Soltis, S. M.; Kuhn, P. J. Synchrotron Rad. 2002, 9,401−406.(34) Brennan, S.; Cowan, P. L. Rev. Sci. Instrum. 1992, 63, 850−853.(35) Bruker SAINT; Bruker-AXS Inc., Madison, WI, 2001.(36) SADABS; Bruker-AXS Inc., Madison, WI, 2001.(37) CrysAlis PRO; Agilent Technologies UK Ltd, Yarnton, England,2012.(38) Kabsch, W. J. J. Appl. Crystallogr. 1993, 26, 795−800.(39) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112−122.(40) Sheldrick, G. M. SHELXL-97, Programs for X-ray CrystalStructure Refinement; University of Gottingen, Gottingen, Germany,1997.(41) Dolomanov, O. V.; Bouhis, L. J.; Gildea, R. J.; Howard, J. A. K.;Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−341.(42) Etter, M. C. Acc. Chem. Res. 1990, 23, 120−126.(43) Kumar, N. S. S.; Gujrati, M. D.; Wilson, J. N. Chem. Commun.2010, 46, 5464−5466.(44) Boer, S. A.; Hawes, C. S.; Turner, D. R. Chem. Commun. 2014,50, 1125−1127.(45) Bhosale, S. V.; Jani, C. H.; Langford, S. J. Chem. Soc. Rev. 2008,37, 331−342.(46) (a) McCormick, L. J.; Turner, D. R. CrystEngComm 2013, 15,8234−8236. (b) Boer, S. A.; Nolvachai, Y.; Kulsing, C.; McCormick, L.J.; Marriott, P. J.; Turner, D. R. Chem. Eur. J. 2014, 20, 11308−11312.(47) Pan, M.; Lin, X.-M.; Li, G.-B.; Su, C.-Y. Coord. Chem. Rev. 2011,255, 1921−1936.(48) Sarma, R.; Kalita, D.; Baruah, J. B. Dalton Trans. 2009, 36,7428−7436.(49) Singh, U. P.; Tyagi, P.; Pal, S. Inorg. Chim. Acta 2009, 362,4403−4406.(50) Ehlert, M. K.; Rettig, S. J.; Storr, A.; Thompson, R. C.; Trotter,J. Can. J. Chem. 1993, 71, 1425−1436.(51) Marquet, J.; Morenomanas, M.; Pacheco, P.; Vallribera, A.Tetrahedron Lett. 1988, 29, 1465−1468.

Crystal Growth & Design Article

dx.doi.org/10.1021/cg501004u | Cryst. Growth Des. XXXX, XXX, XXX−XXXL