Secondary Building Unit (SBU) Controlled Formation of aCatalytically Active Metal−Organic Polyhedron (MOP) Derived from aFlexible Tripodal LigandMithun Paul,†,§ N. N. Adarsh,‡ and Parthasarathi Dastidar*,†,§

†Department of Organic Chemistry, Indian Association for the Cultivation of Science (IACS), 2A & 2B Raja S. C. Mullick Road,Kolkata 700032, West Bengal, India

*S Supporting Information

ABSTRACT: A nanosized truncated octahedron-shaped metal−organic-polyhedron (MOP) namely [{Cu12(TMBTA)8(DMA)4(H2O)8}·8H2O·X]MOP-TO (X = 48 H2O molecules as per SQUEEZE calculation and TGAdata) was successfully derived from a flexible C3-symmetric ligand (2,4,6-trimethylbenzene)-1,3,5-triacetic acid (TMBTA) and Cu(NO3)2 indimethyl acetamide (DMA) and EtOH under solvothermal conditions.The nanocage was well-characterized by single crystal X-ray diffraction(SXRD) and electron spray ionization mass spectrometry (ESI-MS).Remarkably, the nanocage molecules could be seen under high-resolutiontransmission electron microscope (HR-TEM). It was evident that theCu(II) paddle wheel secondary building unit (CPWSBU) was responsiblefor the formation of the nanocage, as the corresponding reactions ofTMBTA with other metal ions (e.g., Co(II) and Zn(II) resulted in theformation of two coordination polymers, namely [{Co(μ-TMBTA)-(H2O)4}]∝ TMBTA-Co(II) and [{(H2O)2Zn(μ-TMBTA)Zn·K}·2H2O]∝ TMBTA-Zn(II). Interestingly, the nanocage MOP-TO was exploited in catalyzing (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO)-assisted aerobic oxidation of benzyl alcohol tobenzaldehyde.

Building complex architecture with function is one of themajor goals in supramolecular chemistry.1 Various non-

covalent interactions such as hydrogen bonding, charge-assistedhydrogen bonding, halogen bonding, charge transfer inter-actions, π−π stacking, etc. have been exploited to generateintriguing supramolecular entities that often displayed usefulfunctions such as sensing,2 catalysis,3 immobilizing liquids(gelation),4 opto-electronic properties,5 drug-delivery,6 bio-medical applications,7 etc. One of the most widely usedsupramolecular tools to construct intriguing supramoleculararchitecture is metal−ligand coordination. For example,construction of highly porous and/or catalytic metal−organicframeworks (MOFs) also known as coordination polymers isbased on the exploitation of metal−ligand coordination.8

Discrete supramolecular species such as metal−organicpolyhedra9 (MOP, also known as nanocage, nanoballs, etc.),on the other hand, has attracted much attention during the lastdecade or so because of their inherent structural complexity,aesthetic appeal and consequently synthetic challenges, andvarious potential applications such as recognition,10 stora-ge,11catalysis,12 their relevance in biological self-assembly,13 etc.Usually MOPs are synthesized by spontaneous self-assembly ofa suitably chosen metal center or secondary building unit(SBU) comprised of a metal−ligand cluster having predefinedspatial geometry and rigid ditopic or tritopic ligands with ∼90°or ∼120° ligating topology, respectively.14 Both edge-directed

and face-directed self-assembly approaches have been ex-ploited.15 Pyridyl-based donors and acceptors like cappedmetal centers [e.g., Pd(II) or Pt(II)] having predefinedgeometry were used to achieve various MOPs in most of thecases.16

Paddle-wheel cluster derived from Cu(II) acetate,Cu2(CO2)4, represents one of the most successful SBUs indesigning highly microporous functional MOFs17 whereinpolytopic carboxylate linkers were used; CPWSBU iscomprised of two square planar Cu(II) metal centers connectedby four carboxylate linkers offering an octahedral node forgenerating such microporous MOFs. In polyhedras liketruncated octahedron, truncated cuboctahedron, and truncatedicosidodecahedron, the vertices of the parent polyhedras arereplaced by squares, and CPWSBU can be represented as asquare considering the plane connected by the four C atoms ofthe carboxylate linkers connected to the Cu(II) metal centers(Scheme 1). Thus, CPWSBU has been exploited in generatingMOPs.14

In the present work, a conformationally flexible tripodalligand namely (2,4,6-trimethylbenzene)-1,3,5-triacetic acid(TMBTA) has been utilized to synthesize a discrete truncated

Received: December 9, 2013Revised: January 20, 2014Published: January 20, 2014

Article

pubs.acs.org/crystal

© 2014 American Chemical Society 1331 dx.doi.org/10.1021/cg4018322 | Cryst. Growth Des. 2014, 14, 1331−1337

octahedron MOP, namely [{Cu12(TMBTA)8(DMA)4(H2O)8}·8H2O·48H2O] MOP-TO by exploiting CPWSBU. Both singlecrystal X-ray diffraction (SXRD) and ESI-MS supported theformation ofMOP-TO. The diameter of the polyhedral capsuleMOP-TO was around 2.6 nm as revealed both by SXRD andHR-TEM. Syntheses of two coordination polymers namely[{Co(μ -TMBTA)(H2O)4}]∝ TMBTA-Co(II) and[{(H2O)2Zn(μ-TMBTA)Zn·K}·2H2O]∝ TMBTA-Zn(II) de-rived from Co(II) and Zn(II), respectively, emphasized the roleof CPWSBU in generating MOP-TO. Remarkably, MOP-TOwas able to catalyze TEMPO-assisted aerobic oxidation ofbenzyl alcohol to benzaldehyde.

■ RESULTS AND DISCUSSIONCambridge Structural Database (CSD) Search. CSD

(version 1.15) search revealed that there were 36 crystalstructures of MOPs involving CPWSBU (Table S1 of theSupporting Information). Out of these 36 MOPs, 10 structureswere of the type of cryptand (having two CPWSBU connectedby four ditopic ligands) and 26 structures were of the type ofcages or nanoballs (having more than two CPWSBU and manyditopic or tritopic ligands). Majority of the MOPs found in thisCSD search represented truncated cuboctahedron (TCO) (16nos.), and half of that represented truncated octahedron (TO)structures. Close examination of the CSD search pointed to thefact that in most of the cases, the organic ligands used wererigid and had mostly 120° angle between the functional groups.Only in a few cases (4 structures), conformationally flexibleligands were used.Since conformationally flexible ligands have large numbers of

degrees of freedom, it is difficult to achieve one particularconformation required for cagelike MOP architecture. Theligand TMBTA, we chose to work with, should display twodifferent types of conformations, namely syn-syn-syn and syn-syn-anti (Figure 1). Understandably, the syn-syn-syn conformation isrequired for MOP formation.Single Cryrstal X-ray Crystallography. Single crystals of

all the compounds namely MOP-TO, TMBTA-Co(II), andTMBTA-Zn(II) were obtained under solvothermal (exper-imental) conditions and were subjected to SXRD (Table 1).[{Cu12(TMBTA)8(DMA)4(H2O)8}·8H2O·48H2O]MOP-TO.

Reaction of TMBTA with Cu(NO3)2 in DMA and EtOH undersolvothermal condition resulted in green-colored block-shapedsingle crystals. SXRD revealed that the crystals of MOP-TObelonged to the centrosymmetric orthorhombic space groupCcca.The crystal structure of MOP-TO was composed of large

discrete molecules constructed from Cu(II)-paddle-wheel SBU(square SBU) connected by the tripodal ligand TMBTAdisplaying syn−syn−syn conformation. The structure may bestbe described as a truncated octahedron, wherein 6 vertices and8 faces of an octahedron were replaced by the squares arisingfrom the paddle-wheel SBUs and tripodal ligands, respectively.

All Cu(II) metal centers embedded within the cage werecoordinated by water molecules, whereas the peripheral Cu(II)were coordinated by DMA and water molecules. Furthermore,eight uncoordinated water molecules were found within themolecular cage, sustained by participating in hydrogen-bondinginteractions [O···O = 2.910(6) − 2.948(8) Å] with the adjacentcoordinated water molecules. One of the peripherallycoordinated DMA molecules was found to be disordered(Figure 2). The cage molecules were packed in 2D runningparallel to the a−c plane, sustained by the C−H···π interactions(3.868 Å) involving the benzyl CH and aromatic ring of theadjacent molecules. Such 2D layers were further packed in aparallel fashion via dispersion forces. Overall packing of themolecules revealed the existence of continuous channelsrunning down the a axis, having an approximate size of 7 ×7 Å (Figure 2). Unaccounted electron density peaks wereobserved within such channels during the final cycles ofrefinement, which could not be fit into any reasonable model.SQUEEZE18 calculations revealed that there were 481 electronsper asymmetric unit, which were attributed to ∼48 watermolecules. Thermogravimetric data analyses revealed a weightloss of 35.5% that occurred within a temperature range of40.6−238.5 °C; this was attributed to the weight loss of bothcoordinated and uncoordinated water [16 H2O (located in thedifference Fourier map) + 48 H2O (according to SQUEEZEcalculation)] and 4 DMA molecules (calculated weight loss of34.7%). This data corroborated well with the SQUEEZEcalculations (Figure S1 of the Supporting Information).Remarkably, the discrete molecule of the nanoball MOP-TOcould be seen in HR-TEM. When a dilute solution (0.0597 ×10−2 M) of freshly grown crystals of MOP-TO was drop-castedon a carbon-coated gold grid and observed under HR-TEM,discrete objects having a dimension of ∼2−2.6 nm could beobserved (Figure 3).SXRD data was in good agreement with this observation as

the dimension of each molecule was found to be in the samerange (1.9 × 2.6 nm). Electron diffraction in HR-TEM on theobserved nanoparticle did not show any diffraction, indicatingthat the nanoparticles observed in the HR-TEM wererepresenting a single molecule of the nanocage MOP-TO.Subsequent EDX data showed the existence of the Cu elementon the nanoparticle supporting further the molecular nature ofthe nanoparticles (Figure S4 of the Supporting Information).Existence of the nanocage molecule was also established by

Scheme 1. Truncated Octahedron Containing Six SquareVertices Derived from CPWSBU

Figure 1. Two different conformations syn-syn-syn and syn-syn-anti ofthe ligand TMBTA.

Crystal Growth & Design Article

dx.doi.org/10.1021/cg4018322 | Cryst. Growth Des. 2014, 14, 1331−13371332

ESI-MS. When a dilute solution of MOP-TO crystals wasfurther diluted in MeCN and subjected to ESI-MS, a signal at3345.22 was observed consistently. The signal was attributed tothe nanocage without the peripheral coordinated solventmolecules {i.e., [(MOP-TO)-(4DMA+2H2O)]+ (calcd.

3344.97)}. Remarkably, the water molecules within the cageremained intact during ionization in mass spectrometry.Thus, it was clear that one of the two possible conformations

of TMBTA had to be locked in syn-syn-syn conformation inorder to self-assemble into the nanocage MOP-TO via metal−ligand coordination. To probe the role of metal cluster such asCPWSBU in controlling the conformation of the ligandTMBTA and, subsequently, formation of the nanocage, wefurther reacted TMBTA with Co(II) and Zn(II) salts. In fact,reaction of TMBTA with Co(NO3)2 and ZnCl2 undersolvothermal conditions resulted in two coordination polymers,namely, TMBTA-Co(II) and TMBTA-Zn(II), instead of anyMOP.

[{Co(μ-TMBTA)(H2O)4}]∝. Pink-colored blocked-shapedcrystals of TMBTA-Co(II) belonged to the centrosymmetricorthorhombic space group Pnma. The ligand TMBTAdisplayed syn−syn−anti conformation and was located on a

Table 1. Crystallographic Parameters

crystal parameters MOP-TO TMBTA-Co(II) TMBTA-Zn(II)

CCDC no. 962728 963230 963231empirical formula C136H188Cu12N4O68 C15H24CoO10 C15H23KO10Znformula weight 3729.38 415.21 467.80crystal size (mm) 0.36 × 0.16 × 0.28 0.28 × 0.08 × 0.40 0.72 × 0.12 × 0.05crystal system orthorhombic orthorhombic monoclinicspace group Ccca Pnma C2/ca (Å) 26.138(3) 27.730(3) 15.437(5)b (Å) 35.912(3) 11.6608(11) 15.985(5)c (Å) 22.594(2) 5.1180(5) 16.475(6)α (deg) 90.00 90.00 90.00β (deg) 90.00 90.00 90.145(13)γ (deg) 90.00 90.00 90.00volume (Å3) 21208(4) 1654.9(3) 4065(2)Z 4 4 8Dcalc/g cm−3 1.168 1.699 1.529F(000) 7696 852 1936μ Mo Kα (mm−1) 1.247 1.092 1.461temperature (K) 100(2) 293(2) 293(2)Rint 0.0950 0.0266 0.1174range of h, k, l −27/27, −37/38, −23/23 −32/32, −13/13, −6/6 −17/17, −17/17, −17/18θmin/max (deg) 1.13/22.18 1.47/25.00 1.83/23.39reflections collected/unique/observed [I > 2σ(I)] 75118/6661/3807 14465/1532/1433 15532/2956/1926data/restraints/parameters 6661/10/488 1532/0/129 2956/0/250goodness of fit on F2 1.035 2.097 1.079final R indices [I > 2σ(I)] R1 = 0.0711 R1 = 0.0689 R1 = 0.0627

wR2 = 0.2172 wR2 = 0.2403 wR2 = 0.1734R indices (all data) R1 = 0.1140 R1 = 0.0713 R1 = 0.0955

wR2 = 0.2417 wR2 = 0.2428 wR2 = 0.1916

Figure 2. Crystal structure illustration of MOP-TO. (a) Discretenanocage, (b) MOP-TO molecule displaying the space (yellowsphere) within the nanocage, (c) 2D packing of the cage moleculessustained by C−H···π interactions, and (d) overall 3D packing of themolecules, showing continuous channels down the a axis. The inset isa photograph of the single crystal.

Figure 3. (a) The TEM micrograph of the discrete nanocage MOP-TO. (b) Selected area electron diffraction of the nanocage.

Crystal Growth & Design Article

dx.doi.org/10.1021/cg4018322 | Cryst. Growth Des. 2014, 14, 1331−13371333

mirror plane. Two carboxylate moieties (syn to each other)were found to be coordinated in an extended fashion tooctahedral Co(II) metal centers; the other carboxylateremained free from coordination.The metal center Co(II) was located on a mirror symmetry

and displayed slightly distorted octahedral geometry; theequatorial positions were coordinated by O atoms of twocarboxyates and water, and the axial sites were occupied bywater molecules. The structure may best be described as a 1Dcoordination polymer, wherein the syn-related carboxylatescoordinated the adjacent metal centers, resulting in a 1Dpolymeric chain. The free carboxylate participated in hydrogenbonding with the coordinated water molecule of theneighboring chain (O···O = 2.747(3)−3.013(3) Å]. Thecoordinated carboxylates also participated in hydrogen bondingwith the coordinated water molecule of the neighboring chain[O···O = 2.849(5) Å] resulting in an overall 3D hydrogen-bonded network (Figure 4). Thermogravimetric data analyses

(Figure S2 of the Supporting Information) revealed a weightloss of 17.4% that occurred within a temperature range of55.5−156.2 °C; this was attributed to the weight loss of thefour coordinated water molecules (calculated weight loss of17.0%) corroborating well with the single crystal structure ofTMBTA-Co(II).[{(H2O)2Zn(μ-TMBTA)Zn·K}·2H2O]∝. Colorless plate-

shaped crystals of TMBTA-Zn(II) were found to be crystal-lized in the centrosymmetric monoclinic space group C2/c. Inthe asymmetric unit, one fully occupied ligand, two Zn(II)metal centers located on special positions (center of inversionand 2-fold axis), two water molecules coordinated to one of the

metal centers, two lattice included water, and one K+ ion werelocated. Inclusion of K+ ion was due to KOH used in thesynthesis, and also, it was a requirement to achieve chargebalance.The tripodal ligand adopted syn−syn−syn conformation. All

the carboxylates participated in coordination with the Zn(II)metal center that displayed two different coordination geo-metries: tetrahedral (on a 2-fold axis) and octahedral (on acenter of inversion). The overall coordination network was 3D,wherein a looped-chain type of architecture was formed due toextended coordination of the two carboxylates to tetrahedronZn(II) metal center. The other carboxylate bridged suchlooped-chain via octahedral Zn(II) coordination, generating anoverall 3D coordination network. The lattice occluded watermolecules were found to be participating in hydrogen bondingvia O−H···O interactions [O···O = 2.725(9)−2.930(14) Å]involving the metal-coordinated water and carboxylate Oatoms. Weak interactions such as C−H···π (3.364 Å) involvingthe methyl C−H and π cloud of the adjacent aromatic rings andcation−π (2.996 Å), involving K+ and the aromatic ring werealso observed (Figure 5). Thermogravimetric data analyses

(Figure S3 of the Supporting Information) revealed a weightloss of 15.9% that occurred within a temperature range of28.1−105.2 °C; this was attributed to the weight loss of twocoordinated and two lattice-occluded water molecules (calcu-lated weight loss of 15.4%). This observation was in goodagreement with the single crystal structure of TMBTA-Zn(II).The crystalline phase purity of both the coordination

polymers were established by powder X-ray diffraction(PXRD) (Figure S6−S7 of the Supporting Information).It is understandable that if the axial coordinating ligands are

removed from CPWSBU, the Cu(II) center might act as aLewis acid catalyst in catalyzing important organic trans-formations.19 In fact, in a recent report, it was shown that aMOF having CPWSBU was able to catalyze aerobic oxidationof benzyl alcohol to benzaldehyde, wherein a continuous

Figure 4. Crystal structure illustration of TMBTA-Co(II). (a) Parallelpacking of 1D polymeric chain displaying H-bonding interaction. (b)Overall 3D hydrogen-bonded network. The inset is a photograph ofthe single crystal.

Figure 5. Crystal structure illustration of TMBTA-Zn(II). (a) 1Dpolymeric-looped chain displaying tetrahedral (light green) andoctahedral (blue) Zn(II) metal centers, (b) cation−π interactionsinvolving the K+ ion and phenyl ring, and (c) overall 3D networkcontaining lattice-occluded water molecules (red balls). The inset is aphotograph of the single crystal.

Crystal Growth & Design Article

dx.doi.org/10.1021/cg4018322 | Cryst. Growth Des. 2014, 14, 1331−13371334

channel exposing the catalytic metal center Cu(II) wasavailable.20 On the other hand, MOPs are unlikely to pack insuch a way that continuous channels exposing the catalyticmetal centers are formed. To demonstrate the Lewis acidbehavior in catalysis of CPWSBU in MOP, Zhou et al.functionalized a CPWSBU-based MOP to make it soluble in anoncoordinating solvent to achieve homogeneous catalysis.21

With this background, we decided to carry out the possibility ofexploiting the Lewis acid behavior of Cu(II) in CPWSBU inMOP-TO in a heterogeneous fashion. For this purpose, wechose to study the aerobic oxidation of benzyl alcohol tobenzaldehyde using TEMPO as a radical initiator (Scheme 2).

In the crystal structure of MOP-TO (vide supra), thenanocage molecule itself did not have any porosity. Packing ofthe MOP molecules resulted in a continuous channel runningdown the a axis, which did not expose the Cu(II) metal center.In fact, the continuous channels were occupied by solventmolecules. In order to access the Cu(II) metal center forcatalysis, we first dispersed MOP-TO crystals in CHCl3 byrepeated washing (for 3 days), followed by heating undervacuum (100 °C, 2 h) with the hope that axially free randomaggregation of the nanocage molecules would be formed in thebulk solid. MOP-TO so activated was then used in catalyticamount (3 mol % of the substrate) in TEMPO to catalyzeaerobic oxidation of benzyl alcohol. GC/MS analyses revealedthat the reaction was 99.0% complete within 12 h (Table S2 ofthe Supporting Information). To probe the nature of thecatalysis (homogeneous or heterogeneous), we allowed thereaction to proceed up to 38% conversion (in 3 h), and afterfiltering off the solid catalyst, we continued the reaction foranother 9 h, which resulted in another 10% conversion. In thecontrol experiment without any catalyst, the reaction did notproceed, even after 9 h, thereby indicating that some amount ofCu(II) was leached out into the solution. In fact, atomicabsorption spectroscopy (AAS) of the reaction mixturerevealed that 0.4% Cu was leached out into the solution thatpresumably contributed to the 10% conversion observed duringthe leaching experiment (Supporting Information). Theseresults indicated that the reaction was mainly heterogeneouslycatalyzed. We tried to monitor the fate of the catalyst duringreaction by FT-IR. A comparison FT-IR spectra comprised offreshly grown crystals of MOP-TO, activated MOP-TO, andMOP-TO after the reaction revealed that they were almostidentical, indicating nondegradation of the molecular structureof MOP-TO; in the spectra, metal-bound antisymmetric andsymmetric stretching of COO− could be seen within the rangeof 1609−1622 and ∼1400 cm−1, respectively. The O−Hstretching frequency of the occluded water molecules withinthe nanocage could also be observed at ∼3570 cm−1 in all thesespectra, thereby indicating that during washing, activation, and

catalysis, the nanocage molecule could retain the integrity of itsmolecular structure (Figure S8 of the Supporting Information).Interestingly, the FT-IR of the recovered catalyst after thesecond cycle (that displayed 99% completion of the reactionafter 14 h instead of 12 h in the first cycle) showed significantdifferences, indicating disintegration of the molecular structureof MOP-TO after the second cycle. It may be mentioned herethat since MOP-TO crystals were unstable outside its motherliquor due to fast evaporation of the lattice-occluded solvents,monitoring the fate of the crystalline phase of the catalyst undervarious conditions by PXRD was not possible. However, it waspossible to obtain the PXRD pattern of the freshly grown bulkcrystals of MOP-TO by placing the crystals in thediffractometer almost instantaneously after removing themfrom the mother liquor. Remarkably, this PXRD patternmatched quite well with the simulated pattern, indicating thecrystalline phase purity of MOP-TO. Upon exposure to theenvironment for even a short period of time,MOP-TO resultedin an amorphous PXRD pattern (Figure S5 of the SupportingInformation).

■ CONCLUSIONS

A truncated octahedron-shaped metal-organic-polyhedronderived from a tripodal C3-symmetric tricarboxylate ligandand Cu(NO3)2 was synthesized solvothermally and charac-terized by SXRD and ESI-MS. Interestingly, MOP-TOmolecules could be seen under HR-TEM as well. Subsequentformation of two coordination polymers namely TMBTA-Co(II) and TMBTA-Zn(II) derived from the same ligandunder similar solvothermal conditions emphasized the role ofthe Cu(II) paddle wheel SBU in generating the nanocagestructure MOP-TO. The Lewis acid character of the Cu(II)metal center in MOP-TO was exploited to catalyze aerobicoxidation of benzyl alcohol to benzaldehyde assisted byTEMPO. MOP-TO belonged to the rare class of metal−organic cage molecule derived from flexible ligand likeTMBTA.

■ EXPERIMENTAL SECTIONMaterials and Method. All the chemicals were commercially

available and used without further purification. Ligand TMBTA wassynthesized by following reported procedures with significantmodification.22 Elemental analyses ware carried out using a Perkin-Elmer 2400 Series-II CHN analyzer. FT-IR spectra were recordedusing Perkin-Elmer Spectrum GX, and TGA analyses were performedon a SDT Q Series 600 Universal VA.2E TA Instruments. Powder X-ray diffraction patterns were recorded on a Bruker AXS D8 AdvancePowder (Cu Kα1 radiation, λ = 1.5406 Å) diffractometer. The TEMwere recorded in the Jeol instrument using carbon-coated 300 meshAu grid at 200 KV. The mass spectrum was recorded on QTOF MicroYA263. NMR spectra (1H and 13C) were recorded using a 300 MHzBruker Avance DPX300 spectrometer. GC/MS measurements werecarried out with a Perkin-Elmer Clarus 680GC and SQ8T MS, usingcolumn Elite 5 MS (30 m × 0.25 mm × 0.25 μm) with a maximumtemperature of 300 °C. The copper content in a sample was estimatedby using a Shimadzu AA-6300 atomic absorption spectrometer (AAS)fitted with a double beam monochromator.

Characterization Ddata of (2,4,6-Trimethylbenzene)-1,3,5-Triacetic acid (TMBTA). (Yield: 486 mg, ∼97%). M.p: 268−269 °Cafter recrystallization from H2O/MeOH (1: 2 v/v). Anal. Data calcdfor C15H18O6: C, 61.22; H, 6.16. Found: C, 61.41; H, 6.33.

1H NMR(300 MHz, DMSO-d6): δ = 2.16 (s, 9H), 3.63 (s, 6H), 12.24 (s, 3H).ESI-MS: calcd for C15H18O6 295.20 (M+1). Found: [M + Na]+

317.10. FT-IR (KBr, cm−1): 3003, 3082, 1693s, 2974, 2897, 2638m,

Scheme 2. Oxidation of Benzyl Alcohol to Benzaldehydeusing MOP-TO with Oxygen

Crystal Growth & Design Article

dx.doi.org/10.1021/cg4018322 | Cryst. Growth Des. 2014, 14, 1331−13371335

2360m, 1411m, 1392m, 1286m, 1240m, 1188m, 1018m, 923m, 825m,680m, 653m cm−1.[{Cu12(TMBTA)8(DMA)4(H2O)8}·8H2O·48H2O] MOP-TO was

synthesized under solvothermal condition from a DMA−ethanolsolution of a mixture of TMBTA (97 mg, 0.33 mmol), Cu(NO3)2·3H2O (241.6 mg, 1 mmol), and pyridine (79 μL, 1 mmol). Themixture was taken carefully in a 25 mL sealed glass tube, heated at 85°C for 60 h, and allowed to cool slowly (5 °C per hour in 12 h). Aftercooling, good-looking block-shaped green crystals were obtained. Thecrystals were carefully characterized by SXRD, elemental analysis,PXRD, and FT-IR. Yield: ∼32% (100 mg, 0.321 mmol). FT-IR (KBr,cm−1): 3412, 1633, 1616, 1402s, 2933m, 1284m, 1201m, 1022s, 835m,756m, 713s, 642m, 590m cm−1. Due to the gradual loss of latticeoccluded solvents, elemental analysis of the crystals of MOP-TO wasinconsistent and, thus, not reported.[{Co(μ-TMBTA)(H2O)4}]∝TMBTA-Co(II) was synthesized

under solvothermal condition from a DMF−ethanol solution of amixture of TMBTA (97 mg, 0.33 mmol), Co(NO3)2·6H2O (291 mg, 1mmol), and pyridine (79 μL, 1 mmol). The mixture was takencarefully in a 25 mL sealed glass tube, heated at 80 °C for 72 h, andallowed to cool slowly (5 °C per hour in 12 h). After cooling, good-looking block-shaped pink crystals were obtained. The crystals werewashed with ethanol−water and carefully characterized by SXRD,elemental analysis, PXRD, and FT-IR. Yield: ∼59% (250 mg, 0.590mmol). Elemental analysis calcd for C15H24CoO10 (%): C, 42.56; H,5.72. Found: C, 42.07; H, 5.43. FT-IR (KBr, cm−1): 3358, 1718, 1560,1649, 1381, 2947, 2204m 1267s, 1201m, 1157s, 1026m, 831m, 750m,792m, 686m cm−1.[{(H2O)2Zn(μ-TMBTA)Zn·K}·2H2O]∝ TMBTA-Zn(II) was syn-

thesized under solvothermal condition from a water−ethanol solutionof a mixture of potassium salt of TMBTA (60 mg, 0.1468 mmol),ZnCl2 (57 mg, 0.42 mmol). The mixture was taken carefully in a 25mL Teflon-coated autoclaved bomb, heated at 120 °C for 48 h, andallowed to cool slowly. After cooling, good-looking plate-shapedcolorless crystals were obtained. The crystals were washed withethanol−water and carefully characterized by SXRD, elementalanalysis, PXRD, and FT-IR. Yield: ∼49% (50 mg, 0.1468 mmol).Elemental analysis calcd for C15H23KO10Zn (%): C, 38.51; H, 4.96.Found: C, 38.04; H, 4.88. FT-IR (KBr, cm−1): 3396, 3240, 1604,1556s, 1384s, 2978brs, 1271s 1228m, 1188m, 1022m, 904m, 831m,812m, 744m, 692s, 615m, 542m cm−1.Catalysis. In a three-neck round-bottomed flask, an appropriate

amount of activated catalyst MOP-TO (50 mg, 3 mol %), sodiumcarbonate (53 mg, 1 eqiv.), and TEMPO (39.5 mg, 0.5 equiv) weretaken. To this mixture, 5 mL of acetonitrile was added, followed by theaddition of benzyl alcohol (52 μL, 1 equiv). The reaction mixture wasstirred vigorously at 60 °C under oxygen atmosphere. The progress ofthe reaction was monitored by GC/MS of the aliquots, taken after acertain interval. After the reaction was over, the mixture was cooled toroom temperature. The catalyst was centrifuged out, and thesupernatant organic part was characterized by GC/MS.Single-Crystal X-ray Crystallography. Single-crystal X-ray

diffraction data were collected using Mo Kα (λ = 0.7107 Å) radiationon a BRUKER APEX II diffractometer equipped with a CCD areadetector. Data collection, data reduction, and structure solution/refinement were carried out using APEX II. All the structures [MOP-TO, TMBTA-Co(II), and TMBTA-Zn(II)] were solved by directmethods and refined in a routine manner. In all the cases,nonhydrogen atoms were treated anisotropically. Whenever possible,the hydrogen atoms were located on a difference Fourier map andrefined. In other cases, the hydrogen atoms were geometrically fixed.CCDC no. 962728, 963230, and 963231 contains the supplementarycrystallographic data for this paper. These data can be obtained free ofcharge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from theCambridge Crystallographic Data Centre, 12 Union Road, CambridgeCB21EZ, U.K, by fax: (+44) 1223−336−033, or via e-mail:deposit@ccdc.cam.ac.uk).Powder X-ray diffraction. PXRD data were collected using a

Bruker AXS D8 Advance Powder (Cu Kα1 radiation, λ = 1.5406 Å)diffractometer equipped with a super speed LYNXEYE detector. The

sample was prepared by making a thin film of finely powdered sample(∼30 mg) over a glass slide. The experiment was carried out with ascan speed of 0.3 s/step (step size = 0.02°) for the scan range of 5−35° 2θ.

■ ASSOCIATED CONTENT*S Supporting InformationCambridge Structural Database, molecular plots, and H-bonding parameters of MOP-TO, TMBTA-Zn(II), andTMBTA-Co(II), TGA, PXRD, EDX, AAS, FT-IR, and CIFcheck reports. This material is available free of charge via theInternet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: ocpd@iacs.res.in.Present Addresses‡Institute of Condensed Matter and Nanosciences,Universite Catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve, Belgium.§Department of Organic Chemistry, Indian Association for theCultivation of Science, 2A and 2B Raja S. C. Mullick Road,Kolkata 700032, West Bengal, IndiaNotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSP.D. thanks the Department of Science & Technology (DST),New Delhi, India, for financial support. M.P. and N.N.A. thankCSIR and IACS for research fellowships, respectively. Singlecrystal X-ray diffraction was performed at the DST-fundedNational Single Crystal Diffractometer Facility at the Depart-ment of Inorganic Chemistry, IACS.

■ REFERENCES(1) (a) Perry, J. J.; Perman, J. A.; Zaworotko, M. J. Chem. Soc. Rev.2009, 38, 1400. (b) Uemura, T.; Yanai, N.; Kitagawa, S. Chem. Soc.Rev. 2009, 38, 1228. (c) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J.Chem. Soc. Rev. 2011, 111, 6810. (d) Furukawa, H.; Cordova, K. E.;O’Keeffe, M.; Yaghi, O. M. Nature 2013, 341, 974. (e) Tam, A. Y.-Y.;Yam, V. W.-W. Chem. Soc. Rev. 2013, 42, 1540. (f) Safont-Sempere, M.M.; Fernandez, G.; Wurthner, F. Chem. Rev. 2011, 111, 5784.(2) Wang, C.; Zhang, T.; Lin, W. Chem. Rev. 2012, 112, 1084.(3) (a) Corma, A.; García, H.; Llabres I Xamena, F. X. Chem. Rev.2010, 110, 4606. (b) Uemura, T.; Kitaura, R.; Otha, Y.; Nagaoka, M.;Kitagawa, S. Angew. Chem., Int. Ed. 2006, 45, 4112. (c) Zou, R.-Q.;Sakurai, H.; Han, S.; Zhong, R.-Q.; Xu, Q. J. Am. Chem. Soc. 2007, 129,8402. (d) Yoon, M.; Srirambalaji, R.; Kim, K. Chem. Rev. 2012, 112,1196. (e) Lee, J. Y.; Farha, O. K.; Roberts, J.; Scheidt, K. I.; Nguyen, S.T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450.(4) (a) Dastidar, P. Chem. Soc. Rev. 2008, 37, 2699. (b) Terech, P.;Weiss, R. G. Chem. Rev. 1997, 97, 3133. (c) Molecular Gels. Materialswith Self-Assembled Fibrillar Networks; Weiss, R. G., Terech, P., Eds.;Springer: Dorrdecht, The Netherlands, 2005. (d) Estroff, L. A.;Hamilton, A. D. Chem. Rev. 2004, 104, 1201. (f) Meazza, L.; Foster, J.A.; Fucke, K.; Metrangolo, P.; Resnati, G.; Steed, J. W. Nat. Chem.2013, 5, 42.(5) Cui, Y.; Yue, Y.; Chen, B. Chem. Rev. 2012, 112, 1126.(6) Eltoukhy, A. A.; Chen, D.; Alabi, C. A.; Langer, R.; Anderson, D.G. Adv. Mater. 2013, 25, 1487.(7) Muraoka, T.; Koh, C.-Y.; Cui, H.; Stupp, S. I. Angew. Chem., Int.Ed. 2009, 48, 5946.(8) (a) Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.; Choi, S. B.;Choi, E.; Yazaydin, A. O.; Snurr, R. Q.; O’Keeffe, M.; Kim, J.; Yaghi,O. M. Science 2010, 329, 424. (b) Sanchez, C.; Shea, K. J.; Kitagawa, S.

Crystal Growth & Design Article

dx.doi.org/10.1021/cg4018322 | Cryst. Growth Des. 2014, 14, 1331−13371336

Chem. Soc. Rev. 2011, 40, 471. (c) Subramanian, S.; Zaworotko, M. J.Angew. Chem., Int. Ed. 1995, 34, 2127. (d) Adarsh, N. N.; Dastidar, P.Chem. Soc. Rev. 2012, 41, 3039. (e) Tanabe, K. K.; Cohen, S. M. Chem.Soc. Rev. 2011, 40, 498. (f) Li, M.; Li, D.; O’Keeffe, M.; Yaghi, O. M.Chem. Rev. 2014, 114, 1343−1370. (g) Thallapally, P. K.; Tian, J.;Kishan, M. R.; Fernandez, C. A.; Dalgarno, S. J.; Mcgrail, P. B.;Warren, J. E.; Atwood, J. A. J. Am. Chem. Soc. 2008, 130, 16842.(h) Cook, T. R.; Zheng, Y.-R.; Stang, P. J. Chem. Rev. 2013, 113, 734.(i) Wang, X.-S.; Chrzanowski, M.; Gao, W.-Y.; Wojtas, L.; Chen, Y.-S.;Zaworotko, M. J.; Ma, S. Chem. Sci. 2012, 3, 2823.(9) (a) Eddaoudi, M.; Kim, J.; Wachter, J. B.; Chae, H. K.; O’Keeffe,M.; Yaghi, O. M. J. Am. Chem. Soc. 2001, 123, 4368. (b) Olenyuk, B.;Whiteford, J. A.; Fechtenkotter, A.; Stang, P. J. Nature 1999, 398, 796.(c) Sun, Q.-F.; Sato, S.; Fujita, M. Nat. Chem. 2012, 4, 330.(d) Hiraoka, S.; Fujita, M. J. Am. Chem. Soc. 1999, 121, 10239. (e) Li,D.; Zhou, W.; Landskron, K.; Sato, S.; Kiely, J. C.; Fujita, M.; Liu, T.Angew. Chem., Int. Ed. 2011, 50, 5182. (f) Li, J- R.; Zhou, H.-C. Nat.Chem. 2010, 2, 893. (g) Sun, L.-B.; Li, J.-R.; Lu, W.; Gu, Z.-Y.; Luo, Z.;Zhou, H.-C. J. Am. Chem. Soc. 2012, 134, 15923. (h) Prakas, M. J.; Oh,M.; Liu, X.; Han, K. N.; Seong, G. H.; Lah, M. S. Chem. Commun.2010, 46, 2049. (I) Zhang, Z.; Wojtas, L.; Zaworotko, M. J. Chem. Sci.2014, DOI: 10.1039/c3sc53009j.(10) (a) Tashiro, S.; Tominaga, M.; Kawano, M.; Therrien, B.; Ozeki,T.; Fujita, M. J. Am. Chem. Soc. 2005, 127, 4546. (b) Davis, A. V.;Raymond, K. N. J. Am. Chem. Soc. 2005, 127, 7912.(11) Mal, P.; Breiner, B.; Rissanen, K.; Nitschke, J. R. Science 2009,324, 1697.(12) (a) Pluth, M. D.; Bergman, R. G.; Raymond, K. N. Science 2007,316, 85. (b) Yoshizawa, M.; Tamura, M.; Fujita, M. Science 2006, 312,251.(13) Jung, M.; Kim, H.; Baek, K.; Kim, K. Angew. Chem., Int. Ed.2008, 47, 5755.(14) Tranchemontagne, D. J.; Ni, Z.; O’Keeffe, M.; Yaghi, O. M.Angew. Chem., Int. Ed. 2008, 47, 5136.(15) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972.(16) (a) Kuehl, C. J.; Huang, S. D.; Stang, P. J. J. Am. Chem. Soc.2001, 123, 9634. (b) Bunzen, J.; Iwasa, J.; Bonakdarzadeh, P.; Numata,E.; Rissanen, K.; Sato, S.; Fujita, M. Angew. Chem., Int. Ed. 2012, 51,3161. (c) Murase, T.; Nishijima, Y.; Fujita, M. J. Am. Chem. Soc. 2012,134, 162.(17) (a) Chen, B.; Eddaoudi, M.; Reineke, T. M.; Kampf, J. W.;O’keefe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2000, 122, 11559.(b) Zheng, B.; Bai, J.; Duan, J.; Wojtas, L.; Zaworotko, M. J. J. Am.Chem. Soc. 2011, 133, 748. (c) Zou, Y.; Park, M.; Seunghee, H.; Lah,M. S. Chem. Commun. 2008, 2340. (d) Chui, S. S.-Y.; Lo, S. M.-F.;Charmant, J. P. H.; Orpen, G.; Williums, I. D. Science 1999, 283, 1148.(18) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.(19) (a) Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Adv. Synth.Catal. 2010, 352, 3022. (b) Schlichte, K.; Kratzke, T.; Kaskel, S.Microporous Mesoporous Mater. 2004, 73, 81. (c) Corma, A.; Iglesias,M.; Llabr_es i Xamena, F. X.; Sanchez, F. Chem.Eur. J. 2010, 16,9789. (d) Luz, I.; Llabr_es i Xamena, F. X.; Corma, A. J. Catal. 2010,276, 134. (e) Alaerts, L.; Seguin, E.; Poelman, H.; Thibault-Starzyk, F.;Jacobs, P. A.; De vos, D. E. Chem.−Eur. J. 2006, 12, 7353.(f) Fernandez, C. A.; Thallapally, P. K.; Liu, J.; Peden, C. H. F.Cryst. Growth Des. 2010, 10, 4118.(20) Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. ACS Catal. 2011,1, 48.(21) Lu, W.; Yuan, D.; Yakovenko, A.; Zhou, H.-C. Chem. Commun.2011, 47, 4968.(22) (a) Van der Made, A. W.; Van der Made, R. H. J. Org. Chem.1993, 58, 1262. (b) Mahnke, D. J.; Mcdonald, R.; Hof, F. Chem.Commun. 2007, 3738. (c) Kim, J.; Ryu, D.; Sei, Y.; Yamaguchi, K.;Ahn, K. H. Chem. Commun. 2006, 1136.

Crystal Growth & Design Article

dx.doi.org/10.1021/cg4018322 | Cryst. Growth Des. 2014, 14, 1331−13371337