ARTICLE

DOI: 10.1002/zaac.200800393

Solvent-Induced Pseudopolymorphism of a New Dinuclear Oxovanadium(V)Compound Based on 2,6-Di(hydroxymethyl)-4-methylphenol

Lian Chen,[a] Feilong Jiang,*[a] Mingyan Wu,[a] Ning Li,[a] Wentao Xu,[a] Chunfeng Yan,[a]

and Maochun Hong*[a]

Keywords: Vanadium; Pseudopolymorphism; Hydrogen bonds

Abstract. Reactions of VO2(acac) (Hacac � acetylacetone) and2,6-Di(hydroxymethyl)-4-methylphenol (H3L) in different organicsolvents give rise to two pseudopolymorphs of a new dinuclearoxovanadium(V) compound, [Et3NH]2[V2O4(HL)2] (1) and[Et3NH]2[V2O4(HL)2] ·H2O (2). The compounds have been synthe-

Introduction

The family of vanadium compounds has received consider-able attention for a long time due to its rich applicationsin many fields [1�7]. The vanadium compounds play animportant role in many enzymatic reactions such as hal-ogenation of organic substrate and fixation of nitrogen[8�10]. In vivo, it also shows insulin-mimetic responsewhich can simulate the uptake and metabolism of glucose[11�13]. During the last decade, great efforts have beenmade to prepare and investigate oxovanadium compoundsderived from various ligands in order to extend the searchfor more efficacious compounds and finally fully under-stand the exact role of vanadium compounds in biologicalsystem [14�22]. Based on the observation that many va-nadium complexes derived from polydentate ligands withoxygen donors can induce very desirable biological effects,specific examination of the structure of vanadium com-plexes with di- or polydented ligands is important to under-stand the modes by which vanadium acts in biological sys-tems.

On the other hand, supramolecular isomerism, which re-fers to the phenomenon of more than one type of supra-molecular networks formed from the same building blocks,is one of the most important aspect of supramolecularchemistry and crystal engineering and has attracted great

* F. JiangTel.: 0591-83714605E-Mail: fjiang@fjirsm.ac.cn

* M. HongE-Mail: hmc@fjirsm.ac.cn

[a] Key Laboratory of Optoelectronic Chemistry and PhysicsFujian Institute of Research on the Structure of MatterChinese Academy of SciencesFuzhou, Fujian 350002, P. R. China

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sized and characterized by elemental analyses, IR spectra andsingle-crystal X-ray diffraction. X-ray diffraction analyses revealthat 1 and 2 have different weak interactions and display remark-ably distinct hydrogen-bonded networks.

interest in recent years [23�30]. It is interesting in appreci-ating molecular arts and important in understanding struc-tural chemistry and exploring crystal engineering methods.The crystal structural analysis is the most effective methodin observing such phenomenon. However, the control ofcrystal and network structures in a predictable manner stillremains an elusive task. In true supramolecular isomerism,the building blocks and all the other components must beidentical. However, to satisfy the packing, solvent (guest)molecules are often included in the crystal lattice of thecoordination polymers, thereby making it difficult to obtaintrue supramolecular isomers. Thus, the coordination poly-mers having different solvent content (nature, composition,etc.) displaying different supramolecular structures areknown as pseudo-supramolecular isomers, which are closelyrelated to pseudo-polymorphs. In this paper, we employ thetridentate O donor ligand, 2,6-di(hydroxymethyl)-4-meth-ylphenol (H3L), to investigate the coordination chemistryof oxovanadium compounds, and describe the preparationsand crystal structures of two pseudo-supramolecular struc-tural isomers of a new dinuclear oxovanadium(V) complexbased on 2,6-di(hydroxymethyl)-4-methylphenol.

Experimental Section

Materials and Methods

All chemical reagents are commercially available without furtherpurification except that VO2(acac) was prepared as described in theliterature [31]. The C, N, H elemental analyses were performed ona German Elementary Vario EL III instrument. The FT-IR spectrawere recorded on a Nicolet Magna 750 FT-IR spectrometer usingKBr pellets in the range of 4000�400 cm�1. Crystal structure de-termination was performed on the Mercury CCD diffractometer.

L. Chen, F. Jiang, M. Wu, N. Li, W. Xu, C. Yan, M. HongARTICLESynthesis of [Et3NH]2[V2O4(HL)2] (1)

To the solution of VO2(acac) (183 mg, 1.0 mmol) in acetonitrile(30 ml), Et3N (0.14 mL, 1.0 mmol) and H3L (164 mg, 1.0 mmol)was added with stirring at room temperature for one day. Afterfiltration, the yellow filtrate was kept evaporating at room tempera-ture for crystallization. The prism, yellow crystals of 1 (237.5 mg)suitable for X-ray diffraction were obtained in a few days. The yieldwas 67.6 % (based on vanadium). Elemental analysis calculated forC15H26NO5V: C 51.28; H 7.46; N 3.99 %. Found: C, 51.25; H, 7.48;N, 4.02 %. IR(KBr pellet): 3337(br, m), 2980 (m), 2928(m),2847(m), 2689(m), 1608(w), 1472(sh, s), 1396(m), 1362(m),1266(sh), 1042(m), 1020(sh), 940(sh, s), 816(sh, s), 807(m), 687(m),588(s) and 560(sh) cm�1.

Synthesis of [Et3NH]2[V2O4(HL)2] ·H2O (2)

The procedure is similar to the synthesis of 1 except that tetra-hydrofuran was used instead of acetonitrile. The yield was 51.6 %(based on vanadium). Elemental analysis calculated forC30H54N2O11V2: C 50.00; H 7.55; N 3.89 %. Found: C, 50.22; H,7.48; N, 3.92 %. IR(KBr pellet): 3357(br, m), 2982 (m), 2929(m),2845(m), 1479(sh, s), 1390(m), 1360(m), 1265(sh), 1040(m), 1021(sh),941(sh, s), 895(sh, s), 808(m), 685(m), 587(s) and 561(sh) cm�1.

Crystal Structure Determination

Prism single crystals of 1 (0.40 mm � 0.30 mm � 0.20 mm) and 2(0.30 mm � 0.25 mm � 0.20 mm) were selected and mounted ona glass fiber, respectively. All intensity data were collected on aMercury CCD area-detector diffractometer equipped with a graph-ite-monochromatic Mo-K� radiation (λ � 0.71073 A) at 293(2) Kusing a ϕ-ω scan mode in the ranges of 2.63°<θ<27.48° for 1 and2.27°<θ<25.03° for 2. A total of 6541 reflections for 1 and 22118for 2 were collected, of which 3828 were unique (Rint � 0.0161)and 3448 were observed with I > 2σ(I) for the former while 6206were unique (Rint � 0.0303) and 5559 were observed for the latter.The data were corrected for Lp correction. The structure was

Table 2. Selected bond lengths /A and bond angles /° for compounds 1 and 2

1V(1)-O(5) 1.6400(14) V(1)-O(2) 1.9150(14) V(1)-O(1) 2.0219(14)V(1)-O(4) 1.6443(13) V(1)-O(1)#1 2.0049(13) O(1)-V(1)#1 2.0049(13)

O(5)-V(1)-O(4) 109.26(7) O(4)-V(1)-O(1)#1 95.17(7) O(2)-V(1)-O(1) 83.57(6)O(5)-V(1)-O(2) 100.74(6) O(2)-V(1)-O(1)#1 151.75(5) O(1)#1-V(1)-O(1) 68.56(6)O(4)-V(1)-O(2) 97.98(7) O(5)-V(1)-O(1) 122.92(6) V(1)#1-O(1)-V(1) 111.44(6)O(5)-V(1)-O(1)#1 98.32(6) O(4)-V(1)-O(1) 126.63(7)

2V(1)-O(4) 1.616(3) V(1)-O(1) 2.004(3) V(2)-O(6) 1.988(3)V(1)-O(5) 1.641(3) V(2)-O(10) 1.614(4) V(2)-O(6)#2 1.999(3)V(1)-O(2) 1.908(3) V(2)-O(9) 1.645(3) O(1)-V(1)#1 1.992(3)V(1)-O(1)#1 1.992(3) V(2)-O(7) 1.896(3) O(6)-V(2)#2 1.999(3)

O(4)-V(1)-O(5) 109.06(17) O(5)-V(1)-O(1) 131.99(16) O(9)-V(2)-O(6) 120.69(17)O(4)-V(1)-O(2) 101.81(15) O(2)-V(1)-O(1) 83.81(12) O(7)-V(2)-O(6) 84.11(14)O(5)-V(1)-O(2) 96.87(14) O(1)#1-V(1)-O(1) 69.45(14) O(10)-V(2)-O(6)#2 95.89(18)O(4)-V(1)-O(1)#1 97.76(16) O(10)-V(2)-O(9) 109.8(2) O(9)-V(2)-O(6)#2 96.10(16)O(5)-V(1)-O(1)#1 95.29(15) O(10)-V(2)-O(7) 97.81(17) O(7)-V(2)-O(6)#2 152.87(14)O(2)-V(1)-O(1)#1 152.09(12) O(9)-V(2)-O(7) 101.10(15) O(6)-V(2)-O(6)#2 69.04(15)O(4)-V(1)-O(1) 117.80(16) O(10)-V(2)-O(6) 128.18(19)

Symmetry transformations used to generate equivalent atoms: for 1, #1, �x�1,�y�1,�z�1; for 2, #1, �x,�y,�z, #2, �x�1,�y,�z.

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Table 1. Crystallographic data for compounds 1 and 2

Compound 1 2

Formula C15H26N1O5V1 C30H54N2O11V2

Formula Weight 351.31 720.63Crystal size /mm 0.40 � 0.30 � 0.20 0.30 � 0.25 � 0.20Crystal system triclinic monoclinicSpace group P1 P21/ca /A 8.5083(17) 16.278(7)b /A 9.7192(19) 17.970(8)c /A 11.302(2) 12.076(5)α /° 84.56(3)β /° 84.36(3) 94.398(6)γ /° 65.94(3)V /A3 847.7(3) 3522(3)Z 2 4Dc /Mg · m�3 1.376 1.359μ /mm�1 0.607 0.588F (000) 372 1528T /K 293(2) 293(2)λ (Mo-Kα) /A 0.71073 0.71073Reflns. Collected 6541 22118Reflns. Unique 3828 6206Parameters 204 404θ range for data collection(°) 2.63 to 27.48 2.27 to 25.03Rint 0.0161 0.0303Goodness-of-fit on F2 1.065 1.076R1, wR2 (I>2σ(I))a) 0.0367,0.0843 0.0773,0.2132R1, wR2 (all data)b) 0.0426,0.0889 0.0848,0.2194Max, min Δρ /e · A�3 0.336 and �0.285 1.097 and �0.556

a) R � Σ(�Fo���Fc�) / Σ�Fo�, b) wR � {Σw[(Fo2�Fc

2)2] / Σw[(Fo2)2]}1/2.

solved by direct methods and refined by full-matrix least-squarestechniques on F2. All hydrogen atoms, except two (H11A andH11B) of the isolated water, were calculated on the ideal positionsand refined isotropically, and all non-hydrogen atoms were refinedanisotropically. The programs for structure solution and refinementare SHELXS-97[32] and SHELXL-97[33], respectively. The maincrystallographic data are summarized in Table 1, and the selectedbond distances and bond angles in Table 2.

Pseudopolymorphism of a New Dinuclear Oxovanadium(V) Compound

Figure 1. ORTEP representation of dinuclear structure of 1. Thethermal ellipsoid are drawn at 30 % probability. (Symmetric code:A: �x�1,�y�1,�z�1).

Crystallographic data have been deposited with the CambridgeCrystallographic Data Centre, CCDC No. 689700 and No. 689701.Copies of this information can be obtained free of charge fromThe Director, CCDC, 12 Union Road, Cambridge CB2, 1EZ, UK(fax; �44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk orhttp://www.ccdc.cam.ac.uk).

Results and Discussion

Single-crystal X-ray diffraction study performed on 1 re-vealed that the compoundcrystallizes in the triclinic systemwith the space group P-1, and the asymmetric unit of com-plex 1 consists of a protonated triethylamine cation(Et3NH�) and one half of dinuclear oxovanadium anion[V2O4(HL)2]2�. Figure 1 shows a centrosymmetric structureof the dinuclear vanadium anion. Each vanadium center isfive-coordinated and adopts a highly distorted square pyra-mid coordination geometry. The coordination sphere iscomposed of five oxygen atoms, in which, three (O1, O2,O1A) are from two HL2� ligands with the V�O distanceranging from 1.9150(14) to 2.0219(14) A and the other two(O4 and O5) are terminal oxygen with the V�O distanceranging from 1.6400(14) to 1.6443(13) A. The distinct bonddistances suggest that the former (O1, O2, O1A) are singlebonded to the vanadium center while the latter (O4 andO5) are double bonded. The potentially tridentate ligand isonly doubly deprotonated i.e. HL2�. In each ligand mol-ecule, one oxygen atom (O2) from phenolato group acts asa terminal donor, whereas the deprotonated benzyl al-coholato donor acts as a μ2-bridge between the vanadiumatoms. The non-deprotonated benzyl alcohol functionsform intermolecular hydrogen bonds with the coordinatedterminal oxygen (O5) with the distance of O3�H3···O5 be-ing 2.8683(21) A, which link the neighboring dinuclearunits and lead 1 to form an infinite supramolecular chainalong c axis as Figure 2 illustrated. The protonated triethyl-amine molecules, which act as counterions to balance thecharge, are hydrogen bonded to the other terminal oxygenatoms (O4) and located in the two sides of the above infinitesupramolecular chains. The chains array in parallel and a3D view of 1 seen from the a axis is shown in Figure 3.

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Figure 2. The O�H···O hydrogen bonds link the neighboring dinuc-lear units forming an infinite supramolecular chain in compound 1.

Figure 3. Packing diagram of the compound 1 viewed along thea direction.

Compound 2 crystallizes in the monoclinic system withthe space group P21/c, and the asymmetric unit of 2 con-sists of two half of two dinuclear oxovanadium anion[V2O4(HL)2]2�, two protonated triethylamine cations(Et3NH�), and a lattice water molecule (Fig. 4). 1 and 2contain the same dinuclear building unit [V2O4(HL)2]2�,however, they display totally different arrangement andsupramolecular structures. Different from 1, the non-depro-tonated benzyl alcohol functions in 2 do not form hydrogenbonds with the coordinated terminal oxygen atoms, instead,the lattice water molecule (O11) is hydrogen bonded withthe coordinated terminal oxygen atoms (O5 and O10) anduncoordinated benzyl alcohol oxygen atom (O10). The hy-drogen bonding interactions extend 2 into a three-dimen-sional supramolecular structure showing one-dimensionallarge channels (Fig. 5). Et3NH� cations are located in thechannels and form hydrogen bonding with the lattice watermolecules with the N�H···O distance of 2.881(6) A. Thehydrogen bonds of 1 and 2 are listed in Table 3.

To balance the charge, the two vanadium atoms in thedouble-ring unit are both considered to be in V5� oxidationstates. The assignments are in good agreement with the re-sults of the valence sums [34] (Σs � expΣ[(1.803�d)/0.37],d�V�O distance in A) of the two compounds (4.961 for 1,5.141 and 5.172 for 2). The FT-IR spectrum of 1 confirmsthe result of the crystal structure determination. Symmetricand asymmetric stretching of different kinds of V�O bondsis observed: The peaks at 940 cm�1 are ascribed to terminalV�O bonds; strong bands at 807�816 and 588�687 cm�1

L. Chen, F. Jiang, M. Wu, N. Li, W. Xu, C. Yan, M. HongARTICLE

Figure 4. The asymmetric unit of complex 2 with atomic labeling.

Figure 5. Perspective view of the three-dimensional supramolecularstructure of 2 showing 1D channels. Et3NH� cations are omittedfor clarity.

Table 3. Hydrogen bonds lengths/A and bond angles/° of 1 and 2

D�H···A d(D�H) d(H···A) d(D···A) angle (DHA)

1O(3)�H(3)···O(5)#1 0.84 2.03 2.868(2) 172.7N(1)�H(1)···O(4) #1 0.93 1.76 2.683(2) 174.2O(3)#1�H(3)#1···O(5) 0.84 2.03 2.868(2) 172.7

2N(1)�H(1)···O(3) 0.91 2.02 2.881(6) 158.6N(2)�H(2)···O(9) 0.91 1.90 2.783(7) 164.4O(3)�H(3)···O(11) 0.86 2.12 2.771(2) 143.4O(11)�H(11A)···O(5)#1 0.88(2) 2.07(3) 2.906(2) 157.5(2)O(11)�H(11B)···O(10)#1 0.87(2) 1.81(4) 2.762(3) 166.1(2)

D: donor; A: acceptor.Symmetry transformations used to generate equivalent atoms: for 1, #1,�x�1,�y�1,�z; for 2, #1, x,�y�1/2,z�1/2.

are assigned to the antisymmetric stretching vibrations ofV�O�V features. One strong absorption for the stretchingfrequencies of the phenolic C�O bond can be observed at1265 cm�1 and the bonds at 1040 cm�1 and 1021 cm�1 areascribed to the benzylic C�O bonds. The FT-IR spectrumof 2 is quite similar to 1.

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Conclusions

Two supramolecular pseudopolymorphs of a new di-nuclear oxovanadium complex based on a tridentate Odonor ligand 2,6-di(hydroxymethyl)-4-methylphenol havebeen synthesized and crystallographically characterized.The pseudopolymorphs display distinct hydrogen-bondednetworks, which is supposed to be induced by different sol-vents. The result is expected to afford important infor-mation for not only vanadium coordination chemistry butalso modern crystal engineering. However, due to the smallfree energy differences between supramolecular pseudopo-lymorphs, to investigate the detailed formation mechanismof them is still underway.

Acknowledgement

This work was supported by the grants of 973 Program(2006CB932900), National Nature Science Foundation of Chinaand Nature Science Foundation of Fujian Province, NSF for YoungScientists of China (20801056), Young Scientist Funds of FujianProvince (No. 2007F3111).

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Received: June 19, 2008Accepted: September 9, 2008