Inorganic Chemistry Communications 15 (2012) 5–7

Contents lists available at SciVerse ScienceDirect

Inorganic Chemistry Communications

j ourna l homepage: www.e lsev ie r .com/ locate / inoche

A novel peculiar vanadium(IV) complex with 2-pyridinaldoxime: Synthesis,structure, electrochemical behavior and DNA binding

Xin Tan, Xiaojia Han, Jingnan Feng, Jinli Liu, Yinzhuang Zhou ⁎Department of Chemistry, Capital Normal University, Beijing 100048, PR China

⁎ Corresponding author. Tel.: +86 10 68902491.E-mail address: zhouyz7813@x263.net (Y. Zhou).

1387-7003/$ – see front matter © 2011 Published by Eldoi:10.1016/j.inoche.2011.09.015

a b s t r a c t

a r t i c l e i n f o

Article history:Received 26 May 2011Accepted 5 September 2011Available online 21 September 2011

Keywords:VanadiumTetranuclear complex2-pyridinaldoximeElectrochemical behaviorDNA binding

A novel tetranuclear vanadium(IV) complex, [VIV4O4(μ4-O)(μ-OCH3)2(pyCHNO)4·H2O] (1) (pyCHNOH=2-

pyridinaldoxime), was synthesized and characterized. The binding propensity of the complex 1 to calf thymusDNA (CT-DNA)was studied by fluorescence spectroscopy, UV–vis absorption and viscosity measurement. Singlecrystal X-ray diffraction analysis reveals that the complex 1 possesses centrosymmetric structure and pseudo-tetrahedron conformation. Electrochemical behavior indicates the quasi-reversible nature of the electron-transfer process in the complex 1. The results suggest the groove-binding propensity of the complex 1.

sevier B.V.

© 2011 Published by Elsevier B.V.

Introduction

Researches on the vanadium(IV) complexes have receivedmuch at-tention owing to their ability of binding and cleaving DNA under phys-iological conditions [1,2], and they can be potentially applied asidentifying cytotoxic agents with potent activity against cancer cells[3], and probes for genomic research [4,5] as well as for conformationalstudies of nucleic acid. Therefore, the synthesis of vanadium(IV) com-plexes is very appealing and challenging.

The ligand wemake use of, 2-pyridinaldoxime, is a versatile ligandsupporting different types of complexes, which is a result of thisligand system being prone to coordinate through their pyridyl andoximato groups, acting both as chelating and/or bridging bi-, tri-and tetra-dentate agent [6]. Numerous high nuclearity transitionmetal complexes have been successfully synthesized due to thecombination of flexibility and variety of coordination modes of 2-pyridinaldoxime [7–9]. Practically little is known about the vanadi-um(IV) coordination chemistry of 2-pyridinaldoxime [10], and thefact has prompted us to investigate their vanadium(IV) coordinationchemistry.

Hereinwe report on the synthesis and characterization of a novel andpeculiar tetranuclear vanadium(IV) complex [VIV

4O4(μ4-O)(μ-OCH3)2(pyCHNO)4·H2O] (1). The tetranuclear complex exhibits multifold char-acters in its own structure, such as centrosymmetric and papilionaceousconfiguration. The complex 1 possesses pseudo-tetrahedron conforma-tion with four VIV centers bridged by one μ4-O atom. In recent years

several structurally characterized tetranuclear vanadium complexeshave been reported [11–13]. To the best of our knowledge, only onecomplex [11] indicates formation of a distorted tetrahedron of VIII cen-ters bound to a central μ4-oxide ligand. So the complex 1 is the firstobtained tetranuclear vanadium(IV) compound by using 2-pyridinal-doxime, inwhich it adopts centrosymmetric structure and pseudo-tetra-hedron conformation with four VIV centers bridged by one μ4-O atom.

A mixture of 2-pyridinaldoxime ligand (0.061 g, 0.5 mmol), indene-1,2,3-trione (0.096 g, 0.5 mmol) and VO(acac)2 (acac=acetylacetone)(0.133 g, 0.5 mmol) in 10 mL methanol was stirred in one-pot for 10 hin ambient atmosphere. The brown green transparent liquid was filteredfollowed by addition of diethyl ether on the filtrate. The filtrate was keptat room temperature and black green clubbed crystals suitable for X-raydiffraction were harvested in 40% yield after standing for two months.Anal. Calcd. for C26H28N8O12V4 (848.32): C, 36.81%; H, 3.33%; N, 13.21%.Found: C, 36.14%; H, 3.53%; N, 13.14%. IR spectrum (cm−1, KBr pellet):3443(vs), 2926(w), 2826(w), 1605(s), 1545(w), 1530(w), 1473(m),1431(w), 1384(w), 1345(w), 1300(w), 1252(w), 1221(w), 1112(m),1087(s), 975(m) 961(s), 914(w), 890(w), 778(w), 753(w), 691(m),647(w), 564(s), 465(w), 411(w). ESI–MS (+): m/z 830.4 [VIV

4O4(μ4-O)(μ-OCH3)2(pyCHNO)4]+.

Single-crystal X-ray diffraction [14] study performed on the titlecomplex revealed that the complex 1 possesses centrosymmetricstructure and pseudo-tetrahedron conformation with four VIV centersbridged by one μ4-O atom (Figs. 1 and 2). In this arrangement, V1 isoctahedrally coordinated by N1, N2 from one 2-pyridinaldoxime li-gand, O2A from another 2-pyridinaldoxime ligand, O4 from onebridged oxygen atom, O6 from one bridged methanol group and O3from the terminal oxo group V1=O3. N1, O2A, O4 and O6 occupythe equatorial positions of V1. The vanadium atom is 0.3706 Å away

Fig. 1. Crystal structure of the complex [VIV4O4(μ4-O)(μ-OCH3)2(pyCHNO)4] (hydrogen

atoms are omitted).

6 X. Tan et al. / Inorganic Chemistry Communications 15 (2012) 5–7

from the least-squares plane defined by the equatorial atoms, withinthe normal range for vanadyl complexes [15,16]. Similarly, N3, O1A,O4, O6 occupy the equatorial positions of V2, and O5, N4 occupy theaxes. V1A and V2A arrangements are the same to V1 and V2, respec-tively. The V1–N2 bond distance of 2.260 Å trans to the V1=O3 bondis 0.129 Å longer than the V1–N1 bond in the equatorial plane, as aconsequence of the strong trans influence of the oxo group. The situ-ation has been found in the previous vanadium complexes researches[17,18]. The dihedral angle of V1-N1-C2-C1-N2 plane and N1-C6-C5-C4-C3-C2 plane is 4.7°, and the dihedral angle of V2-N4-C7-C8-N3plane and N3-C8-C9-C10-C11-C12 plane is 11.5°. Because of its cen-trosymmetric conformation, the corresponding dihedral angles forV1A, V2A are also 4.7° and 11.5°, respectively. Since the dihedralangles are fairly small, the interrelated two planes of them can beconsidered approximately as one plane. However, the V1-N1-C6-C5-C4-C3-C2-C1-N2 plane is nearly vertical to the V2A-N4A-C7A-C8A-

Fig. 2. The pseudo-tetrahedron conformation of the complex 1.

C9A-C10A-C11A-C12A-N3A plane by reason of the dihedral angle(91.7°). Fig. S1 shows the papilionaceous structure of the complex 1.

The complex 1 has redox activity and its electrochemical behavior isshown in Fig. S2. The nature of the 2-pyridinaldoxime ligand attached tothe [VIVO]2+ centre results in the quasi-reversible nature of theelectron-transfer process. The binding propensity of the complex 1 tocalf thymus DNA (CT-DNA) was studied by fluorescence spectroscopy,UV–vis absorption and viscosity measurement (Fig. S3, Fig. S4, Fig. S5).The complex 1 shows moderate binding propensity to CT-DNA at thegroove.

In summary, a novel vanadium complex 1 has been synthesized andcharacterized. The tetranuclear vanadium(IV) complex with μ4-O andsolvent molecule bridging is peculiar in the coordination chemistry ofvanadium. In addition, the results reveal the groove-binding nature ofthe complex 1.

Acknowledgement

Thisworkwas supported by the Scientific Research CommonProgramof Beijing Municipal Commission of Education (KM200910028011).

Appendix A. Supplementary material

CCDC 703824 contains the supplementary crystallographic data forthis paper. These data can be obtained free of charge from theCambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this articlecan be found in the online version.

Supplementary data to this article can be found online at doi:10.1016/j.inoche.2011.09.015.

References

[1] N. Butenko, A.I. Tomaz, O. Nouri, E. Escribano, V. Moreno, S. Gama, V. Ribeiro, J.P.Telo, J.C. Pesssoa, I. Cavaco, DNA cleavage activity of VIVO(acac)2 and derivatives,J. Inorg. Biochem. 103 (2009) 622–632.

[2] P.K. Sasmal, Saha Sounik, R. Majumdar, R.R. Dighe, A.R. Chakravarty, Photocytotoxicoxovanadium(IV) complexes showing light-induced DNA and protein cleavageactivity, Inorg. Chem. 49 (2010) 849–859.

[3] R.K. Narla, Y.H. Dong, O.J. D'Cruz, C. Navara, F.M. Uckun, Bis(4,7-dimethyl-1,10-phenanthroline) sulfatooxovanadium(IV) as a novel apoptosis-inducing anti-cancer agent, Clin. Cancer Res. 6 (2000) 1546–1556.

[4] M. Sam, J.H. Hwang, G. Chanfreau, M.M. Abu-Omar, Hydroxyl radical is the activespecies in photochemical DNA strand scission by bis(peroxo)vanadium(V)phenanthroline, Inorg. Chem. 43 (2004) 8447–8455.

[5] D.W.J. Kwong, O.Y. Chan, R.N.S. Wong, S.M. Musser, L. Vaca, S.I. Chan, DNA-photocleavage activities of vanadium(V)-peroxo complexes, Inorg. Chem. 36(1997) 1276–1277.

[6] C.J. Milios, T.C. Stamatatos, S.P. Perlepes, The coordination chemistry of pyridyloximes, Polyhedron 25 (2006) 134–194.

[7] T.C. Stamatatos, C. Papatriantafyllopoulou, E. Katsoulakou, C.P. Raptopoulou, S.P.Perlepes, 2-Pyridyloximate clusters of cobalt and nickel, Polyhedron 26 (2007)1830–1834.

[8] T.C. Stamatatos, D. Foguet-Albiol, C.C. Stoumpos, C.P. Raptopoulou, A. Terzis, W.Wernsdorfer, S.P. Perlepes, G. Christou, Initial example of a triangular single-molecule magnet from ligand-induced structural distortion of a [MnIII3O]7+ complex,J. Am. Chem. Soc. 127 (2005) 15380–15381.

[9] T. Weyhermüller, R. Wagner, S. Khanra, P. Chaudhuri, A magnetostructural study oflinear NiIIMnIIINiII, NiIICrIIINiII and triangular NiII3 species containing (pyridine-2-aldoximato)nickel(II) unit as a building block, Dalton Trans. (2005) 2539–2546.

[10] E.E. Hamilton, P.E. Fanwick, J.J. Wilker, The elusive vanadate (V3O9)3−: isolation,crystal structure, and nonaqueous solution behavior, J. Am. Chem. Soc. 124(2002) 78–82.

[11] S. Khanra, M. Kloth, H. Mansaray, C.A. Muryn, F. Tuna, E.C. Sañudo, M. Helliwell,E.J.L. McInnes, R.E.P. Winpenny, Synthesis of molecular vanadium(III) phospho-nates, Angew. Chem. Int. Ed. 46 (2007) 5568–5571.

[12] J.K. Jabor, R. Stösser, M. Feist, P. Neubauer, M. Meisel, New directions in the preparationand redox chemistry of fluoride-templated tetranuclear vanadium phosphonate cagecompounds, Mn+[(V2O3)2(RPO3)4CF]n, Inorg. Chem. 47 (2008) 9293–9302.

[13] A. Sarkar, S. Pal, Divanadium(V) and trapped valence linear tetravanadium(IV,V,V,IV) complexes, Eur. J. Inorg. Chem. (2009) 5391–5398.

[14] Crystal structure analysis of 1: The data were collected at 293±2 K using aSiemens SMART-CCD X-ray single diffractometer (graphite monochromatized MoKα radiation;λ=0.71073 Å). The structurewas solved by directmethods (SHELXTLVersion 5.10) and refined by full-matrix least squares on F2. Crystal data for [VIV

4O4

(μ4-O)(μ-OCH3)2(pyCHNO)4·H2O] (1): M=848.32, monoclinic, C2/c, a=19.410(4)

7X. Tan et al. / Inorganic Chemistry Communications 15 (2012) 5–7

Å, b=12.183(2)Å, c=14.349(3)Å, α=γ=90°, β=98.46(3)°, Z=4,μ=1.152 mm−1, R1=0.0337 (IN2σ(I)), wR2=0.0877 (all data), and thegoodness-of-fit on F2 is 1.070.

[15] L.F. Vilas Boas, J. Costa Pessoa, Chapter on Vanadium, in: G. Wilkinson, R.D.Gillard, J.A. McCleverty (Eds.), Comprehensive Coordination Chemistry, vol. 3,Pergamon Press, Oxford, 1987, pp. 453–583.

[16] C.E. Holloway, M. Melnik, Vanadium coordination compounds: classification andanalysis of crystallographic and structural data, Rev. Inorg. Chem. 7 (1985)75–159.

[17] R. Tawa, K. Uchida, J. Taniyama, Y. Fujisawa, S. Fujimoto, T. Nagaoka, K. Kanamori,H. Sakurai, A new insulin-mimetic vanadyl complex, (N-pyridylmethylaspartate)oxovanadium(IV) with VO(N2O2) coordination mode, and evaluation of its effecton uptake of D-glucose by Ehrlich ascites tumor cells, J. Pharm. Pharmacol. 51(1999) 119–124.

[18] H. Yue, D. Zhang, Y. Chen, Z. Shi, S. Feng, An oxovanadium(IV) complex derivedfrom L-histidine, [V2O2(L-his)2(2,2′-bipy)2]·[C2H6O2·(2,2′-bipy)]: Hydrothermalsynthesis, crystal structure and magnetic properties, Inorg. Chem. Commun. 9(2006) 959–961.