Oxovanadium(IV) and -(V) Complexes of Dithiocarbazate-Based Tridentate Schiff Base Ligands: Syntheses, Structure, and Photochemical Reactivity of Compounds Involving Imidazole Derivatives as Coligands

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• 作者：Satyabrata Samanta ; Dipesh Ghosh ; Suman Mukhopadhyay ; Akira Endo ; Timothy J. R. Weakley ; and Muktimoy Chaudhury
• 刊名：Inorganic Chemistry
• 出版年：2003
• 出版时间：March 10, 2003
• 年：2003
• 卷：42
• 期：5
• 页码：1508 - 1517
• 全文大小：198K
• 年卷期：v.42,no.5(March 10, 2003)
• ISSN：1520-510X

文摘

The tridentate dithiocarbazate-based Schiff base ligands H₂L (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocarbazate,R = NO₂, L = L²; R = Br, L = L³) react with [VO(acac)₂] in the presence of imidazole derivatives as coligandsto form oxovanadium(IV) and cis-dioxovanadium(V) complexes. With benzimidazole and N-methylimidazole, theproducts are oxovanadium(IV) complexes, viz. [VOL³(BzIm)]·0.5CH₃CN (1a) and [VOL(N-MeIm)₂] (L = L³, 1b; L =L², 1c), respectively. In both 1a,b, the O and S donor atoms of the tridentate ligand are cis to the terminal oxogroup (in the "equatorial" plane) and mutually trans, but the N donor atom is respectively cis and trans to the oxoatom, as revealed from X-ray crystallography. When imidazole or 4-methylimidazole is used as the ancillary ligand,the products obtained are water-soluble cis-dioxovanadium(V) complexes [VO₂L(R'-ImH)] (L = L³ and L², R' = Hand Me, 2a-d). These compounds have zigzag chain structures in the solid state as confirmed by X-raycrystallographic investigations of 2a,d, involving an alternating array of LVO₂^- species and the imidazolium counterionsheld together by Coulombic interactions and strong hydrogen bonding. Complexes 2a-d are stable in water ormethanol. In aprotic solvents, viz. CH₃CN, DMF, or DMSO, however, they undergo photochemical transformationwhen exposed to visible light. The putative product is a mixed-oxidation divanadium(IV/V) species obtained byphotoinduced reduction as established by EPR, electronic spectroscopy, and dynamic ¹H NMR experiments.