Synthesis, structural characterization and electrochemical activity of oxidovanadium(IV/V) complexes of a diprotic ONS chelating ligand
Graphical abstract
Exploration of structural, electrochemical and chemical reactivity some new oxidovanadium(IV/V) complexes of a diprotic tridentate ONS chelating ligand is reported. Structural features, spectroscopic and electrochemical properties of the complex 1 involving a ONS donor ligand are compared with a similar type oxidovanadium(V) complex of a ONO donor ligand.
Introduction
Compared to chemistry of vanadium ligated to various types of N–O donor ligands [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33] vanadium complexes in total or partial sulfur coordination have received much less attention. It is rather surprising because some vanadium complexes in total or partial sulfur environment were known for the last three decades. Such vanadium complexes are found to be involved in conducting vanadium–sulfur materials [34], in the removal of vanadium from crude oils [35], as catalysts for oxidizing sulfides to sulfoxides [36]. The thiolato complexes containing vanadium(III) [37], vanadium(IV) [38], oxidovanadium(IV) [38], [39] and vanadium(V) [40] cores are also reported along with a structurally characterized V(V) thiolate complex [40] and the VO3+ complex [VO(SCH2–CH2)3N] [41]. A few other vanadium–sulfur systems also received limited attention [42], [43], [44], [45], [46], [47], [48], [49], [50]. From 1997 onwards Chaudhury and his group explored synthesis, structural characterization, magnetic, chemical, electrochemical and photochemical properties of oxidovanadium complexes involving a series of tridentate ONS donor ligands [51], [52], [53], [54], [55], [56], [57]. In this backdrop and in continuation of our work in the complex chemistry of vanadium in +3, +4 and +5 oxidation states [3], [10], [27], [28], [30], [31], [32], [33], specially in the form of oxidovanadium species, the present study of oxidoalkoxido containing vanadium complexes involving a ONS donor ligand are under taken. The complex [VO(OEt)L] (1) [where H2L is a diprotic tridentate ONS ligand, S-benzyl-β-N-(2-hydroxyphenylethylidine) dithiocarbazate] is pentacoordinate and so has one position vacant in the coordination octahedron which can be utilized as a substrate binding site for neutral monodentate N-heterocyclic bases and are also amenable to the formation of binuclear complexes utilizing suitable neutral exobidentate ligands like 4,4′-bipyridine. The present work reports the findings enumerated below: (a) synthesis, structural characterization, examination of chemical and electrochemical properties of the monooxidoalkoxidovanadium(V) complex [VO(OEt)L] (1), the mixed ligand oxidovanadium(V) complex [VO(N–O)L] (3), a binuclear complex [VO(OEt)L]2(μ-4,4′-bipy) (2) and the mixed ligand oxidovanadium(IV) complexes of the type [VO(N–N)L] (4,5) where H2L is a diprotic tridentate ONS donor ligand, N–O = 8-hydroxy quinoline and N–N = 2,2′-bipyridine, 1,10-phenanthroline.
Section snippets
Materials
[VO(acac)2] was prepared as described in literature [58] and was used as the source of vanadium. Reagent grade solvents were dried and distilled prior to use. All other chemicals were reagent grade, obtained from commercial sources and used without further purification. Spectroscopic grade solvents were used for spectral measurements.
Synthesis of the ligand H2L
The Schiff base ligand, S-benzyl-β-N-(2-hydroxyphenylethylidine) dithiocarbazate (H2L) was prepared by using a reported procedure [59]. Yield ∼80%, m. p. ∼148 °C.
Results and discussion
The monooxidoethoxidovanadium(V) complex [VO(OEt)L] (1) was obtained as yellowish brown crystalline solid by refluxing an equimolar solution of [VO(acac)2] and the ligand H2L in ethanol medium [(L)2− = dianion of the ONS donor ligand ] in ∼70% yield. V(IV) was found to be oxidized to V(V) during the reaction period. Similar complexes containing other coordinated alkoxides could also be prepared easily using appropriate alcohols. However, detailed characterization of the other alkoxido complexes
Conclusion
This work reports synthesis and characterization of three five coordinated distorted square planar oxidovanadium(V) complexes [VO(OEt)L] (1), the binuclear V(V)–V(V) complex [VO(OEt)L]2-μ-(4,4′-bipy) (2) and the six coordinate mixed ligand complex [VO(8-HQ)L] (3). Two six coordinate oxidovanadium(IV) complexes [VO(o-phen)L] (4) and [VO(2,2′-bipy)L] (5) are also discussed. Of these five complexes, 1 and 5 are structurally characterized by single crystal X-ray crystallography. We have recently
Acknowledgements
M.S. is grateful to the Council of Scientific and Industrial Research (New Delhi) for the award of senior research fellowship. We thank EPSRC and the University of Reading for funds for the Image Plate System.
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