A study on the electronic effect of para substituents in the aryloxy ring of the hydrazone ligands on the vanadium centre in a family of mixed-ligand [VVO(ONO)(OO)] complexes

Abstract

V IV O(acac) 2 ] reacts with the methanolic solutions of tridentate dibasic ONO donor hydrazone ligands derived from the condensation of benzoyl hydrazine with either 2-hydroxyacetophenone (H 2 L 1 ) or its para-substituted derivatives (H 2 L 2-4 ) (general abbreviation H 2 L), in the presence of vanillin (Hvan) in equimolar ratio under aerobic conditions generating the mixed-ligand oxovanadium(V) complexes of the type [V V O(L)(van)], (1)-(4) in good yield. All the complexes are diamagnetic and exhibit only ligand-to-metal charge transfer (l.m.c.t.) band near 510 nm in addition to intra-ligand (p fi p*) transition band near 330 nm in CH 2 Cl 2 solution. 1 H-n.m.r. spectra of the complexes in CDCl 3 solution indicate the presence of two isomeric forms [(1A), (1B); (2A), (2B); (3A), (3B) and (4A), (4B)]in different ratios, which is explained by the interchange of the two binding sites of van ) motif between its coordinated equatorial and axial positions. Complexes display two quasi-reversible one electron reduction peaks near +0.10 V and near +0.30 V versus s.c.e. in CH 2 Cl 2 solution which are attributed to the successive reduction of V V fi V IV and the V IV fi V III motifs, respectively. k max (for l.m.c.t. transition), and the two reduction potential values (E 1/2 ) I (average of the first step anodic and first step cathodic peak potentials) and (E 1/2 ) II (average of the second step anodic and second step cathodic peak potentials) of the complexes, are found to be linearly related to the Hammett constants (r) of the substituents in the aryloxy ring of the hydrazone ligands. k max , (E 1/2 ) I and (E 1/2 ) II values show large dependence: dk max /dr = 37.29 nm, d(E 1/2 ) I /dr = 0.21 V and d(E 1/2 ) II /dr = 0.21 V, respectively, on r.

A journey into the electrochemistry of vanadium compounds

“…VO 3+ species contained the vanillin anion as O-O heteroligand [163]. All the complexes exhibited two one-electron quasi-reversible reduction peaks in DCM, that were attributed to successive reductions of the VO 3+ motif, first to VO 2+ and then to VO + (Table 5, entries 51-54).…”

Oxidovanadium(v) complexes of aroylhydrazones incorporating heterocycles: synthesis, characterization and study of DNA binding, photo-induced DNA cleavage and cytotoxic activities

“…The dioxidovanadium(V) complexes (1 and 2) are found to display two quasi reversible reduction wave at E 1/2 values within the potential window À0.87 to À0.70 V and À1.11 to À1.02 V, which are assigned to the V(V)/V(IV) and V(IV)/V(III) redox pair of the metal respectively. 69 3.…”

N′-(3-Bromo-2-hydroxybenzylidene)isonicotinohydrazide and its oxovanadium(V) complex: synthesis, structures, and catalytic properties

“…Hydrazones are a polydentate ligand in coordination chemistry. The synthesis, characterization, and reactivity studies of oxovanadium complexes with hydrazone ligands have been reported [11][12][13][14]. Some of the complexes show interesting catalytic properties [15][16][17].…”