| Abstract
| - Alkoxo bound monooxo- anddioxovanadium(V) complexes of the structural types of(VOL)2, (VOHL)2, VOLHQ,K(VO2HL), K(VO2H2L), and(salampr)+(VO2L)- {whereL = Schiff base; HQ = 8-hydroxyquinoline; salampr = cation of areduced Schiff base} have been synthesized, characterized, andstructurally analyzed by single crystal X-ray studies. Solutionstability, reactivity, and interconversion betweenVO2+ and VO3+ have beenaddressed on the basis of absorption studies, 51V NMR, andcyclic voltammetry. Several correlations were drawn betweenspectral and structural data.
- A large variety of oxovanadium(V) complexes, mononuclearVO2+ and VO3+ in addition tothe dinuclear VO3+,of the structural type (VOL)2, (VOHL)2, VOLHQ,K(VO2HL), K(VO2H2L), or(salampr) (VO2L) {where L =Schiff base ligand possessing alkoxo group(s); HQ =8-hydroxyquinoline; salampr = cation of reduced Schiffbase derived from salicylaldehyde and 2-amino-2-methylpropan-1-ol},bound to alkoxo, phenolate and iminegroups have been synthesized in high yields and characterized byseveral spectral and analytical methods, includingsingle crystal X-ray studies. While the mononuclearVO2+ complexes have been synthesized atalkaline pH, thedinuclear VO3+ complexes have been synthesized underneutral conditions using alkoxo rich Schiff base ligands.The X-ray structures indicate that the cis-dioxo complexes showedlonger V−Oalkoxo bond lengths compared tothe monooxo counterparts. The plot of V−Ophen bonddistances of several VO3+ complexes vs the lmctshoweda near linear correlation with a negative slope. The cyclicvoltammograms revealed a reversible V(V)/V(IV)couple with the reduction potentials increasing to more negative onesas the number of alkoxo groups bound toV increases from 1 to 2. Moreover, the cis-dioxoVO2+ complexes are easier to reduce thantheir monooxocounterparts. The solution stability of these complexes wasstudied in the presence of added water (1:4, water:solvent), where no decomposition was observed, unlike other Schiff basecomplexes of V. The conversion of thedioxo complexes to their monooxo counterparts in the presence ofcatalytic amounts of acid is also demonstrated.The reactivity of alkoxo bound V(V) complexes is also reported.X-ray parameters are as follows.H4L3: monoclinic space group, P21/c;a = 10.480(3), b = 8.719(6),c = 12.954(8) Å; β = 101.67(4)°;V = 1126(1) Å3;Z = 4; R = 0.060, Rw= 0.058. Complex 1: monoclinic space group,P21/n; a =12.988(1), b = 9.306(2), c=19.730(3) Å; β = 99.94(1)°; V =2348.9(7) Å3; Z = 4; R =0.031, Rw = 0.027. Complex2: monoclinic spacegroup, P21/n; a =12.282(3), b = 11.664(2), c =12.971(4) Å; β = 97.89(2)°; V =1840.5(8) Å; Z = 4; R =0.035, Rw = 0.038. Complex5: monoclinic space group,P21/c; a =17.274(2), b = 6.384(2), c =16.122(2) Å;β = 116.67(1)°; V = 1588.7(7)Å3; Z = 4; R = 0.039,Rw = 0.043. Complex 8: monoclinic space group,P21/c;a = 11.991(1), b = 11.696(4),c = 12.564(3) Å; β = 110.47(1)°;V = 1650.8(8) Å3; Z = 2;R = 0.045, Rw =0.049.
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