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A study deals with the selection and pattern of trianionic symmetrical heptadentate ligands and the binding of these to vanadium. The research work presented offers an invaluable understanding of the synthetic approach in the field of mixed-valence chemistry of vanadium.

A non-porphyrinic [N.sub.4][O.sub.3]-coordinating heptadentate ligand was used to synthesis and characterize various properties of two new binuclear copper(II) complexes, [[Cu.sub.2]([H.sub.2]L)([mu]-OH)][(Cl[O.sub.4]).sub.2] and [[Cu.sub.2](L)[([H.sub.2]O).sub.2]P[F.sub.6]. The complexes were found to exhibit antiferromagnetic interaction in solid state and catecholase activity at pH 8.5.

The N4O3 coordinating heptadentate ligand afforded binuclear complex [Cu2(H2L)(μ-OH)](ClO4)2 (1) and [Cu2(L)(H2O)2]PF6 (2). In complex 1, two copper ions are held together by μ-phenoxo and μ-hydroxo bridges, whereas in complex 2, the copper centers are connected only by a μ-phenoxo bridge. In 1, both the Cu(II) centers have square pyramidal geometry (r = 0.01-0.205), whereas in the case of 2, one Cu(II) center has square pyramidal (r = 0.2517) and other one has square based pyramidal distorted trigonal bipyramidal (r = 0.54) geometry. Complexes 1 and 2 show an strong intramolecular and very weak antiferromagnetic interaction, respectively. Density-functional theory calculations were performed to establish the magneto structural correlation between the two paramagnetic copper(II) centers. Both of the complexes display a couple of one-electron reductive responses near -0.80 and -1.10 V. The complexes show significant catalytic activity at pH 8.5 on the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ), and the activity measured in terms of kcat = 29-37 h-1. [ABSTRACT FROM AUTHOR]

Dinuclear (VIVVV) oxophenoxovanadates of general formula [V2O3L] have been synthesized in excellent yields by reacting bis(acetylacetonato)oxovanadium(IV) with H3L in a 2:1 ratio in acetone under an N2 atmosphere. Here L3- is the deprotonated form of 2,6-bis[{{(2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L¹), 2,6-bis[{.{(5-methyl-2-hydroxy-benzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L²), 2,6, bis[{{(5-tert-butyl-2-hydroxybenzyl)(N'-N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L³), 2,6-bis[{{(5chloro-2-hydroxybenzyl)(N'-N'-(dimethylamino)ethyl)}amino}methyl]-4-methylpheno(H3L4), 2,6-bis[{{(5-bromo-2hydroxybenzyl)(N'N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L5), or 2,6-bis[{{(5-methoxy-2hydroxybenzyl)(N'N'-(dimethylamino)ethyl)}methyl]-4-methylphenol (H3L6). In [V2O3L¹], both the metal atoms have distorted octahedral geometry. The relative disposition of two terminal V=O groups in the complex is essentially cis. The O=V…V=O torsion angle is 24.6(2)°. The V-Ooxo-V and V-Ophenoxo-V angles are 117.5(4) and 93.4(3)°, respectively. The V…V bond distance is 3.173(5) Å. X-ray crystallography, IR, UV-vis, and ¹H and 51V NMR measurements show that the mixed-valence complexes contain two indistinguishable vanadium atoms (type III). The thermal ellipsoids of 02, 04, C10, C14, and C15 also suggests a type III complex in the solid state. EPR spectra of solid complexes at 77 K display a single line indicating the localization of the odd electron (3dxy&supl;). Valence localization at 77 K is also consistent with the 51V hyperfine structure of the axial EPR spectra (3dxy¹ ground state) of the complexes in frozen (77 K) dichloromethane solution: S= ½, gII ∼ 1.94, g⊥ ∼ 1.98, AII ∼ 166 x 10-4 cm-1, and A⊥ ∼ 68 x 10-4 cm-1. In contrast isotropic room-temperature solution spectra of the family have 15 hyperfine lines (giso ∼ 1.974 and Aiso ∼ 50 x 10-4 cm-1) revealing that the unpaired electron is delocalized between the metal centers. Crystal data for the [V2O3L¹]·CH2Cl2 complex are as follows: chemical formula, C32H43O6N4Cl2V2; crystal system, monoclinic; space group, C2/c; a: 18.461(4), b = 17.230(3), c = 13.700(3) Å; β = 117.88(3)°; Z = 8. [ABSTRACT FROM AUTHOR]