PEROXO MALATO VANADATES(V) - SYNTHESES, SPECTRA AND STRUCTURE OF THE (NH4)(2)[VO(O-2)(C4H4O5)](2)2H(2)O DIMER WITH A RHOMBOIDAL V2O2(HYDROXYL) BRIDGING CORE

Crystalline peroxo malato vanadates(V) of the formula M[VO(O-2(C4H4O5)]H2O, where M=Na, K, NH4, Cs, obtained from aqueous solutions and characterized by IR and UV spectroscopy are described. X-ray structure analysis of (NH4)(2)[VO(O-2)(C4H4O5)](2)2H(2)O shows that the complex crystallizes in the triclinic space group, P ($) over bar 1, with a = 9.157(4), b = 9.662(5), c = 14.203(5) Angstrom, a = 104.58(3), beta = 90.52(3), gamma = 115.50(2)degrees, V=1088 Angstrom(3), Z=2. The structure contains a dimer with a novel tridentate coordination of the malato ion. Two bridging hydroxyl oxygens enclose a symmetrical rhomboidal V2O2 plane, binding two distorted pentagonal bipyramidal vanadium polyhedra. The peroxo groups, with O-O bond lengths of 1.442(2) Angstrom, are located in the equatorial plane across from the bridging hydroxyl oxygens, and the fifth side of the pentagonal plane is occupied by the oxygen of the vicinal carboxylic group. The second carboxylic group is coordinated at the apical position, bans to the oxo group. In the UV spectra all the compounds show the typical broad [monoperoxo --> vanadium] charge transfer band at a lambda(max) = 425 nm. Characteristic very strong IR bands were assigned by comparison with the spectra of malic acid and numerous other heteroligand peroxo vanadates(V). The v(O-O) stretch appears in the vicinity of 922 cm(-1), and the v(V=O) band near 977 cm(-1). The stereochemistry and the relationship of these compounds to the biochemistry of vanadium are discussed.