CONVENIENT ROUTE TO NIOBIUM IN LOWER OXIDATION-STATES - SYNTHESIS ANDCRYSTAL-STRUCTURE OF K-4[NB(C2O4)(4)]CENTER-DOT-4H(2)O-CENTER-DOT-1 2H(2)C(2)O(4)/

A convenient preparative route to an Nb(IV) complex, K-4 [Nb(C2O4)(4)] . 4H(2)O . 1/2H(2)C(2)O(4), is obtained by zinc reduction of concentra ted hydrochloric acid-ethanol solutions of niobium pentachloride follo wed by in situ complexation with oxalate. This direct method of synthe sis of an Nb(IV) complex may serve to open up a new avenue to the aque ous solution chemistry of niobium in lower oxidation states. The struc ture of the complex, as determined by X-ray crystallography, is a squa re-antiprism tetrakis-chelate arrangement of the oxalate ligand coordi nated to an Nb(IV) center. The brown complex crystallizes in the tricl inic space group P (1) over bar, with Z= 2, a = 11.219(4), b = 12.931( 5), c=9.257(4) Angstrom, alpha=110.79(3), beta=114.15(2), gamma=88.56( 3)degrees, V=1134.4(9) Angstrom(3), M-r=718.46, D-calc=2.10 g cm(-3), R=0.029 and R-w=0.0049. (C) 1997 Elsevier Science S.A.