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 concentrated hydrochloric acid-ethanol solutions of niobium pentachloride followed by in situ complexation with oxalate. This direct method of synthesis of an Nb(IV) complex may serve to open up a new avenue to the aqueous solution chemistry of niobium in lower oxidation states. The structure of the complex, as determined by X-ray crystallography, is a square-antiprism tetrakis-chelate arrangement of the oxalate ligand coordinated to an Nb(IV) center. The brown complex crystallizes in the triclinic 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.