A NOVEL NONAIRON(III) CITRATE COMPLEX - A FERRIC TRIPLE-DECKER

The novel nonairon(III) citrate complex [Fe9O(cit)(8)(H2O)(3)](7-) (3) [cit = C(O-)(COO-)(CH2COO-)(2)] was prepared as its neocuproinium sal t by reacting ferric nitrate, sodium citrate, and neocuproine (neo: 2, 9-dimethyl-1,10-phenanthroline) in a 1:1:1 ratio in aqueous solution. The compound (Hneo)(7). 3 . neo . 61H(2)O crystallizes in the monoclin ic space group P2(1)/c with unit cell parameters of a = 21.910(3) Angs trom, b = 25.788(5) Angstrom, c = 39.653(6) Angstrom, beta = 99.47(1)d egrees, V = 22 099(7) Angstrom(3). and Z = 4. The anionic complex cons ists of three parallel triangular Fel units, 5.6 Angstrom apart, formi ng a slightly distorted trigonal prism. The outer two units are connec ted by three bridging tetradentate cit(4-) ligands to the central one, and each of the terminal Fe-3 units is capped by another cit(4)- liga nd. The central Fe3 unit has the oxo-bridged basic iron carboxylate st ructure, whereas the two terminal ones have a ''voided cubane'' struct ure with an {Fe3O4} core. Mossbauer spectra are composed of two subspe ctra (''a'' and ''b'') with intensity ratio 2:1, reflecting the existe nce of two inequivalent trivalent iron sites. Subspectra ''a'' are ass igned to the three equivalent iron atoms of the terminal Fe? units, an d subspectra ''b'' to the three equivalent iron atoms of the central u nit.