Tuning of Electronic Coupling Between Metals in a Family of Cyano Bridged Mixed Valence Trinuclear Compounds

P. ALBORÉS; L. D. SLEP; T. WEYHERMÜLLER; L. M. BARALDO

Valparaíso

Simposio; Simposio Interacción Metal-Metal en Química de Coordinación de Complejos Polinucleares de Metales de Transición; 2003

The ability of cyanide to bridge between metals has been successfully employed to produce molecular materials with interesting properties, but most of this materials lack manageable processing properties being insoluble and unfusible. A few soluble oligomers have been reported and structural determinations of cyano bridged oligomers containing at least three metal atoms are still limited. In this communication we report the synthesis and a complete structural, electrochemical and spectroscopic characterization of three soluble trinuclear compounds [RuIIL4(FeIII(CN)6)2] 4-(1, L = pyridine and 2, L=  4-tert-butylpyridine 3, L = 4-methoxypyridine). Heating to reflux a suspension of  Ru(L)4Cl2 and a large excess of K3[Fe(CN)6] in a mixture of water/methanol (4:1) affords an homogeneous green solution which was purified by exclusion chromatography. Slow diffusion of diethyl ether on a methanolic solution of the tetraphenylphosphonium salt of 1 or 2 produced pale green crystals suitable for X-ray analysis. Both structures of 1 and 2 revealed an almost linear cyano bridged  array of metals. The spectroscopic and electrochemical characterization of these trinuclear heterometallic compounds suggests coupling between the two terminal irons, distant ca. 10 Å. The cyclic voltammetry of 3 in water shows two reversible processes at 0.225 and –0.046 V (vs.Ag/AgCl) which correspond to the reduction of the terminal ferricyanide moieties. The DE½ .of ca. 300 mV indicates a strong communication between the two iron centers through the CNRuNC bridge. In solvents with a lower acceptor number DE½ is smaller.