Structural characterization of a cyano bridged mixed valence trinuclear compound

P. ALBORÉS; J.A.OLABE; L.D.SLEP; T.WEYHERMÜLLER; L.M.BARALDO

Heidelberg

Conferencia; XXXVth International Conference on Coordination Chemistry; 2002

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, magnetochemical, spectroscopic characterization of two soluble trinuclear compounds [RuIIL4(FeIII(CN)6)2] 4-(1, L = pyridine and 2, L= tert-butyl pyridine). 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 2 produced pale green crystals suitable for X-ray analysis. The structure of 2 revealed an almost linear cyano bridged array of metals. The spectroscopic and electrochemical characterization of both trinuclear heterometallic compounds suggests coupling between the two terminal irons, distant 10.17 Å. The cyclic voltammetry of 2 in water shows two reversible processes at 0.23 and 0.03 V (vs. SCE) which correspond to the reduction of the terminal ferricyanide moieties. The E½ .of ca. 200 mV indicates a strong communication between the two iron centers through the CNRuNC bridge. In solvents with a lower acceptor number E½ is smaller.