HETEROBIMETALLIC, TRIMETALLIC AND TETRAMETALLIC CYANIDE-BRIDGED COMPLEXES BASED ON PENTACARBONYLCYANOCHROMATE(0) AND PENTAAMMINERUTHENIUM(III), CIS-TETRA-AMMINERUTHENIUM(III) AND FAC-TRI-AMMINERUTHENIUM(III) GROUPS - OPTICAL METAL-METAL CHARGE-TRANSFER AND ELECTROCHEMICAL CHARACTERISTICS

The heterobi-, tri- and tetra-metallic Robin-Day Class II mixed-valenc e complexes, [(OC)(5)Cr(mu-CN)Ru(NH3)(5)](2+) (CrRu), cis-[{(OC)(5)Cr( mu-CN)}Ru-2(NH3)(4)](+) (Cr2Ru) and fac-[{(OC)(5)Cr(mu-CN)}Ru-3(NH3)(3 )] (Cr3Ru) have been synthesised directly by coupling [Cr(CO)(5)CN](-) with an appropriate penta-, tetra- or tri-ammineruthenium precursor a nd characterised by electrochemical, analytical and spectroscopic meth ods. The complexes exhibit solvent-ammine hydrogen-bonding induced sol vatochromism in the MMCT energy which linearly varies with the Gutmann solvent donor number (DN) at 219, 158 and 116(+/-7) cm(-1)/DN respect ively which corresponds to a linear variation of 51(+/-6) cm(-1)/DN/NH 3 group. Electrochemical and spectroscopic evidence points to the liga ting equivalence of [Cr(CO)(5)CN](-) and NH3 groups in this series. Cy clic and square-wave voltammograms, CV and SWV, show reversible couple s at +0.45 and -0.36 V (versus ferrocene) for the chromium(0/I) and ru thenium(III/II) potentials in the complex set. Dispersion in CV and pe ak broadening in SWV, for CrxRu (x = 2, 3), indicate weak Cr-Cr coupli ng through the ammineruthenium centre corresponding to a separation of similar to 65 mV. We report electrochemical data for [(OC)(5)Cr(mu-CN )Os(NH3)(5)](2+) (CrOs) and its visibly spectacular solvatochromism (1 88 cm(-1)/DN) from blue to purple, red, orange and yellow colourations .