African Journal of Pure and Applied Chemistry Vol. 3 (9), pp. 170-176, September, 2009 Available online at http://www.academicjournals.org/AJPAC ISSN 1996 - 0840 © 2009 Academic Journals Full Length Research Paper Vitamin B 12 models: Synthesis and characterization of cyano bridged dicobaloximes and antimicrobial activity Bakheit Mustafa Mohamed Salih and S. Satyanarayana* Department of Chemistry, Osmania University, Hyderabad, 500007. Andhra Pradesh, India. Accepted 15 June, 2009. Reactions of the cyanide complexes of the type Co(CN)(DH) 2 L moiety (where L= thiourea, acetamide, formamide, semicarbazide, pyrazole and aniline; DH = dimethylglyoxime) with the corresponding benzyl(aqua)cobaloxime PhCH 2 Co(DH) 2 OH 2 gives a series of homometallic cyano-bridged compounds of the type PhCH 2 Co(DH) 2 CNCo(DH) 2 L. All these complexes have been synthesized and characterized by means of IR, LC/MS, 1 H, 13 C NMR and (C, H, N) analysis as well as their antimicrobial activities. The formation of cyanide bridge is evident from the IR spectra by the appearance of (CN) shifts with respect to the mononuclear parent complex. Key words: Cyano-bridged, bimetallic complexes, antimicrobial activity. INTRODUCTION It is well known that the cyanide ion can connect two metal ions as a bridging ligand. Linear cyanide-bridged bimetallic complexes of the type M–CN–M have been extensively studied (Rigo and Turco, 1974; Davies et al., 1985; Mohan et al., 1987; Deeming and Proud, 1988; Darensbourg et al., 1996; Ramsharan and Dikshit, 1993). Cyanide-bridged, dinuclear transition metal compounds are widely used in the areas of electron delocalization and charge transfer studies (Zhou et al., 1990; Agnus et al., 1989; Burewiez and Haim, 1988; Chrisstofides et al., 1990; Scandola et al., 1993). The most successful and often the sole strategy for preparing these materials still consists in assembling building blocks, usually transition metal complexes, one having potential bridging ligands with another species possessing empty or available co- ordination sites. This ambidentate behavior is evident in cyanide compounds of the main group (Kawai and Kane- saka, 1969) elements and transition metal complexes. The-cyano bridged dimetal systems have been of interest since the early recognition that ligand bridged complexes play an important role in inner-sphere electron transfer reaction (Paul and Alvin, 1976). For example; remarkable degrees of metal-metal electronic coupling can be observed across cyanide bridges (Scandola et al., 1993). This synthetic strategy has been often utilized to provide a general route to synthesize neutral dinuclear *Corresponding author. E-mail: ssnsirasani@yahoo.com. Tel.: 91-40-23234231 or 09246521145. cyano-bridged complexes and this strategy consists in protecting the equatorial positions of the metal atoms with a planar pseudo macrocyclic group and carry out ligand substitution reactions on axial positions leading to bridge formation, thus avoiding undesired side reactions usually observed when preparing cyano-bridged complexes, such as cis  trans, isomerization (Ribas et al., 1980; Ribas et al., 1979). In this study, we describe the synthe- sis of cyano-bridged dinuclear complexes formed from the reaction between the appropriate Co(CN)(DH) 2 L and PhCH 2 Co(DH) 2 OH 2 fragment (DH = dimethylglyoxime). Experimental All chemicals and solvents used for the synthesis were of reagent grade. Infrared spectra were recorded on Perkin-Elmer FTIR-1600 spectrophotometer in the range 4000-400 cm -1 as KBr pellets. 1 H and 13 C NMR spectra were recorded on a GE QE 300 NMR spec- trometer at 25°C using a 5 mm broad band probe. Samples were prepared by dissolving 25-50 mmoles in DMSO-d6. Elemental analyses were carried out using a Perkin-Elmer 2400 elemental analyzer. Preparation of K[NCSCo(DH)2SCN This complex was prepared by the method of Ablov and Syrtosova (Ablov and Syrtsova, 1975; Crumbliss and Gaus, 1975) which was converted to [NH3Co(DH)2SCN] by treatment with concentrated NH4OH as described by Crumbliss and Gaus (1976). This ammonia complex was treated with an equimolar amount of KCN dissolved in minimum amount of water to obtain the salt K [Co(CN)(DH)2SCN] in 80% yield. Then this potassium salt of cyano