Structural and bonding trends in osmium carbonyl cluster chemistry: metal–metal and metal–ligand bond lengths and calculated strengths, relative stabilities and enthalpies of formation of some binary osmium carbonyls, [Osx(CO)y]

Abstract

The metal–metal bond distances [d(M–M)] in the published structures of the osmium carbonyl clusters [Os₃(CO)₁₂], [Os₄(CO)₁₄], [Os₄(CO)₁₅], [Os₄(CO)₁₆, [Os₅(CO)₁₆], [Os₅(CO)₁₈], [Os₅(CO)₁₉], [Os₆(CO)₁₈] and [Os₇(CO)₂₁] have been used to calculate bond-enthalpy terms E(M–M) using the relationship E(M–M)= 1.928 × 10¹³[d(M–M)]^–4.6, itself derived from published structural and enthalpy data. Summation of the bond-enthalpy terms has revealed the varying efficiency with which these compounds use their skeletal bonding electrons and allowed estimates to be made of their enthalpies of disruption into gaseous metal atoms and carbon monoxide and of their enthalpies of formation, so providing insight into their relative stabilities. Correlations are noted between the metal : ligand ratios and metal–metal bond enthalpies, and with the metal–ligand bonding as reflected in metal–carbon and carbon–oxygen bond lengths.