W0145

Metallic Bond Order Sums in Transition Metal Organometallic Compounds. Gregory Jancy and Ronald F. See, Department of Chemistry, Saint Louis University, St. Louis, MO 63103

The relationship between coordination sphere, d-electrons and metal-ligand bond distance was determined for organometallic compounds of the transition metals. Metal-carbon bond distances were compiled for the ligands CO, CN^-, CH₃ and C₅H₅^- through searches of the Cambridge Structure Database. The Bond Distance-Bond Order relationship was employed in the analysis, as it allows direct comparison of bond orders for a wide variety of bonds, and is insensitive to the polarity of these bonds. In an earlier study, the sum of the metal-ligand bond orders in coordination compounds showed strong correlation to the oxidation state of the metal center; for organometallic compounds, this is not the case. The sums of the metal-carbon bond orders are, in all cases, much larger than those for the metal(II)-coordination compounds, ranging from slightly above 5 (for V(CO)₆^-) to well above 7 (for several metals). The bond order sums for differing coordination numbers to the same metal (i.e. 5-coordinate Mn and 6-coordinate Mn) were consistent, confirming that the variation of metal-ligand bond distance with coordination number is primarily a function a constant bond order sum at the metal center. Bond order sums for metals in the same group also were consistent (i.e. - Co, Rh and Ir compounds all display a sum of approximately 5.5 bond order units). The implications of these results on the theoretical treatment of metal-carbon bonding, and on the differences between metal-carbon bonds and metal-Lewis base (coordination) bonds will also be discussed.