Metal-Metal Bond Distances and Bond Orders for Binuclear Complexes of 3d-Block Metals Ti through Zn: Theory and Experiment Compared
Richard H. Duncan Lyngdoh1, R. Bruce King2 and Henry F. Schaefer, III2
1Department of Chemistry, North-Eastern Hill University, Shillong 793022, India
2Center for Computational Quantum Chemistry, University of Georgia, Athens GA 30602
Metal-metal (MM) bond distances in binuclear complexes of the 3d-block elements titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc are well documented, where computational results are much more plentiful than experimental findings. MM bond distances are influenced by (a) the formal MM bond order, (b) the size of the metal atom/ion, (c) the metal oxidation state, (d) effects of ligand basicity, and (e) the ligand-to-metal coordination mode. Specific factors are found to have their expected impact on MM bond lengths within various series of complexes. Computationally-derived MM bond lengths are found to be in good agreement with the experimental values in numerous cases. The presence of carbonyl ligands is noted to have a general MM bond lengthening effect. MM bond length ranges in binuclear complexes for single, double, triple, quadruple, and quintuple MM bonds are systematically related to the available information on metal atomic radii. Finally, we propose “best” values for MM bond distances covering all types (Ti-Ti through Zn-Zn, single through quintuple) based upon joint consideration of experimental and computational results.