Cone packing model — a geometrical approach to coordination and organometallic chemistry of lanthanides and actinides

Abstract

By projection of the ligands to a unit sphere centred at the metal ion, steric effects, both local and overall, can be studied quantitatively in terms of solid angle factor ( SAF), fan angle ( FA), coordination vector, gap and hole. The packing saturation rule and the packing centre rule have been determined by treatment of more than 400 structures of lanthanide and actinide coordination and organometallic compounds. A ligand packing model was thus adopted with cones joined at the same apex. ‘Coordination Saturation’ in f-block chemistry was clarified to be saturation in coordination space, implying an equilibrium between bonding and steric effects. Molecular structures could be simulated on the basis of a uniform packing principle. The cone packing model has been applied to inorganic preparation, synergistic extraction and structure prediction. These predictions have been clearly substantiated experimentally, and the results are reported. A dynamic packing model was also suggested to study the reaction pathways by simulating the relative positions during the reaction process and the size and shape of holes, which correspond to the reaction areas in the coordination sphere. Lewis base association and dissociation, and the metal- carbon bond thermolysis of structural pattern MCp 3L were explained as examples.