van der Waals Radii of Pt(II) and Pd(II) in Molecular Mechanics Models and an Analysis of Their Relevance to the Description of Axial M.H(-C), M.H(-N), M.S, and M.M (M = Pd(II) or Pt(II)) Interactions.
Parameters have been developed for the molecular mechanics modeling of nonbonded interactions involving Pt(II) and Pd(II). The value obtained for the van der Waals radius-about 1.7 Å-accords well with the value proposed by Bondi (J. Chem. Phys. 1964, 68, 441-451). This model has been used to investigate close M.H(-C), M.H(-N), M.H(-O), M.S, and M.M (M = Pd(II) or Pt(II)) contacts that have previously been described as weak or agostic bonds. It is argued that the M.H(-C) interactions are best described as van der Waals interactions that are in the repulsive region but the results are in accord with the description of M.H(-N) and M.H(-O) contacts as weak hydrogen bonds. M.S and M.M separations in systems without pi-acceptor ligands were accurately reproduced by using the same van der Waals parameters.
Hambley
Trevor W.
TW
School of Chemistry, University of Sydney, N.S.W. 2006, Australia.