ORIGIN AND FINE-TUNING OF THE STABILITY OF 5-COORDINATED PLATINUM(II)AND PALLADIUM(II) SPECIES - A QUANTUM-MECHANICAL STUDY

Ab initio computations have been performed to characterize the ground state geometries of a number of platinum and palladium complexes [M(N- N)(C2H4)XY] (N-N=bidentate N-donor ligand; X,Y=monodentate ligands) an d their stability toward the loss of ethylene, The results have been i nterpreted by an energy component analysis, The computations point out the respective roles of electron donation from ethylene and of back-d onation from the metal in determining the relative stabilities of diff erent five-coordinated complexes with respect to their four-coordinate d counterparts. Experimental trends are correctly reproduced and inter preted in terms of these two effects. Modifications induced by the def ormation energy connected to the addition of a fifth ligand are probab ly overestimated by our computational model.