Geometry Optimizations of the Ground and Excited Triplet State Structures of the Low-Valent Metal−Metal Bonded Isocyanide and Carbonyl Di- and Trinuclear Palladium Complexes Using Density Functional Theory

Abstract

In relation to the known complexes Pd2(CNMe)62+ and Pd2(CN-t-Bu)4Cl2, Pd2(tmb)2Cl2 (tmb = 2,5-dimethyl-2‘,5‘-diisocyanohexane) and Pd3(dppm)3CO2+ (dppm = ((C6H5)2P)2CH2), respectively, the ground and lowest energy triplet excited state geometries of the model compounds Pd2(CNMe)4Cl2 and Pd2(CN(CH2)4NC)2Cl2, and Pd3(PH3)6CO2+ have been optimized using density functional theory. The computations for ground state structures are in excellent agreement with the X-ray data. In the excited states, bond lengthening (due to the change in Pd−Pd bond order 0 → 1) is predicted. In the bridged species, Pd2(CN(CH2)4NC)2Cl2, the computations reveal that twisting of the dihedral angle must occur in order to account for the large change in Pd−Pd distance. Finally, the Pd−Pd bond lengthening for the Pd3(dppm)3CO2+ cluster in the 3A2 excited state is predicted to be ∼0.19 Å relative to the ground state. This value has also been confirmed by an analysis of the emission band using Heller's time-dependent theory.