The electronic structure of the tris(ethylene) complexes [M(C2H4)(3)] (M=Ni, Pd, and Pt): A combined experimental and theoretical study

In this article we analyze in detail the electronic properties of the D-3h-Symmetric tris(ethylene) complexes of nickel, palladium, and platinum ([M(C2H4)(3)] M=Ni, Pd, Pt). In the case of [Pd(C2H4)(3)] the analysis is based on new experimental IR and Raman spectra for the matrix-isolated molecules and in all cases on the results of quantum-chemical (DFT) calculations. The experimental spectra collected for [Pd(C2H4)(3)] provide evidence for several previously unobserved vibrational modes, including the in-phase and out-of-phase nu(C-C) and delta(CH2) modes, and the in-phase nu(M-C) mode. Special consideration is given to possible inter-ligand interactions. The interaction force constant f(CC,CC) between two C2H4 ligands can be directly estimated from the spectra, and its very small value (0.002 Nm(-1)) indicates the absence of any significant inter-ligand interaction. An analysis of the topology of the theoretical electron density distribution, rho(r), and the corresponding Laplacian, del(2)rho(r), for [Pd(C2H4)(3)] and its lighter and heavier homologues [Ni(C2H4)(3)] and [Pt(C2H4)(3)], respectively, is in full agreement with the conclusions drawn from the experimental results. The combined experimental and quantum-chemical results provide detailed insights in the electronic properties of these prototypical ethylene complexes.