Electronic structure of transition-metal tetracoordinated complexes. 4. Theoretical ab initio and UV-photoelectron spectroscopy study of nickel(II) and palladium(II) complexes of N,N′-1,3-propaneaminebis(1H-pyrrol-2-ylmethylene) Schiff base

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Structural and bonding properties of the Ni and Pd complexes of the title Schiff base have been studied with the aid of both the pseudopotential ab initio method, in partial geometry optimizations, for investigation of ground-state electronic structure and for evaluation of ionization energies, and of He I/He II photoelectron spectroscopy. Theoretical results have provided an accurate description of metal-ligand bonding. It appears dominated by σ interactions involving the upper lying MOs mainly N 2p lone pair in character and, though to a different extent, valence metal subshells. Despite the different functionalities existing in the ligand chromophore, comparable bonding properties, and hence similar Pd-N distances, have been found for the four nitrogen donor atoms. A theoretical explanation of this behaviour is provided. Low ionization energy structures of photoelectron spectra have been assigned in accordance with Δ SCF calculations.