Coordination and ligands’ effects in trinuclear [Pd3(COT)2(L)]2+ (L = H2O, CO, N2, HCN, HNC, NH3, PH3, PCl3, PF3, CS, CH2) sandwich complexes of cyclooctatetraene: theoretical investigation

This paper reports the molecular structure, the electronic structure, and the decomposition energies of the [M 3 (COT) 2 (L)] 2+ (M = Cr, Fe, Pd, and L = H 2 O, CO, N 2 , HCN, HNC, NH 3 , PH 3 , PCl 3 , PF 3 , CS, CH 2 , and COT = C 8 H 8 ) complexes obtained by means of DFT method using BP86 and PW91 functionals with the TZP basis set. The Pd–L bonding between the Pd 3 moiety and both COT ligands is weakly sensitive to the nature of the ancillary L ligands. In accordance with the coordination modes, the COT behaves as neutral distorted ligand deviating from the planarity. The calculations showed that the various complexes are found to have a low spin ground state. The MO plots and Wiberg bond indices provide further information about the nature of the Pd–Pd bonding. The Ziegler–Rauk energy decomposition analysis scheme was employed to characterize the geometry distortion and steric interaction (electrostatic and Pauli) and orbital interaction terms in the total bonding energy of Pd complexes. The results showed that the interaction terms are governed by one third covalent and two third ionic characters, in agreement with the Δ E elstat (electrostatic) and Δ E orb (orbital) contributions, respectively, into the total attractive interaction (Δ E elstat + Δ E orb ) for the studied complexes except for those of PCl 3 and N 2 ligands, which are almost of half covalent and half ionic characters. The σ-donation and π-backdonation amounts indicate that the CH 2 is the strongest donor ligand; however, the HCN is revealed to be the weakest σ-donor and π-acceptor one. The σ-donation and π-backdonation are in perfect accord with the natural charges of the interacting fragments.