M. Wrighton and H. B. Gray, J. Coord. Chem., 1972, 2, 159;
FMO approach, an interaction diagram can be constructed
(Fig. 5) showing the interaction between the metal ion atomic
orbitals and the fragment orbitals of the two ligands. The EHT
energy levels for the fragments and for the complex were
obtained using the DFT-optimised geometry, regularised to
preserve the inversion centre. The five degenerate d-orbital
energy levels of PdII are shown on the right hand side of Fig. 5,
while the FMOs of the two ligand units are represented on the
left. As the five degenerate d orbitals of the d8 metal ion interact
with the FMOs of the ligands they mix and split into five MOs,
with the four occupied orbitals [in which the main contribu-
tion comes from the dx Ϫ y (61), dxy(46), dxz(43) and dz (62%)
atomic orbitals, respectively] in a very short range of energy.
These orbitals are slightly destabilised by antibonding inter-
action with the FMOs of the I moieties; the dyz orbitals become
the lowest unoccupied MOs, depending on the results obtained
at the Hybrid-DFT level.
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This research was financially supported by the “Regione
Autonoma della Sardegna”. We are grateful to the “Ministero
dell’Università
e della Ricerca Scientifica e Tecnologica
(M.U.R.S.T.)” for grants, to the “Centro Interdipartimentale
Grandi Strumenti (C.I.G.S.)” of the University of Modena and
Reggio Emilia for providing X-rays, and to the “Centro Inter-
dipartimentale di Calcolo Automatico ed Informatica
Applicata (C.I.C.A.I.A.)” of the University of Modena and
Reggio Emilia for computing facilities.
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