Theoretical Analysis of Low-Lying Charge Transfer States in [Ru(X)(Me)(CO)_2(Me-DAB)](X=Cl,I;DAB=1 ,4-diaza-1 ,3-Butadiene)Complexes by TDDFT and CASSCF/CASPT2 Methods

摘要

The near-ultraviolet(UV)/visible electronic spectroscopy of [Ru(X)(Me)(CO)_2(Me-DAB)](X=Cl or I;DAB=1,4-diaza-1,3-butadiene),model complexes for a series of alpha-diimine halide complexes of ruthenium is investigated by means of time-dependent density functional theory(TDDFT)and complete active space self-consistent field/CAS second-order perturbation theory(CASSCF/CASPT2)methods.The convergence on the calculated transition energies to the low-lying metal-to-ligand-charge-transfer(MLCT),X-to-ligand-charge-transfer(XLCT)with X a halide ligand)or sigma-bond-to-ligand-charge-transfer(SBLCT)is analyzed for both methods with respect to various methodological aspects:basis set effects and functional influence on the TDDFT results versus the influence of the size and quality of the CASSCF and of the level of the perturbational treatment(single-state or multi-state)on the CASSCF/ CASPT2 transition energies.On the basis of these accurate calculations,it is shown that whereas the lowest singlet state can be assigned to a nearly pure XLCT state in [Ru(I)(Me)(CO)_2(Me-DAB)],its character is mainly MLCT in [Ru(Cl)(Me)(CO)_2(Me-DAB)],in agreement with time-resolved emission/infrared(IR)and resonance Raman experimental data.The experimental bands are well reproduced by the CASSCF/CASPT2 calculations despite the difficulty at converging to stable transition energies when enlarging the CASSCF.The TDDFT transitions energies are affected dramatically by the percentage of Hartree-Fock exchange in the hybrid functional.