Mono- and dinitrosyls on copper(I) site in a zeolite model: effects of static correlation.

Multiconfigurational RASSCF/RASPT2 approach has been applied to investigate bonding of one and two nitric oxide (NO) molecules to a simple model of Cu(I) site in zeolite environment, Cu(I)[Al(OH)(4)]. Two binding modes were considered for the mononitrosyls and four alternative structures for the dinitrosyls (each one in either singlet or triplet state). Stabilities of the mono- and dinitrosyl complexes obtained from the multireference calculations were compared to the previously reported coupled cluster CCSD(T) results, as well as to DFT calculations performed here with various functionals, either hybrid or nonhybrid ones. RASSCF calculations provided also a qualitative insight into the electronic structure of the studied complexes, concerning mainly the interaction between the Cu and the NO ligand, and between the two NO fragments. Whereas the electronic structure of the mononitrosyls is dominated by a single configuration, the dinitrosyls have a considerably multireference character. Various effects of nondynamical correlation have been pointed out for these interesting species, trying to assess their impact on performance of the tested DFT methods.