Spectroscopic and computational studies of a series of high-spin Ni(II) thiolate complexes

Abstract

The electronic structures of a series of high-spin Ni(ll)-thlolate complexes of the form [PhTt tBu]NI(SR) (R = CPh 3,2; C 6F 5, 3; C 6H 5, 4; PhTt tBu = phenyltrls((/erf-butylthlo)methyl)borate) have been characterized using a combined spectroscopic and computational approach. Resonance Raman (rR) spectroscopic data reveal that the ν Ni-SR vibrational feature occurs between 404 and 436 cm -1 In these species. The corresponding rR excitation profiles display a striking de-enhancement behavior because of Interference effects involving energetically proximate electronic excited states. These data were analyzed In the framework of time-dependent Heller theory to obtain quantitative insight into excited state nuclear distortions. The electronic absorption and magnetic circular dlchroism spectra of 2-4 are characterized by numerous charge transfer (CT) transitions. The dominant absorption feature, which occurs at ~18,000 cm -1 In all three complexes, is assigned as a thiolate-to-Ni CT transition involving molecular orbitais that are of re-symmetry with respect to the Ni-S bond, reminiscent of the characteristic absorption feature of blue copper proteins. Density functional theory computational data provide molecular orbital descriptions for 2-4 and allow for detailed assignments of the key spectral features. A comparison of the results obtained in this study to those reported for similar Ni-thiolate species reveals that the supporting ligand plays a secondary role In determining the spectroscopic properties, as the electronic structure Is primarily determined by the metal thiolate bonding interaction. © 2010 American Chemical Society.