Excited-State Distortions in Bis[hydrotris(3,5-dimethyl-1-pyrazolyl)borato]copper(II) Determined from Resonance Raman Intensities and a Normal Coordinate Analysis

Abstract

Resonance Raman spectra, a normal coordinate analysis, and calculation of excited-state bond lengths and angles of bis[hydrotris(3,5-dimethyl-1-pyrazolyl)borato]copper(II) are reported. Raman spectra are obtained in resonance with a ligand field state and the lowest ligand-to-metal charge transfer (LMCT) excited state. A normal coordinate analysis is carried out using Raman and IR frequencies and resonance Raman intensities to assist in the assignment of the symmetric modes. Potential energy distributions (PED) and force constants are reported. The individual bond length changes are calculated by using the resonance Raman intensities and the PED. Bond length and angle changes throughout the entire three-dimensional skeleton are reported. The signs of the bond length changes in the pyrazolyl borate ring are interpreted in conjunction with the results of a molecular orbital calculation. The N N bond length decreases by 0.02 Å, the C N bond lengths increase by 0.05 and 0.08 Å, the Cu−N bond increases by 0.10 Å and the N B N angle decreases by 2° in the LMCT excited state.