Ultrafast Vibrational Response of Activated C-D Bonds in a Chloroform-Platinum(II) Complex.

The vibrational response of the activated C-D bond in the chloroform complex [Pt(CH)(btz-,')·CDCl, where btz = 2,2'-bi-5,6-dihydro-4-1,3-thiazine] is studied by linear and nonlinear two-dimensional infrared (2D-IR) spectroscopy. The change of the C-D stretching vibration of metal-coordinated CDCl relative to the free solvent molecule serves as a measure of the non-classical Pt···D-C interaction strength. The stretching absorption band of the activated C-D bond displays a red shift of 119 cm relative to uncoordinated CDCl, a strong broadening, and an 8-fold enhancement of spectrally integrated absorption. The infrared (IR) absorption and 2D-IR line shapes are governed by spectral diffusion on 200 fs and 2 ps time scales, induced by the fluctuating solvent CDCl. The enhanced vibrational absorption and coupling to solvent forces are assigned to the enhanced electric polarizability of the activated C-D bond. Density functional theory calculations show a significant increase of C-D bond polarizability of CDCl upon coordination to the 16 valence electron Pt(II) complex.