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

Abstract

The vibrational response of the activated C–D bond in the chloroform complex [Pt(C6H5)2(btz-N,N′)·CDCl3, where btz = 2,2′-bi-5,6-dihydro-4H-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 CDCl3 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–1 relative to uncoordinated CDCl3, 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 CDCl3. 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 CDCl3 upon coordination to the 16 valence electron Pt(II) complex.