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 chloroformcomplex [Pt(C6H5)2(btz-N,N ')middotCDCl3, where btz = 2,2 '-bi-5,6-dihydro-4H-1,3-thiazine] isstudied by linear and nonlinear two-dimensional infrared (2D-IR) spectroscopy. The changeof the C-D stretching vibration of metal-coordinated CDCl3relative to the free solventmolecule serves as a measure of the non-classical PtmiddotmiddotmiddotD-C interaction strength. Thestretching absorption band of the activated C-D bond displays a red shift of 119 cm-1relativeto uncoordinated CDCl3, a strong broadening, and an 8-fold enhancement of spectrallyintegrated absorption. The infrared (IR) absorption and 2D-IR line shapes are governed byspectral diffusion on 200 fs and 2 ps time scales, induced by thefluctuating solvent CDCl3.The enhanced vibrational absorption and coupling to solvent forces are assigned to theenhanced electric polarizability of the activated C-D bond. Density functional theorycalculations show a significant increase of C-D bond polarizability of CDCl3uponcoordination to the 16 valence electron Pt(II) complex.