Molecular Structure of Dimethyldichlorotitanium(IV) by Gas-Phase Electron Diffraction, IR and NMR Spectroscopies, and Density Functional Theory Calculations. Unexpected Distortion from Tetrahedral Coordination Geometry

The molecular structure of (CH 3 ) 2 TiCl 2 has been determined by gas-phase electron diffraction. The bond distances are Ti−C = 205.8(4) pm and Ti−Cl = 219.6(3) pm, and the valence angles are Cl−Ti−Cl = 117.3(3)°, Cl−Ti−C = 108.9(2)°, and C−Ti−C = 102.8(9)°. The larger valence angles at Ti are thus those spanned by the more electronegative substituents. This is opposite to the trend observed in the main group analogues (CH 3 ) 2 ECl 2, E = Si, Ge, or Sn. Density functional theory (DFT) calculations with a triple-ζ basis yield an optimal structure in good agreement with experiment. There is nothing in the gas-phase electron diffraction structure, DFT calculations, gas-phase IR spectra, or the NMR spectra of (CH 2 D) 2 TiCl 2 hinting at unusual methyl group geometries or agostic Ti···H−C interactions.