The crystal structure of tetrakis(dimethylamino)titanium(IV)

Ti(NMe2)4 is a monomeric species in the gas phase and in solution, and this remains true on crystallisation. The crystal structure is triclinic, with space group P1¯, and unit cell dimensions a = 8.277(6), b = 8.407(6), c = 11.167(7) Å, α = 105.36(4)°, β = 97.03(3)° and γ = 116.01(2)° at 105 K. Electron-diffraction measurements show that in the gas-phase Ti(NMe2)4 takes the form of a slightly flattened tetrahedron with overall S4 symmetry. In the solid state the symmetry changes to C1; the reduction of point-symmetry results from the twisting of one of the amino groups away from its gas-phase configuration. DFT calculations indicate that the energy of the C1 structure lies only 0.2 kJ mol−1 above that of the S4 conformer. The change in structure on crystallisation can be ascribed to the avoidance of prohibitively short intermolecular methyl–methyl interactions which would have been formed had the S4 structure been retained.

Although Ti(NMe2)4 has S4 symmetry in the gas phase, in the solid state it has C1 symmetry in order to avoid the formation of short methyl–methyl contacts.Figure optionsDownload as PowerPoint slide