Theoretical investigation of a titanium-aniline complex with and without an alkyl chain

Density functional theory computations are employed to investigate the geometric, electronic, and vibrational properties of a neutral Ti(aniline) experimentally soft-landed onto an alkanethiol self-assembled monolayer (CH-SAM) matrix. Five optimized structures of a bare Ti(aniline) are obtained: Three of the five optimized structures show Ti-phenyl ring bonds with singlet, triplet, and quintet spin states and the other two show Ti-N bonds with triplet and quintet states. For their calculated IR spectra in the range 0-2000 cm ^-1, the peak position and intensity of the NH₂ scissor mode (∼1600 cm^-1) are insensitive to the Ti binding and spin states, whereas those of the NH₂-C₆H₅ intergroup stretching (∼1200 cm^-1) and NH₂ inversion (500-1000 cm^-1) modes are sensitive to these factors. To study Ti(aniline) in a CH-SAM matrix, geometric structures of a modeled system of Ti(aniline)-C₃H₈ are optimized and their infrared reflection absorption spectra are directly calculated by projecting the normal mode derivatives of the dipole moment of the system onto the surface normal. C₃H₈ stabilizes Ti(aniline) by about 8-10 kcal/mol but causes little change in the IR spectrum in the range 1300-1700 cm^-1, except for the quintet state. From a comparison of the predicted IRAS spectra with the experiment, Ti(aniline) in CH-SAM is concluded to be in a triplet state with a Ti-phenyl ring bond.