M. Ystenes et al., SCALED QUANTUM-MECHANICAL (SQM) VIBRATIONAL ANALYSIS OF ALCL3, AL2CL6AND THE FREE-ION ALCL4-, Spectrochimica acta. Part A: Molecular spectroscopy, 50(2), 1994, pp. 233-242
A series of basis sets are evaluated for AlCl3 and AlCl4- and a common
scaling factor derived for these compounds was transferred to Al2Cl6.
6-31G calculations, scaled with a common factor of 0.92, give a good
fit to all vibrational frequencies for AlCl3, AlCl4 and Al2Cl6, and t
here is also a qualitative fit between calculated and observed IR inte
nsities. Extending the basis set does not lead to significant improvem
ents, either for the geometry or for the vibrational frequencies. The
calculations verify earlier assignments based on general valence force
fields and predict frequencies for some unobserved bands. The SQM for
ce fields for aluminium chlorides show large similarities with the iso
electronic thiophosphates; the main deviations can be attributed to mo
re ionic bonds in the aluminium chlorides. A significant influence on
the out-of-plane vibration in AlCl3 by the basis set on the d-orbitals
may indicate that pi(d-p) bonding plays a role. A remarkable and unex
pected basis set sensitivity is found for the nu6(B1g) ring vibration
in Al2Cl6.