Ab Initio Bonding, Molecular Structure, and Quadrupole Coupling Constants of Aluminum Chlorides

The ab initio structures and energies of a series of gas-phase aluminum chlorides have been calculated at the RHF/6-31G* and MP2/6-31G* levels. The vibrational spectra of AlCl 3, Al 2 Cl 6, AlCl 4 -, EtAlCl 3 -, Al 2 Cl 7 -, Et 2 Al 2 Cl 5 -, and trans -Et 2 Al 2 Cl 4 are calculated at the RHF/6-31G* level. The theoretical vibrational spectra closely match the experimental (liquid state) infrared and Raman spectra and require a scale factor of 0.97 to yield a correlation coefficient ( R 2 ) of 0.999. The 27 Al quadrupole coupling constants and asymmetry parameters of the electric field gradient tensor have been calculated for a series of aluminum compounds (Al 2 Br 6, Al 2 Cl 6, AlF, Al 2 (CH 3 ) 6 ) at the HF/3-21G, B3LYP/6-31G*//HF/3-21G, HF/6-31G*//HF/3-21G, HF/6-31G*, B3LYP/6-31G*//HF/6-31G*, B3LYP/6-31G*, and B3LYP/cc-pVTZ levels. The correlation coefficient between experimental and theoretical 27 Al nuclear quadrupole coupling constants (NQCC) varies from 0.984 for the HF/3-21G calculation to 0.9986 for the density functional theory (DFT) B3LYP/cc-pVTZ result. The theoretical values of the 27 Al NQCC vary from −46.92 MHz (HF/3-21G) to −37.17 MHz (B3LYP/cc-pVTZ).