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 chl orides have been calculated at the RhF/6-31G* and MP2/6-31G* levels. The vi brational spectra of ALCL(3), AL(2)Cl(6), AlCl4-, EtAlCl3-, Al2Cl7-, Et2Al2 Cl5-, and trans-Et2Al2Cl4 are calculated at the RHF16-31G* level. The theor etical vibrational spectra closely match the experimental (liquid state) in frared and Raman spectra and require a scale factor of 0.97 to yield a corr elation coefficient (R-2) of 0.999. The Al-27 quadrupole coupling constants and asymmetry parameters of the electric field gradient tenser have been c alculated for a series of aluminum compounds (Al2Br6, Al2Cl6, AlF, Al-2(CH3 )(6)) at the HF/3-21G, B3LYP/6-31G*//HF/3-21G, HF/6-31G*//HF/3-21 G, HF/6-3 1G*, B3LYP/ 6-31G*//HF/6-31G*, B3LYP/6-31G*, and B3LYP/cc-pVTZ levels. The correlation coefficient between experimental and theoretical Al-27 nuclear quadrupole coupling constants (NQCC) varies from 0.984 for the HF/3-21C cal culation to 0.9986 for the density functional theory (DFT) B3LYP/cc-pVTZ re sult. The theoretical values of the Al-27 NQCC vary from -46.92 MHz (HF/3-2 1G) to -37.17 MHz (B3LYP/cc-pVTZ).