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Hartree-Fock-Slater calculations have been carried out on Ni(CO)3L for a number of different ligands (L) in order to investigate the abilities of the ligands to act as donors and x acceptors. The order, based on extent of electron transfer, for donation is CS =* CO > CNCH3 > N2 ~PF3 and for x back-bonding is CNCH3 > CS > CO > PF3 > N2. The contributions to the total bonding energy between Ñi(CO)3 and L from donation and x back-donation are evaluated by the Hartree-Fock-Slater transition-state method, and the same method is used to optimize the Ni-L bond distances.Calculations on the stretching frequency vCo of carbon monoxide complexed to Ni(CO)3 showed that vCo is decreased by the x back-donation but is increased by the steric interaction energy between Ni(CO)3 and CO. Thus the decrease in vCo is not a reliable measure of the extent of x back-bonding in the metal-ligand bond. The calculated influence on vCo from donation was negligible.

The chemistry of Alzheimer's disease is largely centred on the amyloid beta-peptide, its formation, structure, and interactions with metals, membranes, proteins and other species. This critical review summarizes the current state of knowledge (252 references).

The translation of G2, G2(MP2), and G2(MP2,SVP) total energies to heats of formation via atomization and formation reaction procedures is evaluated. While both approaches give similar results, the former is shown to perform somewhat better, especially for organic molecules. The recommended general procedure for obtaining heats of formation at 0 K from G2-type total energies is to use G2-type atomization energies in conjunction with experimental gas-phase heats of formation for the constituent atoms. The corrections required to give heats of formation at finite temperatures can be obtained using scaled theoretically derived vibrational frequencies for the species under consideration together with temperature correction terms for the constituent elements based on experimental data. While the harmonic oscillator model is a good approximation for most vibrational modes, internal rotations with relatively low frequencies are more accurately treated within the free rotor approximation.

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