The O–H(D) stretching potentials of the hydrogen bonded water molecules in MCl2·2H2O (M∈{Mn, Co, Fe}). Ab initio and density functional study

Abstract

The uncoupled anharmonic O–H(D) stretching vibrations of the hydrogen bonded water molecules with local C2 symmetry in compounds of the type MCl2·2H2O (where M∈{Mn, Co, Fe}) were studied at various levels of theory, within the finite-cluster approach. The studied clusters consisted of one water molecule coordinated to the metal atom and hydrogen bonded to two chloride anions. The vibrational potential energy curves for the uncoupled OH stretching vibrations were obtained from pointwise energy calculations at HF, MP2 and gradient-corrected B3-LYP density functional levels of theory. To solve the HF or the Kohn–Sham equations, the standard 6-311G(d,p) basis set was used on O, H and Cl, while the transition metal atoms were treated within the LANL2DZ basis, employing an effective core potential (ECP) description of the inner shell electrons. From the calculated energies of the vibrational eigenstates, both the fundamental anharmonic and harmonic vibrational frequencies, as well as the anharmonicity constants were computed.