Structure and energy stability of lanthanum and lutetium trihalide dimer molecules

Abstract

The geometrical parameters of lanthanum and lutetium trihalide dimer molecules Ln2X6 (Ln = La, Lu; X = F, Cl, Br, I) and dissociation energies of Ln2X6 → 2LnX3 were calculated in terms of Mo ller-Plesset fourth order perturbation theory including single, double, triple, and quadruple excitations (SDTQ-MP4). Variation of the properties of molecules in series of compounds Ln2F6 → Ln2Cl6 → Ln2Br6 → Ln2I6 from lanthanum La2X6 to lutetium Lu2X6 compounds and from monomer LnX3 to dimer Ln2X6 molecules has been studied (the parameters of LnX3 molecules were determined in the same SDTQ-MP4 approximation). The lanthanide compression of the metal-halogen internuclear distance Δr(Ln-X) = re(La-X)-re(Lu-X) depends on the nature of the ligand X and coordination number of Ln. The calculated data are compared with previously published experimental and theoretical data on the structure and dissociation energies of Ln2X6 molecules.