Theoretical Study of Mixed LiLnX₄(Ln = La, Dy; X = F, Cl, Br, I) Rare Earth/Alkali Halide Complexes

Abstract

The structure, bonding and vibrational properties of the mixed LiLnX4 (Ln = La, Dy; X = F, Cl, Br, I) rare earth/alkali halide complexes were studied using various quantum chemical methods (HF, MP2 and the Becke3-Lee-Yang-Parr exchange-correlation density functional) in conjunction with polarized triple-zeta valence basis sets and quasi-relativistic effective core potentials for the heavy atoms. Our comparative study indicated the superiority of MP2 theory while the HF and B3-LYP methods as well as less sophisticated basis sets failed for the correct energetic relations. In particular, f polarization functions on Li and X proved to be important for the Li...X interaction in the complexes. From the three characteristic structures of such complexes, possessing 1-(C3v), 2-(C2v), or 3-fold coordination (C3v) between the alkali metal and the bridging halide atoms, the bi- and tridentate forms are located considerably lower on the potential energy surface then the monodentate isomer. Therefore only the bi- and tridentate isomers have chemical relevance. The monodentate isomer is only a high-lying local minimum in the case of X = F. For X = Cl, Br, and I this structure is found to be a second-order saddle point. The bidentate structure was found to be the global minimum for the systems with X = F, Cl, and Br. However, the relative stability with respect to the tridentate structure is very small (1-5 kJ/mol) for the heavier halide derivatives and the relative order is reversed in the case of the iodides. The energy difference between the three structures and the dissociation energy decrease in the row F to I. The ionic bonding in the complexes was characterized by natural charges and a topological analysis of the electron density distribution according to Bader's theorem. Variation of the geometrical and bonding characteristics between the lanthanum and dysprosium complexes reflects the effect of "lanthanide contraction". The calculated vibrational data indicate that infrared spectroscopy may be an effective tool for experimental investigation and characterization of LiLnX4 molecules.

The NaDyBr4 complex; its molecular structure and thermodynamic properties

“…At the same time, for the tridentate structure the degree of degeneracy is only four (according to the four sides of a tetrahedron). The different degrees of degeneracy of the bi-and tridentate forms have an influence on their relative abundance at high temperatures, as it was already suggested by Groen et al [28,29]. They showed that the equilibrium constant at high temperatures depends mostly on the entropy difference, S • (T), and not on which structure is actually more stable at zero Kelvin.…”

“…Simple Hartree-Fock level computations have been performed together with mass spectrometric studies of NaCeCl 4 and NaNdCl 4 [14,15]. Later, Groen et al [27][28][29] studied the structures of LiLnX 4 (Ln = La, Ce, Dy; X = F-I) and MLaX 4 (M = Na, K, Cs; X = F-I) complexes at the MP2 and density functional levels. In this paper we report the structure, dynamics and thermodynamic properties of the NaDyBr 4 complex based on high-level computations.…”

Theoretical Study of Mixed MLaX4 (M = Na, K, Cs; X = F, Cl, Br, I) Rare Earth/Alkali Metal Halide Complexes

“…The two-parameter set of f functions for La was taken from ref 24 La and the f polarization functions for Cl, Br, and I have been optimized in our previous study (exponents: R gLa ) 0.731; R fCl ) 0.720; R fBr ) 0.581; R fI ) 0.426). 19 The 2d and f functions for potassium and cesium were obtained in this study according to the procedure described in ref 28 (exponents: R dK ) 2.048, 0.512; R fK ) 1.174; R dCs ) 0.706, 0.1765; R fCs ) 0.610). For F the 6-311+G-(2df) and for Na the 6-311G(2df) basis sets were applied.…”

Combinatorial Computational Chemistry Approach for Materials Design:Applications in deNOx Catalysis, Fischer-Tropsch Synthesis, Lanthanoid Complex, and Lithium Ion Secondary Battery

“…The electronic structure of molecular systems containing lanthanoid elements has been the object of numerous experimental [53,54] and theoretical [55][56][57][58][59][60][61][62] studies. In this framework, one of the most challenging topics is the "chemical" description of the lanthanoid-ligand or actinide-ligand interactions in terms of ionic versus covalent interaction [63][64].…”