Lanthanide monofluorides

The ground state configurations of the lanthanide monofluorides may be assumed to arise from either of the two superconfigurations (SC) ... 

Binding energies ) bond lengths R, vibrational frequencies Wj and dipole moments for the lanthanide monofluorides from configuration interaction calculations including the Langhoff-Davidson size-consistency correction in comparison with experimental data ... 

The results of our previous analysis (Chervonnyi and Chervonnaya, 2004d, 2007e) showed that, in the absence of sufficient experimental and/or theoretical data on the molecular constants of lanthanide monofluorides and monochlorides, their thermodynamic fimctions can be... 

Kitaev, A.A., 1988. Lanthanide Monofluorides Energy of Ionization, Electronic Structure and Characteristics of Chemical Bonds. Candidate s Dissertation in Chemistry, Ivanovo (in Russian). 

Y. Wasada-Tsutsui, Y. Watanabe, and H. Tatewaki, Electronic structures of lanthanide monofluorides in the ground state Frozen-core Dirac-Fock-Roothaan calculations, Int. J. Quantum Chem. 109, 1874 -1885 (2009). 

Solvent extraction, potentiometry, and calorimetry have been used to determine the thermodynamic parameters of the formation of the monofluoride complex of the trivalent lanthanide ions at 25°C. and an ionic strength of IM (NaClOj ). The enthalpies were all endothermic, ranging from 4.0 to 9.5 Kcal./mole consequently, the large, positive entropies, ranging from 25 to 48 cal./°C./mole, explain the high stability constants. This large entropy results from the decrease in overall water structure when the fluoride ion is complexed. The difference in the enthalpies of formation of LnF and LnAc " can possibly be explained by a difference in covalence for Ln-F and Ln-O bonds. 

The main difficulty here is to clearly separate effects that can hardly be separated, namely relativistic and electron-correlation effects. Nevertheless, pioneering studies of this effect date back to the mid 1970s [1140]. Four-component methods have been employed to determine the contribution which is solely due to relativity [1141]. The four-component approach, for which Dirac-Hartree-Fock and — to also account for correlation effects — relativistic MP2 calculations have been utilized, confirms results first obtained with relativistic effective core potential methods [1142,1143]. It has been found [1141] that between 10% and 30% of the lanthanide contraction and 40% to 50% of the actinide contraction are caused by relativity in monohydrides, trihydrides, and monofluorides of La, Lu and Ac, Lr, respectively. 

Two factors prevent this problem from being completely solved. First, no experimental data are available dealing with the equilibria involving other lanthanide monohalides, except monofluorides, which have been comprehensively addressed. Indeed, equilibrium constants for 30 gas-phase reactions involving RF t (R = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm k = 1-3) were measured by mass spectrometry (Hildenbrand and Lau, 1995 Kleinschmidt et al., 1981 Zmbov and Margrave, 1966a,c, 1967a, 1968). From these data, AatH°(RX, 0) values for nine of the fifteen monofluorides RF can be calculated. 

The effect of lanthanide contraction for monofluorides has been considered by Wang and Schwarz (1995). DFT calculations in this work showed that in going from LaF to LuF, the interatomic distance decreases by 0.12 A. Kiichle et al. (1997) subsequently demonstrated that the influence of interatomic distances on the other molecular constants (Rg/ e) of lanthanum and lutetium monofluorides is reflected by calculations with the pseudopotential method. 

The thermodynamic functions of RX, RF2, and RF3 were used in the calculations of the enthalpies of reactions. In addition, calcium and barium monofluorides, tungsten tetra- and hexafluorides, and barium monochloride are among the reaction components. Their thermodynamic functions, as well the thermodynamic fimctions of lanthanides in the gas phase, were taken from the database IVTANTERMO (2004). 

A study of the monohydrides, monoxides, and monofluorides of lanthanides and actinides using ab initio all-electron and pseudopotential techniques is also available. The spectroscopic constants of low-lying electronic states of ThO " ... 

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