Lanthanide tetrad effect in the Ln3+ ionic radii and refined spin-pairing energy theory

Abstract

The refined spin-pairing energy theory (RSPET) has been improved in order to understand quan titatively the tetrad or double-double effects recognized in the Ln3+ ionic radii. Since the ionic radii have been determined from the lattice constants and structural parameters of Ln01.5 and LnF3, the lattice energies of the compounds and the enthalpy difference of d Hf (LnF3)-A Hf (LnO1,5) have been exam ined by the improved RSPET. The RSPET parameters for the lowest levels of 4fq electronic configura tions strongly depend upon the effective nuclear charge (Z*). Such effects due to Z* have been taken into account. This made it possible to separate the variations in the lattice energies and the enthalpy difference across the Ln3+ series into the following two parts: (1) the large variation as a smooth func tion of q (the lanthanide contraction trend), and (2) the small zig-zag variation referred to the tetrad or double-double effect. The lattice energy of Ln01.5 and A Hf (LnF3)-A Hf (Ln01.5) exhibit upward con cave tetrad curves in their plots against q of Ln3+. The tetrad effect in the lattice energy of LnF3 is less conspicuous. This means that the Racah parameters for Ln3+ decrease very slightly in going from the gaseous free Ln3+ to LnF3, and then decrease greatly to Ln01.5, in accordance with the nephelauxetic series. The differences in Racah parameters between LnF3 and Ln01,5 have been estimated from A Hf(LnF3) -A Hf(Ln01.5) by means of an inversion technique based on the improved RSPET. The RSPET results for the thermochemical data are consistent with the careful spectroscopic determinations of Racah parameters for NdF3 and Nd01.5. Both the tetrad effect and the smooth lanthanide contraction seen in the Ln3+ ionic radii can be interpreted in terms of the quantum mechanical energetics of 4f elec trons.

Characteristics of rare earth element abundances in shallow marine continental platform carbonates of Late Neoproterozoic successions from India.

“…(2)) between REE(III) complexes in seawater (Kawabe et al, 1998), 3 ) parameters for 4f electron repulsion in REE 3+ , the logarithms of concentration ratios between the pair of species show a REE fractionation trend characterized by tetrad effect (Jørgensen, 1979;Kawabe, 1992;Minami et al, 1998;Kawabe and Masuda, 2001). In fact Racah E 1 and E 3 parameters for REE sesquioxide (REEO 1.5 ) and REE(OH) 3 are significantly smaller than those for REECO 3 + (aq) and slightly smaller than those of REE(CO 3 ) 2 -(aq) in seawater solution (Ohta and Kawabe, 2000).…”

Origin of blueschist-facies clasts in the Mariana forearc, Western Pacific.

“…Samarium is plotted on a point lower than the Nd Gd join and Dy is plotted below the Gd-Er join. This type of REE pattern is well known for sea water and is thought to reflect the lanthanide tet rad effect (Masuda and Ikeuchi 1979;Kawabe 1992), suggesting that hydrous alteration consid erably modified the REE chemistry of the Group 3 clasts. In general, rare earth elements are be lieved to be immobile during sea water alteration, especially for heavy REE (Ludden and Thompson, 1978).…”

Thermochemical parameters for solution of lanthanide(III) ethylsulphate and trichloride hydrate series: Tetrad effects and hydration change in aqua Ln3+ ion series.

“…LnF3 is a representative compound having largest Racah parameters close to those of free Ln3+ ion, whereas Ln015 is an other representative one characterized by small est Racah parameters. According to RSPET, the Racah parameters for 4f electron repulsion in Ln3+ ion contribute to the electronic configuration en ergy of the Ln3+ ion (Kawabe, 1992). Hence, a tetrad effect comes out in the series variation of…”

“…It therefore cannot deal with struc tural changes across Ln(III) complex series at all. The RSPET implicitly requires a data set of AHr for a pair of Ln(III) complexes both of which are fully isomorphous series (Kawabe, 1992). When the Ln(III) series are partly isomorphous, the ir regularities due to structural changes across the series must be removed from experimental LtHr data by referring to structural information as to the Ln(III) complex series individually.…”

“…The refined spin-pairing energy theory (RSPET) by Jorgensen (1979) is a theoretical ba sis of lanthanide tetrad effects. Kawabe (1992) improved the formulation of RSPET, and ex plained quantitatively the tetrad effects in lattice energies of LnO1 .5 and LnF3 and in the series vari ation of AHf (LnF3) AHf (LnO1 .5). This accounts for the obvious tetrad effect in ionic radii for VILn3+ and no substantial tetrad effect in the radii for VIIILn3+.…”