Peculiarities of crystal structure of terbium (III) trifluoroacetate trihydrate

TL;DR

This study compares the crystal and molecular structures of terbium trifluoroacetate trihydrates prepared from different sources, revealing structural differences, magnetic behaviors, and the influence of hydrogen bonding on their properties.

Contribution

It provides the first detailed structural and magnetic analysis of terbium trifluoroacetate trihydrates, highlighting the role of hydrogen bonds in their magnetic ordering.

Findings

Both compounds are centrosymmetric dimers with different hydrogen atom positions.

Tb-I exhibits ferromagnetic ordering at low temperatures.

Tb-II shows antiferromagnetic ordering at low temperatures.

Abstract

A comparative study of the crystalline and molecular structures of trifluoroacetate trihydrates of Tb(III) prepared from Tb(OH)_3 and Tb_2(CO_3)_3 by reaction with trifluoroacetic acid is made. Elemental analysis of the two reaction products in indicated them to be compounds of the same C_6H_6F_9O_9Tb. According to the X-ray structural analysis the molecular structure of the first product is described by the average statistical formula Tb_2(CF_3COO)_5(CF_3COOH)(H_2O)_5(OH) (Tb-I) and the compound is a dimer with a centre of inversion. In the second case the product is also a centrosymmetric dimer but its formula is Tb_2(CF_3COO)_6(H_2O)_6 (Tb-II). The compounds only difference is in the crystallographic positions of their hydrogen atoms. A luminescent analysis using Tb^{3+} ^5D_4-> ^7F_0 transition indicated the presence within the structure of Tb-I of the structure of Tb-II. Magnetic measurements showed that Tb-II has an antiferromagnetic ordering at low temperatures. In the case of Tb-I there also appears a ferromagnetic ordering. On the basis of the available experimental results such a behaviour was explained to be the result of some peculiar features of the hydrogen bonds in the molecules.