Thorium Tetrabromide: An Old Compound Restudied by Actinide Chemistry

Abstract

Crystallogenesis /Luminescence /Radioluminescence /Commensurate-incommensurate phase transition /Absorption spectroscopy/ Emission spectroscopy/Tetravalent actinidesAbstract Some properties of thorium tetrabromide which have become apparent since 1975 are examined. Until the discovery of its radioluminescence, no particular attention was given to this halide, but subsequently research on this compound was intensified.Owing to the exceptional radioresistance of the material, studies concerning the possibilities of using ThBr 4 as a radiation detector, a target detector for nuclear reactions and a converter of nuclear energy into luminous energy have been given priority. Later, its use as a matrix for high resolution spectroscopy of M 4+ actinide ions (because of the properties of the Th 4+ ) ion was considered. The interpretation of the absorption and emission spectra required a complete characterization of vibrational and structural properties of ThBr 4 , especially at low temperature. It was only then discovered that ThBr 4 underwent a commensurate -incommensurate phase transition towards 90 Κ and that the modulated phase still existed at 4 K. Extensive research was begun which later expanded into numerous fields; some of these, such as phase transitions dynamics and the effect of the incommensurability on spectroscopic and thermodynamic properties are presently under study. Much of this work required the availability of large (several cm 3 ) single crystals of ThBr 4 and consequently production of this compound on the kilogram scale was carried out.

Advances in Chemistry of the Actinide Elements

“…An excellent example of a Compound whose properties have generated enormous contemporary interest, yet which only a few years ago was an unimportant classical substance, is thorium tetrabromide [2]. Its potential as ahost matrix, with a diamagnetic and optically transparent/® configuration, has made its synthesis important for optical and magnetic studies of tetravalent actinide ions [3].…”

“…Below 92 K, j3-ThBr4 displays Splitting of a Raman Vibration and of a bromine nuclear quadrupole resonance line, and new X-ray and neutron diffraction lines appear [2,7]. These observations are not consistent with any conventional superlattice of the tetragonal unit cell, and are caused by a second-order phase transition in which bromine atoms along the c ciystallographic axis are displaced sinusoidally from their sites with a repeating distance of 3.201 c. This phenomenon is a subject of intense investigation and illustrates how careful measurements on pure, Single ciystals can reveal new scientific ideas.…”

A Simple Access to Pure Thorium(IV) Halides (ThCl4, ThBr4, and ThI4)

“…The crystal structure of ThCl 4 was first determined by Mooney from powder X‐ray diffraction data and was confirmed later by Mucker and co‐workers in 1969 , . Two polymorphs, a tetragonal high and a tetragonal low temperature form, were observed for both ThCl 4 and ThBr 4 , . The high temperature α‐modification of ThCl 4 is stable above 405 °C, the one of ThBr 4 above 430 °C.…”

“…[31,32] Two polymorphs, a tetragonal high and a tetragonal low temperature form, were observed for both ThCl 4 and ThBr 4 . [33,34] The high temperature α-modification of ThCl 4 is stable above 405 °C, the one of ThBr 4 above 430 °C.…”