Effects of applied pressure on the Ln(OH)₂Cl series

Trivalent lanthanide (Ln) species are often utilized as analogues for trivalent actinide experiments, reducing the cost and risk of experimental research. The monoclinic Ln(OH)₂Cl series consists of remarkably inert structures in neutral conditions, credited to their 8-coordinate structures and substantially linked frameworks [1]. This makes their actinide analogues ideal candidates for use in nuclear fuel storage. The later lanthanides, however, favorably crystallize in an orthorhombic, but similarly 8-coordinate, structure. Here, we computationally model the high-pressure behavior of this lanthanide series to investigate the monoclinic and orthorhombic polymorphism using first-principles total-energy calculations. We hypothesize that a 9-coordinate environment, which is likely prevented in the orthorhombic structure by the electronic repulsion of bound ligands and nearby chloride ions, may be accessible under hydrostatic pressure.

[1] R. A. Zehnder, D. L. Clark, B. L. Scott, R. J. Donohoe, P. D. Palmer, W. H. Runde, and D. E. Hobart, Inorg. Chem. 49, 4781 (2010).