Updated Structure Determination of La(OH)₂Cl

A revised crystal structure of La(OH) 2 Cl is reported. This material is found to crystallize in space group P 2 1 / m and is isostructural to a series of Ln (OH) 2 Cl ( Ln = Ce – Lu excluding Pm). The Ln (OH) 2 Cl series has been thoroughly studied, serving as analogues to proposed actinide structures for used nuclear fuel storage. The P 2 1 / m space group has been reported for each isostructural variant in this series. La(OH) 2 Cl is described in the context of the structural trends identified with this series. A lanthanum variant has previously been reported, however, with symmetry corresponding to the space group P 2/ m . The data collected herein are compared to the previously published La(OH) 2 Cl in the space group P 2/ m . Herein, an updated hydrothermal synthesis and revised crystallographic structure for La(OH) 2 Cl in P 2 1 / m are reported. The reflection conditions of the collected X‐ray diffraction data, the bond valence sums of both structures, and total energy calculations based on density functional theory support the revised space group assignment.