Ca3GeO4Cl2 with a norbergite‐like structure

The title compound, tricalcium monogermanate dichloride, is orthorhombic and consists of one distinct Ge site on special position 4c, site symmetry m, and two different Ca sites, Ca1 and Ca2, one on general position 8d, site symmetry 1, and the other on special position 4c. Two of the O atoms occupy the 4c position (symmetry m); the third O atom is situated on the general 8d position, symmetry 1, as is the one distinct Cl position. By sharing common edges, the distorted Ca1 octahedra form infinite crankshaft‐like chains parallel to the b direction. Along a and c, these chains are connected to one another via common corners, thereby forming a three‐dimensional framework of edge‐ and corner‐sharing Ca1O₄Cl₂ octahedra. Triangular prisms of Ca2O₄Cl₂ polyhedra and GeO₄ tetrahedra fill the interstitial space within the Ca1 polyhedral framework. Relationships between the structures of the title compound and the humite‐type materials norbergite (Mg₃SiO₄F₂) and Mn₃SiO₄F₂ are discussed.