A New High‐Pressure Polymorph of MgTe ₂ O ₅ with a Unique Crystal Structure

A high‐pressure polymorph of MgTe 2 O 5 was synthesized under multianvil high‐pressure and high‐temperature conditions (8 GPa and 800 °C). Single‐crystal diffraction data of this phase are presented, and the unique crystal structure is compared to its ambient‐pressure counterpart and other oxidotellurates(IV) of the same composition. HP‐MgTe 2 O 5 crystallizes in the orthorhombic space group Pbam and is characterized by the lattice parameters a = 749.53(5), b = 920.28(5), and c = 643.69(4) pm. The crystal structure consists of trigonal‐pyramidal [Te IV O 3 ] 2– and pseudooctahedral [Te IV O 5 ] 6– polyhedra forming infinite chains of fused sechser rings. The lone electron pairs of the Te 4+ cations were localized based on geometric principles. The [MgO 6 ] octahedra also form infinite chains through edge‐sharing of these octahedra. Temperature‐dependent powder X‐ray diffraction revealed stability up to 450 °C followed by a phase transformation to the ambient‐pressure modification.