ISODISTROTLaMTeO 6 (M = Ga 3+ and Mn 3+ ): the critical role of electronic configuration and cation ordering in crystal structures.

In this work, PbSb 2 O 6 -type oxides LaMTeO 6 (M = Ga 3+ and Mn 3+ ) were synthesized and structurally characterized by Rietveld refinements against high-resolution X-ray powder diffraction data. The Ga 3+ /Te 6+ partial ordering within the honeycomb-like two-dimensional [GaTeO 6 ] 3- anionic layer leads to the loss of the inversion center between Ga 3+ and Te 6+ ; however the inversion center on the 3̄-roto-inversion axis is preserved, thereby resulting in a 2-fold PbSb 2 O 6 -type superstructure by doubling the c -axis associated with a structural symmetry descending from the original P 3̄1 m to P 3̄1 c symmetry. In contrast, LaMnTeO 6 ( P 2 1 / c ) adopts a monoclinically distorted 4-fold superstructure with lattice dimensions of a ≈ a H , b ≈ √3 a H , c ≈ 2 c H , where a H and c H represent the lattice parameters of trigonal PbSb 2 O 6 . The formation of this P 2 1 / c -superstructure is attributed to the combination of complete Mn 3+ /Te 6+ ordering and the first-order Jahn-Teller distortion of Mn 3+ with the electronic configuration of d 4 . Such a monoclinic distortion can effectively lift the Mn 3+ spin moments arranged on the triangular sublattice, resulting in a sharp peak for antiferromagnetic transition, which is in stark contrast to subtle magnetic transitions for PbSb 2 O 6 -type tellurates AMn(VI)TeO 6 (A = alkaline earth and Pb 2+ ) and LnCrTeO 6 (Ln = rare earth) with higher structural symmetry. Our findings highlight that the electronic configuration effects of M-cations play a critical role in controlling the structure symmetry of LaMTeO 6 , providing a strategy to fine-tune the crystal structures and physical properties.