Six New Members of the A2MIIMIV3Q8 Family and Their Structural Relationship

Abstract

The A2MIIMIV3Q8 family (A = alkali metal; MII = divalent metal; MIV = tetravalent metal; Q = chalcogenide) has attracted much attention because of its diverse structures and properties. Herein, we have successfully synthesized six new compounds as the first Mn-containing members of this family, Cs2MnGe3S8 (1), Cs2MnGe3Se8 (2), Cs2MnSn3Se8 (3), Rb2MnGe3S8 (4), Rb2MnGe3Se8 (5), and Rb2MnSn3Se8 (6). Compounds 1 and 6 crystallize in the monoclinic space group P21/n (No. 14) and P21 (No. 4), respectively, whereas compounds 2–5 crystallize in the non-centrosymmetric orthorhombic P212121 (No. 19). According to our theoretical calculations, their energy gaps are mainly dominated by s states of MIV and p states of Q and minor Mn 3d. Plate-like crystals with sizes about 20 × 5 × 1 mm3 of 2 and 3 are obtained by the Bridgeman method. In addition, we propose a structure mismatch factor that is defined as F = rMII+ rMIV + 2rQ2– – 2rA+ to provide a clear description of how three different structure types distribute among the A2MIIMIV3Q8 family; when 1.2 < F < 1.9, members will adopt a P212121-type structure; when F is too small (<1.2) or too large (>1.9), P21/n or P21-type, respectively, will be taken.