Six New Members of the A2MIIMIV3Q8 Family and Their Structural Relationship

The A 2 M II M IV 3 Q 8 family (A = alkali metal; M II = divalent metal; M IV = 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, Cs 2 MnGe 3 S 8 ( 1 ), Cs 2 MnGe 3 Se 8 ( 2 ), Cs 2 MnSn 3 Se 8 ( 3 ), Rb 2 MnGe 3 S 8 ( 4 ), Rb 2 MnGe 3 Se 8 ( 5 ), and Rb 2 MnSn 3 Se 8 ( 6 ). Compounds 1 and 6 crystallize in the monoclinic space group P 2 1 / n (No. 14) and P 2 1 (No. 4), respectively, whereas compounds 2 – 5 crystallize in the non-centrosymmetric orthorhombic P 2 1 2 1 2 1 (No. 19). According to our theoretical calculations, their energy gaps are mainly dominated by s states of M IV and p states of Q and minor Mn 3d. Plate-like crystals with sizes about 20 × 5 × 1 mm 3 of 2 and 3 are obtained by the Bridgeman method. In addition, we propose a structure mismatch factor that is defined as F = r M II + r M IV + 2 r Q 2– – 2 r A + to provide a clear description of how three different structure types distribute among the A 2 M II M IV 3 Q 8 family; when 1.2 < F < 1.9, members will adopt a P 2 1 2 1 2 1 -type structure; when F is too small (<1.2) or too large (>1.9), P 2 1 / n or P 2 1 -type, respectively, will be taken.