Quaternary selenodiphosphates(IV): MIMIII[P2Se6], (MI =Cu, Ag; MIII = Cr, Al, Ga, In)

The layered compounds CuCr[P2Se6] (m.p. 730 °C, incongruent), AgCr[P2Se6] (m.p. 720 °C, incongruent), AgAl[P2Se6] (m.p. 588 °C, congruent), CuIn[P2Se6] (m.p. 642 °C, incongruent), AgIn[P2Se6] (m.p. 673 °C, congruent), α-AgGa[P2Se6] (m.p. 450 °C, congruent) and β-AgGa[P2Se6] (metastable) were prepared from the elements in evacuated silica tubes (molar ratios MI:MIII:P:Se=1:1:2:6) by heating up to 750 °C (10 h) followed by quenching/annealing or by cooling from the melt (Bridgman technique). The crystal structures of CuIn[P2Se6], AgIn[P2S6] (trigonal, P3̄1c; a=639.2(0), 648.3(1); c=1333.8(1), 1333.0(4) pm; Z=2) and β-AgGa[P2Se6] (trigonal, P3̄1c; a=637.5(6), c=1332.0(1) pm; Z=2) are related to the CdI2 structure type whereas the crystal structures of CuCr[P2Se6], AgCr[P2Se6] and AgAl[P2Se6] (monoclinic, C2/m; a=619.3(3), 630.5(8), 634.8(5); b=1072.4(2), 1091.7(3); 1098.9(3); c=690.9(9), 699.1(1), 702.8(4) pm; β=107.2(7), 107.7(1), 107.2(1)°; Z=2) are related to the CdClz structure type. α-AgGa[P2Se6] (orthorhombic, Pbca; α=1216.9(5), b=2248.4(6), c=747.3(2) pm; Z=4) shows close relationships to the crystal structure of Ag4[P2Se6].