Na4P2Se6 (1) crystallizes in the orthorhombic space group Cmca (No. 64) with a = 11.836(3) Å, b = 13.311(4) Å, c = 8.061(2) Å, V = 1270.0(6) Å3, Z = 4, and, Dc = 3.283 g/cm3. Na4P2Se6 belongs to the family of compounds with the general formula \documentclass[12pt]{minimal}
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\begin{document}$$[({\rm A}^{ + x} )_{y/x} ({\rm P}_2^{{\rm iv}} {\rm Q}_6 )^{ - y}]$$\end{document} where A = Na+ and Q = Se2−. The crystal structure consists of isolated ethane-like P2Se\documentclass[12pt]{minimal}
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\begin{document}$$_6^{4-}$$\end{document} anions surrounded by Na+ cations. Cs3PSe4 (2) crystallizes in the orthorhombic space group Pnma (No. 62) with a = 10.0146(9) Å, b = 11.9899(10) Å, c = 9.9286(9) Å, V = 1192.17(18) Å3, Z = 4, and, Dc = 4.154 g/cm3. Cs3PSe4 belongs to the family of compounds with the general formula [(A+x)z/x(PvQ4)−z] where A = Cs+ and Q = Se2−. The crystal structure consists of isolated methane-like PSe\documentclass[12pt]{minimal}
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\begin{document}$$_4^{3-}$$\end{document} anions surrounded by Cs+ cations. Rb4P2Se9 (3) crystallizes in the monoclinic space group C2/c (No. 15), a = 9.725(2) Å, b = 10.468(3) Å, c = 19.155(5) Å, β = 93.627(5)°, V = 1946.1(8) Å3, Z = 4, Dc = 3.804 g/cm3. Rb4P2Se9 belongs to the family of compounds with the general formula [(A+x)(2z−2)/x(Q3PQ′—Q″—Q′PQ3)−(2z−2)] where A = Cs+ and Q = Se2−, Q′ = Se1−, Q″ = Se0. The crystal structure consists of isolated P2Se\documentclass[12pt]{minimal}
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\begin{document}$$_9^{4-}$$\end{document} anions surrounded by Rb+ cations.
