Formation of M sub(4)Se sub(4) cuboids (M = As, Sb, Bi) viasecondary pnictogen-chalcogen interactions in the co-crystals MX sub(3).Se&z.dbd; P(p-FC sub(6)H sub(4)) sub(3 ) (M = As, X = Br; M = Sb, X = Cl; M = Bi, X = Cl, Br)

The reactions of the group 15 trihalides, MX sub(3) (M = As, Sb, Bi; X = Cl, Br), with the phosphine selenide SeP(p-FC sub(6)H sub(4)) sub(3) result in the formation of co-crystals of formula MX sub(3).SeP(p-FC sub(6)H sub(4)) sub(3). No reaction was observed with MI sub(3) (M = As, Sb, Bi). The structures of MX sub(3).SeP(p-FC sub(6)H sub(4)) sub(3) (M = As, X = Br 2; M = Sb, X = Cl 3; M = Bi, X = Cl 5; M = Bi, X = Br 6) have been established, and are isomorphous, crystallising in the cubic I23 space group. All the structures feature a primary MX sub(3) unit, which has three weak secondary M...Se interactions to SeP(p-FC sub(6)H sub(4)) sub(3) molecules. However, each of these SeP(p-FC sub(6)H sub(4)) sub(3) molecules bridges three MX sub(3) molecules, resulting in the generation of an M sub(4)Se sub(4) (M = As, Sb, Bi) distorted cuboid linked by the pnictogen-chalcogen interactions. Four opposing corners of the cuboid are occupied by the M atom (M = As, Sb, Bi) of an MX sub(3) pyramid, and the other four by the selenium atom of the phosphine selenide.