Formation of M 4Se 4 cuboids (M = As, Sb, Bi) via secondary pnictogen-chalcogen interactions in the co-crystals MX 3·SeP(p-FC 6H 4) 3 (M = As, X = Br; M = Sb, X = Cl; M = Bi, X = Cl, Br)

The reactions of the group 15 trihalides, MX 3 (M = As, Sb, Bi; X = Cl, Br), with the phosphine selenide SeP(p-FC 6H 4) 3 result in the formation of co-crystals of formula MX 3·SeP(p-FC 6H 4) 3. No reaction was observed with MI 3 (M = As, Sb, Bi). The structures of MX 3·SeP(p-FC 6H 4) 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 3 unit, which has three weak secondary M⋯Se interactions to SeP(p-FC 6H 4) 3 molecules. However, each of these SeP(p-FC 6H 4) 3 molecules bridges three MX 3 molecules, resulting in the generation of an M 4Se 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 3 pyramid, and the other four by the selenium atom of the phosphine selenide. © 2012 The Royal Society of Chemistry.