Can the solid state structures of the dihalogen adducts R3EX2 (E = P, As; R = alkyl, aryl; X = Br, I) with the molecular spoke geometry be considered good mimics of the gold(i) systems [(R3E)AuX] (E = As, P; R = alkyl, aryl; X = Cl, Br, I)?

The solid-state structures of compounds of the type R3EX2 and [(R3E)AuX] (R = alkyl, aryl, E = As, P, X - Cl, Br, I) have been compared on the basis that they have similar molecular shape and volume with a view to determine whether this is a good approach to understand the formation of aurophilic interactions. To aid in the discussion the new compounds Ph-2(C6H5-C6H4)P1, Ph-2(C6H5-C6H4)PI2 1a, [Ph-2(C6H5-C6H4)PAuX] (X = Cl 2a, Br 2b, I 2c) and [(LAu)-C6H4-2-OMe] (L = PPh3 3a, PCy3 3b; PPh2-1-naphthyl 3c; PPh2-2-MeO-C6H4 3d) and [(LAu)-C6H3-2,5-(OMe)(2)] (L = PPh3 4a, PCy3 4b; PPh2-1-naphthyl 4c; PPh2-2-MeO-C6H4 4d, which have all been fully spectroscopically characterised and for 1a, 2a-c, 3a and 3c by X-ray crystallography, have been synthesised. It is found that in some cases the group 15 dihalogen adducts mimic the solid state structures of the gold halide complexes extremely well indicating the packing requirements of the ligand are dominant. In many other cases there are significant differences and these differences shed light on why it is difficult to predict with certainty the presence of an Au center dot center dot center dot Au contact. It also appears that complexes with an Au-I bond are most likely to form an Au center dot center dot center dot Au contact as the Au-I bond is the weakest hydrogen bond acceptor.