Structural relationships between o-, m- and p-tolyl substituted R3EI2 (E = As, P) and [(R3E)AuX] (E = As, P; X = Cl, Br, I)

The compounds R3EI2 (R = o-tolyl, E = As, 1a; R = m-tolyl, E = P 1c; R = p-tolyl, E = As, 1d, P, 1e), which display the charge transfer spoke structure, and [(o-tolyl(3)As)AuCl](2) have been synthesised and their solid state structures compared to the related complexes [(R3P)AuX] (R = o-tolyl, X = Cl, I, Ia; Br, II; I, III; R = m-tolyl, X = Cl, IV; R = p-tolyl, X = Cl, V, Va; Br, VI; I, VII) on the basis of a similarity of their molecular shape and volume. All of the new compounds 1a, 1c-1e and 2 have been fully spectroscopically characterised and by single crystal X-ray crystallography. The sterically demanding exo(3) o-tolyl ring conformation is observed for 1a, which is comparable to that reported for o-tolyl(3)PI(2) 1b, with a long As-I bond 2.7351(14)angstrom and short I...I distance 2.9528(11)angstrom. The exo(3) o-tolyl ring conformation is maintained on complexation to gold(I) in 2, but has no significant impact on the expected bond lengths, with As-Au 2.3443(15)angstrom and Au-Cl 2.284(4)angstrom. The exo(3) conformation appears to be stabilised in both cases by the formation of a six-fold edge-to-face (EF)(6) embrace. It is found that in some cases the structures of the dihalogen adducts and the gold(I) complexes are isomorphous indicating that ligand packing requirements are most significant i.e. for 1c and IV. Where the structures digress this is due either to the greater ability of the dihalogen adduct to engage in hydrogen bonding 1a, b and I-III; or subtle changes in the nature of the tolyl ring embraces 1d, e and V-VII. Subtle changes in the nature of the tolyl ring embraces also account for the different polymorphs I and Ia and V and Va. There is no credible evidence to suggest that the aurophilic contact, seen in only one polymorph Va, exerts any influence on the overall crystal packing. The structural comparisons presented here add further to the applicability of the recently recognised structural mimicking ability of the R3PX2 systems and [R3PAuX] complexes, and that the aurophilic contact is a poor supramolecular synthon.