Polymorphs and Aurophilic Interactions in Colorless Crystals of Au2(μ-1,2 bis-(diphenylarsino)ethane)X2, (X = Cl, Br, I)

Solutions containing the components Au+, dpae (dpae is 1,2 bis-(diphenylarsino)­ethane), and X– (X is Cl, Br, or I) can produce two different types of crystals with the composition Au2(μ-dpae)­X2: colorless blocks and colorless needles. Crystallographic studies of these crystals show that they are polymorphs with different structural motifs. In the α-polymorphs, which are isostructural, individual molecules of Au2(μ-dpae)­X2 form discrete dimers through two identical Au···Au contacts. In the β-polymorphs, which each have unique crystallographic parameters, the Au2(μ-dpae)­X2 molecules assemble into polymeric chains through aurophilic interactions. The Au···Au contacts in the α-polymorph (3.1163(2), 3.1064(3), and 3.0842(2) Å for Cl, Br, I, respectively) are somewhat shorter than those in the β-polymorph (3.1668(3), 3.1042(8), and 3.1046(2) for Cl, Br, I respectively). The systematic study we now report shows an increase in the strength of this aurophilic interaction for the α-form in the series X = Cl < Br < I, which is in good agreement with theoretical studies by Pyykkö and his co-workers.