Crystal supramolecularity: multiple phenyl embraces formed by [AsPh 4] + cations

Abstract

Analysis of the 483 crystals in the Cambridge Structural Database containing [AsPh 4] + cations has revealed mutually attractive interactions between the cations leading to the formation of supramolecular motifs. The types of inter-cation interaction can be classified by a combination of the C distalP⋯P angle and the angle between CPC planes on adjacent interacting cations. Interactions with a C distalP⋯P angle of greater than 168° indicate a six-fold phenyl embrace (6PE), whilst those at lower angles form either offset six-fold phenyl embraces (O6PEs) or four-fold phenyl embraces, which are distinguished by approximately parallel (P4PE) or orthogonal (O4PE) CPC planes. Of the selected [AsPh 4] + structures, 45% have well-defined intercationic motifs, of which 88% are 6PEs, 8% O6PEs and are 4% 4PEs. This distribution of embrace type is analogous to interactions between previously studied [PPh 4] + cations. However, the embraces formed by [AsPh 4] + cations have comparatively longer As⋯As separations, and contain less-well directed local interactions between the component phenyl rings than their phosphonium counterparts. The individual embraces combine to form zig–zag chains of 6PEs (ZZI6PEs) or linear chains of O4PEs (LIO4PEs) leading to either columnar or layered structures. In general, ZZI6PEs form with dianions, whereas LIO4PEs occur more frequently in monoanionic salts. The crystal lattice formed does not depend on anion size. Computation of the energies of attraction between the cations gives values of −3.8, −2.0, −1.8 and −1.4 kcal mol −1 for the 6PE, O6PE, P4PE and O4PE, respectively, comparable to the corresponding embraces formed by [PPh 4] + cations.