Interplay of Ionic Species in Salts of Homoleptic Quaternary Phosphonium Cations Bearing Linear Biphenyl Moieties

Quaternary phosphonium salts are popular candidates used in many chemical transformations and synthetic chemistry, notably in catalysis. We have examined the single crystals of two bulky phosphonium compounds, tetra([1,1 '-biphenyl]-4-yl) phosphonium dicyanamide (C48H36P+center dot N(CN)(2)(-), compound 1), and tetra([1,1 '-biphenyl]-4-yl) phosphonium bromide hydrate (C48H36P+center dot Br-, CH3CN, H2O, compound 2), and herein report the structural properties for the compounds with an emphasis on the influence of the ion-ion interaction towards self-assembly; the overall self-assembly for both structures is very similar, with subtle differences in the cell parameters. The symmetrical tetra ([1,1 '-biphenyl]-4-yl) phosphonium cations in both compounds self-assembled to form robust stacked columns in the solid-state, with voids occupied by anions or solvent molecules. Quantitative examination of intermolecular interactions using Hirshfeld surface analysis found that classical and non-classical hydrogen bonding appears to be the dominant contributor in stabilizing the self-assembly in both cases. The present work can not only benefit in understanding the mutual interaction between the sterically encumbered tetra ([1,1 '-biphenyl]-4-yl) phosphonium cations and between counterions, but also provide insights for the self-assembled arrays in the solid-state.

Automated summary

This study examines the single crystal structures of two bulky phosphonium compounds and investigates their self-assembly behavior. It is found that the organic cations form stable stacked columns with voids occupied by anions or solvent molecules. The analysis suggests that hydrogen bonding plays a dominant role in stabilizing the self-assembly.