Charge density and quantum-chemical study of triphenylguanidine and triphenylguanidinium trifluoroacetate

Abstract This study investigates the molecular changes in triphenylguanidine and triphenylguanidinium trifluoroacetate as temperature decreases, utilizing variable-temperature single-crystal X-ray diffractometry (VT-SCXRD). The Hansen-Coppens multipole formalism is employed for aspherical atom refinement, enabling the retrieval of solid-state polarizability and hyperpolarizability tensorial coefficients ( $$\varvec{\alpha }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:math> and $$\varvec{\beta }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>β</mml:mi> </mml:mrow> </mml:math> ). Furthermore, the research examines the molecular basis for variations in the thermal expansivity of the crystalline solid forms, namely, in the polymorphic forms of triphenylguanidine. The aromaticity of the central core and the phenyl rings of triphenylguanidine is monitored as temperature changes, using the HOMA and NICS indices. The results indicate a clear increase in the aromaticity of the phenyl rings. Topological analysis of charge density is used to identify regions of high and low electron density. Evidence is provided for weak attractive interactions between the trifluoro groups of neighboring anions.