Phase transition in 2-nitroanilinium bisulphate. Graph-set analysis, spectroscopic and theoretical studies

Abstract

The 2-nitroanilinium bisulphate, (H2NA)HSO4, crystallizes in triclinic symmetry, space group P–1. Isosymmetric phase transition is discontinuous and it proceeds at 232 K. Bisulphate anions are connected to each other by two hydrogen bonds forming the (HSO4−)2 dimers, which lay on the inversion center. A hopping of two hydrogen atoms is observed towards their parent acceptor oxygen atoms during phase transition. Calculations of the relaxed potential surface for the (HSO4−)2 dimer reveal two characteristic points at the transition state area. A maximum refers to the [SO42−⋯2H+⋯SO42−] system of Ci point group symmetry, but a local minimum lays 3.17 kcal/mol lower and it is related to the [H2SO4⋯SO42−] complex. Additionally, mathematical operations on graph-set descriptors of hydrogen bonding patterns were used to describe changes of intermolecular interactions occurred during phase transition. Phase transition was also monitored by FT-IR and DSC experiments.