Supramolecular characterisation of salts of 4-(2-methoxyphenyl)piperazin-1-ium and 4-phenylpiperazin-1-ium cations with simple-organic anions; a closer look at the binding energies of cation-anion pairs formed by charge-assisted (+)N−H···O(-) and (+)N−H···O hydrogen bonds

Abstract

Six new salts prepared by acid-base reactions containing 4-(2-methoxyphenyl)piperazin-1-ium cation (2-MeOPP) with simple organic-acid anions, namely pentafluorobenzoate, (I); (2R,3R)-tartrate dihydrate, (II); succinate trihydrate, (III); or 4-phenylpiperazin-1-ium cation (PP) with 4-chlorobenzoate monohydrate, (IV); 3-chlorobenzoate monohydrate, (V) and succinate (VI) have been structurally characterised using single-crystal X-ray diffraction. Crystal-packing architectures have been described in the context of the supramolecular assemblies they form. The most important structural motifs are generated through hydrogen bonds between 2-MeOPP or PP cations and associated anions, assisted by their charges. To quantify these charge-assisted hydrogen bonds: (+)N−H····O(-) and (+)N−H····O, the binding energies of the ionic pairs have been calculated and compared. We considered a set of 72 ionic pairs of the structures analysed in this article and those published previously by our groups. As a result, we have plotted lines of trends found for DFT-binding energies vs normalised H···O proton···acceptor distances, and correlation between normalised geometrical parameters for aromatic and aliphatic anions. A comparison between DFT-energies and model pairwise energies (CE-B3LYP) has also been made.