Molecular and crystal structure of 1,1′-diamino-2,2′-bipyridinium and 1,1′-diamino-4,4′-bipyridinium dimesitylenesulphonates: A combined experimental and theoretical study

The purpose of the present work is to study molecular and crystal structures of 1,1′-diamino-2,2′-bipyridinium (1a) and 1,1′-diamino-4,4′-bipyridinium (1b) dimesitylenesulphonates by experimental (X-ray, NMR) and theoretical (DFT, RI-B3LYP and RI-MP2) methods. The NNH2 bond lengths determined by X-ray diffraction are close to that of single NN bond and considerably longer than that of double NN bond. The bipyridine fragment in dications is slightly asymmetric (σ–π distortion). The dihedral angle between the two pyridine planes in dication (1a) is essentially larger than that in dication (1b). The NH2 groups have a pyramidal structure. The crystal structure of 1,1′-diamino-2,2′-bipyridinium dimesitylensulphonate is a stack of layers of cations and anions. The basic supramolecular synthon is NH⋯O. The directed along a + b axis zig-zag ribbons of cations in a crystal of 1,1′-diamino-4,4′-bipyridinium dimesitylenesulphonate are formed due to such a synthon and pseudo-para arrangement of amino groups. DFT and RI-MP2 calculations give geometry of the dications similar to the experimental one. The conformational analyses of dications (1a) and (1b) have been carried out using RI-B3LYP method. Non-planar conformation of dication (1a) in DMSO solution is confirmed by 1H NMR data. Calculation of HOMAd index for the dications from the experimental bond lengths gives values which indicate their aromatic character.