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

Abstract 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 N NH 2 bond lengths determined by X-ray diffraction are close to that of single N N bond and considerably longer than that of double N N 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 NH 2 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 N H⋯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 1 H NMR data. Calculation of HOMA d index for the dications from the experimental bond lengths gives values which indicate their aromatic character.