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 (OFF, RI-B3LYP and RI-MP2) methods. The N-NH2 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 (sigma-pi 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 N-H center dot center dot center dot 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. OFT 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 H-1 NMR data. Calculation of HOMA(d) index for the dications from the experimental bond lengths gives values which indicate their aromatic character. (c) 2012 Elsevier B.V. All rights reserved.