New examples of metal coordination architectures of 3,3′,4,4′- biphenyltetracarboxylic acid - syntheses, crystal structures, and physical properties

Four new metal-organic frameworks [Cu₂(2,2′-bipy) ₂(ox)(H₂O)₂]·(H₂bptc) (1), [Cu(bptc)_0.5(phen)(H₂O)]·H₂O (2), Co₂(bptc)(bmb)_1.5 (3) and [Cd₂(bptc) (bmb)] ·3H₂O (4) (H₄bptc = 3,3′,4,4′- biphenyltetracarboxylic acid, ox = oxalate, phen = 1,10-phenanthroline, 2,2′-bipy = 2,2′-bipyridine and bmb = 4,4′-bis((1H-imidazol-1- yl)methyl)biphenyl), were obtained by reactions of the corresponding metal salts with H₄bptc and N-containing auxiliary ligands and their structures were determined by single-crystal X-ray diffraction. The results reveal that 1 has a 0-D structure consisting of discrete ionic entities, while 2 features a 1-D ladder structure. Additionally, there exist ?-? stacking and intermolecular hydrogen-bonding interactions in 1 and 2, respectively, forming 3-D supramolecular structures. In 3-4, undulating 2-D metal-bptc layer structures are formed with two different coordination modes of bptc carboxylate groups, respectively, which are further extended by bmb into 3-D structures. Magnetic properties of 1 and 3 have been studied. The photoluminescence property of 4 has also been investigated. Moreover, nonlinear optical measurements showed that 4 displayed a second-harmonic-generation (SHG) response of 0.7 times of that for urea.