New porous coordination polymers based on expanded pyridyl-dicarboxylate ligands and a paddle-wheel cluster

Solvothermal reactions of Cu(NO3)(2) and 4,4'-([3,4'-bipyridine]-2',6'-diyl)dibenzoic acid (H(2)L1), 3,3'-([4,4'-bipyridine]-2,6-diyl)dibenzoic acid (H(2)L2), or 4,4'-([4,4'-bipyridine]-2,6-diyl)dibenzoic acid (H(2)L3) yielded three new metal-carboxylate frameworks (MCF-28, MCF-29 and MCF-30) with a common formula [Cu-2(L)(2)] (H2L = pyridyldicarboxylic acid). X-ray crystallography showed that MCF-28, MCF-29, and MCF-30 are three-dimensional (3,6)-connected rtl, eea and pyr networks, respectively, based on 3-connected tripodal ligands and 6-connected Cu-2(RCOO)(4)(py)(2) units (RCOO and py denote carboxylate and pyridyl groups, respectively). Thermogravimetry, powder X-ray diffraction, and gas adsorption measurements indicated that the three compounds became shrunk and amorphous structures after guest removal. Interestingly, single-crystal X-ray diffraction showed that MCF-28 exhibited drastic temperature-induced framework breathing.