Microporous Materials Constructed from the Interpenetrated Coordination Networks. Structures and Methane Adsorption Properties

Abstract

Five new coordination compounds with 4,4‘-azopyridine (azpy), [Mn(azpy)(NO3)2(H2O)2]·2EtOH (1·2EtOH), [Co2(azpy)3(NO3)4]·Me2CO·3H2O (2·Me2CO·3H2O), [Co(azpy)2(NCS)2]·0.5EtOH (3·0.5EtOH), [Cd(azpy)2(NO3)2]·(azpy) (4·azpy), and [Cd2(azpy)3(NO3)4]·2Me2CO (5·2Me2CO), have been synthesized and structurally characterized. The reaction of Mn(NO3)2·6H2O with azpy in ethanol/acetone affords 1·2EtOH, whose network consists of one-dimensional chains of [Mn(azpy)(H2O)2]n. The chains are associated by hydrogen bonding to provide a logcabin-type three-dimensional structure, which creates about 8 × 8 Å of channels, filled with ethanol molecules. The treatment of Co(NO3)2·6H2O and Co(NCS)2·4H2O with azpy produces 2·Me2CO·3H2O and 3·0.5EtOH, respectively, which have a brick-wall and a rhombus-type two-dimensional networks. The reaction of Cd(NO3)2·4H2O with azpy affords 4·azpy from the ethanol/H2O media, while the reaction in the ethanol/acetone media provides 5·2Me2CO. 4·azpy and 5·2Me2CO form a square-grid- and a herringbone-type two-dimensional networks, respectively. The two-dimensional sheets of 4·azpy stack without interpenetration, leading to large size of channels, which are filled with free azpy molecules. The two-dimensional networks of 2·Me2CO·3H2O, 3·0.5EtOH, and 5·2Me2CO are quadruply, doubly, and triply interpenetrated, respectively. Despite the interpenetration, their networks create the microporous channels filled with guest solvent molecules. The dried compounds 2, 3, and 5 adsorb methane between 1 and 36 atm at 25 °C, in which 3 and 5 exhibit Langmuir-type isotherms. The inherent micropore volumes for 3 and 5 are 0.685 and 3.30 mmol/g, respectively. XRPD measurements under reduced pressure at 100 °C reveal that the channel structure of 3 is the most stable in these compounds; the observed XRPD pattern is in good agreement with that of the simulated pattern of the single-crystal model. Compounds 2 and 5 also retain the porous structures, however, their pore structures are distorted upon loss of guest included molecules.