Self-encapsulation of [MII(phen)2(H2O)2]2+ (M = Co, Zn) in one-dimensional nanochannels of [MII(H2O)6(BTC)2]4- (M = Co, Cu, Mn):: A high HQ/CAT ratio catalyst for hydroxylation of phenols

Four novel three-dimensional (3D) microporous supramolecular compounds containing nanosized channels, namely, [Co(phen)(2)(H2O)(2)](2)[CO(H2O)(6)] center dot 2BTC center dot 21.5H(2)O (1), [Co(phen)(2)(H2O)(2)](2)[Cu(H2O)(6)] center dot 2BTC center dot 21.5H(2)O (2), [Co(phen)(2)(H2O)(2)](2)[Mn(H2O)(6)] center dot 2BTC center dot 18H(2)O (3), and [Zn(phen)(2)(H2O)(2)](2)(Mn(H2O)(6)] center dot 2BTC center dot 22.5H(2)O (4), were synthesized from 1,3,5-benzenetricarboxylate (BTC), 1,10-phenanthroline (phen), and the transition-metal salt(s) by self-assembly. Single-crystal X-ray structural analysis showed that the resulting 3D microporous supramolecular frameworks consist of a two-dimensional (2D) hydrogen-bonded host framework of [M-II(H2O)(6)(BTC)(2)](4-) (M = Co for 1, Cu for 2, Mn for 3, 4) with rectangular-shaped cavities containing [M-II(phen)(2)(H2O)(2)](2+) (M = Co for 1-3, Zn for 4) guests. The guest complex is encapsulated in the 2D hydrogen-bonded host framework by hydrogen bonding and aromatic stacking interactions, forming the 3D hydrogen-bonded framework. The catalytic activities of 1, 2, 3, and 4 were studied using hydroxylation of phenols with 30% aqueous H2O2 as a test reaction. The compounds displayed a good phenol conversion ratio and excellent channel selectivity in the hydroxylation reaction, with a maximum hydroquinone (HQ)/catechol (CAT) ratio of 3.9.