Soft synthesis of a metal-organic framework based on a tribarium building block

Abstract

Reaction of MCO3 (M = Ba or Ca) with benzene-1,3,5-tricarboxylic acid (H(3)btc) in aqueous medium at room temperature affords in good yields the metal-organic framework material [Ba-3(btc)(2)(H2O)(8)].2H(2)O (1) or the layer compound [Ca-3(btc)(2)(H2O)(12)] (2). The structure of (1) is a three-dimensional polymer based on a tribarium building unit. In the trinuclear building block, the central Ba(II) situated on an inversion centre exhibits ten coordination, while the symmetry equivalent terminal Ba(II) ions are eight coordinated. The mu(6)-heptadentate bridging binding mode of the unique btc ligand in (1) results in a 3-D structure with two water molecules situated in the pores. Compound (2) exhibits a two-dimensional structure, unlike the compositionally similar d-block compounds [M-3(btc)(2)(H2O)(12)] (M = Co, Ni, Zn) which are one-dimensional. A comparative study of several compounds containing the {M-3(btc)(2)} unit is described.