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 (H₃btc) in aqueous medium at room temperature affords in good yields the metal-organic framework material [Ba₃(btc)₂(H₂O)₈]·2H₂O (<b style="mso-bidi-font-weight:normal">1</b>) or the layer compound [Ca₃(btc)₂(H₂O)₁₂] (<b style="mso-bidi-font-weight:normal">2</b>). The structure of (<b style="mso-bidi-font-weight:normal">1</b>) 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 μ₆-heptadentate bridging binding mode of the unique btc ligand in (<b style="mso-bidi-font-weight: normal">1</b>) results in a 3-D structure with two water molecules situated in the pores. Compound (<b style="mso-bidi-font-weight:normal">2</b>) exhibits a two-dimensional structure, unlike the compositionally similar <i style="mso-bidi-font-style:normal">d</i>-block compounds [M₃(btc)₂(H₂O)₁₂] (M = Co, Ni, Zn) which are one-dimensional. A comparative study of several compounds containing the {M₃(btc)₂} unit is described.