Structure and Characterisation of a Novel 3-D Ba(II)–MOF Based on the {Ba₄O₇} Core

A novel three-dimensional barium metal–organic framework [Ba3(btc)2(H2O)4]·0.5H2O (H3btc = 1,3,5-benzenetricarbox-ylic acid) has been synthesised under hydrothermal conditions, and characterised by single-crystal X-ray structure determination, thermogravimetric analysis, X-ray powder diffraction, IR, and photoluminescence studies. The volume of the tunnel formed by the two-dimensional layers is 341.9 Å3 per unit cell using PLATON based on the crystal structures, comprising 14.3% of the crystal volume 2387.2 Å3. The solid-state fluorescence measurement of this compound at room temperature reveals a fluorescent emission band at 454.5 nm under the excitation of 337 nm, assigned to a charge-transfer transition.