A twofold interpenetrated three-dimensional barium(II) metal–organic framework constructed from 2,2′-[terephthaloylbis(azanediyl)]diacetate: synthesis, structure, dihydrogen bonding and spectroscopic properties

A new twofold interpenetrated 3D metal-organic framework (MOF), namely, poly[[μ-aqua-diaqua{μ₄-2,2'-[terephthaloylbis(azanediyl)]diacetato}barium(II)] dihydrate], {[Ba(C₁₂H₁₀N₂O₆)(H₂O)₃]·2H₂O}_n, (I), has been assembled through a combination of the reaction of 2,2'-[terephthaloylbis(azanediyl)]diacetic acid (TPBA, H₂L) with barium hydroxide and crystallization at low temperature. In the crystal structure of (I), the nine-coordinated Ba^II ions are bridged by two μ₂-aqua ligands and two carboxylate μ₂-O atoms to form a 1D loop-like Ba-O chain, which, together with the other two coordinated water molecules and μ₂-carboxylate groups, produces a rod-like secondary building unit (SBU). The resultant 1D polynuclear SBUs are further extended into a 3D MOF via the terephthalamide moiety of the ligand as a spacer. Two intramolecular dihydrogen bonds (DHBs) between the imine H atoms and the arene H atoms contribute to maintaining the 3D structure. In the crystal, two independent MOFs interpenetrate each other, thereby producing a twofold interpenetrated 3D architecture with a 4-connected PtS-X topology. Intermolecular hydrogen bonding and π-π interactions contribute to the stability of the twofold interpenetrated 3D architecture. The noncovalent interactions in the coordination polymer (CP) were further investigated by Hirshfeld surface analysis and the results show that the prominent interactions are H...O (39.6%) and H...H (34.4%), as well as Ba...O (9.8%), contacts. The 3D CP (I) exhibits a fluorescence emission with a quantum yield of 0.134.