Syntheses, structures and characteristics of four alkaline-earth metal-organic frameworks (MOFs) based on benzene-1,2,4,5-tetracarboxylicacid and its derivative ligand

Two new pillar-layered Ba(II)-based 3D frameworks and two new Ca(II)-based 3D supramolecular frameworks, [Ba2(dbtec)(H2O)2]n (1), [Ca2(dbtec)(H2O)8]n (2), {[Ba2(H2btec)·H2O]·0.5H2O}n (3) and [Ca(H2btec)·H2O]n (4) (H4dbtec = 3,6-dibromobenzene-1,2,4,5-tetracarboxylic acid; H4btec = benzene-1,2,4,5-tetracarboxylic acid), have been synthesized under similar reaction conditions and stoichiometry. Single crystal X-ray diffraction study reveals axial-orientation Br···π supramolecular interactions exist in the crystal structure of 1, which keeps an 3D binodal network with the (32.412.510.62.72)(32.46.56.6)2 topology. Whereas in 2, intramolecular and intermolecular H-bonding interactions with the ligated water molecules promote the formation of 3D supramolecular frameworks network. For 3, a new 3D 3-nodal network occurs in the structure and some rare coordination modes for the H4btec are observed. There is a 2D double layer with the thickness of 7.60 Å in 4. In addition, besides the high thermal stability, the FTIR spectra, PXRD patterns and the photoluminescent of these compounds are also discussed.