Synthesis, structures, and fluorescent properties of four new calcium(II) metal–organic frameworks

Abstract

Four calcium(II) metal–organic frameworks, [Ca(BD)DMF]·DMF·H2O (1), [Ca2(EDDA)(H2O)2(DMA)]·3H2O (2), [Ca(TTD)(Diox)]·2H2O (3), and [Ca2(DBBD)(H2O)2(DMF)]·2DMF·H2O (4) were designed and constructed by using four different carboxylate ligands, i.e., [2,2′-bipyridine]-5,5′-dicarboxylic acid (H2BD), (E)-5,5′-(diazene-1,2-diyl) diisophthalic acid (H4EDDA), 2′,3′,5′,6′-tetramethyl-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid (H2TTD), and (E)-4′,4‴-(diazene-1,2-diyl)bis(([1,1′-biphenyl]-3,5-dicarboxylic acid)) (H4DBBD), respectively (DMF = N,N-Dimethylformamide; DMA = Dimethylacetamide; Diox = 1,4-Dioxane). The differences in terms of lengths (6.95–17.68 Å), steric hindrance and configurations among the four ligands lead to four different structures of the final calcium complexes. In addition, the solid-state fluorescence of all the complexes have been studied at room temperature, showing shifted maximum emission bands or enhanced fluorescent properties compared to that of free organic ligands.