Construction of Ba(II) Coordination Polymers Based on Imidazole-Based Dicarboxylate Ligands: Structural Diversity Tuned by Alcohol Solvents

Four novel three-dimensional (3D) barium–organic coordination polymers formulated as [Ba­(μ5-H2hmIDC)­(μ2-H2O)]n (1), [Ba­(μ3-H3hmIDC)2(μ1-H2O)]n (2), [Ba­(μ5-H2hmIDC)­(μ2-O2)0.5]n (3), and [Ba­(μ3-H3hmIDC)­(μ4-H3hmIDC)]n (4) were synthesized under the solvothermal conditions of 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylic acid (H4hmIDC) with BaCl2·2H2O using a combination of water or dimethyl formamide (DMF) with various alcohol solvents (methanol, ethanol, n-propanol, isopropanol, and n-butanol). Complex 1 is a 3D framework based on two-dimensional secondary building units (SBUs) and μ5-H2hmIDC2– pillars. This complex contains a unique alb network topology with the Schläfli symbol (45·6)2(410·614·84). Complex 2 is a (3,10)-connected framework with binuclear [Ba2(COO)2] SBUs as 10-connected nodes and two types of μ3-H2hmIDC2– ligands as 3-connected nodes. Complex 3 is a 3D framework formed with one-dimensional (1D) SBUs and μ5-H2hmIDC linkers, wherein the unprecedented oxygen molecules are coordinated using a linear-μ-η1:η1-peroxo fashion, showing (5,6)-connected network topology with the Schläfli symbol (46·53·6)­(46·54·65). Complex 4 is a 3D framework based on 1D SBUs with μ3-H3hmIDC and μ4-H3hmIDC as linkers. This complex exhibits a trinodal (3,4,7)-connected 3D framework with the Schläfli symbol (42·6)­(43·63)­(48·611·82). The results revealed that the alcohol solvent plays a subtle yet essential role in the crystallization and construction of Ba­(II)-organic coordination frameworks with diverse 3D structures, although these alcohol molecules do not appear in the frameworks.