Tuning the Dimensionality of Inorganic Connectivity in Barium Coordination Polymers via Biphenyl Carboxylic Acid Ligands

The synthesis and characterization of three barium coordination polymers with one-, two-, and three-dimensional (1-D, 2-D, 3-D) inorganic connectivity based on biphenyl carboxylic acid ligands are described. Employing biphenyl-3,3′,5,5′-tetracarboxylic acid (H4BTTC) as a ligand, [Ba2(BTTC)­(H2O)2]n (1, space group = Pn21a, a = 7.059(1) Å, b = 12.432(2) Å, c = 19.090(3) Å), a coordination polymer with 1-D inorganic connectivity (I1O2), can be synthesized. The coordinated water is strongly coordinated and removed at 270 °C. By using 4,4′-biphenyldicarboxylic acid (H2BPDC), [Ba­(BPDC)]n (2, space group = C2/m, a = 6.955(2) Å, b = 5.947(1) Å, c = 13.852 (4) Å, β = 92.399(4)°) a coordination polymer with 2-D inorganic connectivity (I2O1) is obtained. The connection of the Ba–O bonds in each layer is topologically similar to CaF2. Using biphenyl-3,5,5′-tricarboxylic acid (H3BPTC) as a ligand, [Ba3(BPTC)2(NMF)5⊃2NMF]n (3, space group = I4̅2d, a = 25.984(3) Å, c = 13.999(2) Å) (NMF = N-methyl formamide), a structurally porous coordination polymer with rare 3-D inorganic connectivity (I3O0) can be synthesized. Hence, barium as a metal is extremely malleable with respect to construction of coordination polymers of different inorganic dimensionalities. 2 with I2O1 connectivity demonstrates extraordinary thermal stability and maintains its crystallinity until decomposition at 590 °C. The luminescence behavior of 1, 2, and 3 at room temperature has been investigated and is predominantly intraligand based.