Syntheses, Structures, and Properties of Two-Dimensional Alkaline Earth Metal Complexes with Flexible Tripodal Tricarboxylate Ligands

Two new coordination polymers [Ca3(bta)2(H2O)8]·3H2O (1) and Ba3(bta)2(H2O)8 (2) were obtained by
self-assembly of the corresponding metal carbonate with a flexible tripodal ligand, benzene-1,3,5-triacetic acid (H3bta), and their structures were determined by single-crystal X-ray diffraction studies. The results revealed that
complex 1 crystallizes in the triclinic space group P1̄ with a = 8.3045(10) Å, b = 10.4883(10) Å, c = 11.0184(16) Å,
α = 102.703(3)°, β = 100.001(4)°, γ = 108.842(7)°, V = 854.36(18) Å3, and Z = 1; compound 2 is in the monoclinic
space group C2/c with a = 23.4363(8) Å, b = 6.9782(3) Å, c = 21.7150(8) Å, β = 111.4480(10)°, V = 3305.4(2) Å3, and
Z = 4. Complexes 1 and 2 have two-dimensional network structures, and each bta3- ligand coordinates to Ca(II) or
Ba(II) atoms using two of three carboxylate groups adopting different coordination modes:  μ3-η2:η2-bridging and
μ2-η2:η-bridging coordination modes in 1 or μ3-η:η2-bridging and μ3-η2:η1-bridging coordination modes in 2. The
noncoordinated carboxylic group forms hydrogen bonds with an adjacent network to generate a three-dimensional
structure. The luminescence properties of 1 and 2 were investigated and found that the complexes showed
photoluminescence in the solid state at room temperature.