Syntheses, Structures, and Photoluminescence Properties of Metal(II) Halide Complexes with Pyridine-Containing Flexible Tripodal Ligands

Seven coordination compounds, [Zn(L3)Cl2]·MeOH·H2O (1), [Mn(L3)2Cl2]·0.5EtOH·0.5H2O (2), [Cu3(L2)2Cl6]·2DMF
(3), [Cu3(L2)2Br6]·4MeOH (4), [Hg2(L4)Cl4] (5), [Hg2(L4)Br4] (6), and [Hg3(L4)2I6]·H2O (7), were synthesized by the
reactions of ligands 1,3,5-tris(3-pyridylmethoxyl)benzene (L3), 1,3,5-tris(2-pyridylmethoxyl)benzene (L2), and 1,3,5-tris(4-pyridylmethoxyl)benzene (L4) with the corresponding metal halides. All the structures were established by
single-crystal X-ray diffraction analysis. In complexes 1 and 2, L3 acts as a bidentate ligand using two of three
pyridyl arms to link two metal atoms to result in two different 1D chain structures. In complexes 3 and 4, each L2
serves as tridentate ligand and connects three Cu(II) atoms to form a 2D network structure. Complexes 5 and 6
have the same framework structure, and L4 acts as a three-connecting ligand to connect Hg(II) atoms to generate
a 3D 4-fold interpenetrated framework, while the structure of complex 7 is an infinite 1D chain. The results indicate
that the flexible ligands can adopt different conformations and thus can form complexes with varied structures. In
addition, the coordination geometry of the metal atom and the species of the halide were found to have great
impact on the structure of the complexes. The photoluminescence properties of the complexes were investigated,
and the Zn(II), Mn(II) and Hg(II) complexes showed blue emissions in solid state at room temperature.