Cd(II) Coordination Architectures with Mixed Ligands of 3-(2-Pyridyl)pyrazole and Pendant Carboxylate Ligands Bearing Different Aromatic Skeletons: Syntheses, Crystal Structures, and Emission Properties

To investigate the influences of the geometries of pendant carboxylate ligands and some intramolecular/intermolecular
weak interactions on the structures of transition metal complexes, five new Cd(II) complexes, Cd2(HL)2(L)4 (1), Cd2(HL1)2(L)4
(2), {[Cd2(HL1)(L)4(H2O)2](H2O)}∞ (3), [Cd(L1)(L)]∞ (4), and Cd2(L1)2(HL1)2(L4)2 (5) (HL1 = 3-(2-pyridyl)pyrazole, HL2 =
benzoic acid, HL3 = naphthalene-carboxylic acid, HL4 = 9-anthracene-carboxylic acid, and HL5 = isonicotinic acid), have been
synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction analyses. 1
and 2 have a similar dinuclear structure, which is further assembled to form a one-dimensional (1D) chain by π···π stacking and/or
hydrogen-bonding interactions. 3 possesses a 1D chain structure that is further interlinked via intermolecular π···π stacking, resulting
in a two-dimensional (2D) network, while 4 has a 2D (4,4) network with channel dimension of 9.34 × 9.34 Å2 and further assembles
into a three-dimensional (3D) network by interlayer π···π stacking. 5 also possesses a dinuclear structure and then forms a 2D
network through intermolecular π···π stacking and C−H···O hydrogen-bonding interactions. Interestingly, 3 and 5 were obtained
simultaneously in the same reaction system. The structural differences of those complexes show the influences of the geometries of
the pendant carboxylate ligands. This result also shows that intramolecular/intermolecular weak interactions play important roles in
the formation of coordination architectures, especially in the aspect of linking multinuclear discrete subunits or low-dimensional
entities into high-dimensional supramolecular frameworks. In addition, complexes 1, 2, and 4 exhibit blue emission in the solid state
at room temperature.