Crystal Structures, Photoluminescence, and Magnetism of Two Novel Transition-Metal Complex Cocrystals with Three-Dimensional H-Bonding Organic Framework or Alternating Noncovalent Anionic and Cationic Layers

Abstract

Cocrystallization may alter material physicochemical properties; thus, the strategy of forming a cocrystal is generally used to improve the material performance for practical applications. In this study, two transition-metal complex cocrystals [Zn(bpy)3]H0.5BDC·H1.5BDC·0.5bpy·3H2O (1) and [Cu2(BDC)(bpy)4]BDC·bpy·2H2O (2) have been achieved using a hydrothermal reaction, where bpy and H2BDC represent 2,2-bipyridine and benzene-1,3-dicarboxylic acid, respectively. Cocrystals were characterized by microanalysis, infrared spectroscopy, and UV-visible spectroscopy. Cocrystal 1 contains five components and crystallizes in a monoclinic space group P21/n. The H0.5BDC1.5-, H1.5BDC0.5-, and H2O molecules construct three-dimensional H-bonding organic framework; the [Zn(bpy)3]2+ coordination cations and uncoordinated bpy molecules reside in channels, where two coordinated bpy ligands in [Zn(bpy)3]2+ and one uncoordinated bpy adopt sandwich-type alignment via π···πstacking interactions. Cocrystal 2 with four components crystallizes in a triclinic space group P-1 to form alternating layers; the binuclear [Cu2(bpy)4(BDC)]2+ cations and uncoordinated bpy molecules build the cationic layers, and the BDC2- species with disordered lattice water molecules form the anionic layers. Cocrystal 1 shows intense photoluminescence at an ambient condition with a quantum yield of 14.96% and decay time of 0.48 ns, attributed to the π∗ → πelectron transition within phenyl/pyridyl rings, and 2 exhibits magnetic behavior of an almost isolated spin system with rather weak antiferromagnetic coupling in the [Cu2(bpy)4(BDC)]2+ cation.