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

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]H_0.5BDC·H_1.5BDC·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 H_0.5BDC^1.5-, H_1.5BDC^0.5-, 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 BDC^2- 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.