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 _0.5 BDC·H _1.5 BDC·0.5bpy·3H ₂ O ( 1 ) and [Cu ₂ (BDC)(bpy) ₄ ]BDC·bpy·2H ₂ O ( 2 ) have been achieved using a hydrothermal reaction, where bpy and H ₂ BDC 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 P 2 ₁ / n . The H _0.5 BDC ^1.5- , H _1.5 BDC ^0.5- , and H ₂ O 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···π stacking interactions. Cocrystal 2 with four components crystallizes in a triclinic space group P -1 to form alternating layers; the binuclear [Cu ₂ (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* → π electron transition within phenyl/pyridyl rings, and 2 exhibits magnetic behavior of an almost isolated spin system with rather weak antiferromagnetic coupling in the [Cu ₂ (bpy) ₄ (BDC)] ²⁺ cation.
Competing Interests: The authors declare no competing financial interest.