Architecture of Hydrogen-Bonded Three-Dimensional NbO Net Based on Hydrogen Carbonate or Trimesic Acid Using a Hydrophobic, Predesigned, Cubic Cation [Co(H₂O)₆⊂Co₈L₁₂] as a Template

A nanocage complex [Co(H₂O)₆⊂Co₈L₁₂](NO₃)₆·12H₂O (1) (HL = 2-amino-4,6-bis(2-pyridyl)-1,3,5-triazin) has been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction. A [Co(H₂O)₆]²⁺ ion as a guest is included in the central cavity of the cubelike nanocage [Co(H₂O)₆⊂Co₈L₁₂]⁶⁺ cation, assembled by 8 cobalt ions at the corners and 12 bis-bidentate ligands L at the edges, via the formation of 12-fold strong hydrogen bonds between the six coordinated water molecules and the nitrogen atoms of 12 L ligands. When compound 1 cocrystalizes with KHCO₃ and trimesic acid (H₃TMA), complexes [Co(H₂O)₆⊂Co₈L₁₂](HCO₃)₆·24H₂O (2) and [Co(H₂O)₆⊂Co₈L₁₂](H₂TMA)₆·6EtOH·3H₂O (3) are obtained, respectively. In 2, a planar [(HCO₃)₂]²⁻ dimer motif R₂²(8) synthon plus six lattice water molecules constitute a planar supramolecular synthon R₈⁸(20), which acts as a 4-connector, generating a three-dimensional (3D) hydrogen-bonded NbO net with an approximately 20 Å diameter cavity. In 3, the R₄⁴(24) synthon, regarded as a 4-connector, connects each other via the phenyl ring of H₃TMA as a spacer into a NbO net with a cavity of ∼20 Å diameter. The hydrophobic, cubic, nanosize cations [Co(H₂O)₆⊂Co₈L₁₂]⁶⁺ embed in the cavities of NbO nets as templates and play an indispensable role in the formation of 3D hydrogen-bonded networks. The work presented here seems to suggest that the nanosize complex as a template plays a crucial role in the formation and stabilization of supramolecular architecture and crystal engineering.