Cu(II)-Based Molecular Hexagons Forming Honeycomb-like Networks Exhibit High Electrical Conductivity

Four new Cu(II)-based hexagonal complexes with the metallomacrocycle formulae [Cu₆(5-nip)₆(3-py)₆(H₂O)₁₂] (1), [Cu₆(5-nip)₆(3-Clpy)₆(H₂O)₁₂] (2), [Cu₆(5-nip)₆(3-Brpy)₆(H₂O)₁₂] (3), and [Cu₆(5-nip)₆(3-Ipy)₆(H₂O)₁₂] (4) have been synthesized using 5-nitroisophthalic acid (H₂5-nip) and pyridine (py)/3-halopyridine (3-Xpy; X = Cl, Br, and I) ligands. The structural features and supramolecular interactions of compounds 1-4 have been investigated using the single-crystal X-ray diffraction (SCXRD) technique. Interestingly, the hexagonal complexes undergo hydrogen bonding and π···π stacking interactions to form fascinating two-dimensional (2D) honeycomb-like structures. The synthesized complexes exhibit high electrical conductivity, arising from charge transport through space via π···π contacts. However, complexes containing 3-Brpy (3) and 3-Ipy (4) exhibit photosensitivity due to the presence of halogens with a larger size and lower ionization energy. The conductivity results are also in accordance with the theoretical prediction calculated by density functional theory (DFT) study.