Hierarchical Assembly of Extended Coordination Networks Constructed by Novel Metallacalix[4]arenes Building Blocks

Five interesting metal-organic nanostructures and networks, [Ni-4(HL)(4)(bpy)(py)(H2O)(5)](2)center dot 0.5H(2)O (1), [Co-4(HL)(4)-(bpy)(py)(H2O)(5)](2)center dot 0.5H(2)O (2), [Ni-4(HL)(4)(H2O)(7)](n)center dot nH(2)O (3), [Ni-4(HL)(4)(bpy)(2)(H2O)(4)](n) (4), and [Cd-4(HL)(4)(H2O)](n) (5), were synthesized hydrothermally [H3L = 2-(pyridin-2-yl)-1H-imidazole-4,5-dicarboxylate acid, py = pyridine, and bpy = 4,4'-bipyridine]. Intriguingly, all compounds consist of novel metallacalix[4]arene building blocks M-4(HL)(4), where doubly deprotonated HL in the same bichelating fashion of mu-kN,N':kO,N '' displays a strong coordination orientation by cooperation of the 4,5-imidazoledicarboxylate and 2-pyridyl groups. Very interestingly, the symmetry of M-4(HL)(4) and the linkage styles between metal nodes and HL in M-4(HL)(4) are sensitive to the reaction conditions, and the resulting structural motifs vary with secondary ligands and metal nodes. In 1 and 2, two C-1-symmetric M-4(HL)(4) units are bpy-bridged into dimeric chiral nanomolecules with two different cavities. As deprotonated with NaOH, the combination of Ni-II and HL forms a pseudo-S-4- or S-4-symmetric M-4(HL)(4), which further assembles into 1D chiral crystals 3 or rare 3D crystals 4 of bpy-bridged 5-fold interpenetrating diamondoid architecture with metallacalix[4]arene building blocks as novel 4-connecting nodes, and the combination of Cd-II and HL forms an 8-connected C-2-symmetric M-4(HL)(4) that fabricates the alpha-Po net of 5. Notably, those large M-4(HL)(4) units are potentially highly connected building blocks in a hierarchical assembly of metal-organic networks. Magnetic studies disclose antiferromagnetic interactions in M-4(HL)(4) of 1-4. The magnetic data for 1, 3, and 4, all containing isomeric Ni-4(HL)(4) units, are analyzed by an equilateral quadrangle isotropic model combined with the molecular-field approximation with J= -4.00(2), -3.39(2), and -2.72(3) cm(-1), respectively, presenting a stronger comparison between the structure and magnetism. The emission of 5 is odd, which perhaps is relative to the bichelating fashion of ligand HL and a rare coordination geometry of Cd-II. Moreover, the thermal stability and gas sorption properties of these compounds were measured.