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

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journal contribution
posted on 2010-03-15, 00:00 authored by Xia Li, Benlai Wu, Ruiying Wang, Hongyun Zhang, Caoyuan Niu, Yunyin Niu, Hongwei Hou
Five interesting metal−organic nanostructures and networks, [Ni4(HL)4(bpy)(py)(H2O)5]2·0.5H2O (1), [Co4(HL)4(bpy)(py)(H2O)5]2·0.5H2O (2), [Ni4(HL)4(H2O)7]n·nH2O (3), [Ni4(HL)4(bpy)2(H2O)4]n (4), and [Cd4(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 M4(HL)4, where doubly deprotonated HL in the same bichelating fashion of μ-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 M4(HL)4 and the linkage styles between metal nodes and HL in M4(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 C1-symmetric M4(HL)4 units are bpy-bridged into dimeric chiral nanomolecules with two different cavities. As deprotonated with NaOH, the combination of NiII and HL forms a pseudo-S4- or S4-symmetric M4(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 CdII and HL forms an 8-connected C2-symmetric M4(HL)4 that fabricates the α-Po net of 5. Notably, those large M4(HL)4 units are potentially highly connected building blocks in a hierarchical assembly of metal−organic networks. Magnetic studies disclose antiferromagnetic interactions in M4(HL)4 of 14. The magnetic data for 1, 3, and 4, all containing isomeric Ni4(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 CdII. Moreover, the thermal stability and gas sorption properties of these compounds were measured.