The reactions between a tetrahedrally-shaped tecton, tetrakis(4-(iodoethynyl)phenyl)methane, and tetraphenylphosphonium halides readily afford interpenetrated and densely packed diamondoid architectures sustained by C-IX (X = chloride, bromide, iodide) interactions. In all these halogen-bonded networks, the halide anions act as four-connecting nodes, while the tetraphenylphosphonium cations provide essential templating information and structural support.
Three isomeric forms of 1-(pyridylmethyl)-2,2'-biimidazole, A1-A3, have been synthesized and subjected to systematic co-crystallizations with selected hydrogen- and halogen-bond donors in order to explore the impact of electrostatics and geometry on the resulting supramolecular architectures. The solid-state supramolecular behavior of A1-A3 is largely consistent in halogen-bonded co-crystals. Only two types of primary interactions, the N-HN/NH-N homomeric hydrogen-bond interactions responsible for the pairing of biimidazole moieties and the IN(pyridine) halogen bonds responsible for the co-crystal formation and structure extension, are present in these systems. The co-crystallizations with hydrogen-bond donors (carboxylic acids), however, lead to multiple possible structural outcomes because of the presence of the biimidazole-acid N-HO[double bond, length as m-dash]C/NH-O heterosynthon that can compete with biimidazole-biimidazole N-HN/NH-N homosynthon. In addition, the somewhat unpredictable nature of proton transfer makes the hydrogen-bonded co-crystals structurally less consistent than their halogen-bonded counterparts.
Hetero-bifunctional ligands can pave the way for elaborate metallo-supramolecular systems and are also useful for combining metal−ligand bonding with other types of noncovalent interactions. We synthesized two new pyridylacetylacetonate ligands, 3-(4-(pyridin-4-yl)phenyl)pentane-2,4-dione (L1) and 3-(4-(pyridin-4-ylethynyl)phenyl)pentane-2,4-dione (L2), and explored their metal binding ability with selected di-and trivalent transition metal ions. As expected, the acetylacetonate ligation with metal dications remains consistent among four structures,, and [Zn-(L2) 2 (MeOH) 2 ]; the metal is four-coordinate and resides in a square planar environment. Differences in the overall architectures arise basically from the role played by the terminal heterocycle (i.e., the pyridyl group). In [Cu(L1) 2 (MeOH) 2 ] n and [Co(L2) 2 ] n , the heterocyclic end directly binds to the metal (through vacant axial positions), thereby producing coordination networks. In [Cu(L2) 2 (MeOH) 2 ] and [Zn(L2) 2 (MeOH) 2 ], metal-methanol coordination and intermolecular O− H(methanol)•••N(pyridine) hydrogen-bond interactions work in concert to weave those bis-acetylacetonate complexes into ribbon-like supramolecular polymeric arrays. Somewhat surprisingly, the only tris-chelated acetylacetonate complex characterized in this study, [Fe(L2) 3 ], essentially exists as discrete dimeric aggregates.
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