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首页> 外文期刊>Acta crystallographica. Section C, Structural chemistry. >Supramolecular networks supported by the anion center dot center dot center dot pi linkage of Keggin-type heteropolyoxotungstates
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Supramolecular networks supported by the anion center dot center dot center dot pi linkage of Keggin-type heteropolyoxotungstates

机译：Keion Center Dot Center Dot Pi Pi Pi PI PI PI PI PI PI PI PI PI键的超分子网络

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摘要

Anion center dot center dot center dot pi interactions are newly recognized weak supramolecular forces which are relevant to many types of electron-deficient aromatic substrates. Being less competitive with respect to conventional hydrogen bonding, anion center dot center dot center dot pi interactions are only rarely considered as a crystal-structure-defining factor. Their significance dramatically increases for polyoxometalate (POM) species, which offer extended oxide surfaces for maintaining dense aromatic/inorganic stacks. The structures of tetrakis(caffeinium) mu(12)-silicato-tetracosa-mu(2)-oxido-dodecaoxidododecatungsten trihydrate, (C8H11N4O2)(4)[SiW12O40]center dot 3H(2)O, (1), and tris(theobrominium) mu(12)-phosphato-tetracosa-mu(2)-oxido-dodecaoxidododecatungsten ethanol sesquisolvate, (C7H9N4O2)(3)[PW12O40]center dot 1.5C(2)H(5)OH, (2), support the utility of anion center dot center dot center dot pi interactions as a special kind of supramolecular synthon controlling the structures of ionic lattices. Both caffeinium [(HCaf)(+) in (1)] and theobrominium cations [(HTbr)(+) in (2)] reveal double stacking patterns at both axial sides of the aromatic frameworks, leading to the generation of anion center dot center dot center dot pi center dot center dot center dot anion bridges. The latter provide the rare face-to-face linkage of the anions. In (1), every square face of the metal-oxide cuboctahedra accepts the interaction and the above bridges yield flat square nets, i.e. {(HCaf(+))2(-)[SiW12O40](4)-}(n). Two additional cations afford single stacks only and they terminate the connectivity. Salt (2) retains a two-dimensional (2D) motif of square nets, with anion center dot center dot center dot pi center dot center dot center dot anion bridges involving two of the three (HTbr)(+) cations. The remaining cations complete a fivefold anion center dot center dot center dot pi environment of [PW12O40](3-), acting as terminal groups. This single anion center dot center dot center dot pi interaction is influenced by the specific pairing of (HTbr)(+) cations by double amide-to-amide hydrogen bonding. Nevertheless, invariable 2D patterns in (1) and (2) suggest the dominant role of anion center dot center dot center dot pi interactions as the structure-governing factor, which is applicable to the construction of noncovalent linkages involving Keggin-type oxometalates.
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