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Supramolecular networks supported by the anion…π linkage of Keggin‐type heteropolyoxotungstates
Author(s) -
Panteleieva Olha S.,
Ponomarova Vira V.,
Shtemenko Alexander V.,
Domasevitch Kostiantyn V.
Publication year - 2020
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s205322962000950x
Subject(s) - synthon , supramolecular chemistry , chemistry , crystallography , stacking , polyoxometalate , ion , hydrogen bond , amide , ionic bonding , crystal structure , stereochemistry , molecule , catalysis , organic chemistry
Anion…π 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…π 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) μ 12 ‐silicato‐tetracosa‐μ 2 ‐oxido‐dodecaoxidododecatungsten trihydrate, (C 8 H 11 N 4 O 2 ) 4 [SiW 12 O 40 ]·3H 2 O, (1), and tris(theobrominium) μ 12 ‐phosphato‐tetracosa‐μ 2 ‐oxido‐dodecaoxidododecatungsten ethanol sesquisolvate, (C 7 H 9 N 4 O 2 ) 3 [PW 12 O 40 ]·1.5C 2 H 5 OH, (2), support the utility of anion…π 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…π…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 [SiW 12 O 40 ] 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…π…anion bridges involving two of the three (HTbr) + cations. The remaining cations complete a fivefold anion…π environment of [PW 12 O 40 ] 3− , acting as terminal groups. This single anion…π 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…π interactions as the structure‐governing factor, which is applicable to the construction of noncovalent linkages involving Keggin‐type oxometalates.