title: Anion-π interactions: generality, binding strength, and structure.
abstract: Anion-π interactions have been systematically studied using tetraoxacalix[2]arene[2]triazine 1, an electron-deficient and cavity self-tunable macrocyclic host, as an electron-neutral molecular probe. As revealed by electrospray ionization mass spectrometry (ESI-MS), fluorescence titration and X-ray crystallography, tetraoxacalix[2]arene[2]triazine has been found to form 1:1 complexes with four typical polyatomic anions of different geometries and shapes in the gaseous phase, in solution, and in the solid state. The association constants for the formation of anion-π complexes in acetonitrile are in the range of 239 to 16950 M(-1), following the order of 1·NO(3)(-) > 1·BF(4)(-) > 1·PF(6)(-) > 1·SCN(-). X-ray molecular structures of the complexes showed that two opposing triazine rings of tetraoxacalix[2]arene[2]triazine act as a pair of tweezers to interact with the included anions through cooperative anion-π and lone-pair electron-π interactions. The generality of anion-π interactions and diverse anion-π interaction motifs can provide a new dimension in the study of molecular recognition and self-assembly. Moreover, this study potentiates the effect of anion-π interactions in chemical and biological systems, especially those involving anion and electron-deficient aromatic species.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China. dxwang@iccas.ac.cn
authors.forename: De-Xian
authors.initials: DX
authors.lastname: Wang
authors.forename: Mei-Xiang
authors.initials: MX
authors.lastname: Wang
mesh_terms: D000838:Anions / Q000737:chemistry; D047250:Calixarenes / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D021241:Spectrometry, Mass, Electrospray Ionization; D014227:Triazines / Q000737:chemistry*
chemical_list: D000838:Anions; D056831:Coordination Complexes; D014227:Triazines; C532848:tetraoxacalix(2)arene(2)triazine; D047250:Calixarenes