title: Anion binding in the C3v-symmetric cavity of a protonated tripodal amine receptor: potentiometric and single crystal X-ray studies.
abstract: Tris(2-aminoethyl)amine (tren) based pentafluorophenyl-substituted tripodal L, tris[[(2,3,4,5,6-pentafluorobenzyl)amino]ethyl]amine receptor is synthesized in good yield and characterized by single crystal X-ray diffraction analysis. Detailed structural aspects of binding of different anionic guests toward L in its triprotonated form are examined thoroughly. Crystallographic results show binding of fluoride in the C(3v)-symmetric cavity of [H(3)L](3+) where spherical anion fluoride is in tricoordinated geometry via (N-H)(+)···F interaction in the complex [H(3)L(F)]·[F](2)·2H(2)O, (3). In the case of complexes [H(3)L(OTs)]·[OTs](2), (4) and [H(3)L(OTs)]·[NO(3)]·[OTs], (5), tetrahedral p-toluenesulphonate ion is engulfed in the cavity of [H(3)L](3+) via (N-H)(+)···O interactions. Interestingly, complex [(H(3)L)(2)(SiF(6))]·[BF(4)](4)·CH(3)OH·H(2)O, (6) shows encapsulation of octahedral hexafluorosilicate in the dimeric capsular assembly of two [H(3)L](3+) units, via a number of (N-H)(+)···F interactions. The kinetic parameters of L upon binding with different anions are evaluated using a potentiometric study in solution state. The potentiometric titration experiments in a polar protic methanol/water (1:1 v/v) binary solvent system show high affinity of the receptor toward more basic fluoride and acetate anions, with a lesser affinity for other inorganic anions (e.g., chloride, bromide, nitrate, sulfate, dihydrogenphosphate, and p-toluenesulphonate).
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata 700 032, India.
authors.forename: Purnandhu
authors.initials: P
authors.lastname: Bose
authors.forename: I
authors.initials: I
authors.lastname: Ravikumar
authors.forename: Pradyut
authors.initials: P
authors.lastname: Ghosh
mesh_terms: D000588:Amines / Q000737:chemistry* / Q000378:metabolism; D000838:Anions / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D004784:Environmental Monitoring / Q000379:methods*; D005029:Ethylenediamines / Q000737:chemistry; D005459:Fluorides / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D011199:Potentiometry; D011522:Protons; D012824:Silicic Acid / Q000737:chemistry; D012996:Solutions
chemical_list: D000588:Amines; D000838:Anions; D005029:Ethylenediamines; D008024:Ligands; D011522:Protons; D012996:Solutions; D012824:Silicic Acid; C004832:hexafluorosilicate; C099539:tris(2-aminoethyl)amine; D005459:Fluorides