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Various Coordination Modes of Sulfate by Cyanuric Acid Platform‐Based First‐ and Second‐Generation Urea Receptors
Author(s) -
Dutta Ranjan,
Ghosh Pradyut
Publication year - 2013
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201201559
Subject(s) - chemistry , cyanuric acid , hydrogen bond , urea , crystallography , crystal structure , coordination complex , receptor , tris , stereochemistry , molecule , metal , organic chemistry , biochemistry , melamine
Cyanuric acid platform‐based first‐generation p ‐nitrophenyl‐ ( L1 ), p ‐cyanophenyl‐ ( L2 ) and pentafluorophenyl‐ ( L3 ) substituted tris‐ureas and second‐generation p ‐nitrophenyl‐functionalized hexakis‐urea receptor ( L4 ) have been synthesized. Detailed solid‐state structural studies on the binding of sulfate to L1 , L2 and L4 have been examined thoroughly by single‐crystal X‐ray diffraction and compared with the binding modes of SO 4 2– to the pentafluorophenyl analogue of the tris‐urea receptor L3 to evaluate the various modes of SO 4 2– binding in this new generation of cyanuric acid platform‐based anion receptors. The crystallographic results show a 1:1 binding pattern between L1 and SO 4 2– through six N–H ··· O interactions with the three urea moieties of the receptor and one C–H ··· O interaction with one of the tetrabutylammonium counter cations in complex 1 . Thus, this complex shows an uncommon example of a seven‐coordinate SO 4 2– , which is structurally similar to that of the sulfate‐binding protein (SBP). Interestingly, L2 shows a 2:1 host/guest binding pattern with SO 4 2– that generates a dimeric capsular assembly with dimensions of approximately 10.398 Å in complex 2 . In this case, each of the oxygen atoms of SO 4 2– forms a trifurcated hydrogen bond with the urea NH groups and thus a total of 12 N–H ··· O hydrogen‐bonding interactions can be observed for SO 4 2– . In contrast, L3 shows 11 hydrogen‐bonding interactions with the encapsulated SO 4 2– in complex 3 assisted by two n Bu 4 N + counter cations through six N–H ··· O and five C–H ··· O interactions. In the case of the SO 4 2– complex of L4 , complex 4 shows 1:1 encapsulation of SO 4 2– in its inner cavity with 10 N–H ··· O interactions. A binding study of SO 4 2– in solution was performed with L4 in dmso by isothermal titration calorimetry (ITC). This study also showed a 1:1 binding pattern of SO 4 2– with an association constant of approximately 5.11 (log K ). Furthermore, the binding of SO 4 2– in the gas phase was examined by ESI mass spectrometry.