Anions can be recognized by either pos. charged or neutral artificial receptors. Pos. charges within a receptor's cavity can be provided by transition metal ions (e.g. CuII) which offer a binding site to one donor atom of the anion. Dicopper(II) bis(tren) cryptates are ideal receptors for ambidentate anions capable of bridging the two CuII centers. The size of the ellipsoidal cavity and consequent inclusion selectivity can be modulated by varying the length of the spacers linking the two tren subunits. Examples of the selective recognition of halides, polyat. anions and arom. and aliph. dicarboxylates are discussed. Among neutral receptors attention is centered on systems contg. the urea subunit. Urea behaves as a bifurcate H-bond donor towards oxoanions. On the basis of equil. studies in aprotic solvents (mainly MeCN and DMSO) it is shown that the energy of the hydrogen bonding interaction and the selectivity are solely related to the acidic tendencies of the receptor and to the basic properties of the anion. In particular, the H-bond interaction can be conveniently viewed as an advanced (and "frozen") proton transfer from the -N-H fragment of urea and the oxygen atom of the anion. Addn. of excess fluoride may induce deprotonation of the -NH fragment due to the unique stability of the [HF2]- species which forms.
Some guidelines for the design of anion receptors
AMENDOLA, VALERIA;BONIZZONI, MARCO;FABBRIZZI, LUIGI;LICCHELLI, MAURIZIO;TAGLIETTI, ANGELO MARIA
2006-01-01
Abstract
Anions can be recognized by either pos. charged or neutral artificial receptors. Pos. charges within a receptor's cavity can be provided by transition metal ions (e.g. CuII) which offer a binding site to one donor atom of the anion. Dicopper(II) bis(tren) cryptates are ideal receptors for ambidentate anions capable of bridging the two CuII centers. The size of the ellipsoidal cavity and consequent inclusion selectivity can be modulated by varying the length of the spacers linking the two tren subunits. Examples of the selective recognition of halides, polyat. anions and arom. and aliph. dicarboxylates are discussed. Among neutral receptors attention is centered on systems contg. the urea subunit. Urea behaves as a bifurcate H-bond donor towards oxoanions. On the basis of equil. studies in aprotic solvents (mainly MeCN and DMSO) it is shown that the energy of the hydrogen bonding interaction and the selectivity are solely related to the acidic tendencies of the receptor and to the basic properties of the anion. In particular, the H-bond interaction can be conveniently viewed as an advanced (and "frozen") proton transfer from the -N-H fragment of urea and the oxygen atom of the anion. Addn. of excess fluoride may induce deprotonation of the -NH fragment due to the unique stability of the [HF2]- species which forms.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.