The synthesis and characterization of the new 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo-[19.5.5.05,8.014,17]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Δ5,8, Δ14,17-diene (L) are reported. L incorporates two squaramide functions in a over structured chain connecting two opposite nitrogen atoms of the Me2[12]aneN4 polyaza-macrocyclic base to obtain a cage topology. The basicity and binding properties of L towards Cu(II), were determined by means of potentiometric measurements in aqueous solution (298.1 ± 0.1 K, I = 0.15 mol dm-3). L behaves as a diprotic base under the experimental conditions used. L forms only mono-nuclear Cu(II)-complexes in which the squaramide moieties are not involved in the stabilization of the metal ion which is stabilized by the amine functions of the polyaza-base inside the tridimensional cavity. The [CuL]2+ species was tested as host for the series of halide anions. UV-Vis spectrophotometric experiments permitted to determine the addition constants of halides to the Cu(II) complexed species. The [CuL]2+ species binds the anions F-, Cl-, and Br- by forming the [CuLX]+ species, but not the biggest I-. A trend of selectivity as a function of the H-bond capability and the dimensions of the anion were retrieved; the maximum value was found for the addition of F- (logK = 4.8). This selectivity is due to the presence of the overstructured chain containing the squaramide groups up to the Me2[12]aneN4 macrocyclic base. The squaramide groups, by furnishing H-bond contacts, permit the [CuL]2+ species to selectively bind these anions via formation of a H-bond network with F- and Cl-. The crystal structures of the [CuLF]+ and [CuLCl]+ cations support the results obtained in aqueous solution.
A New Macrocyclic Cryptand with Squaramide Moieties: An Overstructured Cu(II) Complex That Selectively Binds Halides: Synthesis, Acid/Base- and Ligational Behavior, and Crystal Structures
AMBROSI, GIANLUCA;FORMICA, MAURO;FUSI, VIERI;GIORGI, LUCA;MICHELONI, MAURO SERGIO;PONTELLINI, ROBERTO;
2007
Abstract
The synthesis and characterization of the new 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo-[19.5.5.05,8.014,17]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Δ5,8, Δ14,17-diene (L) are reported. L incorporates two squaramide functions in a over structured chain connecting two opposite nitrogen atoms of the Me2[12]aneN4 polyaza-macrocyclic base to obtain a cage topology. The basicity and binding properties of L towards Cu(II), were determined by means of potentiometric measurements in aqueous solution (298.1 ± 0.1 K, I = 0.15 mol dm-3). L behaves as a diprotic base under the experimental conditions used. L forms only mono-nuclear Cu(II)-complexes in which the squaramide moieties are not involved in the stabilization of the metal ion which is stabilized by the amine functions of the polyaza-base inside the tridimensional cavity. The [CuL]2+ species was tested as host for the series of halide anions. UV-Vis spectrophotometric experiments permitted to determine the addition constants of halides to the Cu(II) complexed species. The [CuL]2+ species binds the anions F-, Cl-, and Br- by forming the [CuLX]+ species, but not the biggest I-. A trend of selectivity as a function of the H-bond capability and the dimensions of the anion were retrieved; the maximum value was found for the addition of F- (logK = 4.8). This selectivity is due to the presence of the overstructured chain containing the squaramide groups up to the Me2[12]aneN4 macrocyclic base. The squaramide groups, by furnishing H-bond contacts, permit the [CuL]2+ species to selectively bind these anions via formation of a H-bond network with F- and Cl-. The crystal structures of the [CuLF]+ and [CuLCl]+ cations support the results obtained in aqueous solution.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
