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N,N',N'',N'''-Tetranaphthylmethylcyclam: a Versatile Sensor for H+, Transition Metal ions and Anions
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A chromogenic penta-aza scorpionand for nickel(II) and copper(II) ions.
No full textThe nickel(II) and copper(II) complexes of a new scorpionand in which the side chain has been functionalized with the powerful
chromophore 4-amino-7-nitro-benzo-2-oxa-1,3-diazole have been prepared. The pendant arm of the new ligand undergoes pHdependent complexation/decomplexation to the metal centre, with simultaneous deprotonation of the aniline nitrogen atom of the pendant arm, thus inducing drastic modifications of the spectral features of the chromophore and a sharp colour change. The pKa values observed for both complexes change according to the metal promoting the deprotonation, being lower for the Ni complex than for the Cu species, because of the different coordination geometries adopted by the two ions
Supramolecular functions related to the redox activity of transition metals
No full textThe combination of the properties of different subunits in a multicomponent system may give rise to a function which is defined supramolecular. The presence of transition metals in one or more subunits may induce inter-component processes related to their redox and electron transfer (eT) properties, which trigger the supramolecular function (SF). The following examples are considered: (I) a receptor for transition metals is covalently linked to a fluorescent fragment; following recognition, a metal-to-fluorophore eT process quenches the fluorescence. SF: fluorosensing. (2) an azacyclam macrocycle, hosting the Ni-II/Ni-III redox couple, is covalently linked to a photoactive fragment: the Ni-III state quenches the neighboring fluorophore through an eT mechanism, the Ni-II state does not. SF: redox switching of a fluorescent signal. (3) a Cull ion is coordinated by two 2,2`-bipyridine molecules, each bearing a cyclam subunit containing a nickel centre; when nickel is in the divalent state, an inorganic anion X- (N-3(-),NCO-, NCS-) is bound to Cu-II on oxidation, X- moves to the Ni-III centre. SF: electrochemically triggered translocation of X- from copper to nickel and vice vers
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