1,721,058 research outputs found
Sensors and switches from supramolecular chemistry
No full textEfficient sensors for metal ions can be made by assembling an appropriate receptor with a fluorescent fragment. The occurrence of the receptor/cation interaction is signalled through a sharp change of the fluorescence emission. The situation is esp. favorable in the case of transition metal ions, which are typically redox active and provide an electron release to the excited fluorophore (or uptake therefrom), causing fluorescence quenching. Thus, the supramol. design of fluorescent sensors should consider a ligating subunit able to promote the redox activity of the envisaged metal ion. An identical approach can be used for the synthesis of mol. redox switches, i.e. systems in which the distinctive property of a given subunit (e.g. fluorescence) is controlled by an adjacent control subunit, sensitive to the variation of the redox potential. Couples involving metal centers can be conveniently used to switch on/off the fluorescence of the proximate fluorophore through the variation of the redox potential
Aqueous copper(III) and nickel(III) tetraaza macrocyclic complexes
No full text[Cu(III)L]+ and [Ni(III)L(H2O)2]+ (L = I) were prepd. from the Cu(II) and Ni(II) analogs by, chem. (K2S2O8) or anodic (Pt gauze electrode, ∼0.8 V vs. SCE) oxidn. The aq. complexes were unstable, decompg. during a few h at room temp. The oxidn. state was detd. by voltammetric and ESR studies. The stabilities of the complexes are discussed relative to those of the tetraamine macrocycle-complexed analogs
Formation of nickel(III) complexes with n-dentate amine macrocycles (n = 4, 5, 6). ESR and electrochemical studies
No full textLow-spin Ni(III) complexes with the complete series of 12- to 16-membered cyclic tetraamines, with the novel series of 15- to 17-membered cyclic pentaamines, and with the 18-membered cyclic hexamine were prepd. in MeCN by anodic and/or chem. oxidn. of the corresponding Ni(II) complexes. Spin state and stereochem. of the Ni(III) complexes were deduced from the ESR spectra of the frozen solns. (77 K). The half-wave potential values, E1/2, assocd. to the 2+/3+ quasi-reversible redox change in the considered complexes were obtained through voltammetry expts. at a Pt electrode. E1/2 Values show that for tetraamine complexes the attainment of the Ni(III) state is easiest with the 14-membered macrocycle and is dramatically affected by contraction or expansion of the ligand cavity. This ring-size-dependent redox selectivity is drastically reduced in the complexes with pentadentate macrocycles. The synthesis of this novel series of cyclic pentaamines is described in detail
The deprotonated amido vs. the amino group in the stabilization of coordinated trivalent copper and nickel cations. An electrochemical evaluation.
No full textThe M2+/M3+ redox change in the Cu and Ni complexes with 2 types of 14-membered tetraaza macrocycles contg. (1) 4 amine N atoms (cyclam) and (2) 2 amine N atoms and 2 deprotonated amido groups was studied by voltammetric techniques. Replacement of 2 amino groups by 2 deprotonated amido groups involves a dramatic decrease of the CuIII/CuII redox potential (of ∼0.8 V), but does not affect greatly the potential of the NiIII/NiII redox change. This behavior is related to the enhanced donor properties of the type dioxocyclam and benzyldioxocyclam macrocycles and to the more or less favorable CFSE (crystal field stabilization energy) contribution from which the M2+/M3+ change profits
Oxidation and reduction of copper(II) complexes with saturated polyaza macrocycles of varying size and denticity
No full textThe oxidn. and redn. of Cu(II) complexes with the tetra- and pentadentate amine macrocycles I (n-n2 = 0, 1) and II (n-n2 = 0; n = 1, n1 ≠ n2 = 1, 0) in CH3CN were studied by electrochem. methods. The redox changes Cu(III) → Cu(II) and Cu(II) → Cu(I) were detected through cyclic voltammetry at high potential scan rates. The half-wave potentials are discussed in terms of the properties and structural features of the macrocyclic ligands
Oxidation and reduction behavior of copper(II) complexes with open-chain analogs of tetraaza macrocycles
No full textElectrochem. methods were used to study the redox behavior of the Cu(II) complexes of H2N(CH2)nNH(CH2)mNH(CH2)nNH2 (n, m = 2, 3) in MeCN. Cu(III) complexes persisted in soln. only on the time-scale of the cyclic voltammetry expt., whereas fairly stable Cu(I) complexes were obtained with both the shortest- and longest-chain ligands studied. Electrode potentials for both the Cu(III) → Cu(II) and Cu(II) → Cu(I) redox reactions were compared with those reported for the corresponding complexes with macrocyclic tetraamines
A prototype for the chemosensing ofBa2+ based on self-assemblingfluorescence enhancement
No full textBarium ion can be revealed at the micromolar concentration level by the blue-green fluorescence which arises upon the self-assembling
process involving the metal ion and a bis-15-crown-5-naphthalene-diimide derivative
1,4,8,11-Tetraazacyclotetradecane-5,7-dione (dioxocyclam) copper(II) and aqueous copper(III) complexes
No full textDioxocyclam (H2L = 1,4,8,11-tetraazacyclotetradecane-5,7-dione), prepd. from di-Et malonate and 1,9-diamino-3,7-diazanonane, was reacted with Cu(OAc)2.H2O in aq. EtOH to give CuL. CuL was electrochem. or chem. (by K2S2O8) oxidized to [CuL]+
Tetra-aza macrocycles containing a pyridine ring. The oxidation and reduction behavior of their nickel(II) complexes
No full textThe Ni complexes [NiL](ClO4)2, where L = I (R = R1 = H, Me; R = Me, R1 = H) and II, were prepd. by reaction of NiCl2 with diacetyl- or diformylpyridine and the appropriate triamine under mild conditions (low concns. and low temp.) in aq. EtOH to study the effects of modification of the ligand framework on their redox properties. Insertion of 2 Me groups in the C-backbone in I (R = Me, R1 = H) makes oxidn. to Ni(III) easier, partly as a result of their inductive effect which makes electron abstraction from Ni(II) less difficult because of the increase of electron d. on the adjacent N atoms. However, the advantage of a Me group on the central amine N atom is more than compensated for by the steric effects introduced and this makes oxidn. to Ni(III) of Ni in the complex with I (R = R1 = H) is much easier than that of the other 3 complexes; redn. is particularly sensitive to methylation of the amine N atom and to enlargement of the ring in the Ni-II complex
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