Browsing by Author "Castro, Baltazar de"
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- Electrochemical and structural studies of nickel (II) Schiff base complexes derived from salicylaldehyde. Structural effects of bridge substituents on the stabilisation of the +3 oxidation statePublication . Santos, Isabel C.; Vilas-Boas, Miguel; Piedade, M.F.M.; Freire, Cristina; Duarte, M.T.; Castro, Baltazar deThe oxidative chemistry of three Ni(II) complexes with Schiff base ligands derived from salicylaldehyde and diamines with different steric demands, N,N9-2-methylpropane-2,3-diyl-bis(salicylideneiminate)nickel(II) (1), N,N9-1,2-cyclohexyl-1,2-dyil-bis(salicylideneiminate)- nickel(II) (2) and N,N9-2,3-dimethylbutane-2,3-diyl-bis(salicylideneiminate)nickel(II) (3), was studied by cyclic voltammetry and chronoamperometry in N,N9-dimethylformamide and (CH3)2SO.
- Electrochemical characterization of a novel salen type modified electrodePublication . Vilas-Boas, Miguel; Freire, Cristina; Castro, Baltazar de; Hillman, A. RobertThe nickel(II) complex with H2saltMe, a N2O2 Schiff base ligand derived from salicylaldehyde, was oxidatively electropolymerized on Pt electrodes in CH3CN/0.1 mol dm-3 tetraethylammonium perchlorate (TEAP) to generate polymer films that exhibit reversible oxidative electrochemical behavior in a wide potential range (0.0-1.3 V), high conductivity, and stability/durability.
- New Insigths into the structure and properties of electroactive polymer filmes derived from Ni(salen)polymerPublication . Vilas-Boas, Miguel; Freire, Cristina; Castro, Baltazar de; Christensen, Paul A.; Hillman, A. RobertOxidative electrochemical polymerization of (N,N'-ethylenebis(salicylideneaminato)) nickel(II), [Ni(salen)], in acetonitrile/TEAP was reinvestigated. The polymers were characterized by in situ FTIR and UV-visible spectroscopies in order to explore film structure and to clarify the electronic states as a function of the electrochemically controlled applied redox potential; oxidized species involved in polymerization and oxidative switching of the polymer were also assessed by ex situ EPR experiments.
- Spectroelectrochemical characterisation of a poly[Ni(saltMe)] modified electrodePublication . Vilas-Boas, Miguel; Freire, Cristina; Castro, Baltazar de; Christensen, Paul A.; Hillman, A. RobertElectrogenerated polymers based on the nickel(II) compIex 2,3-dimetbyl- N,N -bis(salicylidene )butane-2,3- diaminatoniekel(II), poly[Ni(saltMe)], were characterized by in situ FTIR and UV/Vis spectroscopy and ex-situ EPR spectroscopy in order to gain insights into film structure, electronic states and charge conduction. The role of the nickel ions during film oxidation was probed by using EPR to study naturally abundant Ni and 61Ni-enriehed polymers.
- Spectroelectrochemical characterisation of copper salen-based polymer modified electrodePublication . Martins, Madga; Vilas-Boas, Miguel; Castro, Baltazar de; Hillman, A. Robert; Freire, CristinaElectrogenerated polymers based on copper salen-type complexes were characterised electrochemically and by in situ UV–vis and ex situ EPR spectroscopy. The films, poly[Cu(salen)] and poly[Cu(saltMe)], exhibit reversible oxidative electrochemical behaviour in a wide potential range (0.0–1.5 V). Different regimes for charge transport behaviour are accessed by manipulation of film thickness and experimental time scale: thin films (surface concentration, Γ < ca. 80 nmol cm−2) show thin-layer/surface behaviour in the scan rate range used (0.020–2.0 V s−1), whereas thicker polymers (Γ > ca. 90 nmol cm−2) exhibit a changeover from thin-layer to diffusion control regime at a critical scan rate that depends on polymer and film thickness: 0.15–0.20 V s−1 for poly[Cu(salen)], 90 < Γ < 130 nmol cm−2 and 0.20–0.30 V s−1 for poly[Cu(saltMe)], 170 < Γ < 230 nmol cm−2. UV–vis and EPR spectroscopies have allowed the characterisation of electronic states in the reduced and oxidised forms. The role of the copper atom during film oxidation was probed by combining UV–vis data with EPR on copolymers of the copper and nickel complexes. Data from both techniques are consistent and indicate that polymerisation and redox switching are associated with ligand-based processes. EPR of Ni-doped Cu polymers provided evidence for the non-involvement of the metal centre in polymer oxidation; like the analogous nickel polymers, copper polymers behave like delocalised π-system (‘conducting’) rather than discrete site (‘redox’) polymers.