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The Halogen Effect on the Magnetic Behaviour of Dimethylformamide Solvates in [Fe(halide-salEen)2]BPh4
Publication . Marques, Rafaela T.; Martins, Frederico F.; Bekiş, Deniz F.; Vicente, Ana I.; Ferreira, Liliana P.; Gomes, Clara S. B.; Barroso, Sónia; Kumar, Varun; Garcia, Yann; Bandeira, Nuno A. G.; Calhorda, Maria José; Martinho, Paulo N.; LAQV@REQUIMTE; UCIBIO - Applied Molecular Biosciences Unit; DQ - Departamento de Química; MDPI - Multidisciplinary Digital Publishing Institute
Complexes [Fe(X-salEen)2]BPh4·DMF, with X = Br (1), Cl (2), and F (3), were crystallised from N,N′-dimethylformamide with the aim of understanding the role of a high boiling point N,N′-dimethylformamide solvate in the spin crossover phenomenon. The counter ion was chosen for only being able to participate in weak intermolecular interactions. The compounds were structurally characterised by single crystal X-ray diffraction. Complex 1 crystallised in the orthorhombic space group P212121, and complexes 2 and 3 in the monoclinic space group P21/n. Even at room temperature, low spin was the predominant form, although complex 2 exhibited the largest proportion of the high-spin species according to both the magnetisation measurements and the Mössbauer spectra. Density Functional Theory calculations were performed both on the periodic solids and on molecular models for complexes 1–3 and the iodide analogue 4. While all approaches reproduced the experimental structures very well, the energy balance between the high-spin and low-spin forms was harder to reproduce, though some calculations pointed to the easier spin crossover of complex 2, as observed. Periodic calculations with the functional PBE led to very similar ΔEHS-LS values for all complexes but showed a preference for the low-spin form. However, the single-point calculations with B3LYP* showed, for the model without solvate, that the Cl complex should undergo spin crossover more easily. The molecular calculations also reflected this fact, which was more clearly defined when the cation–anion–solvate model was used. In the other models there was not much difference between the Cl, Br, and I complexes.
Mechanistic insights into the electrochemical reduction of CO2 to CO on Ni(salphen) complexes
Publication . Realista, S.; Costa, Paulo J.; Maia, Luísa; Calhorda, Maria José; Martinho, Paulo N.; LAQV@REQUIMTE; DQ - Departamento de Química; RSC - Royal Society of Chemistry
Cyclic voltammetry and bulk electrolysis showed that [Ni(ii)(salphen)] [1], [Ni(ii)(tBu-salphen)] [2], and a binuclear Ni(ii) compound combining salphen and tBu-salphen [3] react with CO2 to yield a metal-carbonyl species that is stable under an oxygen free atmosphere. Upon exposure to air, a stoichiometric amount of CO is released (detected by gas chromatography) and protonation regenerates the initial complex. To shed light on the mechanism of CO2 reduction and O2-dependent CO release by [1], UV-vis, EPR and SEC-IR spectroscopy studies complemented with DFT calculations were performed. It is proposed that the mono reduced [Ni(i)(salphen)]−, 2[1]−, formed a CO2 complex, 2[1(CO2)]−, which was then further reduced to 3[1(CO2)]2−. After addition of two protons, the coordinated CO2 was reduced to CO and released, regenerating 1[1]. Alternatively, 2[1(CO2)]− is protonated and then reduced to the same intermediate as before, continuing the same way. In the second cycle, the CO released competed with CO2 and coordinated to 2[1]− much more strongly, thereby deactivating the system. The new 2[1(CO)]− was reduced to 3[1(CO)]2− which was identified by comparison of experimental spectroscopic (UV-vis, EPR, SEC-IR) data with DFT calculated parameters.
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Fundação para a Ciência e a Tecnologia
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CEEC IND 2017
Número da atribuição
CEECIND/00509/2017/CP1387/CT0029