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The rare organocopper(II) complex [Cu(Metren)(CHCN)] (Metren = tris(2-(dimethylamino)ethyl)amine) has emerged as an important model of potential byproducts in copper-catalyzed atom transfer radical polymerization. This complex has been generated by controlled potential electrolysis of [Cu(Metren)(NCMe)] in the presence of BrCHCN. Time-resolved UV-vis and continuous wave and pulse electron paramagnetic resonance (EPR) spectra identified [Cu(Metren)Br] as an intermediate. Hyperfine sublevel correlation and electron nuclear double resonance spectroscopy of samples at different timepoints reveal signals that are assigned to a C-bound cyanomethylate ligand, with distinct N and H hyperfine coupling constants in comparison with the corresponding N-bound acetonitrile and bromido complexes. The experimental EPR data are supported by density functional theory calculations to understand how the geometries of the species involved produce distinct spectroscopic signatures, and a clear picture of how this unusual organocopper(II) complex is formed has emerged.

The preparation of a series of alkali-metal inclusion complexes of the molecular cube [{CoIII(Me3-tacn)}4{FeII(CN)6}4]4- (Me3-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), a mixed-valent Prussian Blue analogue bearing bridging cyanido ligands, has been achieved by following a redox-triggered self-assembly process. The molecular cubes are extremely robust and soluble in aqueous media ranging from 5 M [H+] to 2 M [OH-]. All the complexes have been characterized by the standard mass spectometry, UV-vis, inductively coupled plasma, multinuclear NMR spectroscopy, and electrochemistry. Furthermore, X-ray diffraction analysis of the sodium and lithium salts has also been achieved, and the inclusion of moieties of the form {M-OH2}+ (M = Li, Na) is confirmed. These inclusion complexes in aqueous solution are rather inert to cation exchange and are characterized by a significant decrease in acidity of the confined water molecule due to hydrogen bonding inside the cubic cage. Exchange of the encapsulated cationic {M-OH2}+ or M+ units by other alkali metals has also been studied from a kineticomechanistic perspective at different concentrations, temperatures, ionic strengths, and pressures. In all cases, the thermal and pressure activation parameters obtained agree with a process that is dominated by differences in hydration of the cations entering and exiting the cage, although the size of the portal enabling the exchange also plays a determinant role, thus not allowing the large Cs+ cation to enter. All the exchange substitutions studied follow a thermodynamic sequence that relates with the size and polarizing capability of the different alkali cations; even so, the process can be reversed, allowing the entry of {Li-OH2}+ units upon adsorption of the cube on an anion exchange resin and subsequent washing with a Li+ solution., Financial support by Grant PID2019-107006GB-C21 funded by MCIN/AEI/10.13039/501100011033 is acknowledged.

Air oxidation of methanolic solutions of biologically active tridentate pyridyl thiosemicarbazone (TSC) complexes of the general formula [FeII(TSC)2] has been studied at varying dioxygen concentrations, temperatures, and pressures. The data collected indicate that the activation entropy of the reaction increases linearly with the redox potential of the complexes in a more definite way than the activation enthalpy. However, a very distinct behavior is observed for the values of the activation volumes, which do not follow the expected entropy-volume parallel trend for all of the systems studied. The involvement of important interactions between the terminal NH groups of the coordinated TSC ligand and molecular dioxygen has been found to be significant by measurements carried out at varying hydrostatic pressures. Kinetic experiments run on analogous N-deuterated complexes confirm the importance of these noncovalent interactions, which are weaker for the less acidic ND groups. These interactions show the existence of an ordering/expansion process upon going from the reactants to the transition state, whenever an interaction between the polar terminal amino groups and dioxygen can be established.

Novel types of water-soluble anionic cubic cages, K4[{CoIII(Me3-Tacn)}4{FeII(CN)6}4] and Na4[{CoIII(Me3-Tacn)}4{FeII(CN)6}4] (Me3-Tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), were prepared by means of a mechanistically designed self-assembly process between [Co(Me3-Tacn)Cl3] and A4[FeII(CN)6] (M = Na or K), consisting of a rate-limiting outer-sphere redox step, followed by a fast substitution/inner-sphere redox reaction sequence. These compounds show remarkable stability in aqueous solution at different pH ranges, displaying neat protonation processes and reversible oxidation with peroxodisulfate to its neutral {FeIII4CoIII4} form. Furthermore, the cages behave as a robust and water-soluble molecular Prussian Blue analogue capable of encapsulating {Na-OH2}+ pairs and K+ cations in aqueous solution, with the cubic structure of the complex being preserved. Substitution of the {Na-OH2}+ pairs by K+ is easily accomplished, and the electrochemical properties of the sodium and potassium salts of the new cages have been found to be dramatically dependent on the encapsulated units.

The kinetics of oxidation of different biologically-active FeII bis-thiosemicarbazone complexes in water has been monitored at varying dioxygen concentration, temperature, pressure, and pH. The oxidation reactions observed can be resolved as a single-step process, producing the expected ferric complex, with rates increasing with decreasing pH. From the pH-dependence of the observed rate constants, a rate law with two terms can be derived, one of them being independent of the acid concentration and the other term showing a saturation behaviour with respect to [H+]. These results indicate the existence of two parallel pathways for oxidation: the acid-independent pathway is only operative for the complexes with ligands bearing terminal, non-coordinated, unsubstituted amines, whereas the term with a [H+]-limiting kinetic behaviour is observed for all the complexes and indicates that the reacting species has to be protonated prior to the oxidation step. From the data collected, the rate law and the thermal and pressure activation parameters have been used to interpret the operating reaction mechanisms. Given the fact that the empirical trends rule out an outer-sphere oxidation process, DFT calculations have been carried out to explain the results and suggest the likely formation, under steady-state very low concentration conditions, of FeIII superoxo and hydroperoxo intermediates.