Molecular Approach to Alkali-Metal Encapsulation by a Prussian Blue Analogue FeII/CoIII Cube in Aqueous Solution: A Kineticomechanistic Exchange Study

Enhanced catalytic activity of solubilised species obtained by counter-cation exchange of K{CoII 1.5[FeII(CN)6]} for water oxidation

A cyano-bridged coordination polymer, K{CoII 1.5[FeII(CN)6]} {(K)Co-Fe}, reported as a highly active heterogeneous catalyst for water oxidation was solubilised by a conventional counter-cation exchange of K+ with Me4N+ ions to provide the homogeneous catalyst of (Me4N){CoII 1.5[FeII(CN)6]} {(Me4N)Co-Fe}. (Me4N)Co-Fe exhibited enhanced catalytic activity for photocatalytic water oxidation using [Ru(2,2'-bipyridine)3]2+ and S2O8 2- as a photosensitiser and a sacrificial electron acceptor, respectively, in terms of the initial reaction rate (1.26 μmol min-1), which is about twice that of (K)Co-Fe (0.61 μmol min-1). Powder X-ray diffraction, pair distribution function and electrospray ionization mass spectrometry measurements of (Me4N)Co-Fe manifested that small heptanuclear clusters of {Co4[Fe(CN)6]3}4- formed by depolymerisation are catalytically active species in solution.

No Switching Cooperativity between Coordinated Azo Ligands on Complexes Having {MII(phosphane-κ2P)}2+ (M = Pd, Pt) Scaffolds

A series of square-planar palladium and platinum compounds with cis-blocking phosphanes and terminal azobenzene ligands [M(dppp)(azo)2](OTf)2 (azo = CN(C6H4)-N═N-(C6H4)CN (iso-cyano), CN(C6H4)-N═N-(C6H5) (iso-Ph)) and [{M2(tpbz)}(azo)4](OTf)4 (azo = CN(C6H4)-N═N-(C6H5) (iso-Ph)) have been synthesized and fully characterized. Similarly to the uncoordinated ligands, the new coordination compounds have shown to be photochemically active with respect to their trans-to-cis isomerization process. Their cis-to-trans back spontaneous reaction have been studied as a function of solvent, temperature and pressure and the corresponding activation parameters determined in order to investigate the mechanism of these transformations. The results obtained are indicative of the operation of a rotational mechanism with no cooperativity between the azo ligands attached to the same metal. Density functional theory calculations have been carried out in order to estimate the relative energies of the different photoisomers for the theoretical interpretation of the experimental data.

Iron complexes of bridging azo ligands in aqueous solution: changes in the thermal switching mechanism on coordination and oxidation state of metal centres

Three azobenzenes CN(C₆H₄)-NN-(C₅H₄N) (py-iso), CN(C₆H₄)-NN-(C₆H₄)CN (cyano-iso) and CN(C₆H₄)-NN-(C₆H₄)NC (iso-iso) with good coordinating groups (pyridine, phenylcyano or phenylisocyano) at the ends of the diazenyl unit have been synthesized and fully characterised. These compounds have been used as ligands in the synthesis of water-soluble metallic species by coordination to {Fe^II(CN)₅^3-} units, either in one or two of the anchoring groups of the derivatives. Both the azo derivatives and their complexes are photochemically active with respect to their trans-to-cis isomerisation process. Their cis-to-trans reverse thermal reaction has been thoroughly studied as a function of the donor groups, solvent, temperature and pressure, in order to gain insight into the rotation or inversion mechanisms involved in the process. A comparison of the isomerisation mechanism between the iron complexes and the corresponding free ligands revealed an interesting fine tuning of the process on coordination of the {Fe^II(CN)₅^3-} moieties, which may even produce, in some cases, non-photoswitchable species containing typically photoactive units.