A thorough characterization of the Ru-Hbpp (in,in-{[Ru(II)(trpy)(H(2)O)](2)(mu-bpp)}(3+) (trpy is 2,2':6',2''-terpyridine, bpp is bis(2-pyridyl)-3,5-pyrazolate)) water oxidation catalyst has been carried out employing structural (single crystal X-ray), spectroscopic (UV-vis and NMR), kinetic, and electrochemical (cyclic voltammetry) analyses. The latter reveals the existence of five different oxidation states generated by sequential oxidation of an initial II,II state to an ultimate, formal IV,IV oxidation state. Each of these oxidation states has been characterized by UV-vis spectroscopy, and their relative stabilities are reported. The electron transfer kinetics for individual one-electron oxidation steps have been measured by means of stopped flow techniques at temperatures ranging from 10 to 40 degrees C and associated second-order rate constants and activation parameters (DeltaH() and DeltaS()) have been determined. Room-temperature rate constants for substitution of aqua ligands by MeCN as a function of oxidation state have been determined using UV-vis spectroscopy. Complete kinetic analysis has been carried out for the addition of 4 equiv of oxidant (Ce(IV)) to the initial Ru-Hbpp catalyst in its II,II oxidation state. Subsequent to reaching the formal oxidation state IV,IV, an intermediate species is formed prior to oxygen evolution. Intermediate formation and oxygen evolution are both much slower than the preceding ET processes, and both are first order with regard to the catalyst; rate constants and activation parameters are reported for these steps. Theoretical modeling at density functional and multireference second-order perturbation theory levels provides a microscopic mechanism for key steps in intermediate formation and oxygen evolution that are consistent with experimental kinetic data and also oxygen labeling experiments, monitored via mass spectrometry (MS), that unambiguously establish that oxygen-oxygen bond formation proceeds intramolecularly. Finally, the Ru-Hbpp complex has also been studied under catalytic conditions as a function of time by means of manometric measurements and MS, and potential deactivation pathways are discussed.

The complexes [Cu2(dpt)2Cl2]X2 (dpt = dipropylenetriamine; X = Cl, 1; X2 = (Cl)(BPh4), 2) have been prepared and their magnetic properties studied. The crystal structure of complex 1 has been solved. The compound belongs to the C2/c space group with Z = 4, a = 17.201(2) Å, b = 10.873(2) Å, c = 11.835(2) Å, and β = 99.720(10)°. The geometry about each copper approximates that of a distorted square pyramid. The three N-atoms of the dpt ligand and one of the Cl bridging ligands form the base of the pyramid while the other chloro bridging ligand occupies the axial site. The two pyramids share a base-to-apex edge with the basal planes being perpendicular, an arrangement which had not been previously observed for this type of dimers. The chloro counterions are responsible for interdimer interactions through hydrogen bonding forming chains of dimers throughout the lattice. Magnetic susceptibility data show a ferromagnetic coupling between the two Cu(II) centers (J = 42.94 cm-1 for 1 and J = 13.89 cm-1 for 2). Dimer−dimer interaction and ZFS have been considered with the J ‘ parameter (1, J ‘ = −3.92 cm-1; 2, J ‘ = −2.9 cm-1). Extended Hückel calculations on complex 1 clearly reveal that the intradimer magnetic interaction only takes place through the basal chloro bridging ligand (with a CuCl(1)Cu angle of 91.4°) which in turn is consistent with the observed ferromagnetic coupling.

We have prepared a new family of ruthenium complexes containing the bpea ligand (where bpea stands for N,N-bis(2-pyridyl)ethylamine), with general formula [Ru(bpea)(bpy)(X)](n+) (2, X = Cl(-); 3, X = H(2)O; 4, X = OH(-)), and the trisaqua complex [Ru(bpea)(H2O)(3)](2+), 6. The complexes have been characterized through elemental analyses, UV-vis and (1)H NMR spectroscopy, and electrochemical studies. For complex 3, the X-ray diffraction structure has also been solved. The compound belongs to the monoclinic P2(1)/m space group, with Z = 2, a = 7.9298(6) A, b = 18.0226(19) A, c = 10.6911(8) A, and beta = 107.549(8) degrees. The Ru metal center has a distorted octahedral geometry, with the O atom of the aquo ligand placed in a trans position with regard to the aliphatic N atom of the bpea ligand so that the molecule possesses a symmetry plane. NMR spectra show that the complex maintains its structure in aqueous solution, and that the corresponding chloro complex also has a similar structural arrangement. The pH dependence of the redox potential for the complex [Ru(bpea)(bpy)(H2O)](PF(6))(2) is reported, as well as the ability of the corresponding oxo complex to catalyze the oxidation of benzylic alcohol to benzaldehyde in both chemical and electrochemical manners.