Probing the electronic delocalization in a cyclic pyrazine ruthenium cluster hexamer

[Ru(3)O(CH(3)COO)(6)(pz)(CO)](6) is a cyclic hexamer species encompassing six triangular ruthenium cluster centers bridged by pyrazine ligands. The electronic communication among the cluster units strongly depends on their oxidation states, and has been successfully probed by means of cyclic voltammetry and UV-vis spectroelectrochemistry. (C) 2010 Elsevier B.V. All rights reserved.FAPESPCNP

Contrasting photoelectrochemical behaviour of two isomeric supramolecular dyes based on meso-tetra(pyridyl)porphyrin incorporating four (mu(3)-oxo)- triruthenium(III) clusters

A saddle shaped tetracluster porphyrin species containing four [Ru(3)O(OAc)(6)(py)(2)](+) clusters coordinated to the N-pyridyl atoms of 5,10,15,20-tetra(3-pyridyl)porphyrin, H(2)(3-TCPyP), has been investigated in comparison with the planar tetra(4-pyridyl) porphyrin analogue H(2)(4-TCPyP). The steric effects from the bulky peripheral complexes play a critical role in the H(2)(3-TCPyP) species, determining a non-planar configuration around the porphyrin centre and precluding any significant pi-electronic coupling, in contrast with the less hindered H(2)(4-TCPyP) species. Both systems exhibit a photoelectrochemical response in the presence of nanocrystalline TiO(2) films, involving the porphyrin excitation around 450 nm. However, only in the H(2)(4-TCPyP) case do the cluster moieties also contribute to the photoinduced electron injection process at 670 nm, reflecting the relevance of the electronic coupling between the porphyrin centre and the peripheral complexes

Effects of a strong pi-accepting ancillary ligand on the water oxidation activity of weakly coupled binuclear ruthenium catalysts

Significant differences were found in the proton-coupled redox chemistry and catalytic behavior of the binuclear [{Ru(H2O)(bpz)}(2)(tpy(2)ph)](PF6)(4) complex [bpz = 2,2-bipyrazine; tpy(2)ph = 1,3-bis(4-2,2:6,2-terpyridin-4-yl)benzene] as compared with the structurally analogous derivative with 2,2-bipyridine (bpy) instead of bpz. The differences were assigned to the stronger -accepting character of bpz relative to bpy as the ancillary ligand. The expectation of a positive shift for the Ru-centered redox potentials was confirmed for the lower oxidation state species, but that trend was reversed in the formation of the high-valence catalytic active species as shown by a negative shift of 0.14 V for the potential of the [Ru-IV/V?O] process. Moreover, DFT calculations indicated a significant decrease of about 15% on the spin density and oxyl character of the [Ru-V?O](3+) fragment. The significantly lower k(cat)(O-2) for the bpz system was attributed to these combined electronic effects48930093017CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP310779/2016-2; 465452/2014-02013/22127-3; 2014/50906-9; 2018/03576-

Synthesis of rhenacyclopentadienes and eta(2):eta(2)-diyne complexes from a labile dirhenium carbonyl and pi-conjugated 1,7-octadiynes: Structural and photophysical characterization

A series of dirhenium carbonyl compounds containing pi-conjugated diyne ligands and symmetrical 2,5-bis(aryl)rhenacyclopentadienes has been synthesized by reaction of [Re-2(CO)(8)(CH3CN)(2)] and 1,8bis(aryl)-1,7-octadiyne derivatives [aryl = 2-thienyl (a), 2-pyridyl (b), 2-quinolyl (c) and 9-phenanthrenyl (d)]. We found that diyne ligands undergo coordination to the labile rhenium dinuclear in bridging or chelate modes, however, the formation of metallacyclopentadiene complexes was favorably observed. All products were fully characterized by IR, NMR, ESI-MS, UV-Vis and fluorescence spectroscopy. Single-crystal structures of three new 2,5-bis(aryl) rhenacyclopentadienes [Re-2(CO)(7)(mu-eta(1):eta(1):eta(2):eta(2)-C16H14S2)] (1a), [Re-2(CO)(6)(CH3CN)(mu-eta(1):eta(1):eta(2):eta(2)-C16H14S2)] (2a) and [Re-2(CO)(6)(CH3CN)(mu-eta(1):eta(1):eta(2):eta(2)-C26H20N2)] (2c) are described. DFT calculations were used to evaluate the proposed geometries for the two eta(2):eta(2)-diyne complexes [Re-2(CO)(6)(CH3CN)(2)(mu-eta(2):eta(2)-C18H16N2)] (3b), [Re-2(CO)(6)(CH3CN)(2)(eta(2):eta(2)-C26H20N2)] (4c), and the rhenacyclopentadiene [Re-2(CO)(6)(CH3CN)(mu-eta(1):eta(1):eta(2):eta(C36H26)-C-2)] (2d). The photophysical properties of all complexes were assessed, in that they exhibited fluorescence between 408 and 599 nm with quantum yields of Phi(f) = 0.02-0.09. An exceptional fluorescence quantum yield of Phi(f) = 0.64 was found for [Re-2(CO)(6)(CH3CN)(2)(eta(2):eta(2)-C26H20N2)] (4c), which has been attributed to its rigid chelate structure. This work represents the second example of fluorescent 2,5-bis(aryl)rhenaclyclopendadienes reported up to date8813444CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP310779/2016-22013/22127-2Instituto Venezolano de Investigaciones Cientificas [1082]; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo - FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2013/22127-2]; INOMAT - INCT for Science, Technology and Innovation in Functional Complex Materials [2014/50906-9]; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico - CNPqNational Council for Scientific and Technological Development (CNPq) [310779/2016-2

Analysis of solvent-accessible voids and proton-coupled electron transfer of 2,6-bis(1H-imidazol-2-yl)pyridine and its hydrochloride

The crystal structures of the solid form of solvated 2,6-bis(1H-imidazol-2-yl)pyridine (H(2)dimpy) trihydrate, C11H9N5 center dot 3H(2)O center dot[+solvent], I, and its hydrate hydrochloride salt 2-[6-(1H-imidazol-2-yl)pyridin-2-yl]-1H-imidazol-3-ium chloride trihydrate, C11H10N5+center dot Cl-center dot 3H(2)O, II, are reported and analysed in detail, along with potentiometric and spectrophotometric titrations for evaluation of the acid-base equilibria and proton-coupled electron-transfer reactions. Compound I crystallizes in the high-symmetry trigonal space group P3(2)21 with an atypical formation of solvent-accessible voids, as a consequence of the 3(2) screw axis in the crystallographic c-axis direction, which are probably occupied by uncharacterized disordered solvent molecules. Additionally, the trihydrated chloride salt crystallizes in the conventional monoclinic space group P2(1)/c without the formation of solvent-accessible voids. The acid-base equilibria of H(2)dimpy were studied by potentiometric and spectrophotometric titrations, and the results suggest the formation of H(3)dimpy(+) (pK(a1) = 5.40) and H(4)dimpy(2+) (pK(a2) = 3.98), with the electrochemical behaviour of these species showing two consecutive irreversible proton-coupled electron-transfer reactions. Density functional theory (DFT) calculations corroborate the interpretation of the experimental results and support the assignment of the electrochemical behaviour751013591371CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP142440/2015-9; 142386/2016-2; 120469/2018-9não tem2013/22127-2; 2014/50906-9; 2017/23960-

Synthesis, crystallographic studies, molecular modeling and in vitro biological studies of silver(I) complexes with aminoadamantane ligands

Silver(I) complexes with amantadine (atd) and memantine (mtn) were synthesized and characterized. Elemental, thermogravimetric and mass spectrometric analyses indicated a 1:2 metal/ligand ratio, with the molecular composition AgC20H34N2 center dot NO3 for Ag-atd and AgC24H42N2 center dot NO3 center dot H2O for Ag-mtn. The crystal structures of the silver(I) complexes were determined by single crystal X-ray diffractometric studies and show the coordination of amantadine and memantine to the Ag(I) ion by the nitrogen atom of the NH2 group. The spectral analysis by infrared and H-1, C-13 and {N-15, H-1} nuclear magnetic resonance (NMR) spectroscopies confirmed the coordination sites of the ligands to the silver ions. Computational studies revealed modes of vibration and bond lengths similar to those found experimentally. The in vitro antibacterial activity assays showed that amantadine is not active over the tested strains while memantine showed a low activity against Staphylococcus aureus and Pseudomonas aeruginosa. On the other hand, the complexes had a pronounced antibacterial activity over the same strains with minimum inhibitory concentration (MIC) values in the micromolar range. Biophysical assays based on fluorescence spectroscopy indicated that the silver(I) complexes interact weakly with bovine serum albumin, while agarose gel electrophoresis and competitive binding experiments revealed that the compounds interact with DNA by non-covalent interactions.173CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP407012/2018-4; 164658/20181Sem informação2013/22127-2; 2014/50906-9; 2015/20882-3; 2017/25995-6; 2018/12062-4; 2018/12590-