[Co(tpy)(phen)Cl](PF6)2?0.25CH3CN (where tpy = 2,2?;6?,2?-terpyridine and phen = 1,10-phenanthroline) was prepared from a one pot mixture involving stoichiometric quantities of tpy and phen. The structure of [Co(tpy) (phen)Cl](PF6)2?0.25CH3CN was confirmed by elemental analysis, high resolution mass spectroscopy (HRMS), various spectroscopic analyses, and X-ray crystallography. Density functional theory calculations were also carried out. The crystal structure of [Co(tpy)(phen)Cl](PF6)2?0.25CH3CN, which was grown from acetonitrile, revealed a monoclinic crystal system with a C2/c space group. The cyclic voltammogram which was acquired in acetonitrile revealed reversible CoIII/II, CoII/I, and CoI/0 mixed with ligand-based redox couples at E1/2 = +0.35, ?0.81, and ?1.37 V (vs Ag/AgCl), respectively. In the presence of p-cyanoanillinium tetrafluoroborate with acetonitrile as the solvent, [Co(tpy)(phen)Cl](PF6)2?0.25CH3CN displayed electrocatalytic hydrogen evolution activity at a 830 mV overpotential, as evidenced by a catalytic wave which was observed in the voltammogram, and by the detection of hydrogen in the headspace of the reaction vessel of a controlled potential electrolysis experiment. Photocatalytic hydrogen evolution studies with [Co(tpy)(phen)Cl](PF6)2?0.25CH3CN produced a turnover frequency (TOF) of 3300 mmol H2 mol- 1 CAT min-1 when compared to [Co(dmgH)2(py)Cl] (where dmgH = dimethylglyoximato), which had a TOF of 4500 mmol H2.mol- 1 CAT min-1 under the same conditions. [Co(tpy)(phen)Cl](PF6)2?0.25CH3CN produced a turnover number (TON) of 79 when compared to 141 for [Co (dmgH)2Cl(py)] in DMF in ca 3 h.

Optical and electrochemical properties of the homoleptic cobalt(III/II) complexes mer,mer-[Co(tpy-N-3,N,N)](n+) and mer,mer-[Co(bqp-N-3,N,N)](n+) (n = 3+ or 2+) are presented [tpy = 2,2:6,2-terpyridine; bqp = 2,6-bis(8-quinolinyl)pyridine]. Both [Co(tpy)(2)](3+/2+) and [Co(bqp)(2)](3+/2+) systems have been used to formulate redox-mediator electrolytes for application in dye-sensitized solar-cell (DSSC) devices with the MK-2 dye TiO2 sensitizer. The [Co(tpy)(2)](3+/2+)-based electrolyte shows a slightly higher percentage power-conversion efficiency ( = 4.47%) in a DSSC device relative to the [Co(bqp)(2)](3+/2+)-based electrolyte ( = 3.73%). Although the [Co(bqp)(2)](3+/2+) electrolyte shows a slightly higher open-circuit potential (V-OC = 0.79 V), it suffers from a reduced short-circuit current (J(SC) = 6.21 mAcm(-2)) relative to that of the [Co(tpy)(2)](3+/2+) system (J(SC) = 10.84 mAcm(-2)). Tafel and electrochemical impedance analysis (EIS) of symmetric FTO/Pt||Pt/FTO cells, as well as EIS and chronocoulometry of the functional DSSC device are presented. Collectively, this data points toward a decreased turnover of the Co-III/II redox couple at the Pt counter electrode for the [Co(bqp)(2)](3+/2+) system concomitant with an increased resistance to mass-transfer diffusion.

Coordination of the 2,6-bis(8′-quinolinyl)pyridine (bqp) ligand to a cobalt (Co) core and its influence to electron spin and configuration on the structures and properties of the resulting complexes has been investigated. The homoleptic complexes Co(mer-bqp-κ3N,N′,N″)]2+ (1) and [Co(mer-bqp-κ3N,N′,N″)]3+ (2) were prepared and characterized. X-ray structure determinations of complexes 1 and 2 revealed twisted, near-octahedral arrangements relative to the cobalt center. The magnetic data for 1 is typical of those for distorted octahedral (i.e., D4h symmetry) high-spin d7 species despite the near-ideal octahedral coordination of the bqp ligand around the Co(II) core. Electronic spectra for 1 and 2 have been investigated and assigned. Both complexes exhibit intense π–π∗ bqp ligand centered transitions in the UV region and low intensity mixed charge transfer transitions in the visible region. Neither complex strongly absorbs in visible spectral region. The electrochemistry of these compounds has been studied and compared to that of similar cobalt terpyridine compounds. A metal-centered Co2+/3+ redox wave and ligand-based reduction processes were observed for 1 and 2 in acetonitrile. The metal-centered redox potentials were reversible with potentials more positive than comparable cobalt-terpyridine complexes. Density functional theory (DFT) calculations of the electronic and ground state properties are in good agreement with the experimental data.

The reactivity of a rhenium complex containing an NAD(+) model ligand was examined toward photochemical formation of the corresponding NADH-like dihydro form of the complex and electrochemical CO2 reduction. The hydricity of the NADH-like complex was estimated by a thermodynamic cycle and reaction with Ph3C(+).

2,6-Bis(8′-quinolinyl)pyridine (bqp) reacts with cobalt (II) acetate tetrahydrate in methanol with subsequent oxidation to give mer-[Co(bqp-κ3N,N′,N″)2](Br3)3. X-ray crystallographic data on mer-[Co(bqp-κ3N,N′,N″)2](Br3)3 show that the bqp ligands achieve a mutually meridional arrangement and adopt a twisted, near-octahedral arrangement relative to the cobalt center. UV–vis absorption and cyclic voltammetry data suggests that the complex is highly promising for applications in a DSSC. Electronic and structural characteristics are supported by DFT calculations.

2,6-Bis(8′-quinolinyl)pyridine (bqp) reacts with pentacarbonyl rhenium chloride in toluene to give fac,fac-[Re(bqp-κ3N)(CO)3](Cl). X-ray crystallographic data on fac,fac-[Re(bqp-κ3N)(CO)3](Cl) show that the bqp ligand and carbonyl ligands achieve a mutually facial arrangement. A mix of MLCT and π–π* ligand centered transitions is observed for the low energy UV–vis absorption bands. The complex is emissive in solution and appears to be dominated by a MLCT-based process. Electronic and structural characteristics are supported by DFT calculations.

The ligand-to-metal charge transfer (LMCT) excited state luminescence of [Tc(dmpe)3](2+) (dmpe is 1,2-bis-(dimethylphosphino)ethane) has been measured in solution at room temperature and is compared to its Re analogue. Surprisingly, both [M(dmpe)3](2+)* (M = Re, Tc) species have extremely large excited-state potentials (ESPs) as oxidants, the highest for any simple coordination complex of a transition metal. Furthermore, this potential is available using a photon of visible light (calculated for M = Tc; E°'* = +2.48 V versus SCE; λmax = 585 nm). Open shell time-dependent density functional theory (TDDFT) calculations support the assignment of the lowest energy transition in both the technetium and rhenium complexes to be a doublet-doublet process that involves predominantly LMCT (dmpe-to-metal) character and is in agreement with past assignments for the Re system. As expected for highly oxidizing excited state potentials, quenching is observed for the excited states of both the rhenium and technetium complexes. Stern-Volmer analysis resulted in quenching parameters for both the rhenium and technetium complexes under identical conditions and are compared using Rehm-Weller analysis. Of particular interest is the fact that both benzene and toluene are oxidized by both the Re and Tc systems.

Light-induced electron and energy transfer in molecular systems is being extensively studied in view of artificial photosynthesis [1-3], molecular electronics [4] and biomedical applications. [5] An ideal photosensitizer should absorb light across a significant portion of the visible spectrum and possess an appropriately aligned excited state energy with sufficiently long lifetime to promote the desired electron transfer process. In this context, complexes of Re(I) containing polypyridine or diimine donors, usually with three carbon monoxide co-ligands, continue to be of great interest. These complexes have been well-investigated because of their intense visible emission properties, capability as building blocks for supramolecular systems, and catalytic activities. [6-8] However, photoinduced CO ligand dissociation, lack of significant visible light absorption, and the inherent potential chirality of polypyridine donors hinders the overall effectiveness of these systems. Previously, we prepared a homologous series of meridionallycoordinated tridentate terpyridine Re(I) complexes containing two carbon monoxide co-ligands. [9,10] The complexes all absorb light throughout a significant portion of the visible spectrum, and several of them absorb light throughout the entire visible A Novel 2,6-Bis(8’-quinolinyl)pyridine Rhenium Compound

A homologous series of meridionally-coordinated tridentate 2,2':6',2''-terpyridine Re(I) dicarbonyl complexes have been prepared and investigated. The complexes mer,cis-[Re(tpy-κ(3)N)(CO)2(L)](n) (L = Cl(-) (1), OSO2CF3(-) (2), NCCH3 (3), CN(-) (4), NC5H5 (5), PMe3 (6), PEt3 (7), PPh3 (8), P(OMe)3 (9) and P(OEt)3 (10); n = 0 or +1) have been synthesized and characterized by elemental analysis, (1)H NMR and infrared spectroscopy. The electrochemistry of these compounds has been studied and compared to that of other known rhenium compounds using an electrochemical parameterization model. Cyclic voltammetry measurements have shown that the first oxidation of the complexes varies systematically in potential as the ligand L is altered. Many of these one-electron oxidations occur at lower potentials compared to more familiar bidentate diimine Re(I) tricarbonyl complexes. A correlation exists between CO, a strong π-acidic ligand, and deviations of the observed reduction potentials from the calculated values. Many of the complexes absorb light throughout a significant portion of the visible spectrum. Two of these complexes, mer,cis-Re(tpy-κ(3)N)(CO)2Cl (1) and mer,cis-Re(tpy-κ(3)N)(CO)2CN (4), absorb light throughout the entire visible spectrum. Low temperature emission spectra were obtained for the compounds mer,cis-Re(tpy-κ(3)N)(CO)2Cl (1) and mer,cis-[Re(tpy-κ(3)N)(CO)2(P(OEt)3)](+) (10) at 77 K in a 4 : 1 methanol-ethanol glass matrix and give metal-to-ligand charge transfer ((3)MLCT) luminescence. Density functional theory (DFT) calculations of the electronic structure are in good agreement with the experimental data.

The synthesis and characterization for a series of meridionally-coordinated terpyridine rhenium(I) dicarbonyl complexes from mer,cis-Re(tpy-κ3N)(CO)2Cl, 2, are described. Reaction of the mer,cis-Re(tpy-κ3N)(CO)2Cl via halide extraction in acetonitrile produced the complex mer,cis-[Re(tpy-κ3N)(CO)2(NCCH3)]+, 3. Complex 3 was found to undergo thermal substitution to produce mer,cis-[Re(tpy-κ3N)(CO)2(L)]+ (where L = PPh3 (4), NC5H5 (5), and PEt3 (6)). The spectroscopic and structural characterizations are discussed.

The structures of novel Tc(V) complexes trans-[TcO(2)(py)(4)]Cl·2H(2)O (1a), trans-[TcO(2)(pic)(4)]Cl·2H(2)O (2a), and trans-[TcO(2)(pic)(4)]BPh(4) (2b) were determined by X-ray crystallography, and their spectroscopic characteristics were investigated by emission spectroscopy and atomic scale calculations. The cations adopt a tetragonally distorted octahedral geometry, with a trans orientation of the apical oxo groups. trans-[TcO(2)(pic)(4)]BPh(4) has an inversion center located on technetium; however, for trans-[TcO(2)(py)(4)]Cl·2H(2)O and trans-[TcO(2)(pic)(4)]Cl·2H(2)O, a strong H bond formed by only one of the oxo substituents introduces an asymmetry in the structure, resulting in inequivalent trans Tc-N and Tc═O distances. Upon 415 nm excitation at room temperature, the complexes exhibited broad, structureless luminescences with emission maxima at approximately 710 nm (1a) and 750 nm (2a, 2b). Like the Re(V) analogs, the Tc(V) complexes luminesce from a (3)E(g) excited state. Upon cooling the samples from 278 to 8 K, distinct vibronic features appear in the spectra of the complexes along with increases in emission intensities. The low temperature emission spectra display the characteristic progressions of the symmetric O═Tc═O and the Tc-L stretching modes. Lowest-energy, triplet excited-state distortions calculated using a time-dependent theoretical approach are in good agreement with the experimental spectra. The discovery of luminescence from the trans-dioxotechnetium(V) complexes provides the first opportunity to directly compare fundamental luminescence properties of second- and third-row d(2) metal-oxo congeners.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The synthesis and spectral properties of a new 2,2'-bipyridinium ion, 1,1'-dimethyl-4,4'-(dimethylamino)-2,2'-bipyridinium bis(tetrafluoroborate) are reported. Rotation of the dimethylamino group is slow at room temperature on the 400 MHz 1H and 100 MHz 13C NMR time scales. Complete line shape fit of the dynamically broadened NMR spectra was used to determine the activation barriers for this process. The first complete set of UV-vis spectra for a 2,2'-bipyridinium dication and its one- and two-electron reduced products was reported. TD-DFT calculations were used to help assign the origin of the long wavelength absorptions in these species. The effect of substituents on the energies and conformational potential energy surfaces of all three species were also examined using the B3LYP/6-31G(d) computational method.

Computational and experimental evidence that participation of a remote heteroatom occurs during the formation and decomposition of persulfoxides is presented. The experimental ramifications of remote participation includes a dramatic increase in the rate of reaction with singlet oxygen and a decrease in the conformationally dependent ability of sulfides to physically deactivate singlet oxygen. The ability of different heteroatoms to participate is evaluated with a natural bond orbital analysis, and a comparison of the extent of participation in persulfoxides and their homologous sulfoxides is presented. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:591–599, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20343

Like the Re analogue, the ligand-to-metal charge transfer (LMCT) excited-state of [Tc(dmpe)3]2+ (dmpe is bis-1,2-(dimethylphosphino)ethane) is luminescent in solution at room temperature. Surprisingly, both [M(dmpe)3]2+* species have extremely large excited-state potentials (ESPs) as oxidants-the highest for any simple coordination complex of a transition metal. Furthermore, this potential is available using a photon of visible light (calculated for M = Re(Tc); E1/2* = +2.61(2.52) V versus SCE; lambdamax = 526(585) nm). Using a Rehm-Weller analysis with a series of aromatic hydrocarbons as electron-transfer quenchers, E1/2(Re2+*/Re+) has been determined to be 2.58 V, in good agreement with the calculated value. Both [M(dmpe)3]2+* species are quenched by chloride ion and both can function as excited-state oxidants in water solution.