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 ligand-to-metal charge transfer state (LMCT) of [(dmpe)3Re](2+) (dmpe = 1,2-bis(dimethylphosphino)ethane) has been demonstrated to be a potent oxidant (E(0)(Re(2+*)/Re(+)) = 2.61 V vs standard calomel electrode). This complex has been traditionally prepared by nontrivial routes in low yields, and very little has been achieved in optimizing the ground state and emission energy properties of the general class of complexes [(PP)3Re](2+) (PP = chelating diphosphine) through phosphine modification. Improved syntheses for Re(I) tris-homoleptic diphosphine complexes [(PP)3Re](+) (PP = 1,2-bis(dimethylphosphino)ethane (dmpe), 1,2-bis(diethylphosphino)ethane (depe), bis(dimethylphosphino)methane (dmpm), bis(diphenylphosphino)methane (dppm), Me2PCH2PPh2, 1,3-bis(dimethylphosphino)propane (dmpp), or 1,2-bis(dimethyl-phosphino)benzene (dmpb)) were achieved by single-pot reactions exploiting the reducing potential of the phosphines when reacted with Re(V) oxo-complexes in 1,2-dichlorobenzene at 160-180 °C. Single-electron chemical oxidation of [(PP)3Re](+) yields luminescent Re(II) analogues; appropriate use of Ph3C(+), Cp2Fe(+), or (4-BrC6H4)3N(+) B(C6F5)4(-) salts produced [(PP)3Re](2+) complexes in good yields. Crystallographic trends for the Re(+)/Re(2+) pairs show significantly lengthened Re(2+)-P bonds for [(PP)3Re](2+) relative to the corresponding [(PP)3Re](+) system. The redox and luminescence behavior of the complexes indicates the luminescence is from a ligand P(σ)-to-metal (Re(dπ)) charge transfer ((2)LMCT) state for all the complexes. Structured luminescence at 77 K is postulated to originate from relaxation of the (2)LMCT state into two spin-orbit coupled states: the ground state and a state ∼ 3000 cm(-1) above the ground state. The excited-state reduction potential (Re(II*/I)) for [(depe)3Re](2+) was determined from the free energy dependence of luminescence quenching rate constants. Yields for formation of charge separated ions were determined for three of the complexes with a variety of electron donors. Despite favorable electrostatics, no charge separated ions were observed for radical ion pairs for which the energy of back electron transfer exceeded 1.1 V.

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.

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.

We have studied theoretically the complexes of model N-phenylguanidine/ium derivatives with PtCl3(-) and PtCl2 in different coordinating modes (mono- and bidentate) with different N atoms of the guanidine/ium moiety using the B3LYP/6-31+G** and LANL2DZ mixed basis set. This will aid the understanding of the complexation between platinum and the guanidine or guanidinium moiety in order to design dual anticancer agents that combine a guanidine-based DNA minor groove binder and a cisplatin-like moiety. Calculated interaction and relative energies, analysis of the electron density, and examination of the orbital interactions indicate that the most stable type of complex is that with a monodentate interaction between PtCl3(-) and guanidinium established through one of the NH2 groups. Next, we optimized the structure of three bis-guanidinium diaromatic systems developed in our group as DNA minor groove binders and their complexation with PtCl3(-), finding that the formation of Pt complexes of these minor groove binders is favorable and would produce stable monodentate coordinated systems.

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.

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.

Many studies have shown that the concentration of aqueous Fe2+ increases in surface waters during exposure to sunlight and attribute this phenomenon either to photoreductive dissolution of ferric minerals/colloids or to ligand-to-metal charge transfer within organic complexes of Fe3+. In a multi-summer study of iron redox cycling in a relatively high pH stream (Middle Crow Creek, MCC) that drains a mostly-granitic watershed at an altitude of 2400m, aqueous Fe3+ (not Fe2+) concentrations were correlated with both sunlight and temperature. A steady state model fails to explain the [Fe2+] and [Fe3+] data from this stream. However, Fe2+ concentrations can be explained using a simple kinetic model in which rate constants for oxidation and reduction were obtained by fitting data from in situ oxidation experiments, including first-order thermal (nonphotochemical) reduction of Fe3+. Rate constants obtained from experiments in the dark result in too much Fe2+ to match the data from illuminated experiments, requiring a net photooxidation process to explain [Fe3+] measured in MCC. The organic content of MCC results in high concentrations of Fe–DOM complexes that not only act as a reservoir contributing to daily changes in [Fetot] as measured by our methods, but whose photochemistry may contribute highly oxidizing reactive oxygen species to the stream. In situ studies suggest that photochemical reduction of organically bound Fe3+ occurs, followed by thermal release of Fe2+ to the water column and subsequent rapid re-oxidation.

An evaluation of flow-injection analysis with chemiluminescence detection (FIA-CL) to quantify Fe2+(aq) in freshwaters was performed. Iron-coordinating and/or iron-reducing compounds, dissolved organic matter (DOM), and samples from two natural water systems were used to amend standard solutions of Fe2+(aq). Slopes of the response curves from ferrous iron standards (1 – 100 nM) were compared to the response curves of iron standards containing the amendments. Results suggest that FIA-CL is not suitable for systems containing ascorbate, hydroxylamine, cysteine or DOM. Little or no change in sensitivity occurred in solutions of oxalate and glycine or in natural waters with little organic matter.

Reaction of the new precursor cis, trans-Ru(cod)(anln)2Cl2 with the diphosphine 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane (o-dppc) unexpectedly results in two new ruthenium(II) hydrides, trans-Ru(o-dppc) 2(H)Cl and the neutral, five-coordinate complex Ru(o-dppc)(nido-dppc)(H), depending upon the reaction conditions [anln is aniline and nido-dppc is 7,8-(Ph2P)2C2B9H10(-)]. Chloride abstraction from trans-Ru(o-dppc)2(H)Cl leads to another five-coordinate hydride, [Ru(o-dppc)2(H)](+), which is isolated as either a triflate or hexafluorophosphate salt. On the basis of labeling and reactivity studies, the source of the hydride appears to be the cod ligand.

This investigation utilizes surface plasmon resonance (SPR) spectroscopy to detect and quantify human epidermal growth factor receptor 2 (HER-2), an oncogene product that is over-expressed in some aggressive forms of breast cancer. Specifically, the HER-2 trans-membrane protein p185 and its extra cellular fragment p105 are analytes targeted in this work by using a gold-based biosensor slide on which an anti-HER-2 antibody has been immobilized by attachment to Protein G that is fixed to the gold film. A detection limit of > or =11 ng/mL for p185 resulted when trastuzumab was used as the anti-HER-2 antibody on the biosensor slide. Experiments with semi-purified p105 revealed that it binds weakly and reversibly to trastuzumab, therefore complicating its detection and quantification. Results of studies that reacted a 13-amino-acid peptide (PP13) from the HER-2 kinase domain with its specific antibody were critically different than p185 and p105 studies. Spectral analysis of the reflectivity at constant bulk buffer refractive index revealed a progressive negative SPR shift over time. A negative shift suggests that a loss of protein mass from the anti-PP13 antibody-Protein G biosensor is occurring. Several possibilities that may explain these negative SPR shifts are discussed.

We report the first examples of excited-state luminescence from technetium complexes. We have examined a series of trans-dioxo complexes of Tc(V) and a Tc(I/II) phosphine complex and compare their respective photophysical properties with the corresponding rhenium analogues. When excited with a 415 nm laser, the Tc(V) complexes luminesce in the 700-800 nm range and have excited state lifetimes in the range of several microseconds at room temperature. The low-temperature luminescence spectra of the technetium complexes have also been investigated. Distinct vibrational band progressions are resolved in the low-temperature luminescence spectra. Excited state lifetimes at 5 K vary between tens of microseconds to several milliseconds for the dioxo-technetium complexes. In addition, a previously known Tc(I) complex, [Tc(DMPE) 3]+ which has been used as a radiography imaging agent has been demonstrated in our labs to fluoresce in the visible wavelength region upon a one-electron reversible oxidation to form the Tc(II), [Tc(DMPE)3]2+ complex in aqueous solution. The luminescence of [Tc(DMPE)3]2+ was observed by illuminating the solution complex with a 404 nm excitation while performing the reversible electrochemical experiment. In a recent application, we have focused on making thin chemically-selective films for sensing radioactive technetium compounds and in this effort have developed a fluorescence-basedmore » spectroelectrochemical sensor. Characterization of the new dioxo-technetium(V) and technetium(II)phosphine excited states as well as application of the respective chromophores for use in a spectroelectrochemical sensor for pertechnetate will be discussed.« less

A series of mixed-ligand 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) rhenium(I) dicarbonyl complexes that are emissive in fluid solution has been prepared, which includes a new class of the type cis-[Re(CO)2(P-P)(N-N)]+ (where P-P is a chelating diphosphine and N-N is a chelating polypyridine ligand). The four synthetic routes that have been developed rely on either reactive triflate displacement or abstraction of labile chloro ligands, followed by the use of the strong trans-labilizing effect of P donors or direct use of the trans effect of P donors. The spectroscopic, photophysical, and electrochemical properties of these new complexes systematically vary with the net donor ability of the ligands in the coordination sphere, as shown by correlations with Lever's E(L) parameters. Lifetimes and quantum yields of the bipyridine complexes encompass a broad range, 25-1147 ns and ca. 0.002-0.11, respectively.

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.

The luminescence of trans-[TcO2(L)4]+ (L = pyridine (py) or picoline (pic)) and trans-[TcO2(CN)4]3- at room and low temperature is described and represents the first example of room temperature excited-state luminescence observed for Tc complexes. At room temperature, the complexes exhibited broad luminescence with emission maxima ranging from 745 to 780 nm. Analogous to the Re complexes (emission at 635-655 nm), the low-temperature emission spectra of microcrystalline samples of [TcO2(py)4]BPh4 and [TcO2(pic)4]BPh4 display the characteristic progressions of the symmetric O=Tc=O and Tc-L stretching modes. DFT/TDDFT calculations were performed on the trans-[MO2(L)4]+ (M = Re, Tc) congeners and predicted the dioxotechnetium emission to be 0.41 eV lower in energy than its Re analogue. Low-temperature lifetimes (8 K) ranging from 15 to 1926 mus for the series of Tc complexes are consistent with the Re analogues.

Preparations of the first metal complexes of triethynylphosphine (TEP) are described. They are of the type fac-Re(bpy)(CO)(3)(TEP)(+) (1) and cis,trans-[Re(bpy)(CO)(2)(TEP)L](n)(+) (CH(3)CN, n = 1, complex 2; Cl, n = 0, complex 3), where bpy is 2,2'-bipyridine. Complex 1 displays unusual photochemical behavior compared to analogous fac-[Re(bpy)(CO)(3)(PR(3))](+) complexes in that it emits from a state that has pi-pi* character but undergoes competitive photosubstitution of both TEP and CO. Density functional theory (DFT)/time-dependent DFT calculations predict that the lowest emitting state should, in fact, have pi-pi* character.