D. Paul Rillema

Crystal and molecular structure of [N, N′-ethylenebis(methyl-2-amino-1-cyclopentenedithiocarboxylato)]copper(II): A quantitative relationship between tetrahedral distortion and redox potentials in copper N2S2 compounds and the relevance to type I copper(II) centers ☆

The crystal and molecular structure of the copper(II) complex of the N2S2 tetradentate ligand, ethylenebis(methyl-2-amino-1-cyclopentenedithiocarboxylate), was solved at room temperature by a single crystal x-ray diffraction study. The complex crystallizes in the orthorhombic space group P212121 with a = 7.739(1) A, b = 13.893(2) A, c = 17.096(3) A, V = 1838(1) A3, ϱobserved = 1.56 g cm−3 and ϱcalculated = 1.57 g cm−3 for a molecular weight of 434.2, and Z = 4. Diffraction data were collected with a Syntex P diffractometer using graphite-monochromatized Cu (λ = 1.5418 A) radiation. The heavy atoms were located from a Patterson synthesis; all other nonhydrogen atoms were located using difference Fourier techniques, and hydrogen atoms were placed in calculated positions. Final refinement resulted in discrepancy indices of R = 0.067 and goodness of fit of 2.92 for all 995 reflections (5° < 2θ < 100°) greater than three times their standard deviation. The molecules are monomeric and well separated. Bond distances in the two ”halvesldquo; of the ligand are sufficiently different to suggest that different resonance structures exist in each portion. This agrees with the rhombic symmetry displayed by the frozen glass esr spectrum of the compound (xx ≠ gyy). The dihedral angle between the planes defined by the CuN2 and CuS2 planes is 20.0°, indicating a rather distorted inner coordination sphere. The copper(II)-copper(I) reduction potentials found for this compound and the trimethylene and tetramethylene analogs were determined to be −1.01, −0.79, and −0.64 V respectively. A quantitative relationship between tetrahedral distortion and redox potentials is obtained, and these results are discussed in terms of ”blueldquo; copper(II) sites in proteins. Trends in CuS and CuN bonding patterns in the same three compounds are discussed with regard to the short CuS (cys) bond distance in plastocyani Finally, a brief discussion of the optical spectra of these three compounds, their variation, and their significance with respect to tetrahedral symmetry in copper(II) protein sites is presented.

Structure, physical, chemical and photophysical properties of Pt(bph) (CO)2, where bph is the biphenyl dianion

The complex Pt(bph) (CO)2 crystallizes in the space group Cmcm with a = 18.647(6), b = 9.566(2) and c = 6.4060(5) A. The geometry of the molecule is slightly distorted from square planar with a PtC(CO) bond distance of 1.98(2) A and a PtC(bph) bond distance of 2.04(2) A. The Pt(bph)(CO)2 complex serves as a precursor for the preparation of a wide variety of Pt(bph)X2 complexes, where X = monodentate ligands such as acetonitrile, pyridine, etc., and X2 = bidentate ligands such as bypyridine, 1,10-phenanthroline, etc. In the solid state, the complex exhibits a green color, but when ground with an alkali metal salt turns deep blue to purple. In CH2Cl2, the color disappears but optical transitions are observed at 271 nm (2.7 × 104 M−1 cm−1), 303 nm (1.1 × 104 M−1 cm−1) and 330 nm (5.5 × 103 M−1 cm−1). The complex is a weak emitter exhibiting a structured spectrum in CH2Cl2 at r.t. with maxima located at 562 and 594 nm and an emission lifetime of 3.1 μs when excited at 337 nm.

Solvent dependent behavior of energy transfer in a mixed metal ruthenium(II)/rhenium(I) complex

Abstract The absorption and emission properties of (bpy) 2 Ru(bb) 2+ , Ru(bpy) 2 (bb)Re(CO) 3 py 3+ and (bb)Re(CO) 3 py 1+ , where bpy is 2,2′-bipyridine, bb is 1,2-bis(4-methyl-2,2′-bipyridyl-4′-yl)ethane and py is pyridine, were studied in various solvents. Absorptions attributed to dπ(Ru) → π*(1)(bpy) were located between 400 and 500 nm, those attributed to dπ(Ru) → π*(2)(bpy) and dπ(Re) → π*(bb) were found between 300 and 400 nm, and those attributed to π → π* (intraligand) were observed between 200 and 300 nm. The absorption energy maxima of the dπ(Ru) → π*(1)(bpy) transition followed the optical dielectric constant of the solvent defined by the (1− D op )/ (2 D op +1) relationship. In the heterometallic complex, absorption of light in the 300–400 nm region was partitioned between the ruthenium and rhenium centers. Emission in solution at roam temperature was observed from the ruthenium center upon excitation at either 436 or 355 nm. While emission was also observed from the rhenium center in (bb)Re(CO) 3 py 1+ when excited at 355 nm, none was observed from the rhenium site of the mixed metal complex. The excitation energy absorbed by the rhenium center in this complex was transferred to the ruthenium center with greater than 80% efficiency. The energy transfer process was rapid as noted by the transient absorption spectrum of the heterometallic complex, which contained only the features related to the bpy − radical and the Ru(II) bleach. In addition, an inverse (1− D op )/(2 D op +1) dependence on the emission energy maxima of (bb)Re(CO) 3 py 1+ was observed.

Carbon dioxide reduction mediated by electro-polymerized electrodes of a nickel tetraazaannulene complex, Ni[Me4Bzo2[14]tetraeneN4]

Etudes par voltammetrie cyclique de la reduction de CO 2 sur une a disque de carbone vitreux, ou par electrolyse sous potentiel controle sur une electrode de Pt modifiee par le tetraazaannulene de Ni polymerise, qui joue le role de catalyseur

Crystal structure, physical, and photophysical properties of a ruthenium(II) bipyridine diazafluorenone complex

The complex [Ru(bpy)2(dafo)](PF6)2, where bpy is 2,2′-bipyridine and dafo is diazafluorenone crystallizes in the space group P21/n witha=9.505(3) Å,b=14.002(4) Å andc=25.783(8) Å. The coordination geometry of the Ru atom is that of a distorted octahedron with a RuN6 core. The two Ru-N bond distances to the dafo ligand are 2.13(1) and 2.15(1) Å; the four Ru-N bond distances to the bipyridine ligands are 2.03(1), 2.05(1), 2.06(1), and 2.07(1) Å. The three shortest Ru-N distances aretrans to the three longest Ru-N distances. The complex is oxidized and reduced reversibly at 1.41 and −0.65 V vs. SSCE, respectively. It displays absorptions at 438 nm (1.6×104), 285 nm (6.2×104), and 240 nm (4.1×104) and a broad emission centered at 626 nm in water at room temperature. The emission lifetime is 420 ns and the emission quantum yield is 5.3×10−4.

Efficient Preparative Rentes to 6,6′-Dibromo-2-2′-bipyridine and 6-Bromo-2,2′-bipyridine

Abstract The preparation of 6,6′-dibromo-2,2′-bipyridine and 6-bromo-2,2′-bipyridine are described. The dibromo compound was prepared by way of an improved cuprate synthesis resulting in a 72% yield. The monobromo species was prepared from the dibromo compound by way of metal-halogen exchange in 88% yield.

A comparison between chemically and photochemically driven electron transport reactions in immobilized liquid membranes

Abstract Electron transport in immobilized liquid membranes using a microporous polypropylene film as the support was studied in the reagent concentration independent regime and was kinetically controlled under the conditions employed in this study. The velocities depended on the concentration of the carrier (Vitamin K 3 ) in the membrane and varied exponentially with the reciprocal of the absolute temperature. Neither the membrane thickness, concentration of the oxidant (Fe( o phen) 3 3+ ) nor the concentration of reductant (S 2 O 4 2- or MV + generated photochemically) affect the electron transport rate. Maximum velocities at 25°C (7.8 μmol-cm -2 -hr -1 and 2.5 μmol-cm -2 -hr - for the S 2 O 4 2- and MV + driven reactions, respectively) were obtained in the pH range of 6-7 for the reductant compartment and in the 0 to - 1 pH range in the oxidant compartment. The respective turnover rates were 2.1 hr -1 and 0.65 hr -1 based on 2e - /Vitamin K 3 for the S 2 O 4 2- and MV + driven reactions, respectively. The mechanism of electron transport is best interpreted to involve formation of the hydroquinone in the membrane which then reacts with Fe( o -phen) 3 3+ in the rate-limiting electron transfer step.

Ion-interaction chromatography : a study of the distribution of n-alkylammonium ions on an ODS-2 column

The distribution of n-alkylammonium ions on a Whatman ODS-2 reversed-phase column was investigated. It was found that only about 24% of the retained n-alkylammonium ions act as ion-pairing reagents on the column surface. Approximately 76% of the n-alkylammonium ions are electrostatically interacting with the deprotonated surface silanols.

Behavior of simple salts on silica and C18 columns : Retention dynamics of cations, anions and ion pairs

Abstract The retention behavior of simple inorganic salts on silica and ODS columns was investigated by high-performance liquid chromatography with methanol-water (80:20, v/v) as the mobile phase. Both a major (dissolved salt) and a minor (ion pair) peak were observed on the ODS columns; only the major peak was present on silica columns. The retention time of the major peak was a function of the number of moles of salt placed on the column and was sigmoidal with respect to the logarithm of the number of moles analyzed. The retention time of the minor peak was dependent upon the composition of the mobile phase. It disappeared in a mobile phase of water and was absent on a silica column. The general behavior was independent of the anion or cation being analyzed. The sigmoidal behavior of salt retention was attributed to both cationic and anionic exchange at the silica surface: the ion pair retention was attributed to solubility in the C 18 phase of the ODS columns. The areas under the major peak and the minor peak were used to calculate ion pair formation constants. For sodium nitrate, K = 15 · 10 −3 M −1 , for sodium nitrite, K = 2.0 · 10 −3 M −1 . The ion pair formation constants were used to calculate the theoretical distance of closest approach between the ions based on Bjerrum theory. For sodium nitrate, the distance calculated between center of Na + and NO − 3 in the ion pair was 6.5 A.

Crystal and molecular structure of the photocatalyst tris(2,2′-bipyrazine)ruthenium(II) hexafluorophosphate

The X-ray structure determination of the complex tris(2,2′-bipyrazine)ruthenium(II) hexafluorophosphate, [Ru(C8N4H6)3](PF6)2, has shown that the compound crystallizes in the monoclinic space group P21/c witha=13.459(5),b=23.486(8),c=17.913(10) Å,β=139.85(1)°, andZ=4. Each asymmetric unit also contains one dimethylformamide and one water molecule. Least-squares refinement led to an R factor of 0.074 based on 3463 reflections for which I>2σ(I). The [Ru(C8N4H6)3]2+ cation has no crystallographic symmetry, but the requirements for point symmetry 32 are nearly met. The six Ru-N bond lengths agree within experimental error and have an average length of 2.05(1) Å.