Mohammed Bakir

Electrochemical properties of the first Re(I)–carbonyl compound of di-2-pyridyl ketone.oxime (dpk.oxime), fac-Re(CO)3(dpk.oxime)Cl, in non-aqueous media

The reaction between Re(CO)5Cl and di-2-pyridyl ketone.oxime (dpk.oxime) in refluxing toluene gave fac-Re)(CO)3 (dpk.oxime)Cl (2) in good yield. This marks the first time that a rhenium compound of di-2-pyridyl ketone.oxime has been isolated. The formulation of (2 )a sfac-Re(CO)3(dpk.oxime)Cl is based on the results of a number of spectroscopic measurements and a comparison of these results with those reported for fac-Re(CO)3(dpk)Cl (3) (dpk di-2-pyridyl ketone) and other compounds of the a-diimine ligands of the type fac-Re(CO)3(L‐L)X (L‐La-diimine and X halide). Compound (2) exhibits rich spectroscopic and electrochemical properties. Electrochemical measurements reveal that the oxime moiety in fac-R(CO)3(dpk.oxime)Cl acts as an electron sink:reservoir and its first reduction potential dpk.oxime:dpk.oximei in non-aqueous media is solvent dependent and controlled by the proton accepting ability of the solvent. Plausible mechanisms for the reduction and oxidation of facRe(CO)3(dpk.oxime)Cl to fac-Re(CO)3(dpkH.NH2)Cl and fac-Re(CO)3(dpk)Cl are proposed which are consistent with the chemical transformations following electronic transfers.

Polymer-supported CuPd nanoalloy as a synergistic catalyst for electrocatalytic reduction of carbon dioxide to methane.

Significance Photo- and electrochemical CO2 reduction to carbon fuels is not only an attractive solution to the greenhouse effect, but could also become an integral part of a global energy storage strategy with renewable electrical energy sources used to store energy in the chemical bonds of carbon fuels. A novel electrodeposition strategy is reported here for the preparation of highly dispersed, ultrafine metal nanoparticles and nanoalloys on an electroactive polymeric film. It is shown that a bimetallic Cu–Pd nanoalloy exhibits a greater than twofold enhancement in Faradaic efficiency for CO2 reduction to methane compared with a state-of-the-art nanoCu catalyst. The fabrication procedure for the alloy nanoparticles is straightforward and applicable as a general procedure for catalytic electrodes for integrated electrolysis devices. Developing sustainable energy strategies based on CO2 reduction is an increasingly important issue given the world’s continued reliance on hydrocarbon fuels and the rise in CO2 concentrations in the atmosphere. An important option is electrochemical or photoelectrochemical CO2 reduction to carbon fuels. We describe here an electrodeposition strategy for preparing highly dispersed, ultrafine metal nanoparticle catalysts on an electroactive polymeric film including nanoalloys of Cu and Pd. Compared with nanoCu catalysts, which are state-of-the-art catalysts for CO2 reduction to hydrocarbons, the bimetallic CuPd nanoalloy catalyst exhibits a greater than twofold enhancement in Faradaic efficiency for CO2 reduction to methane. The origin of the enhancement is suggested to arise from a synergistic reactivity interplay between Pd–H sites and Cu–CO sites during electrochemical CO2 reduction. The polymer substrate also appears to provide a basis for the local concentration of CO2 resulting in the enhancement of catalytic current densities by threefold. The procedure for preparation of the nanoalloy catalyst is straightforward and appears to be generally applicable to the preparation of catalytic electrodes for incorporation into electrolysis devices.

Electrochemical reactions of CO2 with fac-Re(dpk)(CO)3Cl (dpk = di-2-pyridyl ketone)

Abstract The electrochemical reactions between CO 2 and fac -Re(dpk)(CO) 3 cl ( 1 ) are solvent dependent, controlled by the rate of diffusion of electroactive species from the electrode surface. Fast diffusion due to solvent or scan rate variations inhibits the carboxylation of the carbonylic carbon atom of the radical anion fac -Re(C 5 H 4 N) 2 (CO) ⪰ (CO) 3 Cl ( II ) and leads to the generation of a coordinatively unsaturated fac -Re[(C 5 H 4 N) 2 (CO) ⪰ ](CO) 3 ( VIII ) that binds CO 2 at the metal center to form fac -Re[(C 5 H 4 N) 2 (CO) ⪰ ](CO) 3 (CO 2 ) ( IX ). Slow diffusion facilitates the carboxylation of the carbonylic carbon atom of II to form fac -Re[(C 5 H 4 N) 2 C(O − )(CO 2 . )](CO) 3 ( III ) that undergoes a second electronic transfer followed by chemical steps leading to the formation of fac -Re[(C 5 H 4 N) 2 C(O)(CO 2 H)](CO) 3 ( VI ).

Electro-optical properties of the first rhenium-hydrazone complex, fac-Re(CO)3(dpknph)*Cl

Reaction between Re(CO)5Cl and dpknph in PhMe under reflux gave fac-Re(CO)3(dpknph)Cl in good yield. Both dpknph and fac-Re(CO)3(dpknph)Cl exhibit rich electro-optical properties that are sensitive to their surroundings and point to the potential use of these compounds in nonlinear optics and molecular sensing. Spectroscopic and electrochemical measurements on solutions of dpknph and fac-Re(CO)3(dpknph)Cl show that the metal complex undergoes faster electron/charge-transfer than the free ligand. Solvent variations show that the rate increases in the following order: DMSO>DMF>MeCN.

Optosensing properties of fac-Re(CO)(3)(dpknph)Cl (dpknph=di-2-pyridyl ketone p-nitrophenyl hydrazone).

Optical and thermodynamic measurements on fac-Re(CO)(3)(dpknph)Cl in polar non aqueous solvents revealed the existence of two interlocked conformational forms for fac-Re(CO)(3)(dpknph)Cl. The equilibrium distribution of the low (alpha-) and high (beta-) energy conformations is solvent dependent, controlled by the dipole moment of the solvent molecules and their orientation around the total dipole of fac-Re(CO)(3)(dpknph)Cl. The interplay between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl, allowed calculations of their extinction coefficients, by forcing the equilibrium to shift to one conformation, using chemical stimuli. In DMSO and DMF extinction coefficients of 87 000+/-2000 and 35 000+/-2000 M(-1) cm(-1) were calculated for the beta- and alpha-conformations of fac-Re(CO)(3)(dpknph)Cl at lambda(max.), respectively. Thermo-optical measurements on fac-Re(CO)(3)(dpknph)Cl, allowed calculations of the activation parameters for the interconversion between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl. In DMSO and DMF changes in enthalpy (DeltaH(ø)) of -11.2+/-1.3 and 10.9+/-0.5 kJmol(-1), entropy (DeltaS(ø)) of -12.7+/-4.3 and 29.4+/-1.7 JK(-1) mol(-1), and free energy (DeltaG(ø)) of -7.5+/-0.2 and+2.2+/-0.2 kJmol(-1) and hence equilibrium constants of 20.9+/-1.7 and 0.4+/-0.1 were calculated for fac-Re(CO)(3)(dpknph) at 295 K. The high values for the extinction coefficients and low values for the activation parameters for the interconversion between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl, in polar non aqueous solvents allowed the use of these systems as molecular sensors to probe their structural relaxation and interactions with their surroundings. These systems (fac-Re(CO)(3)(dpknph)Cl and surrounding solvent molecules) optically sense chemical and physical stimuli and their sensing power depends on the intensity and nature of these stimuli, i.e. the systems exhibit a high degree of sensitivity and selectivity.

Synthesis, Characterization and Structural Studies on the First Rhenium Complex with Di(2-pyridyl) Ketone 2,4-Dinitrophenylhydrazone (dpkdnph), fac-[Re(CO)3(dpkdnph)Cl]

When di(2-pyridyl) ketone 2,4-dinitrophenylhydrazone (dpkdnph) was allowed to react with [Re(CO)5Cl] in refluxing toluene fac-[Re(CO)3(dpkdnph)Cl] was formed in good yield. Spectroscopic measurements on fac-[Re(CO)3(dpkdnph)Cl] revealed strong solvent dependence as manifested by the high sensitivity of its electronic absorption spectra to solvent variation. Electrochemical measurements on fac-[Re(CO)3(dpkdnph)Cl] in DMF show electrochemical properties with quasi-reversible reductions following an irreversible one-electron transfer. Structural studies on a brown crystal of fac-[Re(CO)3(dpkdnph)Cl]·CH3CN grown from an acetonitrile solution of fac-[Re(CO)3(dpkdnph)Cl] show well separated linear CH3CN and pseudo-octahedral fac[Re(CO)3(dpkdnph)Cl], with the major distortion about rhenium being due to the bidentate binding of dpkdnph to form a six-membered Re−N−C−C−C−N metallacyclic ring in a boat conformation. The molecular packing shows a web of fac-[Re(CO)3(dpkdnph)Cl]·CH3CN units interlocked via a network of intra- and intermolecular non-covalent interactions that include donor/acceptor and hydrogen bonds.

Optical, electrochemical and structural studies of the first rhenium compound of di-2-pyridylketone benzoylhydrazone (dpkbz) fac-Re(CO)3(dpkbh)Cl

Abstract The reaction between Re(CO)5Cl and di-2-pyridylketone benzoylhydrazone (dpkbh) in refluxing toluene gave fac-Re(CO)3(dpkbh)Cl in good yield. Spectroscopic and electrochemical measurements on fac-Re(CO)3(dpkbh)Cl revealed strong solvent–solute interaction, as manifested by the sensitivity of its reduction potentials and electronic absorption spectra to solvent variations. Spectroscopic and thermo-optical measurements in polar solvents in the presence of NaBH4 and NaBF4, or NaOH and citric acid reveal reversible interconversion between the low- and high-energy electronic states of fac-Re(CO)3(dpkbh)Cl at 440 and 318 nm. Electrochemical measurements on fac-Re(CO)3(dpkbh)Cl show irreversible redox processes pointing to electrochemical transformations following the first electronic transfer(s). Crystals of fac-Re(CO)3(dpkbh)Cl obtained from an acetonitrile solution of fac-Re(CO)3(dpkbh)Cl are centric and crystals of fac-Re(CO)3(dpkbh)Cl·dmso obtained from a dmso solutions of fac-Re(CO)3(dpkbh)Cl are acentric. Structural studies show non-identical twins of fac-Re(CO)3(dpkbh)Cl and fac-Re(CO)3(dpkbh)Cl·dmso with distorted octahedral coordination about rhenium and the conformation about the amide group is syn- in fac-Re(CO)3(dpkbh)Cl and anti- in fac-Re(CO)3(dpkbh)Cl·dmso. The packing of molecules shows a web of hydrogen bonds that may account for the stability of different conformations observed in the solid state.

Synthesis and characterization of a cadmium-dichloro compound of N , N , O -di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (η 3-dpktch). The structure of [CdCl2(η 3-dpktch)]

The reaction between dpktch and CdCl2 in refluxing acetonitrile gave [CdCl2(η3-dpktch)] in good yield. Spectroscopic measurements divulge the coordination of dpktch and the elemental analysis confirmed its formulation. Optical measurements in N,N-dimethylformamide (dmf) and dimethylsulfoxide (DMSO) in the absence and presence of a proton donor/acceptor disclosed two highly sensitivity interlocked intra-ligand-charge-transfer transitions (ILCT) that are sensitive to their surroundings. Under basic conditions, a low-energy electronic transition with an extinction coefficient of 17,400 ± 2000 M−1cm−1 appeared at ∼403 nm and a peak minimum appeared at 326 nm. Under acidic conditions, a high energy electronic transition with extinction coefficient of 13,500 ± 2000 M−1cm−1 appeared at ∼330 nm and a shoulder appeared at ∼400 nm. The addition of an acid to a dmf solution of [CdCl2(η3-dpktch)] caused the disappearance of the low energy absorption band at 403 nm and a peak maximum appeared at 330 nm. The reverse was observed when a base was added to a DMSO solution of [CdCl2(η3-dpktch)]. Electrochemical measurements reveal reduction of coordinated CdCl2 and oxidation of electrodeposited cadmium metal along with ligand-based redox processes. X-ray crystallographic analysis on a monoclinic, P21/n single crystal of [CdCl2(η3-dpktch)], confirmed the N,N,O-coordination of dpktch and revealed digitated units of [CdCl2(η3-dpktch)] interlocked via a web of hydrogen bonds.

Optosensing properties of fac-Re(CO)3(dpknph)Cl (dpknph=di-2-pyridyl ketone p-nitrophenyl hydrazone) toward chemotactic N-formylamino acids

Optical measurements on fac-Re(CO)(3)(dpknph)Cl in polar non-aqueous solvents in the presence and absence of NaBH(4)/KPF(6) revealed reversible interconversion between the high (beta-) and low (alpha-) energy electronic states of fac-Re(CO)(3)(dpknph)Cl. The reversibility of these interactions and the disturbance of the equilibrium distribution of the low (alpha-) and high (beta-) energy electronic state upon addition of NaBH(4)/KPF(6) mark improvement in the optosensing properties of fac-Re(CO)(3)(dpknph)Cl. The optical behavior of fac-Re(CO)(3)(dpknph)Cl in the presence and absence of the l-methionine and chemotactic N-formylamino acids: N-formyl-l-methionine (NFM), N-formyl-l-glycine (NFG) and N-formyl-l-phenylalanine (NFP) shows the alpha- and beta-electronic states of fac-Re(CO)(3)(dpknph)Cl to be insensitive to l-methinonine and highly sensitive to N-formylamino acids. N-formylamino acids in concentrations <1.0x10(-5) M can be determined using the optical sensor fac-Re(CO)(3)(dpknph)Cl in non-aqueous polar solvents. The optosensing power of fac-Re(CO)(3)(dpknph)Cl towards N-formylamino acids depends on the concentration and polarity of the side chain of the amino acids and increases in the following order: NFM>NFG>NFP.

Manganese carbonyl compounds of N,N-bidentate di-2-pyridylketone (dpk) and N,O,N-tridentate hydroxybis(2-pyridyl)methanolato (dpkO,OH). The structure of fac-[Mn(CO)3(dpkO,OH)]

Abstract Electrochemical measurements on fac -[Mn(CO) 3 (dpk)Br] and fac -[Mn(CO) 3 (dpkO,OH)] revealed solvent dependence and rich redox properties and X-ray studies on fac -[Mn(CO) 3 (dpkO,OH)] show distorted octahedral geometry around manganese with the major distortion is due to the binding of hydroxybis(2-pyridyl)methanolato (dpkO,OH) anion and anti-parallel tapes of fac -[Mn(CO) 3 (dpkO,OH)] interlocked via a network of hydrogen bonds. When di-2-pyridyl ketone (dpk) was allowed to react with [Mn(CO) 5 Br] in dry diethyl ether under ultrasonic conditions fac -[Mn(CO) 3 (dpk)Br] was isolated in good yield and when the same reaction was carried out under reflux conditions in toluene fac -[Mn(CO) 3 (dpkO,OH)] was isolated. Infrared spectra of the isolated compounds confirmed their fac -geometry and the presence and absence of the ketonic group of dpk. Electrochemical measurements on fac -[Mn(CO) 3 (dpk)Br] reveal sensitivity to solvents and the presence of reversible and irreversible electronic transfers. In contrast to fac -[Re(CO) 3 (dpk)Cl] where noteworthy electrochemical reactions with CO 2 were observed, the electrochemical reactions of CO 2 with fac -[Mn(CO) 3 (dpk)Br] disclosed no significant reaction. However, when fac -[Mn(CO) 3 (dpk)Br] was allowed to electrochemically interact with group I and II metal ions considerable electrochemical changes were noted on the second reduction wave that may point to the possible use of fac -[Mn(CO) 3 (dpk)Br] as an electrochemical sensor for group I and II metal ions. The electrochemical properties of fac -[Mn(CO) 3 (dpkO,OH)] show the presence of closely spaced irreversible oxidations and probable electrochemical oxidation of coordinated dpkO,OH anion to dpk in dmf. Crystals of fac -[Mn(CO) 3 (dpkO,OH)] obtained from dimethyl sulfoxide (dmso) solution of fac -[Mn(CO) 3 (dpkO,OH)] are in the monoclinic C2/c space group. Structural analysis on fac -[Mn(CO) 3 (dpkO,OH)] disclosed distorted octahedral coordination about manganese with the major distortion due to the tridentate coordination of dpkO,OH anion and the packing of molecules show stacks of anti-parallel tapes of fac -[Mn(CO) 3 (dpkO,OH)] interlocked via a network of hydrogen bonds.