J.O. Dziȩgielewski

Application of the molybdenum(IV) hydride complexes in cyclohexane solutions to the radiation-catalytic reduction of molecular nitrogen

Abstract The two molybdenum(IV) hydride complexes [MoH4(dppe)2][dppe = (C6H5)2 PCH2CH2P(C6H52] and [MoH4(dtpe)2] [dtpe =(o-CH3C6H4)2PCH2CH2P(o-CH3C6H4)2] were applied in a process of radiation-catalytic reduction of molecular nitrogen. The yields of ammonia and hydrazine were determined for different concentrations of these complexes in cyclohexane solutions. The mechanism of the reduction of molecular nitrogen by γ-radiation is suggested. It has also been discovered that the [MoH4(LL)2] complexes are useful in the process of radiation-catalytic fixation and reduction of nitrogen.

Radiation-chemical processes as disclosure of electronic states in a bis(dinitrogen) molybdenum complex

Abstract On the basis of experimental data the energy levels of the central-atom orbitals in the complex [Mo(N2)2(dppe)2] [dppe = 1,2-bis(diphenylphosphine)ethane] were calculated. Using the diagram thus obtained the eletronic configuration of the irradiation-generated ion, [Mo(N2)2(dppe)2]−, was determined to be as follows: (b2g)2 (eg)4 (b1g)1 or (b2g)2 (eg)4 (eu). The yields from the decomposition of [Mo(N2)2(dppe)2] in the solid phase in a hydrogen atmosphere were determined on the basis of the decrease in band intensities at 306 and 377 nm: G(− MoN2)306nm = 0.01, and G(− MoP)377nm = 0.1 (molecules per 100 eV). In toluene solution it was found that G(− MoN2) > G(− MoP). The yields observed were in accordance with the calculated levels. Using a mass spectrometer the volatile products of [Mo(N2)2(dppe)2] radiolysis in H2 and O2 atmospheres were identified as H3N, H4N2, NO and N2O. In the light of the results mentioned above (as well as the IR results) a mechanism for the radiolysis of [Mo(N2)2(dppe)2] in the solid phase was proposed.

Determination of penicillin complexation sites in the presence of Zn(II) ions by AM1 and PM3 methods

Abstract In this study we have carried out semiempirical AM1 and PM3 calculations on a simplified penicillin molecule (i.e. methylpenicillin) in the presence of the Zn(II) ion to assess the probable complex structures and to gain additional information on the mechanism of the metal-ion promoted hydrolysis of penicillins. Theoretical investigations based on calculated heats of formation Δ H f predict formation of two complexes of comparable thermochemical stability in aqueous solutions of methylpenicillin in the presence of Zn(II): by the COO − group alone and by the COO − group and β-lactam ring nitrogen atom. The former structure, with four watermolecules, is slightly favoured Δ H f lower by 6.5 kcal mol −1 (AM1)and 10.7kcal mol −1 (PM3)). A complex involving binding to the C6 substituent described in some earlier works was not found. The calculated lengthening of the ligand C7-N4 bond upon coordination suggests easier Nu − attack at the β-lactam carbon atom, which facilitates the degradation of penicillin. The results also indicate that both methods can be applied to calculations on penicillins. Generally, the PM3 bond lengths are longer than the AM1 values; however, the former reproduces better the first coordination sphere of the Zn(II) ion.

Radiation induced conversion of N2 to amines in the presence of [WH4(dppe)2] and [WH5(dppe)2]+ in solution

Abstract The complexes [WH4(dppe)2] and [WH5(dppe)2][HSO4] were applied in the fixation and reduction of molecular nitrogen in a γ-radiation field. The mechanism of the process involving the reactions with the solvent molecules was presented. Dependences of the yields of the amines formed on the dose and concentrations of the catalyst were shown.

Copper-d-penicillamine complex as potential contrast agent for MRI

In vitro and in vivo proton T1 data are reported that demonstrate that the paramagnetic copper-D-penicillamine complex can be applied as a potential contrast agent to magnetic resonance imaging.

The cyclic fixation and reduction of molecular nitrogen with [WH4(Ph2PCH2CH2PPh2)2] in γ-irradiated solutions

Abstract Yields of NH3 and N2H4 in radiation-catalytic reduction of N2 by means of a hydride complex of WIV with dppe in thf solution and in mixtures of thf with other solvents have been estimated. A mechanism proposed earlier of reduction of coordinated N2 has been confirmed and the role of solvent in reduction of N2 to NH3 and amines has been explained.

Radiation-catalytic reduction of molecular nitrogen with application of the tungsten(IV) hydride complexes

Abstract A radiation-catalytic experiment of the fixation and reduction of molecular nitrogen has been carried out. The [WH 4 (dtpe) 2 ] complex was applied to fix molecular nitrogen in a γ-radiation field. Plots of the dependence of either the number of molecules of ammonia or hydrazine vs dose are presented. A mechanism for the radiation-catalytic fixation and reduction of molecular nitrogen using the [WH 4 (dtpe) 2 ] complex is suggested. The unusually high radiation yields of ammonia and hydrazine are explained as due to a cyclic process.

A new radiation-catalytic route to hydrazine and ammonia

Abstract In methanol solution, nitrogen was reduced to H 4 N 2 and H 3 N using the molybdenum(IV) complex with dppe and γ-radiation. Radiation-catalytic yields of hydrazine and ammonia were determined. These yields increase with increasing concentration of the molybdenum(IV) complex. [Mo(N 2 ) 2 (dppe) 2 ], H 4 N 2 and H 3 N were isolated and identified. Other intermediates of the reduction were also observed. The initial form of the catalyst was reproduced by oxidation of molybdenum(O) to molybdenum(IV) with the coordinated nitrogen. The solvent participated in the latter reaction. The process of N 2 fixation and reduction is a chain-reaction (see yields of H 4 N 2 and H 3 N in Table 1). The mechanism of the radiation-catalytic reduction of N 2 was suggested.

Photoreduction of molecular nitrogen using the complex [ReH5(dppe)(PPh3)]

Abstract A ReV hydrido complex with bis-1,2-(diphenylphosphine)ethane and triphenylphosphine was employed for the photochemically induced fixation and reduction of dinitrogen. Tetrahydrofuran/cyclohexane (1 : 1) solutions, acidified and non-acidified, were examined in the UV radiation field.

Hydride complexes of tungsten in photocatalytic dinitrogen reduction

Abstract [WH 4 (dpmp) 4 ] and [WH 4 (trifos)(PPh 3 )] complexes were used photochemically to reduce fixed molecular nitrogen. Tetrahydrofuran-cyclohexane (1: 1) acidified and non-acidified solutions under UV irradiation were examined.