Crystal structure and magnetic measurements of [Cr(en)3] [ZnCl4]Cl

The compound [Cr(en)₃][ZnCl₄]Cl has been synthesized by reaction of CrCl₃·6H₂O, Zn and [Cr(en)₃]₂(SO₄)₃ in HCl. Its molecular and crystalline structure was determined by X-ray diffraction methods, being monoclinic, P2₁/c, a=21.215(3), b=12.532(2), c=13.707(2) Å, β=95.21°, V= 3629(2) ų, D_x=1.738g cm⁻³, MW=474.9, Z= 8, F(000)=1928, λ(Mo Kα)=0.71069 Å, μ(Mo Kα)= 27.04 cm⁻¹, 288 K. No significant exchange interactions between Cr(III) cations in the crystalline lattice were found. Curie-Weiss behavior was found in the three directions tested (g₁=2.06±0.02,g₂= 2.08±0.02,g₃=2.09±0.01), T=1.2-1.4 K.     

Platinum(II) complexes of methyl-substituted xanthines: crystal structures of K[Pt(theobromine)Cl3]·H2O,trans-[ Pt(isocaffeine)2Cl2]·H2O and K(isocaffeinium)[PtCl4]·H2O

The preparations of Pt(theophylline)₂Cl₂, K[Pt- (theophylline)Cl₃], K[Pt(theobromine)Cl₃]·H₂O (1), trans-[Pt(isocaffeine)₂Cl₂]·H₂O (2), and K(isocaffeinium)[PtCl₄]·H₂O (3) are reported.Crystals of 1 are monoclinic P2₁/n with a=7.641- (2), b=11.873(3), c=15.868(4) Å, β=90.80(2)°, Z=4. The structure was refined on 1443 reflections to R=0.028. In the planar [Pt(theobromine)Cl₃]⁻ anion Pt-N(9)=2.016(6) Å, Pt-Cl=2.299(2), 2.289(2), and 2.303(2) Å. The imidazole ring is rotated away from the coordination plane by 79.8°. Symmetry related theobromine units pack parallel to each other with a mean inter-ring separation of 3.27 Å.Crystals of 2 are monoclinic P2₁/a with a=7.345- (2), b=20.021(5), c=8.031(2) Å, β=104.18(2)°, Z=2. The structure was refined on 1132 reflections to R=0.029. The Pt-N(7) distance is 2.003(3) Å and Pt-Cl=2.298(1) Å. The imidazole ring is rotated away from the PtCl₂N₂ plane by 76.8°. In this compound, the isocaffeine units do not stack, but form a staggered arrangement within the unit cell.Crystals of 3 are monoclinic P₁/c with a= 7.382- (1), b=14.014(4), c=15.757(4) », β=92.30(2)°, Z=4. The structure was refined on 2057 reflections to R=0.032. The isocaffeine is protonated at N(7). The Pt-Cl distances in the PtCl₄²⁻ anion range between 2.29–2.31 Å. The protonated isocaffeine cations and the PtCl₄²⁻ anions form a very nearly parallel infinitely stacked arrangement with minimum interlayer atomic separations of 3.37 and 3.44 Å.     

Crystal structure of a new form of copper(II)—inosine 5′-monophosphate—2,2′-dipyridylamine ternary complex

Two crystalline forms of the [Cu(II) (IMP) (DPA) (H₂O)]₂·nH₂O (IMP=inosine 5′-monophosphate, DPA=2,2′-dipyridylamine) complex were obtained from aqueous solution at pH=6.2. The crystals of the two forms belong to the monoclinic system, space group P2₁. The cell parameters are: a=9.445(2), b=33.902(4), c=7.802(2) Å, β=90.48(2)°, Z= 2, D_c=1.69g cm⁻³ and μ(Mo Kα) = 10.49cm⁻¹ (form α, n=4), and a=7.828(2), b=18.552(3), c=17.378(3) Å, β=91.16(2)°, Z=2, D_c=1.66 g cm⁻³, μ(Mo Kα) = 10.40 cm⁻¹ (form β, n=3.62). Bau and coworkers reported the preparation of form α by vapor diffusion of CH₃CN into aqueous solution containing Cu(NO₃)₂, Na₂IMP and DPA in a 1:1:1 molar ratio and the analysis of the compound by single crystal X-ray diffraction [1].Intensities for 3412 reflections were collected from a crystal of form β in the present work. Graphite-monochromatized Mo Kα radiation was employed. The structure was refined to final R and R_w values of 0.1000 and 0.1115 respectively. The dimeric units contain two copper ions in square-pyramidal coordination polyhedra. Each polyhedron consists of two nitrogen atoms of DPA, two oxygen atoms from two phosphate groups and a water molecule in the axial position. A statistical disorder was found in a nucleotide moiety of the dimer. Two sets of atomic positions corresponding to the purine system were refined with site occupation factors of 0.62(1) and 0.38(1) respectively. Also the ribose ring shows a disorder with two possible conformations. The puckering mode of the prevailing conformation is C(3′)-endo. In the other nucleotide molecule of the dimer the furanose puckering mode is C(3′)-endo. The rotation around the glycosyl linkages can be described as ‘anti’ in the structure of form β. The C(4)N(9)C(1′)O(4′) torsion angle values are −97(2) and −94(3)° for the disordered nucleotide molecule and +91(2)^o for the other nucleotide moiety. Strong intermolecular DPADPA and purine-purine stacking interactions stabilize the crystal lattice. The differences on the nucleotide conformation between the structure of form α and form β can probably be ascribed to differences in the hydrogen bonds and stacking interactions.     

Exchange rates of pyridine on ferro- and ferriprotoporphyrin (IX) dimethylester in chloroform.

Nuclear magnetic resonance line-widths data have been used to determine the rate of solvent exchange from the first coordination sphere of ferro-and ferriprotoporphyrin(IX) dimethylester (Fe-PPD) in pyridine/chloroform. The average values of kinetic parameters for pyridine (PY) exchange indicate an SN2 mechanism tor Fe(III)-PPD(ΔH^&;#; = 36 kJ · mol⁻¹ ; ΔS^&;#; = −53 J·mol⁻¹K⁻¹; T_M(298 K) = 0.07 msec) and an SNI mechanism for Fe(II)-PPD (ΔH^&;#; = 67 kJ·mol⁻¹; ΔS^&;#; = 42 J · mol⁻¹K⁻¹; T_M(298 K) = 0.06 msec). Parallel to the accelerated ligand exchange rate at rising temperatures a redistribution of the electrons causing a transition of the metal porphyrin from the low-spin state to the high-spin state is observed. Enthalpy and entropy of the thermodynamic equilibrium between low- and high-spin Fe-PPD have been determined from experimental values of the average magnetic moment. A mean lifetime of low-spin Fe(III)-PPD was estimated from line. widths changes (T_L→H(298 K)≈ 20 msec) and the corresponding activation parameters have been obtained (ΔH^&;#;_L→H(298 K) = 26 kJ · mol⁻¹; ΔS^&;#;_L→H(298K) = −125 J · mol⁻¹K⁻¹).     

New method for the determination of doxorubicin, 4′-epidoxorubicin and all known metabolites in cardiac tissue

4′-Epidoxorubicin, doxorubicin (internal standard) and eight metabolites were extracted from heart tissue homogenate by a mixture of tetrahydrofuran-water (1:2, v/v) and purified by C₁₈ Sep-Pak cartridges. The buffer used to prepare the homogenate contained glucaric acid-1,4-lactone and glucose, to prevent decomposition of the 4′ -epidoxorubicin glucuronides. Anthracyclines were separated by high-performance liquid chromatography within 14 min and detected by fluorescence. Recoveries ranged from 49 to 75%. The detection limits of the individual anthracyclines ranged from 0.5·10⁻¹¹ to 2.5·10⁻¹¹ mol/g wet weight. The peak-height ratios of the fluorescence intensities of the anthracyclines versus doxorubicin were linear from 2.5·10⁻¹¹ to 250·10⁻¹¹ mol/g wet weight. Within- and between-day precisions of the assay varied between the anthracyclines and were in the ranges 3–12% (n=6) and 2–11% (n=6), respectively.     

Preparation and properties of hydrated uranium(III) complex chlorides. Part I. Uranium trichloride heptahydrate

The synthesis of uranium trichloride heptahydrate together with some of its structural, spectroscopic and magnetic properties is reported. The compound possesses the triclinic lattice of LaCl₃·7H₂O (space group P$\text{1}$). Controlled vacuum thermal dehydration of the substance enabled the preparation of the anhydrous trichloride in gram quantities. Magnetic susceptibilities of polycrystalline samples were measured by the Faraday method in the 6.5–295 K range. The uranium trichloride heptahydrate follows in this region the Curie-Weiss law with C = 1.0839 emu K mol^?1 and θ = ?32.7 K.     

Thermodynamics of hexokinase-catalyzed reactions.

The enthalpies of the hexokinase-catalyzed phosphorylation or glucose, mannose, and fructose by ATP to the respective hexose 6-phosphates have been measured calorimetrically in TRIS/TRIS HCl buffer at 25.0, 28.5, and 32.0°C. The effects on the measured enthalpy of the glucose/hexokinase reaction due to variation of pH (over the range 6.7 to 9.0) and ionic strength (over the range 0.02 to 0.25) have been examined. Correction for enthalpy of buffer protonation leads to δH^o and δC_p^o values for the processes: eq-D-hexose + ATP⁴⁻ = eq-D-hexose 6-phosphate²⁻ + ADP³⁻+ H⁺. Results are δH^o = −23.8 ± 0.7 kJ · mol⁻¹ and δC_p^o = −156 ± 280 J·mol⁻¹·K⁻¹ for glucose. δH^o = −21.9 ± 0.7 kJ·mol⁻¹ and δC_p^o = 10 ± 140 J·mol⁻¹·K⁻¹ for mannose, and δH^o = −15.0 ± 0.9 kJ·mol⁻¹ and δC_p^o = −41 ± 160 J·mol⁻¹·K⁻¹ for fructose. Combination of these measured enthalpies with Gibbs energy data for hydrolysis of ATP⁴⁻ and that for the hexose 6-phosphates lead to δS^o values for the above hexokinase-catalyzed reactions.     

Algal biomass production,N uptake and N2 fixation in a synthetic medium

An experiment was conducted in the growth chamber to quantify the biomass production, N removal and N₂ fixation from a synthetic medium by Chlamydomonas reinhardtii and Anabaena flos-aquae. Nitrogen was supplied at a concentration of 100 mg liter⁻¹ of NO₃⁻−¹⁵N and NH₄⁺−¹⁵ (3·5 atom %), respectively. After 21 days Chlamydomonas reinhardtii removed an average of 83·8 and 78·7 mg N liter⁻¹ as NO₃⁻ and NH₄⁺, respectively. Averages of 0·89 and 0·71 g liter⁻¹ (first batch), 1·63 and 0·95 g liter⁻ (second batch) algal biomass were collected from NO₃⁻ and NH₄⁺ media, respectively. Uptake rates of 0·11 mg ¹⁵N g⁻¹ algae day⁻¹ from NO₃⁻ medium and 0·10 mg ¹⁵N g⁻¹ algae day⁻¹ from NH₄⁺ medium were calculated. Algal cells grown in NO₃⁻ and NH₄⁺ medium contained 71 and 65 g N kg⁻¹ (first batch), 39 and 58 g N kg⁻¹ (second batch), respectively. Anabaena flos-aquae produced averages of 0·58 and 0·46 g liter⁻¹ (first batch), 0·55 and 0·48 g liter⁻¹ (second batch) after 14 days of growth from NO₃⁻ and NH₄⁺ media, respectively. Blue-green algal biomass contained higher N (81–98 g kg⁻¹) than green algae. Isotope dilution method for determining N₂ fixation indicated that 55% and 77% of total N of blue-green algae grown in NO₃⁻ and NH₄⁺ media, respectively, was derived from the atmosphere.     

The preparation and structure of tris[bis(pyrazolyl)borate]indium(III)

The compound In[(pz)₂BH₂]₃ (pz = 1-pyrazolyl, C₃H₃N₂⁻) was prepared from In(NO³)₃ and K[(pz)₂-BH₂] in water, and characterised by spectroscopic and X-ray methods. Crystals are orthorhombic,Pna2₁,a = 20.279(4),b = 8.884(2),c = 13.411(2)Å;R = 0.0285. Individual molecules contain a near-regular six-coordinate indium atom with In–N (av.) 2.241(5)Å. The pyrazolyl borate ligands are puckered, with dihedral angles between the two rings of each ligand in the range 133–144°.     

The synthesis and reaction kinetics of some Co(IIl) and Cr(III) chloro complexes of 1,4,8-Triazaoctane (2,3-tri) and the isolation of chiral trans-dichloro [CoCl2(NH3)(2,3-tri)] ClO4

The reaction of 2,3-tri with CrCl₃·6H₂O₁, dehydrated in boiling DMF, results in the formation of mer-CrCl₃(2,3-tri) and anation of hydrolysed solutions of mer-MCl₃(2,3,-tri) (M=Co, Cr) with 6 M HCl containing HClO₄, forms trans-dichloro- mer-[MCl₂(2,3-tri)(OH₂)]ClO₄·H₂O (M=Cr, Co; I, II). trans-Dinitro-mer-[Co(NO₂)₂(NH₃)(2,3-tri)] ClO₄ crystallises from the reaction between mer-Co(NO₂)₃(2,3-tri) and aqueous 7 M ammonia, on addition of NaClO₄·H₂O, and trans-dichloro-mer-[CoCl₂(NH₃)(2,3-tri)]ClO₄ (III) can be isolated by treatment of the dinitro with 12 M HCl. Reaction of mer-CoCl₃(2,3-tri) with C₂O₄₂⁻, followed by addition of aqueous NH₃ and NaClO₄·H₂O results in the isolation of racemic mer-[Co(ox)(NH₃)(2,3-tri)]ClO₄· H₂O. This complex was resolved into its enantiomeric forms and treatment of these with SOCl₂/MeOH/ HClO₄ gave the chiral forms of trans-dichloro-mer- [CoCl₂(NH₃)(2,3-tri)]ClO₄ (R or S at the see-NH center). The rates of loss of the first chloro ligand from these dichloro complexes have been measured spectrophotometrically in 0.1 M HNO₃ over a 15 K temperature range to give the following kinetic parameters; (I) k_H(298)=7.25 × 10⁻⁵ s⁻¹, E_a=78.5 kJ mol⁻¹, δS₂₉₈^#=₋69 J K⁻¹ mol⁻¹; (II) k_H(298)=4.00 × 10⁻³ s⁻¹, E_a=89.9, δS₂₉₈^#= +87.5; (III) k_H(298)=3.09 × 10⁻⁴ s⁻¹, E_a=103, δS₂₉₈^#=+27. Treatment of the dichloro cations with Hg²⁺/HNO₃ results in the generation of mer- M(2,3-tri)(OH₂)₃³⁺ (M=Cr, Co; IV, V) and trans- diaqua-mer-Co(NH₃)(2,3-tri)(OH₂)₂³⁺ (VI). The Co(III) cations isomerise to the fac configuration with (V) K_isom(298) μ=1.0 M)=2.97 × 10⁻⁵ s⁻¹, E_a=115, δS₂₉₈^#=+46. (VI) K_isom(298) (μ=1.0 M)=4.13 × 10⁻⁵ s⁻¹, E_a=113, δS₂₉₈^#=+52.     

Thermodynamics and coordination characteristics of the hydronium-uranium(VI)-dicyclohexano-24-crown-8 extraction complex

The extraction equilibrium of the hydronium-uranium(VI)-dicyclohexano-24-crown-8 complex was carried out in the crown ether1,2-dichloroethaneHCl aqueous solution system at different temperatures. The extraction complex has the overall composition (L)₂·(H₃O⁺·χH₂O)₂·UO₂Cl₄²⁻ (L = dicyclohexano-24-crown-8). The values of the extraction equilibrium constants (K_ex) increase steadily with a decrease in temperature: 13.5 (298 K), 7.96 (301 K), 4.20 (303 K) and 2.07 (305 K). A plot of log K_ex against 1/T shows a straight line. The value of the enthalpy change, ΔH°, was calculated from the slope and equals −212 kJ mol⁻¹. The value of the entropy change, ΔS°, was calculated from ΔH° and K_ex and equals −690 J K⁻¹ mol⁻¹, whereas ΔG° = −6.45 kJ mol⁻¹. Comparing these thermodynamic parameters with those of the dicyclohexano-18-crown-6 isomer A [1] (ΔS° = −314 J K⁻¹ mol⁻¹, ΔH° = −101 kJ mol⁻¹ and ΔG° = −8.37 kJ mol⁻¹), it can be seen that ΔH° and ΔS° are more negative for the former than for the latter, and both are enthalpy-stabilized complexes. The molecular structure of the complex has the feature that there are two H₅O₂⁺ ions in it, in contrast to the H₃O⁺ ions in the dicyclohexano-18-crown-6 isomer A complex [1]. Each of the H₅O₂⁺ ions is held in the crown ether cavity by four hydrogen bonds. The H₅O₂⁺ ion has a central bond. The uranium atom forms UO₂Cl₄²⁻ as a counterion away from the crown ether. The formation of this complex is in good agreement with more negative entropy change and less negative free energy change, as mentioned above.     

The molecular structure and magnetic properties of the dimeric N,N′-ethylenebis(salicylamine)Fe(II)-μ-methoxo-N,N′-ethylene(o-hydroxylphenylglycine)salicylamine Fe(III): A complex with a μ-monodentate acetato bridge

We have prepared and characterized a dimeric complex of the formula Fe₂L(OCH₃)L′·solvent where L = N,N′-ethylenebis(salicylamine) and L′ = N,N′-ethylene(o-hydroxylphenylglycine)salicylamine. Crystals of the methanol solvate were found to be orthorhombic, space group P2nb, with a = 13.748 (5), b = 22.426(9), c = 11.762(6) Å and d_calc = 1.41 g/cm³. Least squares refinement of 966 reflections gave a final R factor of 0.066. The structure shows that the two iron atoms are coordinated to two different ligands and are bridged by a methoxide ion and a μ-monodentate acetate oxygen from the pendant arm of L′. The magnetic susceptibility was measured over the range 2–300 K and gave a spin coupling constant J = −8.3 cm⁻¹. The significance of acetate bridges to the exchange coupling pathway is discussed.     

Influence of the concentrations of d-xylose and yeast extract on ethanol production by Pachysolen tannophilus

To determine the most favorable conditions for the production of ethanol by Pachysolen tannophilus, this yeast was grown in batch cultures with various initial concentrations of two of the constituents of the culture medium: d-xylose (s_o), ranging from 1 g·l⁻¹ to 200 g·l⁻¹, and yeast extract (l_o), ranging from 0 g·l⁻¹ to 8 g·l⁻¹. The most favorable conditions proved to be initial concentrations of S_o=25 g·l⁻¹ and l_o=4 g·l⁻¹, which gave a maximum specific growth rate of 0.26 h⁻¹, biomass productivity of 0.023 g·l⁻¹·h⁻¹, overall biomass yield of 0.094 g·g⁻¹, specific xylose-uptake rate (q_s) of 0.3 g·g⁻¹·h⁻¹ (for t=50 h), specific ethanol-production rate (q_E) of 0.065 g·g⁻¹·h⁻¹ and overall ethanol yield of 0.34 g·g⁻¹; q_s values decreased after the exponential growth phase while q_E remained practically constant.     

Activation parameters for directly determined first order rate constants for outer sphere electron transfer reactions,and crystal structure of a pertinent pentaammine of CoIII

The outer sphere reductions of Co(NH₃)₅B³⁺ by Fe(CN)₅A³⁻ have been studied. The observed pseudo first order rate constants (Co complex in excess) obey the dependence k_obs=K_osk_et[Co]/(1 +K_os[Co]), as expected for outer sphere electron transfer reactions. Values of the fundamental electron transfer rate constants k_et have been determined, along with the equilibrium constant K_os for a range of reactions in which A and B are pyridyl ligands of different sizes. The first order electron transfer rate constants vary in a manner that is consistcnt with adiabatic electron transfer. The outer sphere ion pairing equilibrium constants K_os have been calculated: K_os=8.6 ± 0.1 × 10² M⁻¹ when A and B=pyridine; K_os=1.07 ± 0.09 × 10³ M⁻¹ where A=pyridine, B=1-phenyl-3-(4-pyridyl)propane; K_os=1.86 ± 0.11 × 10³ M⁻¹ when A=4,4′-bipyridine, B=pyridine; K_os=1.27 ± 0.08 × 10³ M⁻¹ when A=4,4′-bipyridine, B=4-phenylpyridine. Distances of closest approach between the metal centers in the reactive ion pairs are compared, and it is concluded that there is a common mechanism, in which the ammonia side of the cobalt complex approaches the cyano side of the iron complex in each reactive ion pair.The distance of closest approach between the two metal centers (a) was calculated from the experimental values for the ion pairing equilibrium constant K_os at 25 °C: 5.2 Å when A=4,4′-bipyridine, B=pyridine; 5.4 Å when A=4,4′-bipyridine, B=4-phenylpyridine; 5.5 Å when A=pyridine, B=1-phenyl-3-(4-pyridyl)propane; 5.7 Å when A=B=pyridine. These relatively short metal-metal distances, when compared to the X-ray structure of the compound [Co(NH₃)₅(4-phenylpyridine)]₂[S₂O₆]₃· 4H₂O, do not support an ion pair orientation in which the two substituted pyridine ligands A and B are oriented toward each other. [P2₁/c,a=7.399(3), b=22.355(10), c=13.776(4) Å, β=92.02(3)°, R=0.070.] The crystallographic results show that if the two pseudo-octahedral coordination spheres are oriented in the reactive ion pair so that an ammonia face of the cobalt complex is at hydrogen bonding distance from a cyano face on the iron complex, the metal-metal distance is 5.3 Å, a distance which is in agreement with the kinetic results.     

Preparation,properties and crystal structures of nickel(II) complexes with acyclic schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane or 3,3′-diamino-N-methyl-dipropylamine

Nickel(II) complexes with the compartmental Schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane (H₂L¹) or 3,3′-diamino-N-methyl-dipropylamine (H₂L²) were synthesized, and the crystal structures of [Ni(L¹)- (py)₂] and [Ni(L²)(dmf)]·H₂0 were determined by X-ray crystallography.Ni(L¹)(py)₂ is monoclinic, space group C2/c, with a= 18.457(6), b = 11.116(7), c= 16.098(6) Å, and β = 115.79(5)°; D_c = 1.49 g cm⁻³ for Z = 4. The structure was refined to the final R of 6.9%. The molecule has C₂ symmetry. The nickel atom is six-coordinated octahedral. Selected bond lengths are: NiO 2.04(1) Å, NiN (L¹) 2.08(1) Å, NiN(py) 2.17(1) Å.[Ni(L²)(dmf)]·H₂O is monoclinic, space group P2₁/n, with a = 17.329(6), b = 13.322(7), c = 12.476(7) Å and β = 95.43(5)°; D_c = 1.45 g cm⁻³ for Z = 4. The structure was refined to the final R of 5.1%. The nickel atom is bonded in the octahedral geometry to the bianionic pentadentate ligand L² and to one molecule of dimethylformamide. Selected bond lengths are: NiO (charged) 2.063(3) Å (mean value), NiO (neutral) 2.120(3) Å, NiN (planar) 2.050(3) Å (mean value), NiN (tetrahedral) 2.177(3) Å.     

Nucleophilic attack at the carbon atom of a dithiocarbene ligand by coordinated carbon disulphide: The molecular structure of [(dppe)IPt(μ-C(S)SC(SMe)2)Pt(dppe)]+I− (dppe=1,2-bis(diphenylphosphino)ethane)

Reaction of the complex [Pt(η²-CS₂)(dppe)] [dppe=1,2-bis(diphenylphosphino)ethane] with excess methyl iodide results in the formation in high yield of the dimeric complex [(dppe)IPt(μ-C(S)SC(SMe)₂)Pt(dppe)]⁺I⁻·C₇H₈·Et₂O, the crystal structure of which has been determined. Crystals of the complex are monoclinic, space group P2₁/c, with Z=4, in a unit cell with lattice parameters a=21.082(4), b=17.304(3), c=21.423(3) Å, and β=116.62(1)°. The structure has been refined to R₁=0.054 (R₂=0.059) for 4512 unique data and 333 variables. The complex consists of two distorted square-planar Pt fragments which are held together by a novel bridging CS₂C(SMe)₂ group. The complex has been independently prepared by the reaction of [Pt(η²-CS₂)(dppe)] with the carbene complex [Pt(I)(dppe){C(SMe)₂}]⁺I⁻, and has been further characterized by elemental analysis, ¹H, ³¹P{¹H} NMR, IR spectroscopy, and conductivity measurements.     

Dioxo-, oxothio- and dithio-tungsten(VI) and tungsten(V) complexes of the ligand N,N′-Dimethyl-N,N′-bis(2-mercaptophenyl)ethylenediamine

Synthesis of complexes cis,cis-W^VOXL (X=Cl, NCS), cis,trans-W^VOXL (X=Cl, OPh, SPh) and cis,trans-W^VIE₂L (E₂=O₂, OS, S₂) of the title ligand LH₂ are reported. cis,cis-W^VOCIL crystallises in space group P2₁/c with a=13.6541(9) Å, b=7.1555(11) Å, c=18.198(2) Å, β=95.294(6)°, V=1770.4(3) ų and Z=4 while the cis,trans isomer crystallises in space group P2₁/n with a=10.361(3) Å, b=14.141(4) Å, c=12.213(5) Å, β=102.56(3)°, V=1747(2) ų and Z=4. cis,trans-W^VIS₂L crystallises in space group P2₁/n with a=10.645(2) Å, b=13.929(2) Å, c=12.189(2) Å, β=103.14(2)°, V=1760(1) ų and Z=4. A short CH₃···Cl distance of 3.067(7) Å and an acute OWCl angle of 94.1(2)° are seen in cis,cis-W^VOClL, which converts to the cis,trans form on heating in MeCN. The latter isomer features a CH₃···Cl distance of 3.38(2) Å and an OWCl angle of 105.1(8)°. Electrochemical and EPR data are reported. In particular, cis,trans-W^VIE₂L may be reduced to [W^VE₂L]^–. EPR properties of these anions and those of complexes W^VOXL are discussed in the context of W^V centres in tungsten enzymes.