Showing papers in "Journal of The Chemical Society-dalton Transactions in 1985"

SUPERQUAD: an improved general program for computation of formation constants from potentiometric data

Abstract: A new computer program has been developed in which formation constants are determined by minimisation of an error-square sum based on measured electrode potentials. The program also permits refinement of any reactant concentration or standard electrode potential. The refinement is incorporated into a new procedure which can be used for model selection.

Hydrogen generation by hydrolysis of sodium tetrahydroborate: effects of acids and transition metals and their salts

Abstract: A study was undertaken in order to investigate the potential of NaBH4 as a precursor fuel source for a hydrogen–oxygen (air) fuel cell. At appropriate initial acid concentration, hydrolysis of NaBH4 is nearly 80% complete in 2.5 min, and nearly 90% complete in 10 min at 21.7 °C. Transition metals and their salts also accelerate hydrolysis of NaBH4. The effect of transition metals is characterized by zero-order kinetics.

Kinetics and mechanism of ortho-palladation of ring-substituted NN-dimethylbenzylamines

Abstract: Addition of excess of NN-dimethylbenzylamine to a chloroform solution of [Pd3(O2CMe)6] leads to instantaneous depolymerisation of the trimer giving the monomer trans-[Pd(O2CMe)2(PhCH2NMe2)2]. Reversible dissociation of the amine from the latter affords a pseudo-three-co-ordinate 14-electron intermediate [Pd(O2CMe)2(PhCH2NMe2)] which undergoes subsequent rate-limiting ortho-palladation to form the cyclopalladated acetate-bridged dimer [{Pd(O2CMe)(C6H4CH2NMe2)}2]. The rate-limiting step is electrophilic in character; the slope of the corresponding Hammett plot for differently ring-substituted NN-dimethylbenzylamines is –1.6. The kinetic isotope effect, kH/kD, for PhCH2NMe2 is 2.2 ± 0.2. The activation entropy for the rate-limiting step is very negative, ca. –250 J K–1 mol–1 for PhCH2NMe2, suggesting a highly ordered tight transition state. This dissociative path is a factor of ca. 100 faster than a parallel one, involving the 16-electron monomer trans-[Pd(O2CMe)2(PhCH2NMe2)2] but without loss of the amine. Ortho-palladation is not rate-limiting in acetic acid solvent, where slow cleavage of acetate bridges in polynuclear palladium species occurs, affording a vacant co-ordination site for subsequent rapid ortho-palladation. A comparison of intra- and inter-molecular activations of carbon-hydrogen bonds in arenes by palladium(II) in terms of ‘effective molarities’ shows that the ratio kintra/kinter is not less than 3.6 × 102 mol dm–3.

Studies on singlet oxygen in aqueous solution. Part 3. The decomposition of peroxy-acids

Abstract: The decompositions of peroxyacetic acid, peroxymonosulphuric acid (Caro's acid), and mono-peroxyphthalic acid have been studied in aqueous solution at pH values close to the pKa of the acids. When precautions are taken to eliminate metal-ion catalysis, essentially quantitative yields of 1O2, are obtained, as determined using the caesium salt of anthracene-9,10-bis(ethanesulphonate)(aes) as a trap for 1O2. With peroxypivalic acid the maximum yield of 1O2, was only ca. 80%, but in this case non-1O2 attack on the aes also occurred. Negligible amounts of 1O2 are formed when H2O2 reacts with monoperoxyphthalate or peroxyacetate anions at pH ca. 10.7 under normal ‘clean’ conditions. However, the presence of the chelating agent diethylenetriamine-NNN′N″N″-penta-(methylphosphonic acid) produces a dramatic decrease in the reaction rates. It is concluded that the reactions of H2O2 with peroxy-acid anions are extremely sensitive to catalysis, probably by transition-metal ions.

On the possibility of determining the thermodynamic parameters for the formation of weak complexes using a simple model for the dependence on ionic strength of activity coefficients: Na+, K+, and Ca2+ complexes of low molecular weight ligands in aqueous solution

Abstract: Alkali-metal and calcium(II) complexes of monocarboxylate A–(acetate and salicylate), dicarboxylate A2–(malonate, maleate, succinate, malate, tartrate, phthalate, and oxydiacetate), or amino acid HA (glycine or L-histidine) ligands have been studied potentiometrically, using a glasssaturated calomel electrode, at different temperatures and ionic strengths. The monocarboxylate ligands form [MA] and the dicarboxylates [MA] and [M(HA)] species (charges omitted) with both alkali metals and calcium. Glycine and L-histidine form [MA]+ and [M(HA)]2+{and [M(H2A)]3+ for L-histidine} complexes with Ca2+, whilst alkali metals form only [M(HA)]+ with glycine. Some interesting regularities in the formation constants are pointed out. From the dependence on temperature of formation constants, values of ΔH⊖ and ΔS⊖ have been determined. The function log β=f(I) has been carefully studied in the range 0.02 ⩽I⩽ 1 mol dm–3. The reliability of a new model for the dependence on ionic strength of formation constants (when dealing with weak complexes it is in practice impossible to use the constant ionic medium method) is widely discussed. Two methods of calculation are described and the more general method has been checked by simulated curves.

Unidentate versus symmetrically and unsymmetrically bidentate nitrate co-ordination in pyrazole-containing chelates. The crystal and molecular structures of (nitrato-O)[tris(3,5-dimethylpyrazol-1-ylmethyl)amine]copper(II) nitrate, (nitrato-O,O′)[tris(3,5-dimethylpyrazol-1-ylmethyl)amine]nickel(II) nitrate, and (nitrato-O)(nitrato-O,O′)[tris(3,5-dimethylpyrazol-1-ylmethyl)amine]cadmium(II)

Abstract: The crystal structures of three compounds ML(NO3)2 are described, where M = Cu, Ni, or Cd and L is the tripodal quadridentate ligand tris(3,5-dimethylpyrazol-1-ylmethyl)amine. The structure of the copper compound can best be described as tetragonally distorted trigonal bipyramidal. As in the other compounds, the ligand L utilizes each of its four potential donor sites. One nitrate ion is unidentate, yielding a CuN4O chromophore. In the nickel compound a nitrate ion is symmetrically bidentate, yielding a distorted octahedral cis-NiN4O2 chromophore. In the cadmium compound one of the nitrate ions is unsymmetrically bidentate, the other symmetrically bidentate, yielding a CdN4O3 chromophore. The structure is best described as distorted bicapped octahedral. The nitrate co-ordination modes were investigated using several spectroscopic techniques. Criteria to differentiate between the unidentate, unsymmetrically bidentate, and symmetrically bidentate modes are presented. In this type of compound discrimination between the co-ordination modes solely on the basis of spectroscopic behaviour appears not to be possible. Slight changes in the i.r. spectra of CuL(NO3)2, and of the analogous cobalt and zinc compounds, upon applying pressure can be understood in terms of changes in the nitrate co-ordination.

Molecular structure and solid-state properties of the two-dimensional conducting mixed-valence complex [NBu4]0.29[Ni(dmit)2] and the neutral [Ni(dmit)2](H2dmit = 4,5-dimercapto-1,3-dithiole-2-thione); members of an electron-transfer series

Abstract: Single crystals of the mixed-valence radical salt [NBu4]2[Ni(dmit)2]7·2CH3CN {ignoring the solvent molecules, the formula may be written as [NBu4]0.29[Ni(dmit)2]; H2dmit = 4,5-dimercapto-1,3-dithiole-2-thione} were obtained by galvanostatid oxidation of [NBu4][Ni(dmit)2] in acetonitrile. The crystal structure of this compound has been determined at 118 K by X-ray diffraction studies: crystals are triclinic, space group P1 or P(assumed), with Z= 2 and unit-cell dimensions a= 13.425(2), b= 22.791(3), c= 24.183(4)A, α= 108.49(1), β= 103.02(1), and γ= 89.82(1)°. The structure was solved by direct methods and refined by least squares to R= 0.038 for 7 170 unique, observed, diffractometer data. It consists of thick layers of stacked Ni(dmit)2 entities parallel to (001), and separated by sheets of [NBu4]+ cations and CH3CN molecules. Strong π interactions within a stack are evidenced by the short stacking distances (3.48–3.57 A). There is also an extensive interleaving of the Ni(dmit)2 which involves close S ⋯ S interstack contacts. As a result, this structural arrangement is nearly two-dimensional. Conductivity measurements, carried out using a four-probe technique, show a high (σ= 1–10 Ω–1 cm–1 at 300 K) thermally activated (Ea= 0.1–0.02 eV) conductivity. Measurements of the conductivity along the b and a axes, using the Montgomery method, show a low anisotropy (σb/σaca. 1), consistent with the two-dimensional nature of this compound. The related neutral member of the [Ni(dmit)2]n– electron-transfer series (n= 0) has been isolated for the first time and its crystal structure determined: crystals are monoclinic, space group P21/a, with Z= 2, a= 17.108(9), b= 5.302(4), c= 7.720(4)A, and β= 77.09(4)°. The structure was solved by direct methods and refined by least squares to R= 0.041 for 772 unique, observed, diffractometer data. The structure of this semi-conducting compound consists of regular stacks of Ni(dmit)2 along the [010] direction with short interstack S ⋯ S distances.

Lewis-base adducts of Group 1B metal(I) compounds. Part 16. Synthesis, structure, and solid-state phosphorus-31 nuclear magnetic resonance spectra of some novel [Cu4X4L4](X = halogen, L = N, P base)‘cubane’ clusters

Abstract: Recrystallization of [Cu4l4(PPh3)4] from toluene has yielded a new polymorph of that compound, (1), which has been shown by single-crystal X-ray diffraction analysis to have a tetrametallic ‘cubane’ structure rather than the expected ‘step’ structure. Crystals are monoclinic, space group P21/n, with a= 19.47(1), b= 26.94(1), c= 13.528(5)A, β= 98.98(4)°, Z= 4 tetramers; R was 0.06 for No= 3 681. Cu–I distances range from 2.653(3) to 2.732(3)A, with Cu ⋯ Cu 2.874(5)–3.164(4) and I ⋯ I 4.234(2)–4.496(3)A. All adducts of stoicheiometry [M4X4(PPh3)4](M = Cu or Ag; X = Cl, Br, or I) have now been synthesized and structurally characterized in a cubane configuration. Recrystallization of copper(I) chloride and bromide from triethylamine also yields tetrameric cubane 1 : 1 adducts [X = Cl (2) or Br (3)], as does the reaction of copper(I) chloride with the very bulky ligand 2-[bis(trimethylsilyl)methyl]pyridine, to give [Cu4Cl4(tmspy)4](4). These three complexes have also been crystallographically characterized, (2) and (4) being the first reported cubane type tetramers for the copper(I) chloride–nitrogen base system. Complexes (2) and (3) are isostructural with their triethylarsine and -phosphine counterparts, being cubic, space group I3m, with a= 12.162(5)A in (2) and 12.368(3)A in (3); Z= 2 tetramers. Cu–Cl,Br distances are 2.441(4) and 2.537(3)A respectively. For (4), the crystals are tetragonal, space group I41/a, with a= 18.620(4), c= 20.079(5)A, Z= 4 tetramers. Although the Cu4Cl4 cubane core of the molecule has crystallographically imposed symmetry, the geometry is very unsymmetrical as a consequence of the ligand bulk, with Cu–Cl 2.225(2)–2.636(2), Cu ⋯ Cu 2.960(2)–3.194(2), and Cl ⋯ Cl 3.838(3)–3.866(3)A. Residuals R for (2), (3), (4) were 0.040, 0.038, and 0.040 respectively for No= 136, 136, and 1 008 ‘observed’ reflections. The solid-state 31P n.m.r. spectra of the triphenylphosphine cubane clusters show significant differences to those with a ‘step’ geometry; these differences are related to the crystallographic environment of the phosphorus nuclei.

Heteropolytungstates as catalysts for the photochemical reduction of oxygen and water

Abstract: A series of polytungstate anions [XW12O40]n–(X = P, Si, Fe, Co, or H2; n= 3,4,5,6, and 6 respectively), spanning a range of reduction potentials, have been studied as sensitizers for the photoreduction of water and O2. [SiW12O40]4– was the most efficient sensitizer for H2 evolution in the presence of colloidal platinum. Saturation kinetics were found with respect to the concentrations of Pt,[SiW12O40]4–, and CH3OH as predicted by a simple kinetic scheme. The maximum rate depended on competition between the natural decay of the excited polyanion and quenching by alcohol. Electron transfer from photoreduced polyanions to O2 was also investigated by flash photolysis. Rate constants depended on the reduction potential of the polyanion and increased by a factor of 3 700 on going from [PW12O40]3– to [FeW12O40]5–, in line with the Marcus equation for adiabatic electron-transfer reactions.

Magnetic and spectroscopic properties of some heterotrinuclear basic acetates of chromium(III), iron(III), and divalent metal ions

Abstract: Reaction of Fe3+, M2+, and acetate ions in aqueous solution gives [FeIII2MIIO(MeCO2)6(H2O)3]·3H2O (M = Mg, Mn, Co, Ni, or Zn), which on crystallisation from pyridine (py) is converted into [FeIII2MIIO(MeCO2)6(py)3]. Reaction of chromium(II) acetate with metal(II) acetate in pyridine in the presence of air gives [CrIII2MIIO(MeCO2)6(py)3](M = Mg, Co, or Ni), and with [FeIII2MIIO-(MeCO2)6(py)3] in pyridine inthe absence of air gives [CrIIIFeIIIMnIIO(MeCO2)6(py)3](M = Mn or Fe) and [CrIII2FeIIIO(MeCO2)6(py)3]. The compounds with co-ordinated pyridine have been examined crystallographically and magnetically. The Cr2Mg, Cr2Ni, Fe2Ni, and CrFeNi compounds crystallise in the monoclinic system, space group Cc or C2/c, Z= 4, but the other seven compounds are rhombohedral and isomorphous with [M3O(MeCO2)6(py)3]·py (M = Mn or Fe), indicating that the three metal atoms are crystallographically equivalent as a result of disorder in the molecular orientation. Powder magnetic susceptibilities for the Cr2Co and Cr2Ni compounds(4.2–60 K), for the Fe2Mn and Fe2Ni compounds (4.2–295 K), and for the Fe2Ni(aquo) and Fe2Mg compounds (80–295 K) have been fitted by use of an exchange Hamiltonian to yield values of the exchange parameters J for the Cr–Cr, Fe–Fe, Cr–Ni, Fe–Ni, and Fe–Mn interactions, which are discussed in terms of superexchange mechanisms. The values of JFeFe in the Fe2Mg, Fe2Mn, and Fe2Ni compounds and of JCrCr in the Cr2Co and Cr2Ni compounds are approximately twice their values in the cations [MIII3O(MeCO2)6(H2O)3]+(M = Cr or Fe), indicating that the µ3-O atom provides the main super-exchange pathway. Diffuse-reflectance and solution spectra (6 000–40 000 cm–1) of the compounds have been recorded at room temperature and are discussed in terms of the ligand-field model; a band in the spectra of the FeIII2FeII and CrIIIFeIIIFeIII compounds at ca. 7 000 cm–1 is assigned to intervalence transfer. The room-temperature spectra of [M3O(MeCO2)6L3]Cl (M3= CrIII3, CrIII2FeIII, CrIIIFeIII2 or FeIII3; L = H2O or py) have also been obtained, and intense absorption bands at ca. 19 000 and 26 000 cm–1 are tentatively assigned to simultaneous (Cr3+, Fe3+) double excitations.

Preparation and characterisation of 2,2′-bipyridine-4,4′-disulphonic and -5-sulphonic acids and their ruthenium(II) complexes. Excited-state properties and excited-state electron-transfer reactions of ruthenium(II) complexes containing 2,2′-bipyridine-4,4′-disulphonic acid or 2,2′-bipyridine-4,4′ dicarboxylic acid

Abstract: We report the syntheses of 2,2′-bipyridine-4,4′-disulphonic acid (H2bp-4,4′-ds) and 2,2′-bipyridine-5-sulphonic acid (Hbp-5-s), and several ruthenium(II) complexes derived therefrom, including [Ru(bp-4,4′-ds)3]4–,[Ru(bipy)(bp-4,4′-ds)2]2–(bipy = 2,2′-bipyridine), [Ru(bipy)2(bp-4,4′-ds)], and [Ru(bp-5-s)3]– and their 2,2′-bipyridine-4,4′-dicarboxylic acid (H2bpdc) analogues, viz. [Ru(bpdc)3]4–, [Ru(bipy)(bpdc)2]2–, and [Ru(bipy)2(bpdc)]. Some novel thioalkyl derivatives of 2,2′- bipyridine, including 4,4′-di(methylthio)-2,2′-bipyridine, 4,4′-di(ethylthio)-2,2′-bipyridine, and 4,4′,6,6′-tetra(methylthio)-2,2′-bipyridine, were also prepared and characterised during the course of this investigation. The luminescent states of the complexes [Ru(bp-4,4′-ds)3]4–,[Ru(bipy)(bp-4,4′ds)2]2–, [Ru(bpdc)3]4–, [Ru(bipy)(bpdc)2]2–, and [Ru(bipy)2(bpdc)] were studied using variabletemperature lifetime measurements. Studies of the quenching of {[Ru(bipy)3]2+}*, {[Ru(bipy)2(bpdc)]}*, {[Ru(bipy)(bp-4,4′-ds)2]2–}*, and {[Ru(bp-4,4′-ds)3]4–}* by 1,1′-dimethyl-4,4′-bipyridinium bromide (methyl viologen) in aqueous solution as a function of ionic strength have demonstrated that the effects of charge in these electron-transfer reactions can be understood in terms of conventional theories of ionic reactions whilst, at the same time, confirming the effective charges of the ruthenium(II) complex ions. The rate constants for the quenching of {[Ru(bp-4,4′-ds)3]4–}* and {[Ru(bipy)(bp-4,4′-ds)2]2–}* by copper(II) ions in neutral aqueous solution show unusual (non-Arrhenius) temperature dependences. A novel kinetic scheme involving parallel innerand outer-sphere quenching mechanisms has been proposed to account for the observed behaviour. The luminiscence decay of {[Ru(bipy)2(bpdc)]}* in the presence of aqueous copper(II) ions at pH 3.5 is non-exponential. This is interpreted in terms of a combination of static and dynamic quenching effects.

Synthesis and properties of the divalent 1,2-bis(dimethylphosphino)ethane (dmpe) complexes MCl2(dmpe)2 and MMe2(dmpe)2 (M=Ti, V, Cr, Mn, or Fe). X-ray crystal structures of MCl2(dmpe)2 (M=Ti, V, or Cr), MnBr2(dmpe)2, TiMe1.3Cl0.7(dmpe)2, and CrMe2(dmpe)2

Abstract: The reaction of transition-metal dichlorides with 1,2-bis(dimethylphosphino)ethane (dmpe) leads to the brightly coloured, highly-crystalline octahedral complexes trans-MCl2(dmpe)2(M = Ti, V, Cr, or Fe). Although the Mn analogue could not be prepared, both trans-MnBr2(dmpe)2 and trans-Mnl2(dmpe)2 can be obtained from the respective dihalides. Alkylation of the MX2(dmpe)2(X = halide) compounds with either LiMe or MgMe2 leads to the dimethyl complexes trans-MMe2(dmpe)2(M = V, Cr, or Mn); the titanium complex isolated under these conditions is a mixture of trans-TiMeCl(dmpe)2 and trans-TiMe2(dmpe)2, while the iron species obtained is cis-FeMe2(dmpe)2. Magnetic susceptibility and e.s.r. measurements indicate a low-spin state for all the complexes except the manganese halide derivatives, and metal–ligand bond lengths observed in those complexes structurally characterised by X-ray crystallographic methods are consistent with the proposed ground-state configurations. There is a similarity between the electronic structures of the MCl2(dmpe)2 species and the metallocenes M(η5-C5H5)2, while the MMe2(dmpe)2 compounds resemble M(η5-C5Me5)2. Our studies indicate a progressive change in the nature of the M–Me groups upon lowering the electron count from 18 (Fe) to 14 (Ti). Thus, the titanium complex trans-TiMe1.3Cl0.7(dmpe)2 appears to contain a distorted methyl group involving a Ti ⋯ H–C interaction due to donation of C–H bond electrons into an empty orbital on the metal.

Subvalent group 4B metal alkyls and amides. Part 7. Transition-metal chemistry of metal(II) bis(trimethylsilyl)amides M′(NR2)2(R = SiMe3; M′= Ge, Sn, or Pb)

Abstract: The transition-metal (M) chemistry of the compounds M′(NR2)2(M′= Ge, Sn, or Pb; R = SiMe3) falls into three categories. These heavy Group 4B atom carbene analogues behave as (a) M′-centred neutral ligands with respect to Lewis acids, (b) co-ordinatively unsaturated fragments, by inserting into transition-metal M–X bonds, or (c) as sources of other bivalent molecules M′X′2. Reactions of class (a) afford complexes in which the Group 4 metal atom is usually [but note: [W(CO)5{SnCl(NR2)(thf)}](thf = tetrahydrofuran) in a three-co-ordinate environment, as in [M(CO)5{M′(NR2)2}](M = Cr, Mo, or W; M′= Ge or Sn), trans-[M(CO)4{M′(NR2)2}2](M = Mo or W, M′= Ge or Sn), [Sc(η-C5H5)2-Me{Sn(NR2)2}], or cis-[Pd(η-C3H5)Cl{M′(NR2)2}](M′= Sn or Pb). Reactions of class (b) afford complexes in which the Group 4 metal atom is in a four-co-ordinated environment, as in [Mn(CO)5-{SnBr(NR2)2}], [Fe(η-C5H5)(CO)2{Sn(NR2)2X}](X = F, I, or Me), [{Pt(µ-Cl)[M′Cl(NR2)2](PEt3)}2](M′= Ge, Sn, or Pb), or cis-[Pd(cod){SnCl(NR2)2}2](cod = cyclo-octa-1,5-diene). A product of a reaction of type (c) is [Sn{Mo(η-C5H5)(CO)3}2]. Type (a) reactions are those in which an M′(NR2)2 ligand either displaces another neutral ligand (CO or olefin) from the inner co-ordination sphere of a transition metal, or effects the nucleophilic cleavage of an M(µ-Cl)2M bridge. Type (b) reactions are insertions of an M′(NR2)2 moiety into a transition metal–halide or –alkyl bond, while the sole type (c) reaction demonstrates the facility with which the N(SiMe3)2– group is displaced from the Group 4 metal M′ by a transition metal-centred nucleophile.

Synthesis of gold-(I) and -(III) complexes with carbonyl-stabilized phosphorus ylides. Crystal structure of [{Au(PPh3)}2{µ-C(PPh3)CO2Et}]ClO4

Abstract: Phosphonium salts (Ph3PCH2CO2R)ClO4(R = Me or Et) react with [Au(acac)L′](acac = acetylacetonate, L′= PPh3 or AsPh3), displacing acac as acetylacetone and yielding cationic complexes of the corresponding phosphorus ylides L (L = Ph3PCHCO2Me, L′= PPh3; L = Ph3PCHCO2Et, L′= PPh3 or AsPh3). These complexes react with [Au(acac) L′] to give dinuclear species [(AuL′)2{µ-C(PPh3)CO2R}]ClO4(R = Et, L′= PPh3 or AsPh3; R = Me, L′= PPh3). The displacement of the ligand tetrahydrothiophene (tht) in [AuCl(tht)] by the ylides Ph3PCHCO2R (R = Me or Et) forms complexes [AuCl(L)], which react (i) with chlorine to give [AuCl3L] or (ii) with L in the presence of NaClO4 to give complexes [AuL2]ClO4, which also react with chlorine to form gold(III) complexes [AuCl2L2]ClO4. The crystal structure of the complex [{Au(PPh3)}2{µ-C(PPh3)CO2Et}]ClO4 has been determined: space group P21/c, with a= 18.666(6), b= 17.490(5), c= 16.413(5)A, β 95.10(3)°, and R= 0.055. A short Au ⋯ Au contact of 2.892(2)A is observed.

Water photolysis. Part 1. The photolysis of co-ordinated water in [{MnL(H2O)}2][ClO4]2(L = dianion of tetradentate O2N2-donor Schiff bases). A model for the manganese site in photosystem II of green plant photosynthesis

Abstract: A number of manganese(III) complexes of the type [{MnL(H2O)}2]2+(L = dianion of O2N2 tetradentate Schiff base), in aqueous solution, have been shown to liberate dioxygen and reduce p-benzoquinone to hydroquinone when irradiated with visible light. The photoactivity is critically dependent on the structure of the ligand, the complex [{Mn(salpd)(H2O)}2][ClO4]2[salpd = propane-1,3-diylbis(salicylideneiminate)] being the most active. All the active complexes exhibit a band at 590 nm in the electronic spectrum, which is absent for the inactive complexes. Amongst the parameters of the photolysis which have been studied are: wavelength of light, temperature, complex and quinone concentrations, ligand structure, pH, and solvent nature. The rate of dioxygen evolution is dependent on the manganese(III) complex (first order) and quinone concentrations (order, 0.5) and the pH of the reaction medium, but is independent of solvent. The water which is photolysed is that bound to the manganese (suggesting that a model for the manganese site of photosystem II of the green plant is represented by these complexes). The energy of activation for O2 evolution in [{Mn(salpd)(H2O)}2][ClO4]2 is ca. 80 kJ mol–1, and the evidence points to homolytic, rather than heterolytic, fission of water. The manganese complex is converted to [{Mn(salpd)}2O] in the photolysis, i.e. no oxidation state change of manganese is involved. In addition to p-benzoquinone, methylene blue has been shown to be a hydrogen acceptor in this system.

Lewis-base adducts of Group 1B metal(I) compounds. Part 19. Crystal structures of bis(1,10-phenanthroline)copper(I) perchlorate and dibromocuprate(I)

Abstract: The crystal structures of the title compounds [Cu(phen)2][ClO4](1) and [Cu(phen)2][CuBr2](2)(phen = 1,10-phenanthroline) have been established by single-crystal X-ray diffraction methods at 295 K. Crystals of (1) are monoclinic, P2/c, a= 10.037(3), b= 14.518(6), c= 7.672(3)Aβ= 97.82(3)°, Z= 2. R was 0.056 for 709 independent ‘observed’ reflections. Crystals of (2) are monoclinic, C2/c, a= 17.206(4), b= 13.365(2), c= 10.920(3)A, β= 115.43(2)°, Z= 4. R was 0.048 for 1 091 independent ‘observed’ reflections. Surprisingly, complex (2) is not a di-µ-bromo- bridged dimer, [(phen)CuBr2Cu(phen)], but ionic [Cu(phen)2][CuBr2]. In both (1) and (2), the [Cu(phen)2]+ cation has crystallographic 2 symmetry; in (1), the 2 axis passes through the ligands so that the overall symmetry is close to 222, but in (2) it passes between the ligands, so that the cation geometry is very far removed from 222 symmetry. In (1), Cu–N are 2.045(8), 2.053(9)A; in (2), 2.006(8) and 2.071(5)A. The linear anion in (2) has Cu–Br 2.209(2) and 2.223(2)A. The dihedral angles for each compound differ significantly, being 49.9° for (1) and 76.8° for (2), the former being the lowest value yet observed for a copper(I) cation with two bidentate ligands.

Ion exchange of K4Nb6O17·3H 2O

Abstract: Ion exchange of the layered compound K4Nb6O17·3H2O with mono- and bi-valent cations (Li+, Na+, Ca2+, and Ni2+) has been carried out in the aqueous chloride solutions at 90 °C. Only Na+ was found to attain to complete exchange. For exchange with Li+, almost all the K+ ions in the interlayers seemed to be replaced, although partial decomposition was observed. The degrees of exchange with the bivalent cations were found to be < 50%. The interlayer spacings of interlayers I (hydrated) and II (not hydrated) in K4Nb6O17·nH2O and derivatives were determined from electrondensity projections along the b axes. From the change in interlayer spacings, it is considered that K+ ions in interlayer II are only substituted by monovalent cations whereas both mono- and bi-valent cations exchange for K+ in interlayer I. By exchanging K+ in interlayer II with Li+ or Na+, this interlayer becomes hydrated.

Reactions of co-ordinated ligands. Part 33. Mononuclear η2-vinyl complexes: synthesis, structure, and reactivity

Abstract: Treatment of the four-electron alkyne cation [Mo(η2-PhC2Ph){P(OMe)3}2(η-C5H5)][BF4] with K[BHBus3] affords the η2-vinyl or metallacyclopropene complex [[graphic omitted]HPh}{P(OMe)3}2(η-C5H5)](2). The related complexes [[graphic omitted]HPh}{P(OMe)3}2(η-C5H5)](3),[[graphic omitted]H(C6H4Me-4)}{P(OMe)3}2(η-C5H5)](4), [[graphic omitted]H(C6H4Me-4)}{P(OMe)3}2(η-C5H5)](5), and [[graphic omitted]Ph2}{P(OMe)3}2(η-C5H5)](6) are obtained on reaction of the corresponding lithium diarylcuprate with the respective alkyne cation [Mo(η2-R1C2R2){P(OMe)3}2(η2-C5H5)][BF4](R1= But, R2= H; R1= Pri, R2= H; R1= Me, R2= Ph). The structures of (2), (3), and (6) have been determined by single-crystal X-ray diffraction studies. The molecules show close similarities; each has a molybdenum atom to which a vinyl moiety is co-ordinated via one short and one long Mo–C bond. These molecules may be described either as η2(3e)-vinyl or metallacyclopropene complexes. The orientation of the C2 vinyl group relative to the Mo{P(OMe)3}2(η-C5H5) fragment is discussed in terms of the torsion angles. In (2) and (3), Cα of the vinyl group lies closer to the plane of the η-C5H5, ligand than does Cβ, whereas in (6) the reverse orientation is observed. The solution n.m.r. spectra of (2) and (3) have distinct 31P environments, whereas in (6) the phosphorus environments are equivalent. This is discussed in terms of a rotational movement, an extended Huckel molecular orbital analysis suggesting that the orientation and fluxional behaviour of the η2-vinyl ligands parallel those of the related alkyne complexes. Reaction of [Mo(η2-PhC2CH2Ph){P(OMe)3}2(η-C5H5)][BF4] with K[BHBus3] affords a separable mixture of isomeric complexes [[graphic omitted]HPh}{P(OMe)3}2(η-C5H5)], which differ only in the orientation of the η2-vinyl moiety. The complex (6) slowly rearranges in solution to an η3-allylic complex this being explained in terms of an η2 to σ change in the bonding mode of the vinyl ligand. A similar transformation is suggested to explain the formation of η3- allylic complexes on reaction of [Mo(η2-RC2H){P(OMe)3};2(η-C5H5)][BF4](R = But or Pri) with LiCuMe2. Extension of the dimethyl- or diphenyl-cuprate reactions to the cations [Mo(η2- R1C2R2){P(OMe)3}2(η-5H5)][BF4] provides evidence for competing reaction pathways involving either direct attack on the metal centre or on a co-ordinated alkyne carbon. The regioselectivity of the latter reaction is discussed in terms of steric and electronic effects.

Kinetic and structural investigations of [FeIII(edta)]–[edta = ethylenediaminetetra-acetate(4–)] catalysed decomposition of hydrogen peroxide

Abstract: A detailed kinetic analysis is given of hydrogen peroxide decomposition catalysed by [FeIII(edta)]–[edta = ethylenediaminetetra-acetate(4–)]. Structural investigations have been made using n.m.r. And electronic absorption spectroscopy. It is demonstrated that the monohydroxy complex, [Fe(edta)(OH)]2–, is the primary active catalyst and this reacts with the hydrogenperoxide ion to produce the well known purple complex [Fe(edta)(OH)(HO2)]3–. Decomposition of hydrogen peroxide conforms to Michaelis–Menten kinetics, the rate-determining step involving breakdown of this complex. In contrast to earlier reports, it is shown that the HO2– ion displaces a carboxy-group from [Fe(edta)(OH)]2– rather than the hydroxy group. The dihydroxy complex [Fe(edta)(OH)2]3– is also shown to form a purple peroxy-complex with HO2–, but its breakdown occurs at a much slower rate. The results are consistent with formation of radicals upon breakdown of the peroxy-complex and in subsequent reactions.

Lewis-base adducts of group 1B metal(I) compounds. Part 13. Crystal structure determinations of tetrakis(triphenylphosphine)-copper(I) and -silver(I) perchlorates, bis(pyridine)bis(triphenyl-phosphine)copper(I) perchlorate, (2,2′-bipyridyl)bis(triphenyl-phosphine)copper(I) perchlorate, and tetrahydroboratobis-(triphenylphosphine)copper(I)–pyridine (1/0.5)

Abstract: The crystal structures of [Cu(PPh3)4]ClO4(1) and [Ag(PPh3)4]ClO4(2) have been determined by single-crystal X-ray diffraction methods at 295 K, being refined by least-squares methods to residuals of 0.10 and 0.08 for 591 and 1 294 independent ‘observed’ reflections respectively. The two compounds are isomorphous (rhombohedral, space group R, and Z= 2) with a= 19.02(2)A, α= 44.06(6)° and a= 19.085(5)A, α= 43.90(1)° respectively; the cation lies on a site of 3 symmetry, while the anion is disordered about a site of symmetry. The metal-atom geometry is pseudo-tetrahedrai [Cu–P = 2.60(1), 2.52(1)A; Ag–P = 2.650(2)A, with all P–M–P angles lying between 109.3 and 109.7 °]. For the structure determination of [Cu(PPh3)2(py)2]ClO4(3) obtained by the recrystallization of [Cu(PPh3)4]ClO4 from pyridine (py), 2 843 ‘observed’ reflections were refined to a residual of 0.052. Crystals are triclinic, space group P, with a= 15.599(4), b= 13.413(4), c= 10.982(4)A, α= 79.51(3), β= 70.47(3), γ= 860.3(3)°, and Z= 2. Cu–P = 2.271(4), 2.295(3)A and Cu–N = 2.102(7), 2.115(8)A in a pseudo-tetrahedral copper(I) environment, with P–Cu–P = 115.85(9)° and N–Cu–N = 101.5(2)°. The 2,2′-bipyridyl (bipy) analogue [Cu(PPh3)2(bipy)]ClO4(4) is monoclinic, space group P21/c, with a= 10.210(3), b= 15.085(4), c= 28.455(9)A, β= 109.13(2)°, and Z= 4. Cu–P = 2.246(3), 2.256(3)A and Cu–N = 2.056(8), 2.113(9)A, with P–Cu–P = 125.4(1) and N–Cu–N = 79.6(4)°. R was 0.081 for 2 605 reflections. [Cu(BH4)(PPh3)2], by contrast, yields a hemipyridine solvate, (5), on recrystallization from pyridine; crystals are triclinic, space group P, with a= 12.849(6), b= 10.319(5), c= 13.618(6)A, α= 102.91(4), β= 101.91(4)γ= 73.42(4)°, and Z= 2. The structure was refined to a residual of 0.051 for 3 633 independent ‘observed’ reflections, and is isomorphous with the hemibenzene solvates of [CuX(PPh3)2](X = Cl or Br) and [AuCl(PPh3)2].

Mono-η-cycloheptatrienyltitanium chemistry: synthesis, molecular and electronic structures, and reactivity of the complexes [Ti(η-C7H7)L2X](L = tertiary phosphine, O- or N-donor ligand; X = Cl or alkyl)

Abstract: Bis(η-toluene)titanium reacts with cycloheptatriene in the presence of (AlEtCl2)2, at > 60 °C to form [Ti(η-C7H7)(η-C7H9)] and at room temperature [{Ti(η-C7H7)(thf)(µ-Cl)}2](thf = tetrahydrofuran) is also formed. The crystal structure of the latter has been determined. The dimer reacts with the ligands L2= R2PCH2CH2PR2(R = Me or Ph), trans-1,2-bis(dimethylphosphino)cyclopentane, MeOCH2CH2OMe, 2PMe3 or Me2NCH2CH2NMe2, forming the compounds [Ti(η-C7H7)L2Cl]. Reaction of alkyl Grignard reagents with the appropriate chloroderivatives gives the titanium–alkyls [Ti(η-C7H7)L2R][L2= Me2PCH2CH2PMe2, R = Me or Et; L2=trans-1,2-C5H8(PMe2)2, R = Me]. The crystal structure of [Ti(η-C7H7)(Me2PCH2CH2PMe2)Et] has been determined: there is no evidence for Ti–H–C interactions between the Ti and the hydrogens of the ethyl group. The photoelectron spectra of several Ti(η-C7H7) compounds are discussed in terms of the nature of the Ti(η-C7H7) bonding. It is proposed that the chemistry of the Ti(η-C7H7) system corresponds most closely to a formal description of the η-C7H7 group as having a –3 charge rather than the more conventional description as +1. Homogeneous mixtures of [{Ti(η-C7H7)(thf)(µ-Cl)}2] and aluminium alkyls are shown to catalyse ethylene polymerisation.

Magnetic exchange interactions in perovskite solid solutions. Part 5. The unusual defect structure of SrFeO3 –y

Abstract: Mesures d'effet Mossbauer 57 Fe, de diffraction RX et de susceptibilite magnetique, entre 4,2 et 900 K, sur SrFeO 3−y pour 0,15

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution. Part 13. A potentiometric and 27Al nuclear magnetic resonance study of speciation and equilibria in the aluminium(III)-oxalic acid-hydroxide system

Abstract: Equilibria between Al3+, oxalic acid (H2L), and OH– were studied in 0.6 mol dm–3 NaCl medium at 25 °C. Potentiometric titrations (glass electrode) and 27Al n.m.r. measurements were performed to study speciation and equilibria within the concentration ranges 0.2 ⩽–log [H+]⩽ 7.2, 0.0005 ⩽b⩽ 0.02 mol dm–3, 0.0005 ⩽c⩽ 0.025 mol dm–3, and 0.5 ⩽c/b⩽ 16 [b and c are the total concentrations of aluminium(III) and oxalic acid respectively]. Besides a series of [AILn]3 – 2n complexes with n= 1,2, and 3, the formation of the polynuclear mixed hydroxo-complexes Al3(OH)3L3 and [Al2(OH)2L4]4 – were established. N.m.r. data also indicated the formation of an [AlHL]2+ complex in strongly acidic solutions: pKa([AlHL]2+)≈ 0.0. The significance of the different Al complexes to conditions prevailing in natural waters is discussed, including a model calculation of the solubility of a clay mineral (kaolinite) in the presence of oxalate. Data were analysed using the least-squares computer program LETAGROPVRID.

The hydrolysis of metal ions. Part 8. Aluminium(III)

Abstract: An automated potentiometric titration technique has been used to study the hydrolytic behaviour of the aluminium(III) ion in 0.10 mol dm–3 sodium nitrate at 25 °C. Low aluminium(III) concentrations (up to 0.1 mol dm–3) were used so that the monomeric species, [Al(OH)]2+ and [Al(OH)2]+, could be identified. The data treatment indicates the presence of the species [Al(OH)]2+, [Al(OH)2]+, [Al3(OH)4]5+, and a high-molecular-weight polymer with a q/p ratio (OH/Al) of ca. 2.46 and a p value between 6 and 14. The –log βpq values for these species {βpq=[Alp(OH)q(3p–q)+][H+]q/[Al3+]p} are estimated to be 5.33 (0.009), 10.91 (0.04), 13.13 (0.005), and 5.73 – 3.6p+ 4.64q(0.04) respectively, the estimated standard deviations being given in parentheses.

The chemistry of heteroarylphosphorus compounds. Part 16. Unusual substituent effects on selenium-77 nuclear magnetic resonance chemical shifts of heteroaryl- and aryl-phosphine selenides. X-Ray crystal structure of tri(2-furyl)phosphine selenide

Abstract: Crystals of PR3Se (R = 2-furyl) are monoclinic, space group Cc, with a= 11.720(6), b= 12.527(9), c= 8.569(5)A, and Z= 4. The structure was solved using multisolution direct methods and refined by least squares to R 0.038 (R′ 0.041) for 1 030 observed diffractometer data. Phosphorus adopts a distorted tetrahedral geometry with mean Se–P–C and C–P–C angles of 114.9 and 103.4°, respectively. The molecule has almost ideal C3 symmetry. The C–P–C angle is the smallest reported for a tertiary phosphine selenide. The average P–C bond length [1.778(6)A] and the P–Se bond length (2.094 A) are both considerably shorter than found in other arylphosphine selenides. The oxygen atoms of the 2-fury1 groups are arranged about the selenium atom, with an average Se ⋯ O distance of 3.577 A. 77Se N.m.r. studies show that the selenium atom is shielded by 86 p.p.m. compared with that in triphenylphosphine selenide, implying a ‘through-space’ interaction involving the 2-fury1 oxygen atoms. Selenium-77 chemical shifts have also been determined for a range of heteroaryl-and substituted phenyl-phosphine selenides. Whereas the 2-furyl group causes the selenium to become shielded, the related 2-thienyl group causes it to become deshielded. Deshielding of selenium is also experienced on introduction of ortho substituents in arylphosphine selenides. Thus, for example, the selenium atom of tris(2,4,6-trimethoxyphenyl)phosphine selenide is deshielded by 240 p.p.m. compared with that in triphenylphosphine selenide. Possible origins of these effects are considered.

The synthesis, magnetic, electrochemical, and spectroscopic properties of diruthenium(II,II) tetra-µ-carboxylates and their adducts. X-Ray structures of Ru2(O2CR)4L2(R = Me, L = H2O or tetrahydrofuran; R = Et, L = Me2CO)

Abstract: The interaction of the reduced ‘blue solutions’ of ruthenium chloride in methanol with alkali-metal carboxylates yields the air-sensitive paramagnetic complexes, Ru2(µ-O2CR)4(R = H, Me, CH2Cl, Et, or Ph), that form weakly end-co-ordinated bis adducts, Ru2(µ-O2CR)4L2[L = H2O, MeOH, tetrahydrofuran (thf), Me2CO, or MeCN]. Electrochemical measurements, electronic and i.r. absorption spectra, and magnetic susceptibility data are given. The structures of Ru2(O2CMe)4L2(L = H2O or thf) and Ru2(O2CEt)4(Me2CO)2 have been determined by X-ray crystallography and the well known D4h symmetry of binuclear tetracarboxylates established. The Ru2(O2CR)4 core shows a constant geometry with Ru–Ru = 2.261 ± 0.001 A. The three axial donor ligands show slightly varying Ru ⋯ O distances of 2.335(4), 2.363(5), and 2.391(5)A for water, acetone, and thf respectively.

Actinide structural studies. Part 7. The crystal and molecular structures of (2,2′-bipyridyl)dinitratodioxo-uranium(VI) and -neptunium(VI), and diacetato-(2,2′-bipyridyl)dioxo-uranium(VI) and -neptunium(VI)

Abstract: The crystal structures of the title compounds, [MO2(bipy)(NO3)2][M = U (1) or Np (2)] and [MO2(bipy)(CH3COO)2][M = U (3) or Np (4)](bipy = 2,2′-bipyridyl) have been determined using X-ray diffraction techniques. Complexes (1) and (2) are isomorphous and isostructural crystallising in the monoclinic system, space group C2/c; (3) and (4) are also isomorphous and isostructural, crystallising in the monoclinic system, space group P21/n. All four complexes exhibit hexagonal-bipyramidal co-ordination about the central metal atom. The M–O bond lengths in the MO22+ cations are 1.763(13)(1), 1.728(7)(2), 1.770(8)(mean)(3), and 1.729(10)A(mean)(4). The bidentate oxy-anions have M–O distances of 2.472(8)–2.494(13)A in (1) and (2), and 2.429(9)–2.476(9)A in (3) and (4). For the bidentate 2,2′-bipyridyl group the M–N distances are 2.578(13)(1), 2.564(9)(2), 2.631 (10) and 2.642(9)(3), and 2.835(13) and 2.842(13)A(4). This anomalous increase in the M–N distance between complexes (3) and (4) is attributed to overcrowding around the NpO22+ ion.

Studies on spin-equilibrium iron(III) complexes. Part 1. Syntheses and magnetic properties of a new family of spin cross-over iron(III) complexes with a unidentate ligand over a wide range of the spectrochemical series and a quinquedentate ligand derived from salicylaldehyde and di(3-aminopropyl)amine. X-Ray crystal structure of [4-azaheptamethylene-1,7-bis(salicylideneiminato)](4-methylpyridine)iron(III) tetraphenylboratet

Abstract: Iron(III) complexes of general formula [Fe(X)L]n+(n= 0 or 1) have been prepared and characterized, where X is a unidentate ligand such as Cl–, N3–, NCO–, CN–, pyridine (py), 3-methylpyridine (3Me-py), 4-methylpyridine (4Me-py), 4-aminopyridine (apy), 3,4- dimethylpyridine (3,4Me,-py), imidazole (Him), N-methylimidazole (mim), or 2- methylimidazole (2Me-im), and L denotes a quinquedentate Schiff base derived from salicylaldehyde and di(3-aminopropyl)amine. On the basis of the cryomagnetic data, these complexes can be classified into three groups: high spin (S=5//2) for X = Cl, N3, Him, mim; low spin (S=5//2) for X = CN; spin cross-over (S =½⇌S=5//2) for X = py, 3Me-py, 4Me-py, 3,4Me2-py, 2Me-im. This indicates that the spin state for the series of complexes depends predominantly on the order in the spectrochemical series of the ligand X. The magnetic moments for the spin cross-over complexes increased gradually with increase of the temperature and showed no thermal hysteresis, indicating that the present complexes are of continuous spin-transition type. The spin cross-over complexes showed a thermochromism both in the solids and solutions, changing colour from dark violet to blue green, with decreasing temperature, and the thermochromism was studied by the temperature dependence of the electronic spectra in dichloromethane solution. The temperature dependence of the Mossbauer spectra for [Fe(2Me-im)L]BPh4 and [Fe(4Me-py)L]BPh4 has also provided evidence that the spin transition between the high- and low-spin states takes place and that the rate of spin interexchange is as fast as the inverse of the lifetime (1 × 10–7 s) of the Mossbauer nucleus. One of the complexes, [Fe(4Me-py)L] BPh4, was also subjected to a single-crystal X-ray analysis. The result verified the detailed structure in which the iron(III) atom assumes a pseudo-octahedral co-ordination geometry with a trans geometry for the two salicylideneiminate moieties, and the two axial positions are occupied by the secondary amine nitrogen of the di(3-aminopropyI)amine moiety of L and the nitrogen atom of the 4-methylpyridine ligand.

The preparation and properties of some diphosphines R2PCH2CH2PR2(R = alkyl or aryl) and of their rhenium(I) dinitrogen derivatives

Abstract: The synthesis of a range of diphosphines R2PCH2CH2PR2 from Cl2PCH2CH2PCl2 is described. The properties of a series of complexes [ReCl(N2)(R2PCH2CH2PR2)2] derived from them are discussed. The relationship between the values of E½ox and ν(N2) for the complexes suggests that electron-withdrawing substituents on the diphosphine upset the usual balance of σ and π effects in rhenium–dinitrogen bonding.

Rhenium nitrosyl complexes with simple and with sterically demanding aromatic thiolate ligands: X-ray crystal structures of [PPh4][Re2(SC6H4Me-4)7(NO)2]·CH2Cl2 and [Re(SC6H3Pri2-2,6)4(NO)]

Abstract: Reaction of [ReCl2(OMe)(NO)(PPh3)2] with a range of thiophenols under basic conditions gives one of two classes of products depending on the steric requirements of the thiols. A representative member of each class has been characterised by an X- ray crystal structure determination. Thiophenols with methyl or isopropyl groups in their ortho positions give the mononuclear complexes [Re(SR)4(NO)](SR = SC6H2Pri3-2,4,6, SC6H3Pri2-2,6, SC6H2Pri2-2,6-4- Br, or SC6H2Me3-2,4,6) which are trigonal bipyramidal with an axial NO group. Thiophenols without ortho-substituents give the dinuclear anions [Re2(SR)7(NO)2]–(SR = SPh or SC6H4Me-4) which contain a triple thiolate bridge between two equivalent rhenium atoms. These anions show a fluxionality involving intramolecular exchange of six thiolato-ligands.