Robert Greatrex

CHIRAL ALUMINIUM COMPLEXES AS PHOSPHO-TRANSFER CATALYSTS

Abstract Readily accessible, chiral complexes of aluminium are effective and enantioselective catalysts for the phospho-aldol reaction under aerobic conditions.

Ruthenium-99 Mössbauer studies of the magnetic properties of ternary and quaternary ruthenium(IV) oxides

Ruthenium-99 Mossbauer spectra have been obtained for the ternary oxides SrRuO3, CaRuO3, BaRuO3, and Y2Ru2O7 and for the quaternary oxides Sr(Ru1–xIrx)O3(x= 0·1 and 0·2) and Sr(Ru0·7Mn0·3)O3. The spectrum of SrRuO3 reveals the first example of a hyperfine magnetic field in a ruthenium compound; the internal field of 352 kG at 4·2 K is compatible with the ferromagnetic moment derived from neutron-diffraction data, and confirms the collective-electron magnetism model for this perovskite. A more precise value for the E2/M1 mixing ratio of 2·72 ± 0·17 has been obtained for the 99Ru Mossbauer γ transition. The oxide CaRuO3 shows only a single line and hence no magnetic ordering even at 4·2 K; it is not antiferromagnetic as previously reported but is Curie-Weiss paramagnetic. The oxide BaRuO3 also gives a singlet; there is no long-range antiferromagnetic ordering, but within each cluster of three face-sharing RuO6 units localised pairing of the 4d electrons takes place. The oxide Y2Ru2O7 is magnetically ordered at 4·2 K, with a hyperfine field of 126 kG. Substitution of ruthenium by iridium in the oxide SrRuO3 reduces the field at ruthenium by approximately 60 kG for each iridium nearest neighbour, whereas in the case of manganese substitution the reduction for each manganese neighbour is only 22 kG.

A study of the new perovskite solid solution series SrFexRu1−xO3−y by ruthenium-99 and iron-57 Mössbauer spectroscopy

Abstract The magnetic and structural properties of the solid solution SrFexRu1−xO3−y (0 ⩽ x ⩽ 0.5) have been studied using 57Fe and 99Ru Mossbauer spectroscopy and other techniques. These phases, which are here reported for the first time, have a distorted perovskite structure. The iron substitutes exclusively as Fe3+ and thereby causes oxygen deficiency, but has little effect on the magnetic behaviour of the Ru4+ until x > 0.2, whereupon the metallic band system begins to revert to a localized electron structure. The properties of a sample with x = 0.3 are complex and intermediate in character. For x > 0.3 the oxygen deficiency is reduced by substantial oxidation to Ru5+ until at x = 0.5 the system corresponds to Sr2Fe3+Ru5+O6.

Reactions of metal carbonyl derivatives : XVII. Tri- as well as di-nuclear products from the reactions of bis(dicarbonyl-η-cyclopentadienyliron) with various dialkyl disulphides1.

Abstract The reaction of [Fe(η-C5H5)(CO)2]2 with the dialkyl and diaryl disulphides R2S2 (R = CH3, C2H5, i-C3H7, t-C4H9, CH2C6H5 and C6H5) produces a trinuclear product characterised as [Fe3(η-C5H5)3(CO)2(S)SR], as well as the dinuclear derivatives [Fe(η-C5H5)(CO)SR]2. The spectroscopic properties, including Mossbauer, and the electrochemical behaviour of the trinuclear species are discussed. Whereas the alkyl sulphido complexes [Fe(η-C5H5)(CO)SR]2 (R = CH3, C2H5, i-C3H7 and n-C4H9) can be isolated in two isomeric forms, corresponding derivatives of the bulkier disulphides R2S2 (R = t-C4H9 and CH2C6H5) are obtained as single isomers only. On the other hand three isomers of the phenyl sulphido derivative [Fe(/gh-C5H5)(CO)SC6H5]2 can be isolated. The nature of the isomerism is discussed.

A study of the new cubic, ordered perovskites BaLaMRuO6 (M = Mg, Fe, Co, Ni, or Zn) and the related phases La2MRuO6 (M = Mg, Co, Ni, or Zn) by 99Ru Mössbauer spectroscopy and other techniques

Abstract 57 Fe and 99 Ru Mossbauer spectroscopy, coupled with magnetic susceptibility measurements down to 4.2 K, have been used to study the electronic and magnetic properties of the new cubic-ordered perovskites BaLa M RuO 6 ( M = Mg, Fe, Co, Ni, or Zn). The ruthenium is present in the +5 oxidation state in all the compounds except BaLaFeRuO 6 which contains iron(III) and ruthenium(IV). All the compounds exhibit long-range antiferromagnetic order, with Neel temperatures in the range 20–40 K. Mossbauer spectra for the new compound La 2 CoRuO 6 and the isostructural cubic perovskites La 2 M RuO 6 ( M = Mg, Ni, or Zn) confirm the presence of ruthenium(IV) in these phases and indicate that they are not ordered magnetically at 4.2 K.

A study of the ruthenium(V) perovskites M2LnRuO6 (M = Ca, Ln = Y, La, or Eu; M = Sr, Ln = Y; M = Ba, Ln = La or Eu) by 99Ru Mössbauer spectroscopy and other techniques

Abstract Ruthenium-99 Mossbauer spectroscopy has been used in conjunction with other techniques to examine the new perovskite phases Ca 2 Ln RuO 6 ( Ln = Y, La, or Eu) and the recently reported analogous strontium and barium compounds M 2 Ln RuO 6 ( M = Sr, Ln = Y; M = Ba, Ln = La or Eu). At 4.2°K the spectra show widely split magnetic hyperfine patterns ( B = 56–60 T) having chemical isomer shifts in the range 0.13-0.18 mm sec −1 relative to ruthenium metal, thereby confirming the presence of magnetically ordered ruthenium(V)ions in these phases. The computed linewidths for the yttrium compounds are close to the natural value, indicative of unique ruthenium environments and the existence of crystallographic order between Ru V and Y III ions on the B -sites. This is further corroborated by the observation of superlattice reflections in the X-ray powder diffraction pattern of Ca 2 YRuO 6 . Superlattice reflections are also observed for Ca 2 LaRuO 6 , Ba 2 LaRuO 6 , and Ba 2 EuRuO 6 . The Mossbauer spectra for the barium compounds feature sharp paramagnetic components in addition to the magnetically split ruthenium(V) resonances, and possible explanations for these unusual results are discussed. Magnetic susceptibility measurements above 80°K show that all the compounds follow a Curie-Weiss law with negative paramagnetic Curie temperatures, indicative of antiferromagnetism. Measurements down to 4.2°K for the calcium compounds reveal Neel temperatures in the region of 15°K when Ln = Y or La, whereas Ca 2 EuRuO 6 appears to be ferrimagnetic. Electrical resistivity measurements on compacted powders indicate that the materials are not metallic conductors. Mossbauer and powder X-ray diffraction measurements for the phase reported as Sr 2 LaRuO 6 indicate that it is in fact a mixture of Sr 2 RuO 4 and a solid-solution phase of the type Sr 2 La x Ru 1− x O 4 .

A study of the perovskite solid solution series LaxSr1−xRuO3 and LaxCa1−xRuO3 by ruthenium-99 Mössbauer spectroscopy

Abstract The magnetic, electronic, and structural properties of the solid solutions La x Sr 1− x RuO 3 and La x Ca 1− x RuO 3 have been studied by 99 Ru Mossbauer spectroscopy and other techniques. The La x Ca 1− x RuO 3 phases are reported for the first time and have been shown by powder X-ray diffraction measurements to be orthorhombically distorted perovskites. Electrical resistivity measurements on compacted powders show that all the phases are metallic with p ∼ 10 −3 , ohm-cm. Progressive substitution of Sr 2+ by La 3+ in ferromagnetic SrRuO 3 leads to a rapid collapse of the magnetic hyper-fine splitting at 4.2°K. For x = 0.25 some ruthenium ions still experience a magnetic field but for 0.4 ⩽ x ⩽ 0.75 only single, narrow resonance lines are observed, consistent both with the complete removal of the ferromagnetism and with the presence of an averaged ruthenium oxidation state in each phase, i.e., La x 3+ Sr 1− x 2+ Ru (4− x )+ O 3 rather than La x 3+ Sr 1− x 2+ Ru x 3+ Ru 1− x 4+ O 3 . LaRuO 3 and CaRuO 3 both give essentially single-line spectra at 4.2°K, indicating that the ruthenium ions in these oxides are not involved in long-range antiferromagnetic order but are paramagnetic. The solid solutions La x Ca 1− x RuO 3 (0 x ⩽ 0.6) give sharp symmetrical singlets with chemical isomer shifts (relative to the Ru metal) which move progressively from the value characteristic of Ru 4+ (−0.303 mm sec −1 ) toward the value for Ru 3+ (−0.557 mm sec −1 ), consistent with the presence of intermediate ruthenium oxidation states in these phases also.

A study of the magnetic superexchange interactions in the solid-solution series CaxSr1−xRuO3 by ruthenium-99 Mo¨ssbauer spectroscopy

Abstract Ruthenium-99 Mo¨ssbauer spectroscopy has been used to examine magnetic superexchange interactions in the distorted perovskite solid-solutions CaxSr1−xRuO3 (x = 0.1, 0.2, 0.3, 0.4, and 0.5). The end members of this series also have a slightly distorted perovskite structure but CaRuO3 is Curie-Weiss paramagnetic, with only a single-line Mo¨ssbauer spectrum, whereas SrRuO3 is ferromagnetic and shows a broad well-resolved hyperfine pattern. For x ⩽ 0.2 a substantial proportion of the ruthenium atoms experience a magnetic flux density (hyperfine magnetic field) close to 35T, but inward collapse of the spectrum suggests that an increasing proportion of ruthenium atoms experience smaller flux densities. For samples with x ⩽ 0.3 there is an intense central “paramagnetic” component which increases rapidly with increasing x. The observed behaviour is incompatible with a conventional localized electron structure but can be interpreted satisfactorily on a collective electron model in which the average spin moment and hence the magnetic flux density at any given ruthenium atom is proportional to the strength of the exchange interactions with the six nearest-neighbour ruthenium atoms. The results imply that the greater electron-pair acceptor strength (Lewis acidity) of Ca2+ compared to Sr2+ results in a more effective competition with ruthenium for the oxygen anion orbitals involved in the superexchange interaction. It appears that, for a ruthenium to have a coupled spin-moment, it must have at least two exchange interactions through cube faces containing at least three strontium atoms. Possible origins of the reduced magnetic moment of SrRuO3 are discussed and it is suggested that the latter probably stems from spin-canting rather than from partial overlap of spin-up and spin-down bands.

Even more reliable NMR chemical shift computations by the GIAO-MP2 method

Correlated ab initio(GIAO-MP2) chemical shift computations agree excellently with the newly remeasured 11B and 13C NMR values for the problem carboranes, 1 and 2, which had given poor IGLO results.

Reactions of metal carbonyl derivatives. Part IX. The synthesis, infrared spectra, and Mössbauer spectra of some tertiary and ditertiary phosphine, arsine, and stibine derivatives of bis(µ-methylsulphido-, -ethylsulphido-, and -phenylsulphido-tricarbonyliron)

The reactions of [Fe(CO)3SR]2(R = Me or Et) with the ditertiary phosphines L = Ph2P·[CH2]N·PPh2(n= 1 or 2), cis-Ph2P·C2H2·PPh2 and Ph2P·NEt·PPh2 and the ditertiary arsines L = Ph2As·[CH2]n·AsPh2(n= 1 or 2) under various experimental conditions have been studied. A number of different types of products have been isolated. These include [Fe2(CO)5L(SR)2] and [Fe(CO)2LSR]2 in which the ligands are monodentate, [{Fe(CO)2SR}2L] in which the ligand bridges two iron atoms, [Fe(CO)3(SR)2Fe(CO)L] in which the ligand is chelated to a single iron atom and [Fe2(CO)3L2(SR)2] in which one ligand is bidentate and the other monodentate. The nature of the product is shown to depend on the ligand and the reaction conditions. The reactions of [Fe(CO)3SMe]2 with the ligands L′= PEt3, PPh3, P(OMe)3, AsPh3, and SbPh3 have also been studied and the mono-substituted [Fe2-(CO)5L′(SMe)2], bis-substituted [Fe(CO)2L′SMe]2, and tris-substituted [Fe2(CO)3L′3(SMe)2] derivatives have been isolated.Mossbauer and i.r. spectroscopy have been used to elucidate the structures of the above derivatives as well as those of the products of the reactions of [Fe(CO)3SPh]2 with various tertiary and ditertiary phosphines. Systematic variations in the chemical isomer shift and quadrupole splitting are discussed in relation to the bonding in these compounds.