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The Carpentaria province (McArthur basin and Mount Isa inlier) in northern Australia is one of the most important districts for clastic-dominated (CD-type) massive sulfide deposits. The George Fisher Zn-Pb-Ag deposit, located in this province, is hosted by the carbonaceous Urquhart Shale Formation (ca. 1654 Ma) in a region that has an active history of metamorphism and tectonism. In this study, paragenetically constrained pyrite in samples from the George Fisher deposit and unmineralized Urquhart Shale have been analyzed in situ using secondary ion mass spectrometry (SIMS) of sulfur isotopes (δ34S values). Samples were taken from four drill cores through the main orebodies at George Fisher and one drill core through correlative, unmineralized Urquhart Shale (Shovel Flats area). Five generations of pyrite were identified at George Fisher and record a protracted history of sulfate reduction under diagenetic and subsequent hydrothermal conditions: (1) fine-grained, subhedral-spheroidal pyrite (Py-0), (2) coarse-grained, anhedral pyrite (Py-1) associated with ore-stage 1 sphalerite and galena, (3) coarse-grained, euhedral pyrite (Py-2) associated with ore-stage 2 sphalerite, galena, and pyrrhotite, (4) massive subhedral to euhedral pyrite (Py-3) associated with ore-stage 3 chalcopyrite, pyrrhotite, galena, and sphalerite, and (5) coarse-grained euhedral pyrite (Py-euh), which occurs only in unmineralized rocks. In the unmineralized Shovel Flats drill core, only Py-0 and Py-euh are present. Whereas pre-ore pyrite (Py-0) preserves negative δ34S values (–8.1 to 11.8‰), the ore-stage pyrites (Py-1, Py-2, and Py-3) have higher δ34S values (7.8–33.3, 1.9–12.7, and 23.4–28.2‰, respectively). The highest δ34S values (7.2–33.9‰) are preserved in Py-euh. In combination with petrographic observations, the δ34S values of pyrite provide evidence of three different processes responsible for the reduction of sulfate at George Fisher. Reduced sulfur in fine-grained pyrite (Py-0) formed via microbial sulfate reduction (MSR) under open-system conditions prior to the first generation of hydrothermal pyrite (Py-1) in ore-stage 1, which most likely formed via thermochemical sulfate reduction (TSR). During deformation, previously formed sulfide phases were then recycled and replaced during a second hydrothermal event (ore-stage 2), resulting in intermediate sulfur isotope values. Another syndeformational hydrothermal Cu event, involving a sulfate-bearing fluid, formed ore-stage 3 via TSR. This study demonstrates that the fine-grained pyrite formed pre-ore under conditions open to sulfate and outlines the role of multiple stages of sulfide formation in producing high-grade Zn-Pb-Ag orebodies in the Mount Isa inlier.

Heavy metal and metalloid (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) levels in 284 topsoil (0–30 cm) samples were measured from 20,000 km2 of southern New Zealand in a systematic survey and the concentrations and patterns between samples sites were studied. Samples were analysed by the inductively coupled mass spectrometry method on an aqua regia digest. Except for Hg, median concentrations from land classed as high producing exotic grassland (pasture; 241 samples) were consistently elevated relative to median natural background levels under native vegetation. The major control of heavy metal enrichment in pasture is P-based fertiliser application (Cd, Cu, Zn), the soil parent material (Ni, Hg) or a combination of both (As, Cr, Pb), with Pb also affected by proximity to urban centres and major roads. There may be a trend of increasing heavy metal concentration with increasing intensity of land use. Comparison shows there is strong, regional variation in median heavy metal concentrations in topsoil around New Zealand and highlight a need for systematic and consistent study of heavy metals in soil nationally.

The d4 halide complexes [MX(CO)(η-RCCR)Tp′] {R = Me, M = W, X = F; R = Ph, M = Mo or W, X = F or Cl; Tp′ = hydrotris(3,5-dimethylpyrazolyl)borate} undergo two-electron oxidation in the presence of a halide source to give the d2 monocations [MX1X2(η-PhCCPh)Tp′]+ (R = Me, M = W, X1 = X2 = F; R = Ph, M = Mo, X1 = X2 = F or Cl; M = W, X1 = X2 = F or Cl; X1 = F, X2 = Cl). Each monocation (R = Ph) shows two reversible one-electron reductions (the second process was not detected for R = Me) corresponding to the stepwise formation of the neutral d3 and monoanionic d4 analogues, [MX1X2(η-PhCCPh)Tp′] and [MX1X2(η-PhCCPh)Tp′]− respectively; the potentials for the two processes can be ‘tuned’ over a range of ca. 1.0 V by varying M and X. Chemical one-electron reduction of [MX2(η-PhCCPh)Tp′]+ gave [MX2(η-PhCCPh)Tp′] (M = Mo or W, X = F or Cl). X-Ray structural studies on the redox pairs [WX2(η-PhCCPh)Tp′]z (X = F and Cl, z = 0 and 1+) show the alkyne to bisect the X–W–X angle in the d2 cations but align more closely with one M–X bond in the neutral d3 molecules, consistent with the anisotropic ESR spectra of the latter; the solution ESR spectrum of [MoF2(η-PhCCPh)Tp′] showed equivalent fluorine atoms, i.e the alkyne oscillates at room temperature. The successful isolation of [MX2(η-PhCCPh)Tp′]+ and [MX2(η-PhCCPh)Tp′] completes a series in which d6 to d2alkyne complexes are linked in a redox family tree by sequential one-electron transfer and substitution reactions. The implications for such trees in the production of new species and the selective synthesis of paramagnetic complexes acting as synthetically useful ‘alkyne radicals’ are discussed.

From the reaction of in situ generated 1,2-di(4-tert-butylphenyl)ethylene-1,2-dithiol, 2LH2, and Na[AuCl4].2H2O in 1,4-dioxane, green brown crystals of diamagnetic [N(n-Bu)4][AuIII(2L)2] (1) were obtained. As shown by cyclic voltammetry, 1 is a member of an electron-transfer series comprising the dianion [AuII(2L)2]2-, the monoanion [AuIII(2L)2]-, the neutral species [AuIII(2L*)(2L)]0--[AuIII(2L)(2L*)]0, and the monocation [AuIII(2L*)2]+. (2L*)1- represents the pi radical anion (Srad = 1/2) of the one-electron oxidized closed-shell dianion (2L)2-. Oxidation of 1 in CH2Cl2 with ferrocenium hexafluorophosphate affords green, paramagnetic microcrystals of [AuIII(2L*)(2L)]--[AuIII(2L)(2L*)] (2) (S = 1/2). Complexes 1 and 2 have been characterized by X-ray crystallography. Both species possess square-planar monoanions and neutral molecules, respectively. From the oxidation reaction of 1 or [N(n-Bu)4][AuIII(3L)2] with 2-3 equiv of [NO]BF4 in CH2Cl2, a green solution of [AuIII(2L*)2]+ and green microcrystals of [AuIII(3L*)2]BF4 (3) were obtained, respectively; (3L)2- represents the dianion 1,2-di(4-diphenyl)ethylene-1,2-dithiolate, and (3L*)1- is its pi radical monoanion. The electronic structures of this series of gold species have been elucidated by UV-vis, EPR spectroscopies, and DFT calculations. It is shown computationally by density functional theoretical (DFT) methods that the electronic structure of [AuIII(1L*)2]+ is best described as a singlet diradical (St = 0); the ligand mixed valency in the neutral species 2 is of class (III) (delocalized); the monoanion in 1 contains a AuIII ion and two closed-shell dianionic ligands; and the corresponding dianions [Au(L)2]2- are best described as an intermediate AuII/AuIII species with a metal-ligand delocalized SOMO (25% Au 5d, 75% 3p of four S atoms). (1L)2- is the dianion 1,2-di(phenyl)ethylene-1,2-dithiolate, and (1L*)1- is the pi radical monoanion. The neutral species [PdII(2L*)2] (4) has also been synthesized and characterized by X-ray crystallography. Its electronic structure is the same as described for [AuIII(1L*)2]+ (singlet diradical), whereas that of the monoanion [PdII(2L*)(2L)]---[Pd(2L)(2L*)]- corresponds to that of the neutral gold complex 2. Anodic oxidation of the analogous monoanion [AuIII(mnt)2]-, where mnt = maleonitriledithiolate, gave the neutral complex [Au(mnt)(mnt*)] (E1/2 = 0.91 V vs Fc+/Fc). The optical and EPR spectroscopies of [Au(mnt)(mnt*)] were consistent with those observed for the corresponding di(tert-butylphenyl)ethylenedithiolate complex 2.

The d4 halide complexes [MX(CO)(η-RCCR)Tp′] {X = F, Cl, Br or I; R = Me or Ph; M = Mo or W; Tp′ = hydrotris(3,5-dimethylpyrazolyl)borate} undergo one-electron oxidation to the d3 monocations [MX(CO)(η-RCCR)Tp′]+, isolable for M = W, R = Me. X-Ray structural studies on the redox pairs [WX(CO)(η-MeCCMe)Tp′]z (X = Cl and Br, z = 0 and 1), the ESR spectra of the cations [WX(CO)(η-RCCR)Tp′]+ (X = F, Cl, Br or I; R = Me or Ph), and DFT calculations on [WX(CO)(η-MeCCMe)Tp′]z (X = F, Cl, Br and I; z = 0 and 1) are consistent with electron removal from a HOMO (of the d4 complexes) which is π-antibonding with respect to the W–X bond, π-bonding with respect to the W–C(O) bond, and δ-bonding with respect to the W–Calkyne bonds. The dependence of both oxidation potential and ν(CO) for [MX(CO)(η-RCCR)Tp′] shows an inverse halide order which is consistent with an ionic component to the M–X bond; the small size of fluorine and its closeness to the metal centre leads to the highest energy HOMO and the lowest oxidation potential. In the cations [MX(CO)(η-RCCR)Tp′]+ electronegativity effects become more important, leading to a conventional order for Cl, Br and I. However, high M–F π-donation is still facilitated by the short M–F distance.

Reduction of [M(CO)2(η-RCCR′)Tp′]X {Tp′ = hydrotris(3,5-dimethylpyrazolyl)borate, M = Mo, X = [PF6]−, R = R′ = Ph, C6H4OMe-4 or Me; R = Ph, R′ = H; M = W, X = [BF4]−, R = R′ = Ph or Me; R = Ph, R′ = H} with [Co(η-C5H5)2] gave paramagnetic [M(CO)2(η-RCCR′)Tp′], characterised by IR and ESR spectroscopy. X-Ray structural studies on the redox pair [Mo(CO)2(η-PhCCPh)Tp′] and [Mo(CO)2(η-PhCCPh)Tp′][PF6] showed that oxidation is accompanied by a lengthening of the CC bond and shortening of the Mo–Calkyne bonds, consistent with removal of an electron from an orbital antibonding with respect to the Mo–alkyne bond, and with conversion of the alkyne from a three- to a four-electron donor. Reduction of [Mo(CO)(NCMe)(η-MeCCMe)Tp′][PF6] with [Co(η-C5H5)2] in CH2Cl2 gives [MoCl(CO)(η-MeCCMe)Tp′], via nitrile substitution in [Mo(CO)(NCMe)(η-MeCCMe)Tp′], whereas a similar reaction with [M(CO){P(OCH2)3CEt}(η-MeCCMe)Tp′]+ (M = Mo or W) gives the phosphite-containing radicals [M(CO){P(OCH2)3CEt}(η-MeCCMe)Tp′]. ESR spectroscopic studies and DFT calculations on [M(CO)L(η-MeCCMe)Tp′] {M = Mo or W, L = CO or P(OCH2)3CEt} show the SOMO of the neutral d5 species (the LUMO of the d4 cations) to be largely dyz in character although much more delocalised in the W complexes. Non-coincidence effects between the g and metal hyperfine matrices in the Mo spectra indicate hybridisation of the metal d-orbitals in the SOMO, consistent with a rotation of the coordinated alkyne about the M–C2 axis.

Cationic nitrile complexes and neutral halide and cyanide complexes, with the general formula [MnL1L2(NO)(eta-C5H4Me)]z, undergo one-electron oxidation at a Pt electrode in CH2Cl2. Linear plots of oxidation potential, Eo', vs. nu(NO) or the Lever parameters, EL, for L1 and L2, allow Eo' to be estimated for unknown analogues. In the presence of TlPF6, [MnIL'(NO)(eta-C5H4Me)] reacts with [Mn(CN)L(NO)(eta-C5H4Me)] to give [(eta5-C5H4Me)(ON)LMn(mu-CN)MnL'(NO)(eta5-C5H4Me)][PF6] which undergoes two reversible one-electron oxidations; DeltaE, the difference between the potentials for the two processes, differs significantly for stable cyanide-bridged linkage isomers. Novel pentametallic complexes such as [Mn[(mu-NC)Mn(CNBut)(NO)(eta5-C5H4Me)]4(OEt2)][PF6]2 and [Mn[(mu-NC)Mn(CNXyl)(NO)(eta5-C5H4Me)]4(NO3-O,O')][PF6], containing a trigonal bipyramidal and a distorted octahedral Mn(II) centre, respectively, result either from slow decomposition of the binuclear cyanide-bridged species or from the reaction of anhydrous MnI2 with four equivalents of [Mn(CN)L(NO)(eta5-C5H4Me)] in the presence of TlPF6.

A series of 4-(X)-substituted naphthalimides (X = ethenylFc, ethynylFc, piperidinyl, ethenylpiperidinyl, ethenylpyrrolidinyl) with ferrocenyl headgroups (R = Fc(CH2)n, n = 1, 5, 11) and analogous ethenylFc, ethynylFc, and ethynylFc# (Fc# = octamethylferrocenyl) compounds with a methyl headgroup have been investigated. These are the first 4-enamine-1,8-naphthalimides to be reported. Spectrochemical properties for all compounds are presented and the X-ray structures of 4-piperidinyl and 4-ethynylferrocenyl derivatives described. This series of donor−acceptor derivatives allows a correlation between the degree of internal charge separation, UV−vis and emission properties, and mediation by the organometallic redox couple. Charge separation increases in the order 4-amino ≪ 4-CC-amino ≅ 4-C⋮CFc ≅ 4-CCFc < 4-C⋮CFc#. The unsaturated spacer is the key influence on both λflu and φf, but λflu is independent of the headgroup due to the imide node. In contrast, φf shows a “distance” effect for the ferrocenyl headgroup...

The complex [Rh(CO)2{HC(pz′)3}][PF6], 1+[PF6]− {HC(pz′)3 = tris(3,5-dimethylpyrazolyl)methane}, prepared by reacting [{Rh(CO)2(μ-Cl)}2] with HC(pz′)3 in the presence of Tl[PF6], has a distorted square pyramidal structure with a κ3-HC(pz′)3 ligand. Carbonyl substitution with Lewis bases gives [Rh(CO)L{HC(pz′)3}][PF6] {L = PPh3, 2+[PF6]−; L = AsPh3, 3+[PF6]−; L = P(o-tolyl)3, 4+[PF6]−}, which have square planar κ2 structures, confirmed by X-ray crystallography for 2+[PF6]−. The cations 2+ and 3+ have the third pyrazolyl ring orientated pseudo-parallel to the square planar metal whereas 4+ more likely has the third ring orientated exo to that plane. One-electron oxidation of 2+ and 3+ gives the Rh(II) dications [Rh(CO)(PPh3){HC(pz′)3}]2+, 22+, and [Rh(CO)(AsPh3){HC(pz′)3}]2+, 32+, characterised by ESR spectroscopy. Complex 1+[PF6]−reacts with PhCCPh to give [Rh(CO)(η2-PhCCPh){HC(pz′)3}][PF6], 5+[PF6]−, in which the two-electron donor alkyne occupies an equatorial position in a trigonal bipyramidal κ3 structure. With MeCCR (R = Me or Et), 1+[PF6]− gives the κ2 square planar complexes [Rh{η4-C4Me2R2C(O)}{HC(pz′)3}][PF6] (R = Me, 6+[PF6]−; R = Et, 7+[PF6]−) in which the cyclopentadienone ligands are coordinated via two Rh–monoalkene bonds; the structurally characterised form of 7+ has the two alkyne units linked head-to-head with the CEt termini bound to the ketonic CO group. With HCCPh or HCCH, 1+ gives the octahedral, κ3 rhodium(III) metallacyclopentadienes [Rh(CO)(η1:η1′-CHCRCHCR){HC(pz′)3}][PF6] (R = Ph, 8+[PF6]−; R = H, 9+[PF6]−) with the two alkynes linked head-to-tail in 8+. The reaction of 1+ with HCCH also gives the cycloheptatrienone (tropone) derivative [Rh{η4-C6H6C(O)}{HC(pz′)3}][PF6], 10+[PF6]−, with a κ3 ligand and the cycloheptatrienone ligand bound to the metal via two Rh–C σ-bonds and one Rh–monoalkene interaction.

Frozen solution electron paramagnetic resonance (EPR) spectra are reported for [(η 4 -cod)Rh(μ-RNNNR) 2 -Ir(CO) 2 ] + (cod = 1,5-cyclooctadiene), [(PPh 3 )(CO)Rh(μ-RNNNR) 2 Ir(CO)(PPh 3 )] + (R = p-tolyl) and [Tp'Ir-(CO)(PPh 3 ] + (Tp' = hydrotris(3,5-dimethylpyrazolyl)borate). In the first spectrum, the Rh hyperfine coupling dominates and there are no significant quadrupolar effects. In the second spectrum, the low-field (g x and g y ) features are 1:2:1 triplets rather than 1:1:1:1 quartets (I = 3/2 for 1 9 1 Ir and 1 9 3 Ir), and in the third, the x and y features appear to be doublets. These anomalies result from the very large quadrupole moment for the iridium isotopes. This can be partially understood from a perturbation theory treatment, but quantitative simulations require direct matrix diagonalization and careful treatment of the problem, with respect to the orientation of the electron spin and nuclear spin quantization axes. The theoretical aspects of the calculations are presented, together with an interpretation of the results in terms of the electronic structures of the complexes.

Rearrangement of fac-[Cr(CO) 3 (η 2 -L 2 )(η 1 -L 2 )] + to mer-[Cr(CO) 3 (η 2 -L 2 )(η 1 -L 2 )] + (L 2 is a bidentate phosphine or arsine ligand) is a rapid thermally activated process. Loss of CO from mer-[Cr(CO) 3 (η 2 -L 2 )(η 1 -L 2 )] + to form trans-[Cr(CO) 2 (η 2 -L 2 ) 2 ] + is shown to be a clean photochemical process, perhaps the first example of a quantitative photochemical transformation for a Cr(I) complex. The bidentate phosphonite ligand, L 2 = (MeO) 2 PCH 2 CH 2 P(OMe) 2 , behaves quite differently: fac-[Cr(CO) 3 (η 2 -L 2 )(η 1 -L 2 )] + undergoes photochemical loss of CO to form a five-coordinate complex which converts slowly via thermal activation to trans-[Cr(CO) 2 (η 2 -L 2 ) 2 ] + .

X-Ray structural studies on the redox pair [Cr(CO)2(η-PhCCPh)(η-C6Me5H)]z (z = 0 and 1) show that one-electron oxidation of the neutral complex results in a shortening of the Cr–Calkyne bonds and a lengthening of the Cr–C(O) bonds, consistent with depopulation of a HOMO antibonding with respect to the metal–alkyne interaction. Oxidation leads to an increase in the substitutional lability of the Cr–CO bonds so that [Cr(CO)2(η-RCCR)(η-C6Me6)]+ (R = Ph or C6H4OMe-p) reacts with Lewis bases to give [Cr(CO)L(η-RCCR)(η-C6Me6)]+ {L = CNXyl, P(OMe)3 and P(OCH2)3CEt}, X-ray studies on which show a rotation of the alkyne to align with the remaining Cr–CO bond. ESR spectroscopic studies on [Cr(CO)L(η-RCCR)(η-C6Me6)]+ show delocalisation of the unpaired electron onto the alkyne ligand, consistent with its description as a three-electron donor. The cations [Cr(CO)L(η-RCCR)(η-C6Me6)]+ undergo both one-electron reduction and oxidation, and chemical oxidation of [Cr(CO){P(OCH2)3CEt}(η-p-MeOC6H4CCC6H4OMe-p)(η-C6Me6)]+ with AgPF6 gives the dication [Cr(CO){P(OCH2)3CEt}(η-p-MeOC6H4CCC6H4OMe-p)(η-C6Me6)]2+. Thus the two-electron alkyne of [Cr(CO)2(η-RCCR)(η-C6Me6)] is converted into the four-electron alkyne of [Cr(CO)L(η-RCCR)(η-C6Me6)]2+ by an ECE (E = electrochemical, C = chemical) process in which all of the intermediates have been fully characterised.

The complexes [Rh(CO)LTp′] {Tp′ = HBR3, R = 3,5-dimethylpyrazolyl; L = PPh32, PCy33, L = P(NMe2)34, P(C6H4Me-p)35 or P(C6H4Me-m)36}, prepared from [Rh(CO)2Tp′] 1 and L, and [Rh(PPh3)2L′] [L′ = Tp′ 8, Tp 9 or B(pz)410 {Tp = HB(pz)3, pz = pyrazolyl}] and [Rh(dppe)Tp′] 11, prepared from [{Rh(μ-Cl)(PPh3)2}2] or [{Rh(μ-Cl)(dppe)}2] and KL′, adopt four-co-ordinate κ2 structures, confirmed in the cases of 2–4, 6 and 8 by X-ray structural studies. By contrast, complex [Rh(CO){P(OPh)3}Tp′] 7 has a distorted five-co-ordinate square pyramidal structure with a long Rh ⋯ N contact [2.764(2) A] in the apical site and an essentially planar Rh(CO)PN2 basal plane. Each complex undergoes fluxional processes on the NMR timescale. One-electron oxidation of 1–11 gives the κ3 rhodium(II) cations 1+++–11++; the crystal structures of salts of 2+ and 8+ confirm stabilisation of the unusual rhodium(II) oxidation state by axial co-ordination of the third pyrazolyl ring as a result of oxidatively induced κ2–κ3 isomerisation. These structures and ESR spectroscopy are consistent with a five-co-ordinate square pyramidal geometry with the unpaired electron in a σ* Rh–Naxial orbital.

The cobaltafluorene complex Cp(PPh3)CoC12H8 (1) undergoes an electrochemically irreversible one-electron reduction in THF (Ep,c = ca. −2.56 V vs ferrocene) with release of PPh3 to give a persistent 17-electron Co(II) monoanion, 2-, which was characterized by electrochemistry and by ESR spectroscopy. The unpaired spin density in 2- is highly delocalized, with the majority being located in the cyclopentadienyl ring rather than the cobaltacyclic fragment. Reoxidation of 2- in the presence of L (L = phosphines, phosphites) forms Cp(L)CoC12H8 in high yield. Slow electron-transfer-catalyzed (ETC) substitution processes are found when 1 is electrolyzed in the presence of P(OMe)3, with the efficiency of the catalysis being dependent on both the relative and absolute concentrations of 1 and P(OMe)3. The substitution reaction is accounted for by a model in which the anion 2- is in equilibrium with the 19-electron adducts [Cp(L)CoC12H8]-, where L = THF, PPh3, P(OMe)3. Further reduction of 2- is possible in a reversi...

UV irradiation of [M(CO)3(η-arene)] and Me3SiCCSiMe3 gives [M(CO)2{CC(SiMe3)2}(η-arene)] (M = Cr, arene = C6H2Me4-1,2,3,5 2V, C6H3Me3-1,2,3 3V or C6H6 4V; M = Mo, arene = C6Me6 5V or C6H3Me3-1,3,5 6V). The crystal structure of [Cr(CO)2{CC(SiMe3)2}(η-C6H6)] 4V confirms the presence of the vinylidene ligand; the complex has approximate Cs symmetry with the C(SiMe3)2 plane orthogonal to the arenecentroid–Cr–Cα–Cβ plane. Voltammetry and IR and NMR spectroscopy show that in solution [Mo(CO)2{CC(SiMe3)2}(η-C6H3Me3-1,3,5)] 6V thermally equilibrates with the alkyne isomer [Mo(CO)2(η-Me3SiCCSiMe3)(η-C6H3Me3-1,3,5)] 6A. The vinylidene complexes [M(CO)2{CC(SiMe3)2}(η-arene)] 2V–6V undergo one-electron oxidation to the alkyne cations [M(CO)2(η-Me3SiCCSiMe3)(η-arene)]+ 2A+–6A+via fast, redox-induced vinylidene-to-alkyne isomerisation. These cations are reduced to the neutral alkyne complexes [M(CO)2(η-Me3SiCCSiMe3)(η-arene)] 2A–6A which slowly isomerise thermally to the neutral vinylidene complexes 2V–6V. Paramagnetic vinylidene and alkyne complex cations have been characterised by ESR spectroscopy; unpaired electron density is extensively delocalised from the metal centre to the C2 ligand, in agreement with the results of EHMO calculations.

Oxidations and reductions of a series of 48-electron (e-) metal clusters containing a tricobalt core have been investigated by voltammetry, electrolysis, IR spectroelectrochemistry, and EPR spectroscopy. Three isomers of Cp3Co3(CO)3 have been studied. The all-CO-bridging isomer C3v Cp3Co3(μ-CO)3 (1B) is stable in the 48 e- and 49 e- forms, but the 47 e- cation isomerizes to a doubly-CO-bridging structure 1T+. The other two isomers, Cp3Co3(μ3-CO)(μ-CO)2 (1F) and Cp3Co3(μ-CO)2(CO) (1T), are present in about a 1:1 ratio near room temperature, but their solutions show only Nernstian 1 e- cyclic voltammetry (CV) responses. IR spectroelectrochemistry and analysis of the E1/2 values show that the deceptively simple CV responses arise from a rapid equilibration between isomers 1F and 1T, rather than from a lack of structural change accompanying charge transfer. The cluster Cp*2Cp‘Co3(μ3-CO)(μ-CO)2 (3) (Cp* = C5Me5, Cp‘ = C5MeH4) is shown to retain its isomeric identity through three cluster oxidation states, most...

The preparation and characterization of [Cr(CO)2L(η-C6Me6)] (L = PEt3, PPh3, P(OEt)3 and P(OPh)3, are reported. One-electron oxidation affords unstable Cr(I) cations, [Cr(CO)2L(η-C6Me6)]+, EPR spectra of which are reported. Detailed analysis of the anisotropic 31P hyperfine interaction indicates that, in frozen CH2Cl2/THF, the phosphine and phosphite complexes have 2A‘ and 2A‘‘ ground states, respectively. The hyperfine anisotropy can be accounted for by dipolar interaction of the 31P nucleus with spin density on Cr and, in the case of the phosphite complexes, with ∼0.01 P 3py spin density resulting from π-backbonding. Line width anomalies observed in EPR spectra of these and other Cr(I) and Mn(II) “piano stool” complexes can be understood in terms of molecular distortions resulting from solvation in frozen solutions.

Isotropic and frozen-solution EPR spectra are reported for several Cr(I) carbonyl complexes of the type cis-[Cr(CO)4L2]+, mer- and fac-[Cr(CO)3L3]+, and trans-[Cr(CO)2L4]+, where L is a monodentate (or L2 a bidentate) phosphine or phosphonite ligand. Extended Huckel molecular orbital theory calculations were performed for cis- and trans-[Cr(CO)4L2], mer- and fac-[Cr(CO)3L3], and cis- and trans-[Cr(CO)2L4] (L = PH3, P(OH)3). The EPR results are discussed in light of the electronic structure predictions, which also provide some insights on the oxidation potentials and the isomerization reaction energetics of these complexes. Isotropic 31P hyperfine couplings can be understood in terms of spin densities in the Cr 3d, P 3s, and P 3p orbitals.

Reaction of the tris-chelating hexadentate podand ligand tris[3-(2-pyridyl)pyrazol-1-yl]hydroborate (Tp(Py)) with [Cu(MeCN)(4)][PF(6)] affords [Cu(I)(3)(Tp(Py))(2)][PF(6)] (1), which was crystallographically characterized. 1.(MeCN)(2): C(52)H(44)B(2)Cu(3)F(6)N(20)P, orthorhombic, Pna2(1); a = 24.592(7), b = 16.392(5), c = 13.365(5) Å; Z = 4. Each Cu(I) ion is four coordinated by one N,N '-bidentate arm from each ligand; each ligand therefore donates each bidentate arm to a different Cu(I) ion. The isosceles triangular arrangement of Cu(I) ions with N-donor ligands is reminiscent of the tricopper(I) site of ascorbate oxidase. One-electron oxidation of 1 affords the Cu(I)(2)Cu(II) complex [Cu(3)(Tp(Py))(2)][PF(6)](2) (2). The potentials of the Cu(I)/Cu(II) redox couples are affected by the ease with which the accompanying geometric rearrangement can occur. Thus, the first oxidation of 1 is facile (-0.52 V vs the ferrocene/ferrocenium couple, Fc/Fc(+)), but as a result of the concomitant structural rearrangement the second oxidation is rendered much more difficult (+0.12 V vsFc/Fc(+)) and results in slow decomposition of the product. A third oxidation does not occur at accessible potentials. This complex therefore exhibits negative cooperative behavior, in which the geometric change accompanying one metal-based redox change hinders further redox changes at other sites via an allosteric effect. EPR studies on the mixed-valence complex 2 show that in frozen glasses below 120 K the unpaired electron is delocalized over two metal centers (7-line spectrum), but above 160 K the electron becomes localized and gives a simple axial spectrum. The electronic spectrum of 2 in solution shows an intense band at 910 nm (epsilon 2100 dm(3) mol(-)(1) cm(-)(1)) which we believe to be an IVCT band. The combination of EPR and electronic spectral studies show that 2 is class III (fully delocalized over 2 centers) below 120 K but class II (localized but strongly interacting) at higher temperatures.

Dipolar hyperfine-coupling parameters for transition-metalndand (n+ 1)porbitals and isotropic hyperfine-coupling parameters for (n+ 1)sorbitals are computed from SCF–Hartree–Fock–Slater atomic orbitals. The parameters depend strongly on electronic configuration, particularly on the number ofdelectrons, and empirical equations are presented to allow computation of the parameters, given an assumed configuration.

The radical complex (C5Ph5)Cr(CO)3 reacts with small, neutral, monodentate Lewis bases (PMe3, PMe2Ph, P(OMe)3) in THF at −78 °C (PMe2Ph reacts at ambient temperature) to yield the monomeric substitution products (C5Ph5)Cr(CO)2L·THF as thermally stable solids. Electrochemical and spectroscopic data are provided. An X-ray crystal structure of the hemisolvate (C5Ph5)Cr(CO)2PMe3·0.5THF was obtained. Frozen-solution ESR spectra of (C5Ph5)Cr(CO)2L in toluene are comparable to those of other low-spin d5 “piano-stool” complexes. Rotation of the Cr(CO)2L moiety relative to the C5Ph5 ring is rapid on the ESR time scale in low-temperature liquid solutions and leads to axial powderlike spectra. Analysis of this effect leads to significant insights into the electronic structure.

The ferrocenyl group attached to the benzene ring in (C6H5Fc)Cr(CO)3 (3) functions as a reversible redox switch by providing a mechanism for the chromium center to be oxidatively activated to ligand substitution and addition reactions. Because initial oxidation of 3 occurs at the ferrocenyl group, the potentials required for activation are far lower than would otherwise be the case, and this allows for controlled reactions without the unproductive decomposition that often accompanies oxidation of (arene)Cr(CO)3 complexes. Although the chromium in 3+ is predominantly an 18-electron center, it is sufficiently activated to undergo very rapid CO substitution by P(OEt)3 to afford (C6H5Fc)Cr(CO)2P(OEt)3+ (4+). Internal electron transfer from Cr to Fe accompanies this CO substitution, with the result that the ferrocenium group in 3+ reverts to ferrocenyl in 4+, thus closing the redox switch. Upon oxidation of 4+ to 42+, the switch reopens and the chromium center is again activated, this time being attacked by P(...

The reaction of [Mo2(μ-C8Me8)(η-C5H5)2] (1) with 1 equiv of [Fe(η-C5H5)2][PF6] in CH2Cl2 gives [Mo2(μ-C8Me8)(η-C5H5)2][PF6] (1+[PF6]-), which reacts with a second 1 equiv of [Fe(η-C5H5)2][PF6] or 1 equiv of the trityl radical, •CPh3, to give [Mo2(μ-C8Me7CH2)(η-C5H5)2]+ (2+); depending on the oxidant the activation of one C−H bond of 1, with the formation of 2+, can occur by an EC or EEC mechanism. Complexes 1 and 1+ constitute the first isolable redox pair to show the structural effects of one-electron oxidation on a metal−alkene bond. An X-ray crystal structure analysis shows that the geometry of 1+ is similar to that of 1 and has approximate Cs symmetry. The Mo−Mo distance in 1+ is consistent with the presence of a MoMo double bond. The C8 chain acts as a double μ-allylidene ligand while binding to Mo(2) as an η-alkene through C(4) and C(5). The Mo−C distances for atoms C(1), C(2), C(3), C(6), C(7), and C(8) of the C8 chain are remarkably similar in 1 and 1+ while the Mo(2)−C(4) and Mo(2)−C(5) distances...

The complex [FeL2(NO)2](L = PEt31a, L = PPh31b or L2= dppe 1c) prepared from [{Fe(µ-I)(NO)2}2] and PPh3 or Ph2PCH2CH2PPh2(dppe){in the presence and absence of [Co(cp)2](cp =η5-C5H5) respectively} undergo one-electron oxidation at a platinum electrode in CH2Cl2. The complex [{Fe(µ-dppm)(NO)2}2]2, prepared from [{Fe(µ-I)(NO)2}2] and Ph2PCH2PPh2(dppm) in the presence of [Co(cp)2], undergoes two sequential one-electron oxidations. Complex 1b with [Fe(cp)2]+ gave 1b+, X-ray studies of which show a distorted tetrahedral geometry with near C2v symmetry. Oxidation of 1b leads to substantial lengthening of the Fe–P bonds and changes in the P–Fe–P and N–Fe–N angles. These changes are consistent with significant Fe–P π-bonding character in the singly occupied molecular orbital of 1b+. Cation 1b+ reacts with halide ions, giving [FeX(PPh3)(NO)2](X = Cl or I) and then [FeX2(NO)2]–, and with OPPh3 to give [Fe(OPPh3)(PPh3)(NO)2]+3. X-Ray studies on the last, as its [PF6]– salt, show a distorted tetrahedral geometry; the co-ordination angles at iron approach trigonal bipyramidal with the PPh3 ligand in one apical site and the other apical site vacant. The complex [Fe(OPPh3)2(NO)2]+4+ resulted from the reaction between [{Fe(µ-I)(NO)2}2] and OPPh3 in the presence of TlPF6. An analysis of the ESR spectra of the paramagnetic cations 1b+, 3+ and 4+, together with extended-Huckel MO calculations on models of 1b+ and 3+, suggest that the complex catalysts formed from [{Fe(µ-Cl)(NO)2}2] and Ag+ or Tl+ are also four-co-ordinate 17-electron radicals. A crystallographic database study of four-co-ordinate dinitrosyl complexes of iron and other metals confirms that the N–Fe–N and O ⋯ Fe ⋯ O angles are linearly related. Consideration of these geometric effects, and those resulting from oxidation of 1b, in the light of a model proposed by Summerville and Hoffmann provides insight into the bonding in these and related species.

The ESR spectra have been recorded for a series of cobalt dithiolene complexes [Co(S2C2R2)2L][R = CF3; L = P(OMe)3, P(OEt)3, P(OBun)3 or PPh(OMe)2]. In toluene, tetrahydrofuran or CH2Cl2–1,2-C2H4Cl2 solutions containing a small excess of L, reversible spectral changes are observed between 165 and 130 K which correspond to the addition of a second ligand to form a six-co-ordinate complex. For L = P(OMe)3 in toluene, equilibrium constants were estimated from the spectra which lead to ΔH°=–10 kJ mol–1, ΔS°=–68 J K–1 mol–1 for the five-/six-co-ordinate equilibrium. Ligand addition is not observed when CF3 is replaced by Ph, 4-MeC6H4 or 4-MeOC6H4 or L = PPh3, PEt3, P(OPri)3, P(OCH2CF3)3 or P(OPh)3. Complexes with L =(Ph2P)2CH2, (Ph2PCH2)2 or [(MeO)2PCH2]2 are five-co-ordinate with no evidence for chelation. Thus both steric and electronic effects are critical to the ability of the five-co-ordinate complex to add a sixth ligand. Unlike the five-co-ordinate complexes which are significantly distorted from ideal C2v symmetry, the six-co-ordinate complexes are highly symmetrical with greater delocalization of the unpaired electron onto the phosphite ligands.

The reaction of [Cu(NCMe)4][PF6] with 2 equivalents of [Mn(CN)Lx]{Lx=(CO)(dppm)2, cis-or trans-(CO)2[P(OR)3](dppm)(R = Ph or Et, dppm = Ph2PCH2PPh2)} in CH2Cl2 gave [Cu{µ-NC)MnLx}2][PF6]. With 2 equivalents of [Mn(CN)Lx] in toluene, AgPF6 gave [Ag{(µ-NC)MnLx}2]+{Lx=cis- or trans-(CO)2[P(OR)3](dppm)(R = Ph or Et)} but in CH2Cl2cis-[Mn(CN)(CO)2(PEt3)(dppe)](dppe = Ph2PCH2CH2PPh2) or trans-[Mn(CN)(CO)(dppm)2] and AgX (X = BF4–, PF6– or SbF6–) gave the tricationic manganese(II) complexes [Ag{(µ-NC)Mn(CO)(dppm)2}2][PF6]3 and [Ag{(µ-NC)MnLx}2]X3{Lx=trans-(CO)2(PEt3)(dppe)]; the complexes [Ag{(µ-NC)MnLx}2][PF6]3{Lx=trans-(CO)2(P(OR)3](dppm)(R = Ph or Et)} were prepared directly from Ag[PF6] and trans-[Mn(CN)(CO)2{P(OR)3}(dppm)][PF6](R = Ph or Et) in CH2Cl2. Treatment of [AuCl(tht)](tht = tetrahydrothiophene) with [Mn(CN)Lx] in CH2Cl2 in the presence of Tl[PF6] yielded [Au{(µ-NC)MnLx}2][PF6]{Lx=(CO)(dppm)2, cis- or trans-(CO)2[P(OR)3](dppm)(R = Ph or Et)}. X-Ray structural studies on [Ag{(µ-NC)MnLx}2][PF6]{Lx=trans-(CO)2[P(OPh)3](dppm)}, [Au{(µ-NC)MnLx}2][PF6]{Lx=trans-(CO)2[P(OEt)3](dppm)}, and [Ag{(µ-NC)MnLx}2][PF6]3[Lx=(CO)(dppm)2] showed, in each case, near linear Mn–CN–M′–NC–Mn skeletons (M′= Ag or Au); the Mn–P and P–substituent bond lengths are consistent with octahedral MnI and MnII centres in the monocations and trication respectively. Each of the complexes [M′{(µ-NC)MnLx}2][PF6]{M′= Cu or Au, Lx=(CO)(dppm)2; M′= Cu or Ag, Lx=trans-(CO)2[P(OR)3](dppm)(R = Ph or Et)} showed one reversible two-electron oxidation wave at a platinum electrode in CH2Cl2; the trication [Cu{(µ-NC)Mn(CO)(dppm)2}2]3+ was generated in solution by controlled potential electrolysis of [Cu{(µ-NC)Mn(CO)(dppm)2}2]+, and [Au{(µ-NC)Mn(CO)(dppm)2}2][PF6]3 was prepared by chemical oxidation of [Au{(µ-NC)Mn(CO)(dppm)2}2][PF6] with [Fe(cp)2][PF6](cp =η-C5H5) in CH2Cl2. Magnetic and ESR spectroscopic studies provided further evidence for the presence of two isolated low-spin MnII centres in the trications [Ag{(µ-NC)MnLx}2]3+{Lx=(CO)(dppm)2, trans-(CO)2[P(OR)3](dppm)(R = Ph or Et) or trans-(CO)2(PEt3)(dppe)}. By contrast, [Au{(µ-NC)MnLx}2]+{Lx=trans-(CO)2[P(OR)3(dppm)(R = Et or Ph)} showed two reversible one-electron oxidation waves corresponding to the stepwise formation of di- and tri-cations. Electrolytic oxidation of [Au{(µ-NC)MnLx}2]+ in tetrahydrofuran, or chemical oxidation with [N(C6H4Br-p)3]+ or [Fe(η-C5H4COMe)(cp)]+ in CH2Cl2, gave solutions of [Au{(µ-NC)MnLx}2]2+{Lx=trans-(CO)2[P(OEt)3](dppm)}, IR spectroscopic and voltammetric studies on which are compatible with weak interaction between the two manganese centres in the mixed-valence dication.

A discussion of the connection between EPR parameters and the electronic structures of mono-nuclear low-spin d 5 complexes, including systems with orbitally degenerate ground states which undergo Jahn-Teller distortions. EPR experimental results are critically surveyed for complexes of Ti(—I), V(0), Cr(I), Mn(II), Fe(III), Co(IV), and their heavier congeners. A review with 426 references.

The rate law for the manganese(II)-induced decomposition of peroxomonosulfate ion, HOOSO 3 − , is with rate constants k Mn = (5.1±0.3)×10 −3 and (9.7±0.2)×10 −3 M − 1 2 s −1 at 50 °C in H 2 SO 4 and HClO 4 media, respectively. The rate constant is sensitive to the nature and concentration of the anion. The values of Δ H ‡ and Δ S ‡ are 31±2 kJ mol −1 and −194±5 J mol −1 K −1 , respectively, in 1 M H 2 SO 4 . The presence of manganese(III) as an intermediate and as a minor product is confirmed. Peroxodisulfate, a minor product presumably from chain termination, has been used to estimate the chain length. On the basis of all the data, a mechanism quite different from most metal-induced peroxomonosulfate decompositions is postulated and some consequences and complications are elaborated.

The X-ray crystal structure analyses of the three redox pairs [Rh 2 (CO) 2 LL'{μ-PhNC(Me)NPh)} 2 ] z [z=0,1; L=L'=PPh 3 (1, 1 + ); L=L'=P(OPh) 3 (1, 1 + ); L=PPh 3 , L'= P(OPh) 3 (3, 3 + )] are reported and the molecular structures compared with those of [Rh 2 (CO) 2 (PPh 3 ) 2 (μ-RNNNR) 2 ] z [z=0,1; R=p-tolyl (4, 4 + )]

Infared, ERS, and electronic absorption spectroscopic studies are reported on the 18+δ Ci(CO) 3 L 2 complex. (L 2 is the chelating phosphine ligand 2,3-bis(diphenylphosphino)malec anhydride. 18+δ complexes are 19-electron complexes in which the unpaired electron is primarily localized on a ligand.) The spectra are solvent dependent and are interpreted in terms of increased delocalization of the unpaired electron form an L 2 (π * ) orbital onto the Co(CO) 3 portion of the molecule with decreasing solvent polarity

The EPR spectra (characteristic of triplet species) of the complexes [Cu2L12(µ-1,3-O2CMe)][PF6]1[HL1= 6-(2-hydroxyphenyl)-2,2′-bipyridine] and [Cu2L22(µ-1,3-O2CMe)][PF6]2[HL2= 2-(2-hydroxyphenyl)-1,10-phenanthroline], previously structurally characterised as containing Cu2(µ-O)2 cores in which the phenolate oxygen atoms of L1 and L2 bridge both copper(II) centres, have been successfully modelled using a perturbation-theory approach. The Cu ⋯ Cu distances calculated from the spectra are in reasonable agreement with the values given by the crystal structures. By measuring the variation in intensity of the spectrum of 1 with temperature it was established that 1 is antiferromagnetic with J= 52 ± 8 cm–1. Variable-temperature magnetic susceptibility measurements on 1 and 2 confirm the presence of moderate antiferromagnetic couplings, although the presence of a mononuclear impurity in each case precludes use of the Bleaney–Bowers equation to obtain more accurate values of J.

The d4 halide complexes [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp'] [R = Me, M = W, X = F; R = Ph, M = Mo or W, X = F or Cl; Tp' = hydrotris(3,5-dimethylpyrazolyl)borate] undergo two-electron oxidation in the presence of a halide source to give the d2 monocations [MX1X2(eta-PhC[triple bond, length as m-dash]CPh)Tp']+ (R = Me, M = W, X1 = X2 = F; R = Ph, M = Mo, X1 = X2 = F or Cl; M = W, X1 = X2 = F or Cl; X1 = F, X2 = Cl). Each monocation (R = Ph) shows two reversible one-electron reductions (the second process was not detected for R = Me) corresponding to the stepwise formation of the neutral d3 and monoanionic d4 analogues, [MX1X2(eta-PhC[triple bond, length as m-dash]CPh)Tp'] and [MX1X2(eta-PhC[triple bond, length as m-dash]CPh)Tp']- respectively; the potentials for the two processes can be 'tuned' over a range of ca. 1.0 V by varying M and X. Chemical one-electron reduction of [MX2(eta-PhC[triple bond, length as m-dash]CPh)Tp']+ gave [MX2(eta-PhC[triple bond, length as m-dash]CPh)Tp'] (M = Mo or W, X = F or Cl). X-Ray structural studies on the redox pairs [WX2(eta-PhC[triple bond, length as m-dash]CPh)Tp']z (X = F and Cl, z = 0 and 1+) show the alkyne to bisect the X-W-X angle in the d2 cations but align more closely with one M-X bond in the neutral d3 molecules, consistent with the anisotropic ESR spectra of the latter; the solution ESR spectrum of [MoF2(eta-PhC[triple bond, length as m-dash]CPh)Tp'] showed equivalent fluorine atoms, i.e the alkyne oscillates at room temperature. The successful isolation of [MX2(eta-PhC[triple bond, length as m-dash]CPh)Tp']+ and [MX2(eta-PhC[triple bond, length as m-dash]CPh)Tp'] completes a series in which d6 to d2 alkyne complexes are linked in a redox family tree by sequential one-electron transfer and substitution reactions. The implications for such trees in the production of new species and the selective synthesis of paramagnetic complexes acting as synthetically useful 'alkyne radicals' are discussed.

Influence de la temperature sur les spectres RPE d'un marqueur de spin (TEMPO) dans une solution de DMSO afin de montrer l'existence ou non d'une microphase liquide