A tris(thioxanthate) of nickel(II) and its transformation to a dinuclear trithiocarbonate complex. Synthesis and structure of [Et<SUB>4</SUB>N]<SUB>2</SUB>[Ni<SUB>2</SUB>(SEt)<SUB>2</SUB>(CS<SUB>3</SUB>)<SUB>2</SUB>]

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Nickel(III)-sulfur binding. Chemistry of the tris(xanthate) family

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Sulfur-ligated nickel oxidation states. Chemistry of a family of NizS<SUB>2</SUB>N<SUB>4</SUB> (z = +2, +3, +4) complexes incorporating hexadentate thioether-imine-oxime binding

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Binding of bi- and tri-valent nickel by azophenolates incorporating thioether/ether donor sites

Nickel(II) complexes of tri- and hexa-dentate ligands in which the donors are azo nitrogen, phenolic oxygen and thioether sulfur or ether oxygen have been isolated. Structure determination of three complexes has established the presence of distorted octahedral NiN₂O₂X₂(X = S or O) co-ordination spheres. In dichloromethane solution the nickel(III)–nickel(II) couple is electrochemically observable for the thioether complexes with E½ in the range 0.65–0.85 V vs. saturated calomel electrode. The blueviolet nickel(III) species can be quantitatively electrogenerated in solution. Upon freezing (77 K) axial EPR spectra (g∥≈ 2.18, g⊥&#8776;2.06) compatible with the uncommon hole configuration (d_x²–_y²)1 are observed. The ether complexes are more difficult to oxidise and the nickel(III) species are not tractable. This is consistent with the higher strength of nickel–thioether compared to –ether binding

Azooximates of bi- and tri-valent nickel

The reaction of arylazooximes, RC(NOH)NNPh (HL^R, R = Me or Ph), with nickel(II) acetate tetrahydrate in methanol under anaerobic conditions afforded [NiL^R₃]^- isolated as the NEt₄⁺ salt. One (L^Ph)^- ligand in [NiL^Ph₃]^- underwent facile displacement by L–L ligands like 2,2′-bipyridine (bipy) furnishing [NiL^Ph₂ (bipy)]. The Ni^III–Ni^II reduction potential of [NiL^R₃]^- in acetonitrile is ≈ 0.1 V vs. saturated calomel electrode. The trivalent complex [NiL^R₃] was quantitatively isolated via constant-potential electrolysis at 0.3 V. The Ni^IV–Ni^III couple of the tris chelate was observed near 0.9 V, but the nickel(IV) complex could not be isolated in the solid state. The relatively low metal reduction potential allowing facile preparation of the stable [NiL^R₃] system is attributed to the strong-field nature of the oximato-N atom. In going from [NiL^Ph₃]^- to [NiL^Ph₂ (bipy)] the Ni^III–Ni^II reduction potential increases by ≈ 0.3 V showing that (L^Ph)^- is a much better stabiliser of Ni^III than is bipy. The crystal structures of [NEt₄][NiL^Ph₃] and [NiL^Ph₂ (bipy)] have been determined. The geometry of [NiL^R₃] (S = ½) was studied with the help of its EPR spectrum (d_z2 ground state) in the [CoL^R₃] lattice. Both [NiL^R₃]^- and [NiL^R₃] have exclusive meridional geometry consistent with steric and angular-overlap considerations. In [NiL^Ph₂ (bipy)] the two anionic oximato functions are placed in mutually trans positions. The oximato-N ligand displays substantial trans influence. Thus in [NiL^Ph₃]^- the Ni–N (azo) bond lying trans to Ni–N (oxime) is ≈ 0.05 Å longer than the other two mutually trans Ni–N (azo) bonds. The average Ni–N (azo) distance in [NiL^Ph₂ (bipy)] is ≈ 0.04 Å shorter than that in [NiL^Ph₃]^- because none of the Ni–N (azo) bonds in the former complex is subject to the trans influence of Ni–N (oxime). In both complexes the Ni–N (oxime) lengths are significantly shorter than the Ni–N (azo) lengths, consistent with stronger Ni–N (oxime) σ bonding which is also a reason behind the strong-field nature of the oximate ligand

Nickel complexes of tridentate ligands incorporating thioether and triazene-1-oxide functions. Synthesis, structure and metal redox

The reaction of nickel(II) acetate with RN(O)NNHC6H4SMe (HL1 : R = Me; HL2 : R = Prn; general abbreviation HL) in aqueous ethanol affords [NiL2] as brown crystalline solids. The X-ray structure of [NiL22] is reported. Each ligand acts in the tridentate meridional SNO fashion. The Ni(SNO)2 coordination sphere is severely distorted from octahedral geometry. The Ni---S distances, 2.519(2) and 2.549(2) &#197;, constitute the longest nickel(II)---thioether bonds reported so far. Due to low symmetry, the octahedral &#957;1 band of the complexes are split into components lying at ca 1400 and 1000 nm. The complexes display quasireversible cyclic voltammograms corresponding to the metal redox couple [NiIIIL2]+/[NiIIL2], E1/2 &#8776; 0.75 V (vs S.C.E.). Coulometrically generated [NiIIIL2]+ displays rhombic EPR spectra, the g values of the erpendicular components being larger than that of the parallel component corresponding to the (dz2)1 ground state

Chemistry of ferro- and ferriverdins. Iron redox and geometrical stereodynamism

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Synthesis and structure of binuclear thioazobenzene pallada-cycles and their reaction with m-chloroperbenzoic acid: formation and structure of dinuclear azophenolates

The cyclopalladation of 1,3-bis(2-thioazobenzene)propane (L<SUP>1</SUP>H<SUB>2</SUB>) and its methyl substituted derivative L<SUP>2</SUP>H<SUB>2</SUB> affords complexes of the type LPd<SUB>2</SUB>Cl<SUP>2</SUP> (where L represents L<SUP>1</SUP> or L<SUP>2</SUP> which have been characterised by spectroscopy and X-ray crystallography. The crystal structure of L<SUP>1</SUP>Pd<SUP>2</SUP>C<SUP>2</SUP> has revealed that each azobenzene fragment along with its thioether sulphur acts in the tridentate (C,N,S) fashion and the fourth coordination position is occupied by a chloride ion. The complexes are thus of type [Pd(C,N,S)Cl]<SUB>2</SUB>, with a Pd Pd contact of 5.420(1) &#197;. The metallated carbon atom exerts a strong trans influence on the Pd---S bond. The reaction of LPd<SUB>2</SUB>Cl<SUB>2</SUB> with am-chloroperbenzoic acid leads to smooth oxygen insertion into both the Pd---C bonds to give excellent yields of dinuclear azophenolato complexes o-LPd<SUB>2</SUB>Cl<SUB>2 </SUB>having the coordination sphere [Pd(O,N,S)Cl]<SUB>2</SUB>. The crystal structure of o-L<SUP>1</SUP>Pd<SUB>2</SUB>Cl<SUB>2</SUB> is similar to that of L<SUP>1</SUP>Pd<SUB>2</SUB>Cl<SUB>2</SUB> but with a somewhat longer Pd...Pd distance of 5.890(1) &#197;. The insertion reaction has a negative entropy of activation, in keeping with an associative transition state for the electrophilic incorporation of oxygen. Reduction of the azophenolato complexes with hydrazine hydrate affords the free azophenols (o-LH<SUB>2</SUB>) in high yields. Thus organometallic route to o-LH<SUB>2</SUB> from LH<SUB>2</SUB> is provided