Square-planar imido complexes of cobalt: synthesis, reactivity and computational study.

Treatment of [Co(N)(PNP)] (PNP = anion of 2,5-bis(di--butylphosphinomethyl)pyrrole) with one equivalent of an aryl azide generates the four-coordinate imido complexes [Co(NAr)(PNP)] (Ar = mesityl, phenyl, or 4-Bu-phenyl). X-ray crystallographic analysis of the compounds shows an unusual square-planar geometry about cobalt with nearly linear imido units. In the presence of the hydrogen atom donor, TEMPOH, [Co(NPh)(PNP)] undergoes addition of the H atom to the imido nitrogen to generate the corresponding amido complex, [Co(NHPh)(PNP)], whose structure and composition were verified by independent synthesis.

Assessment of Iron-Based Spin-Orbit Coupling Effects in Pt-Fe Heterobimetallic Lantern Complexes via Fe Mössbauer Spectroscopy.

A series of heterobimetallic lantern complexes, [PtFe(SOCR)(pyX)] where R = Me, X = H (), X = NH (), X = SMe (); R = Ph, X = H (), X = NH (), X = SMe (), have been prepared and characterized spectroscopically. Compounds , , and are reported herein for the first time. The high-spin iron(II) sites of - have been investigated using Fe Mössbauer spectroscopy.

The Active-Site [4Fe-4S] Cluster in the Isoprenoid Biosynthesis Enzyme IspH Adopts Unexpected Redox States during Ligand Binding and Catalysis.

()-4-Hydroxy-3-methylbut-2-enyl diphosphate reductase, or IspH (formerly known as LytB), catalyzes the terminal step of the bacterial methylerythritol phosphate (MEP) pathway for isoprene synthesis. This step converts ()-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP) into one of two possible isomeric products, either isopentenyl diphosphate (IPP) or dimethylallyl diphosphate (DMAPP). This reaction involves the removal of the C4 hydroxyl group of HMBPP and addition of two electrons.

Spectroscopic and Theoretical Investigation of High-Spin Square-Planar and Trigonal Fe(II) Complexes Supported by Fluorinated Alkoxides.

The electronic structures and spectroscopic behavior of three high-spin Fe complexes of fluorinated alkoxides were studied: square-planar {K(DME)}[Fe(pin)] () and quasi square-planar {K(222)}[Fe(pin)] () and trigonal-planar {K(18C6)}[Fe(OCF)] () where pin = perfluoropinacolate and OCF = -perfluoro--butoxide. The zero-field splitting (ZFS) and hyperfine structure parameters of the = 2 ground states were determined using field-dependent Fe Mössbauer and high-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopies. The spin Hamiltonian parameters were analyzed with crystal field theory and corroborated by density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations.

Homologous acetone carboxylases select Fe(II) or Mn(II) as the catalytic cofactor.

Acetone carboxylases (ACs) catalyze the metal- and ATP-dependent conversion of acetone and bicarbonate to form acetoacetate. Interestingly, two homologous ACs that have been biochemically characterized have been reported to have different metal complements, implicating different metal dependencies in catalysis. ACs from proteobacteria and share 68% sequence identity but have been proposed to have different catalytic metals.

Evolution of Bonding and Magnetism Changes in Valence Electron Count in CuFeCoGe.

A series of solid solutions, CuFeCoGe ( = 0, 0.2, 0.4, 0.

Electronic Structure of Tetrahedral, = 2, [Fe{(EPPr)N}], E = S, Se, Complexes: Investigation by High-Frequency and -Field Electron Paramagnetic Resonance, Fe Mössbauer Spectroscopy, and Quantum Chemical Studies.

In this work, we assessed the electronic structures of two pseudotetrahedral complexes of Fe, [Fe{(SPPr)N}] ) and [Fe{(SePPr)N}] (), using high-frequency and -field EPR (HFEPR) and field-dependent Fe Mössbauer spectroscopies. This investigation revealed = 2 ground states characterized by moderate, negative zero-field splitting (zfs) parameters . The crystal-field (CF) theory analysis of the spin Hamiltonian (sH) and hyperfine structure parameters revealed that the orbital ground states of and have a predominant d character, which is admixed with d (∼10%).

Insights into Molecular Magnetism in Metal-Metal Bonded Systems as Revealed by a Spectroscopic and Computational Analysis of Diiron Complexes.

A pair of bimetallic compounds featuring Fe-Fe bonds, [Fe(PrNPPh)FeR] (R = PMe, ≡NBu), have been investigated using High-Frequency Electron Paramagnetic Resonance (HFEPR) as well as field- and temperature-dependent Fe nuclear γ resonance (Mössbauer) spectroscopy. To gain insight into the local site electronic structure, we have concurrently studied a compound containing a single Fe(II) in a geometry analogous to that of one of the dimer sites. Our spectroscopic studies have allowed for the assessment of the electronic structure via the determination of the zero-field splitting and Fe hyperfine parameters for the entire series.

Model Dimeric Manganese(IV) Complexes Featuring Terminal Tris-hydroxotetraazaadamantane and Various Bridging Ligands.

A series of model dinuclear manganese(IV) complexes of the general formula [(HCOH)(L')Mn(μ-L)Mn(L')(HOCH)] is presented. These compounds feature capping 4,6,10-trihydroxo-3,5,7-trimethyl-1,4,6,10-tetraazaadamantane ligands derived from a polydentate oxime compound (L'). The bridging ligands L include azide (), methoxide (), and oxalate () anions.

Homoleptic mono-, di-, and tetra-iron complexes featuring phosphido ligands: a synthetic, structural, and spectroscopic study.

We report the first series of homoleptic phosphido iron complexes synthesized by treating either the β-diketiminato complex [(Dippnacnac)FeClLi(dme)] (Dippnacnac = HC[(CMe)N(CH-2,6-iPr)]) or [FeBr(thf)] with an excess of phosphides RPLi (R = tBu, tBuPh, Cy, iPr). Reaction outcomes depend strongly on the bulkiness of the phosphido ligands. The use of tBuPLi precursor led to an anionic diiron complex 1 encompassing a planar FeP core with two bridging and two terminal phosphido ligands.

Valence tautomerism in a cobalt-verdazyl coordination compound.

Coordination of 1-isopropyl-3,5-dipyridyl-6-oxoverdazyl to cobalt results in a dication best described in the solid state as a high spin cobalt(ii) ion coordinated to two radical ligands with an S = 3/2 ground state. On dissolution in acetonitrile, the cobalt(ii) form equilibrates with a cobalt(iii) valence tautomer with an S = 1/2 ground state.

Advanced Paramagnetic Resonance Studies on Manganese and Iron Corroles with a Formal d Electron Count.

Metallocorroles wherein the metal ion is Mn and formally Fe are studied here using field- and frequency-domain electron paramagnetic resonance techniques. The Mn corrole, Mn(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole trianion), exhibits the following = 2 zero-field splitting (zfs) parameters: = -2.67(1) cm, || = 0.

Radical Dimerization in a Plastic Organic Crystal Leads to Structural and Magnetic Bistability with Wide Thermal Hysteresis.

The nitroxyl radical 1-methyl-2-azaadamantane -oxyl (Me-AZADO) exhibits magnetic bistability arising from a radical/dimer interconversion. The transition from the rotationally disordered paramagnetic plastic crystal, Me-AZADO, to the ordered diamagnetic crystalline phase, (Me-AZADO), has been conclusively demonstrated by crystal structure determination from high-resolution powder diffraction data and by solid-state NMR spectroscopy. The phase change is characterized by a wide thermal hysteresis with high sensitivity to even small applied pressures.

Transition metal-mediated reductive coupling of diazoesters.

The first transition metal mediated reductive coupling of diazoesters through the terminal nitrogens is reported. The resulting tetrazene-bridged bis(diazenylacetate) serves as a novel dinucleating ligand to iron(III). DFT calculations suggest that the reductive coupling takes place via a κ intermediate, which induces significant radical character on the terminal nitrogen.

Square-planar Co(iii) in {O} coordination: large ZFS and reactivity with ROS.

Oxidation of distorted square-planar perfluoropinacolate Co compound [CoII(pinF)2]2-, 1, to [CoIII(pinF)2]1-, 2, is reported. Rigidly square-planar 2 has an intermediate-spin, S = 1, ground state and very large zero-field splitting (ZFS) with D = 67.2 cm-1; |E| = 18.

Observation of current rectification by the new bimetallic iron(iii) hydrophobe [Fe(L)] on Au|LB-molecule|Au devices.

Targeting the development of stimulus-responsive molecular materials with electronic functionality, we have synthesized and studied the redox and electronic properties of a new bimetallic iron hydrophobe [FeIII2(LN4O6)] (1). The new H6LN4O6 ligand displays bicompartmental topology capable of accomodating two five-coordinate HSFeIII ions bridged by tetraaminobenzene at a close distance of ca. 8 Å.

Catalytic Nitrene Homocoupling by an Iron(II) Bis(alkoxide) Complex: Bulking Up the Alkoxide Enables a Wider Range of Substrates and Provides Insight into the Reaction Mechanism.

The reaction of HOR' (OR' = di-t-butyl-(3,5-diphenylphenyl)methoxide) with an iron(II) amide precursor forms the iron(II) bis(alkoxide) complex Fe(OR')(THF) (2). 2 (5-10 mol %) serves as a catalyst for the conversion of aryl azides into the corresponding azoarenes. The highest yields are observed for aryl azides featuring two ortho substituents; other substitution patterns in the aryl azide precursor lead to moderate or low yields.

BaFeIrO: A Polar Semiconducting Triple Perovskite with Near Room Temperature Magnetic Ordering.

The crystal chemistry and magnetic properties for two triple perovskites, BaFeIrO and BaNiIrO, grown as large, highly faceted single crystals from a molten strontium carbonate flux, are reported. Unlike the idealized AMM'O hexagonal symmetry characteristic of most triple perovskites, including BaNiIrO BaFeIrO possesses significant site-disorder, resulting in a noncentrosymmetric polar structure with trigonal symmetry. The valence of iron and iridium in the heavily distorted Fe/Ir sites was determined to be Fe(III) and Ir(V) by X-ray absorption near edge spectroscopy (XANES).

Chemical reaction within a compact non-porous crystal containing molecular clusters without the loss of crystallinity.

The very rare occurrence of a gas-solid chemical reaction has been found to take place on a molecule within a compact non-porous crystal without destroying its long-range structural order and retaining similar crystal structures when yellow crystals of FeII4()Cl(MeOH) were exposed to air to give black [FeIII4()Cl(OH)]·2HO. The latter cannot be synthesised directly. The original cluster underwent an exchange of methanol to hydroxide, an oxidation of Fe(ii) to Fe(iii), a change in stereochemistry and hydration while the packing and space-group remained unaltered.

Heteroleptic Fe(II) Complexes with NS Coordination as a Platform for Designing Spin-Crossover Materials.

Heteroleptic complexes [Fe(bpte)(bim)]X and [Fe(bpte)(xbim)]X (bpte = S,S'-bis(2-pyridylmethyl)-1,2-thioethane, bim = 2,2'-biimidazole, xbim = 1,1'-(α,α'-o-xylyl)-2,2'-biimidazole, X = ClO, BF, OTf) were prepared by reacting the corresponding Fe(II) salts with a 1:1 mixture of the ligands. All mononuclear complexes exhibit temperature-induced spin crossover (SCO) with the onset above room temperature. The SCO is rather gradual, due to low cooperativity of interactions between the cationic complexes, as revealed by crystal structure analyses.

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe(μ-O)] Cluster.

The synthesis, X-ray crystal and electronic structures of [Fe(μ-O)(mpmae)(OAc) Cl], 1, where mpmae-H = 2-(N-methyl-N-((pyridine-2-yl)methyl)amino)ethanol, are described. This cluster comprises three high-spin ferric ions and exhibits a T-shaped site topology. Variable-frequency electron paramagnetic resonance measurements performed on single crystals of 1 demonstrate a total spin S = 5/2 ground state, characterized by a small, negative, and nearly axial zero-field splitting tensor D = -0.

Synthetic, Structural, and Spectroscopic Characterization of a Novel Family of High-Spin Iron(II) [(β-Diketiminate)(phosphanylphosphido)] Complexes.

This work describes a series of iron(II) phosphanylphosphido complexes. These compounds were obtained by reacting lithiated diphosphanes RPP(SiMe)Li (R = t-Bu, i-Pr) with an iron(II) β-diketiminate complex, [LFe(μ-Cl)Li(DME)] (1), where DME = 1,2-dimethoxyethane and L = Dippnacnac (β-diketiminate). While the reaction of 1 with t-BuPP(SiMe)Li yields [LFe(η-MeSiPP-t-Bu)] (2), that of 1 with equimolar amounts of i-PrPP(SiMe)Li, in DME, leads to [LFe(η-i-PrPPSiMe)] (3).

Dinuclear Metallacycles with Single M-X-M Bridges (X = Cl, Br; M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)): Strong Antiferromagnetic Superexchange Interactions.

A series of monochloride-bridged, dinuclear metallacycles of the general formula [M(μ-Cl)(μ-L)](ClO) have been prepared using the third-generation, ditopic bis(pyrazolyl)methane ligands L = m-bis[bis(1-pyrazolyl)methyl]benzene (L), M = Cu(II), Zn(II), and L = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (L*), M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II). These complexes were synthesized from the direct reactions of M(ClO)·6HO, MCl, and the ligand, L or L*, in the appropriate stoichiometric amounts. Three analogous complexes of the formula [M(μ-Cl)(μ-L)](BF), L = L, M = Cu(II), and L = L*, M = Co(II), Cu(II), were prepared from the reaction of [M(μ-F)(μ-L)](BF) and (CH)SiCl.

Synthesis of a Ferrolite: A Zeolitic All-Iron Framework.

Crystals of the first sodalite-type zeolite containing an all-iron framework, a ferrolite, Ba (Fe O )Na (OH) ⋅x H O, were synthesized using the hydroflux method in nearly quantitative yield. Ba (Fe O )Na (OH) ⋅x H O crystallizes in the cubic space group Pm3‾m with a=10.0476(1) Å.