Hexanuclear Iron Research Articles

A (3,6)-connected metal-organic framework consisting of chair-like {Fe6} clusters and BTC linkers

A 2-D framework composed of a chair-like {Fe6} cluster and BTC linkers, [Fe6(BTC)2(HCOO)6(DMF)6] (1, BTC = 1,3,5-benzenetricarboxylate), has been synthesized under solvothermal conditions and characterized by elemental analysis, infrared spectroscopy, thermal gravimetric analysis, and single-crystal X-ray diffraction analysis. The {Fe6} cluster contains six iron ions and six formate ligands, with each formate coordinating with three iron ions to construct the hexa-nuclear iron wheel. The {Fe6} wheels are further connected via BTC ligands resulting in the first example of a 2-D framework based on {Fe6} clusters and BTC linkers. A magnetic study indicates that intramolecular antiferromagnetic interactions exist in the hexa-nuclear iron cluster.

Visible-Light Generation of the Naked 12-Electron Fragment C5H5Fe+: Alkyne-to-Vinylidene Isomerization and Synthesis of Polynuclear Iron Vinylidene and Alkynyl Complexes Including Hexairon Stars

Visible-light photolysis of [FeCp(η(6)-C(6)H(5)CH(3))][PF(6)] using a simple 100-W bulb or a compact fluorescent light bulb in the presence of terminal alkynes and dppe yielded the vinylidene complexes [FeCp(═C═CHR)(dppe)][PF(6)] that were deprotonated by t-BuOK to yield the alkynyl complexes [FeCp(-C≡CR)(dppe)]. The reaction has been extended to the synthesis of bis-, tris, tetra-, and hexanuclear iron complexes including three alkynes of the ferrocenyl family.

{Fe₆O₂}-Based Assembly of a Tetradecanuclear Iron Nanocluster.

The tetradecanuclear FeIII pivalate nanocluster [Fe14O10(OH)4(Piv)18], comprising a new type of metal oxide framework, has been solvothermally synthesized from a hexanuclear iron pivalate precursor in dichlormethane/acetonitrile solution. Magnetic measurements indicate the presence of very strong antiferromagnetic interactions in the cluster core.

ChemInform Abstract: A New Hexanuclear Iron—Selenium Nitrosyl Cluster: Primary Exploration of the Preparation Methods, Structure, and Spectroscopic and Electrochemical Properties.

AbstractThe structures of the nitrosyl complexes (II) and (IV) are determined by single crystal XRD.

2,6‐Bis(pyrazol‐3‐yl)pyridine as Meridional Capping Ligand: Synthesis, Characterization, and Crystal Structure of the First Corresponding Hexanuclear Iron(III) Complex

AbstractBased on the 2,6‐bis(pyrazol‐3‐yl)pyridine ligand (H2bpp) the hexanuclear iron(III) complex [Fe6(bpp)4(μ3‐O)2(μ‐OMe)3(μ‐OH)Cl2] (1) was synthesized. The reaction with iron(II) chloride and additional pyridine leads to the exclusive formation of the complex through self‐assembly process. Six octahedrally coordinated iron atoms are linked through the pyrazolido groups of four H2bpp ligands. These are further linked through bridging hydroxido, methoxido, and oxido groups. The complex has been characterized by IR spectroscopy, ESI mass spectrometry, elemental analysis and X‐ray crystallography. Temperature‐dependent magnetic measurements indicate strong antiferromagnetic exchange interaction between the high‐spin iron(III) ions within the complex, which leads to an S = 0 spin ground state. As a result of the two Fe3(μ3‐O) fragments two frustrated exchange pathways are present. In addition the properties of H2bpp as a potential capping ligand for the synthesis of heteroleptic trinuclear complexes based on the triaminoguanidine core is investigated.

Synthesis, Structures, and Magnetic Properties of N‐Trialkylsilyl‐8‐amidoquinoline Complexes of Chromium, Manganese, Iron, and Cobalt as well as of Wheel‐Like Hexanuclear Iron(II) and Manganese(II) Bis(8‐amidoquinoline)

AbstractThe transamination of 8‐(tert‐butyldimethylsilylamino)quinoline with (thf)2Cr[N(SiMe3)2]2 yields monomeric bis[8‐(tert‐butyldimethylsilylamido)quinoline]chromium(II) (1). Similar reactions of M[N(SiMe3)2]2 (M = Mn, Fe, Co) with 8‐(trialkylsilylamino)quinoline lead to the formation of monomeric bis[8‐(trialkylsilylamido)quinoline]metal(II) [M = Mn, SiR3 = SiMe2tBu (2a), SiiPr3 (2b); M = Fe, SiR3 = SiMe2tBu (3a),SiiPr3 (3b); M = Co, SiR3 = SiMe2tBu (4a), SiiPr3 (4b)]. The transamination of 8‐aminoquinoline with M[N(SiMe3)2]2 (M = Mn, Fe, Co) allows the isolation of the heteroleptic 1:1 and homoleptic 2:1 products. The 1:1 complexes bis[8‐amidoquinoline metal(II)bis(trimethylsilyl)amide] [M = Mn (5), Fe (6), Co (7)] are dimeric with bridging 8‐amidoquinoline moieties. The 2:1 complexes of Mn and Fe, bis(8‐amidoquinoline)manganese(II) (8) and bis(8‐amidoquinoline)iron(II) (9), form hexamers with wheel‐like molecular structures consisting of metal‐centered nitrogen octahedra interconnected by common N···N edges. The cobalt complex, bis(8‐amidoquinoline)cobalt(II) (10), precipitates as a microcrystalline powder. Investigations of the magnetic properties by DFT corroborate the experimental data for the Mn derivative 8, where an antiferomagnetic coupling is observed. By contrast, calculations on the Fe6‐wheel 9 yield very close‐lying ferromagnetically and antiferromagnetically coupled states.

Fe3s X-ray photoelectron spectra of polynuclear iron complexes

Specific features of the electronic structure and spin magnetic state of iron atoms in bi-, tri-, and hexanuclear iron trimethylacetate complexes were studied by X-ray photoelectron spectroscopy. A correlation was found between the ionicity (of the spin state of iron atoms) and Fe3s binding energies, exchange splitting of the final photoionization state, and the energy position and intensity of charge-transfer satellites. Nonequivalent iron states were identified in tri- and hexanuclear complexes. The overall magnetic moment of the complexes was found to decrease with an increase of the individual magnetic moments of iron atoms, which is evidence of complicated mutual orientation of atomic magnetic moments in the complexes.

Nanostructured α-Fe2O3 Thin Films for Photoelectrochemical Hydrogen Generation

α-Fe2O3 thin film photoelectrodes were fabricated by aerosol-assisted chemical vapor deposition (AACVD) using a new hexanuclear iron precursor [Fe6(PhCOO)10(acac)2(O)2(OH)2]·3C7H8 (1) (where PhCOO = benzoate and acac = 2,4-pentanedionate). The precursor (1) designed for AACVD has a low decomposition temperature and sufficient solubility in organic solvents and was synthesized by simple chemical techniques in high yield. It was characterized by melting point, FT-IR, X-ray crystallography, and thermogravimetry (TGA). The TGA analysis proved that complex (1) undergoes facile thermal decomposition at 475 °C to give iron oxide residue. In-house designed AACVD equipment was used to deposit highly crystalline thin films of α-Fe2O3 on fluorine-doped SnO2 coated glass substrates at 475 °C in a single step. The material properties were characterized by XRD, XPS, and Raman spectroscopy, and the results confirmed that films were highly crystalline α-Fe2O3 and free from other phases of iron oxide. Further analysis of ...

New Family of Ferric Spin Clusters Incorporating Redox-Active ortho-Dioxolene Ligands

Seven new di-, tri-, tetra-, and hexanuclear iron complexes that incorporate a polydentate Schiff base and variously substituted catecholate ligands have been synthesized from the trinuclear precursor [Fe(3)(OAc)(3)(L)(3)] (1), where LH(2) = 2-[[(2-hydroxyethyl)imino]phenylmethyl]-phenol. These were isolated as the compounds [Fe(3)(OAc)(Cat)(L)(3)] (2), [Fe(6)(OAc)(2)(Cat)(4)(L)(4)] (3), [Fe(4)(3,5-DBCat)(2)(L)(4)] (4), [Bu(4)N][Fe(4)(OAc)(3,5-DBCat)(4)(L)(2)] (5a, 5(-) is the complex monoanion [Fe(4)(OAc)(3,5-DBCat)(4)(L)(2)](-)), [Fe(4)(OAc)(3,5-DBCat)(3)(3,5-DBSQ)(L)(2)] (6), [Fe(2)(Cl(4)Cat)(2)(L)(LH(2))(H(2)O)] (7), and [Et(3)NH](2)[Fe(2)(Cl(4)Cat)(2)(L)(2)] (8a, 8(2-) is the complex dianion [Fe(2)(Cl(4)Cat)(2)(L)(2)](2-)), where CatH(2) = catechol; 3,5-DBCatH(2) = 3,5-di-tert-butyl-catechol; 3,5-DBSQH = 3,5-di-tert-butyl-semiquinone, and Cl(4)CatH(2) = tetrachlorocatechol. While compounds 2-4, 5a, 7, and 8a were obtained by directly treating 1 with the appropriate catechol, compound 6 was synthesized by chemical oxidation of 5a. These compounds have been characterized by single crystal X-ray diffraction, infrared and UV-visible spectroscopy, voltammetry, UV-visible spectroelectrochemistry, and magnetic susceptibility and magnetization measurements. An electrochemical study of the three tetranuclear complexes (4, 5(-), and 6) reveals multiple reversible redox processes due to the o-dioxolene ligands, in addition to reductive processes corresponding to the reduction of the iron(III) centers to iron(II). A voltammetric study of the progress of the chemical oxidation of compound 5a, together with a spectroelectrochemical study of the analogous electrochemical oxidation, indicates that there are two isomeric forms of the one-electron oxidized product. A relatively short-lived neutral species (5) that possesses the same ligand arrangement as complex 5(-) is the kinetic product of both chemical and electrochemical oxidation. After several hours, this species undergoes a significant structural rearrangement to convert to complex 6, which appears to be largely driven by the preference for the 3,5-DBSQ(-) ligand to bind in a non-bridging mode. Variable temperature magnetic susceptibility measurements for compounds 3, 4, 5a, 6, 7, and 8a reveal behavior dominated by pairwise antiferromagnetic exchange interactions, giving rise to a poorly isolated S = 0 ground state spin for compound 3, well-isolated S = 0 ground state spins for complexes 4, 5(-), 7 and 8(2-), and a well-isolated S = 1/2 ground state spin for complex 6. The ground state spin values were confirmed by low temperature variable field magnetization measurements. The thermal variation of the magnetic susceptibility for compounds 3, 4, 5a, 6, 7, and 8a were fitted and/or simulated using the appropriate Hamiltonians to derive J values that are consistent with magnetostructural correlations that have been reported previously for alkoxo-bridged ferric complexes.

Synthesis and magnetic properties of a new hexanuclear iron(III) compound

NNSF of China [20671079, 20721001]; Key Project of Chinese Ministry of Education [107068]; 973 project [2007CB815301]; [NCET-08-0470]

A hexanuclear iron(iii) complex of a hexadentate fully conjugated diimine ligand derived from 1,4-diformyl-2,3-dihydroxybenzene

A fully conjugated acyclic diimine ligand, H4L3, formed from 1,4-diformyl-2,3-dihydroxybenzene and 2-aminophenol, was reacted with iron(II) acetate to give the hexanuclear complex [FeIII6(L3)4(μ-OMe)(μ-OH)(MeOH)4] (2). Crystals of 2·ADPOX·7.5MeOH·H2O, where ADPOX is 2-amino-10,10a-dihydro-3H-phenoxazin-3-one, were obtained by slow evaporation and the X-ray structure determination revealed that the six octahedral iron(III) ions are bridged by four fully-deprotonated (L3)4− ligands that are arranged in a [2 × 2] grid-like arrangement relative to one another.

X-Ray photoelectron spectra of iron trimethylacetate complexes

Bi-, tri-, and hexanuclear iron(II,III) trimethylacetate complexes were studied by X-ray photoelectron spectroscopy. The compounds differed in the number of Fe-O and Fe-N coordination bonds. The Fe 2p, Fe 3p, and N 1s X-ray photoelectron spectra were examined and the role of the ligand in their formation was elucidated. Based on the calculated multiplet splittings, numerous states were discerned in the Fe 2p spectra. This made it possible to reveal a correlation between the magnetic moment and some spectral parameters, such as the relative intensity and energy position of the satellites.

Water Substitution on Iron Centers: from 0D to 1D Sandwich Type Polyoxotungstates

Four novel polyoxotungstates have been synthesized by reaction of the sandwich type compound [Fe (III) 4(H 2O) 10(B-beta-SbW 9O 33) 2] (6-) (noted Fe 4(H 2O) 10Sb 2W 18) with ethylenediamine (en) and/or oxalate (ox) ligands under various conditions. The one-dimensional (1D) compound [enH 2] 3[Fe (III) 4(H 2O) 8(SbW 9O 33) 2].20H 2O ( 1) is isolated at 130 degrees C and results from the elimination of two water molecules and the condensation of the polyoxotungstate precursor. The reaction of Fe 4(H 2O) 10Sb 2W 18 with oxalate ligands affords the molecular complex Na 14[Fe (III) 4(ox) 4(H 2O) 2(SbW 9O 33) 2].60H 2O ( 2) where two organic ligands substitute four water molecules, while the same reaction in the presence of en molecules at 130 degrees C leads to the formation of the functionalized 1D chain [enH 2] 7[Fe (III) 4(ox) 4(SbW 9O 33) 2].14H 2O ( 3) with protonated ethylenediamine counterions. Finally, at 160 degrees C a rearrangement of the Fe 4(H 2O) 10Sb 2W 18 polyoxotungstate is observed, and the sandwich type compound [enH 2] 5[Fe (II) 2Fe (II) 2(enH) 2(Fe (III)W 9O 34) 2].24H 2O ( 4) crystallizes. In 4, the heteroelement is a Fe (III) ion, and the water molecules on the two outer Fe (II) centers are bound to pendant monoprotonated en ligands. The four compounds have been characterized by IR spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. A detailed study of the magnetic properties of the mixed-valent hexanuclear iron complex in 4 shows evidence of an S = 5 ground-state because of spin frustration effects. A quantification of the electronic parameters characterizing the ground state ( D = +1.12 cm (-1), E/ D = 0.15) confirms that polyoxotungstate ligands induce large magnetic anisotropy.

A novel hexanuclear iron(III) complex containing three-coordination symmetries with two bridging μ-alkoxo groups, two μ3-oxo and four μ-catecholato bridges

The reaction of stoichiometric amount of FeCl3, Schiff-base ligand, NaBPh4 in CH3CN and 3,5-DTBC in CH3OH under O2 did produce a new μ-oxo-bridged hexanuclear iron(III) cluster [Fe6(L)2(μ3-O)2(μ-3,5-DTBC)4(μ-CH3O)2(Cl)2] (BPh4)2·2H2O (1) (L=N,N-diethylenetriamino-bis(imidazolaldiminato) with a spin ground state of S=5.

Synthesis, spectra and X-ray crystal structure of a new type of macrocyclic hexanuclear iron(III) cluster

A macrocyclic iron(III) 18-azametallacrown-6 compound, [Fe6(5-Brashz)6(H2O)6] · 20H2O(5-Brashz = N-acetyl-(5-bromosalicylhydrazide)), where the pentadentate ligands bridge the metal ions, was synthesized and characterized. Due to the meridional coordination of the ligand to the metal ion, the ligand is not only bridging the ring metal ions using a hydrazide N–N group, but also enforcing the stereochemistry of the metal ions as a propeller shape with alternating Λ/Δ configuration. The disc-shaped hexanuclear cluster is about 14.5 Å in diameter, 16.8 Å in thickness and has a vacant cavity in the center of the cluster.

A Hexanuclear Iron(III) Carboxylate with an [Fe6(μ3‐O)3(μ2‐OH)]11+ Core as an Efficient Catalyst for Cycloalkane Oxidation

Six of one: A hexanuclear iron p-nitrobenzoate compound (see structure; green Fe, red O, blue N, gray C), a novel type of iron cluster was prepared and characterized. The complex has an [Fe6(μ3-O)3(μ2-OH)]11+ core and shows a remarkable catalytic activity in the oxidation of cyclohexane.

57Fe Mössbauer spectroscopy on the cyclic spin-cluster Fe6(tea)6(CH3OH)6

We present 57Fe Mossbauer spectroscopy experiments on the cyclic spincluster Fe6(tea)6(CH3OH)6 (tea=triethanolaminatot-(-3)). In former studies, the spin cluster has been treated as a homogenous, quasi-one-dimensional spin S=5/2 Heisenberg antiferromagnet. Our experiments reveal spectra, which consists of two different quadrupolar doublets. In consequence, there are two different Fe sites among the hexanuclear iron spin-cluster.

Large spin differences in structurally related Fe6 molecular clusters and their magnetostructural explanation.

The syntheses, crystal structures, and magnetic characterizations of three new hexanuclear iron(III) compounds are reported. Known [Fe(6)O(2)(OH)(2)(O(2)CBu(t))(10)(hep)(2)] (1) is converted to new [Fe(6)O(2)(OH)(O(2)CBu(t))(9)(hep)(4)] (3) when treated with an excess of 2-(2-hydroxyethyl)-pyridine (hepH). Similarly, the new compound [Fe(6)O(2)(OH)(2)(O(2)CPh)(10)(hep)(2)] (2), obtained from the reaction of [Fe(3)O(O(2)CPh)(6)(H(2)O)(3)] with hepH, is converted to [Fe(6)O(2)(OH)(O(2)CPh)(9)(hep)(4)] (4) when treated with an excess of hepH. This can be reversed by recrystallization from MeCN. The cores of the four Fe(6) complexes all comprise two triangular [Fe(3)(mu(3)-O)(O(2)CR)(3)(hep)](+3) units connected at two of their apices by two sets of bridging ligands. However, 1 and 2 differ slightly from 3 and 4 in the precise way the two Fe(3) units are linked together. In 1 and 2, the two sets of bridging ligands are identical, consisting of one mu-hydroxo and two mu-carboxylate groups bridging each Fe(2) pair, i.e., a (mu-OH(-))(mu-O(2)CR(-))(2) set. In contrast, 3 and 4 have two different sets of bridging ligands, a (mu-OH(-))(mu-O(2)CR(-))(2) set as in 1 and 2, and a (mu-OR(-))(2)(mu-O(2)CR(-)) set, where RO(-) refers to the alkoxide arm of the hep(-) chelate. Variable-field and -temperature dc magnetization measurements establish that 1 and 2 have S = 5 ground states and significant and positive zero-field splitting parameters (D), whereas 3 and 4 have S = 0 ground states. This dramatic difference of 10 unpaired electrons in the ground state S values for near-isomeric compounds demonstrates an acute sensitivity of the magnetic properties to small structural changes. The factors leading to this have been quantitatively analyzed. The semiempirical method ZILSH, based on unrestricted molecular orbital calculations, was used to obtain initial estimates of the Fe(2) pairwise exchange interaction constants (J). These calculated values were then improved by fitting the experimental susceptibility versus T data, using a genetic algorithm approach. The final J values were then employed to rationalize the observed magnetic properties as a function of the core topologies and the presence of spin frustration effects. The large difference in ground state spin value was identified as resulting from a single structural difference between the two types of complexes, the different relative dispositions (cis vs trans) of two frustrated exchange pathways. In addition, use of the structural information and corresponding J values allowed a magnetostructural correlation to be established between the J values and both the Fe-O bond distances and the Fe-O-Fe angles at the bridging ligands.

Methanolysis and phenolysis routes to Fe6, Fe8, and Fe1) complexes and their magnetic properties: a new type of Fe8 ferric wheel.

Alcoholysis of preformed tetranuclear and hexanuclear iron(III) clusters has been employed for the synthesis of four higher-nuclearity clusters. Treatment of [Fe(4)O(2)(O(2)CMe)(7)(bpy)(2)](ClO(4)) with phenol affords the hexanuclear cluster [Fe(6)O(3)(O(2)CMe)(9)(OPh)(2)(bpy)(2)](ClO(4)) (1). Reaction of [Fe(6)O(2)(OH)(2)(O(2)CR)(10)(hep)(2)] (R = Bu(t) or Ph) with PhOH affords the new "ferric wheel" complexes [Fe(8)(OH)(4)(OPh)(8)(O(2)CR)(12)] [R = Bu(t) (2) or Ph (3)]. Complexes 2 and 3 exhibit the same structure, which is an unprecedented type for Fe(III). In contrast, treatment of [Fe(6)O(2)(OH)(2)(O(2)CBu(t))(10)(hep)(2)] with MeOH leads to the formation of [Fe(10)(OMe)(20)(O(2)CBu(t))(10)] (4), which exhibits the more common type of ferric wheel seen in analogous complexes with other carboxylate groups. Solid-state variable-temperature magnetic susceptibility measurements indicate spin-singlet ground states for complexes 2 and 4. The recently developed semiempirical method ZILSH was used to estimate the pairwise exchange parameters (J(AB)) and the average spin couplings S(A)[empty set].S(B)[empty set] between the Fe(III) centers, providing a clear depiction of the overall magnetic behavior of the molecules. All exchange interactions between adjacent Fe(III) atoms are antiferromagnetic.

Synthesis and structure of a new iron–molybdenum–oxygen cluster with α-furoic acid

A new hexanuclear iron–molybdate cluster containing the α-furoic acid ligand, [Fe4IIIMo2VIO10(C4H3OCOO)4(DMF)4]·2 DMF, has been synthesised by a solid state reaction and characterised by X-ray crystallography, EPR, XPS and IR spectroscopy.