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.     

Discrete and monodimensional heteropolynuclear structures formed by tetracarboxylatodiruthenium(II,III) and perrhenato fragments

Reaction between cationic units of carboxylate-bridged diruthenium complexes [Ru(2)(mu-O(2)CR)(4)](+) (R = Me, CMePh(2), CMe(3), CH(2)CH(2)OMe, C(Me)=CHEt, C(6)H(4)-p-OMe, Ph) and tetrabutylammonium perrhenate gives complexes with different arrangements in the solid state. Thus, the compounds Ru(2)(mu-O(2)CR)(4)(ReO(4)) [R = Me (1), CMePh(2) (2), CMe(3) (3), CH(2)CH(2)OMe (4), C(Me)=CHEt (5), C(6)H(4)-p-OMe (6), Ph (7)] have polymeric structures with the diruthenium units linked by perrhenate ligands in the axial positions. The structures of complexes 3.THF and 4 were established by single-crystal X-ray diffraction. The tetrahedral geometry of the ReO(4)(-) anion permits the formation of a chain close to the linearity. In contrast to the polymeric chains observed in complexes 1-7, the reaction of [Ru(2)(mu-O(2)CPh)(4)](+) with NBu(4)ReO(4) also affords the compounds Ru(2)(mu-O(2)CPh)(4)(ReO(4))(H(2)O) (8) and NBu(4)[Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)] (9) depending on the reaction conditions. The structure of 8 consists of cationic and anionic units, [Ru(2)(mu-O(2)CPh)(4)(H(2)O)(2)](+) and [Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)](-), linked by hydrogen bonds, which give a three-dimensional net. The structure of complex 9.0.5H(2)O has an anionic unit similar to that of 8, whose counterion is NBu(4)(+). The Ru-Ru bond distances are slightly longer in [Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)](-) than in the polymeric compounds Ru(2)(mu-O(2)CR)(4)(ReO(4)). The magnetic behavior owes to the existence of zero-field splitting (ZFS) and a weak antiferromagnetic coupling. The experimental data are fitted with a model that considers the ZFS effect using the Hamiltonian (D) = SDS. The weak antiferromagnetic coupling is introduced as a perturbation, using the molecular field approximation.     

Dioxygen-initiated oxidation of heteroatomic substrates incorporated into ancillary pyridine ligands of carboxylate-rich diiron(II) complexes

Progress toward the development of functional models of the carboxylate-bridged diiron active site in soluble methane monooxygenase is described in which potential substrates are introduced as substituents on bound pyridine ligands. Pyridine ligands incorporating a thiol, sulfide, sulfoxide, or phosphine moiety were allowed to react with the preassembled diiron(II) complex [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(THF)(2)], where (-)O(2)CAr(R) is a sterically hindered 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh). The resulting diiron(II) complexes were characterized crystallographically. Triply and doubly bridged compounds [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-MeSpy)] (4) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-MeS(O)py)(2)] (5) resulted when 2-methylthiopyridine (2-MeSpy) and 2-pyridylmethylsulfoxide (2-MeS(O)py), respectively, were employed. Another triply bridged diiron(II) complex, [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(3)-(O(2)CAr(4)(-)(FPh))(2-Ph(2)Ppy)] (3), was obtained containing 2-diphenylphosphinopyridine (2-Ph(2)Ppy). The use of 2-mercaptopyridine (2-HSpy) produced the mononuclear complex [Fe(O(2)CAr(Tol))(2)(2-HSpy)(2)] (6a). Together with that of previously reported [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-PhSpy)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-Ph(2)Ppy)] (1), the dioxygen reactivity of these iron(II) complexes was investigated. A dioxygen-dependent intermediate (6b) formed upon exposure of 6a to O(2), the electronic structure of which was probed by various spectroscopic methods. Exposure of 4 and 5 to dioxygen revealed both sulfide and sulfoxide oxidation. Oxidation of 3 in CH(2)Cl(2) yields [Fe(2)(mu-OH)(2)(mu-O(2)CAr(4)(-)(FPh))(O(2)CAr(4)(-FPh))(3)(OH(2))(2-Ph(2)P(O)py)] (8), which contains the biologically relevant {Fe(2)(mu-OH)(2)(mu-O(2)CR)}(3+) core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analogue 1 yielded a hexanuclear species, 7, upon oxidation.     

Synthesis, characterization, and preliminary oxygenation studies of benzyl- and ethyl-substituted pyridine ligands of carboxylate-rich diiron(II) complexes

In this study benzyl and ethyl groups were appended to pyridine and aniline ancillary ligands in diiron(II) complexes of the type [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(L)(2)], where (-)O(2)CAr(R) is a sterically hindered terphenyl carboxylate, 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh, respectively). These crystallographically characterized compounds were prepared as analogues of the diiron(II) center in the hydroxylase component of soluble methane monooxygenase (MMOH). The use of 2-benzylpyridine (2-Bnpy) yielded doubly bridged [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Bnpy)(2)] (1) and [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(2)(O(2)CAr(4)(-)(FPh))(2)(2-Bnpy)(2)] (4), whereas tetra-bridged [Fe(2)(mu-O(2)CAr(Tol))(4)(4-Bnpy)(2)] (3) resulted when 4-benzylpyridine (4-Bnpy) was employed. Similarly, 2-(4-chlorobenzyl)pyridine (2-(4-ClBn)py) and 2-benzylaniline (2-Bnan) were employed as N-donor ligands to prepare [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-(4-ClBn)py)(2)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Bnan)(2)] (5). The placement of the substituent on the pyridine ring had no effect on the geometry of the diiron(II) compounds isolated when 2-, 3-, or 4-ethylpyridine (2-, 3-, or 4-Etpy) was introduced as the ancillary nitrogen ligand. The isolated [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Etpy)] (6), [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(3-Etpy)] (7), [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(4-Etpy)] (8), and [Fe(2)(mu-O(2)CAr(4)(-FPh))(2)(O(2)CAr(4)(-)(FPh))(2)(2-Etpy)(2)] (9) complexes all contain doubly bridged metal centers. The oxygenation of compounds 1-9 was studied by GC-MS and NMR analysis of the organic fragments following decomposition of the product complexes. Hydrocarbon fragment oxidation occurred for compounds in which the substrate moiety was in close proximity to the diiron center. The extent of oxidation depended upon the exact makeup of the ligand set.     

Sterically hindered carboxylate ligands support water-bridged dimetallic centers that model features of metallohydrolase active sites

The synthesis and characterization of carboxylate-bridged dimetallic complexes are described. By using m-terphenyl-derived carboxylate ligands, a series of dicobalt(II), dicobalt(III), dinickel(II), and dizinc(II) complexes were synthesized. The compounds are [Co(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (1), [Co(2)(mu-OH(2))(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (2a-c), [Co(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (3), [Ni(2)(mu-O(2)CAr(Tol))(4)L(2)] (4), [Ni(2)(mu-HO...H)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (5), and [Zn(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (6), where Ar(Tol)CO(2)H = 2,6-di(p-tolyl)benzoic acid and L = pyridine, THF, or N,N-dibenzylethylenediamine. Structural analysis of these complexes revealed that additional bridging ligands can be readily accommodated within the [M(2)(mu-O(2)CAr(Tol))(2)](2+) core, allowing a wide distribution of M...M distances from 2.5745(6) to 4.0169(9) A. Unprecedented bridging units [M(2)(mu-OH(2))(2)(mu-O(2)CR)(2)](n+) and [M(2)(mu-HO...H)(2)(mu-O(2)CR)(2)](n+) were identified in 2a-c and 5, respectively, in which strong hydrogen bonding accommodates shifts of protons from bridging water molecules toward the dangling oxygen atoms of terminal monodentate carboxylate groups. Such a proton shift along the O...H...O coordinate attenuates the donor ability of the anionic carboxylate ligand, which can translate into increased Lewis acidity at the metal centers. Such double activation of bridging water molecules by a Lewis acidic metal center and a metal-bound general base may facilitate the reactivity of metallohydrolases such as methionine aminopeptidase (MAP).     

One-dimensional phosphinite platinum chains based on hydrogen bonding interactions and phosphinite tetranuclear platinum(II)-thallium(I) complexes

The mononuclear pentafluorophenyl platinum complex containing the chelated diphenylphosphinous acid/diphenylphosphinite system [Pt(C(6)F(5)){(PPh(2)O)(2)H}(PPh(2)OH)] 1 has been prepared and characterised. 1 and the related alkynyl complex [Pt(C[triple bond, length as m-dash]CBu(t)){(PPh(2)O)(2)H}(PPh(2)OH)] 2 form infinite one-dimensional chains in the solid state based on intermolecular O-H[dot dot dot]O hydrogen bonding interactions. Deprotonation reactions of [PtL{(PPh(2)O)(2)H}(PPh(2)OH)] (L = C(6)F(5), C[triple bond, length as m-dash]CBu(t), C[triple bond, length as m-dash]CPh 3) with [Tl(acac)] yields tetranuclear Pt(2)Tl(2) complexes [PtL{(PPh(2)O)(2)H}(PPh(2)O)Tl](2) (L = C(6)F(5) 4, C[triple bond, length as m-dash]CBu(t), C[triple bond, length as m-dash]CPh ). The structure of the tert-butylalkynyl derivative , established by X-ray diffraction, shows two anionic discrete units [Pt(C[triple bond, length as m-dash]CBu(t)){(PPh(2)O)(2)H}(PPh(2)O)](-) joined by two Tl(i) centres via Tl-O and Pt-Tl bonds. Despite the existence of Pt-Tl interactions, they do not show luminescence.     

Dodecanuclear manganese(III) phosphonates with cage structures

Treatments of Mn(O(2)CR)(2) (R = Me, Ph) with NBu(4)MnO(4) in CH(3)CN or CH(3)CN/CH(2)Cl(2) in the presence of acetic acid, delta(1)-cyclohexenephosphonic acid (C(6)H(9)PO(3)H(2)), and 2,2'-bipyridine or 1,10-phenanthroline result in three novel dodecamanganese(III) clusters [Mn(12)O(8)(O(2)CMe)(6)(O(3)PC(6)H(9))(7)(bipy)(3)] (1), [Mn(12)O(8)(O(2)CPh)(6)(O(3)PC(6)H(9))(7)(bipy)(3)] (2), and [Mn(12)O(8)(O(2)CPh)(6)(O(3)PC(6)H(9))(7)(phen)(3)] (3). They have a similar Mn(12) core of [Mn(III)(12)(mu(4)-O)(3)(mu(3)-O)(5)(mu-O(3)P)(3)] with a new type of topologic structure. Solid-state dc magnetic susceptibility measurements of complexes 1-3 reveal that dominant antiferromagnetic interactions are propagated between the magnetic centers. The ac magnetic measurements suggest an S = 2 ground state for compounds 1 and 3 and an S = 3 ground state for compound 2.     

Synthesis and characterization of the tetranuclear iron(III) complex of a new asymmetric multidentate ligand. A structural model for purple acid phosphatases

The ligand, 2-((2-hydroxy-5-methyl-3-((pyridin-2-ylmethylamino)methyl)benzyl)(2-hydroxybenzyl)amino)acetic acid (H(3)HPBA), which contains a donor atom set that mimics that of the active site of purple acid phosphatase is described. Reaction of H(3)HPBA with iron(III) or iron(II) salts results in formation of the tetranuclear complex, [Fe(4)(HPBA)(2)(OAc)(2)(mu-O)(mu-OH)(OH(2))(2)]ClO(4) x 5H(2)O. X-Ray structural analysis reveals the cation consists of four iron(III) ions, two HPBA(3-) ligands, two bridging acetate ligands, a bridging oxide ion and a bridging hydroxide ion. Each binucleating HPBA(3-) ligand coordinates two structurally distinct hexacoordinate iron(III) ions. The two metal ions coordinated to a HPBA(3-) ligand are linked to the two iron(III) metal ions of a second, similar binuclear unit by intramolecular oxide and hydroxide bridging moieties to form a tetramer. The complex has been further characterised by elemental analysis, mass spectrometry, UV-vis and MCD spectroscopy, X-ray crystallography, magnetic susceptibility measurements and variable-temperature M?ssbauer spectroscopy.     

Single-molecule magnets: a new family of Mn(12) clusters of formula [Mn(12)O(8)X(4)(O(2)CPh)(8)L(6)

The reaction of (NBu(n)(4))[Mn(8)O(6)Cl(6)(O(2)CPh)(7)(H(2)O)(2)] (1) with 2-(hydroxymethyl)pyridine (hmpH) or 2-(hydroxyethyl)pyridine (hepH) gives the Mn(II)(2)Mn(III)(10) title compounds [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hmp)(6)] (2) and [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hep)(6)] (3), respectively, with X = Cl. Subsequent reaction of 3 with HBr affords the Br(-) analogue [Mn(12)O(8)Br(4)(O(2)CPh)(8)(hep)(6)] (4). Complexes 2.2Et(2)O.4CH(2)Cl(2), 3.7CH(2)Cl(2), and 4.2Et(2)O.1.4CH(2)Cl(2) crystallize in the triclinic space group P1, monoclinic space group C2/c, and tetragonal space group I4(1)/a, respectively. Complexes 2 and 3 represent a new structural type, possessing isomeric [Mn(III)(10)Mn(II)(2)O(16)Cl(2)] cores but with differing peripheral ligation. Complex 4 is essentially isostructural with 3. A magnetochemical investigation of complex 2 reveals an S = 6 or 7 ground state and frequency-dependent out-of-phase signals in ac susceptibility studies that establish it as a new class of single-molecule magnet. These signals occur at temperatures higher than those observed for all previously reported single-molecule magnets that are not derived from [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(x)]. A detailed investigation of forms of complex 2 with different solvation levels reveals that the magnetic properties of 2 are extremely sensitive to the latter, emphasizing the importance to the single-molecule magnet properties of interstitial solvent molecules in the samples. In contrast, complexes 3 and 4 are low-spin molecules with an S = 0 ground state.     

Synthetic analogue of the [Fe(2)(mu-OH)(2)(mu-O(2)CR)](3+) core of soluble methane monooxygenase hydroxylase via synthesis and dioxygen reactivity of carboxylate-bridged diiron(II) complexes

We describe the synthesis and dioxygen reactivity of diiron(II) tetracarboxylate complexes [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(N,N-Me(2)en)(2)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(N,N-Bn(2)en)(2)] (6), where Ar(Tol)CO(2)(-) = 2,6-di(p-tolyl)benzoate. These complexes were prepared as models for the diiron(II) center in the hydroxylase component of soluble methane monooxygenase (MMOH). Compound 6 reacts with dioxygen to afford PhCHO in approximately 60(5)% yield, following oxidative N-dealkylation of the pendant benzyl group on the diamine ligand. The diiron(III) complex [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(O(2)CAr(Tol))(3)(N-Bnen)(N,N-Bn(2)en)] (8) was isolated from the reaction mixture. The 4.2 K M?ssbauer spectrum of 8 displays a single quadrupole doublet with parameters delta = 0.48(2) mm s(-1) and Delta E(Q) = 0.61(2) mm s(-1). The [Fe(2)(mu-OH)(2)(mu-O(2)CR)](3+) core structure in 8 matches that of the fully oxidized form of MMOH. The conversion of 6 to 8 closely parallels the chemistry of MMOH in which an O(2)-derived oxygen atom is inserted into the C-H bond of methane. Several reaction pathways are considered to account for this novel chemical transformation, and these are compared with mechanistic frameworks previously developed for related cytochrome P450 and copper(I) dioxygen chemistry.     

The role of diisopropanolamine (dipaH3) in cluster dimerisation and polymerisation: from spin frustrated S= 5 FeIII 6 clusters to the novel 1-D covalent polymer of mixed valence [CoII3CoIII] tetramers

The synthesis, crystal structures and magnetic properties of two hexanuclear Fe(6) clusters of general formula [Fe(6)(O)(2)(OH)(2)(O(2)CR)(10)(dipaH(2))(2)].xMeCN.yH(2)O (R = Ph, x= 5.5, y= 1 (1), R = C(Me)(3), x= 2, y= 3 (2)) are reported. The presence of the flexible amino-alcohol ligand diisopropanolamine (dipaH(3)) induces the dimerisation of two trinuclear Fe(III) complexes, [Fe(3)O(O(2)CPh)(6)(H(2)O)(3)](NO(3)) and [Fe(3)O(O(2)CC(Me)(3))(6)(H(2)O)(3)](O(2)CC(Me)(3)), to form the hexanuclear clusters 1 and 2. DC magnetic susceptibility measurements on 1 and 2 assign ground spin states of S= 5, with zero-field splitting parameters (D) of ca. 0.25 cm(-1) obtained from magnetisation isotherms. AC susceptibilities showed no maxima as a function of frequency, at low temperatures, and this confirmed the lack of single-molecule magnetic behaviour. Clusters 1 and 2 are isostructural, consisting of two fused {Fe(3)O} trinuclear units, bridged in two positions by one mu(2)-OH(-) unit and two mu(2)-O(2)CR(-) bridging carboxylates (R = Ph (), C(Me)(3)()). The two singly deprotonated dipaH(2)(-) bridging ligands span the Fe1-Fe2 edges in and via one micro(2)-bridging alcohol arm and one terminal nitrogen atom while the second alcohol arm remains free. The ground spin state of S= 5 in 1 and 2 can be attributed to the presence of spin frustration within the system. 1 and 2 join a small family of spin frustrated S= 5 Fe(6) systems the magnetism of which give weight to a recent report that it is the trans position of the two shortest Fe(2) pair frustrated exchange pathways in these Fe(6) clusters that gives rise to a ground spin state of S= 5 (trans) and not a ground spin state of S= 0 (cis). The M?ssbauer spectra of 1 and 2 show two quadrupole doublets, as expected, at 295 K, but a broad asymmetric lineshape at 77 K. The synthesis and magnetic properties of {[Co(II)(3)Co(III)(OH)(O(2)CC(Me)(3))(4)(HO(2)CC(Me)(3))(2)(dipaH)(2)].2MeCN}(n)(3) are reported. 3 is a covalently bonded 1D polymer of tetrameric cobalt clusters. The presence of the dipaH(3) ligand here not only dimerises the [Co(II)(2)(micro-H(2)O)(O(2)CC(Me)(3))(4)(HO(2)CC(Me)(3))(4)] starting complex into the tetranuclear species but also polymerises the [Co(II)(3)Co(III)] clusters in 3 by acting as the propagating ligand in the 1D chain. Magnetic susceptibility measurements on show each [Co(4)] moiety exhibits weak antiferromagnetic coupling between the three Co(II)S= 3/2 metal centres and fitted J values are given. The ambiguity in assignment of the spin ground state of S= 1/2 or 3/2 is discussed.     

Investigation of the zinc(II)-benzoate-2-pyridinealdoxime reaction system

The employment of pyridine-2-carbaldehyde oxime (paoH) in zinc(II) benzoate chemistry, in the absence or presence of azide ions, is described. The syntheses, crystal structures and spectroscopic characterization are reported for the complexes [Zn(O(2)CPh)(2)(paoH)(2)] (1), [Zn(12)(OH)(4)(O(2)CPh)(16)(pao)(4)] (2) and [Zn(4)(OH)(2)(pao)(4)(N(3))(2)] (3). The Zn(II) centre in octahedral 1 is coordinated by two monodentate PhCO(2)(-) groups and two N,N'-chelating paoH ligands. The metallic skeleton of 2 describes a tetrahedron encapsulated in a distorted cube. The {Zn(12)(μ-OH)(4)(μ(3)-ΟR)(4)}(16+) core of the cluster can be conveniently described as consisting of a central {Zn(4)(μ(3)-ΟR)(4)}(4+) cubane subunit (RO(-) = pao(-)) linked to four {Zn(2)(μ-OH)}(3+) subunits via the OH(-) group of each of the latter, which becomes μ(3). The molecule of 3 has an inverse 12-metallacrown-4 topology. Two triply bridging hydroxido groups are accommodated into the metallacrown ring. Each pao(-) ligand adopts the η(1)?:?η(1)?:?η(1)?:?μ coordination mode, chelating one Zn(II) atom and bridging a Zn(II)(2) pair. Complexes 1 and 2 display photoluminescence with maxima at ～355 nm and ～375 nm, upon maximum excitation at 314 nm; the origin of the photoluminescence is discussed.     

Polymetallic clusters of iron(III) with derivatised salicylaldoximes

The synthesis and magnetic properties of the compounds [HNEt(3)][Fe(2)(OMe)(Ph-sao)(2) (Ph-saoH)(2)].5MeOH (1.5MeOH), [Fe(3)O(Et-sao)(O(2)CPh)(5)(MeOH)(2)].3MeOH (2.3MeOH), [Fe(4)(Me-sao)(4)(Me-saoH)(4)] (3), [HNEt(3)](2)[Fe(6)O(2)(Me-sao)(4)(SO(4))(2)(OMe)(4)(MeOH)(2)] (4), [Fe(8)O(3)(Me-sao)(3)(tea)(teaH)(3)(O(2)CMe)(3)] (5), [Fe(8)O(3)(Et-sao)(3)(tea)(teaH)(3)(O(2)CMe)(3)] (6), and [Fe(8)O(3)(Ph-sao)(3)(tea)(teaH)(3)(O(2)CMe)(3)] (7) are reported (Me-saoH(2) is 2'-hydroxyacetophenone oxime, Et-saoH(2) is 2'-hydroxypropiophenone oxime and Ph-saoH(2) is 2-hydroxybenzophenone oxime). 1-7 are the first Fe(III) compounds synthesised using the derivatised salicylaldoxime ligands, R-saoH(2). 1 is prepared by treatment of Fe(2)(SO(4))(3).6H(2)O with Ph-saoH(2) in the presence of NEt(3) in MeOH; 2 prepared by treatment of Fe(ClO(4))(2).6H(2)O with Et-saoH(2) and NaO(2)CPh in the presence of NEt(4)OH in MeOH; 3 prepared by treatment of Fe(ClO(4))(2).6H(2)O with Me-saoH(2) and NaO(2)CCMe(3) in the presence of NEt(4)OH in MeOH; and 4 prepared by treatment of Fe(2)(SO(4))(3).6H(2)O with Me-saoH(2) in the presence of NEt(3) in MeOH. 4 is a rare example of a polynuclear iron complex containing a coordinated SO(4)(2-) ion. Compounds 5-7 are prepared by treatment of Fe(O(2)CMe)(2) with Me-saoH(2) (5), Et-saoH(2) (6), Ph-saoH(2) (7) in the presence of H(3)tea (triethanolamine) in MeOH, and represent the largest nuclearity Fe(III) clusters containing salicyladoxime-based ligands, joining a surprisingly small family of characterised octanuclear Fe complexes. Variable temperature magnetic susceptibilty measurements of 1, 3 and 5-7 reveal all five complexes possess S = 0 spin ground states; 2 possesses an S = 1/2 spin ground state, while 4 has an S = 4 +/- 1 spin ground state.     

2:2 Fe(III):ligand and "adamantane core" 4:2 Fe(III):ligand (hydr)oxo complexes of an acyclic ditopic ligand

A bis-hydroxo-bridged diiron(III) complex and a bis-mu-oxo-bis-mu-hydroxo-bridged tetrairon(III) complex are isolated from the reaction of 2,6-bis((N,N'-bis-(2-picolyl)amino)methyl)-4-tert-butylphenol (Hbpbp) with iron perchlorate in acidic and neutral solutions respectively. The X-ray structure of the dinuclear complex [{(Hbpbp)Fe([mu-OH)}(2)](ClO(4))(4).2C(3)H(6)O (1.2C3H6O) shows that only one of the metal-binding cavities of each ligand is occupied by an iron(III) atom and two [Fe(Hbpbp)]3+ units are linked together by two hydroxo bridging groups to form a [Fe(III)-(mu-OH)](2) rhomb structure with Fe...Fe = 3.109(1)A. The non-coordinated tertiary amine of Hbpbp is protonated. Magnetic susceptibility measurements show a well-behaved weak antiferromagnetic coupling between the two Fe(III) atoms, J= -8 cm(-1). The tetranuclear complex [(bpbp)(2)Fe(4)(mu-O)(2)(mu-OH)(2)](ClO(4))(4)(2) was isolated as two different solvates .4CH(3)OH and .6H(2)O with markedly different crystal morphologies at pH ca. 6. Complex .4CH(3)OH forms red cubic crystals and .6H(2)O forms green crystalline platelets. The Fe(4)O(6) core of shows an adamantane-like structure: The six bridging oxygen atoms are provided by the two phenolato groups of the two bpbp(-) ligands, two bridging oxo groups and two bridging hydroxo groups. The hydroxo and oxo ligands could be distinguished on the basis of Fe-O bond lengths of the two different octahedral iron sites: Fe-mu-OH, 1.953(5), 2.013(5)A and Fe-mu-O, 1.803(5), 1.802(5)A. The difference in ligand environment is too small for allowing Mossbauer spectroscopy to distinguish between the two crystallographically independent Fe sites. The best fit to the magnetic susceptibility of .4CH(3)OH was achieved by using three coupling constants J(Fe-OPh-Fe)= 2.6 cm(-1), J(Fe-OH-Fe)=-0.9 cm(-1), J(Fe-O-Fe)=-101 cm(-1) and iron(III) single ion ZFS (|D|= 0.15 cm(-1)).     

Aggregation control by homologous tripodal tetradentate amino acid ligands in oxo-bridged diiron(III) aquo complexes

Isoelectronic oxo-bridged diiron(III) aquo complexes of the homologous tripodal tetradentate amino acid ligands, N,N'-bis(2-pyridylmethyl)-3-aminoacetate (bpg(-)) and N,N'-bis(2-pyridylmethyl)-3-aminopropionate (bpp(-)), containing [(H(2)O)Fe(III)-(mu-O)-Fe(III)(H(2)O)](4+) cores, oligomerise, respectively, by dehydration and deprotonation, or by dehydration only, in reversible reactions. In the solid state, [Fe(2)(O)(bpp)(2)(H(2)O)(2)](ClO(4))(2) (1(ClO(4))(2)) exhibits stereochemistry identical to that of [Fe(2)(O)(bpg)(2)(H(2)O)(2)](ClO(4))(2) (2(ClO(4))(2)), with the ligand carboxylate donor oxygen atoms and the water molecules located cis to the oxo bridge and the tertiary amine group trans to it. Despite their structural similarity, 1(2+) and 2(2+) display markedly different aggregation behaviour in solution. In the absence of significant water, 1(2+) dehydrates and dimerises to give the tetranuclear complex, [Fe(4)(O)(2)(bpp)(4)](ClO(4))(4) (3(ClO(4))(4)), in which the carboxylate groups of the four bpp(-) ligands act as bridging groups between two [Fe(2)(O)(bpp)(2)](2+) units. Under similar conditions, 2(2+) dehydrates and deprotonates to form dinuclear and trinuclear oligomers, [Fe(2)(O)(OH)(bpg)(2)](ClO(4)) (4ClO(4)) and [Fe(3)(O)(2)(OH)(bpg)(3)](ClO(4)) (5(ClO(4))), related by addition of 'Fe(O)(bpg)' units. The trinuclear 5(ClO(4)), characterised crystallographically as two solvates 5(ClO(4)).3H(2)O and 5(ClO(4)).2MeOH, is based on a hexagonal [Fe(3)(O)(2)(OH)(bpg)(3)](+) unit, formally containing one hydroxo and two oxo bridges. The different aggregation behaviour of 1(ClO(4))(2) and 2(ClO(4))(2) results from the difference of one methylene group in the pendant carboxylate arms of the amino acid ligands.     

Water affects the stereochemistry and dioxygen reactivity of carboxylate-rich diiron(II) models for the diiron centers in dioxygen-dependent non-heme enzymes

Carboxylate-bridged high-spin diiron(II) complexes with distinctive electronic transitions were prepared by using 4-cyanopyridine (4-NCC(5)H(4)N) ligands to shift the charge-transfer bands to the visible region of the absorption spectrum. This property facilitated quantitation of water-dependent equilibria in the carboxylate-rich diiron(II) complex, [Fe(2)(mu-O(2)CAr(Tol))(4)(4-NCC(5)H(4)N)(2)] (1), where (-)O(2)CAr(Tol) is 2,6-di-(p-tolyl)benzoate. Addition of water to 1 reversibly shifts two of the bridging carboxylate ligands to chelating terminal coordination positions, converting the structure from a paddlewheel to a windmill geometry and generating [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(4-NCC(5)H(4)N)(2)(H(2)O)(2)] (3). This process is temperature dependent in solution, rendering the system thermochromic. Quantitative treatment of the temperature-dependent spectroscopic changes over the temperature range from 188 to 298 K in CH(2)Cl(2) afforded thermodynamic parameters for the interconversion of 1 and 3. Stopped flow kinetic studies revealed that water reacts with the diiron(II) center ca. 1000 time faster than dioxygen and that the water-containing diiron(II) complex reacts with dioxygen ca. 10 times faster than anhydrous analogue 1. Addition of {H(OEt(2))(2)}{B}, where B(-) is tetrakis(3,5-di(trifluoromethyl)phenyl)borate, to 1 converts it to [Fe(2)(mu-O(2)CAr(Tol))(3)(4-NCC(5)H(4)N)(2)](B) (5), which was also structurally characterized. Mossbauer spectroscopic investigations of solid samples of 1, 3, and 5, in conjunction with several literature values for high-spin iron(II) complexes in an oxygen-rich coordination environment, establish a correlation between isomer shift, coordination number, and N/O composition. The products of oxygenating 1 in CH(2)Cl(2) were identified crystallographically to be [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(4-NCC(5)H(4)N)(2)].2(HO(2)CAr(Tol)) (6) and [Fe(6)(mu-O)(2)(mu-OH)(4)(mu-O(2)CAr(Tol))(6)(4-NCC(5)H(4)N)(4)Cl(2)] (7).     

Synthesis, structures, and solution behavior of di- and trinuclear titanium(IV)--cyclophosphato complexes

The reaction of the cyclotetraphosphate ion (P(4)O(12)(4)(-)) with [CpTiCl(3)] (Cp = eta(5)-C(5)Me(5)) gives [(CpTi)(2)(P(4)O(12))(2)](2)(-) where the P(4)O(12) ligands adopt a saddle conformation, while that with [(CpTiCl)(3)(mu-O)(3)] leads to [(CpTi)(3)(mu-O)(3)(P(4)O(12))](-) containing a crown form P(4)O(12) ligand; both products feature their unique cage structures. On the other hand, the reactions of the cyclotriphosphate ion (P(3)O(9)(3)(-)) with [(CpTiCl(2))(2)(mu-O)] and [(CpTiCl)(3)(mu-O)(3)] afford [(CpTi)(2)(mu-O)(P(3)O(9))(2)](2)(-) and [(CpTi)(3)(mu-O)(3)Cl(P(3)O(9))](-), respectively, and in both cases the P(3)O(9) ligands bridge two titanium centers with an eta(2):eta(1) mode.     

Synthesis and characterization of carboxylate-rich complexes having the [Fe2(mu-OH)2(mu-O2CR)]3+ and [Fe2(mu-O)(mu-O2CR)]3+ cores of O2-dependent diiron enzymes

The {Fe2(mu-OH)2(mu-O2CR)}3+ and {Fe2(mu-O)(mu-O2CR)}3+ cores of the carboxylate-bridged diiron(III) centers in the enzyme active sites were reproduced by small molecule model complexes that were prepared through direct oxygenation of the mononuclear iron(II) complexes. Upon oxygenation of [Fe(O2CArTol)2(Hdmpz)2], where -O2CArTol is 2,6-di(p-tolyl)benzoate and Hdmpz is 3,5-dimethylpyrazole, [Fe2(mu-OH)2(mu-O2CArTol)(O2CArTol)3(OH2)(Hdmpz)2] was generated and characterized to share close physical properties with sMMOHox, including delta = 0.45 (2) mm/s, DeltaEQ = 1.21 (2) mm/s, and J = -7.2 (2) cm-1. The compound [Fe2(mu-O)(mu-O2CAr4-FPh)(O2CAr4-FPh)3(Hdmpz)3], where -O2CAr4-FPh is 2,6-di(4-fluorophenyl)benzoate, with delta = 0.51 (2) mm/s, DeltaEQ = 1.26 (2) mm/s, and J = -117.4 (1) cm-1, was isolated as the oxygenation product of [Fe(O2CAr4-FPh)2(Hdmpz)2].     

Alkynyldiphenylphosphine d8 (Pt, Rh, Ir) complexes: contrasting behavior toward cis-[Pt(C6F5)2(THF)2

The synthesis and characterization of a series of mononuclear d(8) complexes with at least two P-coordinated alkynylphosphine ligands and their reactivity toward cis-[Pt(C(6)F(5))(2)(THF)(2)] are reported. The cationic [Pt(C(6)F(5))(PPh(2)C triple-bond CPh)(3)](CF(3)SO(3)), 1, [M(COD)(PPh(2)C triple-bond CPh)(2)](ClO(4)) (M = Rh, 2, and Ir, 3), and neutral [Pt(o-C(6)H(4)E(2))(PPh(2)C triple-bond CPh)(2)] (E = O, 6, and S, 7) complexes have been prepared, and the crystal structures of 1, 2, and 7.CH(3)COCH(3) have been determined by X-ray crystallography. The course of the reactions of the mononuclear complexes 1-3, 6, and 7 with cis-[Pt(C(6)F(5))(2)(THF)(2)] is strongly influenced by the metal and the ligands. Thus, treatment of 1 with 1 equiv of cis-[Pt(C(6)F(5))(2)(THF)(2)] gives the double inserted cationic product [Pt(C(6)F(5))(S)mu-(C(Ph)=C(PPh(2))C(PPh(2))=C(Ph)(C(6)F(5)))Pt(C(6)F(5))(PPh(2)C triple-bond CPh)](CF(3)SO(3)) (S = THF, H(2)O), 8 (S = H(2)O, X-ray), which evolves in solution to the mononuclear complex [(C(6)F(5))(PPh(2)C triple-bond CPh)Pt(C(10)H(4)-1-C(6)F(5)-4-Ph-2,3-kappaPP'(PPh(2))(2))](CF(3) SO(3)), 9 (X-ray), containing a 1-pentafluorophenyl-2,3-bis(diphenylphosphine)-4-phenylnaphthalene ligand, formed by annulation of a phenyl group and loss of the Pt(C(6)F(5)) unit. However, analogous reactions using 2 or 3 as precursors afford mixtures of complexes, from which we have characterized by X-ray crystallography the alkynylphosphine oxide compound [(C(6)F(5))(2)Pt(mu-kappaO:eta(2)-PPh(2)(O)C triple-bond CPh)](2), 10, in the reaction with the iridium complex (3). Complexes 6 and 7, which contain additional potential bridging donor atoms (O, S), react with cis-[Pt(C(6)F(5))(2)(THF)(2)] in the appropriate molar ratio (1:1 or 1:2) to give homo- bi- or trinuclear [Pt(PPh(2)C triple-bond CPh)(mu-kappaE-o-C(6)H(4)E(2))(mu-kappaP:eta(2)-PPh(2)C triple-bond CPh)Pt(C(6)F(5))(2)] (E = O, 11, and S, 12) and [(Pt(mu(3)-kappa(2)EE'-o-C(6)H(4)E(2))(mu-kappaP:eta(2)-PPh(2)C triple-bond CPh)(2))(Pt(C(6)F(5))(2))(2)] (E = O, 13, and S, 14) complexes. The molecular structure of 14 has been confirmed by X-ray diffraction, and the cyclic voltammetric behavior of precursor complexes 6 and 7 and polymetallic derivatives 11-14 has been examined.     

Functional mimic of dioxygen-activating centers in non-heme diiron enzymes: mechanistic implications of paramagnetic intermediates in the reactions between diiron(II) complexes and dioxygen

Two tetracarboxylate diiron(II) complexes, [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(C(5)H(5)N)(2)] (1a) and [Fe(2)(mu-O(2)CAr(Tol))(4)(4-(t)BuC(5)H(4)N)(2)] (2a), where Ar(Tol)CO(2)(-) = 2,6-di(p-tolyl)benzoate, react with O(2) in CH(2)Cl(2) at -78 degrees C to afford dark green intermediates 1b (lambda(max) congruent with 660 nm; epsilon = 1600 M(-1) cm(-1)) and 2b (lambda(max) congruent with 670 nm; epsilon = 1700 M(-1) cm(-1)), respectively. Upon warming to room temperature, the solutions turn yellow, ultimately converting to isolable diiron(III) compounds [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (1c), 4-(t)BuC(5)H(4)N (2c)). EPR and M?ssbauer spectroscopic studies revealed the presence of equimolar amounts of valence-delocalized Fe(II)Fe(III) and valence-trapped Fe(III)Fe(IV) species as major components of solution 2b. The spectroscopic and reactivity properties of the Fe(III)Fe(IV) species are similar to those of the intermediate X in the RNR-R2 catalytic cycle. EPR kinetic studies revealed that the processes leading to the formation of these two distinctive paramagnetic components are coupled to one another. A mechanism for this reaction is proposed and compared with those of other synthetic and biological systems, in which electron transfer occurs from a low-valent starting material to putative high-valent dioxygen adduct(s).