Mixed-valent [FeIV(mu-O)(mu-carboxylato)2FeIII]3+ core

The symmetrically ligated complexes 1, 2, and 3 with a (mu-oxo)bis(mu-acetato)diferric core can be one-electron oxidized electrochemically or chemically with aminyl radical cations [*NR3][SbCl6] in acetonitrile yielding complexes which contain the mixed-valent [(mu-oxo)bis(mu-acetato)iron(IV)iron(III)]3+ core: [([9]aneN3)(2FeIII2)(mu-O)(mu-CH3CO2)2](ClO4)2 (1(ClO4)2), [(Me3[9]aneN3)(2FeIII2)(mu-O)(mu-CH3CO2)2](PF6)2 (2(PF6)(2)), and [(tpb)(2FeIII2)(mu-O)(mu-CH3CO2)2] (3) where ([9]aneN3) is the neutral triamine 1,4,7-triazacyclononane and (Me3[9]aneN3) is its tris-N-methylated derivative, and (tpb)(-) is the monoanion trispyrazolylborate. The asymmetrically ligated complex [(Me3[9]aneN3)FeIII(mu-O)(mu-CH3CO2)2FeIII(tpb)](PF6) (4(PF6)) and its one-electron oxidized form [4ox]2+ have also been prepared. Finally, the known heterodinuclear species [(Me3[9]aneN3)CrIII(mu-O)(mu-CH3CO2)2Fe([9]aneN3)](PF6)2 (5(PF6)(2)) can also be one-electron oxidized yielding [5ox]3+ containing an iron(IV) ion. The structure of 4(PF6).0.5CH3CN.0.25(C2H5)2O has been determined by X-ray crystallography and that of [5ox]2+ by Fe K-edge EXAFS-spectroscopy (Fe(IV)-O(oxo): 1.69(1) A; Fe(IV)-O(carboxylato) 1.93(3) A, Fe(IV)-N 2.00(2) A) contrasting the data for 5 (Fe(III)-O(oxo) 1.80 A; Fe(III)-O(carboxylato) 2.05 A, Fe-N 2.20 A). [5ox]2+ has an St = 1/2 ground state whereas all complexes containing the mixed-valent [FeIV(mu-O)(mu-CH3CO2)2FeIII]3+ core have an St = 3/2 ground state. M?ssbauer spectra of the oxidized forms of complexes clearly show the presence of low spin FeIV ions (isomer shift approximately 0.02 mm s(-1), quadrupole splitting approximately 1.4 mm s(-1) at 80 K), whereas the high spin FeIII ion exhibits delta approximately 0.46 mm s(-1) and DeltaE(Q) approximately 0.5 mm s(-1). M?ssbauer, EPR spectral and structural parameters have been calculated by density functional theoretical methods at the BP86 and B3LYP levels. The exchange coupling constant, J, for diiron complexes with the mixed-valent FeIV-FeIII core (H = -2J S1.S2; S(1) = 5/2; S2 = 1) has been calculated to be -88 cm(-1) (intramolecular antiferromagnetic coupling) and for the reduced diferric form of -75 cm(-1) in reasonable agreement with experiment (J = -120 cm(-1)).     

Effect of N-methylation of macrocyclic amine ligands on the spin state of iron(III): a tale of two fluoro complexes

Syntheses and characterization of [(cyclamacetate)FeF]PF6 (1) and the corresponding N-methylated complex [(trimethylcyclamacetate)FeF]PF6 (3) are presented. Compound 1 is prepared in good yields from the analogous chloro complex, whereas 3 is prepared by hydrolysis of the oxo-bridged diiron compound (Me3cyclam-acetate)Fe-O-FeCl3 (2) in the presence of PF(6) anions. Magnetic susceptibility and spectroscopic data including electron paramagnetic resonance and M?ssbauer spectra indicate that 1 contains low-spin Fe(III) (S = 1/2), while 3 is high spin (S = 5/2). Both octahedral fluoro complexes were investigated theoretically by density functional theory in order to determine why the spin states of the two molecules are different. Energies calculated using the B3LYP functional correctly predict 1 to have a low-spin S = 1/2 ground state and 3 to be high spin, regardless of whether a solvation model is included. The difference between 1 and 3 is most likely a combination of steric effects caused by the N-methyl groups, which compel the Fe-N bond distances to be longer in 3 than they ordinarily would be, and also electronic effects, which cause the N-methylated ligand to be a weaker sigma donor than its nonmethylated counterpart.     

Octahedral non-heme oxo and non-oxo Fe(IV) complexes: an experimental/theoretical comparison

Electron-transfer series are described for three ferric complexes of the pentadentate ligand 4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane-1-acetate (Me(3)cyclam-acetate) with axial chloride, fluoride, and azide ligands. These complexes can all be reduced coulometrically to their Fe(II) analogs and oxidized reversibly to the corresponding Fe(IV) species. The Fe(II), Fe(III), and Fe(IV) species have been studied spectroscopically and their UV-vis, M?ssbauer, EPR, and IR spectra are presented. The fluoro species [(Me(3)cyclam-acetate)FeF](n+) (n = 0, 1, 2) have been studied computationally using density functional theory (DFT), and the electronic structure of the Fe(IV) dication [(Me(3)cyclam-acetate)FeF](2+) is compared with that of the isoelectronic Fe(IV) oxo cation [(Me(3)cyclam-acetate)FeO](+); the different properties of the two species are mainly due to the significantly covalent Fe=O pi bonds in the latter.     

Mononuclear (nitrido)iron(V) and (oxo)iron(IV) complexes via photolysis of [(cyclam-acetato)FeIII(N3)]+ and ozonolysis of [(cyclam-acetato)FeIII(O3SCF3)]+ in water/acetone mixtures

Reaction of the monoanionic, pentacoordinate ligand lithium 1,4,8,11-tetraazacyclotetradecane-1-acetate, Li(cyclam-acetate), with FeCl3 yields, upon addition of KPF6, [(cyclam-acetato)FeCl]PF6 (1) as a red microcrystalline solid. Addition of excess NaN3 prior to addition of KPF6 yields the azide derivative [(cyclam-acetato)FeN3]PF6 (2a) as orange microcrystals. The X-ray crystal structure of the azide derivative has been determined as the tetraphenylborate salt (2b). Reaction of 1 with silver triflate yields [(cyclam-acetato)Fe(O3SCF3)]PF6 (3), which partially dissociates triflate in nondried solvents to yield a mixture of triflate and aqua bound species. Each of the iron(III) derivatives is low-spin (d5, S = 1/2) as determined by variable-temperature magnetic susceptibility measurements, M?ssbauer and EPR spectroscopy. The low-spin iron(II) (d6, S = 0) complexes 1red and 2ared have been prepared by electrochemical and chemical methods and have been characterized by M?ssbauer spectroscopy. Photolysis of 2a at 419 nm in frozen acetonitrile yields a nearly colorless species in approximately 80% conversion with an isomer shift delta = -0.04 mm/s and a quadrupole splitting delta EQ = -1.67 mm/s. A spin-Hamiltonian analysis of the magnetic M?ssbauer spectra is consistent with an FeV ion (d3, S = 3/2). The proposed [(cyclam-acetato)FeV=N]+ results from the photooxidation of 2a via heterolytic N-N cleavage of coordinated azide. Photolysis of 2a in acetonitrile solution at -35 degrees C (300 nm) or 20 degrees C (Hg immersion lamp) results primarily in photoreduction via homolytic Fe-Nazide cleavage yielding FeII (d,6 S = 0) with an isomer shift delta = 0.56 mm/s and quadrupole splitting delta EQ = 0.54 mm/s. A minor product containing high-valent iron is suggested by M?ssbauer spectroscopy and is proposed to originate from [((cyclam-acetato)Fe)2(mu-N)]2+ with a mixed-valent (FeIV(mu-N)FeIII))4+S = 1/2 core. Exposure of 3 to a stream of oxygen/ozone at low temperatures (-80 degrees C) in acetone/water results in a single oxidized product with an isomer shift delta = 0.01 mm/s and quadrupole splitting delta EQ = 1.37 mm/s. A spin-Hamiltonian analysis of the magnetic M?ssbauer yields parameters similar to those of compound II of horseradish peroxidase which are consistent with an FeIV=O monomeric complex (S = 1).     

New extended magnetic systems based on oxalate and iron(III) ions

A series of oxalate-bridged iron(III) complexes have been synthesized by the reaction of FeCl 3 with oxalic acid (H 2ox) and XCl, where X is a substituted univalent ammonium or an alkaline cation. We have obtained basically two different types of compounds by varying the nature and the shape of the counterion, with the dimensionality of the resulting product being strongly influenced by the counterion. Three-dimensional (3D) networks of oxo- and oxalato-bridged iron(III) ions of the general formula {X 2[Fe 2O(ox) 2Cl 2]. pH 2O} n have been obtained for X = Li (+) ( 1), Na (+) ( 2), and K (+) ( 3) with p = 4 and X = MeNH 3 (+) ( 4), Me 2NH 2 (+) ( 5), and EtNH 3 (+) ( 6) with p = 2. Similar 3D hydroxo- and oxalato-bridged iron(III) networks of the formula {X[Fe 2(OH)(ox) 2Cl 2].2H 2O} n resulted for X = EtNH 3 (+) ( 7a) and PrNH 3 (+) ( 8). Compound 7a undergoes a solid-to-solid transformation, leading to a new species of the formula {(H 3O)(EtNH 3)[Fe 2O(ox) 2Cl 2].H 2O} n ( 7b). Chainlike compounds of the formula {X 2[Fe 2(ox) 2Cl 4]. pH 2O} n [X = Me 2NH 2 (+)( 9, p = 1), Me 3NH (+) ( 10, p = 2), and Me 4N (+) ( 11, p = 0)] have been obtained for the bulkier alkylammonium cations. Magnetic susceptibility measurements in the temperature range 1.9-295 K show the occurrence of weak ferromagnetic ordering due to spin canting in the 3D networks 1- 8, with the value of the critical temperature ( T c) varying with the cation in the range 26 K ( 2) to 70 K ( 8) without significant structural modifications. The last three one-dimensional compounds exhibit the typical behavior of antiferromagnetically coupled chains of interacting spin sextets [ J = -8.3 ( 9), -6.9 ( 10), and -8.4 ( 11) cm (-1) with H = - J summation operator i S i S i+1 ].     

Inter- and intramolecular spin transfer in molecular magnetic materials. Solid-state NMR spectroscopy of paramagnetic metallocenium ions

To shed light on the interaction in molecule-based magnetic materials, the decamethylmetallocenium hexafluorophosphates, [(C(5)Me(5))(2)M](+) [PF(6)](-) with M = Cr, Mn, Fe, Co, and Ni, as well as the tetracyanoethenides, [(C(5)Me(5))(2)M](+) [TCNE](-) with M = Cr, Mn, Fe, and Co, have been investigated in the solid state by using (1)H, (13)C, (19)F, and (31)P NMR spectroscopy under magic angle spinning (MAS). The isotropic (13)C and (1)H NMR signals cover ranges of about 1300 and 500 ppm, respectively. From the shift anisotropies of the ring carbon signal of the [(C(5)Me(5))(2)M](+) cations, the total unpaired electron spin density in the ligand pi orbitals has been calculated; it amounts up to 36% (M = Ni) and is negative for M = Cr, Mn, and Fe. The radical anion of [(C(5)Me(5))(2)M](+) [TCNE](-) shifts the (13)C NMR signals of all [(C(5)Me(5))(2)M](+) cations to high frequency, which establishes transfer of positive spin density from the anions to the cations. The (19)F and (31)P NMR signals of the paramagnetic salts [(C(5)Me(5))(2)M](+) [PF(6)](-) are shifted up to 13.5 ppm relative to diamagnetic [(C(5)Me(5))(2)Co](+) [PF(6)](-). The signs of these shifts are the same as those of the pi spin density in [(C(5)Me(5))(2)M](+). After consideration of interionic ligand- and metal-centered dipolar shifts, this establishes cation-anion spin delocalization. The mixed crystals [(C(5)Me(5))(2)M(x)Co(1-x)](+)[PF(6)](-) have been prepared for M = Cr and Ni. They are isostructural with [(C(5)Me(5))(2)Co](+) [PF(6)](-) whose single-crystal structure has been determined by X-ray diffraction. The (13)C, (19)F, and (31)P MAS NMR spectra of the mixed crystals show that the respective two closest paramagnetic ions in the lattice delocalize spin density to [(C(5)Me(5))(2)Co](+), [(C(5)Me(5))(2)Ni](+), and [PF(6)](-). In [(C(5)Me(5))(2)M](+), about 10(-4) au per carbon atom are transferred.     

Spin crossover of ferric complexes with catecholate derivatives. Single-crystal X-ray structure, magnetic and Mössbauer investigations

Complexes of general formula [(TPA)Fe(R-Cat)]X.nS were synthesised with different catecholate derivatives and anions (TPA = tris(2-pyridylmethyl)amine, R-Cat2- = 4,5-(NO2)2-Cat2- denoted DNC(2-); 3,4,5,6-Cl4-Cat2- denoted TCC2-; 3-OMe-Cat(2-); 4-Me-Cat(2-) and X = BPh4-; NO3-; PF6-; ClO4-; S = solvent molecule). Their magnetic behaviours in the solid state show a general feature along the series, viz., the occurrence of a thermally-induced spin crossover process. The transition curves are continuous with transition temperatures ranging from ca. 84 to 257 K. The crystal structures of [(TPA)Fe(DNC)]X (X = PF6-; BPh4-) and [(TPA)Fe(TCC)]X.nS (X = PF6-; NO3- and n= 1, S = H2O; ClO4- and n= 1, S = H2O; BPh4- and n= 1, S = C3H6O) were solved at 100 (or 123 K) and 293 K. For those two systems, the characteristics of the [FeN(4)O(2)] coordination core and those of the dioxolene ligands appear to be consistent with a prevailing Fe(III)-catecholate formulation. This feature is in contrast with the large quantum mixing between Fe(III)-catecholate and Fe(II)-semiquinonate forms recently observed with the more electron donating simple catecholate dianion. The thermal spin crossover process is accompanied by significant changes of the molecular structures as shown by the average variation of the metal-ligand bond distances which can be extrapolated for a complete spin conversion from ca. 0.123 to 0.156 A. The different space groups were retained in the low- and high-temperature phases.     

Nickel dithiolene chelate rings in a new role as eta5-coordinating ligands: synthesis, structural characterization, and redox reactivity of an "Fe2Ni" bis-double-decker

A bis-double-decker complex has been assembled from the nickel bisdithiolene complex [Ni(S 2C 2Me 2) 2] (1-/2-) and two [Cp*Fe] (+) units (Cp* = C 5Me 5). The complex, [(eta (5)-Cp*-Fe-mu-eta (5),eta (5)-((S 2C 2Me 2) 2Ni)Fe-eta (5)-Cp*] ( n ) ( 1 ( n )), was isolated in two charge states ( n = 0, 1). The structure of 1 (+) was confirmed by X-ray crystallography for 1 (+)PF 6 (-) and 1 (+)BF 4 (-), and it shows the nickel bisdithiolene units pi-donating to iron centers. Both salts crystallize in a centrosymmetric space group (center of inversion at nickel). Computational (density functional theory) data indicate a highly delocalized spin density for 1 (+). The reaction of 1 with 1 or 2 equiv of HBF 4 leads to oxidation to form 1 (+) or 1 (2+), respectively. On an electrochemical time scale, reversibility is observed for the redox series 1/ 1 (+)/ 1 (2+), with an additional slower step for oxidation of 1 (2+).     

Facile access to redox-active C2-bridged complexes with half-sandwich manganese end groups

The dinuclear mixed-valent complex [(MeC5H4)(dmpe)MnC(2)Mn(dmpe)(C5H4Me)](+)[(eta2-MeC5H4)3Mn](-)[1](+)[2]- (dmpe=1,2-bis(dimethylphosphanyl)ethane) was prepared by the reaction of [Mn(MeC5H4)2] with dmpe and Me(3)SnC[triple chemical bond]CSnMe3. The reactions of [1](+)[2]- with K[PF6] and Na[BPh4] yielded the corresponding anion metathesis products [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][PF6] ([1][PF6]) and [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][BPh4] ([1][BPh4]). These mixed-valent species can be reduced to the neutral form by reaction with Na/Hg. The obtained complex [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)] (1) displays a triplet/singlet spin equilibrium in solution and in the solid state, which was additionally studied by DFT calculations. The diamagnetic dicationic species [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][PF6]2 ([1][PF6]2) was obtained by oxidizing the mixed-valent complex [1][PF6] with one equivalent of [Fe(C5H5)2][PF6]. Both redox processes are fully reversible. The dinuclear compounds were characterized by NMR, IR, UV-visible, and Raman spectroscopy, cyclic voltammetry, and magnetic susceptibility measurements. X-ray diffraction studies were performed on [1][2], [1][PF6], [1][BPh4], and [1][PF6]2.     

A transition-metal-catalyzed enediyne cycloaromatization

The pentamethylcyclopentadienyl iron cation, generated from [(eta5-C5Me5)Fe(NCMe)3]PF6, triggers the room temperature cycloaromatization of acyclic and alicyclic enediynes, in the presence of either 1,4-cyclohexadiene or terpinene as the hydrogen-atom donor, to give metal-arene products in good to excellent yields. Photolysis of the metal-arene complexes liberates the arene from the metal in excellent yield. The first demonstration of a transition-metal-catalyzed cycloaromatization of conjugated enediynes has been achieved under photochemical conditions utilizing either [(eta5-C5Me5)Fe(NCMe)3]PF6 or [(eta5-C5Me5)Fe(eta6-1,2-(Prn)2C6H4)]PF6 as the catalyst precursor. The use of a metal and light has led to a convenient method for cycloaromatization of a trans-enediyne.     

Computational study of iron bis(dithiolene) complexes: redox non-innocent ligands and antiferromagnetic coupling

The molecular and electronic structure of monomeric ([Fe(S2C2H2)2](z), [Fe(S2C2(C6H4-p-OCH3)2)2](z)) and dimeric ([{Fe(S2C2H2)2}2](z)) iron bis(dithiolene) complexes, and of their phosphine adducts ([(PH3)Fe(S2C2H2)2](z), [(P(C6H5)3)Fe(S2C2H2)2](z), [(PH3)Fe(S2C2(C6H4-p-OCH3)2)2](z)), carrying various charges (z = 0, 1-, 2-), have been investigated by density functional theory (DFT). Net total spin polarization values S of zero, two, and four have been considered for all neutral model compounds and their dianions, whereas all monoanions have been examined with net total spin polarization values S of one, three, and five. The DFT calculations utilized the pure functional BP86, as well as the hybrid functionals B3LYP and B3LYP*. For the monomers, the calculations reveal the presence of redox non-innocent dithiolene ligands and antiferromagnetic coupling between the ligands and the metal center. For the dimers, complexes with antiferromagnetically coupled iron centers have been found to represent structures of low energy, if not lowest energy structures. The spin-coupling constant of [{Fe(S2C2H2)2}2](2-) is calculated as J = -230 cm(-1). On the basis of the computational results, a model for reversible, electrochemically controlled binding and release of phosphine ligands to iron bis(dithiolene) complexes is proposed. Only BP86 and B3LYP* results, but not those of B3LYP calculations, are in qualitative agreement with experimental findings. BP86 calculations provide the best quantitative match in comparison with the experiment.     

Gas-phase C-H and N-H bond activation by a high valent nitrido-iron dication and NH-transfer to activated olefins

A tetrapodal pentadentate nitrogen ligand (2,6-bis(1,1-di(aminomethyl)ethyl)pyridine, 1) is used for the synthesis of the azido-iron(III) complex [(1)Fe(N3)]X2 where X is either Br or PF6. By means of electrospray ionization mass spectrometry, the dication [(1)Fe(N3)]2+ can be transferred into the gas phase as an intact entity. Upon collisional activation, [(1)Fe(N3)]2+ undergoes an expulsion of molecular nitrogen to afford the dicationic nitrido-iron species [(1)FeN]2+ as an intermediate, which upon further activation can intramolecularly activate C-H- and N-H bonds of the chelating ligand 1 or can transfer an NH unit in bimolecular reactions with activated olefins. The precursor dication [(1)Fe(N3)]2+, the resulting nitrido species [(1)FeN]2+, and its possible isomers are investigated by mass spectrometric experiments, isotopic labeling, and complementary computational studies using density functional theory.     

Iron-molybdenum charge-transfer hybrids containing organometallic and inorganic fragments bridged by aryldiazenido ligands in a mu-eta(6):eta(1) coordination mode: syntheses, characterization, X-ray structures, electrochemistry, and theoretical investigation

Representative members of a new family of covalently bonded charge-transfer molecular hybrids, of general formula [(eta5-C5H5)Fe(mu,eta6:eta1-p-RC6H4NN)Mo(eta2-S2CNEt2)3] +PF6- (R: H, 5+PF6-; Me, 6+PF6-; MeO, 7+PF6-) and [(eta5-C5Me5)Fe(mu,eta6:eta1-C6H5NN)Mo(eta2-S2CNEt2)3]+PF6-, 8+PF6-, have been synthesized by reaction of the corresponding mixed-sandwich organometallic hydrazines [(eta5-C5H5)Fe(eta6-p-RC6H4NHNH2)]+PF6- (R: H, 1+PF6-; Me, 2+PF6-; MeO, 3+PF6-) and [(eta5-C5Me5)Fe(eta6-C6H5NHNH2)]+PF6-, 4+PF6-, with cis-dioxomolybdenum(VI) bis(diethyldithiocarbamato) complex, [MoO2(S2CNEt2)2], in the presence of sodium diethyldithiocarbamato trihydrate, NaSC(=S)NEt2.3H2O, in refluxing methanol. These iron-molybdenum complexes consist of organometallic and inorganic fragments linked each other through a pi-conjugated aryldiazenido bridge coordinated in eta6 and eta1 modes, respectively. These complexes were fully characterized by FT-IR, UV-visible, and 1H NMR spectroscopies and, in the case of complex 7+PF6-, by single-crystal X-ray diffraction analysis. Likewise, the electrochemical and solvatochromic properties were studied by cyclic voltammetry and UV-visible spectroscopy, respectively. The electronic spectra of these hybrids show an absorption band in the 462-489 and 447-470 nm regions in CH2Cl2 and DMSO, respectively, indicating the existence of a charge-transfer transition from the inorganic donor to the organometallic acceptor fragments through the aryldiazenido spacer. A rationalization of the properties of 5+PF6--8+PF6- is provided through DFT calculations on a simplified model of 7+PF6-. Besides the heterodinuclear complexes 5+PF6--8+PF6-, the mononuclear molybdenum diazenido derivatives, [(eta1-p-RC6H4NN)Mo(eta2-S2CNEt2)3] (R: H, 9; Me, 10; MeO, 11), resulting from the decoordination of the [(eta5-C5H5)Fe]+ moiety of complexes 5+PF6--7+PF6-, were also isolated. For comparative studies, the crystalline and molecular structure of complex 10.Et2O was also determined by X-ray diffraction analysis and its electronic structure computed.     

Initial members of the family of molecular mid-valent high-nuclearity iron nitrides: [Fe4N2X10]4- and [Fe10N8X12]5- (X = Cl-, Br-)

Current theoretical and experimental evidence points toward X = N as the identity of the interstitial atom in the [MoFe7S9X] core of the iron-molybdenum cofactor cluster of nitrogenase. This atom functions with mu6 bridging multiplicity to six iron atoms and, if it is nitrogen as nitride, raises a question as to the existence of a family of molecular iron nitrides of higher nuclearity than known dinuclear Fe(III,IV) species with linear [Fe-N-Fe]5+,4+ bridges. This matter has been initially examined by variation of reactant stoichiometry in the self-assembly systems [FeX4]1-/(Me3Sn)3N (X = Cl-, Br-) in acetonitrile. A 2:1 mol ratio affords [Fe4N2Cl10]4- (1), isolated as the Et4N+ salt (72%). This cluster has idealized C2h symmetry with a planar antiferromagnetically coupled [Fe(III)4(mu3-N)2]6+ core containing an Fe2N2 rhombus to which are attached two FeCl3 units. DFT calculations have been performed to determine the dominant magnetic exchange pathway. An 11:8 mol ratio leads to [Fe10N8Cl12]5- (3) as the Et4N+ salt (37%). The cluster possesses idealized D2h symmetry and is built of 15 edge- and vertex-shared rhomboids involving two mu3-N and six mu4-N bridging atoms, and incorporates two of the core units of 1. Four FeN2Cl2 and four FeN3Cl sites are tetrahedral and two FeN5 sites are trigonal pyramidal. The cluster is mixed-valence (9Fe(III) + Fe(IV)); a discrete Fe(IV) site was not detected by crystallography or M?ssbauer spectroscopy. The corresponding clusters [Fe4N2Br10]4- and [Fe10N8Br12]5- are isostructural with 1 and 3, respectively. Future research is directed toward defining the scope of the family of molecular iron nitrides.     

Electronic structure of mononuclear bis(1,2-diaryl-1,2-ethylenedithiolato)iron complexes containing a fifth cyanide or phosphite ligand: a combined experimental and computational study

A series of mononuclear square-based pyramidal complexes of iron containing two 1,2-diaryl-ethylene-1,2-dithiolate ligands in various oxidation levels has been synthesized. The reaction of the dinuclear species [Fe(III)2(1L*)2(1L)2]0, where (1L)2- is the closed shell di-(4-tert-butylphenyl)-1,2-ethylenedithiolate dianion and (1L*)1- is its one-electron-oxidized pi-radical monoanion, with [N(n-Bu)4]CN in toluene yields dark green crystals of mononuclear [N(n-Bu)4][Fe(II)(1L*)2(CN)] (1). The oxidation of 1 with ferrocenium hexafluorophosphate yields blue [Fe(III)(1L*)2(CN)] (1ox), and analogously, a reduction with [Cp2Co] yields [Cp2Co][N(n-Bu)4][Fe(II)(1L*)(1L)(CN)] (1red); oxidation of the neutral dimer with iodine gives [Fe(III)(1L*)2I] (2). The dimer reacts with the phosphite P(OCH3)3 to yield [Fe(II)(1L*)2{P(OCH3)3}] (3), and [Fe(III)2(3L*)2(3L)2] reacts with P(OC6H5)3 to give [Fe(II)(3L*)2{P(OC6H5)3}] (4), where (3L)2- represents 1,2-diphenyl-1,2-ethylenedithiolate(2-). Both 3 and 4 were electrochemically one-electron oxidized to the monocations 3ox and 4ox and reduced to the monoanions 3red and 4red. The structures of 1 and 4 have been determined by X-ray crystallography. All compounds have been studied by magnetic susceptibility measurements, X-band EPR, UV-vis, IR, and M?ssbauer spectroscopies. The following five-coordinate chromophores have been identified: (a) [Fe(III)(L*)2X]n, X = CN-, I- (n = 0) (1ox, 2); X = P(OR)3 (n = 1+) )3ox, 4ox) with St = 1/2, SFe = 3/2; (b) [Fe(II)(L*)2X]n, X = CN-, (n = 1-) (1); X = P(OR)3 (n = 0) (3, 4) with St = SFe = 0; (c) [Fe(II)(L*)(L)X]n <--> [Fe(II)(L)(L*)X]n, X = CN- (n = 2-) (1red); X = P(OR)3 (n = 1-) (3red, 4red) with St = 1/2, SFe = 0 (or 1). Complex 1ox displays spin crossover behavior: St = 1/2 <--> St = 3/2 with intrinsic spin-state change SFe = 3/2 <--> SFe = 5/2. The electronic structures of 1 and 1(ox) have been established by density functional theoretical calculations: [Fe(II)(1L*)2(CN)]1- (SFe = 0, St = 0) and [Fe(III)(1L*)2(CN)]0 (SFe = 3/2, St = 1/2).     

Fe(II) and Fe(III) mononuclear complexes with a pentadentate ligand built on the 1,3-diaminopropane unit. Structures and spectroscopic and electrochemical properties. Reaction with H2O2

Two new iron complexes, [L(5)(3)Fe(II)Cl]PF(6) (1.PF(6)) and [(L(5)(3)H(+))Fe(III)Cl(3)]PF(6) (2.PF(6)), were synthesized (L(5)(3) = N-methyl-N,N',N'-tris(2-pyridylmethyl)propane-1,3-diamine), and their molecular structures were determined by X-ray crystallography. Their behavior in solution was studied by UV-vis spectroscopy and electrochemistry. Upon addition of a base to an acetonitrile solution of 2, the new unsymmetrical dinuclear complex [L(5)(3)Fe(III)OFe(III)Cl(3)](+) was detected. Treating 1 with hydrogen peroxide has allowed us to detect the low spin [L(5)(3)Fe(III)OOH](2+). Its spectroscopic properties (UV-vis, EPR and resonance Raman) are similar to those reported for related FeOOH complexes obtained with amine/pyridine ligands. Using stopped-flow absorption spectroscopy, the formation and degradation of [L(5)(3)Fe(III)OOH](2+) has been monitored, and a mechanism is proposed to reproduce the kinetic data.     

Binding of pi-acceptor ligands to (triamine)iron(II) complexes

A series of (Me3TACN)FeII derivatives with soft coligands have been investigated, where Me3TACN is N,N',N"-trimethyl-1,4,7-triazacyclononane. Treatment of Me3TACN with FeCl2 afforded a compound with the empirical formula (Me3TACN)FeCl2 (1). Compound 1, which is a versatile precursor reagent, was shown by single-crystal X-ray diffraction to be the salt [(Me3TACN)2Fe2Cl3][(Me3TACN)FeCl3], containing isolated [(Me3TACN)2Fe2Cl3]+ and [(Me3TACN)FeCl3]- subunits. Treatment of 1 with NaBPh4 gave the known [(Me3TACN)2Fe2Cl3]BPh4, while the addition of Me3TACN to FeCl4(2-) gave [(Me3TACN)FeCl3]-. Oxygenation of 1 afforded [(Me3TACN)FeCl2]2(mu-O), which was shown crystallographically to be centrosymmetric with a pair of distorted octahedral Fe centers. The Fe-N bond trans to the Fe-O bond is elongated by 02 A relative to the other Fe-N distances. Solutions of 1 and thiolates absorb CO to give [(Me3TACN)Fe(SPh)(CO)2]BPh4 and (Me3TACN)Fe(S2C2H4)(CO) (nu CO = 1896 cm-1). Treatment of 1 with excess CN- afforded [(Me3TACN)Fe(CN)3]-, isolated as its PPh4+ salt 5. Crystallographic and spectroscopic studies show that 5 is low spin with a C3v structure; its Fe-N distances contracted by 023 A relative to those in [(Me3TACN)FeCl3]-. Aqueous solutions of 1 bind CO upon the addition of CN- to produce (Me3TACN)Fe(CN)2(CO) (6) Analogous to 6 is (Me3TACN)Fe(CN)2(CNMe), prepared by methylation of 5. The metastable dicarbonyl [(Me3TACN)FeI(CO)2]I was prepared by treatment of FeI2(CO)4 with Me3TACN and was crystallographically characterized as its BPh4- salt. Values of E1/2 for [(Me3TACN)FeCl3]-, 5, and 6 are -0409, -0640, and 0533 V vs Fc/Fc+, respectively.