Bridging Oxo Research Articles

Cobalt(II), nickel(II), and copper(II) complexes with Schiff bases, derivatives of 1-amino-8-hydroxynaphthalene-2,4-disulfonic acid

Five new cobalt(II), nickel(II), and copper(II) complexes with Schiff bases have been synthesized. The Schiff bases have been prepared by the condensation of monopotassium 1-amino-8-hydroxynaphthalene-2,4-disulfonate with benzoin (L1) or 2-hydroxy-1-naphthaldehyde (L2). The compounds have been identified and studied by elemental analysis, X-ray diffraction, thermogravimetry, measurements of magnetic susceptibility and electrical conductivity, and IR, ESR, and diffuse reflectance spectroscopy. The dimeric (with oxo bridges) structure of the Co(II) complex with L1 has been additionally confirmed by the EXAFS method.

Sandwich transitional metal complexes with tungstobismuthates and 1-methylimidazole ligands: Syntheses, structures and magnetic properties

Two novel sandwich-type coordination compounds of tungstobismuthate Na 9[{Na(H 2O) 2} 3{Co II(mim)} 3(Bi IIIW VI 9O 33) 2]·36H 2O ( 1) and Na 7H 2[{Na(H 2O) 2} 3{Mn II(mim)} 3(Bi IIIW VI 9O 33) 2]·21H 2O ( 2) (mim = 1-methylimidazole) have been synthesized in alkaline aqueous solution. Their composition and structures were established by elemental analyses, IR spectra, and single crystal X-ray diffraction. These two complexes consist of two tri-vacant [α-B-Bi IIIW VI 9O 33] 9− moieties linked through three Cu II or Mn II and three Na + ions. These Na + cations around the complex anion were bonded with some terminal and bridging oxo atoms from the complex anion and water molecules. In addition to tungstobismuthate ligands, 1-methylimidazoles also coordinate to sandwich transitional metal ions. Magnetic measurement indicates the existence of antiferromagnetic interaction between the trimeric transitional metal ions for 1 and 2.

Synthesis and Electrochemical Properties of Tetranuclear Di-μ-oxo-bis[di-μ-phenolatodiiron(III)] Complexes

Abstract A series of tetrairon(III) complexes of di-μ-oxo-bis[di-μ-phenolatodiiron(III)] core, [{Fe2(L)(L′)}2(μ-O)2](PF6)2 (1–11), where L2− is the phenol-based macrocyclic compartmental ligand and (L′)− is acetate, monochloroacetate, dichloroacetate, trifluoroacetate, pentafluoropropionate, benzoate, p-nitrobenzoate, pentafluorobenzoate, diethyl phosphate, diphenyl phosphate, or diethyldithiophosphate for 1–11, respectively, were synthesized. X-ray crystallographic studies for 4, 7, and 9 indicated that two {Fe2(L)(L′)} units were connected by two oxo bridges to afford a tetranuclear di-μ-oxo-bis[di-μ-phenolatodiiron(III)] core. Cyclic voltammograms of 1–11 in acetonitrile showed a quasi-reversible or irreversible reduction wave between −332 and −620 mV (vs. Ag/Ag+), which were attributed to a two-electron process involving the Fe4III,III,III,III/Fe4II,II,III,III. The Fe4III,III,III,III/Fe4II,II,III,III potential shifted positive with a decrease in the electron-donating ability of the end-cap ligand, and a good linear correlation was found between the potentials and the pKa values of HL′. The Fe4II,II,III,III species were generated in acetonitrile by electrochemical reduction and showed broad intervalence transition bands in the range of 900–1500 nm.

Oxovanadium(V) Tetrathiacalix[4]arene Complexes and Their Activity as Oxidation Catalysts

With the aim of modeling reactive moieties and relevant intermediates on the surfaces of vanadium oxide based catalysts during oxygenation/dehydrogenation of organic substrates, mono- and dinuclear vanadium oxo complexes of doubly deprotonated p-tert-butylated tetrathiacalix[4]arene (H4TC) have been synthesized and characterized: PPh4[(H2TC)VOCl(2)] (1) and (PPh4)2[{(H2TC)V(O)(mu-O)}2] (2). According to the NMR spectra of the dissolved complexes they both retain the structures adopted in the crystalline state, as revealed by single-crystal X-ray crystallography. Compounds 1 and 2 were tested as catalysts for the oxidation of alcohols with O(2) at 80 degrees C. Both 1 and 2 efficiently catalyze the oxidation of benzyl alcohol, crotyl alcohol, 1-phenyl-1-propanol, and fluorenol, and in most cases dinuclear complex 2 is more active than mononuclear complex 1. Moreover, the two thiacalixarene complexes 1 and 2 are in many instances more active than oxovanadium(V) complexes containing "classical" calixarene ligands tested previously. Complexes 1 and 2 also show significant activity in the oxidation of dihydroanthracene. Further investigations led to the conclusion that 1 acts as precatalyst that is converted to the active species PPh4[(TC)V==O] (3) at 80 degrees C by double intramolecular HCl elimination. For complex 2, the results of mechanistic investigations indicated that the oxidation chemistry takes place at the bridging oxo ligands and that the two vanadium centers cooperate during the process. The intermediate (PPh4)2[{H2TCV(O)}2(mu-OH)(mu-OC13H9)] (4) was isolated and characterized, also with respect to its reactivity, and the results afforded a mechanistic proposal for a reasonable catalytic cycle. The implications which these findings gathered in solution may have for oxidation mechanisms on the surfaces of V-based heterogeneous catalysts are discussed.

Tin(IV) Cyanoximates: Synthesis, Characterization, and Cytotoxicity

In recent years, numerous organotin(IV) derivatives have exhibited remarkable cytotoxicity against several types of cancer. However, the properties of the cyanoxime-containing organotin(IV) complexes are unknown. Previously, it has been shown that cyanoximes displayed an interesting spectrum of biological activity ranging from growth-regulation to antimicrobial and pesticide detoxification actions. The work presented here attempts to combine the useful properties of both groups of compounds and investigate the likely antiproliferating activity of the new substances. A series of 19 organotin(IV) complexes, with nine different cyanoxime ligands, were anaerobically prepared by means of the heterogeneous metathesis reaction between the respective organotin(IV) halides (Cl, Br) and ML (M=Ag, Tl; L=cyanoximate anion), using an ultrasound in the CH3CN at room temperature. The compounds were characterized using spectroscopic methods (UV-visible, IR, 1H,13C NMR, 119Sn Mössbauer) and X-ray analysis. The crystal structures of the complexes revealed the formation of two types of tin(IV) cyanoximates: mononuclear five-coordinated compounds of R4-xSnLx composition (R=Me, Et, n-Bu, Ph; x=1, 2; L=cyanoximate anion), and the tetranuclear R8Sn4(OH)2O2L2 species (R=n-Bu, Ph). The latter complex contains a planar [Sn4(OH)2O2]2- core, consisting of three adjacent rhombs with bridging oxo and hydroxo groups. The tin(IV) atoms are five-coordinated and have distorted trigonal-pyramidal surrounding. This is the first instance when the organic anions were found to act as monodentate O-bound planar oxime ligands. All of the compounds were studied in vitro for antiproliferating activity, using human cervical cancer HeLa and WiDR colon cancer cell lines; cisplatin was used as a positive control substance. The two dibutyltin(IV) cyanoximates showed cytotoxicity similar and greater to that of cisplatin.

Structure of the high-valent Fe IIIFe IV state in ribonucleotide reductase (RNR) of Chlamydia trachomatis—Combined EPR, 57Fe-, 1H-ENDOR and X-ray studies

A recently discovered subgroup of class I ribonucleotide reductase (RNR) found in the infectious bacterium Chlamydia trachomatis ( C. trachomatis) was shown to exhibit a high-valent Fe IIIFe IV center instead of the tyrosyl radical observed normally in all class I RNRs. The X-ray structure showed that C. trachomatis WT RNR has a phenylalanine at the position of the active tyrosine in Escherichia coli RNR. In this paper the X-ray structure of variant F127Y is presented, where the tyrosine is restored. Using 1H- and 57Fe-ENDOR spectroscopy it is shown, that in WT and variants F127Y and Y129F of C. trachomatis RNR, the Fe IIIFe IV center is virtually identical with the short-lived intermediate X observed during the iron oxygen reconstitution reaction in class I RNR from E. coli. The experimental data are consistent with a recent theoretical model for X, proposing two bridging oxo ligands and one terminal water ligand. A surprising extension of the lifetime of the Fe IIIFe IV state in C. trachomatis from a few seconds to several hours at room temperature was observed under catalytic conditions in the presence of substrate. These findings suggest a possible new role for the Fe IIIFe IV state also in other class I RNR, during the catalytic radical transfer reaction, by which the substrate turnover is started.

Redox‐Induced μ‐Acetato and μ‐Oxo Core Interconversions in Dinuclear Manganese Tris(2‐methylpyridyl)amine (tpa) Complexes: Isolation and Characterization of [Mn2III(μ‐O)(μ‐O2CCH3)(tpa)2]3+ (Eur. J. Inorg. Chem. 20/2007)

AbstractThe cover picture shows the electro‐induced core interconversions in three dinuclear manganese tris(2‐methylpyridyl)amine (tpa) complexes. The mono‐(μ‐oxo) mono‐(μ‐acetato) [Mn2III,III(O)(O2CCH3)(tpa)2]3+ and the bis‐(μ‐oxo) [Mn2IV,IV(O)2(tpa)2]4+ complexes are selectively and quasi‐quantitatively generated by sequential exhaustive electrochemical two‐electron oxidations of the bis‐(μ‐acetato) [Mn2II,II(O2CCH3)2(tpa)2]2+ complex. At each step one acetato bridge is substituted by an oxo bridge coming from the deprotonation of one residual water molecule in the solvent. The background picture shows some cyclic voltammograms recorded during this study. Details are discussed in the article by M.‐N. Collomb et al. on p. 3179 ff. We thank Dr. Damien Jouvenot for the design of the cover picture.

Spectroscopic and electronic structure studies of intermediate X in ribonucleotide reductase R2 and two variants: a description of the FeIV-oxo bond in the FeIII-O-FeIV dimer.

Spectroscopic and electronic structure studies of the class I Escherichia coli ribonucleotide reductase (RNR) intermediate X and three computationally derived model complexes are presented, compared, and evaluated to determine the electronic and geometric structure of the FeIII-FeIV active site of intermediate X. Rapid freeze-quench (RFQ) EPR, absorption, and MCD were used to trap intermediate X in R2 wild-type (WT) and two variants, W48A and Y122F/Y356F. RFQ-EPR spin quantitation was used to determine the relative contributions of intermediate X and radicals present, while RFQ-MCD was used to specifically probe the FeIII/FeIV active site, which displayed three FeIV d-d transitions between 16,700 and 22,600 cm(-1), two FeIV d-d spin-flip transitions between 23,500 and 24,300 cm(-1), and five oxo to FeIV and FeIII charge transfer (CT) transitions between 25,000 and 32,000 cm(-1). The FeIV d-d transitions were perturbed in the two variants, confirming that all three d-d transitions derive from the d-pi manifold. Furthermore, the FeIV d-pi splittings in the WT are too large to correlate with a bis-mu-oxo structure. The assignment of the FeIV d-d transitions in WT intermediate X best correlates with a bridged mu-oxo/mu-hydroxo [FeIII(mu-O)(mu-OH)FeIV] structure. The mu-oxo/mu-hydroxo core structure provides an important sigma/pi superexchange pathway, which is not present in the bis-mu-oxo structure, to promote facile electron transfer from Y122 to the remote FeIV through the bent oxo bridge, thereby generating the tyrosyl radical for catalysis.

Synthesis, Structure and Photochromic Properties of a Novel 1,6‐Hexanediamine Trimolybdate Supramolecular Compound.

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Synthesis and Reactivity of the Osmium(III) Pentamethylcyclopentadienyl Complex (C5Me5)2Os2Br4. X-ray Crystal Structures of (C5Me5)2Os2Br4, (C5Me5)2Os2(μ-O)Br4, and (C5Me5)2Os2(μ-NPh)2Br2

Treatment of H2OsBr6 with C5Me5H in tert-butyl alcohol affords the dinuclear osmium(III) species (C5Me5)2Os2Br4, a mono(pentamethylcyclopentadienyl) complex that serves as the key synthetic entry into a wide array of “half-sandwich” complexes of osmium. The X-ray crystal structure shows it to contain two bridging and two terminal bromide ligands, with the Os−Br bond distances being shorter for the bridging bromide ligands than for the terminal bromide ligands. The Os−Os distance of 2.970(1) Å is indicative of a single osmium−osmium bond. The compound is weakly paramagnetic in solution and in the solid state, and the magnetic susceptibility determined over the range 4−300 K gives a singlet−triplet splitting of >800 cm-1. The reactions of (C5Me5)2Os2Br4 with oxygen, bromine, lithium anilide, acetonitrile, and norbornadiene (NBD) are described, affording the compounds (C5Me5)2Os2(μ-O)Br4, (C5Me5)OsBr4, (C5Me5)2Os2(μ-NPh)2Br2, [(C5Me5)Os(MeCN)3][BPh4], and (C5Me5)Os(NBD)Br; the crystal structures of the bridging oxo and bridging imido complexes are given.

Synthesis, Structure, and Reactivity of Organometallic Osmium(VI) Hydroxo Compounds

The organometallic osmium(VI) hydroxo compounds [N(n-Bu)4][Os(N)(CH2SiMe3)3(OH)], cis and trans isomers of [N(n-Bu)4][Os(N)(CH2SiMe3)2(OH)2], result from the substitution of chloride for hydroxide ligands in precursor compounds. Depending on the molecular structure, these compounds behave as nucleophiles, Brønsted bases, or Lewis bases in their reactions. One of these, [N(n-Bu)4][cis-Os(N)(CH2SiMe3)2(OH)2], reacts readily with CO2 to produce the carbonate compound [N(n-Bu)4][Os(N)(CH2SiMe3)2(CO3)]. The other isomer, [N(n-Bu)4][trans-Os(N)(CH2SiMe3)2(OH)2], reacts with CO2 to slowly form the same carbonate compound. It is protonated by other acids to give the neutral hydroxo dimer {Os(N)(CH2SiMe3)2(μ-OH)}2. The anti isomer of {Os(N)(CH2SiMe3)2(μ-OH)}2 reacts with Pd(bpy)(OSiMe3)2 to produce the coordinatively unsaturated, heterometallic complex {Os(N)(CH2SiMe3)2}2(μ3-O)2Pd(bpy). The molecular structure of this complex shows two square-pyramidal osmium groups with an anti arrangement of the apical nitrido ligand and a square-planar palladium(II) center, all connected by the triply bridging oxo groups.

Syntheses, structures, and properties of Ag 4(Mo 2O 5)(SeO 4) 2(SeO 3) and Ag 2(MoO 3) 3SeO 3

Ag 4(Mo 2O 5)(SeO 4) 2(SeO 3) has been synthesized by reacting AgNO 3, MoO 3, and selenic acid under mild hydrothermal conditions. The structure of this compound consists of cis-MoO 2 2+ molybdenyl units that are bridged to neighboring molybdenyl moieties by selenate anions and by a bridging oxo anion. These dimeric units are joined by selenite anions to yield zigzag one-dimensional chains that extended down the c-axis. Individual chains are polar with the C 2 distortion of the Mo(VI) octahedra aligning on one side of each chain. However, the overall structure is centrosymmetric because neighboring chains have opposite alignment of the C 2 distortion. Upon heating Ag 4(Mo 2O 5)(SeO 4) 2(SeO 3) looses SeO 2 in two distinct steps to yield Ag 2MoO 4. Crystallographic data: (193 K; Mo Kα, λ=0.71073 Å): orthorhombic, space group Pbcm, a=5.6557(3), b=15.8904(7), c=15.7938(7) Å, V=1419.41(12), Z=4, R( F)=2.72% for 121 parameters with 1829 reflections with I>2 σ( I). Ag 2(MoO 3) 3SeO 3 was synthesized by reacting AgNO 3 with MoO 3, SeO 2, and HF under hydrothermal conditions. The structure of Ag 2(MoO 3) 3SeO 3 consists of three crystallographically unique Mo(VI) centers that are in 2+2+2 coordination environments with two long, two intermediate, and two short bonds. These MoO 6 units are connected to form a molybdenyl ribbon that extends along the c-axis. These ribbons are further connected together through tridentate selenite anions to form two-dimensional layers in the [ bc] plane. Crystallographic data: (193 K; Mo Kα, λ=0.71073 Å): monoclinic, space group P2 1 /n, a=7.7034(5), b=11.1485(8), c=12.7500(9) Å, β=105.018(1) V=1002.7(2), Z=4, R( F)=3.45% for 164 parameters with 2454 reflections with I>2 σ( I). Ag 2(MoO 3) 3SeO 3 decomposes to Ag 2Mo 3O 10 on heating above 550 °C.

Structural and magnetic studies on mono- and polynuclear chromium ascorbate complexes

Polynuclear chromium ascorbate complexes were isolated and physicochemically analyzed in a comparative manner with their mononuclear analog (1). Characterization by elemental analysis, electronic, vibrational, 13C-n.m.r and mass spectroscopies, and variable temperature magnetic susceptibility studies, allowed structural proposals for the binuclear, [Cr2(μ-OH)2(H2O)(C6H7O6)3(OH)] · 4H2O (2), and trinuclear, [Cr3(μ-O)3(H2O)6(C6H7O6)3] · 4 H2O (3) complexes. The pseudo-octahedral Cr III centers were suggested to be connected through hydroxo bridges in (2) and in (3) by oxo bridges forming a hexocyclic ring.

Visible light absorption of binuclear TiOCo II charge-transfer unit assembled in mesoporous silica

Grafting of Co II(NCCH 3) 2Cl 2 onto mesoporous Ti–MCM-41 silica in acetonitrile solution affords binuclear Ti–O–Co II sites on the pore surface under complete replacement of the precursor ligands by interactions with anchored Ti centers and the silica surface. The Co II ligand field spectrum signals that the Co centers are anchored on the pore surface in tetrahedral coordination. FT-infrared action spectroscopy using ammonia gas adsorption reveals Co–O–Si bond modes at 831 and 762 cm −1. No Co oxide clusters are observed in the as-synthesized material. The bimetallic moieties feature an absorption extending from the UV into the visible to about 600 nm which is attributed to the Ti IV–O–Co II → Ti III–O–Co III metal-to-metal charge-transfer (MMCT) transition. The chromophore is absent in MCM-41 containing Ti and Co centers isolated from each other; this material was synthesized by grafting Co II onto a Ti–MCM-41 sample with the Ti centers protected by a cyclopentadienyl ligand. The result indicates that the appearance of the charge-transfer absorption requires that the metal centers are linked by an oxo bridge, which is additionally supported by XANES spectroscopy. The MMCT chromophore of Ti–O–Co II units has sufficient oxidation power to serve as visible light electron pump for driving multi-electron transfer catalysts of demanding uphill reactions such as water oxidation.

Carboxylate-bridged dinuclear manganese systems – From catalases to oxidation catalysis

Dinuclear manganese based enzymes engage in processes as diverse as amino acid hydrolysis and hydrogen peroxide disproportionation. Despite the mechanistic diversity displayed by this class of enzymes, a common feature is the presence of carboxylate residues, which serve to bridge the manganese centres and of hemi-labile oxo-, hydroxyl- and aqua-bridge, which shows considerable redox state dependence on their lability. The role of carboxylate-bridged dinuclear manganese complexes in the disproportionation of hydrogen peroxide is reviewed both in enzymatic and biomimetic systems. The lability of the carboxylate bridge and bridging oxo, hydroxyl and aqua ligands during the catalase cycle is discussed in relation to the redox cycle, which the dinuclear manganese centres undergo. The relationship between catalase activity and catalytic oxidation is discussed briefly with regard to understanding the nature of catalytically active species present during oxidation catalysis.

Redox Chemistry of a Dimanganese(II,III) Complex with an Unsymmetric Ligand: Water Binding, Deprotonation and Accumulative Light‐Induced Oxidation

AbstractA dinuclear manganese complex {[Mn2II,IIIL(μ‐OAc)2]ClO4} has been synthesised, where L is the dianion of 2‐{[bis(pyrid‐2‐ylmethyl)amino]methyl}‐6‐{[(3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)(pyrid‐2‐ylmethyl)amino]methyl}‐4‐methylphenol, an unsymmetric binucleating ligand with two coordinating phenol groups. The two manganese ions, with a Mn–Mn distance of 3.498 Å, are bridged by the two bidentate acetate ligands and the 4‐methylphenolate group of the ligand, resulting in a N3O3 and N2O4 donor set of MnII and MnIII, respectively. Electrochemically [Mn2II,IIIL(μ‐OAc)2]+ is reduced to [Mn2II,IIL(μ‐OAc)2] at E1/2(1) = –0.53 V versusFc+/0 and oxidised to [Mn2III,IIIL(μ‐OAc)2]2+ at E1/2(2) = 0.38 V versus Fc+/0. All three redox states have been characterised by EPR, IR and UV/Vis spectroscopy. Subsequent oxidation of [Mn2II,IIIL(μ‐OAc)2]2+ [E1/2(3) = 0.75 V vs. Fc+/0] in dry acetonitrile results in an unstable primary product with a lifetime of about 100 ms. At high scan rates quasireversible voltammetric behaviour is found for all three electrode processes, with particularly slow electron transfer for the II,III/II,II [k°(1) = 0.002 cm s–1] and III,III/II,III [k°(2) = 0.005 cm s–1] couples, which can be rationalised in terms of major distortions of the MnIII centres. In aqueous media the bridging acetates are replaced by water‐derived ligands. Deprotonation of these stabilises higher valence states, and photo‐induced oxidation of the manganese complex results in a Mn2III,IVLcomplex with oxo or hydroxo bridging ligands, which isfurther oxidised to an EPR‐silent product. These results demonstrate that a larger number of metal‐centred oxidations can be compressed in a narrow potential range if build up of charge is avoided by charge‐compensating reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Rates of Oxygen Exchange between the [HxNb6O19]8-x(aq) Lindqvist Ion and Aqueous Solutions

Oxygen-isotope-exchange rates were measured between sites in the Lindqvist-type [H(x)()Nb(6)O(19)](8)(-)(x)()((aq)) polyoxoanion and aqueous solution as a function of pH and temperature. The ion has a central mu(6)-O that is inert to exchange, 12 mu(2)-O(H), and 6 eta-O. The potassium salt of this ion is recrystallized in (17)O-enriched water to (17)O-label the anion, which is then redissolved into isotopically normal water so that the (17)O NMR signals from structural oxygens can be followed as a function of time. Because the central mu(6)-O retains its (17)O signal throughout the experiments, it is clear that the polyoxoanion remains intact during isotopic equilibration of the other structural oxygens. At pH conditions where the [HNb(6)O(19)](7)(-) ion predominates, the mu(2)-O(H) sites isotopically exchange with solution about an order of magnitude more rapidly than the eta-O sites. Yet, we observe that the terminal and bridging oxo sites react at nearly the same rates when the ion is coordinated to 2-3 protons and possibly when it is unprotonated. On the basis of molecular models and experimental kinetic data, we propose metastable polymorphs of the hexaniobate structure where four of the mu(2)-O(H) and eta-O sites are temporarily equivalent and bonded to a coordinatively unsaturated Nb(V). This hypothesized intermediate allows facile access to bulk water molecules for exchange but cannot fully explain the kinetic results and additional experiments on other Lindvist ions are required.

Synthesis, structure and photochromic properties of a novel 1,6-hexanediamine trimolybdate supramolecular compound

A novel supramolecular compound 1,6-hexanediamine trimolybdate ((C 6H 18N 2)[Mo 3O 10], denoted as HDAMo) has been synthesized by a hydrothermal method and its structure has been characterized by elemental analyses, Fourier transform infrared (FT-IR) spectra, single-crystal X-ray diffraction (XRD) technique. This single crystal compound consists of protonated 1,6-hexanediamine (HDA) cations and polyoxometalate [Mo 3O 10] 2− anions. Its crystal structure belongs to monoclinic system (space group P2 1/ n) with a=7.7508(14), b=11.467(2), c=16.167(3) Å, β=92.689(3)°, V=1435.3(5) Å 3, Z=4 and D calc=2.619 g cm −3. The final statistics based on F 2 are GOF=0.980, R 1=0.0261 and w R 2=0.0506 for I>2 σ( I). XRD analysis revealed that in the crystal structure of HDAMo, novel infinite [Mo 3O 10] 2− chains parallel to a axis are made up of distorted MoO 6 octahedra connected by corners and edges. The protonated HDA cations occupy channels formed by [Mo 3O 10] 2− chains and exhibit strong hydrogen bond interactions to terminal and bridging oxo groups of the chains. The [Mo 3O 10] 2− chains linked through protonated HAD cations formed a one-dimensional network. The HDAMo compound shows novel photochromic properties, i.e., its color changes from white to reddish brown gradually under UV irradiation. XRD, FT-IR, ESR spectra and XPS are used to investigate the photochromic behavior of the compound.

Synthesis, structure and magnetic properties of an oxo-bridged dinuclear iron(III) complex [(TPyA)FFe IIIOFe IIIF(TPyA)](BF 4) 2 · 0.5MeOH (TPyA = tris(2-pyridylmethyl)amine) containing the FFe IIIOFe IIIF linkage

The reaction of [Fe II(H 2O) 6](BF 4) 2 with tris(2-pyridylmethyl)amine (TPyA) and triethylamine in methanol under aerobic conditions forms [(TPyA)FFe IIIOFe IIIF(TPyA)](BF 4) 2 · 0.5MeOH ( 1), in which each Fe(III) ion is coordinated to a TPyA and an F − ion as well as an oxo ion (O 2−) linking two Fe(III) ions. 1 has offset face-to-face π–π interactions between the dimers, and possesses a supramolecular network structure. The magnetic susceptibility of 1 can be fit with g = 2.0, J/k B = − 153 K (106 cm −1), and θ = − 0.3 K [ H = − 2 JS a · S b]. These indicate that very strong antiferromagnetic interactions occur via the oxo bridge within the Fe(III) dimer and weak antiferromagnetic interactions between the dimers.

A linear Fe–O–Fe unit in bis(dibenzyldimethylammonium) μ-oxo-bis[tribromoferrate(III)

The title compound, (C16H20N)2[Fe2Br6O], crystallizes with one dibenzyldimethylammonium cation and one half of a mu-oxo-bis[tribromoferrate(III)] anion in the asymmetric unit. The bridging oxo group is situated on an inversion centre, resulting in a linear conformation for the Fe-O-Fe unit. The iron(III) cations have tetrahedral geometry, with bond angles in the range 106.8 (1)-112.2 (1) degrees . The ion pairs are held together by Coulombic forces and C-H...Br hydrogen bonds. Each Br- anion forms one hydrogen bond. No C-H...O hydrogen bonds are found between the O atom in the Fe-O-Fe unit and surrounding counter-cations, consistent with the linear configuration of the Fe-O-Fe unit.