Polynuclear Iron Complexes Research Articles

Low-Temperature Synthesis of Metal–Organic Coordination Polymers Based on Oxo-centered Iron Complexes: Magnetic and Adsorption Properties

A low-temperature approach is described for preparing mesoporous metal–organic frameworks using nontoxic solvents and pre-synthesized polynuclear iron complexes as secondary building units. The obtained compounds are characterized via IR and Mössbauer spectroscopy, X-ray powder diffraction analysis, thermogravimetric analysis, and differential scanning calorimetry. The specific surface of the obtained compounds and their adsorption capacity for organic dyes methylene blue and Congo red are determined. Particular attention is given to dependences M(T) and M(H) of the magnetic moment of the obtained samples on temperature and strength of the magnetic field, respectively. The dyes’ adsorption characteristics and efficiency of sorption are determined by varying such factors as period of contact, amount of adsorbent, and temperature. The removal of dye at a concentration above 90% is observed as early as 20–30 min after the beginning of adsorption. Langmuir and Freundlich isotherms are used to describe the experimental data. It is shown that the process of adsorption at the initial concentration of the dye is described most accurately by the Langmuir adsorption isotherm. The rate constants of adsorption are calculated using pseudo-second order kinetic equations.

Formation of polynuclear iron(III) complexes of N-(2-pyridylmethyl)iminodipropanol depending on pseudohalide ions: synthesis, crystal structure, and magnetic properties

Five polynuclear iron(III) complexes, [(pmidp)Fe(NCSe)]2 (1), [(pmidp)Fe(NCBH3)]2 (2), [(Hpmidp/pmidp)Fe3(CH3O)2(NCS)4]∙H2O (3), [(pmidp)2Fe6(CH3O)4(N3)4(CH3COO)2O2] (4), and [(pmidp)2Fe6(CH3O)4(NCO)4(CH3COO)2O2]∙2MeOH (5) were isolated through the reactions of N-(2-pyridylmethyl)iminodipropanol (H2pmidp) and iron(III) ions with different pseudohalide ions. The complexes were studied via X-ray crystal diffraction, Mössbauer spectra, and magnetochemistry. The molecular structures of 1 and 2 were formed as the {Fe2(µ2-Opropoxo)2}2+ cores with pmidp2− and NCSe−/NCBH3−. The structure of 3 was formed as a {Fe3(µ2-OCH3)2(µ2-Opropoxo)4}5+ core with Hpmidp−/pmidp2− and NCS−. The structures of 4 and 5 were formed as {Fe6(µ4-O)2(µ2-OCH3)2(η2-OAc)2(µ2-Opropoxo)4} cores with pmidp2− and NCO−/N3−. Structural analyses revealed that the formation of various multinuclear iron(III) moieties depends on the auxiliary ligands. The oxidation states of all the complexes were confirmed as + 3 using the bond valence sum (BVS) calculations and Mössbauer spectral data. The susceptibility data for 1–5 fitted using each spin coupling (J) model indicated that 1–3 showed antiferromagnetic exchange interactions, and 4 and 5 showed the ferromagnetic and antiferromagnetic couplings, simultaneously.

Synthesis, Structures, Electrochemistry, and Catalytic Activity towards Cyclohexanol Oxidation of Mono-, Di-, and Polynuclear Iron(III) Complexes with 3-Amino-2-Pyrazinecarboxylate

The synthesis and characterization of a set of iron(III) complexes, viz. the mononuclear [Fe(L)3] (1) and [NHEt3][Fe(L)2(Cl)2] (2), the dinuclear methoxido-bridged [Fe(L)2(μ-OMe)]2.DMF.1.5MeOH (3), and the heteronuclear Fe(III)/Na(I) two-dimensional coordination polymer [Fe(N3)(μ-L)2(μ-O)1/2(Na)(μ-H2O)1/2]n (4), are reported. Reactions of 3-amino-2-pyrazinecarboxylic acid (HL) with iron(III) chloride under different reaction conditions were studied, and the obtained compounds were characterized by elemental analysis, Fourier Transform Infrared (FT-IR) spectroscopy, and X-ray single-crystal diffraction. Compound 1 is a neutral mononuclear complex, whereas 2 is mono-anionic with its charge being neutralized by triethylammonium cation. Compounds 3 and 4 display a di-methoxido-bridged dinuclear complex and a two-dimensional heterometallic Fe(III)/Na(I) polynuclear coordination polymer, respectively. Compounds 3 and 4 are the first examples of methoxido- and oxido-bridged iron(III) complexes, respectively, with 3-amino-2-pyrazinecarboxylate ligands. The electrochemical study of these compounds reveals a facile single-electron reversible Fe(III)-to-Fe(II) reduction at a positive potential of 0.08V vs. saturated calomel electrode (SCE), which is in line with their ability to act as efficient oxidants and heterogeneous catalysts for the solvent-free microwave-assisted peroxidative oxidation (with tert-butyl hydroperoxide) of cyclohexanol to cyclohexanone (almost quantitative yields after 1 h). Moreover, the catalysts are easily recovered and reused for five consecutive cycles, maintaining a high activity and selectivity.

Polynuclear Iron(II) Complexes with 2,6-Bis(pyrazol-1-yl)pyridine-anthracene Ligands Exhibiting Highly Distorted High-Spin Centers.

Two bis-tridentate ligands L1 and L2 that contain 2,6-bis(pyrazol-1-yl) pyridine N-donor embraces introduced on a anthracene-acetylene backbone were used for the synthesis of a tetranuclear compound [Fe4(L1)4](CF3SO3)8·7CH3CN (1) and a hexanuclear compound [Fe6(L2)6](CF3SO3)12·18CH3NO2·9H2O (2). The polynuclear structures of both complexes were confirmed by X-ray diffraction studies, which revealed a [2 + 2] grid-like complex cation for 1 and a closed-ring hexagonal molecular architecture for the complex cation in 2. Although both compounds contain anthracene moieties arranged in a face-to-face manner, attempts at [4 + 4] photocyclization remain unsuccessful, which can be explained either by steric restraints or by inhibition of the photo-cycloaddition. Magnetic studies identified gradual and half-complete thermal spin crossover in the tetranuclear grid 1, where 50% of ferrous atoms exhibit thermal as well as photoinduced spin state switching and the remaining half of iron(II) centers are permanently blocked in their high-spin state. On the contrary, the hexanuclear compound 2 exhibits complete blocking in a high-spin state. Analysis of the magnetic data reveals the zero-field splitting parameter | D| ≈ 6-8 cm-1 with a large rhombicity for all high-spin iron(II) atoms in 1 or 2. The electronic structures and the magnetic anisotropies were also investigated by the multireference CASSCF/NEVPT2 method, and intramolecular exchange interactions were calculated by density functional theory methods.

1,2,4-Triazole Schiff base directed synthesis of polynuclear iron complexes: Investigating the magnetic properties going from a dimer to a 1D chain to a 3D framework

Based on two functionalized Schiff base ligands 4-(1H-imidazol-5-ylmethylene-amino)-4H-1,2,4-triazole (imztrz) and 4-(p-tolylidene-amino)-4H-1,2,4-triazole (toltrz), a series of three triazole based polynuclear Fe complexes has been prepared. Compounds {[FeII(toltrz)2(C2O4)]·10H2O}n (1) and {[FeII(5-imztrz)(C2O4)]·2H2O}n (2) are oxalate bridged FeII complexes with 1 showing a linear 1D chain structure and 2 exhibiting a zigzag chain based 3D interpenetrating framework. Both structures show rather big voids in the 3D architecture (∼15% of the crystal volume). Compound (5-imztrzH)2[FeIII2(cit4−)2(H2O)2]·6H2O (3) is a binuclear FeIII complex bridging by two citrate ligands to form a face-shared centrosymmetric structure. Magnetic susceptibility measurements indicate that all three compounds show weak antiferromagnetic exchange interaction between the adjacent Fe centers.

Spin crossover in discrete polynuclear iron(ii) complexes.

Iron(ii) spin crossover (SCO) materials have been widely studied as molecular switches with a wide variety of potential applications, including as displays, sensors, actuators or memory components. Most SCO materials have been either monometallic or polymeric, and it is only relatively recently that chemists have really started to focus on linking multiple metal centres together within the one, discrete, molecule in an effort to enhance the SCO properties, such as abrupt, hysteretic, and multistep switching, as well as the potential for quantum cellular automata, whilst still being readily amenable to characterisation. Here we present a review of the ligand designs of the last two decades that have led to self assembly of discrete di- to poly-nuclear iron(ii) complexes of helicate, cage, cube, and other supramolecular architectures with rich SCO activity, and to an increased focus on host-guest interactions. Analysis of selected octahedral distortion parameters (Σ, CShM) reveals interesting differences between these structural types, for example that the iron(ii) centres in grids are generally significantly more distorted than those in squares or cages, yet are still SCO-active. Of the 127 complexes reviewed (79 published 2012-Feb. 2018), 54% are dinuclear, 10% trinuclear, 31% tetranuclear, and the remaining 5% are penta, hexa and octanuclear. Of the 93 designer ligands utilised in these polynuclear architectures: 60 feature azoles; 55 provide all donors to the Fe(ii) centres (no co-ligands coordinated) and form exclusively 5-membered chelate rings via either bidentate azole-imine/pyridine or tridentate heterocycle-imine/amine/thioether/pyridine-heterocycle binding pockets.

Prediction and correlations between the stability constants of mono- and polynuclear chromium(III) and iron(III) complexes

Correlations between the experimentally determined stability constants of mono- and polynuclear chromium(III) and iron(III) complexes are discussed. An equation to evaluate the stability constants of mono- and polynuclear chromium(III) complexes is obtained: \(\log \beta [Cr_p^{3 + } (L_i )_{q_i } ] = 0.84\log \beta [Fe_p^{3 + } (L_i )_{q_i } ]\).

Spin state switching in iron coordination compounds.

The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere. Spin transition in such compounds also occurs under pressure and irradiation with light. The spin states involved have different magnetic and optical properties suitable for their detection and characterization. Spin crossover compounds, though known for more than eight decades, have become most attractive in recent years and are extensively studied by chemists and physicists. The switching properties make such materials potential candidates for practical applications in thermal and pressure sensors as well as optical devices.The article begins with a brief description of the principle of molecular spin state switching using simple concepts of ligand field theory. Conditions to be fulfilled in order to observe spin crossover will be explained and general remarks regarding the chemical nature that is important for the occurrence of spin crossover will be made. A subsequent section describes the molecular consequences of spin crossover and the variety of physical techniques usually applied for their characterization. The effects of light irradiation (LIESST) and application of pressure are subjects of two separate sections. The major part of this account concentrates on selected spin crossover compounds of iron(II), with particular emphasis on the chemical and physical influences on the spin crossover behavior. The vast variety of compounds exhibiting this fascinating switching phenomenon encompasses mono-, oligo- and polynuclear iron(II) complexes and cages, polymeric 1D, 2D and 3D systems, nanomaterials, and polyfunctional materials that combine spin crossover with another physical or chemical property.

Syntheses, crystal structure, spectroscopic, redox and magnetic properties of oxo- and carboxylato-bridged polynuclear iron(III) complexes with phenolate- and pyridine-substituted benzimidazole ligands

Using the same trinuclear [Fe3O]+7 core having oxo and carboxylate bridges, two different types of polynuclear iron(III) complexes have been synthesized. The bidentate ligands, (2-hydroxyphenyl)benzimidazole (HL1) and (2-pyridyl)benzimidazole (L2), produce the dinuclear and tetranuclear complexes [Fe2(L1)4(C6H5COO)]NO3·3H2O (1) and [Fe4O2(C6H5COO)7(L2)2]NO3·H2O·CH3CN (2·CH3CN), respectively. Complex 1 crystallizes in the monoclinic space group P2(1)/c, while 2·CH3CN crystallizes in the monoclinic space group C2/c. In 1, the two hexa-coordinated iron(III) centers are bridged by the two phenolate oxygens of the ligand HL1. The tetranuclear entity 2 consists of a [Fe4(μ3-O)2]8+ unit comprising four FeIII centers with a “butterfly” arrangement. Each pair of iron(III) centers occupy the “body” or “hinge” and “wing-tip” sites, respectively. The Fe2IIIFe2III complex 2 undergoes two stepwise one electron reductions at E1/2=−0.625V and −0.11V, while 1 displays an irreversible reduction wave at EP·C=−0.3V. Variable-temperature magnetic susceptibility measurements have been carried out for 1 and 2 in the temperature range 2–300K. Complex 1 exhibits a very weak Fe⋯Fe exchange interaction, J=−0.24(1)cm−1 (H=−J(S1·S2)). In complex 2, moderate antiferromagnetic exchange interactions occur among the four high-spin FeIII centers. The exchange coupling constant Jbb (body–body interaction) is indeterminate due to the prevailing spin frustration, but the ‘wing-body’ antiferromagnetic interaction (Jwb) is evaluated as −73(3) cm−1, using the spin Hamiltonion model H=−J1(S1·S2+S2·S3+S3·S4+S4·S1)−J2(S2·S4).

Installation of an IR microscope at the nuclear resonance beamline ID18 of ESRF

An IR microscope has been installed at the beamline ID18 at the ESRF in Grenoble, France in order to obtain nuclear inelastic scattering (NIS) data and IR spectra simultaneously. This setup combines the advantages of both spectroscopic methods. The applicability of the installed setup to the study of the spin crossover (SCO) phenomenon in polynuclear iron complexes has been shown.

A hexanuclear iron(III) complex [Fe 6O 2(OH) 2(PhCOO) 10(hedmp) 2]·3CH 3CN assembled from 2-hydroxyethyl-3,5-dimethyl pyrazole

In order to assemble polynuclear iron(III) complexes, the coordination chemistry of the 2-hydroxyethyl-3,5-dimethylpyrazole (hedmp-H) ligand has been investigated. Reaction of hedmp-H with trinuclear iron carboxylate precursor [Fe 3O(PhCOO) 6(H 2O) 3]Cl in acetonitrile yielded the hexanuclear Fe(III) complex [Fe 6O 2(OH) 2(PhCOO) 10(hedmp) 2]·3CH 3CN ( 1). This aggregate has been characterized by employing various analytical techniques, spectroscopic studies and single crystal X-ray diffraction. Detailed magnetic susceptibility measurements revealed that 1 displays an S T = 5 ground state.

Extended Fe4 butterfly complexes: theoretical analysis of magnetic properties and magnetostructural maps

The inclusion of additional metal atoms in Fe₄ butterfly complexes drastically modifies their magnetic properties. Exchange interactions of a Fe₄Y₂ complex have been calculated using theoretical methods based on density functional theory. The calculated values are in good agreement with experimental data showing that the change in the nature of bridging ligands induces a dramatic decrease of the antiferromagnetic wing-body interaction while the body-body interaction between the two central iron atoms is ferromagnetic. Finally, we propose a new tool to facilitate the understanding of the magnetic properties in polynuclear iron complexes. Magnetostructural maps allow us to correlate the calculated exchange coupling constants with metal-metal distances for the dinuclear or polynuclear iron complexes that we have studied.

γ-Fe2O3 nanoparticle in NaY-zeolite matrix: Preparation, characterization, and heterogeneous catalytic epoxidation of olefins

Nano-sized crystals of maghemite iron oxide (γ-Fe2O3) were synthesized onto the surface of NaY-zeolite crystals by immobilizing a polynuclear iron complex [Fe4O2(O2CCH3)7(bpy)2](ClO4) (bpy = 2,2′-bipyridine) and subsequent calcination of the material in oxygen. Superparamagnetic γ-Fe2O3 particles with sizes ∼5 nm were formed on the surface of the zeolite matrix. The nano-composite, γ-Fe2O3@NaY has been subsequently subjected for thorough characterization with several spectroscopic techniques as well as magnetic and transmission electron microscopic measurements. This confirms the formation of maghemite nanoparticles on a NaY-zeolite surface. γ-Fe2O3@NaY shows a remarkable catalytic efficiency in epoxidation reactions with various olefins using tert-BuOOH as oxidant. Notably, styrene shows a remarkable high conversion (90%) as well as epoxide selectivity (95%) while trans-stilbene is completely converted to its oxide with tert-BuOOH over a γ-Fe2O3@NaY catalyst.

Inter‐ and Intrachain Spin‐Transition Processes in One‐Dimensional Polynuclear Iron(III) Complexes of N,N′‐Ethylenebis(acetylacetonylideneimine) Bridged by 1,3‐Bis(4‐pyridyl)propane and 1,4‐Bis(imidazolyl)butane

AbstractTwo one‐dimensional (1D) polynuclear iron(III) complexes, [FeIII(acacen)(bpyp)]BPh4 (1) and [FeIII(acacen)(bimb)]BPh4 (2), were synthesized [acacen = N,N′‐ethylenebis(acetylacetonylideneiminato); bpyp = 1,3‐bis(4‐pyridyl)propane; bimb = 1,4‐bis(imidazolyl)butane]. Complexes 1 and 2 show gradual spin‐crossover (SCO) behavior over a wide temperature range from 100 to 300 K and from 220 to higher than 350 K, respectively. The single‐crystal X‐ray structures of two complexes in the high‐spin (HS), low‐spin (LS), and the midpoint between HS and LS states were determined. Crystal structures of both complexes consist of two molecular units (Fe1 and Fe2), where complex 1 consists of two crystallographically independent 1D chains and complex 2 consists of one 1D chain involving two molecular units. At the temperature midway between the HS and LS states, the Fe–N bond lengths in the two units are different from each other. At the midpoint, complex 1 consists of alternately arrayed independent HS and LS chains, whereas complex 2 consists of alternately arrayed HS and LS units within a chain. The results demonstrate two different SCO mechanisms of a 1D complex, that is, SCO occurs in chain‐by‐chain fashion for 1 and in adjacent Fe units within a chain for 2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

EXAFS Study on the Reactions between Iron and Fulvic Acid in Acid Aqueous Solutions

Iron(III) competes with trace metals for binding sites on organic ligands. We used X-ray absorption fine structure (EXAFS) spectroscopy to determine the binding mode and oxidation state of iron in solutions initially containing only iron(III) and fulvic acid at pHs 2 and 4. EXAFS spectra were recorded at different times after sample preparation. Iron was octahedrally configured with inner-sphere Fe-O interactions at 1.98-2.10 A, depending on the oxidation state of iron. Iron(III) formed complexes with fulvic acid within 15 min. Iron(III) was reduced to iron(II) with time at pH 2, whereas no significant reduction occurred at pH 4. No signs of dimeric/trimeric hydrolysis products were found in any of the solution samples (<0.45 microm). However, the isolated precipitate of the pH 2 sample (>0.45 microm) showed Fe...Fe distances, indicating the presence of tightly packed iron(III) trimers and/or clusters of corner-sharing octahedra. It is suggested that the binding mode of iron(III) to fulvic acid at low pH may be phase-dependent: in solution mononuclear complexes predominate, whereas in the solid phase hydrolyzed polynuclear iron(III) complexes form, even at very low pH values. The observed pH dependence of iron(III) reduction was consistent with expected results based on thermodynamic calculations for model ligands.

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.

Synthesis, Structural Characterization, and Magnetic Studies of Polynuclear Iron Complexes with a New Disubstituted Pyridine Ligand

A series of novel polyiron species have been prepared from the reaction of iron chloride with the 2,5-disubstituted pyridines H2L(n) (H2L1) = N,N'-bis(n-butylcarbamoyl)pyridine-2,6-dicarboxamide; H2L2 = N,N'-bis(n-ethylcarbamoyl)pyridine-2,6-dicarboxamide). By small modifications of the experimental conditions under which the reactions are carried out, it has been possible to prepare the quadruply stranded diiron(II) complex [Fe2(mu-H2L1)4(mu-Cl)2][FeCl4]2 (1), the metallamacrocycle [Fe2(mu-H2L1)2(THF)4Cl2][FeCl4]2 (2), the hexairon(III) compound [Fe6(L1)2(mu-OMe)6(mu4-O)2Cl4] (3), and the mixed-valence trinuclear iron complexes [Fe3(L(n))3(mu3-O)] (n = 1, 4; n = 2, 5). The X-ray crystal structures of 3 and 5 and magnetic studies for all the compounds are herein presented. Interestingly, the structural analysis of 5 at room temperature indicates that one of the iron centers is Fe(III) while the other two have an average valence state between Fe(II) and Fe(III). The five complexes herein presented demonstrate the great versatility that the new ligand has as a building block for the formation of supramolecular coordination assemblies.

Studies of Mono- and Polynuclear Iron Hydroxy Complexes in Brown Coal

Iron hydroxy complexes were added to brown coal by a stepwise pH adjustment of solutions of Fe(III) mixed with coal. The amounts of NaOH used to adjust the pH and the amount of Fe(III) added to coal were consistent with the addition of both mono- and polynuclear iron complexes to coal. Analysis of the bulk sample and of the sample sieved into smaller and larger particles, and SEM-EDX examination of large and small particles, revealed an uneven distribution of iron, with higher concentrations in smaller coal particles. XPS and TOF−SIMS data show that mono- and polynuclear iron species form in the coal samples. Computer molecular modeling has illustrated the structure and bonding of the mono- and polynuclear species in brown coal and the variation in the relative distribution of these species as the amount of added iron is increased. Computer models have also been used to show similarities between low-temperature pyrolysis of brown coal containing large amounts of iron and the thermal decomposition of iron carboxylates.

The investigation of primary physicochemical and pharmaco-biological properties of polynuclear iron(III) complexes with dextran and its derivatives

The results of the investigations of primary physicochemical and pharmaco-biological properties of polynuclear iron(III) complexes with low molecular dextran (LMD), hydrogenated low molecular dextran (H-LMD) and dextran carbonic acid (DCA) are presented. The investigations included the complex resistance to hydrolytic decomposition in highly acidic medium, the (TFH-A)-value, and neutral medium at 120?C, the (TFH-120)-value, the viscosity of the parenteral solutions, iron(III) resorption dynamics to serum after the i.m. and i.v. application of the preparation to rabbits, the acute toxicity (LD50) in mice, and the residual iron(III) quantity at the i.m. application site. Iron(III) complexes with dextran carbonic acid (DCA) appeared to be the most suitable for use in veterinary and human medicine.

Activity of catalysts on the basis of polynuclear iron complexes in hydrocarbon synthesis from CO and H 2

Synthesis from CO and H/sub 2/ is a promising method of making olefins, a valuable raw material for the chemical industry. Catalysts built from mononuclear complexes of K/sub 2/(Fe(CO)/sub 4/) and K/sub 2/(Fe(CO)/sub 2/(C/sub 2/H/sub 5/) on Al/sub 2/O/sub 3/ or SiO/sub 2/, have increased the selectivity of formation of C/sub 2/-C/sub 6/ olefins from CO and H/sub 2/. This study investigates the catalytic properties of polynuclear iron complexes on potassium-containing carriers in the synthesis of hydrocarbons from CO and H/sub 2/. 6 references, 3 tables.