Crystal structure and magnetic properties of dinuclear iron(III) complex with ONNO-donor ligand

A new dinuclear Fe(III) complex, [Fe(5-MeOL1)(OH)_0.86(CH₃O)_0.14]₂?2(CH₃OH), [H₂-5-MeOL1 = N,N′-bis(5-methoxy-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine], 1 has been synthesized and characterized by single crystal structure analysis. The structure of 1 consists of two Fe(III) centers with one tetradentate schiff base ligand (N₂O₂) which are bridged by dihydroxo/dimethoxo groups to yield a Fe₂O₂ core. Complex 1 exhibits weak antiferromagnetic exchange interaction between Fe(III) ions with J = ?0.21 cm^–1.     

Electronic structure of dinuclear iron nitrosyl complexes with different ligands at two iron centers

The electronic structures of three dinuclear iron complexes were determined with the DFT method. The complexes contain a {Fe(NO)₂}⁹ unit and thiolate, nitrosyl, carbonyl and amine ligands at the second iron atom. The two iron atoms are bridged by thiolate ligands. In the lowest energy states of these complexes, the iron atoms possess spin S = 1, 3/2 or 5/2, depending on the coordinated ligands and their mutual arrangement. Nitrosyl is coordinated as NO⁻ antiferromagnetically coupled to iron, and the two iron units are antiferromagnetically coupled to each other.     

Temperature-induced formation of two dinuclear dysprosium complexes with different magnetic properties

A dinuclear Dy (III) complex [Dy₂( L ¹ )₂(NO₃)₄]·2CH₃CN ( 1 ) (H L ¹ = 1,3-bis{[(E)-pyridin-2-ylmethylene]amino}propan-2-ol) was obtained via the reaction of 1,3-diamino-2-propanol, 2-pyridyaldehyde and Dy (NO₃)₃·6H₂O at room temperature. In the structure of complex 1 , two Dy (III) ions are in the N₄O₆ coordination environment provided by NO₃⁻ and ( L ¹ )⁻, and both of these ions are in the sphenocorona configuration. [Dy₂( L ² )₂(NO₃)₄] ( 2 ) [H L ² = 2-(pyridin-2-yl)hexahydropyrimidin-5-ol] was obtained using the same reaction material only when the reaction temperature was changed to 60°C. Structural analysis of complex 2 showed that the two Dy (III) ions with the same coordination configuration are in the N₃O₆ coordination environment provided by NO₃⁻ and ( L ² )⁻ and are in the distorted spherical-capped square antiprism. Surprisingly, H L ² with the parent of bipyridine was synthesized by the Schiff base reaction of 1,3-diamino-2-propanol with 2-pyridoxaldehyde followed by the ring-closing reaction catalyzed by Dy (III) ions. Magnetic measurements of the Dy (III) complexes revealed no obvious frequency-dependent behavior of complex 1 . In contrast, complex 2 showed an obvious frequency dependence (U_eff = 0.49 K and τ₀ = 6.62 × 10⁻⁴ s) under the condition of zero field and a weak double relaxation behavior (U_eff = 9.25 K and τ₀ = 9.70 × 10⁻⁴ s) at 1500 Oe.     

Mono- and dinuclear copper(II) complexes with meta-phenylene-bridging ligands: Synthesis,structure and magnetic properties

The new double-Schiff-base ligand H₆ipa-bhea has been synthesized by condensation of a 4,6-diformylresorcinol derivative (ipa) with two equivalents of N,N-bis-(2-hydroxyethyl)ethylenediamine (bhea). Reaction with copper(II) perchlorate leads to the formation of two different products depending on the reaction conditions. The directed synthesis of either a mononuclear or dinuclear copper(II) complex is reported. The reaction in methanol results in the formation of a dinuclear complex [Cu₂(H₄ipa-bhea)](ClO₄)₂ (1). Whereas in the presence of water as solvent for the reaction, one imine side chain of the ligand is hydrolyzed regenerating the formyl moiety with the mononuclear complex [Cu(H₃hyforsa-bhea)]ClO₄ · 2H₂O (2) as final product. Subsequent reaction of complex 2 with N,N-bis-(pyridin-2-ylmethyl)ethylenediamine (unspenp) as additional amine component results in the formation of the mononuclear complex [Cu(Hhyforsa-unspenp)]ClO₄ (3). All complexes are characterized by IR spectroscopy, elemental analysis and X-ray crystallography. Temperature-dependent magnetic measurements on the dinuclear complex indicate weak antiferromagnetic exchange interactions between the copper(II) ions with a coupling constant of J = ?16.4 cm^?1. Density functional calculations have been used to evaluate the magnetic properties. The exchange coupling constant can be nicely reproduced with the use of the broken symmetry approach. The exchange pathway through the meta-phenylene-linkage is discussed in terms of a competitive spin-polarization and superexchange mechanism as well as geometrical changes at the copper(II) ions.     

New dinuclear nickel(II) complexes: synthesis, structure, electrochemical, and magnetic properties

The reaction of [NiBr(2)(bpy)(2)] (bpy = 2,2'-bipyridine) with organic phosphinic acids ArP(O)(OH)H [Ar = Ph, 2,4,6-trimethylphenyl (Mes), 9-anthryl (Ant)] leads to the formation of binuclear nickel(II) complexes with bridging ArP(H)O(2)(-) ligands. Crystal structures of the binuclear complexes [Ni(2)(μ-O(2)P(H)Ar)(2)(bpy)(4)]Br(2) (Ar = Ph, Mes, Ant) have been determined. In each structure, the metal ions have distorted octahedral coordination and are doubly bridged by two arylphosphinato ligands. Magnetic susceptibility measurements have shown that these complexes display strong antiferromagnetic coupling between the two nickel atoms at low temperatures, apparently similar to binuclear nickel(II) complexes with bridging carboxylato ligands. Cyclic voltammetry and in situ EPR spectroelectrochemistry show that these complexes can be electrochemically reduced and oxidized with the formation of Ni(I),Ni(0)/Ni(III) derivatives.     

Crystal structure and magnetic properties of dicarboxylate-bridged linear chain Mn(II) complexes

Two manganese(II) complexes, [Mn(mtm)(CH₃OH)₂(H₂O)]_n (1) and [Mn₂(mtm)₂(2,2′-bipy)₂]_n (2) (bipy=bipyridine, mtm=[bis(methylthio)methylene]malonate) were synthesized and characterized by X-ray crystallography. Structure of 1 consists of octahedral manganese(II) species which are extended by carboxylate bridges in syn–anti fashion along the c-axis. Chains of 1 are associated by hydrogen bonding among coordinating water and methanol molecules and carboxylate oxygen atoms, forming two-dimensional structures. The crystallographic asymmetric unit of 2 comprises two [Mn(2,2′-bipy)(mtm)] units in which Mn(II) atoms are bridged by μ₂-oxygens from carboxylate to form Mn₂O₂ rhombus. The dimeric units are linked doubly by second carboxylates in syn–anti fashion, resulting in a chain structure. The antiferromagnetic coupling of Mn(II) ions in 1 (−0.2 cm⁻¹) and 2 (−1.57 cm⁻¹) was determined from variable-temperature magnetic susceptibility data in the temperature range of 2–300 K.     

Synthesis, structure and DFT study of dinuclear iron, cobalt and nickel complexes with cyclopentadienyl-metal moieties

Reactions of 1,1'-bis(dipheny1phosphino)cobaltocene with Co(PMe(3))(4), Ni(PMe(3))(4), Fe(PMe(3))(4), Ni(COD)(2), FeMe(2)(PMe(3))(4) or NiMe(2)(PMe(3))(3) afford a series of novel dinuclear complexes [((Me(3)P)[lower bond 1 start]Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2)))((Me(3)P)M[upper bond 1 end](η(5)-C(5)H(4)P[lower bond 1 end]Ph(2)))] (M = Co(1), Ni(2) and Fe(3)) [Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)Ni[upper bond 1 end](COD)](4), [Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)Ni[upper bond 1 end](PMe(3))(2)] (5) and [((Me(3)P)[lower bond 1 start]Co(Me)(η(5)-C(5)H(4)[upper bond 1 start]PPh(2)))((Me(3)P)Fe[upper bond 1 end](Me)(η(5)-C(5)H(4)P[lower bond 1 end]Ph(2)))] (6). Reactions of 1,1'-bis(dipheny1phosphino)ferrocene with Ni(PMe(3))(4), NiMe(2)(PMe(3))(3), or Co(PMe(3))(4) gives rise to complexes [Fe(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)M[upper bond 1 end](PMe(3))(2)] (M = Ni (7), Co (8)). The complexes 1-8 were spectroscopically investigated and studied by X-ray single crystal diffraction. The possible reaction mechanisms and structural characteristics are discussed. Density functional theory (DFT) calculations strongly support the deductions.     

Synthesis,crystal structure,electrochemical and magnetic properties of dinuclear complexes with strong electron-drawing groups in the diphenoxo-tetraaza macrocyclic ligand

Three symmetrical macrocyclic dinuclear complexes [M₂L(H₂O) _n ](ClO₄)₂ (M²⁺ = Cu²⁺, Ni²⁺, Mn²⁺ and n = 0, 2) have been synthesized by cyclocondensation between 2,6-diformyl-4-fluorophenol and 1,4-diaminobutane in the presence of M²⁺ cations. The crystal structure of [Cu₂L](ClO₄)₂ was determined by X-ray diffraction techniques. The electronic and magnetic properties of the complexes were studied by cyclic voltammetry and magnetic susceptibility. The results confirm that the complexes obtain electrons easily and there are very strong antiferromagnetic couplings between two copper(II) ions in [Cu₂L](ClO₄)₂. The strong electron-drawing groups of fluorine attached to the phenyl ring of a macrocyclic complex enhances the antiferromagnetic exchange of the complex and makes it more easily reduced than its analogs.     

Synthesis, structure, and electronic properties of RuN6 dinuclear Ru-Hbpp complexes

A series of RuN(6) dinuclear Ru-Hbpp complexes (Hbpp is the dinucleating tetraaza ligand 3,5-bis(pyridyl)pyrazole) of general formula {[Ru(II)(R(2)-trpy)(MeCN)](2)(μ-R(1)-bpp)}(3+), 10(3+)-14(3+), (R(1) = H, Me, or NO(2). and R(2) = H, Me, MeO; see Scheme 1) has been prepared from their Cl(-) or AcO(-) bridged precursors. The complexes have been characterized by UV-vis, NMR, CV, and some by X-ray. Complexes 10(3+)-14(3+), Ru(2)(II,II), were oxidized by 1 equiv in solution, leading to the mixed valence Ru(2)(II,III) complexes 10(4+)-14(4+) containing one unpaired electron and were characterized by EPR and UV-vis-near-IR, which showed metal-centered spin and the presence of low-energy IVCT bands. The H(ab) parameter indicates a relatively strong electronic coupling between the two ruthenium centers (class II). Further two electron oxidation in solution of the 10(3+)-14(3+) led to the formation of EPR silent Ru(2)(III,III) complexes 10(5+)-14(5+), that were further characterized by UV-vis-NIR. TD-DFT calculations are employed to assign the nature of the UV-vis transitions for the complexes in the various oxidation states, which are of metal to ligand charge transfer (MLCT) type for Ru(2)(II,II) and ligand to metal charge transfer (LMCT) type for Ru(2)(III,II) and Ru(2)(III,III).     

Mono- and dinuclear iron complexes of bis(1-methylimidazol-2-yl)ketone (bik): structure, magnetic properties, and catalytic oxidation studies

The newly synthesized dinuclear complex [Fe(III)(2)(μ-OH)(2)(bik)(4)](NO(3))(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) ?) and Fe-O distances (1.941(2)/1.949(2) ?) compared to other unsupported Fe(III)(2)(μ-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The (57)Fe isomer shift (δ = 0.45 mm s(-1)) and quadrupole splitting (ΔE(Q) = 0.26 mm s(-1)) obtained from Mo?ssbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1)·S(2)) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 ?, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 ?) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe(II)(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe(II)(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe(II)(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O(2), and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions.     

Formal DNA hydrolysis by mono- and dinuclear iron complexes

The complexes CpFe(CO)(2)Ph and [CpFe(CO)(2)](2) cleave DNA in the presence of H2O2 or organic peroxides to give products resulting from the formal hydrolysis of the phosphodiester groups.     

DFT description of the magnetic properties and electron localization in dinuclear di-mu-oxo-bridged manganese complexes

Density functional theory (DFT) was applied to describe the magnetic and electron-transfer properties of dinuclear systems containing the [MnO2Mn]n+ core, with n=0,1,2,3,4. The calculation of the potential energy surfaces (PESs) of the mixed-valence species (n=1,3) allowed the classification of these systems according to the extent of valence localization as Class II compounds, in the Robin-Day classification scheme. The fundamental frequencies corresponding to the asymmetric breathing vibration were also computed.     

Di-radical dinuclear copper complex: synthesis,structure, and magnetic properties

The reaction of Cu(Ac)₂·4H₂O with 2-[(3,5-dichloro-2-hydroxy-benzylidene)-amino]-2hydroxymethyl-propane-1,3-diol (H₄L) and 4,4′-bipyridyl-N,N′-dioxide (4,4′-bipy-NO) in DMF under solvothermal conditions leads to the formation of a di-radical dinuclear copper complex [Cu₂(4,4′-bipy-NO)(dcdmap)₄] (1) (dcdmap is the anion of 2,4-dichloro-6dimethylaminomethyl-phenol, synthesized by an in situ reaction). Compound 1 was characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. Complex 1 displays dominant anti-ferromagnetic interaction between oxyradicals and copper ion and oxyradical.     

Highly luminescent bis-diketone lanthanide complexes with triple-stranded dinuclear structure

A new bis-β-diketone, 3,3'-bis(4,4,4-trifluoro-1,3-dioxobutyl)biphenyl (BTB), has been designed and prepared for the synthesis of a series of dinuclear lanthanide complexes [Ln(2)(BTB)(3)(C(2)H(5)OH)(2)(H(2)O)(2)] [Ln = Eu (1), Gd (2)], [Ln(2)(BTB)(3)(DME)(2)] [Ln = Nd (3), Yb (4); DME = ethylene glycol dimethyl ether] and [Eu(2)(BTB)(3)(L)(2)] [L = 2,2-bipydine (5); 1,10-phenanthroline (6); 4,7-diphenyl-1,10-phenanthroline (7)]. Complexes 1-7 have been characterized by various spectroscopic techniques and their photophysical properties are investigated. X-ray crystallographical analysis reveals that complexes 1, 3 and 4 adopt triple-stranded dinuclear structures which are formed by three bis-bidentate ligands with two lanthanide ions. The complexes 1 and 3-7 display strong visible red or NIR luminescence upon irradiation at ligand band around 372 nm, depending on the choice of the lanthanide. The solid-state photoluminescence quantum yields and the lifetimes of Eu(3+) complexes are determined and described.     

Syntheses and magnetic properties of iron(III) complexes with imidazole groups

Iron(III) complexes with the general formula of [Fe (R-Himap)₂]X and [Fe(R-Himat)₂]X (Himap = shiff-base prepared from the condensation of 4-formylimidazole and 2-aminophenol, Himat = shiff base prepared from the condensation of 4-formylimidazole and 2-aminobenzenethiol, and R = H, Me, Ph; X = ClO₄, NO₃, BPh₄) have been synthesized. The complexes have an N₄O₂ donor set or an N₄S₂ donor set. These complexes have 5 and 5 member rings around an iron(III) atom per one chelate ring, that is, "5-5 member rings". The crystal structure, Mössbauer spectra, magnetic properties and absorption spectra of the complexes were examined. In addition, [Fe (Himsa)₂]ClO₄ having "5-6 member rings" of an N₄O₂ donor set and [Fe (Ph-Himap)(Ph-imap)] obtained by the deprotonation of [Fe (Ph-Himap)₂]ClO₄ have been also synthesized, and the Mössbauer spectra and magnetic properties of those complexes were examined. The X-ray structure of a single crystal of [Fe (Himap)₂]BPh₄ was determined: C₄₄H₃₆N₆BO₂Fe, triclinic, space group P(# 2), a = 12.452(2) Å, b = 12.748(2) Å, c = 11.996(2) Å, = 103.97(1)°, = 90.78(1)°, = 84.70(1)° and Z = 2. The moiety of an iron atom of [Fe(Himap)₂]BPh₄ was a pseudo octahedron with an FeN₄O₂ geometry. [Fe(R-Himap)₂]X was in high-spin state (about 5.9 B.M. at 80 K in solid state), and [Fe(R-Himat)₂]X was in low-spin state (about 2.0 B.M. at 293 K). The complex [Fe(Himsa)₂]ClO₄ with "5-6 member rings" and the deprotonated complex [Fe(Ph-Himap)(Ph-imap)] were in the high-spin state (6.0 B.M. at 80 K). It is concluded that the ligand field strength of an N₄S₂ donor set is stronger than that of an N₄O₂ donor set.     

Modifying the structure of dinuclear ruthenium complexes with antitumor activity

In order to modulate the structure of a recently developed series of antitumor‐active, dinuclear Ru(II)–arene compounds, complexes 1c – 4c were synthesized. The complexes were modified with respect to their pyridinone moieties and the spacer linking the two metal centers. More particularly, the series of dinuclear ruthenium(II) complexes was extended to compounds with longer spacers, i.e. tetradecane and 3,7,10‐trioxotridecane, and the pyridinone ring was modified by replacing the methyl group by an ethyl group and by shifting the position of the methyl group. The organometallic ruthenium compounds were obtained from the reaction between [RuCl₂(η⁶‐p‐isopropyltoluene)]₂ and ligands 1b – 4b with yields ranging from 41 to 67%. All compounds were characterized by standard methods: MS, ¹H and ¹³C NMR spectroscopy and elemental analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and magnetic properties of new dinuclear iron(II) complexes of a phenylene‐bridge shiff base analogue dinucleating ligand

The synthesis and magnetic behavior of four new dinuclear iron(II) complexes Fe₂2a‐d × 4Py with the iron in an octahedral coordination sphere is presented in this paper. The complex c is a high‐spin complex over the whole temperature range investigated, while the complexes a,b , and d perform a partial low‐spin ⇔︁ high‐spin spin transition. In case of Fe₂2b × 4Py, X‐ray structure analysis of the HS/LS state was possible, showing that in one molecule both iron centers are either in the low‐spin or sin the high‐spin state. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:391–397, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20108     

Versatility in the binding of 2-pyrazinecarboxylate with iron. Synthesis, structure and magnetic properties of iron(II) and iron(III) complexes

The synthesis and characterization of two new iron(II) complexes, [Fe(pca)2(py)2].py (1) and {[Fe(pca)2(H2O)].H2O}n (2) and one new iron(III) complex, Na2{[Fe(pca)()]2O}.2H2O.2CH3CN (3) (pca- stands for 2-pyrazinecarboxylate), are reported. Complex 1 is obtained from the reaction of iron powder with 2-pyrazinecarboxylic acid. The reaction of Fe(ClO4)3.10H2O with Hpca in the presence of 3 equiv. of Bu4NOH yields 2, whereas the presence of NaOH yields 3. The molecular structure of 1 contains an iron(II) ion with a pseudo-octahedral environment resulting from the coordination of two pca- ligands in a bidentate chelating fashion and two pyridine molecules; pi-pi stacking interactions between pyridine and pyrazine rings lead to a one-dimensional chain. Complex 2 is an iron(II) coordination polymer with an infinite zig-zag motif and an Fe...Fe separation of 7.1 A. In 2, the pi-pi stacking interactions involving the pyrazine rings and the strong hydrogen bonds between the coordinated water molecule and the carboxylate oxygens of two pca- ligands result in a three-dimensional network structure. Complex 3 consists of an anionic micro-oxo-bridged diiron(III) core with two crystallographically distinct iron(iii) ions; the negative charge is compensated by two sodium cations. Complex 3 is assembled in a three dimensional network structure through coordination of Na(I) and hydrogen bond interactions. Temperature dependent magnetic susceptibility and M?ssbauer spectroscopic studies indicate that 1 and 2 have similar magnetic properties. Both complexes are paramagnetic above 12 K, whereas antiferromagnetic ordering is observed below 12 K. The magnetic properties of reveal strong intramolecular antiferromagnetic interactions between the two iron(III) ions with a J value of -221 cm(-1); no long range intermolecular magnetic coupling is observed between 295 and 4.2 K.