N. S. Ovanesyan

Synthesis and X-ray and Spectral Study of the Compounds [Q4N]2[Fe2(S2O3)2(NO)4] (Q = Me, Et, n-Pr, n-Bu)

Iron nitrosyl complexes with general formula [Q4N]2[Fe2(S2O3)2(NO)4] (Q = Me, Et, n-Pr, n-Bu) were synthesized by the exchange reaction of K2[Fe2(S2O3)2(NO)4] with tetraalkylammonium bromides. The molecular and crystal structure of [(CH3)4N]2[Fe2(S2O3)2(NO)4] were studied by X-ray diffraction analysis. The iron atom in the four-membered cycle of the [2Fe–2S] anion is bound to another Fe atom and to two sulfur atoms and is coordinated by two nonequivalent NO groups, each bridging sulfur atom being bound to the SO3group. The structurally equivalent iron atoms are in the state Fe1–(S= 1/2). The Mössbauer spectroscopy method shows that the complexes are diamagnetic due to the strong Fe–Fe bond. It is found that the SO3group provides higher stability of the thiosulfate anion than the anion in Roussins red salt [Fe2S2(NO)4]2–.

[Fe2(μ-SC5H4N)2(NO)4] as a New Potential NO Donor: Synthesis, Structure, and Properties

A new potential donor of nitrogen monoxide, a binuclear iron sulfur nitroso complex, was prepared by exchange reaction of Na2Fe2(S2O3)2(NO)4 with pyridine-2-thiol in the presence of sodium thiosulfate at pH 12. The molecular and crystal structures of [Fe2(μ-SC5H4N)2(NO)4] were studied by X-ray diffraction analysis. The type of iron coordination by pyridine-2-thiol in the presence of a coordinated NO molecule was determined. In vacuum, the structure of the complex is destroyed, which is accompanied by NO evolution, while exposure to UV radiation results in decomposition of the complex and in a release of N2O.

(Ferrocenylmethyl)trialkyl ammoniums as template cations in optically active two-dimensional oxalate bridged [Cr–Mn] and [Cr–Ni] molecule-based magnets: synthesis and magnetic properties

Abstract A series of (ferrocenylmethyl)trialkyl ammoniums: FcCH2NR3+ with R=CH3 (1), C2H5 (2), n-C3H7 (3), n-C4H9 (4) (X-ray structure provided), n-C5H11 (5) and the planar chiral 1,2-disubstituted Fc(CH3)CH2NBu3+ (6) have been tentatively used as template cation in order to synthesise bidimensional (2D) oxalate bridged molecule-based magnets of general formula {[CrIIIMII(ox)3][FcCH2NR3]}n and{[CrIIIMII(ox)3][Fc(CH3)CH2NBu3]}n (M=Mn2+, Ni2+, ox=C2O42−). These polymeric compounds were obtained only for reactions performed with 2, 3, 4 and 6. Starting from resolved Cr(ox)32−, the networks were prepared in their two enantiomeric forms in the case of {[CrIIINiII(ox)3][FcCH2NBu3]}n ([CrΔ–NiΛ]-4 and [CrΛ–NiΔ]-4) or {[CrIIIMnII(ox)3][FcCH2NBu3]}n ([CrΔ–MnΛ]-4 and [CrΛ–MnΔ]-4)) and characterised by circular dichroism measurements. All these compounds are ferromagnets with a Curie temperature close to 6 K when M=Mn and to 17 K for Ni. While the manganese [Cr–Mn] containing compounds are soft magnets, the [Cr–Ni] networks show coercive force up to 2200 Oe far above those previously reported for these networks.

Synthesis, structure, NO donor activity of iron–sulfur nitrosyl complex with 2-aminophenol-2-yl and its antiproliferative activity against human cancer cells

A new tetranitrosyl binuclear iron complex, [Fe2(SC6H6N)2(NO)4] (1), has been synthesized by two methods. Molecular and crystalline structure of 1 were determined by X-ray analysis; the complex is binuclear of “μ-S” type with ~2.7052(4) Å between the irons. The compound crystallizes in monoclinic, space group P21/n, Z = 2; parameters of the unit cell: a = 6.6257(2) Å, b = 7.9337(2) Å, c = 16.7858(4) Å, β = 96.742(2)°, V = 876.26(4) Å3. Parameters of Mössbauer spectrum for 1 are: isomer shift δFe = 0.096(1) mm/s, quadrupole splitting ΔEQ = 1.122(1) mm/s, line width 0.264(1) mm/s at 293 K. As follows from the electrochemical analysis of aqueous solutions of 1, it generates NO in protonic media without additional activation. NO amount and the rate of its activation are much higher in acidic solutions than in neutral and alkali ones. The constants of hydrolytic decomposition of 1 were calculated. The geometry and electronic structure of isolated 1 were studied using the density functional theory. Differential sensitivity of four lines of human tumor cells of various genesis to 1 has been determined (ovarian carcinoma (SCOV3), large intestine cancer (LS174T), mammary gland carcinoma (MCF7), and non-small cell carcinoma of lung (A549)); dependence of tumor cells amount on the complex concentration has been studied in order to use the complex as a promising antitumor agent for trials in vivo.

Influence of aromatic ligand on the redox activity of neutral binuclear tetranitrosyl iron complexes [Fe2(μ-SR)2(NO)4]: experiments and quantum-chemical modeling

Reduction of neutral binuclear nitrosyl iron complexes of “μ-S” structural type [Fe2(SR)2(NO)4] with R = 3-nitro-phenol-2-yl, 4-nitro-phenol-2-yl, 5-nitropyridine-2-yl and pyridine-2-yl in aprotic solution has been studied by a cyclic voltammetry (CVA) method at a wide range of potential scan rates. A complex with R = 3-nitro-phenol-2-yl was synthesized for the first time; therefore it was studied by X-ray and Mossbauer spectroscopy. The parameters of the Mossbauer spectrum are: isomer shift δFe = 0.115(1) mm s−1, quadrupole splitting ΔEQ = 1.171(1) mm s−1, and line width = 0.241(1) mm s−1 at 85 K. From the current–voltage curve, the transfer of the first electron was found to be reversible, and the redox-potentials of these reactions were determined. The further reduction of the complexes was determined to be irreversible because the product of the second electron addition is instable and decomposes partially during the potential scan. Calculations of geometric and electronic structures of monoanions and dianions of the complexes under study and their theoretical redox-potentials were performed by DFT methods. Introduction of the electron-acceptor NO2 group into the phenyl and pyridine rings of sulfur-containing ligands of the nitrosyl iron complexes was found to affect the geometry of the anions and the distribution of the additional negative charge, as well as to increase the redox-potential and to facilitate reduction of these complexes.

Synthesis, crystal structures, Mössbauer spectra, and redox properties of binuclear and tetranuclear iron-sulfur nitrosyl clusters

The iron-sulfur nitrosyl complexes A[Fe4S3(NO)7], where A=Na+, NH4+, or N(Bun)4+, and B2[Fe2S2(NO)4], where B=Na+, Cs+, or N(Bun)4+, were synthesized. Their structures and properties were studied by X-ray diffraction analysis, Mössbauer spectroscopy, and cyclic voltammetry. The effect of the crystal packing on the geometry of the tetranuclear NH4[Fe4S3(NO)7]·H2O and binuclear Cs2[Fe2S2(NO)4]·2H2O complexes was analyzed. The changes in the Fe57 Mössbauer spectral parameters of the anion in the B2[Fe2S2(NO)4] series depend on the size of the B cation and agree with variations in the structural parameters of the Fe[S2(NO)2] chromophores as well as in the stretching vibrations of the NO groups caused by changes in intermolecular contacts. The presence of electronic states delocalized through the Fe−Fe bonds explains the fact that the electronic states of the Fea(S3NO) and Feb(S2(NO)2) chromophores in the [Fe4S3(NO)7]− anion are nearly identical. The binuclear clusters are unstable upon storage in the solid phase and decompose in solutions to form the tetranuclear [Fe4S3(NO)7]− complexes, sulfur, and nitrogen oxides. The redox properties of the [Fe4S3(NO)7]− and [Fe2S2(NO4)]2− anions in CH3CN and THF solutions were studied. The mechanism of reduction of the anion in the tetranuclear cluster is proposed.

Nitrosyl iron complexes with enhanced NO donating ability: synthesis, structure and properties of a new type of salt with the DNIC cations [Fe(SC(NH2)2)2(NO)2]+

Novel nitrosyl iron complexes [Fe(SC(NH2)2)2(NO)2]2SO4·H2O(I) and [Fe(SC(NH2)2)2(NO)2]2[Fe2(S2O3)2(NO)4](II) have been synthesized via the reactions of FeSO4 and Na2[Fe2(S2O3)2(NO)4], respectively, with acidic solutions of thiocarbamide in water. The structure and properties of I and II were studied using X-ray analysis, Mossbauer, IR, and EPR spectroscopy and amperometry. Both complexes are characterized by a prolonged NO generation without additional activation in aqueous anaerobic solutions, similar to the organic NO donor diethylene triamine; however, they are more effective: at pH 7 the NO amount is ∼32.6 and ∼31.8 nM mol−1 of the complex for I and II, respectively. The obtained results show feasibility for the synthesis of water-soluble hybrid nitrosyl NO-generating complexes, which contain the NO groups both in the cationic and anionic sublattices and provide the control of the NO release kinetics.

Unexpected formation of chiral single crystals of {NH(n-C3H7)3[MnIICrIII(C2O4)3]}, A 2D oxalate-based material

In an attempt to obtain chiral single crystals of a two-dimensional (2D) bimetallic oxalate-based material by enantioselective auto-assembling of Mn2+ and (rac)-[Cr(C2O4)3]3− templated by the optically active complex (+)-(Rp)-[1-CH2(n-C3H7)3-2-CH3(C5H3)Fe(C5H5)]+, we obtained the unexpected 2D network species {NH(n-C3H7)3[MnCr(C2O4)3]}. X-ray diffraction determination of the structure reveals that the complex crystallizes in the enantiomorphous space group P63. The interlayer spacing of 7.93 Å is the lowest found so far for 2D, bimetallic, oxalate-bridged compounds.

(S)-(−)-(2-MeBu)N(Pr)2MeI Salt as Template in the Enantioselective Synthesis of the Enantiopure Two-dimensional (S)-(−)-(2-MeBu)N(Pr)2Me[ΛMnΔCr(C2O4)3] Ferromagnet

We describe herein the synthesis of (rac)- or enantiopure (S)-(-)-(2-MeBu)N(Pr)₂MeI ammonium salts. These racemic and enantiopure ammonium salts were used as cationic templates to obtain new two-dimensional (2D) ferromagnets [(rac)-(2-MeBu)N(Pr)₂Me][MnCr(C₂O₄)₃] and [(S)-(-)-(2-MeBu)N(Pr)₂Me][ΔMnΛ nCr(C₂O₄)₃]. The absolute configuration of the hexacoordinated Cr(III) metallic ion in the enantiopure 2D network was determined by a circular dichroism measurement. The structure of [(2-MeBu)N(Pr)₂Me][MnCr(C₂O₄)₃], established by single crystal X-ray diffraction, belongs to the chiral P63 space group. According to direct current (dc) magnetic measurements, these compounds are ferrromagnets with a temperature Tc = 6°K.

The Enantioselective Role of the [N(C5H11)4]+Organic Cation in the Structure of the Molecular Magnet [N(C5H11)4][MnIIFeIII(C2O4)3]

A crystal of [N(C5H11)4][MnIIFeIII(C2O4)3] was studied by X-ray diffraction analysis: space group C2221, a= 9.653(2) Å, b= 16.201(2) Å, c= 20.193(4) Å. The arrangement of the cations predetermines the formation of the crystal structure from anionic layers of the same chirality. The presence of two types of organic cation does not contradict the formation of crystals with left and right chirality and accounts for the data of Mössbauer spectroscopy, indicating two states of iron.