Heterospin complexes of polynuclear Ni<Superscript>II</Superscript> compounds containing hexafluoroacetylacetonate and pivalate ligands with nitroxides

The heterospin mixed-ligand complex [Ni₆(OH)₄Piv₄(hfac)₄(NIT-Ph)₂] (1) (NIT-Ph is 4,4,5,5-tetramethyl-2-phenyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide, hfac is hexafluoroacetylacetonate, and Piv is pivalate) was synthesized. The method for the synthesis of complex 1 is based on the replacement of acetone molecules in the hexanuclear complex containing the hexafluoroacetylacetonate and pivalate ligands [Ni₆(OH)₄Piv₄(hfac)₄(Me₂CO)₄] by NIT-Ph molecules. Two monodentate NIT-Ph molecules replace four acetone molecules, because the coordination of the O atom of the nitroxide group results in the blocking of one of the positions in the coordination environment of Ni^II the access to which is hindered by the phenyl ring of NIT-Ph. As a result, these ions are in a square-pyramidal environment unusual of Ni^II. In the low-temperature range, the dependence of the magnetization of 1 on the magnetic field is described by the Brillouin function. The reaction of [Ni₆Piv₄(hfac)₄(OH)₄(Me₂CO)₄] with the nitronyl nitroxide radicals 4,4,5,5-tetramethyl-2-(4-pyridyl)-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide (NIT-p-Py) or 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide (NIT-Iz) containing the pyridine or 1-methylimidazol-5-yl substituent, respectively, in the side chain is accompanied by the decomposition of the polynuclear fragment and affords the mononuclear complexes Ni(hfac)₂(NIT-p-Py)₂ and Ni(hfac)₂(NIT-Iz)₂, respectively. The reaction of 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihyd-ro-1H-imidazol-1-oxyl (Im-Iz), which is the imine analog of NIT-Iz, with [Ni₆Piv₄(hfac)₄(OH)₄(Me₂CO)₄] afforded the decanuclear complex [Ni₁₀(OH)₈Piv₄(hfac)₈(Im-Iz)₂(H₂O)₆]. The molecular and crystal structures of all heterospin compounds were determined, and the magnetic properties of all compounds were investigated in the 2–300 K temperature range.     

Dodecanuclear Ni<Superscript>II</Superscript> complex containing pivalate and hexafluoroacetylacetonate ligands

A dodecanuclear complex [Ni₁₂Piv₁₀(hfac)₆(OH)₈(EtOH)₆]·C₆H₁₄ was isolated from various synthetic systems simultaneously containing Ni^II and the pivalate and hexafluoro-acetylacetonate anions. The structure of this complex was determined and the magnetic properties were investigated. The use of EtOH as the solvent or the presence of EtOH in the reagents is the decisive factor for the formation of this complex.     

Mixed ligand complexes of Fe<Superscript>III</Superscript> containing pseudohalides,nitrosyl and some mannich bases

Reactions of Pentapseudohalonitrosyl ferrate(II) with Morpholinobenzyl benzamide(MBB) and Piperidinobenzyl benzamide(PBB) formed complexes of the type, [Fe(X)₃(NO)(L–L)] where X = CN⁻, NCO⁻ and N ₃ ⁻ and L–L = Morpholinobenzyl benzamide(MBB) and Piperidinobenzyl benzamide(PBB). These compounds have been characterized by various physico-chemical techniques such as elemental analysis, molar conductance, magnetic susceptibility measurements, i.r., electronic spectra, thermal gravimetric analysis. The molecular modeling Studies have been carried out for structural analysis for some of the complexes have been carried out using Hyperchem release 7.52 professional version.     

Polynuclear mixed-ligand NiII complexes containing pivalate and hexafluoroacetylacetonate ligands: a new single-molecule magnet

The reaction of NiCl₂ with excess potassium pivalate (KPiv) in ethanol affords the chainpolymeric compound KNi₄(Piv)₇(OH)₂(EtOH)₆. In the solid compound, the tetranuclear nickel fragments alternate with potassium atoms. The use of KNi₄(Piv)₇(OH)₂(EtOH)₆ in the reaction with Ni(hfac)₂ (hfac is the hexafluoroacetylacetonate anion) gave the first polynuclear mixed-ligand complexes [K₂Ni₆(Piv)₇(hfac)₃(OH)₄(HPiv)₂(Me₂CO)₂]·1.5C₇H₁₆, [Ni₆(Piv)₄(hfac)₄(OH)₄(Me₂CO)₄], [K₂Ni₈(Piv)₈(hfac)₄(OH)₆(H₂O)₂(Me₂CO)₆], [Ni₈(Piv)₁₀(hfac)₂(OH)₂(MeO)₂(MeOH)₂(HPiv)₂]·C₆H₁₄, and [Ni₁₆(Piv)₁₀(hfac)₆(OH)₁₀(MeO)₆(MeOH)₈(H₂O)₆]·C₆H₁₄ containing both Piv and hfac as the anionic ligands. The molecular and crystal structures of all these compounds were established, and their magnetic properties were studied. All solids containing simultaneously Piv and hfac ligands tend to undergo ferromagnetic ordering with decreasing temperature. The solid [Ni₈(Piv)₁₀(hfac)₂(OH)₂(MeO)₂(MeOH)₂(HPiv)₂]·C₆H₁₄ undergoes cooperative magnetic ordering below T _c (2.5 K). Dedicated to the 90th anniversary of the L. Ya. Karpov Institute of Physical Chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1175–1182, June, 2008.     

New antiferromagnetic tetranuclear pivalate complex containing Fe<Superscript>III</Superscript> and Fe<Superscript>II</Superscript> atoms

The interaction of [K₂Fe^III ₄(O)₂(OOCCMe₃)₁₀(HOOCCMe₃)₂(H₂O)₂]_n with 2-pyridinecarboxaldehyde results in a mixed-valence complex Fe^IIFe^III ₃(μ₃-O)₂(μ₂-OOCCMe₃)₇L₂··2.5MeCN·3H₂O (L = 2-NC₅H₄COOH_0.75K_0.25). The structure of the complex was established by X-ray analysis. The magnetic properties of the complex were studied. Dedicated to Academician A. L. Buchachenko on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2145–2148, September, 2005.     

Stereo sensitivity of exchange interactions in Ni<Superscript>II</Superscript> and Cu<Superscript>II</Superscript> heterospin complexes with 5-formylpyrrolyl-substituted nitroxides

5-Formylpyrrolyl-substituted nitronyl and imino nitroxide radicals HL¹ and HL² were synthesized. Their solid phases are formed by packing pairs of the molecules. In the {HL¹...HL¹} pairs, the dominant interaction is the ferromagnetic exchange with J/kB = 8.8 K (Hamiltonian \(H = 2J\left( {\overrightarrow {{s_1}} \overrightarrow {{s_2}} } \right)\)). The ferromagnetic exchange occurs also in the heterospin molecules [Ni(L¹)₂], [Cu(L¹)₂], and [Ni(L²)₂(MeOH)₂]. In the complexes [Ni(L¹)₂] and [Cu(L¹)₂], a small change in the mutual orientation of the coordinated ligands has a considerable effect on the value and the sign of the energy of exchange interactions between the unpaired electrons of the metal ion and paramagnetic ligands.     

Heterospin mixed-ligand heterotrinuclear Co<Superscript>II</Superscript>, Gd<Superscript>III</Superscript>, Co<Superscript>II</Superscript> complex with nitronyl nitroxide

A method was developed for the synthesis of mixed-metal heterospin compounds with the direct coordination of the nitroxide fragment based on the replacement of acetonitrile molecules in the heterotrinuclear complex [Co₂Gd(NO₃)Piv₆(CH₃CN)₂] with nitroxide molecules. The molecular and crystal structure of the heterospin mixed-ligand heterotrinuclear Co^II, Gd^III, Co^II complex [Co₂Gd(NO₃)Piv₆(NIT-Me)₂], where NIT-Me is stable nitronyl nitroxide, was established. The magnetic properties of this complex were investigated in the temperature range of 2–300 K. The coordination of nitroxide groups to Co^II ions is responsible for strong exchange interactions between the unpaired electrons in the exchange clusters {>-·O-Co^II}, resulting in the virtually complete spin coupling between each coordinated >N-·O group and one of the unpaired electrons of each Co^II ion at temperatures below 200 K. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1742–1745, September, 2007.     

Polynuclear Ni<Superscript>II</Superscript> and Co<Superscript>II</Superscript> hexafluoroacetylacetonates

Hydrolysis of [M₄(hfac)₄(MeO)₄(MeOH)₄] (М = Сo, Ni and hfac is hexafluoroacetylaceton ate) is a convenient way of obtaining polynuclear complexes [Ni₇(hfac)₆(OH)₈(H₂O)₆]?2H₂O, [Co₁₂(hfac)₁₀(OH)₁₄(H₂O)₈]?2H₂O?2MePh, [Co₁₂(hfac)₁₀(OH)₁₄(H₂O)₄(Me₂CO)₄]?3PhMe, and [Co₁₂(hfac)₁₀(OH)₁₄(H₂O)₆(Me₂CO)₂]?2H₂O?2Me₂CO, whose structures were confirmed by X-ray analysis.     

Chemical assembly of the heteronuclear pivalate complex with the Li<Superscript>I</Superscript> and Fe<Superscript>III</Superscript> ions

The heteronuclear complex [Fe₄Li₂(O)₂(Piv)10(H₂O)₂] (1, Piv is the pivalic acid anion) was obtained by refluxing Fe^III pivalates with Li^I pivalates in toluene and isolated as the 1?PhCH₃ solvate with a toluene molecule. According to X-ray diffraction data, complex 1 contains the {Fe₄Li₂O₂} core. The Mössbauer spectroscopy data indicate that the core comprises para magnetic Fe^III ions in the high-spin state located in the symmetric octahedral environment of oxygen atoms. Thermolysis of 1 studied by simultaneous thermal analysis demonstrated thermal stability of the complex up to 225 °С. The main end product of thermolysis at 600 °С is the mixed oxide LiFe₅O₈.     

Synthesis and photophysical properties of Ir<Superscript>III</Superscript>-Ln<Superscript>III</Superscript> (Ln = Nd,Yb, Er) bimetallic complexes containing bipyrimidines as bridging ligands

Bipyrimidines have been chosen as (N∧N)(N∧N) bridging ligands for connecting metal centers. Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes [Ir(dfppy)₂(μ-bpm)Ln(TTA)₃]Cl were synthesized by using Ir(dfppy)₂(bpm)Cl as the ligand coordinating to lanthanide complexes Ln(TTA)₃·2H₂O. The stability constants between Ir(dfppy)₂(bpm)Cl and lanthanide ions were measured by fluorescence titration. The obvious quenching of visible emission from Ir^III complex in the Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes indicates that energy transfer occurred from Ir^III center to lanthanides. NIR emissions from Nd^III, Yb^III, and Er^III were obtained under the excitation of visible light by selective excitation of the Ir^III-based chromophore. It was proven that Ir(dfppy)₂(bpm)Cl as the ligand could effectively sensitize NIR emission from Nd^III, Yb^III, and Er^III.     

Some novel organometallic Mn<Superscript>III</Superscript> complexes with porphine and 1,6-diaminohexane

A novel series of Mn^III complexes with 5,10,15,20-tetra(p-tolylporphine) and 1,6-diaminohexane has been synthesized. These complexes have been characterized by UV/Vis, IR, ESI-mass spectra, elemental analysis, conductivity and magnetic susceptibility measurements. These Mn^III porphyrins exhibited a blue shift in soret band in comparison to non-metallated porphyrins. The molar conductance values of these complexes show their non-electrolytic nature in ethanol. The tentative structures have also been proposed. All the complexes have good level of water solubility due to which they may have medicinal as well as other valuable biological applications.     

Synthesis,structure, and magnetic properties of a Yb<Superscript>III</Superscript> complex with the iminopyridine radical-anionic ligand

The reaction of equimolar amounts of ytterbocene (C₅Me₄H)₂Yb(THF)₂ and iminopyridine 2,6-Prⁱ₂C₆H₃N=CH(C₅H₄N) accompanied by the one-electron oxidation of the ytterbium ion produced the unique lanthanide complex (C₅Me₄H)₂Yb^III[2,6-Prⁱ₂-C₆H₃NCH(C₅H₄N)]–? with the iminopyridine radical-anionic ligand. The structure of the complex in the crystalline state was established by X-ray diffraction and its magnetic properties were studied in the temperature range of 1.8—300 K.     

Carboxylate clusters with the M<Subscript>4</Subscript>O<Subscript>4</Subscript> cubane-like core: pivalate cocrystal containing Co<Superscript>II</Superscript> and Ni<Superscript>II</Superscript>

Joint thermolysis of the dinuclear pivalate complexes M₂(μ-H₂O)(μ-Piv)₂(Piv)₂(HPiv)₄ (M = Co (1) and Ni (2), Piv^- is the pivalate anion), in decane at 174 °C at the reactant ratio 1: 1 followed by treatment of the dry thermolysis product with methanol afforded crystals of a new cocrystallization product of the molecules containing the heterometallic cubane-like core M₄(Co,Ni)O₄. According to the X-ray diffraction data and the results of magnetic measurements, inductively coupled plasma atomic emission spectrometry (ICP-AES), and investigations of the solid-state thermal decomposition products, the isolated cocrystallization product has the general formula [Co_1.6Ni_2.4(μ₃-OMe)₄(μ₂-Piv)₂(pg² -Piv)₂(MeOH)₄] ·4MeOH (3·4MeOH). Thermolysis of the crystals of the solvate 3·4MeOH is a destructive process accompanied by the intramolecular redox reaction. A mixture of metallic Ni and cobalt oxide (CoO) are the final solid decomposition products of 3 · 4MeOH in an argon atmosphere, whereas a mixture of the phases NiO, Co₃O₄, and NiCo₂O₄ is formed in air.     

Heterospin complexes of fluorinated dinuclear Cu<Superscript>II</Superscript> and Mn<Superscript>II</Superscript> triketonates with nitroxides

Dinuclear heterospin complexes of Cu^II and Mn^II 1,1,1,7,7,7-hexafluoroheptane-2,4,6-trionates ([Cu₂L₂] and [Mn₂L₂], respectively) with nitronyl nitroxides 2-R-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide 1-oxyls (NIT-R, R = H, Me, Et, m-C₅H₄N, m-NCC₆H₄, p-NCC₆H₄, PzMe) and the diradical NIT-Pz-(CH₂)₄-Pz-NIT (Pz is 1,4-pyrazolylene) were synthesized and structurally characterized. In the complexes under study, the CuII atom tends to have the square-pyramidal coordination environment, and the MnII atom is in an octahedral environment. The magnetochemical investigation of the compounds in the temperature range of 2–300 K showed that the antiferromagnetic exchange coupling dominates in the [Cu₂L₂] molecules, whereas this coupling in [Mn₂L₂] is manifested in the experimental plot μ_eff(T) at T < 100 K. The magnetic properties of the heterospin complexes of [Cu₂L₂] with NIT-R are also determined by the intramatrix antiferromagnetic exchange coupling. For the complexes of [Mn₂L₂] with NIT-R, the coordination mode of the nitroxide plays a decisive role.     

New cage-like metallasiloxane containing Fe<Superscript>III</Superscript> ions in different coordination spheres

The first cage-like ferrophenyl siloxane containing Fe^III ions in different coordination spheres (four iron ions have a trigonal-bipyramidal coordination and two iron ions have a distorted octahedral coordination) was synthesized by the exchange reaction of sodium phenylsilanolate with Fe^III chloride. An exotic lantern-like structure is formed with the involvement of two metal oxide fragments Fe—O—Fe. The structure of this compound was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 522–524, March, 2007.     

Synthesis,characterization and DNA-binding studies of 1-(pyridin-2-yl)-3-tosylurea and its Nd<Superscript>III</Superscript>, Eu<Superscript>III</Superscript> complexes

1-(Pyridin-2-yl)-3-tosylurea(HL) and its two lanthanide complexes, LnL₃ · H₂O [Ln = Nd(1), Eu(2)], have been synthesized and characterized on the base of elemental analyses, molar conductivities, IR spectra and thermal analyses. In addition, the DNA-binding properties of the two complexes have been investigated by absorption, fluorescence and viscosity measurements. The experimental results indicated that the complex (1) and (2) can bind to DNA; the binding affinity of the complex (1) is higher than that of complex (2) and the intrinsic binding constants of complex (1) and complex (2) with DNA were 1.24 × 10⁴ m ⁻¹ and 8.7 × 10³ m ⁻¹, respectively. In addition, some factors that influence the fluorescent intensity were also discussed.     

Synthesis,structure, and luminescent properties of Pr<Superscript>III</Superscript> complexes with pyrazole-derived 1,3-diketone and 1,10-phenanthroline

The interaction of PrCl₃ with 1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)-1,3-propanedione in aqueous ethanol in the presence of a base and 1,10-phenanthroline was studied. It was shown that the composition of the products was dependent on the reaction conditions. The solvate [Pr(L)₃(Phen)]?3PrⁱOH crystallizes in a monoclinic crystal system (P2₁/c space group, a = 12.2239(12) Å, b = 20.3403(19) Å, c = 26.134(3) Å, β = 102.380(2)° at 150 K). Absorption spectra of the complex in solution, as well as the spectra and the kinetic parameters of photo-luminescence were investigated.     

Synthesis,Structure, and Magnetic Properties of a Twist Linear Tetranuclear Co<Stack><Subscript>2</Subscript><Superscript>III</Superscript></Stack>Ln<Stack><Subscript>2</Subscript><Superscript>III</Superscript></Stack> Complexes

A series of twist linear tetranuclear 3d–4f Co ₂ ^III Ln ₂ ^III [Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5)] complexes have been prepared under solvothermal conditions and structurally characterized with Schiff-base ligand 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propanediol (H₄L). The two central Co ions are linked by two alkoxyl oxygen atoms, and one Ln ion lying above and the other below the Co–Co dimer, form a twist linear array. The magnetic susceptibility studies reveal antiferromagnetic or ferromagnetic behaviour, whilst dynamic magnetic studies indicate no slow magnetic relaxation for these complexes.     

Spectroscopic and thermal investigations of complexes of Cr<Superscript>III</Superscript>, Mn<Superscript>II</Superscript>, Zn<Superscript>II</Superscript> &; Cd<Superscript>II</Superscript> - carboxamide

Complexes of Cr^III, Mn^II, Zn^II & Cd^II with the polydentate carboxamide ligandN′, N′′-bis(3-carboxy-1-oxoprop-2-enyl) 2-Amino-N-arylbenzamidine (H₂L) have been synthesized and characterized by elemental analyses, spectroscopic studies (Vibrational, electronic, ESR and ¹H-NMR), magnetic susceptibility measurements, thermal studies and powder diffraction studies. The vibrational spectral data are in agreement with coordination of amide and carboxylate oxygen of the ligands with the metal ions. The electronic spectra indicates octahedral or tetrahedral geometry around the metal ions, has been supported by magnetic susceptibility measurements. The results of electron spin resonance & ¹H-NMR spectra have supported the results of other spectral techniques. Kinetic and thermodynamic parameters were computed from the thermal data using Coats and Redfern method, which confirm first order kinetics. Powder diffraction determines the cell parameters of the complexes.     

Formation of homo- and heteronuclear complexes of 1-hydroxyethylidene-1,1-diphosphonic acid with Mn<Superscript>II</Superscript> and Fe<Superscript>III</Superscript> in aqueous solutions

Systems based on 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), iron(iii)—HEDP and manganese(ii)—iron(iii)—HEDP, were studied by pH-potentiometry combined with mathematical modeling and NMR. Diverse and highly stable heteronuclear iron manganese complexes were found to exist in the heteronuclear system. The formation of the MnH₃L₂^3–, FeMnH₃L₂⁰, Fe₂MnHL₃^3–, and MnL^2– complexes was established. The relaxation efficiency coefficient REC₂ (relaxivity) of these complexes was evaluated at ~2000 mol^–1 s^–1 L. Therefore, these systems hold promise as MRI contrast agents.