Synthesis, structure and magnetic properties of lanthanide(III) complexes with new imidazole-substituted imino nitroxide radical

Synthesis, characterization and magnetic properties of new lanthanide-radical complexes, [Ln^III(hfac)₃(IM2imH)] (Ln = Gd, Tb; IM2imH = 2-(2-pyridyl)-4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxy), are described. The molecular structure of the [Tb(hfac)₃(IM2imH)] has been determined by the X-ray diffraction. The magnetic susceptibility data for [Gd(hfac)₃(IM2imH)] show that the Gd-IM2imH magnetic interaction is antiferromagnetic with an exchange coupling constant J = −2.59 cm⁻¹ in contrast to the ferromagnetic interaction in most of Gd(III) complexes containing paramagnetic center, which will be examined in connection with planarity of the IM2imH chelate.     

Syntheses, structures, and magnetic properties of three Fe(II) complexes with reduced radical ligands

Three new Fe(II) complexes [Fe(HIM2py)₂(SCN)₂] (1), [Fe(HIM2py)₂(H₂O)₂](ClO₄)₂ · 2H₂O (2), and [Fe(HIM2py)₂(4,4-bipy)](ClO₄)₂ · 3CH₃CH₂OH (3) (4,4-bipy = 4,4′-bipyridine, HIM2py = 1-hydroxyl-2(2′-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole) have been synthesized and characterized structurally as well as magnetically. The X-ray analysis reveals that HIM2py ligands are coordinated to the metal ions as an unusual six-membered didentate chelate with the κ²N(py), O(HIM) mode. Fe(II) ions in complex 3 are bridged by 4,4-bipy, leading to a 1D chain structure. The magnetic behavior of complex 3 is investigated, showing weak antiferromagnetic interactions.     

A novel ferromagnetic coupling one-dimensional complex {Cu(II)(NIT3Py)2[N(CN)2]2(H2O)2}

The novel ferromagnetic coupling one-dimensional complex {Cu(NIT3Py)₂[N(CN)₂]₂(H₂O)₂} (NIT3Py=2-(3^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) was synthesized and characterized structurally and magnetically. It crystallizes in the monoclinic space group C2/c. The Cu(II) ion is in a distorted octahedral environment. The units of {Cu(NIT3Py)₂[N(CN)₂]₂(H₂O)₂} were connected as one-dimensional structure by the intermolecular hydrogen bonds. Magnetic measurements show that there are intramolecular ferromagnetic interactions and intermolecular antiferromagnetic interactions within the chain.     

Synthesis and structural characterization of trans-[Mo2(H2DMepyF)2(CH3CN)4](BF4)6 (HDMepyF=N,N-di(6-methyl-2-pyridyl)formamidine)

Reaction of Mo₂(O₂CCH₃)₂(DMepyF)₂ (HDMepyF=N,N^′-di(6-methyl-2-pyridyl)formamidine) with HBF₄ in CH₂Cl₂/CH₃CN afforded the complex trans-[Mo₂(H₂DMepyF)₂(CH₃CN)₄](BF₄)₆ (1), which crystallized in two forms, trans-[Mo₂(H₂DMepyF)₂(CH₃CN)₄](ax-CH₃CN)₂(BF ₄)₆ · 2CH₃CN (1a), and trans- [Mo₂(H₂DMepyF)₂(CH₃CN)₄](ax-BF₄) ₂(BF₄)₄ · 2CH₃CN (1b). The molecular structures of complexes (1) consist of two quadruply bonded molybdenum atoms, which are spanned by two trans-bridging formamidinate ligands and coordinated by four trans-CH₃CN. Each H₂DMepyF⁺ ligand adopts an s-cis,s-cis- conformation. The difference between 1a and 1b is that complex 1a contains two CH₃CN molecules as axial ligands, while 1b contains two BF₄⁻ anions as axial ligands. Complex 1 is the first dimolybdenum complex containing a pair of trans bridging ligands and two pairs of trans-CH₃CN ligands.     

Synthesis, crystal structure and magnetic properties of a novel complex Ni(NIT2-thz)3(ClO4)2

A novel Ni(II)-nitronyl nitroxide-substituted thiazole complex, Ni(NIT2-thz)₃(ClO₄)₂ (NIT2-thz = 2-(2′-thiazole)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) was synthesized and characterized structurally and magnetically. It crystallizes in the monoclinic space group P2₁c. The metal coordination sphere is fully occupied by three chelating nitroxide ligands, showing a distorted octahedral geometry. The complex molecules were connected as 1-D chain structure by the intermolecular interaction. Magnetic studies show that antiferromagnetic couplings occurred between the nickel(II) ion and the organic radicals, and ferromagnetic between the adjacent molecules.     

Synthesis and characterization of uranyl(VI) and thorium(IV) complexes with phosphine oxides. The crystal structure of UO2(NO3)2(NO2-C6H4Ph2PO)2

Uranyl(VI) and thorium(IV) complexes of the type UO₂(NO₃)₂(L¹)₂, UO₂(NO₃)₂(L²)₂, UO₂(CH₃COO)₂L¹, UO₂(CH₃COO)₂L², Th(NO₃)₄(L¹)₂ and Th(NO₃)₄(L²)₂ (L¹ = (2-nitro)phenyl-bis-phenyl phosphine oxide, L² = triferrocenylphosphine oxide) are reported, together with their physico-chemical properties.The crystal structure of UO₂(NO₃)₂(L¹)₂ is also reported. The crystals are monoclinic, space group P2₁/n with a = 17.78(1), b = 13.88(1), c = 17.37(1) Å, β = 114.8(1)° for Z = 4. The uranium atom is 8-coordinated, the uranyl(VI) group being equatorially surrounded by an irregular hexagon of six oxygen atoms from two trans neutral ligands and two nitrato groups.     

Oxoselenide triangular molybdenum clusters: Synthesis and characterization of [Mo3SeO3(acac)3(py)3]PF6

New cluster complex [Mo₃SeO₃(acac)₃(py)₃]⁺ was obtained by ligand substitution in the aqua complex [Mo₃SeO₃(H₂O)₉]⁴⁺. Crystal structure was determined for [Mo₃SeO₃(acac)₃(py)₃]PF₆·C₆H₅CH₃. The complex was characterized by ⁷⁷Se NMR, electrospray mass-spectrometry, and cyclic voltammetry. DFT calculations were used to confirm the assignment of chemical shift and to study Mo-Mo bonding in the cluster core.     

One-dimensional coordination polymers made of transition metal-nitronyl nitroxide radical with dicyanoaurate(I) bridges

Three 1-D transition metal-nitronyl nitroxide radical complexes with dicyanoaurate(I) bridges, [M(NIT3py)₂][Au(CN)₂]₂ [NIT3py = 2-(3′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, M = Mn, Co, Zn (1-3)], were synthesized and structurally characterized. Three compounds are all isostructural in monoclinic, C2/c space group with Z = 4. The [Au(CN)₂]⁻ anions link [M(NIT3py)₂] units via μ₂-bridging mode, leading to a linear coordination chain. The M(II) ion adopts a distorted octahedral geometry with four N atoms from [Au(CN)₂]⁻ groups and two pyridyl-N atoms from NIT3py ligands. The magnetic behavior shows that the couplings are both weak antiferromagnetic between Mn(II) and NIT3py and between Co(II) and NIT3py.     

Synthesis and study of Pt(II)-aromatic amines complexes of the types cis- and trans-Pt(amine)2(NO3)2 and cis-Pt(amine)2(R(COO)2)

Complexes of the types cis- and trans-Pt(amine)₂(NO₃)₂ with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear magnetic resonance spectroscopies. The cis complexes could be synthesized pure only with the amines of the type Ph-R-NH₂ (R = alkyl), while pure trans compounds were synthesized with all the studied amines. In ¹⁹⁵Pt NMR spectroscopy, the dinitrato complexes of the amines Ph-R-NH₂ were observed around −1700 ppm for the cis isomers and at about −1580 for the trans complexes. For the other amines, where a phenyl ring is directly attached to the amino group, the signals were observed at lower fields, −1528 ppm for cis-Pt(PhNH₂)(NO₃)₂ and around −1450 ppm for all the trans isomers. There is a linear relationship between the δ(Pt) of the Pt(amine)₂(NO₃)₂ complexes and the pK_a of the protonated amines. The coupling constants ²J(¹⁹⁵Pt-¹HN) are larger in the cis compounds (ave. 76 Hz) than in the trans isomers (ave. 63 Hz). The complexes cis-Pt(amine)₂(R(COO)₂) with bidentate dicarboxylato ligands were also synthesized and characterized mainly by IR spectroscopy. The compounds apparently decompose in DMF and are too insoluble in other solvents for solution studies.     

Synthesis and multinuclear magnetic resonance spectroscopy of the novel ionic Pt(II) mixed-ligands complexes cis- and trans-[Pt(amine)2(pyrimidine)2](NO3)2

Novel ionic mixed-ligands complexes of the types cis- and trans-[Pt(amine)₂(pm)₂](NO₃)₂ (where pm = pyrimidine) were synthesized and studied in the solid state by IR spectroscopy and in aqueous solution by multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopy. The results of the solution NMR characterization have shown that the isolated compounds are pure. In ¹⁹⁵Pt NMR, the cis RNH₂ complexes were observed at slightly lower fields (ave. −2441 ppm) than the equivalent trans analogues (ave. −2448 ppm). For Me₂NH, the difference between the two isomers is larger (29 ppm). The complexes are observed at lower fields (difference of 100 ppm) than the corresponding [Pt(amine)₄]²⁺ complexes, which might indicate the presence of π-backdonation in the Pt-pm bond. In ¹H NMR, the coupling constants ³J(¹⁹⁵Pt-¹H_amine) are larger in the cis compounds (38-48 Hz) than in the trans analogues (30-36 Hz). The ³J(¹⁹⁵Pt-¹H_pm) values are also larger for the cis isomers. In ¹³C NMR spectroscopy, the coupling constants ³J(¹⁹⁵Pt-¹³C_amine) are 36 Hz (ave.) for the cis complexes and 26 Hz (ave.) for the trans isomers, while the ²J(¹⁹⁵Pt-¹³C_amine) are 18 Hz (cis) and 14 Hz (trans), respectively. The ³J(¹⁹⁵Pt-¹³C_5(pm)) values are 36 Hz (cis) and 28 Hz (trans). A few ²J(¹⁹⁵Pt-¹³C_pm) couplings were observed (7-10 Hz).     

Synthesis and multinuclear magnetic resonance spectroscopy of the novel ionic Pt(II) mixed-ligands complexes cis- and trans-[Pt(pyrazine)2(Ypy)2](NO3)2 where Ypy = pyridine derivative

Novel ionic mixed-ligands complexes of the types cis- and trans-[Pt(pz)₂(Ypy)₂](NO₃)₂ (where Ypy is a pyridine derivative and pz = pyrazine) were synthesized and studied mainly in the solid state by IR spectroscopy and in aqueous solution by multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopy. The trans isomers with ligands containing a methyl group in ortho position on the pyridine ring could not be synthesized. The results of the solution NMR characterization have shown that the isolated compounds are pure. In ¹⁹⁵Pt NMR, the cis complexes containing a methyl group in ortho positions were observed at lower field (average −2337 ppm) than the other cis compounds (average −2427 ppm), which is explained by the solvent effect. The trans isomers were observed at very slightly lower fields (average −2422 ppm) than the equivalent cis complexes (average −2427 ppm). In ¹H NMR, the coupling constants ³J(¹⁹⁵Pt-¹H_Ypy) and ³J(¹⁹⁵Pt-¹H_pz) are larger in the cis compounds (∼40 Hz) than in the trans complexes (∼31 Hz). A few ⁴J(¹⁹⁵Pt-¹H_pz) were observed (∼16 Hz). In ¹³C NMR spectroscopy, the coupling constants ³J(¹⁹⁵Pt-¹³C_pz) and ³J(¹⁹⁵Pt-¹³C_Ypy) are also larger in the cis configuration (∼30 and ∼38 Hz, respectively) than in the trans isomers (∼20 Hz). One ⁴J(¹⁹⁵Pt-¹³C_pz) could be calculated (17 Hz). The presence of the syn and anti rotamers were observed in all the cis complexes containing a pyridine derivative with a -CH₃ group in ortho position. They were observed in ¹⁹⁵Pt, ¹H and ¹³C NMR spectroscopy. The proportion of the two rotamers is about 55% and 45%.     

Preparation, structure, solid state and gas phase stability of the mixed neodymium nitrate-chloride complex NdCl(NO3)2{[(MeO)2PO]2C(OH)Bu}2

The preparation and structure of the mixed anion complex NdCl(NO₃)₂{[(MeO)₂PO]₂C(OH)^tBu}₂ are reported. Single crystal X-ray diffraction shows that the bisphosphonate is bonded via both phosphoryl groups and the nitrates act as bidentate ligands. Intramolecular H-bonding is seen between the OH and the coordinated nitrate and chloride ligands. Thermal decomposition in the solid state is by loss of methyl nitrate. Electrospray mass spectrometry shows that loss of chloride is preferred over loss of nitrate in the gas phase. Attempted preparation of NdCl₂(NO₃){[(MeO)₂PO]₂C(OH)^tBu}₂ leads to the formation of a product approximating to [Nd{^tBu(OH)C(PO₃H₂)₂}₂]₂H · NO₃ · (PO₄H₂)₂. Electrospray mass spectrometry and elemental analysis confirm the presence of the [^tBu(OH)C(PO₄H₂)₂]⁻ in the decomposition products.     

Supramolecular assemblies of new 2-D complexes: Syntheses, crystal structures, spectroscopic and magnetic properties of {[MnAu2(CN)4(NITpPy)2(H2O)2]}n and {[Co(N(CN)2)2(NITpPy)2(H2O)2]}n

Two new complexes, {[MnAu₂(CN)₄(NITpPy)₂(H₂O)₂]}_n (1) and {[Co(N(CN)₂)₂(NITpPy)₂(H₂O)₂]}_n (2), have been synthesized and characterized. The single-crystal X-ray analysis for the complexes 1 and 2 demonstrates that each M(II) (M = Mn or Co) ion assumes a distorted octahedral MN₄O₂ coordination polyhedron. Four nitrogen atoms come from the cyanide groups and the pyridyl rings in a common plane, and two oxygen atoms come from the H₂O molecules in trans-positions. The structures of complexes 1 and 2 illustrate that aurophilicity and/or hydrogen bonding interactions play important roles in increasing dimensionality. Magnetic investigations on complexes 1 and 2 show the presence of weak antiferromagnetic interactions.     

Study of Pt(II)-cyclic amines complexes of the types cis- and trans-Pt(amine)2I2 and cis- and trans-Pt(amine)2(NO3)2 and their aqueous products by

Complexes of the types cis- and trans-Pt(amine)₂I₂ containing cyclic amines were synthesized and studied mainly by IR and multinuclear NMR spectroscopies. The compounds were converted to cis- and trans-Pt(amine)₂(NO₃)₂, which were also investigated. The hydrolysis and the aquation reactions of the latter compounds were then studied in D₂O in different conditions of pH. In acidic medium, the aqueous product is [Pt(amine)₂(D₂O)₂]²⁺ and for a few amines, [Pt(amine)₂(D₂O)(NO₃)]⁺ was detected. In basic pH, the main product is Pt(amine)₂(OD)₂ and Pt(amine)₂(OD)(NO₃) was detected for several compounds. In neutral pH, the cis isomers form between two and four species in fresh solutions. The most shielded species in ¹⁹⁵Pt NMR is the monoaqua-monohydroxo complex cis-[Pt(amine)₂(D₂O)(OD)]⁺ and the less shielded compound is the dihydroxo-bridged dimer [Pt(amine)₂(μ-OD)₂Pt(amine)₂]²⁺, which were observed for all the compounds. For a few amines, the monohydroxo-bridged dimer [Pt(D₂O)(amine)₂(μ-OD)Pt(OD)(amine)₂]²⁺ was detected and for cyclohexylamine, a fourth signal was assigned to a cyclic hydroxo-bridged trimer [(Pt(amine)₂(μ-OD))₃]³⁺. ¹⁹⁵Pt NMR spectroscopy has shown that the concentration of the monomer decreases with time, while the concentration of the dimers increases. Only one product was observed for the trans isomers in neutral pH. The signal was assigned to the monoaqua-monohydroxo species trans-[Pt(amine)₂(D₂O)(OD)]⁺. The ¹³C and ¹H NMR spectra of most of the complexes were measured. All the coupling constants ^2,3J(¹⁹⁵Pt-¹H) and ^2,3J(¹⁹⁵Pt-¹³C) are larger in the cis compounds than in the trans isomers.     

Novel long bipyridine-type linking ligands containing an intervening naphthalene fragment: [Zn(L)(NO3)2], [Zn(L)(NO3)2], and [Cd(L)1.5(NO3)2] (L = (4-py)-CHN-C10H6-NCH-(4-py); L = (3-py)-CHN-C10H6-NCH-(3-py))

Novel bipyridine-type linking ligands L¹ ((4-py)-CHN-C₁₀H₆-NCH-(4-py)) and L² ((3-py)-CHN-C₁₀H₆-NCH-(3-py)), a pair of isomers due to possessing different pairs of terminal pyridyl groups, were prepared by the Schiff-base condensation. In ligand L¹, the N?N separation between the terminal pyridyl groups is 16.0 Å, with their nitrogen donor atoms at the para positions (4,4′). The corresponding N?N separation in ligand L² is 14.2 Å, with the nitrogen donor atoms at the meta positions (3,3′). 1-D zigzag-chain coordination polymers [Zn(L¹)(NO₃)₂] (1) and [Zn(L²)(NO₃)₂] (2) were prepared by reactions of Zn(NO₃)₂ · 6H₂O with ligands L¹ and L², respectively, by solution diffusion. Polymer 3, [Cd(L¹)_1.5(NO₃)₂], prepared from Cd(NO₃)₂ · 4H₂O and L¹, exhibits a 1-D ladder structure, whose repeating ladder unit consists of four Cd metals and four L¹ ligands to create a large 76-membered ring with dimensions of 20.8 × 20.8 Å. All products were structurally characterized by X-ray diffraction.     

A new tricarbonyl fac-[M(acac)(isc)(CO)3] complex (M = Re, Tc) with acetylacetonate (acac) and isocyanide (isc) in a 2+1 combination

The synthesis and characterization of the neutral 2+1 mixed ligand complex fac-Re(CO)₃(acac)(isc) (4) with acetylacetonate (acac) as the bidentate ligand and an isocyanide (the isocyanocyclohexane, isc) as the monodentate ligand is described. The synthesis of 4 proceeds through the intermediate formation of the fac-Re(acac)(H₂O)(CO)₃ precursor complex 2. Complex 4 was characterized by elemental analysis, spectroscopic methods, and X-ray crystallography showing a distorted octahedral arrangement of the ligands around Re. At technetium-99m level, the corresponding fac-^99mTc(acac)(isc)(CO)₃ complex 5 was obtained in high yield by reacting the fac-^99mTc(acac)(H₂O)(CO)₃ precursor complex 3 with isocyanocyclohexane and its structure was established by chromatographic comparison with the prototypic rhenium complex using high performance liquid chromatography.     

Synthesis, spectroscopy and magnetism of novel metal complexes of 3-aminoflavone (3-af). X-ray crystal structure of 3-af and [Cu(3-af)2(NO3)2]

The synthesis and characterization of four new complexes with the bioactive ligand 3-aminoflavone (3-af) are reported. The complexes of general formula [M(3-af)₂(H₂O)₂](NO₃)₂ · nH₂O], where M = Co(II), Ni(II), and Zn(II), and n = 0, 2, 0, respectively, and [Cu(3-af)₂(NO₃)₂] compound were prepared and studied. In particular, to investigate the binding in detail, the crystal structures of the free ligand (3-af) and [Cu(3-af)₂(NO₃)₂] (1) were determined. The new coordination compounds were identified and characterized by elemental analysis, magnetic measurements, and infrared and ligand-field spectra. The crystal structure of the Cu(II) complex reveals that the ligand acts as a N,O-bidentate chelate ligand forming a five-membered ring with the copper(II) ion. The copper(II) ion is octahedrally surrounded by the two amino nitrogens and two carbonyl oxygens from two chelating organic ligands in trans arrangement. Two molecules of coordinated nitrate anions occupy axial positions. The spectral and magnetic properties are in accordance with the structural data of the copper(II) compound. From X-ray powder-diffraction patterns and IR spectra, the complexes of nickel(II) (2) and cobalt(II) (3) were found to be mutually isomorphous. The results of the spectroscopic studies suggest a mononuclear structure of 2 and 3 complexes. The variable-temperature (1.8-300 K) magnetic susceptibility data of 2 indicate a weak ferromagnetic interaction. The magnetic behavior of complex 3 is characteristic of cobalt(II) systems with an important orbital contribution via spin-orbit-coupling and also suggests a weak ferromagnetic interaction.     

Structure and reactivity of [Ru(2,3-Medpp)2Cl2]

The structure and reactivity of the complex [Ru(2,3-Medpp)₂Cl₂](PF₆)₂ (2,3-Medpp⁺=2-[2-(1-methylpyridiniumyl)]-3-(2-pyridyl)pyrazine) was investigated by X-ray diffraction (XRD), ¹H NMR, redox, and UV-Vis absorption measurements. X-ray analysis shows that crystals obtained from an acetonitrile-toluene solution contain the trans-Cl₂, trans-pyrazine isomeric form, while ¹H NMR and redox measurements on the main product of the synthetic workup indicate the presence of the trans-Cl₂, cis-pyrazine isomer. In the dark at 70 °C, the complex [Ru(2,3-Medpp)₂Cl₂]²⁺ reacts slowly in acetonitrile isomerizing to the cis-[Ru(2,3-Medpp)₂(CH₃CN)Cl]³⁺ species. Under ambient light in the presence of excess AgNO₃ the cis-[Ru(2,3-Medpp)₂(CH₃CN)₂]⁴⁺ species is obtained.     

Crystal structure and linear chain antiferromagnetism in Mn(tricyanomethanide)2(4,4-bipyridine)2

A new linear chain antiferromagnet, namely Mn(tcm)₂(4,4^′-bipy)₂ (tcm=tricyanomethanide and bipy=bipyridine) has been synthesized and characterized by X-ray crystallography and magnetic susceptibility measurements. Each Mn²⁺ is high-spin S=5/2 and linked to nearest-neighbor spin sites via μ-bridged tcm ligands to form a 1D linear chain while the bipy ligands are monodentate and segregate the chains. Magnetically, a broad maximum in χ^′(T) is observed at 2.1 K and likely signifies short-range magnetic order within the chains. A least-squares fit of the χT(T) data to a classical-spin Fisher chain model yielded good agreement for g=2.008(1) and J=−0.217(4) K. No long-range magnetic ordering is observed above 1.6 K due to the presence of very weak interchain magnetic interactions as indicated by inclusion of a mean-field model that gave zJ^′=−0.009(1) K.     

A seven-coordinate Fe compound: [Fe{O(CH2CO2)2}(H2O)2(NO3)]. Preparation, structure and magnetic properties

A seven-coordinate Fe^III complex, [Fe(oda)(H₂O)₂(NO₃)], was obtained after dissolving Fe(NO₃)₃ · 9H₂O in an aqueous solution of oxydiacetic acid (H₂oda) at room temperature. In the solid state, the Fe^III center adopts a pentagonal bipyramid geometry with an {FeO₇} core formed by a tridentate oda²⁻ and a bidentate in the equatorial plane, and two axial water molecules. Magnetic measurements and EPR spectra revealed the presence of S = 5/2 Fe^III centers with rhombic zero field splitting parameters (D = 0.81 cm⁻¹, E/D = 0.33 ). Weak antiferromagnetic interactions with J ≈ −0.06 cm⁻¹ operating between neighboring Fe ions connected through Fe-O-C-O?H-O-Fe paths are estimated using the molecular field approximation.