Nitronyl Nitroxide Radical Complexes Research Articles

Three Novel Cyclic Zn(II)–Nitronyl Nitroxide Radical Complexes: Synthesis, Crystal Structures, and Properties

Three Novel Cyclic Zn(II)–Nitronyl Nitroxide Radical Complexes: Synthesis, Crystal Structures, and Properties

Magnetic slow relaxation of pseudo-binuclear Ln(III)-nitronyl nitroxide radical complexes involving non-covalent O⋯O interactions

Five new nitronyl-nitroxide radical-Ln(III) complexes, [Ln(hfac)3(NITPh-2-OCH2Ph)(IMHPh-2–OCH2Ph)] (Ln = Tb(1), Dy(2)) and [Ln(hfac)3(NITPh-2-OCH2Ph)2] (Ln = Ho(3), Er(4), Yb(5)) (hfac = hexafluoroacetylacetonate, NITPh-2-OCH2Ph = 2-(2-benzyloxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, IMHPh-2-O-CH2Ph = the reduced derivative of NITPh-2-OCH2Ph), have been synthesized and characterized. The single-crystal X-ray diffraction analysis shows that all these complexes crystallize in triclinic P1−space group, and are composed of mononuclear molecules. The central Ln(III) ion is eight-coordinated by three bidentate chelating hfac anions and two monodentate NITR (or IMHR) molecules, with a dodecahedron environment. There arise a common interesting structural feature for these complexes that the mononuclear molecules form pseudo-binuclear structures through intermolecular non-covalent N–O⋯O–N contacts of nitroxide groups. All of them show intramolecular weak antiferromagnetic interactions between Ln(III) ion and radicals. Alternating current (ac) magnetic susceptibilities display a frequency-dependent characteristic for both Tb(1) and Dy(2), typical of magnetic slow relaxation of single-molecule magnet (SMM) behavior.

Slow magnetic relaxation of Ln(III)-nitronyl nitroxide radical complexes with shortest non-covalent O⋯O contacts

Two new complexes, Ln(hfac)3(NITPhOA)2 (Ln = Tb(1), Dy(2); NITPhOA = 2-(4′-amyloxyphenyl)−4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate) have been synthesized and characterized. Single crystal X-ray diffraction analysis reveals that both complexes show mononuclear tri-spin structures. The central Ln(III) ion is eight-coordinated by three hfac anions and two NITPhOA molecules, in which the NITPhOA radical acts as monodentate ligand through the NO groups, and the Ln(III) center exhibits a dodecahedron environment. It's interesting that the mononuclear units form a pseudo-one-dimensional chain structure through intermolecular non-covalent N–O⋯O–N contacts of nitroxide groups for 1. Alternating current (ac) magnetic susceptibilities show a frequency-dependent characteristic for both 1 and 2, typical of slow relaxation of magnetization. It's the first time for a lanthanide–radical complex to form a pseudo one-dimensional structure through non-covalent O⋯O contacts.

A novel rare-earth nitronyl nitroxide radical complex as a high-efficiency sensor for Cr3+ and Cr2O72− ions in aqueous solutions

In this article, a new complex with formula [Eu(hfac)3(NITPh-DOMe)2] (1) (hfac = hexafluoroacetylacetonate, NITPh-DOMe =2-(3′,4′-dioxylmethylene-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) has been successfully synthesized. Central Eu(III) ions of complex 1 are eight coordinated by two NITPh-DOMe radicals and three hexafluoroacetylacetonate ligands. The luminescent explorations show that complex 1 with high sensitivity, selectivity, almost linear at low concentration and the low detection limit for detection of Cr3+ (1 μM) and Cr2O72− (0.1 μM) ions in aqueous solutions.

Three cyclic lanthanide-radical complexes syntheses, crystal structures and magnetic properties

Three lanthanide–nitronyl nitroxide radical complexes [Ln(hfac)3(NIT-2Br-4Py)]2 (Ln(III) = Gd (1), Tb (2), Dy (3); hfac = hexafluoroacetylacetonate; NIT-2Br-4Py = 2-(2′-bromo-4′-pyridyl)-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)) have been synthesized. Single crystal X-ray diffraction analysis reveals that complexes 1–3 are isomorphous in which NIT-2Br-4Py acts as a bridging ligand linking two Ln(III) ions through the nitrogen atom of pyridine ring and the oxygen atom of NO group to form a four-spin system. The magnetic studies show that ferromagnetic coupling interaction between Ln(III) ions and nitronyl nitroxide radical. Moreover, ac measurements show that Tb(III) complex exhibits frequency-dependent signals at low temperature.

Four new rare-earth nitronyl nitroxide radical complexes: Magnetic and luminescent properties

Four new rare-earth nitronyl nitroxide radical complexes, [Ln(hfac)3(NITPh-Pa)2][0.5CH3(CH2)5CH3] (Ln = Gd(1), Tb(2), Dy(3), Ho(4), hfac = hexafluoroacetylacetonate, NITPh-Pa = 2-(3′,4′-dioxylmethylene-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide), have been synthesized. The X-ray crystal structure analysis revealed that four compounds have similar mononuclear tri-spin structures, in which the Ln(III) ions are eight-coordinated by two nitronyl nitroxide radicals and three hexafluoroacetylacetonate ligands to form a slightly distorted dodecahedron. In complexes 1–4, isolated mononuclear molecules connect each other through intermolecular hydrogen bonds to form 3D supermolecular framework. Magnetic investigation indicates there are ferromagnetic interactions between Gd(III) ions and radicals in complex 1. Alternating current(ac) magnetic susceptibilities of complexes 2 and 3 show that there are no non-zero out-of-phase signal, which indicates the inexistence of slow magnetic relaxation. The luminescence properties of complex 2 exhibit the characteristic emission peaks of Tb3+ ions and the potential for recognition of Cr2O72− and Cr3+ ions. Furthermore, nearly linear at low concentration and the low detection limit (0.01 μM) indicate that complex 2 may potentially be acted as luminescence-based sensor for quantitative and highly sensitive detection of Cr2O72− ion.

Crystal Structure and Magnetic Property of Novel Ln(III)-Nitronyl Nitroxide Radical Complex

Four novel rare-earth complexes based on a new nitronyl nitroxide radical have been synthesized and characterized as: {[Ln (hfac)3(NITPhBrF)2]·0.5CH2Cl2}(Ln = Sm (1), Gd (2), Tb (3)), {[Ln (hfac)3(NITPhBrF)2]}(Ln = Dy (4)) (hfac = hexafiuoroacetylacetonate; NITPhBrF = 2-(2-fluoro-5-bromophenyl)-tetramethylimidazoline-1-oxyl-3-oxide). The single-crystal X-ray diffraction revealed that compound 1, 2 and 3 are isostructural, which crystallize in the monoclinic space group P21/n, and compound 4 is in the P-1 triclinic space group. These complexes possess mononuclear structure in which the central Ln (III) is octacoordinated by six oxygen atoms from three bidentate hfac ligands and two oxygen atoms from two NITPhBrF ligands. DC magnetic susceptibilities were measured under 1kOe in the 2 - 300 K range. The studies reveal that there exit ferromagnetic interaction between the Gd (III) and radical ligands, and the antiferromagnetic interaction between the two intramolecular radicals in Gd (2). Meanwhile complexes Tb (3) and Dy (4) exhibit antiferromagnetic interactions.

Three lanthanide–nitronyl nitroxide complexes: Syntheses, crystal structures and magnetic properties

Three rare earth–nitronyl nitroxide radical complexes [Ln(hfac)3(NIT-1′-MeBzIm)] (Ln(III)=Gd 1, Tb 2, Dy 3; hfac=hexafluoroacetylacetonate; NIT-1′-MeBzIm=2-{2′-[(l′-methyl)-benzimidazolyl]}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been successfully prepared and structurally characterized. X-ray crystallographic analysis reveals that all the three complexes are isomorphous. The center lanthanide(III) ions are eight-coordinated to one NIT-1′-MeBzIm and three hexafluoroacetylacetonate ligands. The NIT-1′-MeBzIm acts as a bidentate ligand via its nitrogen atom of the imidazole ring and the oxygen atom of the N–O group. The magnetic properties of complexes 1, 2 and 3 were studied. All of them exhibit ferromagnetic interaction. AC magnetic susceptibility studies show that Tb complex displays frequency-dependent signals at low temperature suggesting that it behaves as SMM.

Single-molecule magnets based on rare earth complexes with chelating benzimidazole-substituted nitronyl nitroxide radicals

Three rare earth-nitronyl nitroxide radical complexes [Ln(tfa)(3)(NIT-BzImH)] (Ln(III) = Gd 1, Tb 2, Dy 3; tfa = trifluoroacetylacetonate; NIT-BzImH = 2-(2'-benzimidazolyl)-4,4,5,5-tetramethylimidazolyl-1-oxyl-3-oxide) have been successfully prepared and structurally characterized. X-Ray crystallographic analysis reveals that all three complexes are isomorphous. Their crystal structures consist of mononuclear molecule units in which lanthanide(III) is 8-coordinated to one NIT-BzImH and three trifluoroacetylacetonate ligands. The NIT-BzImH acts as a bidentate ligand via its nitrogen atom of the imidazole ring and the oxygen atom of the N-O group. The magnetic properties of complexes 1-3 were studied. All the three complexes exhibit ferromagnetic Ln(III)-radical coupling. AC magnetic susceptibility studies of 2 and 3 show slow magnetic relaxation suggesting that they behave as SMMs.

Synthesis, structural and magnetic characterization of a new copper(II)-nitronyl nitroxide radical complex

In this work we describe the structure and the magnetic properties of a new copper(II)-NIT complex, where NIT stands for nitronyl nitroxide radical. This was achieved using (NBu4)4[Cu2(bopba)] as a precursor (where NBu4+ is the tetrabutylammonium cation and bopba is bis-o-phenylenebis(oxamate)), whose crystal structure was resolved and its magnetics properties studied. From the reaction of this precursor with a cationic nitronyl nitroxide radical, a new compound was prepared and magnetically characterized, namely (pEtRad)4[Cu2(bopba)] (where pEtRad+ stands for the cationic para-2-(4-pyridil)-4,4,5,5-tetramethylimidazoline-1 -oxyl-3-oxide radical). The magnetic properties suggest that in this six-spin complex there is a competition between short range ferromagnetic and antiferromagnetic interactions. The ferromagnetic interaction can be explained by the orthogonality of the involved magnetic orbitals.

Ferromagnetic interactions in Ru(iii)–nitronyl nitroxide radical complex: a potential 2p4d building block for molecular magnets

The reaction between [Ru(salen)(PPh3)Cl] and the 4-pyridyl-substituted nitronyl nitroxide radical (NITpPy) leads to the [Ru(salen)(PPh3)(NITpPy)](ClO4)(H2O)2 complex while the reaction with the azido anion (N3-) leads to the [Ru(salen)(PPh3)(N3)] complex 2 (where salen2- = N,N'-ethan-1,2-diylbis(salicylidenamine) and PPh3 = triphenylphosphine). Both compounds have been characterized by single crystal X-ray diffraction. The two crystal structures are composed by a [Ru(III)(salen)(PPh3)]+ unit where the Ru(III) ion is coordinated to a salen2- ligand and one PPh3 ligand in axial position. In 1 the Ru(III) ion is coordinated to the 4-pyridyl-substituted nitronyl nitroxide radical whereas in 2 the second axial position is occupied by the azido ligand. In both complexes the Ru(III) ions are in the same environment RuO2N3P, in a tetragonally elongated octhaedral geometry. The crystal packing of 1 reveals pi-stacking in pairs. While antiferromagnetic intermolecular interaction (J2 = 5.0 cm(-1)) dominates at low temperatures, ferromagnetic intramolecular interaction (J1 = -9.0 cm(-1)) have been found between the Ru(III) ion and the coordinated NITpPy.

A rational approach to the modulation of the dynamics of the magnetisation in a dysprosium–nitronyl-nitroxide radical complex

A control of the dynamics of the magnetisation is chemically achieved in a ring-like Dy-radical based molecule, allowing the estimation of the quantum tunneling frequency with a (4)He-cooled susceptometer.

Ferromagnetic interactions in a Zn(II)–nitronyl nitroxide complex with dicyanoaurate(I) bridges

A two-dimensional Zn(II)-nitronyl nitroxide radical complex, Zn(NIT4Py)2[Au(CN)2]2 (NIT4Py = 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) was synthesized and characterized by elemental analyses, IR spectroscopy and single-crystal X-ray diffraction methods. The complex is monoclinic, space group C2/c, with a = 26.294(9), b = 7.167(2), c = 18.532(6) Å, β = 111.758(5)°, V = 3243.6(18) Å3, Z = 4, and R 1 [I > 2σ (I)] = 0.0348, and has an infinite two-dimensional network motif. Magnetic studies showed ferromagnetic coupling between two radicals through Zn(II).

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 μ 2-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.

One‐dimensional Diamagnetic‐metal Nitronyl Nitroxide Radical Complexes with Dicyanoargentate(I) Bridges: M(NIT4Py)2[Ag(CN)2]2 (M= Zn, Cd)

AbstractTwo diamagnetic‐metal nitronyl nitroxide radical complexes with dicyanoargentate(I) bridges M(NIT4Py)2[Ag(CN)2]2 (M= Zn, Cd) were synthesized. X‐ray crystallography reveals that the two compounds are isomorphous, which crystallize in the triclinic ${\rm P}{\bar 3}$ space group. Their structures consist of infinite chains of M(NIT4Py)2 units linked by [Ag(CN)2]− μ2‐bridging ligands. The magnetic measurements showed that the χMT values are nearly constants at higher temperature for both complexes. The sharp decreasing of χMT values at lower temperature are related to intermolecular antiferromagnetic interactions, which result from the shortest interchain contacts of nitroxide groups in the crystals.

Synthesis, structure and magnetic behavior of a novel 1-D chain tethered by nickel(II)-4-pyridyl-substituted nitronyl nitroxide radical complex and TCB

A novel one-dimensional nickel(II) complex incorporating a nitroxide radical with the formula {[Ni(NITpPy) 2(TCB)(H 2O) 2]·2H 2O} n (NITpPy=2-(4 ′-pyridyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide and TCB=1,4-dicarboxy-2,5-dicarboxylatobenzene dianion) has been synthesized and characterized. Theoretical analysis of the variable-temperature magnetic susceptibility data of the complex reveals that there are two kinds of antiferromagnetic intrachain interactions.