Nitronyl Nitroxide Radical Research Articles

Synthesis and Characterization of Two Chiral Pyrrolyl α-Nitronyl Nitroxide Radicals and Determination of their Cytotoxicity and Radioprotective Properties in C6 Cells and Mice under Ionizing Radiation

In this study, two chiral nitronyl nitroxyl radicals, L1 and D1, were synthesized and evaluated for their potential radioprotective properties invitro and invivo. We synthesized the new stable nitronyl nitroxide radicals, L1 and D1, according to Ullman’s method, and their chemical structures were characterized using UV-vis absorption, electron spin resonance (ESR), and circular dichroism (CD) spectra. The cytotoxicity of L1 and D1 on C6 glioma cells (C6 cells) was examined using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. To study the anti-radiation effects of L1 and D1 on C6 cells, we determined the optical density (OD) values of irradiated C6 cells using the MTT assay. The effects of L1 and D1 on the survival rate of mice after radiation exposure was evaluated. To demonstrate the influence of L1 and D1 pre-treatment on the antioxidant enzyme system, we studied the activities of superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and glutathione peroxidase (GSH) in mouse plasma after exposure to 6.5 Gy gamma radiation. The results showed that L1 and D1 did not have any obvious cytotoxicity at concentrations below 125μgmL−1. Moreover, L1 and D1 had the same cytotoxic effects on C6 cells. L1 and D1 significantly enhanced C6 cell survival after 8, 10, and 12 Gy radiation exposure, and there was no significant difference in the OD values between L1 and D1. The effects of these drugs on mouse survival rates were dose-dependent. Pre-treatment with different concentrations of L1, D1, or WR2721 significantly increased the activity of SOD, CAT, and GSH and significantly decreased the activity of MDA compared with radiation exposure only. In addition, the activities of SOD, CAT, and GSH in the L1 group were higher than those in the D1 group, whereas the activity of MDA was lower. Therefore, L1 and D1 have potential as safe and efficient therapeutic drugs against radiation damage.

Synthesis of a series of hetero-multi-spin Ln2Cu3 complexes based on a methyl-pyrazole nitronyl nitroxide radical with slow magnetic relaxation behaviors.

Multinuclear hetero-tri-spin complexes based on a methyl-pyrazole nitronyl nitroxide radical, namely, [Ln2Cu3(hfac)12(4-NIT-MePyz)4] (Ln = Gd(1), Tb(2), Dy(3); hfac = hexafluoroacetylacetone; 4-NIT-MePyz = 2-{4-(1-methyl)-pyrazolyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been successfully obtained through a one-pot reaction of the radical ligand (4-NIT-MePyz) with Cu(hfac)2 and Ln(hfac)3. These 2p-3d-4f complexes exhibit five-nuclear structures with the sequence [Cu-Rad-Ln-Rad-Cu-Rad-Ln-Rad-Cu], in which each 4-NIT-MePyz radical acting as a bidentate bridging ligand is coordinated to one Ln(hfac)3 unit through one oxygen atom of the NO groups and to one Cu(hfac)2 unit with one nitrogen atom from the pyrazole ring. For complex 1, based on the spin Hamiltonian calculations and MAGPACK program, it is concluded that there exist ferromagnetic couplings between GdIII and NIT radicals, as well as between CuII and free radicals with J1 = 6.8(1) and J3 = 1.3(2) cm-1, respectively, and antiferromagnetic interactions between radical and radical with J2 = -2.8(5) cm-1. Complex 2 shows frequency-dependent out-of-phase signals under a zero or 2000 Oe dc field indicating single-molecule magnetic behavior.

Crystal Structure of Metal Complexes with 2-Imidazoline Nitroxides and Dicyanamide

The structure of heterospin complexes[M(DCA)2L2x]·yH2O, where M = Mn, Co, Ni, Cu, Lx is the nitronyl nitroxide radical; DCA is the dicyanamide anion, y = 0, 1, or 2 is studied. It is found that the nature of[M(DCA)2L2x]·yH2O is characterized by the formation of multiple hydrogen bonds generating ribbons, layers, or frameworks in the crystals. The analysis of magnetostructural correlations by means of band calculations of the electronic structure confirms the occurrence of ferromagnetic exchange between the unpaired electrons of paramagnetic centers in solid [Cu(DCA)2L21]·2H2O when the distances between the copper ion and the coordinated N-O group are short.

Rational Design and Synthesis of a Chiral Lanthanide-Radical Single-Chain Magnet.

By the reaction of an enantiopure nitronyl nitroxide radical, 2-((1 R)-(-)-myrtenal)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide), abbreviated as (1 R)-(-)-myrtenal-NIT, and Dy(hfac)3·2H2O (hfac = hexafluoroacetylacetonate), we successfully obtained a homochiral DyIII-radical chain compound [Dy(hfac)3(1 R)-(-)-myrtenal-NIT] n (1) with full characterization. 1 crystallizes in the chiral P21 space group and exhibits slow magnetization relaxation, holding an effective energy barrier (Δτ/ kB) of 64.6 K (44.9 cm-1) and an attempt time τ0 of 1.0 × 10-7 s. The correlation energy (Δξ/ kB) of this chain is 10.4 K (7.2 cm-1), and the effective Curie constant is 2.8 cm3·K·mol-1. Additionally, 1 exhibits temperature-dependent hysteresis loops below 4 K, with a maximum coercive field of 0.51 T at 2 K.

Two new lanthanide-nitronyl nitroxide complexes: Magnetic and fluorescence properties

Two new lanthanide complexes of nitronyl nitroxide radical have been synthesized and characterized on the structure, magnetism and fluorescence: [Ln(hfac)3(NITPh-(OCH3)2)2](Ln = (Tb(1),Dy(2)), (NITPh-(OCH3)2 = 2-(3′,4′-dimethoxy-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide); hfac = hexafluoroacetylacetonate). Two complexes crystallize in monoclinic space group C2/c, which have similar mononuclear structures. The central metal ion is eight coordinated by six oxygen atoms from three hfac molecules and two oxygen atoms from two nitronyl nitroxide radicals. The varying temperature magnetic susceptibility indicates that there are weak antiferromagnetic interaction between metal ions and nitronyl nitroxide radicals in complexes 1 (zJ′ = −0.145 cm−1) and 2 (zJ′ = −0.140 cm−1). Ac magnetic susceptibility studies exhibit no single-molecule magnet behavior in complexes 1 and 2. In addition, the fluorescence properties of 1 show that it is an excellent fluorescent probe of recognizing Cr2O72− anion. Because of the linear relationship at low concentration and detection limit reached 1 × 10−7 M, it can be used as a luminescence-based sensor for quantitative analysis.

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.

A Crystallographic Study of a Novel Tetrazolyl-Substituted Nitronyl Nitroxide Radical

Spin-labelled compounds are widely used in chemistry, physics, biology, and material sciences, but the directed synthesis of some functionalized organic radicals is still a challenge. We succeeded in the preparation of a tetrazolyl-substituted nitronyl nitroxide radical in pure crystalline form. According to the single-crystal X-ray data, intra- (NH…O, 2.43 Å) and inter-molecular hydrogen bonds (NH…O, 1.91 Å) are formed between NH groups of the tetrazole cycles and O atoms of the paramagnetic moieties. The intermolecular H-bonds connect the molecules forming chains along the a-axis. Moreover, there are short intermolecular contacts between the O atoms (3.096 Å) and between the O and C atoms (3.096 Å) of the nitronyl nitroxide moieties within the chain. The spin-unrestricted broken-symmetry calculations performed at the BS-UB3LYP/def2-TZVP level of theory predicted a sufficient ferromagnetic interaction (J ≈ 20 cm–1) between the adjacent radicals inside the chain, but a weak antiferromagnetic interaction (−J ≤0.2 cm−1) between the nearest radicals belonging to the different chains. Thus, a rare case when stable radicals, the tetrazolyl-substituted nitronyl nitroxides, are ordered into ferromagnetic chains was revealed; an investigation of the magneto-structural correlations inherent in the nitroxide radical will demand a special experiment in the sub-Kelvin regime.

Theoretical insights into the magneto-structural correlation: Comparison between series of copper(I) and silver(I) metal complexes with nitronyl nitroxide radicals

Using nitronyl nitroxide radicals, we presented a comparative study of magneto-structural correlations between series of CuI and AgI models (Cu(a) ∼ Cu(d) and Ag(a) ∼ Ag(d), modified from [CuI(immepy)2]PF6 and [AgI(impy)2]PF6 (Oshio et al., 1997). Cu(a) ∼ Cu(d) possess three characteristics that are significantly different from Ag(a) ∼ Ag(d) for the more utilization of CuI than that of AgI in the ferromagnetic joints of radical networks. (1) Structural shorter Cu-N length in Cu(a) ∼ Cu(d) than corresponding Ag-N length in Ag(a) ∼ Ag(d) leads to the quite larger Wiberg bond index (WBI), ∇2ρ(r) values, and metal atomic spin densities between triplet (T) and broken-symmetry (BS) states (ΔρT-BS) of the former than that of the latter. (2) From each of AgI (Ag(a) ∼ Ag(d)) to the corresponding one of CuI (Cu(a) ∼ Cu(d)), the spin density increases up to one or two order of magnitudes, which indicates the more notable spin delocalization from ONCN groups (paramagnetic centers) to CuI than that to AgI. Changing the dihedral angle (θ) between two radical components, the variation of the magnetic coupling constants (Jab) is directly proportional to the spin density of CuI but inversely proportional to that of one ONCN group. (3) Due to the larger d orbital distributions of CuI than that of AgI in the SOMOs, large metal-ligand charge transfer (MLCT) occurs in Cu(a) ∼ Cu(d) but little in Ag(a) ∼ Ag(d). The broken orthogonality is not evidently associated with the significantly different magnetic coupling interactions between CuI and AgI models.

Nitronyl nitroxide radicals at the interface: a hybrid architecture for spintronics

Cross-fertilization between molecular magnetism and organic spintronics is leading to the development of concepts based on the use of molecules as active elements to influence spin-related transport processes. The research on hybrid devices, where the magnetic molecules in contact with the electrodes influence the spin and charge injection and transport, is moving its first steps but is expected to quickly expand the technological potential of molecular spintronics and quantum computing. New exciting possibilities, linked to the individual properties of these molecular units and to their interaction with novel substrates, are getting disclosed. The chemical functionalization of these molecules is the tool which allows to tune their electronic and magnetic properties and to directly create these hybrid architectures. However, the coupling of molecules with the spin transport phenomena is far from being trivial. First, the stability of molecules in the device environment must be tested and, subsequently, the organization of molecules in the desired architectures must be mastered permitting a careful control of the interactions between inorganic substrates and molecular layers. Here we summarize how this research activity can be developed in the case of one of the simplest magnetic molecules, an organic radical. We will start from an innocent surface, such as gold, to move then toward a real-device environment. We evidence how these efforts can result in a surface-specific molecular-based method to influence the spin injection and transport phenomena, paving the way for developing new devices in which a fine-tuning of magnetic features is required.

Construction and Magnetic Study of One‐Dimensional Lanthanide–Radical Chains Involving Pyridinone‐Substituted Nitronyl Nitroxide Radicals

A new nitronyl nitroxide radical‐containing pyridinone group (NIT‐PhPyO, 1) has been synthesized {NIT‐PhPyO = 2‐[4‐(4‐pyridinone)phenyl]‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide}. By using this functionlized nitronyl nitroxide, two isomorphic lanthanide–nitronyl nitroxide radical compounds [{Ln(hfac)3}3(NIT‐PhPyO)2]n (Ln = Gd 2 and Dy 3; hfac = hexafluoroacetylacetonate) have been successfully obtained. X‐ray spectroscopic analysis reveals that complexes 2 and 3 possess a 1D chain structure with Ln2O2 binuclear units, which represent the first examples of Ln–radical chains involving binuclear Ln2O2 units. Analysis of the magnetic data indicates that a weak antiferromagnetic coupling exists between two Gd3+ ions, while the magnetic interaction between the GdIII ion and the coordinated nitroxide group is ferromagnetic. Alternating current (ac) magnetic studies indicate that compound 3 displays slow magnetic relaxation behavior at low temperature.

Radical Cation π-Dimers of Conjugated Oligomers as Molecular Wires: An Analysis Based on Nitronyl Nitroxide Spin Labels.

Nitronyl nitroxide (NN)-substituted conjugated oligomers, which were expected to self-associate in biradical cation states, were designed to analyze the capability of π-dimers as molecular wires. The oligomer moieties were composed of dithienyl-N-methylpyrrole with methoxy substituents at the inner β-position of thiophene rings (DTP-NN. ) and its propylenedioxythiophene (ProDOT) inserted derivative (DTP-P-NN. ), or two ethylenedioxythiophene (EDOT) and two ProDOT units (E2 P2 -NN. ). Among them, chemical one-electron oxidation gave biradical cations (DTP-P).+ -NN. and (E2 P2 ).+ -NN. that formed π-dimers (DTP-P-NN. )22+ and (E2 P2 -NN. )22+ in dichloromethane at low temperatures. ESR studies of (DTP-P-NN. )22+ and (E2 P2 -NN. )22+ showed the presence of a relatively strong exchange interaction between two NN radicals through the radical cation π-dimer moieties. DFT calculations supported these experimental results and predicted that exchange interactions between two NN radicals were comparable or stronger than those through covalently linked quaterthiophene. Thus, the conjugated oligomer radical cation π-dimers acted as efficient molecular wires for electronic communication.

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.

Electron Spin Resonance Study of Molecular Orientation and Dynamics of Phenyl Imino and Nitronyl Nitroxide Radicals in Organic 1D Nanochannels of Tris( o-phenylenedioxy)cyclotriphosphazene.

Imino and nitronyl nitroxide (IN and NN, respectively) radicals such as phenyliminonitroxide (PhIN) and phenylnitronylnitroxide (PhNN), respectively, were dispersed in the organic 1D nanochannels of tris( o-phenylenedioxy)cyclotriphosphazene (TPP). Electron spin resonance (ESR) measurements were conducted on these inclusion compounds (ICs) in the temperature range 4.2-300 K. The modulated-septet ESR spectra of TPP ICs using PhIN observed in the range 165-258 K were reproduced with the EasySpin program package using a model in which some of the PhIN molecules underwent uniaxial rotational diffusion in the TPP nanochannels around the molecular long axis corresponding to the principal y-axis of the g tensor. However, for the TPP IC using PhNN, complicated ESR spectra were observed, which were not consistent with the modulated quintet observed in solution or in the fast-motion limit in solids. These spectra were reproduced by the superposition of a quintet originating from rotational diffusion of PhNN molecules and a septet based on rotational diffusion of PhIN molecules generated in the synthetic process. The rotational diffusion activation energies of PhIN and PhNN in the TPP nanochannels were estimated to be 19 and 45 kJ mol-1 using an Arrhenius plot, respectively. These were consistent with that for NN radicals in the 1D nanochannels of 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) (37-54 kJ mol-1) with a larger pore diameter than TPP reported in our previous study, or with that for 4-substituted-2,2,6,6-tetramethyl-1-piperidinyloxyl (4-X-TEMPO) in TPP nanochannels (5-26 kJ mol-1) with regard to molecular size or host-guest or guest-guest interactions. These results indicate that not only the NN group but also IN may be used for the clarification of chemical or biological structures of nanomaterials such as nanosized cavities.

Three new lanthanide compounds based on nitronyl nitroxide radical: Crystal structure, magnetic properties, and luminescence properties

Three new lanthanide compounds were obtained using 2-(3-methylthiophene)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) (NIT-3Methien). These compounds, [Gd(hfac)3(NIT-3Methien)2]∙0.5CH3(CH2)5CH3 (1: Half n-heptane trihexafluoroacetylacetonate-di-2-(3-methylthiophene)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide gadolinium(III)), [Tb(hfac)3(NIT-3Methien)2]∙0.5H2O (2: Half Hydrate trihexafluoroacetylacetonate-di-2-(3-methylthiophene)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide terbium(III)), and [Dy(hfac)3(NIT-3Methien)2]∙0.5H2O (3: Half Hydrate trihexafluoroacetylacetonate-di-2-(3-methylthiophene)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide dysprosium(III)), (CH3(CH2)5CH3 = n-heptane), (hfac = hexafluoroacetylacetonate), were characterized structurally and magnetically. The three compounds crystallize in the triclinic space group P1( - ). Ln(III) ion was eight-coordinate by six oxygens from three hfac ligands and two oxygens from two radicals. In 1, direct current (DC) magnetic studies reveal ferromagnetic interactions between the Gd(III) ion and radicals with J1 = 0.94 cm−1. In 2 and 3, there are antiferromagnetic interactions between the Tb(III), or Dy(III) ions and radicals. The luminescence characterizations show that 2 exhibits highly selective luminescent sensing of Cr2O72− ions.

Magnetic Exchange Interaction in Nitronyl Nitroxide Radical-Based Single Crystals of 3d Metal Complexes: A Combined Experimental and Theoretical Study.

Two stable nitronyl nitroxide free radicals {R1 = 4′-methoxy-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (NNPhOMe) and R2 = 2-(2′-thienyl)-4,4,5,5-tetramethylimidazoline 3-oxide 1-oxyl (NNT)} are successfully synthesized using Ullmann condensation. The reactions of these two radicals with 3d transition metal ions, in the form of M(hfac)2 (where M = Co or Mn, hfac: hexafluoroacetylacetone), result in four metal–organic complexes Co(hfac)2(NNPhOMe)2, 1; Co(hfac)2(NNT)2·(H2O), 2; Mn(hfac)2(NNPhOMe)·x(C7H16), 3; and Mn(hfac)2(NNT)2, 4. The crystal structure and magnetic properties of these complexes are investigated by single-crystal X-ray diffraction, dc magnetization, infrared, and electron paramagnetic resonance spectroscopies. The compounds 1 and 4 crystallize in the triclinic, P1̅, space group, whereas complex 3 crystallizes in the monoclinic structure with the C2/c space group and forms chain-like structure along the c direction. The complex 2 crystallizes in the monoclinic symmetry with the P21/c space group in which the N–O unit of the radical coordinates with the Co ion through hydrogen bonding of a water molecule. All compounds exhibit antiferromagnetic interactions between the transition metal ions and nitronyl nitroxide radicals. The magnetic exchange interactions (J/KB) are derived using isotropic spin Hamiltonian H = −2J∑(SmetalSradical) for the model fitting to the magnetic susceptibility data for 1, 2, 3, and 4. The exchange interaction strengths are found to be −328, −1.25, −248, and −256 K, for the 1, 2, 3, and 4 metal–organic complexes, respectively. Quantum chemical density functional theory (DFT) computations are carried out on several models of the metal–radical complexes to elucidate the magnetic interactions at the molecular level. The calculations show that a small part of the inorganic spins are delocalized over the oxygens from hfac {∼0.03 for Co(II) and ∼0.015 for Mn(II)}, whereas a more significant fraction {∼0.24 for Mn(II) and ∼0.13 for Co(II)} of delocalized spins from the metal ion is transferred to the coordinated oxygen atom(s) of nitronyl nitroxide.

1,3-Diaza[3]ferrocenophanes functionalized with a nitronyl nitroxide group

An aza-Wittig reaction of 1,1′-bis(triphenylphosphoranylidenamino)-ferrocene with 4-iodo-, 2,5-difluoro-4-iodo-, pentafluoro-, or 4-methoxycarbonylphenylisocyanates is described here. Intermediate betaines, which are products of a nucleophilic attack of the nitrogen atom of the remaining iminophosphorane moiety on the carbon atom of the carbodiimide functional group, were isolated; their structures were proved by monocrystal X-ray diffraction. Hydrolysis of the betaines under mild conditions gave corresponding arylamino-1,3-diaza[3]ferrocenophanes. On the other hand, as demonstrated, under more rigid conditions, the betaines could be converted into ferrocenophanes with the 1,3-diazetidine-2,4-diimine coupler. The iodo- or diiodo-derivatives of 1,3-diaza[3]ferrocenophanes were cross-coupled with a nitronyl nitroxide-2-ide gold(I) complex to obtain corresponding metallocenophanes functionalized with the nitronyl nitroxide group(s). The molecular and crystal structures of the halogenated and spin-labeled ferrocenophanes were solved by X-ray analysis. In arylamino-1,3-diaza[3]ferrocenophanes, according to cyclic voltammetry, the position of the quasi-reversible oxidation peak associated with the Fe(II)/Fe(III) redox couple deviates within 0.09 V depending on substituents in the arylamino group.

Multifunctional Magnetic Materials of Organic Origin for Biomedical Applications: A Theoretical Study

AbstractSix different diradical systems based on azulene coupler and nitronyl nitroxide radical moieties have been studied theoretically. Among them, three ferromagnetic diradicals are chosen for further calculation to assess their usability in different biological applications such as two‐photon absorption photodynamic therapy (TPA‐PDT) and magnetic reso nance imaging contrast agents (MRICA). The TPA cross‐section values have been calcu lated to judge their efficiency as TPA‐PDT photosensitizing agents. Calculated values of TPA cross‐section lie in the range of commonly used photosensitizers for PDT. It is seen that the ferromagnetic diradicals can act as very good MRI contrast agents due to their high magnetic anisotropy characteristics. In connection to the magnetic anisotropy, the zero‐field splitting (ZFS) parameters are also computed using density functional theory (DFT) based methods. It is found that the proposed diradicals can show good relaxation behaviour and consequently act as efficient MRI contrast agents. Thus, one can anticipate the multifunctional biological activity of these diradicals.

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.

Temperature-Dependent Intramolecular Spin Coupling Interactions of a Flexible Bridged Nitronyl Nitroxide Biradical in Solution.

A biradical consisting of two nitronyl nitroxide (NN) radicals bridged by diphenyl-hexaethylene glycol chain [phenyl-O-(CH2CH2O)6-phenyl (GBN1)] was synthesized and investigated using electron paramagnetic resonance (EPR) spectroscopy in solution at different temperature ranges. The reversible temperature dependence behavior of spin coupling exchange is comprehensively reflected by the different lifetime of conformations due to a tumbling motion of the flexible hexaethylene glycol chain. The influences of different solvent on the exchange interactions between the radical entities are described by a two-conformational model, which was, for the first time, applied for di-NN molecule and revealed the thermodynamic parameters enthalpy and entropy (ΔH and ΔS) of the conformational changes. The positive value of enthalpy indicates lower energy of the stretched form (as calculated) compared to the bent form. The transition enthalpy in polar MeCN is larger than in toluene and the positive entropy sign indicates more chain conformation options in the bent state. The magnetic properties of this molecule were investigated in solid state by magnetization studies and EPR spectroscopy.

A family of multi-spin rare-earth complexes based on a triazole nitronyl nitroxide radical: synthesis, structure and magnetic properties.

The combination of LnIII ions (GdIII, TbIII or DyIII) and a triazole nitronyl nitroxide radical (4-Me-3-NITtrz) as spin carriers results in two mononuclear and one binuclear compounds, namely, [Ln(hfac)3(4-Me-3-NITtrz)(H2O)] (Ln = Gd(1), Tb(2); hfac = hexafluoroacetylacetone; 4-Me-3-NITtrz = 2-[3-(4-methyl-l,2,4-triazolyl)]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and [Dy(hfac)2(4-Me-3-NITtrz)2][Dy(hfac)4]·CHCl3. Compounds 1 and 2 are isostructural and crystallize in the P1̄ space group, whereas compound 3 crystallizes in the P21/n space group. In 1 and 2, the central LnIII ions are nine-coordinated (LnNO8) in a distorted spherical capped square antiprism geometry (C4v) finished by three bischelate hfac anions and one bidentate triazole radical and one aqua molecule. While 3 is a mixed-coordinated binuclear compound with Dy1 in a triangular dodecahedron (D2d) coordination sphere and Dy2 in a biaugmented trigonal prism (C2v) coordination sphere. Magnetic studies show that compound 2 exhibits field-induced single-molecule magnet (SMM) behavior.