Ferromagnetic Intermolecular Interactions Research Articles

Magnetic property and crystal structure of bis [ N-(4-chlorophenyl) salicylideneaminato] oxovanadium (IV)

Crystallographic analyses and magnetic measurements for two polymorphs, the prism form and the needle form of bis [ N-(4-chlorophenyl) salicylideneaminato] oxovanadium (IV) are carried out. The polymeric structure is observed for the needle form against the monomeric structure for the prism form. The ferromagnetic interaction is observed for the needle form, while the appreciable magnetic coupling is not detected for the prism form. The large negative spin density is found on each of the axial oxygen of these crystals. The intermolecular ferromagnetic interaction of these complexes is greatly affected by the formation of polymeric V O⋯V O⋯ structures in the solid state.

Observation of steric hindrance effect controlling crystal packing structures and physical properties in three new isomeric nitronyl nitroxide radicals

Three isomeric nitronyl nitroxide radical compounds, 2-[ n-( N-benzyl)pyridinium]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide bromide ( n = 2, 3 and 4 for 1, 2 and 3, respectively), have been synthesized and structurally characterized. The influence of steric hindrance on the molecular packing structures and physical properties has been observed. In the radical 1, such steric hindrance leads to a folding conformation of the imidazoline and benzene rings and the intramolecular C–H…π interaction between the methyl group and the benzene ring. There is no such effect in 2 and 3. In crystal of 2, there are the intermolecular C–H…π between methyl groups and benzene ring and intermolecular π…π stacking interaction between pyridine and benzene rings. Crystal of 2 with a chiral space group P2 12 12 1 shows the SHG response about 0.4 times as that of urea. In crystal of 3, there are three symmetry-independent radical molecules, which form an unusually six-membered supramolecular ring via intermolecular O…π interactions. For the solid sample of 3, the X-band EPR exhibits an axially symmetric signal and magnetic susceptibility data suggest intermolecular antiferromagnetic (AFM) coupling interactions and very weak intermolecular ferromagnetic (FM) coupling interactions which is more likely caused by magnetic anisotropy, while measurements of both 1 and 2 show isotropic X-band EPR signals and simple Currie–Weiss magnetic behavior.

1-D hydrogen-bonded organization of hexanuclear {3d-4f-5d} complexes: evidence for slow relaxation of the magnetization for [{LMe2Ni(H2O)Ln(H2O)4.5}2{W(CN)8}2] with Ln = Tb and Dy

Heterometallic {3d-4f-5d} aggregates with formula [{LMe2Ni(H2O)Ln(H2O)4.5}2{W(CN)8}2]·15H2O, (LMe2 stands for N,N′-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato) Schiff-base ligand) with Ln = Gd, Tb, Dy, have been obtained by reacting bimetallic [LMe2Ni(H2O)2Ln(NO3)3] and Cs3{W(CN)8} in H2O. The hexanuclear complexes are organized in 1-D arrays by means of hydrogen bonds established between the solvent molecules coordinated to Ln and the CN ligands of an octacyanometallate moiety. The X-ray structure was solved for the Tb derivative. Magnetic behavior indicates ferromagnetic {W–Ni} and {Ni–Ln} interactions (JNiW = 18.5 cm−1, JNiGd = 1.85 cm−1) as well as ferromagnetic intermolecular interactions mediated by the H-bonds. Dynamic magnetic susceptibility studies reveal slow magnetic relaxation processes for the Tb and Dy derivatives, suggesting SMM type behavior for these compounds.

Ab initiostudy of the spin distribution and conductive properties of a Malonato-bridged gadolinium (III) complex

Ab initio computations within the full potential linearized augmented plane wave method with the generalized gradient approximation plus Hubbard potential approach were applied in the study of the electronic structures of the compound [Gd(2)(mal)(3)(H(2)O)(6)]. The present calculations show that the major part of the spin magnetic moment is from Gd(III) ions, and the origin of the ferromagnetic intermolecular interaction of the two interacting Gd(III) ions comes from the spin polarization effect through the oxo-carboxylato and carboxylato bridges. By analysis of the band structure, we find that the compound has a metallic property.

Synthesis, structure and magnetic properties of a novel lead(II) complex containing nitronyl nitroxide radicals

The lead(II) complex with nitronyl nitroxide, [Pb(NIT2Py) 2(NO 3) 2] [NIT2Py = 2-(2′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], has been prepared and characterized by magnetic and single-crystal X-ray diffraction studies. In the complex, the lead(II) ion is coordinated with two bidentate nitronyl nitroxide and two nitrate anions. The lead(II) ion shows seven-coordinate geometry. Magnetic susceptibility data for the title complex has been measured in the range 5–300 K. There are antiferromagnetic interaction between the coordinated nitronyl nitroxides ( J = −19.35 cm −1) and intermolecular ferromagnetic interactions. Thus, we observe the sixth periodic IVA group metal element Pb(II) ion providing an effective pathway for the magnetic exchange interaction between nitronyl nitroxide radicals.

The electronic structure and the ferromagnetic intermolecular interactions in the crystal of a diphenyl nitroxide derivative

Based on the generalized gradient approximation, full potential linearized augmented plane-wave calculations have been performed to study the electronic band structure and the ferromagnetic (FM) interactions of the 9,9-dipropyl-9,10-dihydroacridin-10-yloxyl (DPAO) organic radical. The total and partial density of states and the atomic spin magnetic moments are calculated and discussed. It is found that the unpaired electrons in this radical are localized in a molecular orbital constituted primarily of the π* (NO) orbital, and the main contribution of the spin magnetic moment comes from the NO free radical, with little contributions from other C atoms. The origin of FM interactions is also studied in detail.

Three‐Dimensional Six‐Connecting Organic Building Blocks Based on Polychlorotriphenylmethyl Units—Synthesis, Self‐Assembly, and Magnetic Properties

The synthesis of a three-dimensional, six-connecting, organic building block based on a robust, rigid, and open-shell polychlorotriphenylmethyl (PTM) unit (radical 1) is reported, and its self-assembly properties are described in detail. The tendencies of this highly polar molecule and its hydrogenated precursor, compound 4, to form hydrogen bonds with oxygenated solvents ([1THF(6)] and [4THF(6)]) were reduced by replacing THF with diethyl ether in the crystallization process to yield two-dimensional (2D) hydrogen-bonded structures ([1(Et(2)O)(3)] and [4(Et(2)O)(3)]). The presence of direct hydrogen bonds between the radicals in the latter phase of 1 gives rise to very weak ferromagnetic intermolecular interactions at low temperatures, whereas when the radicals are isolated by THF molecules these interactions are antiferromagnetic and very weak. The role played by the carboxylic groups not only in the self-assembly properties but also in the transmission of the magnetic interactions has been illustrated by determination of the crystal structure and measurement of the magnetic properties of the corresponding hexaester radical 6, in which the close packing of molecular units gives rise to weak antiferromagnetic intermolecular interactions. Attempts to avoid solvation of the molecules in the solid state and to increase the structural and magnetic dimensionality were pursued by recrystallization of both compounds 1 and 4 from concentrated nitric acid, affording two three-dimensional (3D) robust hydrogen-bonded structures. While the structure obtained with compound 4 is characterized by the presence of polar channels and boxes containing water guest molecules along the c axis, radical 1 was oxidized to the corresponding fuchsone 10, which presented a completely different close-packed, guest-free structure.

Electronic structure of the organic half-metallic magnet: 2-(5-pyrimidinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-3-oxoimidazol-1-oxyl

An accurate full-potential density-functional method is used to study the magnetic and half-metallic properties in the pure organic materials: 2-(5-pyrimidinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-3-oxoimidazol-1-oxyl. The total and partial density of states and atomic spin magnetic moments are calculated and discussed. It is found that the unpaired electrons in this compound are localized in a molecular orbital constituted primarily of π*(NO) orbital, and the main contribution of the spin magnetic moment comes from the NO free radicals. It is predicted that this compound is half-metallic magnet. It is also found that there exists ferromagnetic intermolecular interaction in the compound.

Crystal structures and magnetic properties of Ni-bisdithiolene complexes with decamethylmetallocenium cations

Three new compounds of formula ( Cp 2 ∗ Co ) [ Ni ( dmit ) 2 ] ( 1), ( Cp 2 ∗ Mn ) [ Ni ( dmid ) 2 ] · ( CH 3 ) 2 CO ( 2), and ( Cp 2 ∗ Mn ) 2 [ Ni ( dmid ) 2 ] 2 · C 6 H 5 CN ( 3) have been synthesised, and structurally and magnetically characterised (dmit 2− = 1,3-dithiol-2-thione-4,5-dithiolato; dmid 2− = 1,3-dithiol-2-one-4,5-dithiolato). Their structural features and magnetic behaviours are compared with those of ( Cp 2 ∗ Mn ) [ Ni ( dmit ) 2 ] and ( Cp 2 ∗ Mn ) [ Ni ( dmid ) 2 ] · CH 3 CN . The result of this is that the interactions between the Ni(dmit) 2 units in 1 are of ferromagnetic-type, as suggested previously for ( Cp 2 ∗ Mn ) [ Ni ( dmit ) 2 ] . The change from acetonitrile to acetone when going from ( Cp 2 ∗ Mn ) [ Ni ( dmid ) 2 ] · CH 3 CN to 2 results in stronger ferromagnetic intermolecular interactions. This better cooperativity is due to a significant increase of the number of contacts between the various moieties within the ( Cp 2 ∗ Mn ) [ Ni ( dmid ) 2 ] · solvent . On the contrary, the inclusion of larger solvents such as benzonitrile in this type of complexes results in a totally different structural arrangement, which leads to an antiferromagnetic behaviour for 3.

A hybrid density-functional study of the one-dimensional ferromagnetic ordering of (BDTA)[Ni(mnt) 2

The one-dimensional intermolecular ferromagnetic interaction of a charge-transfer (CT) complex, (BDTA)[Ni(mnt) 2] (BDTA: 1,3,2-benzodithiazolyl, mnt: maleonitriledithiolate), is studied by the Kohn–Sham hybrid density functional method, in order to understand the mechanism of the magnetism. All possible effective exchange integrals, J, between the spin pairs of the system indicate that a ferromagnetic interaction ( J = 172 cm −1) exists along the b-axis. Magnetic susceptibility, simulated with the ab initio determined J values by the quantum Monte Carlo (QMC) method, is qualitatively consistent with that measured experimentally.

The electronic structure and the ferromagnetic intermolecular interactions in the crystal of TEMPO radicals

Based on the generalized gradient approximation, full potential linearized augmented plane wave (FP-LAPW) calculations have been performed to study the electronic band structure and the intermolecular ferromagnetic (FM) interactions for the two TEMPO radicals 4-Benzylideneamino-2,2,6,6-tetramethylpiperidin-1-oxyl ( 1) and 4-(2-naphtylmethyleneamino)-2,2,6,6-tetramethylpiperidin-1-oxyl ( 2). The total and the partial density of states and the atomic spin magnetic moments are calculated and discussed. The calculation revealed that the two TEMPO radicals have the intermolecular FM interactions, and the spontaneous magnetic moment is 1.0 μ B per molecule of each crystal, which is in good agreement with the experimental value. It is found that the unpaired electrons in these compounds are localized in a molecular orbital constituted primarily of π* (NO) orbital, and the main contribution of the spin magnetic moment comes from the NO-free radical. The origin of FM is also studied in detail.

Millimetre-wave studies on single crystals of the organic radical 2-benzimidazolyl nitronyl nitroxide

Abstract We report temperature dependent millimetre-wave spectroscopic experiments on single crystals of the organic molecular magnet 2-benzimidazolyl nitronyl nitroxide, in the range 1.4–100 K. This organic radical shows quasi one-dimensional (1-d) ferromagnetic intermolecular interactions with the intrachain exchange coupling constant J/k B = +22 K and interchain coupling constant J ′/ k B = 0.24 K. The linewidth of the electron spin resonance at low temperatures was seen to be considerably broadened as compared to that at higher temperatures. This is consistent with the low dimensional behaviour of the linewidth predicted theoretically. We also see a shift in resonance field at low temperatures. We also present the results of angular dependence experiments carried out at temperatures of 1.4 and 50 K, and frequency dependence experiments at 1.4 and 50 K.

Nickel(II) and iron(II) mononuclear complexes with 1-methylimidazole-2-aldoximate: New building units for molecule-assembled magnetic materials

A new class of mononuclear metal complexes with 1-methylimidazole-2-aldoximate (miao) has been synthesized and characterized: trans-Ni II(Cl) 2(Hmiao) 2 ( 1), trans-Ni II(miao) 2(py) 2 ( 2), NO- trans-Ni II(miao) 2(phen) ( 3), and NO- trans-Fe II(miao) 2(phen) ( 4). The crystal structures of 2, 3, and 4 have been determined by single-crystal X-ray crystallography. Compound 1 having the protonated miao ligand (i.e., Hmiao) is a precursor for synthesizing 2 and 3. Compound 2 is an octahedral Ni II complex surrounded by two miao bidentate ligands and two monodentate ligands of pyridine in a trans-arrangement. Compound 3 is a cis-type octahedral Ni II complex with two miao ligands and a bidentate ligand of 1,10-phenanthroline, in which the ligand arrangement around Ni II center is found in an NO- trans form. Compound 4 is an isostructural Fe II derivative of 3. Compounds 1, 2, and 3 exhibit paramagnetic nature with an S = 1 spin and a positive zero-field splitting, among which it for 3 is overlapped with intermolecular ferromagnetic interaction ( zJ/ k B = +0.16 K). Compound 4 is diamagnetic due to the existence of low-spin Fe II ion.

Theoretical Study on Spin Alignments in Ferromagnetic Heterospin Chains with Competing Exchange Interactions: A Generalized Ferrimagnetic System Containing Organic Biradicals in the Singlet Ground State

Spin alignments in heterospin chains are examined from numerical calculations of model spin Hamiltonians. The Hamiltonians of the heterospin chains mimic an open-shell molecular assemblage composed of an organic biradical in a singlet (S = 0) ground state and a doublet (S = 1/2) monoradical, which are coupled by intermolecular ferromagnetic exchange interactions. It is found from numerical calculations of the spin Hamiltonians that the spin value S2 of the ground-state singlet biradical embedded in the exchange-coupled assemblage deviates from zero and contributes to the bulk magnetization. The alternating chain is found to have two kinds of ground spin states, a high- and a low-spin state. All the spins are parallel to each other in the high-spin state, which is characterized by the spin correlation function of (S(i).S(j)) = 0.25. On the other hand, the spin alignment in the low-spin state is found to be dependent on the topology of the intermolecular exchange interactions. The energy preference of the two states depends on the relative amplitude of the exchange interactions in the chain. The intermolecular ferromagnetic couplings are competing in the ground-state singlet biradical with the intramolecular antiferromagnetic interaction. The appearance of the two kinds of ground states is attributed to a quantum spin frustration effect inherent in the triangular motif of the competing interactions. Magnetic properties of a zigzag chain complex composed of a nitronyl nitroxide biradical with a singlet ground state and Cu(hfac)2 are examined on the basis of the theoretical calculations. The vanishing magnetic moments, or the product of susceptibility and temperature chiT, at low temperatures observed for the complex are consistent with those of the low-spin state predicted in the theoretical calculations.

Copper(II) dimers with ferromagnetic intra- and intermolecular exchange interactions

Dimers based on CuII azomethine complexes exhibited both intra- and intermolecular ferromagnetic exchange interactions, as found from magneto-structural correlations.

Hydrogen-bonded self-assemblies in a polychlorotriphenylmethyl radical derivative substituted with six meta-carboxylic acid groups

The synthesis, self assembly and magnetic properties of a polychlorotriphenylmethyl radical, substituted with six meta-carboxylic groups, are reported showing that radical-radical hydrogen bonds in the solid state yield to very weak intermolecular ferromagnetic interactions.

Novel aromatic N-oxyl radical based on the benzo[ g]quinoline skeleton: synthesis and intermolecular ferromagnetic interaction

A novel stable organic radical, 2,2-diphenyl-1,2-dihydrobenzo[ g]quinoline- N-oxyl ( 2), has been synthesized and structurally characterized in order to examine the ring extension effect on the known derivative, 2,2-diphenyl-1,2-dihydroquinoline- N-oxyl ( 1). Based on SQUID measurement, 2 exhibited a ferromagnetic interaction obeying the Bleaney–Bowers equation with 2 J = +4.6 cm −1. The X-ray analysis revealed an intermolecular edge–edge association of the aryl ring and N-oxyl moiety in the crystal of 2. The bifurcated edge–edge contacts between the α-spin site (nitroxyl O atom) and the β-spin site (aryl-H atoms) are responsible for the ferromagnetic interaction of 2.

The electronic structure and the ferromagnetic properties of the organic radical 4-methacryloyloxy-2,2,6,6-tetramethyl-1-piperidinyloxyl (MOTMP)

The ab initio method of the full potential linearized augmented-plane-wave has been used to study the electronic band structure and the ferromagnetic (FM) properties of the organic radical MOTMP. The total and the partial density of states and the atomic spin magnetic moments are calculated. The calculation revealed that MOTMP has a stable ferromagnetic ground state and the spin magnetic moment is 1.0 μ B per molecule, which is in good agreement with the experimental value. It is found that the unpaired electrons in this compound are localized in a molecular orbital constituted primarily of π*(NO) orbital and the main contribution of the spin magnetic moment comes from the NO free radical. It is also found that there exists ferromagnetic intermolecular interaction in the compound.

N-salicylideneamine derivatives with TEMPO substituents.

Three N-salicylideneamine derivatives bearing TEMPO (2,2,6,6-tetra- methyl-1-piperidinyloxy) substituents were prepared in order to study their structure and property relationships and to investigate the possibilities of the existence of heat and/or light responsive magnetic properties. Curie-Weiss behavior with weak ferromagnetic intermolecular spin-spin interactions was observed in one of the radicals, while antiferromagnetic interactions were predominant for the other radicals and the structure-property relationships were investigated for the radical compounds from their crystal structures obtained by X-ray analyses. Preliminary results of the examination of their responses towards light and heat are also described.

Mixed-valence MnIIIMnIV clusters [Mn7O8(O2SePh)8(O2CMe)(H2O)] and [Mn7O8(O2SePh)9(H2O)]: single-chain magnets exhibiting quantum tunneling of magnetization.

The syntheses, structures, and magnetic properties of two new Mn7 complexes containing phenylseleninate ligands are reported. [Mn7O8(O2SePh)8(O2CMe)(H2O)] (1) and [Mn7O8(O2SePh)9(H2O)] (2) were both prepared by the reaction of 18 equiv of benzeneseleninic acid (PhSeO2H) with [Mn12O12(O2CMe)16(H2O)4] in MeCN. Complex 1 x 6MeCN crystallizes in the triclinic space group P, and complex 2 x 2CH2Cl2 crystallizes in the monoclinic space group P2(1)/m. Both compounds possess an unprecedented [Mn7O8]9+ core comprising a central [MnIII3(micro3-O)4]+ unit attached to [MnIV2(micro-O)2]4+ and [MnIV2(micro-O)(micro3-O)]4+ units on either side. In each cluster, the PhSeO2- groups function as bridging ligands between adjacent Mn centers. The structure reveals strong Se.O intermolecular contacts between Mn7 units to give a one-dimensional chain structure, with weak interchain interactions. Solid-state DC magnetic susceptibility measurements of complexes 1 and 2 reveal that they have very similar properties, and detailed studies on 1 by AC susceptibility measurements confirm an S = 2 ground-state spin value. In addition, out-of-phase AC signals are observed, suggesting slow magnetization relaxation. Magnetization versus DC field sweeps down to 0.04 K reveals hysteresis loops, but the temperature dependence of the coercivity is not what is expected of a single-molecule magnet. Instead, the behavior is due to single-chain magnetism, albeit with weak antiferromagnetic interactions between the chains, with the barrier to relaxation arising from a combination of molecular anisotropy and ferromagnetic intermolecular exchange interactions mediated by the Se...O contacts. An Arrhenius plot was constructed from the magnetization versus time decay data. The thermally activated region at > 0.5 K gave an effective relaxation barrier (Ueff) of 14.2 K. Below approximately 0.1 K, the relaxation is independent of temperature, which is characteristic of magnetization quantum tunneling through the anisotropy barrier. These Mn7 compounds are thus the first single-chain magnets to comprise polynuclear metal clusters and also the first for which the temperature-independent relaxation characteristic of tunneling has been identified. The work also emphasizes that out-of-phase AC signals for ostensibly molecular compounds are not sufficient proof by themselves of a single-molecule magnet.