Intramolecular Ferromagnetic Interaction Research Articles

Two extended structures constructed from sandwich-type polyoxometalates functionalized by organic amines

Two new compounds constructed from tetra-Ni-substituted sandwich-type polyoxometalates functionalized by organic groups, (NH(4))(2)[Ni(4)(enMe)(8)(H(2)O)(2)Ni(4)(enMe)(2)(PW(9)O(34))(2)].9H(2)O (enMe = 1,2-diaminopropane) (1) and Na(2)[H(6)N(2)(CH(2))(6)](2){Ni(4)[H(4)N(2)(CH(2))(6)](2)(H(2)PW(9)O(34))(2)}.7H(2)O (2), have been successfully synthesized under hydrothermal conditions. Single-crystal X-ray diffraction analysis is carried out on these two compounds (1 and 2), which both crystallize in the triclinic system. Compound 1 represents the first example of a 2D layer structure consisting of the sandwich-type polyoxoanions with six supporting [Ni(enMe)(2)](2+) moities and two organic functionalized groups. Compound 2 exhibits a 1D chain-like structure based on sandwich-type polyoxoanions and sodium cations, which are further connected into a 2D layer structure via hydrogen-bonding interactions between the 1,6-hexanediamine molecules and the sandwich-type [Ni(4)(H(4)N(2)(CH(2))(6))(2)(H(2)PW(9)O(34))(2)](6-) polyoxoanions. A magnetic study of the two compounds indicates that intramolecular ferromagnetic Ni-Ni interactions exist in the tetranuclear metal cluster.

One-dimensional Structure Consisting of Pin-wheel Cu4Gd Core and Na+ as Connector

Abstract A 3d–4f complex with the formula of {Na[(CuL)4Gd]}1∞ was prepared, where (CuL)− is a “ligand-complex,” [N-(4-methyl-6-oxo-3-azahept-4-enyl)oxamato]copper(II). The structure consists of a pin-wheel-like Cu4Gd core and Na+ ion as a connector to give a one-dimensional chain. The magnetic data and their analyses demonstrated an intramolecular ferromagnetic interaction within a Cu4Gd core and an intercore antiferromagnetic interaction operating through Na+ ion with the coupling parameters of J=+1.09 cm−1, zJ′=−0.07 cm−1; SCu=1⁄2, SGd=7⁄2).

Dinuclear Oxovanadium(IV) Thiolate Complexes with Ferromagnetically Coupled Interaction between Vanadium Centers

Two dinuclear oxovanadium(IV) thiolate complexes, [N(C5H11)4]2[VOL1]2 (1) and [N(C4H9)4][(VOL2)2(mu-OCH3)] (2) (where L1 = [(CH3)SiO(C6H4-2-S)2]3- and L2 = [(C6H5)PO(C6H4-2-S)2]2-), have been synthesized and characterized. The geometry of the anion in 1 can be classified to an edge-sharing bi-square-pyramid with a syn-orthogonal configuration. The one in 2 can be view as a face-sharing bioctahedron with two oxo groups in syn positions. Of note, these two complexes display intramolecular ferromagnetic interaction between two metal centers.

Molecular Tailoring and Prediction of Strongly Ferromagnetically Coupled Trimethylenemethane-Based Nitroxide Diradicals

We have investigated the magnetic properties of four recently synthesized stable TMM-type nitroxide diradicals. Four new diradicals are proposed by tailoring one of the species in such a way that both conjugation and planarity increase. As a remarkable consequence, the intramolecular ferromagnetic exchange interaction was found to be quite high in the proposed radicals. The calculated coupling constants were in the range of +102 to +140 cm-1. The MO and spin density analysis are provided to interpret the exchange interactions. We observed the existence of intramolecular pi-pi-interactions for the species 2. This slightly increased the J value by shortening the length of the spacer between the two spin sources.

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.

Hydrothermal syntheses, crystal structures and magnetic properties of two copper(ii) complexes involved in situ ligand synthesis

The hydrothermal reaction of Cu(NO(3))(2), isophthalate (ip) and 2,2'-bipyridine (2,2'-bpy) without or with K(2)Cr(2)O(7) affords different complexes, whose structures are controlled only by the addition of the K(2)Cr(2)O(7). The reaction of Cu(NO(3))(2), isophthalate and 2,2'-bipyridine yields a novel one-dimensional double-chain coordination polymer [Cu(3)(ip)(2)(Hipa)(2)(bpy)(2)](n) (1). However, with the addition of K(2)Cr(2)O(7) in the above reaction at the same hydrothermal conditions, a discrete hexanuclear Cu(II) complex [Cu(6)(ipO)(4)(2,2'-bpy)(2)(H(2)O)(2)].6H(2)O (2) (ipOH = 2-hydroxyisophthalate) was isolated. It is interesting to find that the in situ reaction of isophthalate (ip) oxidized to 2-hydroxyisophthalate (ipOH) occurs. K(2)Cr(2)O(7) acts as an oxidant. The magnetic properties of 1 and 2 have been investigated by variable-temperature magnetic susceptibility and magnetization measurements, and the results reveal that intramolecular ferromagnetic interactions exist with weak intermolecular antiferromagnetic interactions at very low temperature in 1 and weak antiferromagnetic interactions admixture with strong ferromagnetic interactions in 2.

Structural and Magnetic Studies on Cyano-Bridged Rectangular Fe2M2 (M = Cu, Ni) Clusters

Using the tricyano precursor, (Bu4N)[(Tp)Fe(CN)3] (Tp = Tris(pyrazolyl) hydroborate) (1), four new tetranuclear clusters, [(Tp)Fe(CN)3Cu(Tp)]2.2H2O (2), [(Tp)Fe(CN)3Cu(bpca)]2.4H2O (3) (bpca = bis(2-pyridylcarbonyl)amidate anion), [(Tp)Fe(CN)3Ni(tren)]2(ClO4)2.2H2O (4) (tren = tris(2-amino)ethylamine), and [(Tp)Fe(CN)3Ni(bipy)2]2[(Tp)Fe(CN)3]2.6H2O (5) (bipy = 2,2'-bipyridine), have been synthesized and structurally characterized. The four clusters possess similar square structures, where FeIII and MII (M = CuII or NiII) ions alternate at the rectangle corners. There exist intermolecular - stacking interactions through pyrazolyl groups of Tp- ligands in complexes 2 and 4, which lead to 1D chain structures. Complex 5 shows a 3D network structure through the coexistence of - stacking effects and hydrogen-bonding interactions. Magnetic studies show intramolecular ferromagnetic interactions in all four clusters. The exchange parameters are +11.91 and +1.38 cm(-1) for clusters 2 and 3, respectively, while uniaxial molecular anisotropy can be detected in complex 3 due to the distorted core in its molecular structure. Complex 4 has a ground state of S = 3 and shows SMM behavior with an effective energy barrier of U = 18.9 cm(-1). Unusual spin-glass-like dynamic relaxations are observed for complex 5.

Mixed-Valent Cobalt Spin Clusters: a Hexanuclear Complex and a One-Dimensional Coordination Polymer Comprised of Alternating Hepta- and Mononuclear Fragments

Reactions between Co(OAc)2 and 2-amino-2-methyl-1,3-propanediol (ampdH2) afford a hexanuclear complex [Co6(H2O)(MeOH)(OAc)6(ampd)4] (1) and a one-dimensional coordination polymer comprised of discrete heptanuclear complexes covalently bound to mononuclear Co centers [Co8(H2O)2(OAc)7(ampd)6]n (2). While 1 is obtained under ambient reaction conditions, the formation of 2 requires solvothermal methods. Both products have been characterized crystallographically and found to be mixed-valent, containing divalent and trivalent Co centers. Down to 30 K, the variable-temperature magnetic susceptibility data of 1 and 2 are dominated by the single-ion properties of high-spin Co(II) centers with distorted-octahedral coordination geometries. Below this temperature, the effect of intramolecular ferromagnetic exchange interactions becomes apparent. The ferromagnetic coupling in 1 has been analyzed in terms of an anisotropic exchange model, and inelastic neutron scattering data are consistent with the proposed model. Although the structure of 2 precludes a quantitative interpretation, the magnetic data suggest ferromagnetic exchange within the heptanuclear unit and negligible interactions along the chain between the hepta- and mononuclear fragments.

Preparation and magnetic properties of 4,6-bis(imino nitroxide)-substituted resorcinol and its Cu-complex

A novel bis(imino nitroxide)-substituted resorcinol 3H, that has two metal-binding sites with two pairs of the phenolate anion and the imino nitrogen atom, was prepared. The powdered sample of 3H showed an intramolecular ferromagnetic interaction ( J/ k B = +5 K) between two (imino nitroxide)s through a m-phenylene bridge and a weak intermolecular antiferromagnetic interaction ( J/ k B = − 0.9 K). The reaction of 3H with copper acetate in methanolic ammonia was examined to give a hardly soluble Cu-complex that exhibited ferromagnetic behavior in relatively high temperatures (298–55 K).

A Ferromagnetically Coupled, Bent, Trinuclear Copper(II) Complex: Synthesis, Structure, Hydrogen‐Bonding Network, Magnetic Properties and DNA Interaction Study

AbstractA bent trinuclear copper(II) complex (1) incorporating μ‐phenoxo, μ‐syn‐syn carboxylato, and μ3‐chloro bridges and an O,N,N‐coordinated reduced Schiff‐base ligand is reported. The complex shows an intramolecular ferromagnetic interaction in the solid state. The EPR spectra also support the magnetic behaviour of the complex. In the compound, each copper centre has a square‐pyramidal geometry. The separation between the adjacent copper ions is about 3.05 Å and that between the terminal copper ions is about 5.0 Å. The complex forms a supramolecular architecture through N–H···Cl hydrogen bonding between the amine group of the reduced Schiff‐base ligand and the counter chloride anions. Absorption and fluorescence spectral studies and viscosity measurements have been performed to determine the type of interaction with calf‐thymus DNA. The nuclease activity of the complex with plasmid DNA is also studied. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

High-Nuclearity Manganese and Iron Complexes with the Anionic Ligand Methyl Salicylimidate

The three novel clusters [Mn6O4(OMe)2(OAc)4(Mesalim)4] (3), [Mn8O2(OH)2(OMe)12(OAc)2(Mesalim)4] (4), and [Fe10O4(OMe)14Cl2(Mesalim)6] (5) have been synthesized from a simple bidentate ligand HMesalim (HMesalim = methyl salicylimidate). Starting from the mononuclear complex [Mn(Mesalim)2(OAc)(MeOH)].MeOH (1), either the hexanuclear complex 3 or the octanuclear complex 4 is obtained after recrystallization, depending upon the reaction conditions and solvents used. Similarly, starting from the purple-colored mononuclear complex [Fe(Mesalim)2Cl] (2), the orange-colored decanuclear iron(III) cluster 5 has been obtained upon recrystallization from methanol. Complex 3, which could also be prepared directly from manganese acetate and the ligand, has a face-sharing double-cubane [Mn6O6] core, unique in transition metal chemistry. Compounds 4 and 5 are composed of [M3O4] partial cubanes. All complexes belong to a class of oxo-bridged cubic close-packed molecular clusters resembling the metal oxide/hydroxide ores. Complex 4 exhibits intramolecular ferromagnetic interactions, as evidenced from dc magnetic susceptibility studies (1.8-300 K), resulting in a high-spin ground state, probably with S(T) = 8. Complex 4 displays single molecule magnet behavior as indicated by frequency and temperature dependences of its ac susceptibility. An Arrhenius plot gave relatively large experimental activation energy of 36.0 K. The magnetic properties of complexes 3 and 5 are dominated by antiferromagnetic interactions leading to zero-spin ground states.

A novel copper(II)-radical complex with ferromagnetic interaction: Synthesis, crystal structure and magnetic properties

A novel copper(II)-radical complex [Cu(NITmPy)(PDA)(H 2O)] · (H 2O) ( 1) (NITmPy = 2-(3′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, H 2PDA = 2,6-pyridinedicarboxylic acid) has been synthesized and structurally characterized by X-ray diffraction methods. It crystallizes in the triclinic space group P 1 ¯ . The Cu(II) ion exists in a distorted square pyramid environment. The molecules of [Cu(NITmPy)(PDA)(H 2O)] · (H 2O) are connected as a two-dimensional structure by the intermolecular hydrogen bonds. Magnetic measurements show intramolecular ferromagnetic interactions between NITmPy and Cu(II) ion and intermolecular antiferromagnetic interactions in 1.

High-Spin Radical Cations of a Dendritic Oligoarylamine

A new dendritic oligoarylamine, N,N,N',N',N",N"-hexakis[4-(di-4-anisylamino)phenyl]- 1,3,5-benzenetriamine (BTA) 2, which contains a 1,3,5-benzenetriamine molecular unit as an potential precursor of a high-spin molecule and three oligoarylamine moieties as spin-carrying units surrounding the core BTA, has been prepared by the sequential palladium-catalyzed amination reactions. The redox property has been investigated by cyclic voltammetry, and the highly charged states up to the hexacation are accessible to 2. The polycationic high-spin species have been generated by stepwise chemical oxidation, and the electronic structures have been examined in detail by the continuous wave (CW) and pulsed ESR spectroscopy in comparison with the previously studied 1. The pulsed ESR technique enabled us to determine the definite spin multiplicity of the generated polycationic species of 2. It was confirmed that the dominant oxidized species observed by the two- and three-electron oxidations were assigned to the spin triplet 2(2+) and the spin quartet 2(3+), respectively. Moreover, these high-spin polycationic species turned out to be far more stable as compared to 1, and the isolation of 2(3+) as the SbCl(6)(-) salt has been accomplished. The temperature dependence of the magnetic susceptibility for the 2(3+)(SbCl(6)(-))(3) salt revealed that the intramolecular ferromagnetic interaction exists in 2(3+), and moreover, the trication 2(3+) was found to be deformed in the solid state.

High‐Spin Molecules with Magnetic Anisotropy Toward Single‐Molecule Magnets

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis, structure, and magnetism of a binuclear Co(II) complex of a potentially bis-tridentate verdazyl radical ligand

The synthesis, structure, and magnetic properties of a dinuclear Co(II) complex of a tridentate verdazyl radical are presented. The reaction of a tetrazane containing a 4,6-bis(2-pyridyl)-pyrimid-2-yl substituent with cobalt chloride hexahydrate in aerated solution leads to in situ oxidation of the tetrazane to a verdazyl radical which is coordinated to Co(II) in a tridentate manner. The second tridentate coordination site of the verdazyl remains vacant. The crystal structure reveals the complex to be dimeric, with the cobalt ions linked by two bridging chlorides. The structure of Co 2Cl 2 core is highly asymmetric, with two short (2.3317 Å) and two long (2.744 Å) Co–Cl bonds. There are relatively short intermolecular contacts between coordinated verdazyl radicals in the solid state. Magnetic susceptibility data from 2 to 300 K suggest intramolecular ferromagnetic interactions, and modeling of the high-temperature data produced a best fit with J Co–verdazyl of +20 cm −1.

High‐Spin Molecules with Magnetic Anisotropy toward Single‐Molecule Magnets

High-spin molecules with easy-axis magnetic anisotropy show slow magnetic relaxation of spin-flipping along the axis of magnetic anisotropy and are called single-molecule magnets (SMMs). SMMs behave as molecular-size permanent magnets at low temperature and magnetic relaxation occurs by quantum tunneling processes; such molecules are promising candidates for use in quantum devices. We first discuss intramolecular ferromagnetic interactions for preparing high-spin molecules. Second, we determine the magnetic anisotropy for single metal ions with d(n) configurations and discuss how molecular anisotropy arises from single-ion anisotropy of the assembled component metal ions.

Crystal structure and magnetic behavior of the new gadolinium complex compound [NH 3C 2H 5][Gd(Cl 2HCCOO) 4

Single crystals of [NH 3C 2H 5][Gd(Cl 2HCCOO) 4] have been obtained by reaction of Gd 2O 3 with NH 3C 2H 5Cl in an aqueous solution of Cl 2HCCOOH. The compound crystallizes in the triclinic space group P 1 ¯ (no. 2, Z = 2, a = 813.7(3) pm, b = 1246.9(4) pm, c = 1263.9(4) pm, α = 61.67(4)°, β = 87.39(4)°, γ = 84.84(4)°). The Gd 3+ ion is eight-fold coordinated by oxygen atoms. The magnetic behavior of the compound was investigated in the temperature range of 1.72–300 K. The magnetic data indicate an intramolecular ferromagnetic interaction within a dimeric unit ( J intra = + 0.029 cm −1) on which an intermolecular antiferromagnetic interaction is imposed ( J inter = −0.010 cm −1).

The first Co(II)-IM2py-κ 2N,O complex with ferromagnetic behavior

A novel cobalt (II) complex 1 [Co(IM2py-κ 2N,O) 2(H 2O) 2](ClO 4) 2 · 2H 2O (IM2py = 2-(2-(pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H-imidazol-1-oxy)), has been synthesized by the direct reaction between Co(ClO 4) 2 · 6H 2O and IM2py at room temperature. The X-ray analysis demonstrates that IM2py ligand is coordinated to cobalt (II) ion as an unusual didentate chelate with the κ 2 N(py),O(IM) mode in 1. The variable temperature magnetic susceptibility data show that there are intramolecular ferromagnetic interactions between Co(II) ion and IM2py radical. The magnetic behavior is discussed with reference to the structural analysis. The spectroscopic properties have also been investigated.

Structure and magnetic properties of 3d–4f heterometallic complexes containing di-2-pyridyl ketoximate: An approach to single-molecule magnets

Abstract [{Ln(hfac)3}2{Ni(dpk)2(phen)}] (1Ln) and [{Ln(hfac)3}2{Ni(dpk)2(py)2}] (2Ln) were synthesized and characterized, where dpk = di-2-pyridyl ketoxmate and Ln = La, Tb, Dy, Ho, Er. The N–O groups from dpk bridged the central nickel(II) ion and terminal lanthanide(III) ions, giving a linear trinuclear array. Dc magnetic susceptibility measurements revealed that they did not possess appreciable intramolecular ferromagnetic or ferrimagnetic interaction. Ac magnetic susceptibility measurements clarified that frequency dependence of out-of-phase ac susceptibility was observed only for Dy derivatives 1Dy and 2Dy, which is regarded as an indication of single-molecule magnets.

Magnetism in organic diradical ion salts based on nitronyl nitroxide

Abstract Magnetism in organic diradical ion salts prepared from the diradicals, pyridine-2,6-diylbis(nitronyl nitroxide) [(2,6-PYBNN) ] and phenol-2,4-diylbis(nitronyl nitroxide) [(2,4-POBNN) ], were investigated by using SQUID magnetometers. The diradical cation salt (2,6-PYBNN) + Cl − shows intramolecular ferromagnetic (FM) interaction with the exchange coupling constant J / k = +9.0 K and intermolecular antiferromagnetic (AFM) interaction with the Weiss constant θ = −0.75 K in the low temperature phase below 4.5 K. Although the intramolecular FM interaction is close to that observed in the neutral diradical 2,6-PYBNN , the intermolecular AFM interaction is significantly reduced from J ′/ k = −57 K due probably to the increase of intermolecular distances by the incorporation of Cl − ions into the salt. We also present and discuss the magnetic behavior in the diradical cation salt ( 2 , 6 - PYBNN ) + BF 4 - and the diradical anion salt (C 4 H 9 ) 4 N + (2,4-POBNN) − .