Dominant Ferromagnetic Interactions Research Articles

Magnetic properties of the layered lanthanide hydroxide series Y(x)Dy(8-x)(OH)20Cl4·6H2O: from single ion magnets to 2D and 3D interaction effects.

The magnetic properties of layered dysprosium hydroxides, both diluted in the diamagnetic yttrium analogous matrix (LYH:0.04Dy), and intercalated with 2,6-naphthalene dicarboxylate anions (LDyH-2,6-NDC), were studied and compared with the recently reported undiluted compound (LDyH = Dy8(OH)20Cl4·6H2O). The Y diluted compound reveals a single-molecule magnet (SMM) behavior of single Dy ions, with two distinct slow relaxation processes of the magnetization at low temperatures associated with the two main types of Dy sites, 8- and 9-fold coordinated. Only one relaxation process is observed in both undiluted LDyH and intercalated compounds as a consequence of dominant ferromagnetic Dy-Dy interactions, both intra- and interlayer. Semiempirical calculations using a radial effect charge (REC) model for the crystal field splitting of the Dy levels are used to explain data in terms of contributions from the different Dy sites. The dominant ferromagnetic interactions are explained in terms of orientations of easy magnetization axes obtained by REC calculations together with the sign of the superexchange expected from the Dy-O-Dy angles.

A cyano-bridged tubular coordination polymer with dominant ferromagnetic interactions.

It is a challenge to synthesize a porous tubular coordination polymer with magnetic properties. Utilizing [Fe(II)(bipy)(CN)4](2-) (bipy = 2,2'-bipyridine) as the building block to react with Mn(2+), we successfully synthesized a cyano-bridged tubular coordination polymer with dominant ferromagnetic interactions. The inner surface of the heterometallic tube is hydrophilic, whereas the outer surface is hydrophobic. The framework is stable up to 320 °C and can adsorb N2 and CO2. The ferromagnetic interactions were transmitted via the diamagnetic N-C-Fe(II)-C-N species between Mn(2+) ions in the tube.

A rare diarboxylate and N-oxide/H2O bridged metal-organic framework with nickel(II)-oxide octahedral chains: synthesis, crystal structure, and magnetic properties with theoretical investigations on the exchange mechanism

One 3D metal-organic framework {[Ni2(1,4-NDC)2(4,4′-dpdo)(H2O)]·3H2O}n1 (1,4-H2NDC=1,4-naphthalenedicarboxylate acid and 4,4′-dpdo=4,4′-Dipyridyl-N,N′-dioxide) has been hydrothermally synthesized and well-characterized. Polymer 1 arranges in the I1O1 fashion. The hexacoordinated Ni(II) centers are triply bridged by two 1,4-NDC2− carboxylate group plus μ-4,4-dpdo or μ–H2O to form an alternating chain. Each metal chain is cross-connected to four other chains to shape a 3D network. Magnetic studies show that 1 exhibits dominant ferromagnetic interactions with intrachain alternating antiferromagnetic/ferromagnetic interactions.

A new family of heterometallic tetranuclear [MnIII2LnIII2] (Ln = Eu, Gd, Tb, Dy) isostructural clusters: Syntheses, crystal structures and magnetic properties

The initial employment of 2-(2-hydroxy-3-methoxybenzylideneamino)phenol (H2L) in Mn–Ln chemistry yields four isostructural MnIII2LnIII2 clusters [MnIII2LnIII2(O)L4(CH3OH)4(Cl)2]·(Ln=Eu (1), Gd (2), Tb (3) and Dy (4)). All four isostructural clusters were structurally and magnetically characterized. Structural analyses reveal that they are tetranuclear isostructural clusters, each consisting of two dinuclear Mn–Ln entities. Static magnetic studies indicate the presence of dominant ferromagnetic interactions in complexes 3 and 4, whereas complex 2, containing Gd, allows quantification of an antiferromagnetic interaction with JMn–Gd=−0.41cm−1. Dynamic measurements reveal that 3 exhibits slow relaxation of the magnetization and 4 displays single-molecule magnet behavior with an energy barrier of Δ=15.8K and a pre-exponential factor of τ0=7.65×10−7s, while 1 and 2 do not show any out-of-phase ac susceptibility signals. This work highlights the different contributions of the respective lanthanide ions to the overall magnetic behavior in MnIII2LnIII2 systems.

Tuning CuII Coordination Polymers Derived from a Bis(pyrazolecarboxylate) Ligand by Solvothermal C–H Bond Activation: Synthesis, Structures, Catalysis, and Magnetic Properties

AbstractA new bis(pyrazolecarboxylate) ligand, 1,3‐phenylenebis(1H‐pyrazole‐5‐carboxylic acid) (H2PBPC) has been synthesized to study the structure and intriguing properties of the resultant coordination polymers synthesized under solvothermal conditions. The reaction of H2PBPC with Cu(ClO4)2 in the presence of NaOH at two different temperatures (80 and 120 °C) resulted in two coordination polymers, namely, [{Cu2Na(H2OPBPC)}]∞ (1) and [{Cu4Na2(H2OPBPC)2}]∞ (2), which display 2D corrugated sheet and 3D staircase architectures, respectively; in these structures, the aromatic C–H bond flanked by the pyrazolecarboxylate moieties was oxidized to form a C–O bond. When 2,2′‐bipyridine (2,2′‐bpy) was used instead of NaOH, [{Cu2(2,2′‐bpy)2(H2PBPC)}(H2O)]∞ (3) formed, and such C–H bond activation was not observed. Interestingly, one of the coordination polymers, namely, 1, displayed catecholase and phosphatase activity. Variable‐temperature magnetic susceptibility data in the range 2–300 K showed that there is antiferromagnetic coupling between the metal centers of 1 and 2 that is mediated through the phenoxo and pyrazole bridges, whereas 3 revealed dominant ferromagnetic interactions between the bis(pyrazolato)‐bridged CuII centers owing to its very unusual Cu–N–N–Cu torsion angles of 75.28 and 69.52°.

From tetranuclear cluster with single-molecule-magnet behavior to 1D alternating spin-canting chain in a Fe(III)–Mn(III) bimetallic system

A tetranuclear cluster and an alternating zigzag chain were synthesized via rational assembly of the same cyanometalate building blocks with different Mn(III) Schiff bases possessing varying proportions of sterically hindered groups causing steric hindrances. The tetranuclear cluster [(Tp*)Fe(CN)3]2[Mn(salen)]2·H2O [1; [(Tp*)Fe(CN)3]− [Tp*=hydrotris(3,5-dimethylpyrazol-1-yl) borate], salen=N,N′-ethylenebis(salicylideneiminato) dianion] was formed with Schiff bases possessing smaller steric hindrances, whereas the one-dimensional alternating zigzag chain {[(Tp*)Fe(CN)3Mn(salcyen)]·2CH3OH·H2O}n [2; salcyen=N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion] was formed with Schiff bases possessing larger steric hindrances. Magnetic measurements revealed that 1 exhibits single-molecule-magnet behavior with dominant ferromagnetic interactions, whereas 2 exhibits spin-canting behavior with dominant antiferromagnetic interactions.

Room Temperature Syntheses, Structures and Magnetic Properties of Two Heterometallic Tetranuclear Clusters

Two new heterometallic tetranuclear clusters [M2Na2(hmb)4(N3)2(CH3CN)2]·(CH3CN)2 (M = Ni (1), M = Co (2), Hhmb is 2-hydroxy-3-methoxy-benzaldehyde) have been synthesized at room temperature and structurally characterized by elemental analysis, IR spectroscopy, and single crystal X-ray diffraction. Intracluster, compounds 1 and 2 display dominant ferromagnetic interaction through double μ 1,1,1-N3 bridges, while intercluster, 1 and 2 display weak anti-ferromagnetic interaction and ferromagnetic interaction, respectively.

Manganese(II) Coordination Polymer with μ1,1‐Azido Bridge: Synthesis, Crystal Structure, and Magnetic Properties

AbstractThe manganese(II) coordination polymer [Mn(2‐Meimi)2(μ1,1‐N3)2]n·nH2O (1) (Meimi = 2‐methyl‐imidazole) with μ1,1‐N3 (end‐on, EO) bridge was synthesized by hydrothermal reaction of MnCl2, NaN3, and Meimi. It was characterized by elemental analysis, IR spectroscopy, powder XRD, and magnetic measurements. Single crystal X‐ray analysis revealed that compound 1 features a one‐dimensional (1D) catenated structure and the 1D chains are further connected by strong intermolecular hydrogen bonds to a 3D supramolecular framework. Variable‐temperature magnetic susceptibility measurements revealed that compound 1 displays dominant ferromagnetic interactions through the μ1,1‐N3 (end‐on, EO) bridging mode.

Cryogenic magneto-caloric effect and magneto-structural correlations in carboxylate-bridged Gd(III) compounds.

Two new infinite coordination chain compounds [Gd(CH3CO2)3(dmf)]∞ (1) and {[Gd(HO(CH2)3CO2)3(H2O)]·H2O}∞ (2) have been obtained attempting to modify a prototype molecular cooler. The structures of both compounds as determined by single-crystal X-ray diffraction are reported, together with a detailed study of their magnetic and thermal properties, describing for both compounds a large magneto-caloric effect. The dominant ferromagnetic interaction present in 2 clearly favours this material at low applied magnetic fields, with respect to 1 that exhibits antiferromagnetic interactions. Magneto-structural correlations of the sign and strength of the magnetic interactions are derived for carboxylato-bridged Gd(III) systems.

Structural variation from heterometallic cluster-based 1D chain to heterometallic tetranuclear cluster: Syntheses, structures and magnetic properties

Using the solvothermal method, we present the comparative preparation of {[Co3Na(dmaep)3(ehbd)(N3)3]·DMF}n (1) and [Co2Na2(hmbd)4(N3)2(DMF)2] (2), where Hehbd is 3-ethoxy-2-hydroxy-benzaldehyde, Hhmbd is 3-methoxy-2-hydroxy-benzaldehyde, and Hdmaep is 2-dimethylaminomethyl-6-ethoxy-phenol, which was synthesized by an in-situ reaction. Complexes 1 and 2 were characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. Complex 1 is a novel heterometallic cluster-based 1-D chain and 2 is a heterometallic tetranuclear cluster. The {Co3IINa} and {Co2IINa2} cores display dominant ferromagnetic interaction from the nature of the binding modes through μ1,1,1-N3– (end-on, EO).

Itinerant and local-moment magnetism inEuCr2As2single crystals

We report on the crystal structure, physical properties, and electronic structure calculations for the ternary pnictide compound ${\text{EuCr}}_{2}$${\text{As}}_{2}$. X-ray diffraction studies confirmed that ${\text{EuCr}}_{2}$${\text{As}}_{2}$ crystalizes in the ${\text{ThCr}}_{2}$${\text{Si}}_{2}$-type tetragonal structure (space group $I4/mmm$). The Eu ions are in a stable divalent state in this compound. Eu moments in ${\text{EuCr}}_{2}$${\text{As}}_{2}$ order magnetically below ${T}_{m}$ = 21 K. A sharp increase in the magnetic susceptibility below ${T}_{m}$ and the positive value of the paramagnetic Curie temperature obtained from the Curie-Weiss fit suggest dominant ferromagnetic interactions. The heat capacity exhibits a sharp $\ensuremath{\lambda}$-shape anomaly at ${T}_{m}$, confirming the bulk nature of the magnetic transition. The extracted magnetic entropy at the magnetic transition temperature is consistent with the theoretical value $Rln(2S+1)$ for $S=7/2$ of the Eu${}^{2+}$ ion. The temperature dependence of the electrical resistivity $\ensuremath{\rho}(T)$ shows metallic behavior along with an anomaly at 21 K. In addition, we observe a reasonably large negative magnetoresistance ($\ensuremath{\sim}\ensuremath{-}24%$) at lower temperature. Electronic structure calculations for ${\text{EuCr}}_{2}$${\text{As}}_{2}$ reveal a moderately high density of states of Cr-3$d$ orbitals at the Fermi energy, indicating that the nonmagnetic state of Cr is unstable against magnetic order. Our density functional calculations for ${\text{EuCr}}_{2}$${\text{As}}_{2}$ predict a G-type AFM order in the Cr sublattice. The electronic structure calculations suggest a weak interlayer coupling of the Eu moments.

Co-existence of ferromagnetic and antiferromagnetic interactions in Mn3Ga(1−x)SnxC

The magnetic properties of the , antiperovskite compounds have been investigated in detail. Though all compounds of this series crystallize in a cubic structure, the Ga rich compounds transform, via a first-order transformation, to an antiferromagnetic ground state and the Sn rich compounds exhibit dominant ferromagnetic interactions at low temperature. In the intermediate range co-existence of ferromagnetic and antiferromagnetic interactions can be seen. The results have been explained to be due to growth of ferromagnetic sub-lattice at the expense of antiferromagnetic sub-lattice with increasing Sn concentration in . This growth occurs to a point where the first-order transition is altered from a ferromagnetic–antiferromagnetic type in Ga rich compounds to a paramagnetic–ferrimagnetic type in .

Ligand induced diversification from tetranuclear to mononuclear compounds: Syntheses, structures and magnetic properties

Using the solvothermal method, we present the comparative preparation of [Ni(L1)Cl(CH3CN)]4 (1), [Ni(L2)Cl(C2H5OH)]4 (2) and [Ni(HL3)2(CH3COO)2]·2DMF (3), where HL1 is (1H-benzimidazol-2-yl)-methanol, HL2 is (6-methyl-1H-benzoimidazol-2-yl)-methanol and HL3 is 1-(1H-benzoimidazol-2-yl)-ethanol. All the compounds were characterized by elemental analysis, IR and X-ray single-crystal diffraction. Compounds 1 and 2 are tetranuclear clusters with a cubane topology, in which the metal ions and the oxygen atoms from the L ligands occupy alternate vertices of the cubane. However, compound 3 is a mononuclear nickel complex with the triclinic crystal system, P1¯ space group, different from that of compounds 1 and 2. These results show that the position and space steric hindrance of the substituents groups are essential in determining the final structures of the assemblies. The magnetic properties of 1 and 2 in the 2–300K temperature range have also been discussed. The {Ni4O4} core displays dominant ferromagnetic interactions.

Microwave‐assisted Synthesis, Structure, and Properties of a Heptanuclear Cobalt Cluster with 2‐Ethyliminomethyl‐6‐methoxy‐phenol

AbstractThe heptanuclear cobalt cluster [Co7(emmp)6(CH3O)6]·(ClO4)2 (1) (Hemmp = 2‐ethyliminomethyl‐6‐methoxy‐phenol) was synthesized by the microwave‐assisted reaction of Co(ClO4)2·6H2O with 3‐ethoxy‐2‐hydroxy‐benzaldehyde (Hehb) and ethylamine in mixed solvent (acetonitrile:methanol = 1:1). Complex 1 was characterized by IR spectroscopy, elemental analysis, and X‐ray single‐crystal diffraction. The magnetic properties of 1 are discussed. Complex 1 displays dominant ferromagnetic interactions from the nature of the binding modes through μ3‐OCH3 and μ2‐phenoxo.

Slow magnetic relaxation in lanthanide ladder type coordination polymers

A series of four isostructural lanthanide-containing one dimensional coordination polymers with picolinic (pic) and glutaric (glu) acids, Ln(glu)(pic)(H2O)2, where Ln = Gd(III) (1), Tb(III) (2), Dy(III) (3) and Er(III) (4) were synthesized under hydrothermal conditions and structurally characterized by powder and single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and thermogravimetric measurements. These compounds are isostructural to the previously reported Sm(glu)(pic)(H2O)2 and the structure consists in pairs of lanthanide ions double bridged by carboxylic groups which are connected along c by the glutaric acid ligands as a ladder type 1D coordination polymer. The magnetic properties of these compounds were studied by static magnetization and AC magnetic susceptibility measurements in the temperature range 1.7-300 K. Weak dominant ferromagnetic interactions between lanthanide cations were found in the compounds, except in compound 3. Compounds 1, 3 and 4 reveal frequency dependent AC susceptibility and slow relaxation of the magnetization under applied external static field. These data classify the Gd(III), Dy(III) and Er(III) compounds as molecular magnets. In spite of the ladder chain structure of the compounds this magnetic behaviour is not due to a single chain but instead it is ascribed to single ion anisotropic effects in the case of 3 and 4 and possibly to a phonon-bottleneck effect of the spin-lattice relaxation in 1.

Square and Butterfly Tetranuclear [Co2Ln2] Clusters Built from the Same Building Blocks but Displaying Different Magnetic Properties: Structural Variation by Means of Solvent and the Radii of Ln3+ Ions

AbstractTwo series of tetranuclear [Ln2Co2] clusters were built from the same [Co(CDTA)]2– building blocks but have different metal skeletons: square 1Ln compounds {[Ln2Co2(CDTA)2(μ4‐OH)(DMF)2(H2O)6]·ClO4·1.5H2O; Ln = La, Gd, and Dy} with a μ4‐OH– bridged Ln–Co–Ln–Co arrangement, and two μ3‐OH–‐bridged “butterfly” 2Ln compounds {[Ln2Co2(CDTA)2(μ3‐OH)2(H2O)6]·6H2O; Ln = Gd, Tb, Dy, and Y} with two Ln3+ ions as the “body” and two Co2+ ions as “wings”. They were prepared from the solvothermal reactions of trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetic acid (H4DCTA), Ln(ClO4)3, and Co(ClO4)2 in DMF/H2O or H2O solvent. Their syntheses are mainly controlled by the solvent and the radii of Ln3+ ions. Light Ln3+ ions with big radii are favorable for the formation of square complexes, whereas heavy Ln3+ ions (including Y3+) with small radii promote the formation of butterfly ones. Remarkably, the middle Ln3+ ions are favorable for the formation of both structures, and in these cases the reactions are controlled by solvent (H2O or H2O + DMF). Magnetic analyses reveal the antiferromagnetic interactions between the two Co2+ ions in 1La and 2Y. Interestingly, other butterfly clusters (2Gd, 2Tb, 2Dy) show dominant ferromagnetic interactions, whereas the other square clusters (1Gd, 1Dy) show overall antiferromagnetic interactions. Details of the magnetic interaction between the metal ions are discussed.

A thermally stable pcu network based on ferromagnetic dinuclear Ni(II) units

A pcu network based on the dinuclear Ni(II) units, [Ni2(hfipbb)2(1,3-bix)2]n (1) (H2hfipbb=4,4′- (Hexafluoroisopropylidene)bis(benzoic Acid); 1,3-bix=1,3-bis(imidazol-1-ylmethyl)benzene), has been hydrothermally synthesized and structurally characterized. Interestingly, the two Ni(II) cations are bridged by two carboxylate groups in the rarely-seen syn-anti mode. The magnetic data reveal the dominant ferromagnetic interactions between Ni(II) ions.

Two disc-like heptanuclear clusters based on Schiff base: syntheses, structure and magnetic properties

Two new disc-like heptanuclear complexes [Ni7(mmimp)6(MeO)6]·2(ClO4) (1), [Ni7(mmimp)6(MeO)6]·2(NO3) (2) were synthesised, where Hmmimp is 2-methoxy-6-methyliminomethyl-phenol. The two compounds were characterised by elemental analysis, IR and X-ray single-crystal diffraction. Compounds 1 and 2 are heptanuclear clusters with the similar cubane topology in which the metal ions and the oxygen, nitrogen atoms from the mmimp− ligands possess a planar hexagonal disc-like structure. Magnetic properties of 1 and 2 have been discussed. The {Ni7} (1) and {Ni7} (2) cores display dominant ferromagnetic interactions from the nature of the binding modes through μ3-OCH3− .

Microwave-Assisted Synthesis, Crystal Structure and Magnetic Behavior of a Schiff Base Heptanuclear Cobalt Cluster

The reaction of Co(ClO4)2·6H2O with 2-hydroxy-3-methoxy-benzaldehyde and an aqueous solution of methylamine in acetonitrile/MeOH under microwave irradiation and controlled temperature/pressure leads to formation of heptanuclear cobalt cluster [Co7(mmp)6(CH3O)6]·(ClO4)2 (1) (mmp is 2-methoxy-6-methyliminomethyl-phenol anion) in only 20 min and also results in higher yields in contrast to other synthesis methods. Complex 1 displays dominant ferromagnetic interactions through μ3-O and μ2-O (oxidophenyl) binding modes.

Synthesis, Magnetism, and Electrochemistry of the Ni14- and Ni5-Containing Heteropolytungstates [Ni14(OH)6(H2O)10(HPO4)4(P2W15O56)4]34–and [Ni5(OH)4(H2O)4(β-GeW9O34)(β-GeW8O30(OH))]13–

The two Ni(2+)-containing heteropolytungstates [Ni14(OH)6(H2O)10(HPO4)4(P2W15O56)4](34-) (Ni14) and [Ni5(OH)4(H2O)4(β-GeW9O34)(β-GeW8O30(OH))](13-) (Ni5) have been successfully synthesized in aqueous, basic media under conventional reaction conditions, and they were characterized by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric and elemental analyses, electrochemistry, and magnetic studies. The cyclic voltammetry (CV) patterns of Ni14 and Ni5 showed chemically reversible multielectronic waves for slow scan time scales. For Ni14, an important acidity inversion effect between its reduced forms was observed. Magnetic studies revealed dominant ferromagnetic interactions among the nickel(II) ions in both polyanions.