Weak Antiferromagnetic Exchange Coupling Research Articles

Coherent magnon transport in a van der Waals antiferromagnet

Recently developed van der Waals magnets offer a promising platform for advancing spintronics. The weak interlayer antiferromagnetic exchange coupling in van der Waals antiferromagnets allows for unique spin dynamics and control over magnons. In this study, we present the excitation and detection of coherent magnon transport in the van der Waals antiferromagnet CrPS4. We observe pronounced coherent magnon–magnon coupling between the optical and acoustic magnon branches, resulting in hybridized magnon modes that can be tuned by modulating the coupling strength, enabling a tunability across a broad frequency range exceeding 10 GHz. The group velocity of the antiferromagnetic magnons is estimated to be approximately 3.8 km/s. Additionally, we experimentally determine the magnon dispersion in CrPS4 by varying the magnon wavevectors and propose an analytical model for the antiferromagnetic magnon dispersion in CrPS4. Our findings open new avenues for energy-efficient magnonic devices based on van der Waals antiferromagnets.

Synthesis, Structures, and Magnetism of Four One-Dimensional Complexes Using [Ni(CN)4]2- and Macrocyclic Metal Complexes.

Four one-dimensional complexes, denoted as [NiL1][Ni(CN)4] (1), [CuL1][Ni(CN)4] (2), [NiL2][Ni(CN)4]·2H2O (3), and [CuL2][Ni(CN)4]·2H2O (4) (L1 = 1,8-dimethyl-1,3,6,8,10,13-hexaaza-cyclotetradecane; L2 = 1,8-dipropyl-1,3,6,8,10,13-hexaazacyclotetradecane) were synthesized by reacting nickel/copper macrocyclic complexes with K2[Ni(CN)4]. Subsequently, the synthesized complexes were characterized using elemental analysis, infrared spectroscopy analysis, thermogravimetric analysis, and X-ray powder diffraction. Single-crystal structure analysis revealed that the Ni(II)/Cu(II) atoms were coordinated by two nitrogen atoms from [Ni(CN)4]2- with four nitrogen atoms from a macrocyclic ligand, forming a six-coordinated octahedral coordination geometry. Nickel/copper macrocyclic complexes were bridged by [Ni(CN)4]2- to construct one-dimensional chain structures in 1-4. The characterization results showed that the four complexes obeyed the Curie-Weiss law with a weak antiferromagnetic exchange coupling.

Spin Crossover Behavior of FeII Complexes Bridged by Thiophene‐Functionalized Triazole Ligands with Different Sizes and Rigidities

AbstractFour thiophene functionalized triazole ligands (L1=4‐(thenyl)‐1,2,4‐triazole, L2=4‐(thiophene ethyl)‐1,2,4‐triazole, L3=N‐Thiophenylidene‐4H‐1,2,4‐triazole‐4‐amine, and L4=(4‐[(E)‐2‐(5‐sulfothiophene)vinyl]‐1,2,4‐triazole) were synthesized. These ligands have different lengths and rigidities, while ligand L4 has a sulfonic acid group that can form a hydrogen bond. Five 1D FeII chain complexes were synthesized: [Fe(L1)3](X)2 ⋅ nH2O [X=BF4−, n=1.5 (C1); X=ClO4−, n=1 (C2)], [Fe(L2)3](BF4)2 ⋅ 1.5H2O (C3); [Fe(L3)3](X)2 ⋅ nH2O [X=BF4−, n=2 (C4); X=ClO4−, n=2.5 (C5)]. The results of temperature‐dependent magnetic susceptibility reveal that complexes C1, C2, and C3 experienced the transition between two spin states. And C4 and C5 maintain high spin states at all temperature ranges. Binuclear complex [Fe2(L3)5(SCN)4] (C6) and mononuclear material [Fe(L4)2(H2O)4] ⋅ 2H2O (C7), these two zero‐dimensional molecules were also synthesized. They all display weak antiferromagnetic exchange coupling and a high spin state in the whole process.

Solvothermal synthesis, crystal structure, thermal, magnetic properties and DFT computations of a Ytterbium(III) complex derived from pyridine-2,6-dicarboxylic acid

A new ytterbium(III) complex, (DMAH2)3[Yb(Pydc)3].4H2O (1) {Pydc = Pyridine-2,6-dicarboxylate anion, DMAH2 = Dimethylammonium} has been prepared under mild solvothermal conditions and characterized by elemental analysis, IR spectroscopy, thermal analysis and single crystal X-ray diffraction. The DMAH2 molecules in 1, generated in situ from hydrolysis of N,N-dimethylformamide are responsible to assemble 2D coordination polymer through N-H···O and O-H···O hydrogen bonding. Magnetic susceptibility measurements indicate that the complex (1) obeys the Curie Weiss law and the overall magnetic behavior is typical for the presence of weak antiferromagnetic exchange coupling interactions. Theoretical data for geometrical parameters of complex 1 agree well with the experimental data. Large HOMO-LUMO energy gap of 4.33 eV has provided kinetic stability to the complex 1. NBO analysis reflects that intramolecular charge transfer occurred between ligand and metal orbitals with the highest stabilization energy of 1024.04 kcal/mol. The negative electrostatic potential at the nitrogen and dianionic pyridine-2,6-dicarboxylate regions confirms that these are dynamic locations for Yb(III) binding.

A Neutral Fe4tBuL4 All Ferric Grid Complex: Structural and Variable Temperature Magnetic Properties

A neutral all ferric [2×2] grid complex Fe4tBuL4 1 was synthesized and characterized in the solid‐state by X‐ray crystallography, variable temperature magnetic susceptibility and Mössbauer spectroscopy. The absence of any coordinate bond or other structural changes between 90(2) and 320(2) K indicated no changes to the electronic structure of 1 occurred in the solid‐state over this temperature range. Variable temperature magnetic susceptibility data were fitted to an isotropic spin Hamiltonian model and suggested weak antiferromagnetic exchange coupling between the high‐spin ferric ions (J = –16.1 cm‐1). Mössbauer spectroscopy parameters (δ = 0.416(9) mm s–1 & ΔEQ = 0.87(7) mm s‐1), powder EPR spectra, and broken symmetry density functional theory calculations supported the high‐spin ferric oxidation state assignment.

Coordination polymers of zinc(II) and manganese(II) made by complexation of calix[4]arene functionalized with carboxylates afford alveolar materials

25,27-bis(methoxycarboxylic acid)-26,28-dihydroxycalix[4]arene (calixH2), so call here calix[4]arene dimethoxycarboxylic acid, was investigated for its ability to build metal–organic frameworks. When reacted with zinc or manganese chloride in DMF and deprotonated with trimethylamine it gives Zn (1) and Mn (2) coordination compounds. These crystallize in the triclinic P-1 space group and are isostructural as shown by X-ray diffraction on single crystals. The crystal structures evidence the coordination of calix[4]arenedimethoxycarboxylic acid through the carboxylate groups. This makes a 1D coordination polymer running along the c axis direction in which [MII2(calix)2(H2O)3(DMF)2] (M = Zn or Mn) neutral units are connected. Last step refinements of the crystal structure reveal a lot of residual electron density which was ascribed to uncoordinated disordered water and DMF molecules. This was treated with the SQUEEZE routine of the program PLATON from which the solvent accessible voids per unit cell volume was calculated to be 24.5% for compound 1 (Zn) and 24.9% for compound 2 (Mn). Complementary differential thermal analyses (DTA) combined with thermogravimety analysis (TGA) and mass spectrometry (MS) are in agreement with large amount of incorporated and non-coordinated water and DMF molecules. Adsorption isotherms of N2 measured for compound 1 do not show any significant porosity. The temperature dependence of the magnetic susceptibility (χ) of compound 2 evidences antiferromagnetic interactions and was best fitted with a weak antiferromagnetic exchange coupling between the manganese(II) ions J = − 1.5 cm−1 and small antiferromagnetic inter-dinuclear interactions zJ = − 1.2 cm−1 (g = 2.02).

FeII Complexes with Triple N1,N2‐Triazole Bridge Schiff Base Ligand: Antiferromagnetic Dimer vs. Spin Conversion Trimer

Based on the p‐tolyl functionalized Schiff base 1,2,4‐triazole ligand 4‐(p‐tolylidene‐amino)‐4H‐1,2,4‐triazole (toltrz), a series of three triazole‐bridged FeII complexes have been prepared. The compounds represent a range of dinuclear and trinuclear species, with µ2‐N1,N2‐triazole bridges linking the FeII centers. Mössbauer spectroscopy and magnetic susceptibility measurements reveal a gradual single‐step spin crossover (SCO) behavior for the trimeric compound 3 on the central FeII site. Single‐crystal X‐ray diffraction at 120 K confirms that the central FeII site undergoes a HS to LS transition while the peripheral FeII remain in HS state (HS = high spin; LS = low spin). Compounds 1 and 2 are isostructures with different terminal ligand XCN (X = S, Se), these two compounds stay in high spin state over the whole temperature range but display weak antiferromagnetic exchange coupling.

Abrupt Spin Crossover Behavior in a Linear N1,N2-Triazole Bridged Trinuclear Fe(II) Complex

The synthesis, structures and magnetic properties of a new trinuclear spin crossover complex [FeII3(pyrtrz)6(TsO)6]·10H2O·2CH3OH (C2) and its analogue binuclear [FeII2(pyrtrz)5(SCN)4]·7H2O (C1), are reported here. These two compounds are synthesized based on the pyrrolyl functionalized Schiff base 1,2,4-triazole ligand 4-((1H-pyrrol-2-yl)methylene-amino)-4H-1,2,4-triazole (pyrtrz), which represent rare discrete multi-nuclear species, with µ2-N1,N2-triazole bridges linking the FeII centers. DC magnetic susceptibility measurements revealed an abrupt single-step spin crossover (SCO) behavior for compound 2 on the central FeII site and single-crystal X-ray diffraction (173 K) showed that this compound crystallizes in the monoclinic space group (P21/c), and multiple intramolecular interactions were found responsible for the abrupt transition. Compound 1 is a binuclear complex with thiocyanate as terminal ligands. This compound stays in high spin state over the whole temperature range and displays weak antiferromagnetic exchange coupling.

Synthesis, crystal structure and magneto-structural studies of 2D copper(II) coordination polymer containing l-alanine amino acid

A 2D coordination polymer of Cu(II) was synthesized by the reaction of CuCl2·2H2O with l-alanine and characterized by elemental analysis, spectroscopic methods and single crystal X-ray studies. X-ray analysis indicated that the compound is a 2D coordination polymer which the carboxylate group of amino acid ligands acts as bridging ligand between Cu(II) ions. The crystal structure of compound is stabilized by intermolecular hydrogen bond interactions. Magnetic susceptibility data of powdered sample between 2 and 300 K were interpreted in terms of a 2D-spin model, with weak antiferromagnetic exchange-coupling through syn-anti carboxylate bridges, with coupling constant J = −0.2 cm−1 between nearest-neighbor Cu(II) ions. The results are compared with those obtained from similar studies in other copper amino acid complexes. DFT studies showed that overlap of magnetic dx2−y2 orbitals of the neighboring Cu(II) ions and the molecular orbitals of bridging carboxylate groups is negligible what makes only weak antiferromagnetic interaction between them. Thermal gravimetric analysis (TGA) indicated that the compound is stable up to 240 °C and it converts to CuO at about 800 °C. Cyclic voltammetry studies showed a quasi-reversible redox and an irreversible peaks which can be attributed to Cu(I)/Cu(II) and Cu(II)/Cu(III) couples, respectively.

Design of a Binuclear Ni(II) Complex with Large Ising-type Anisotropy and Weak Anti-Ferromagnetic Coupling.

The preparation of a binuclear Ni(II) complex with a pentacoordinate environment using a cryptand organic ligand and the imidazolate bridge is reported. The coordination sphere is close to trigonal bipyramidal (tbp) for one Ni(II) and to square pyramidal (spy) for the other. The use of the imidazolate bridge that undergoes π-π stacking with two benzene rings of the chelating ligand induces steric hindrance that stabilizes the pentacoordinate environment. Magnetic measurements together with theoretical studies of the spin states energy levels allow fitting the data and reveal a large Ising-type anisotropy and a weak anti-ferromagnetic exchange coupling between the metal ions. The magnitude and the nature of the magnetic anisotropy and the difference in anisotropy between the two metal ions are rationalized using wave-function-based calculations. We show that a slight distortion of the coordination sphere of Ni(II) from spy to tbp leads to an Ising-type anisotropy. Broken-symmetry density functional calculations rationalize the weak anti-ferromagnetic exchange coupling through the imidazolate bridge.

Structural and Magnetic Characterization of Two Tetranuclear Cu(II) Complexes with Closed‐Cubane‐Like Core Framework

AbstractTwo novel tetranuclear closed‐cubane like core framework complexes [Cu4(L1)4]⋅3(H2O) (1) and [Cu4(H2L2)4(H2O)4] (2) (H2L1=(E)‐2‐((1‐hydroxybutan‐2‐ylimino)methyl)phenol; H4L2=2‐((2‐hydroxy‐3‐methoxybenzylidene)amino)‐2‐hydroxymethylpropane‐1,3‐diol) were synthesized and structurally characterized. Magnetic susceptibility measurements indicate an overall weak antiferromagnetic exchange coupling in 1, while ferromagnetic exchange coupling in 2. In agreement with their closed‐cubane structure, the magnetic behavior of the two complexes have been studied by employing the isotropic spin Hamiltonian of type H=J1 (S1S3 + S1S4 + S2S3 + S2S4) ‐ J2 (S1S2 + S3S4) (J1 describes the magnetic exchange coupling between the four Cu(II) pairs with short Cu⋅⋅⋅Cu distances, while J2 characterizes the magnetic exchange coupling between the remaining two intermetallic pairs with long distances). The PHI program was used to study their magnetic behavior. A good agreement between the experimental and fitted curves was found with the following parameters: g=2.14, J1=‐20.3 cm−1 and J2=0 cm−1 for 1 and g=2.10, J1=101.1 cm−1 and J2=‐51.5 cm−1 for 2.

Design and Magnetic Properties of a Mononuclear Co(II) Single Molecule Magnet and Its Antiferromagnetically Coupled Binuclear Derivative.

The preparations of related mononuclear and binuclear Co(II) complexes with a quasi-identical local C3v symmetry using a cryptand organic ligand are reported. The mononuclear complex behaves as a single molecule magnet (SMM). A relatively weak antiferromagnetic exchange coupling (J) of the same order of magnitude as the local magnetic anisotropy (D) is determined experimentally and theoretically for the binuclear complex. The weak magnitude of the antiferromagnetic exchange coupling, analyzed using a combination of broken-symmetry density functional theory and wave function based calculations, is ascribed to the weak overlap between the singly occupied orbitals because of the local C3v symmetry of the Co(II) ions; the organic ligand was found to contribute to the exchange coupling as the azido bridge that directly links the Co(II) ions. Calculation of the energy and wave functions of the spin states for the binuclear complex, in the general case, allows analysis of the effect of the |J/D| ratio on the magnetic behavior of the binuclear complex and prediction of the optimum range of values for the complex to behave as two weakly interacting SMMs.

Structural and magnetic characterization of three tetranuclear Cu(II) complexes with face-sharing-dicubane/double-open-cubane like core framework

Three novel tetranuclear copper(II) complexes namely [Cu4(L1)4]∙2(dmf) (1), [Cu4(L1)4] (2) and [Cu4(L2)2(HL2)2(H2O)2]∙2(ClO4)·6(H2O) (3) (H2L1, (E)−2-((1-hydroxybutan-2-ylimino)methyl)phenol; H2L2, (E)−2-((1-hydroxybutan-2-ylimino)methyl)−6-methoxyphenol)) were synthesized from the self-assembly of copper(II) perchlorate and the tridentate Schiff base ligands. The structural determination reveals that complex 1 crystallizes in the monoclinic system with space group C2/c, whereas both the complexes 2 and 3 crystallize in the triclinic system with space group P-1. Complexes 1 and 2 possess face-sharing dicubane core, on the other hand complex 3 has double open cubane core structure. The copper(II) ions in the cubane core are in distorted square planar geometries, and weak π…π and C–H…π interactions lead to formation of a 2D supramolecular architecture for complexes 1 and 2. At room temperature complexes 1, 2 and 3, exhibit fluorescence with a quantum yield (Φs) of 0.47, 0.49 and 0.38, respectively. Variable temperature magnetic susceptibility measurements in the range 2–300K indicate an overall weak antiferromagnetic exchange coupling in all complexes. The PHI program was used to study their magnetic behaviour. In agreement with their face-sharing dicubane structure, a Hamiltonian of the type H =– J1(S1S2+S1S2’+S1'S2+S1'S2’) – J2S1S1’, where S1 = S1’ = S2 = S2’ = SCu =1/2, was used for studying complexes 1 and 2. Simulations performed suggest magnetic exchange constants with values close to J1 =−20cm−1 and J2 =0cm-1 for these complexes. On the other hand, the spin Hamiltonian H =– J1(S1S4+S2S3) – J2(S1S3+S2S4) – J3S1S2, where S1 = S2 = S3 = S4 = SCu =1/2, was used to study the magnetic behaviour of the double open cubane core of complex 3 and a good agreement between the experimental and simulated results was found by using the parameters g1 = g2 =2.20, g3 = g4 =2.18, J1 =−36cm-1, J2 =−44cm-1 and J3 =0cm-1.

Magnetic studies reveal near-perfect paramagnetism in the molecular semiconductor vanadyl phthalocyanine (C32H16N8VO)

Temperature (0.5–300K) and magnetic field (H up to 90kOe) dependences of the magnetization (M) of a powder sample of vanadyl phthalocyanine (VOPc) having the Phase II-triclinic structure are measured and analyzed. The data of χ = M/H vs. T measured in H = 1kOe fit the modified Curie-Weiss (CW) law, χ = χo+C/(T−θ), with C = 6.266×10−4 emuK/gOe, θ = −0.1K and χo = −9.3×10−7emu/gOe. The Curie constant C yields magnetic moment μ = 1.704μB, S = 1/2, and g = 1.967 characteristic of VO2+. The magnitude of θ = −0.1K signifying very weak inter-ion antiferromagnetic exchange coupling is supported by the analysis of the variable frequency (9.8–336GHz) electron paramagnetic resonance data. The isothermal data of M vs. H at ten temperatures between 0.5K and 300K when plotted as M vs. H/(T+0.1) collapses on to a single curve given by M = Motanh {gμBH/[2kB(T+0.1)]} with Mo = NgμBS = 9.48emu/g expected for S = 1/2 system, thus signifying near perfect paramagnetism in VOPc.

Exchange Interaction of Strongly Anisotropic Tripodal Erbium Single-Ion Magnets with Metallic Surfaces

We present a comprehensive study of Er(trensal) single-ion magnets deposited in ultrahigh vacuum onto metallic surfaces. X-ray photoelectron spectroscopy reveals that the molecular structure is preserved after sublimation, and that the molecules are physisorbed on Au(111) while they are chemisorbed on a Ni thin film on Cu(100) single-crystalline surfaces. X-ray magnetic circular dichroism (XMCD) measurements performed on Au(111) samples covered with molecular monolayers held at temperatures down to 4 K suggest that the easy axes of the strongly anisotropic molecules are randomly oriented. Furthermore XMCD indicates a weak antiferromagnetic exchange coupling between the single-ion magnets and the ferromagnetic Ni/Cu(100) substrate. For the latter case, spin-Hamiltonian fits to the XMCD M(H) suggest a significant structural distortion of the molecules. Scanning tunneling microscopy reveals that the molecules are mobile on Au(111) at room temperature, whereas they are more strongly attached on Ni/Cu(100). X-ray photoelectron spectroscopy results provide evidence for the chemical bonding between Er(trensal) molecules and the Ni substrate. Density functional theory calculations support these findings and, in addition, reveal the most stable adsorption configuration on Ni/Cu(100) as well as the Ni-Er exchange path. Our study suggests that the magnetic moment of Er(trensal) can be stabilized via suppression of quantum tunneling of magnetization by exchange coupling to the Ni surface atoms. Moreover, it opens up pathways toward optical addressing of surface-deposited single-ion magnets.

Synthesis, Crystal Structure, and Magnetic Properties of Two Manganese(II) and Cobalt(II) Coordination Polymers Based on Biphenyl‐3, 3′,4, 4′‐tetracarboxylic Acid

Abstract Two coordination polymers, [Mn2(btc)(phen)4]n·7nH2O (1) and [Co2(btc)(phen)(H2O)2]n·nH2O (2) (H4btc = biphenyl‐3, 3′,4, 4′‐tetracarboxylic acid, phen = 1, 10‐phenanthroline) were hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. Compound 1 has a 1D chain structure in which the dinuclear Mn2 units are linked through (btc)4– ligands. Magnetic measurements revealed weak antiferromagnetic and ferromagnetic exchange coupling interactions between MnII and CoII ions in 1 and 2, respectively. Moreover, both compounds have good thermal stabilities.

Di‐ and Tetranuclear Complexes of Bis‐Tetradentate Pyrimidine‐Based Ligands with All‐Methylene‐ Versus Mixed Methylene/Ethylene‐Linked Arms

Eleven dinuclear and six tetranuclear complexes of two bis-tetradentate ligands, 4,6-bis[N,N-bis(2???-pyridylmethyl)aminomethyl]-2-phenylpyrimidine (LMe) and 4,6-[(2???-pyridylmethyl)(2???-pyridylethyl)aminomethyl]-2-phenylpyrimidine (LMix), have been prepared through reactions of ligand and metal salt in a ratio of 1:2 in MeCN or MeOH: FeII2LMe(H2O)4(MeCN)2(BF4)4 (1), FeII2LMix(H2O)4(BF4)4 (2), [CoII2LMe(H2O)(MeCN)](BF4)4??3/2H2O (3), [CoII2LMix(H2O)(MeCN)3](BF4)4??2H2O (4), [NiII2LMe(H2O)4](BF4)4??H2O (5), [NiII2LMix(H2O)3(MeCN)](BF4)4 (6), CuII2LMe(H2O)(MeCN)(BF4)4 (7), [CuII2Mix(MeCN)2(BF4)4] (8), [ZnII2LMe(H2O)(MeCN)3(BF4)4] (9), [ZnII2LMix(MeCN)3(H2O)(BF4)4] (10), [ZnII2LMe(H2O)2L(MeCN)2](ClO4)4 (11), FeII2FeIII2(LMe)2F4(BF4)6??1/2H2O (12), FeII4(LMix)2F4(BF4)4??5H2O (13), CoII2CoIII2(LMe)2F4(BF4)6 (14), [CoII4(LMix)2F4](BF4)4??3H2O (15), [NiII4(LMe)2F4](BF4)4 (16) and NiII4(LMix)2F4(BF4)4??8H2O (17). Dinuclear complexes were obtained from the reactions conducted in MeCN, whereas tetranuclear complexes resulted from reactions performed in MeOH. Five dimetallic (3??????6??? and 9???) and one tetrametallic complex (15???) were structurally characterized: the ligands are bis-tetradentate and the metal centres are bridged through the pyrimidine ring. In the tetrametallic 15???, two such dimetallic fragments are bridged by two pairs of fluoride anions. Variable-temperature magnetic susceptibility measurements and Heisenberg fitting of dinuclear 1???8 and tetranuclear 13???15 in all cases revealed weak intramolecular anti-ferromagnetic exchange coupling between the high-spin metal centres. A rigorous spin???orbit and exchange analysis was also performed on the dicobalt(II) complex 4. The dicopper(II) complexes 7 and 8 underwent a two-electron quasi-reversible reduction (CuII2 ??? CuI2), in both cases at a more negative potential (7: Em = ???0.18 V; 8: Em = ???0.19 V vs. 0.01 M AgNO3/Ag) than the analogous LEt (all-ethylene-armed ligand) complex (Em = +0.11 V vs. 0.01 M AgNO3/Ag), consistent with LMe and LMix being better able to stabilize copper(II) than LEt.

Sodium-Centered Dodecanuclear Co(II) and Ni(II) Complexes with 2-(Phosphonomethylamino)succinic Acid: Studies of Spectroscopic, Structural, and Magnetic Properties

Two new isostructural cobalt(II) and nickel(II) polynuclear complexes with 2-(phosphonomethyl)aminosuccinic acid, H4PMAS, namely, Na[Co12(PMAS)6(H2O)17(OH)]·x2H2O, 1·x2H2O, and Na[Ni12(PMAS)6(H2O)17(OH)]·xH2O, 2·xH2O, have been synthesized for the first time from aqueous solutions and studied by single crystal X-ray diffraction, infrared, and UV-visible diffuse reflectance spectroscopy; TG/DTA analysis; and magnetochemistry. Both 1 and 2 crystallize in the rhombohedral crystal system with the R3[overline] space group with 1/6 of the Co12(PMAS)6 or Ni12(PMAS)6 moieties in the asymmetric unit. The X-ray refinements reveal the presence of 18 water sites, but unit cell charge balance requires that one water molecule must be an OH(-) anion, an anion which is disordered over the 18 sites. The PMAS(4-) ligand forms two five-membered and one six-membered chelation ring. Both 1 and 2 contain 24-membered metallacycles as a result of the bridging nature of the PMAS(4-) ligands. The resulting three-dimensional structures have one-dimensional channels with a sodium cation at the center of symmetry. The temperature dependence of the magnetic susceptibility reveals the presence of weak antiferromagnetic exchange coupling interactions in both 1 and 2. Two exchange coupling constants, J1 = -15.3(7) cm(-1) and J2 = -1.06(2) cm(-1) with S1 = S2 = 3/2 for the Co(1)···Co(1) and Co(1)···Co(2) exchange pathways, respectively, are required for 1, and J1 = -1.17(6) cm(-1) and J2 = -4.00(8) cm(-1) with S1 = S2 = 1 for the Ni(1)···Ni(1) and Ni(1)···Ni(2) exchange pathways, respectively, are required for 2, in order to fit the temperature dependence of the observed magnetic susceptibilities.

Spin Crossover in Polymeric Materials Using Schiff Base Functionalized Triazole Ligands

AbstractFunctionalized 1,2,4‐(R)‐triazole‐based Schiff base (R‐N=CH‐R′) ligands have been incorporated into spin crossover 1D materials of the general formula [Fe(Xtrz)3](A)2·2H2O (A = BF4, ClO4, Br, NO3; Xtrz = triazole liands). The ligand N‐salicylidene 4‐amino‐1,2,4‐triazole (Hsaltrz) and the novel ligand N‐cinimalidene 4‐amino‐1,2,4‐triazole (Hcintrz) were targeted to assess the implication of incorporating various aromatic functional groups on the spin crossover properties of this well‐known family of one‐dimensional materials. Magnetic susceptibility measurements on the polycrystalline powdered materials [Fe(Hsaltrz)3](A)2·2H2O [A = BF4 (1), ClO4 (2), Br (3)] and [Fe(Hcintrz)3](A)2·1.5(H2O) [A = BF4 (4), ClO4 (5), Br (6)] revealed spin transitions over the range T${1 \over 2}$ = 100–225 K. The spin crossover properties of the dehydrated materials were also investigated [1–6(dh)]. In attempts to prepare single crystals of these materials a dinuclear {[Fe2(Hsaltrz)5(NCS)4]·2MeOH (7)} and a trinuclear {[Fe3(Hsaltrz)6(H2O)2(EtOH)4](ClO4)6·2(EtOH) (8)} complex were obtained; these materials remain high spin over all temperatures and display weak antiferromagnetic exchange coupling. The structure of the novel ligand Hcintrz (9) is reported.

Synthesis, crystal structure and magnetic characterization of two Mn(III) chains with Schiff-base ligands

Two new one-dimensional manganese(III) complexes [Mn2III(L1)4(piv)2] (1) and [MnIII(L2)(bix)]·2H2O⋅ClO4 (2) (H2L1=N-(2-hydroxyethyl)-3-methoxysalicylaldimine, H2L2=N,N′-bis(salicylidene)phenylenediamine, bix=1,4-bis-(imidazol-1-ylmethyl)benzene, piv=pivalate) have been synthesized and characterized by X-ray crystallography and magnetic measurements. Crystal structure studies reveal that complex 1 consists one-dimensional manganese(III) chains linked by L12- ligand in η1:η1:η1:μ2 mode. In complex 2, the Mn(III) ion is coordinated by the tetradentate L22- ligand in the equatorial plane, whereas bix ligand acts as bridge in the axial direction. Magnetic studies show that both complexes exhibit weak antiferromagnetic exchange coupling between Mn(III) ions.