Antiferromagnetic Complex Research Articles

Antiferromagnetic complex electromotive microscale with first type Schrödinger frame

Antiferromagnetic complex electromotive microscale with first type Schrödinger frame

Disentangling the magnetic dimensionality of an alleged magnetically isolated cuprate spin-ladder CuHpCl system: a long-lasting issue.

The Cu2(1,4-diazacycloheptane)2Cl4 (CuHpCl) crystal is a molecular transition metal antiferromagnetic complex, whose magnetism has been a long-lasting issue. The outcome of a variety of experimental studies (on magnetic susceptibility, heat capacity, magnetization, spin gap and INS) reported many different J values depending on the fitting ladder model used. From all available experimental data, one can infer that CuHpCl is a very complex system with many competing microscopic magnetic JAB interactions that lead to its overall antiferromagnetic behavior. A first-principles bottom-up study of CuHpCl is thus necessary in order to fully disentangle its magnetism. Here we incorporate data from ab initio computations providing the magnitude of the JAB interactions to investigate the microscopic magnetic couplings in CuHpCl and, ultimately, to understand the macroscopic magnetic behavior of this crystal. Strikingly, the resulting magnetic topology can be pictured as a 3D network of interacting squared plaquette magnetic building blocks, which does not agree with the suggested ladder motif (with uniform rails) that arises from direct observation of the crystal packing. The computed magnetic susceptibility, heat capacity and magnetization data show good agreement with the experimental data. In spite of this agreement, only the calculated magnetization data are used to discriminate between the different spin regimes in CuHpCl, namely gapped singlet, partially polarized and fully polarized phases. Additional analysis of the magnetic wavefunction enables the conclusion that long-range spin correlation can be discarded as being responsible for the partially polarized phase, whose magnetic response is in fact due to the complex interplay of the magnetic moments in the 3D magnetic topology.

Crystal structure, optical and magnetic properties of perovskite Gd(Mn0.7Ni0.3)O3 ceramic nanoparticles: An experimental and first-principles studies

The perovskite Gd(Mn 0.7 Ni 0.3 )O 3 ceramic nanoparticles were synthesized by a facile sol-gel technique. The structure, electronic structure, surface morphology, optical and magnetic properties of GdMn 0.7 Ni 0.3 O 3 nanoparticles were investigated. X-ray diffraction pattern confirms the formation of pure orthorhombic perovskite GdMn 0.7 Ni 0.3 O 3 ceramic nanoparticles with Pbnm space group. Spin-polarized band structure and partial density of states reveal the ferromagnetic behavior of the sample. The optical band gap was calculated using the Tauc plot it is found to be 3.2 eV. Magnetization curves such as zero-field-cooled, field-cooled and hysteresis loop are further confirmed that the sample shows paramagnetic at the surface and complex magnetic behavior at low temperature. The mixture of ferromagnetic and antiferromagnetic complex magnetic behavior arises from the distorted crystal structure and coexistence of Gd 3+ , Mn 3+ and Mn 4+ ions with multiple exchange interaction in the sample.

DFT-FPLMTO study of electronic and magnetic structures of half-metallic antiferromagnetic complex perovskite Ba2CoWO6

The ordered complex perovskite Ba2CoWO6 has been studied for the first time by employing both the local spin density approximation (LSDA) and LSDA + U procedure. The crystal structure of Ba2CoWO6 is found to be face-centered cubic (Fm-3m space group) with rock-salt-type cation ordering and lattice constant of (a = 8.031 Å). A detailed study on the electronic and magnetic structures of Ba2CoWO6 has been carried out by using the density functional theory (DFT). Moreover, the crystal-field and spin-exchange splitting together with the [–O2−(2p)–Co2+(3d)–O2−(2p)–W6+(5d)–O2−(2p)–] hybridization have been investigated by means of total and partial density of states (DOS). The 3d electron–electron correlation between Co2+ ions has a great significance to the electronic structure and leads to half-metallic behavior. The theoretical results in this study are in favorable agreement with the previous experimental studies.

Effect of the Schiff-base-containing triazole ligand and counter anion on the construction of dimeric silver and polynuclear copper complexes

Five new complexes, namely [Ag2(tmat)2(MeCN)2](PF6)2 (1), [Ag2(tmat)4](PF6)2 (2), [Ag2(tmat)4](CF3SO3)2 (3), [Cu3(tmat)6(H2O)6](ClO4)6·4H2O (4) and [Cu4(OH)2(OAc)6(tmat)2]·2H2O (5), have been obtained from the reactions of silver(I) or copper(II) salts with (E)-(thiophen-2-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine (tmat). Complexes 1–3 are based on Ag dimers and have extended solid-state structures formed by different weak interactions. The Ag(I) atoms exhibit a Y-shape coordination geometry in dimeric 1, in which Ag–π and Ag⋯S weak interactions can be found. Complex 2 is constructed from dinuclear [Ag2(tmat)4]2+ cations and PF6− anions, which are further connected to form a quasi-3D structure by C–H⋯F hydrogen bonds. In 3, the Ag(I) atoms exhibit a distorted tetrahedral geometry and rich non-classical weak interactions, such as F⋯S, sustain the packing structure. Complexes 4 and 5 are linear trinuclear and planar tetranuclear complexes, respectively. Complex 5 is an antiferromagnetic complex with Jwb=−77.5cm−1, Jbb=−33.8cm−1 (g=2.0). A discussion of the crystal structures, as well as the coordination properties of the tmat ligands with different counter anions, has been provided.

Ferromagnetic and antiferromagnetic copper(ii) complexes: Counterplay between zero-field effects of the quartet ground state and intermolecular interactions

The linear trinuclear Cu(II) complexes [Cu(3)(L(1))(4)(H(2)tea)(2)] (1), [Cu(3)(L(2))(4)(H(2)tea)(2)]·2CH(3)CN (2), [Cu(3)(L(2))(4)(H(2)tea)(2)] (3), [Cu(3)(L(1))(2)(H(2)tea)(2)(NO(3))(2)] (4) and the dinuclear complex [Cu(2)(L(1))(2)(H(2)tea)(2)] (5), where L(1) = 2-thiophene carboxylate, L(2) = 2-(thiophen-2-yl)-acetate and H(2)tea = the single deprotonated form of triethanolamine have been prepared and characterised while the crystal structures of 1-4 have been determined. The variable-temperature magnetic susceptibilities of complexes 1-5 have been measured in the range 2-300 K under various external fields in the range 0.02-1.0 T. X-band EPR spectra of 1-5 compounds were recorded at 4-100 K. Complexes 1, 2 and 3 found to have the same J = 33 cm(-1) and g values 2.16(1), 2.20(1) and 2.16(1) respectively while for 5 J = 15 cm(-1) and g = 2.06(1) revealing a clear ferromagnetic exchange between Cu(II) ions. Complex 4 was found to be antiferromagnetic with J = -28 cm(-1) and g = 2.21(1). The polycrystalline powder X-band EPR spectrum of complexes 1, 2, and 3 at 4 K are dominated by a transition at 1600 G (g = 4.3) which unambiguously identifies the spin of the ground multiplet (S = 3/2) while the antiferromagnetic complex 4 has a derivative centered at g = 2.1 indicative of a ground doublet (S = 1/2). Concerning complex 5 a spectrum of a dominant derivative centered at g = 2.06(1) is observed with a very weak half field transition (ca. 1500 G) indicative of the ferromagnetic nature of the system. Furthermore, for complexes 2 and 3 a strong temperature dependence of this spectroscopic g-factor is revealed and change of the g(eff) from the liquid helium temperature to the room temperature is almost 2 units.

Synthesis, structure, solid-state thermolysis, and thermodynamic properties of new heterometallic complex Li 2Co 2(Piv) 6(NEt 3) 2

The reaction of lithium pivalate, polymeric cobalt pivalate [Co(Piv) 2] n , and triethylamine in THF at 60 °С afforded the new heterometallic antiferromagnetic complex Li 2Co 2(Piv) 6(NEt 3) 2 ( 2). The molecular and crystal structure of complex 2 was established and its magnetic behavior was studied. The vaporization and solid-state thermolysis of 2 were investigated. The thermodynamic characteristics of complex 2 were determined. The results of the present study show that complex 2 can be used as a potential molecular precursor for the synthesis of thin films of lithium cobaltate LiCoO 2.

Magnetic field-induced formation of molecule-based magnetic material [Co 1.5(N 3)(OH)(L)] n with antiferromagnetic coupling

Two identical hydrothermal self-assembly reactions were carried out with and without an applied magnetic field of 0.2 T. Two kinds of single crystals can be both obtained in the two reactions. It is shown that the crystal yield of the magnetic material is remarkably increased after the weak magnetic field is employed. We ascribe the magnetic field effect to the decrease of activation energy of antiferromagnetic complex during the course of the self-assembly reaction. And the decrease of activation energy is because the partial magnetic phase transits from paramagnetic phase to antiferromagnetic phase. Moreover, magnetic measurement data also reveal that the antiferromagnetic coupling interaction of the magnetic material has been enhanced.

Pivalate Bridged High Spin Manganese(II) and Iron(II) Polymers

Antiferromagnetic Mn(II) polymers of general formula {[L2Mn(μ-OOCCMe3)2][Mn2(μ-OOCCMe3)4]}n (L = 1,2-phenylenediamine (3) and 4,5-dimethyl-1,2-phenylenediamine (4)) were synthesized from [Mn(μ-OOCCMe3)2(HOEt)] n (1) polymer and arenediamines in MeCN solution. The tetranuclear cluster Fe4(μ3-OH)2(μ-OOCCMe3)4(η2-OOCCMe3)2(EtOH)6 (5) was prepared by reacting FeSO4·7H2O with KOOCCMe3 in EtOH and was used as starting pivalate iron(II) agent in further reactions. The thermolysis of 5 in MeCN was shown to result in a ferromagnetic polymer [Fe(μ-OOCCMe3)2] n (6) containing tetrahedral iron(II) atoms. Cluster 5 was found to react with o-phenylenediamine giving rise to ferrimagnetic polymer [Fe(μ-OOCCMe3)2(HOEt)]n (7). The reaction 7 with 2,6-diaminopyridine in MeCN results in binuclear antiferromagnetic complex (2,6-(NH2)2C5H3N)2Fe2(μ-OOCCMe3)4· 4MeCN (8). However the reaction of 4,5-dimethyl-1,2-phenylenediamine with polymer 7 yields a polymer {[L2Fe(μ-OOCCMe3)2][Fe2 (μ-OOCCMe3)4]} n (9), which is an analogue of the manganese polymer 4. All newly synthesized compounds were characterized by the by X-ray diffraction studies and magnetic measurement.

Formation of bi- and tetranuclear cobalt(ii) trimethylacetate complexes with 2-amino-5-methylpyridine and 2,6-diaminopyridine

The reactions of the polymeric complex [Co(OH)n(OOCCMe3)2–n ]x (1) with 2-amino-5-methylpyridine (L1) and 2,6-diaminopyridine (L2) under anaerobic conditions at the ratio M : L = 1 : 1 afforded the binuclear complexes Co2(μ-OOCCMe3)4[η-MeC5H3N(NH2)]2 (2) and Co2(μ-OOCCMe3)4[η-C5H3N(NH2)2]2 (3), respectively, with Chinese-lantern-like structures. The reaction of the tetranuclear cobalt(ii) complex Co4(μ3-OH)2(μ-OOCCMe3)4(η2-OOCCMe3)2(EtOH)6 (4) with 2,6-diaminopyridine under anaerobic conditions at the ratio M : L2 = 2 : 1 gave rise to the antiferromagnetic tetranuclear complex Co4(μ4-O)[μ-C5H3N(NH2)2]2(μ-OOCCMe3)4(η2-OOCCMe3)2 (5) with tetradentate-bridging coordination of the oxygen atom. The structures of the compounds synthesized were established by X-ray diffraction analysis.

Spin Structure and Dynamics in a Spin 1/2 One Dimensional Antiferromagnet, [NiBr(chxn)2]Br2 (chxn: 1R,2R-cyclohexanediamine)

Abstract The 1H NMR spin-lattice relaxation time T1 in a spin 1/2 1-D antiferromagnetic complex [NiBr(chxn)2]Br2 was observed down to 1.8 K. The observed T1 temperature dependence was well reproduced by the Sachdev’s treatment giving an exchange interaction energy (J) of ca. 2500 K. 1-D spin migration assignable to paramagnetic electrons in impurity amounts of NiII sites was observed at low temperatures.

Formation of cobalt(iii) cations with semiquinonediimine ligands

The reactions of polynuclear cobalt(ii) trimethylacetates [Co(OH)n(OOCCMe3)2–n]x, Co6(μ3-OH)2(OOCCMe3)10(HOOCCMe3)4, or Co4(μ3-OH)2(OOCCMe3)6(HOEt)6 with an excess of N-phenyl-o-phenylenediamine (1) in toluene followed by treatment with atmospheric oxygen afforded the diamagnetic complex [Co{η2-(NPh)(NH)C6H4}2{η1-(NH2)C6H4(NPhH)}]+(Me3CCOO...H...OOCCMe3)– (3), whose cation contains the CoIII atom. The reaction of Co4(μ3-OH)2(OOCCMe3)6(HOEt)6 with a deficient amount of diamine 1 in acetonitrile under an argon atmosphere gave rise to the antiferromagnetic ionic complex [Co{η2-(NPh)(NH)C6H4}2MeCN]+[Co2(μ2,η2-OOCCMe3)(μ2-OOCCMe3)2(η2-OOCCMe3)2]–·2MeCN (4), whose cation is an isoelectronic analog of the cation in complex 3. The structures of the new compounds were established by X-ray diffraction analysis.

Binuclear and polynuclear transition metal complexes with macrocyclic ligands 1. Synthesis and the structure of an antiferromagnetic binuclear nickel complex prepared by the reaction of o-phenylenediamine with pyrrole-2,5-dicarbaldehyde and nickel pivalate

The reaction of pyrrole-2,5-dicarbaldehyde (1) with o-phenylenediamine (2) in anhyd. EtOH afforded a [1+1]-condensation product, viz., Schiff's base. The structure of the latter was established by NMR spectroscopy and x-ray diffraction anal. The reaction of this product or a mixt. of 1 and 2 with Ni9(mn-OOCBut)12(HOOCBut)4(m4-OH)3(m3-OH)3 in MeCN in the presence of AcOH gave rise to an antiferromagnetic binuclear complex. According to the x-ray diffraction data, the macrocycle in the latter complex is a [2+2]-condensation product of compds. 1 and 2, meff ranging from 0.569 to 2.614 mB (2-301 K), -2J = 360 cm-1. The Ni2(OAc)2 fragment is located in the central cavity of the macrocycle. The structures of the condensation products are discussed based on the results of DFT quantum-chem. calcns.

Synthesis, structures, and magnetic properties of binuclear carboxylate complexes with NiII and NiIII atoms

The reaction of NiCl2·6H2O with Me3CCOOH and KOH taken in a molar ratio of 1:2:2 in water afforded the nonanuclear antiferromagnetic complex Py2Ni2(Me3CCOOH)2(OOCCMe3)2(μ-OOCCMe3)2(μ-OH2), which apparently contains NiII and NiIII atoms. The complex was isolated by extraction with CH2Cl2, benzene, or hexane. The reactions of this complex with pyridine bases (pyridine (Py), 3,4-lutidine (Lut), and nicorandil (Nic)) gave the adducts L4Ni2(OOCCMe3)2(μ-OOCCMe3)2(μ-OH) (L=Py, Lut, or Nic, respectively). According to magnetic measurements, intramolecular ferromagnetic exchange interactions in these adducts are complemented by intermolecular antiferromagnetic interactions. Pyrolysis of the pyridine adduct in air or under an inert atmosphere in xylene yielded the antiferromagnetic complex Py2Ni2(Me3CCOOH)2(OOCCMe3)2(μ-OOCCMe3)2(μ-OH2), which contains NiII atoms. The structures of all the complexes synthesized were established by X-ray diffraction analysis. The electronic absorption spectra of these compounds are considered.

Formation of antiferromagnetic heteronuclear thiolate and sulfide bridged complexes: II. Synthesis, magnetic properties, and molecular structures of the clusters Cp 2Cr 2(μ-SCMe 3) 2(μ 4-S)W 2(μ-I) 2(CO) 4(NO) 2 and Cp 2Cr 2(μ 3-S) 2(μ-SCMe 3) 2W(SCMe 3)(NO)

The reaction between the antiferromagnetic complex Cp 2Cr 2(μ-SCMe 3) 2(μ-S) ( 1) and WI(CO) 4(NO) ( 2) was studied. At 40–50°C the predominant product was the antiferromagnetic adduct Cp 2Cr 2(μ-SCMe 3) 2(μ 4-S)W 2(μ-I) 2(CO) 4 (NO) 2 ( 3) (CrCr 2.764(4) Å, W ⋯ W 3.559(1) Å, −2J = 338 cm −1), in which a sulfur atom bridges all four metal atoms. Further heating of 3 in the presence of an excess of 1 afforded the trinuclear antiferromagnetic cluster Cp 2Cr 2(μ 3-S) 2 (μ-SCMe 3) 2W(SCMe 3)(NO) ( 7) (WCr 3.090(1) Å, CrCr 3.027(1) Å, −2J = 246 cm −1) which can also be prepared by direct reaction between 1 and 2 (ratio 3:2) at 80°C in toluene. It is suggested that this process via the formation of an unstable intermediate CpCr(μ-SCMe 3) 2(μ-S)W(CO) 2(NO). In an attempt to use the trinuclear cluster Fe 3S 2(CO) 9 as a metal containing ligand for 2, the known iron clusters Fe 2S 2(CO) 6 and (ON) 4Fe 4S 4 were isolated. All products, including the two iron clusters, were characterized by X-ray diffraction studies at −60°C.

Antiferromagnetic complexes with metal-metal bonds: XXVII. Synthesis, molecular structures and magnetic properties of Cr,Re-clusters Cp 2Cr 2(μ-SCMe 3) 2(μ 3-S)Re 2(CO) 9] and Cp 2Cr 2(μ 3-SCMe 3) 2(μ 3-S) 2Re 2(CO) 6

The antiferromagnetic complex CP 2Cr 2(μ-SCMe 3) 2(μ 3-S)Re 2(CO) 9 ( II) (−2 J=424 cm −1) was obtained by photochemical reaction of CP 2Cr 2(μ-SCMe 3) 2(μ-S) ( I) with Re 2(CO) 10 in benzene-THF; the dirhenium moiety within complex II (ReRe 3.0691(8) Å) is only bound to the framework of complex I through coordination of the rhenium atom by the sulfide bridge (ReS 2.555(2) Å). It is shown that under more rigorous conditions ( hv, m-xylene, 144°) the reaction proceeds with cleavage of the ReRe bond and formation of a 66e antiferromagnetic cluster Cp 2Cr 2(μ 3-SCMe 3) 2 (μ 3-S) 2 Re 2(CO) 6 ( III) (−2 J = 302 cm −) with a distorted cubane core Cr 2Re 2S 4 (CrS 2.32(1), CrSR 2.39 (2), ReS 2.590(8), ReSR 2.514(8)-2.534(7) Å) which only contains a CrCr bond (CrCr 2.96(1), Cr ... Re 3.645(1) and 3.646(1), Re ... Re 3.938(1) Å).

ChemInform Abstract: NMR Spectroscopy of Paramagnetic Complexes. Part 35. Dialkyl(η5‐cyclopentadienyl)chromium Derivatives with Extreme Values of 1(2)H‐NMR Parameters.

AbstractThe antiferromagnetic complex (I) is cleaved to the half‐sandwich compound (III), which on treatment with an alkyl‐metal compound yields the product (V).

Antiferromagnetic complexes involving metalmetal bonds III. Synthesis, structure and magnetic properties of heterotrinuclear complexes of the type M(CO) 5L (M  Cr, Mo and w) containing [(C 5H 5CrSCMe 3) 2S] as unusual antiferromagnetic ligand L

Isostructural heterotrinuclear complexes (C 5H 5CrSCMe 3) 2S · M(CO) 5 (II–IV) were isolated from photochemical reactions between the antiferromagnetic complex (C 5H 5CrSCMe 3) 2S (I) (with the CrCr bond 2.689 Å long and with the exchange parameter −2 J = 430 cm −1) and metal hexacarbonyls, M(CO) 6, where M is Cr, Mo, or W. According to the X-ray structural data on III and IV, complex I plays the role of an unusual antiferromagnetic ligand L bound to M through the sulphide bridge (M–S 2.58(2) Å). Its geometry remains practically unaffected by the complex formation (the CrCr bond length in III and IV is 2.73(1) Å). The exchange parameter, −2 J (410, 440 and 440 cm −1 in II to IV, respectively), also shifts only insignificantly from that of I, which probably means that indirect exchange via the sulphide bridge in I is of minor importance compared with the direct CrCr exchange. The CrCr bond length may thus be correlated with the observed overall exchange coupling.

Antiferromagnetic complexes involving metalmetal bonds IV. Synthesis, molecular structure and magnetic properties of the heterotrinuclear cluster, (C 5H 5Cr) 2(μ 2-SCMe 3)(μ 3-S) 2Fe(CO) 3, with direct and indirect exchange between Cr III and Fe I centers

The photochemical reaction between the antiferromagnetic complex (C 5H 5-CrSCMe 3) 2S (I) (containing a CrCr bond 2.689 Å long) and Fe(CO) 5 results in the elimination of two carbonyl groups and one tert-butyl radical to give (C 5H 5Cr) 2(μ 2-SCMe 3)(μ 3-S) 2 · Fe(CO) 3 (III). As determined by X-ray diffraction, III contains a CrCr bond of almost the same length as in I (2.707 Å), together with one thiolate and two sulphide bridges. The latter are also linked with the Fe atom of the Fe(CO) 3 moiety (average FeS bond length 2.300 Å). Fe also forms a direct bond, 2.726 Å long, with one of the Cr atoms, whereas its distance from the other Cr atom (3.110 Å) is characteristic for non-bonded interactions. Complex III is antiferromagnetic, the exchange parameter, −2 J, values for CrCr, Cr(1)Fe and Cr(2)…Fe are 380, 2600 and 170 cm −1, respectively. The magnetic properties of III are discussed in terms of the “exchange channel model”. The contributions from indirect interactions through bridging ligands are shown to be insignificant compared with direct exchange involving metalmetal bonds. The effects of steric factors and of the nature of the M(CO) n fragments on the chemical transformations of (C 5H 5CrSCMe 3) 2S · M(CO) n are discussed.

A study of XeFeF 9 from Mössbauer spectra

A study of the new antiferromagnetic complex XeFeF 9 by the Mössbauer effect has contributed experimental data on the temperature dependence of hyperfine splitting parameters of 57Fe. There is evidence that the relative intensity of the lines is affected by the texture. The anomalous spectra in the range 85 – 100 K might be interpreted as superparamagnetism; the corresponding blocking temperature being obtained near 98 K.