Synthesis,Crystal Structure,and Physical Properties of the New Chain Alkalioxocuprate K3Cu2O4

Single crystals of K₃Cu₂O₄ were prepared by the azide/nitrate route from respective stoichiometric mixtures of KN₃, KNO₃ and CuO, at 923 K, whereas powder samples were synthesised by solid state reaction of K₂O, KCuO₂ and CuO, sealed in gold ampoules and treated at 723 K. According to the single crystal structure analysis (Cmcm, Z = 4, a = 6.1234(1), b = 8.9826(2), c = 10.8620(2) Å, R₁ = 0.044, R₂ = 0.107), the main structural feature are undulating CuO₂ chains built up from planar, edge sharing CuO₄ square units. From an analysis of the Cu–O bond lengths, the valence state of either +2 or +3 can be unambiguously assigned to each copper atom. The magnetic susceptibilities show the dominance of antiferromagnetic (AFM) interactions. At high temperatures, the magnetic behaviour can be fitted with the Curie–Weiss law (μ_eff = 1.84μ_B, Θ = –105 K). The experimental data can be very well described by a uniform Heisenberg chain with a nearest‐neighbour spin intrachain interaction (J_nn) of ~ 101 K.     

Reactions between YBa2Cu3O7−δ and La2O3 and SrCO3

Solid state reactions at 925°C between the high-T _c ceramic superconductor YBa₂Cu₃O_7?δ and La₂O₃ and SrCO₃, respectively, mixed in various molar ratiosr=MeO_n/YBa₂Cu₃O_7?δ, were studied using X-ray powder diffraction and scanning electron microscopy. The reaction between YBa₂Cu₃O_7?δ and La₂O₃ yielded (La_1?xBa_x)₂CuO_4?δ, withx≈0.075?0.10. La_2?xBa_1+xCu₂O_6?δ, withx≈0.2?0.25 and La-doped (Y_1?xLa_x)₂BaCuO₅, withx≈0.10?0.15. Forr=3.0, Y-doped La₂BaCuO₅ resulted also. The reaction between YBa₂Cu₃O_7?δ and SrCO₃ yielded (Sr_1?zBa_z)₂CuO₃, withz≈0.1, Y₂(Ba_1?zSr_z)CuO₅, withz=0.1?0.15, and a nonsuperconducting compound with an approximate composition of Y(Ba_0.5Sr_0.5)₅Cu_3.5O_10±δ. At values ofr≤2.0, unsubstituted YBa₂Cu₃O_7?delta was found in the reaction products.     

Low-dimensional Magnetism and Antiferromagnetic Ordering in the Mixed-valence Spin-chain Cuprate TlCu2O2

TlCu₂O₂, a mixed-valence spin-chain cuprate, was synthesized in a piston cylinder system starting from thallium sesquioxide Tl₂O₃, cuprous oxide Cu₂O and copper powder. The main structural characteristics are edge-sharing (CuO₂)_n zigzag chains, which are linked in the perpendicular crystallographic direction by Cu⁺ to form a three-dimensional network. Data from magnetic susceptibility and specific heat measurements show features typical for low-dimensional magnetic exchange interactions. The long-range antiferromagnetic ordering is observed at T_N = 19.7 K. No weak ferromagnetic component can be detected, suggesting a plain Néel-type spin-ordered structure.     

Oxygen diffusion and isotope exchange behaviour of NdBa2Cu3O7−x

The oxygen diffusion and exchange behaviour of NdBa₂Cu₃O_7–x is investigated by means of isothermal and dynamic-thermal analytical techniques. From the results it is concluded that oxygen anions move along vacancies in the CuO₂-layers of the perovskite-like structure. In temperature regions where the diffusion rate is low (665 K<T<773 K) heterogeneous oxygen exchange reactions take place on the phase boundary. The higher the exchange rate the more the partially heterogeneous exchange is favoured in comparison to the completely heterogeneous isotope exchange. Depending on the oxygen deficiency of NdBa₂Cu₃O_7–x the out-diffusion of oxygen becomes dominating at higher temperatures.     

Analysis of the Magnetic Coupling in a Mn(II)-U(V)-Mn(II) Single Molecule Magnet

[{Mn(TPA)I}{UO2(Mesaldien)}{Mn(TPA)I}]I formula (here TPA=tris(2-pyridylmethyl)amine and Mesaldien=N,N’-(2-aminomethyl)diethylenebis(salicylidene imine)) reported by Mazzanti and coworkers (Chatelain et al. Angew. Chem. Int. Ed. 2014 , 53, 13434) is so far the best Single Molecule Magnet (SMM) in the {3d–5f} class of molecules exhibiting barrier height of magnetization reversal as high as 81.0 K. In this work, we have employed a combination of ab initio CAS and DFT methods to fully characterize this compound and to extract the relevant spin Hamiltonian parameters. We show that the signs of the magnetic coupling and of the g-factors of the monomers are interconnected. The central magnetic unit [U^VO₂]⁺ is described by a Kramers Doublet (KD) with negative g-factors, due to a large orbital contribution. The magnetic coupling for the {Mn(II)-U(V)} pair is modeled by an anisotropic exchange Hamiltonian: all components are ferromagnetic in terms of spin moments, the parallel component J_Z twice larger as the perpendicular one J_⊥. The spin density distribution suggests that spin polarization on the U(V) center favors the ferromagnetic coupling. Further, the J_Z/J_⊥ ratio, which is related to the barrier height, was found to correlate to the corresponding spin contribution of the g-factors of the U(V) center. This correlation established for the first time offers a direct way to estimate this important ratio from the corresponding g^S-values, which can be obtained using traditional ab initio packages and hence has a wider application to other {3d–5f} magnets. It is finally shown that the magnetization barrier height is tuned by the splitting of the [U^VO₂]⁺ 5 f orbitals.     

Exchange and Delocalization Effects in [Fe6S6]2+ Superclusters

A theoretical study of Heisenberg exchange and double exchange (delocalization) effects in the iron-sulphur supercluster is presented. Such clusters can play important role in biological systems (proteins and enzymes) acting as so-called active centres. The cluster with valence 2+ can be modelled by two Fe(III) and four Fe(II) ions. An idealized structure of double cubane has been considered instead of a more realistic defected double cubane structure of lower symmetry. Energies of the lowest spin states have been calculated numerically depending on the Heisenberg exchange J _i and double exchange b parameters. Possible spin ground states (S=0, 1, 2, 3, 4, 5) have been predicted. The ground state of a given total spin Sis usually achieved for the intermediate spin value of S ₅₆=4 in the case of fully antiferromagnetic as well as partially ferromagnetic spin interactions. In the case of no double exchange, the ground state with the total spin S=3 should always be observed, while a nonzero hopping effect results in narrowing a parameter region of the ground state. If the double exchange is taken into account, then the spin values depend on the Heisenberg integrals. The model results can be applied in order to interpret many structural and magnetic properties of proteins and enzymes possessing the Fe-S active centres.     

Synthese und Kristallstruktur von Sr3Ga2O5Cl2 und Sr3Fe1.18Al0.82O5Cl2

Solid state reactions, by using a flux, lead to the new compounds Sr₃Ga₂O₅Cl₂ (A) and Sr₃Fe_1.18Al_0.82O₅Cl₂ (B). By means of single crystal X-Ray determinations a monoclinic symmetry (space group C ₂ ² -P2₁, (A):a=9.569 (2) Å; (B):a=9.550 (2) Å,Z=4) was found. Both compounds are not isotypic to Sr₃Fe₂O₅Cl₂ but crystallize like Ba₃Fe₂O₅Cl₂.

     

Synthesis,spectroscopic, and crystallographic characterizations of an antiferromagnetically coupled,oxobridged trinuclear manganese(IV) cluster [Mn3O4(H2O)2(phen)4](NO3)4 · 3H2O [phen = 1,10-phenanthroline]

Design and synthesis of a triangular manganese compound, [Mn₃O₄(H₂O)₂(phen)₄](NO₃)_4?·?3H₂O (1) with mono-µ-oxo and di-µ-oxo, is described. The complex has been characterized by elemental analysis, spectroscopy, single crystal and powder diffraction measurements, thermogravimetric analysis, etc. Bond Valence Sum calculations and X-ray photoelectron spectroscopy reveal that each manganese at each vertex of the triangle is +IV oxidation state. Variable temperature magnetic measurements show strong antiferromagnetic coupling between metal ions with the following set of parameters: g?=?1.99, J ₁?=??50.0?cm^?1, and J ₂?=??90.2?cm^?1 (where J ₁ describes the interaction across the two mono-µ-oxo bridges and J ₂ is the exchange coupling across the di-µ-oxo bridge). The compound breaks down in three steps when heated from room temperature to 900°C. The final ash of the compound is confirmed by infrared spectrum with standard MnO₂.     

A New Hydroxo‐bridged Chromium(III) Dimer [Cr(saltn)OH]2·4H2O: Synthesis,Crystal Structure and Magnetic Properties

A new hydroxo‐bridged dimeric Cr(III) complex [Cr(saltn)OH]₂·4H₂O [H₂saltn=N,N′‐bis(salicylidene)trimethylenediamine] has been synthesized and its structural and magnetic properties have been investigated. The complex crystallizes in the triclinic space group P‐1 with one dimeric formula unit in a cell of dimensions a=0.95828(19) nm, b=0.95926(19) nm, c=1.0437(2) nm, α=86.77(3)°, β=82.48(3)°, and γ=64.93(3)°. The geometry around each chromium(III) center is six‐coordinate, distorted‐octahedral. The bridging Cr₂O₂ unit is strictly planar, as required by the crystallographic symmetry. The Cr? O? Cr′ bridging angle is 99.94(16)°, and the distance between Cr…Cr′ is 0.3019 nm. The magnetic susceptibility of the complex has been examined in the range of 2‐300 K. By using the spin‐spin coupled model for an S₁=S₂=3/2 dimeric system , the magnetic data were fitted to give the parameters of g=2.01(1), J=‐0.85(2) cm^‐1, and zJ' =0.18(3)cm^‐1, indicating the presence of a weak antiferromagnetic spin‐exchange interaction between the Cr(III) ions in the binuclear complex.     

Studies on the magnetic property of μ3-oxotriiron(III) complex [Fe3O(OBz)6(CH3OH)3](NO3)(CH3OH)2 (HOBz?Benzoic acid)

The magnetic property of μ₃-oxotriiron(III) complex [Fe₃O(OBz)₆(CH₃OH)₃](NP₃)-(CH₃OH)₂ (HOBz? benzoic acid) has been studied. We use isosceles triangle model and molecular field correction to fit the experimental magnetic susceptibility data. It shows that an intramolecular antiferromagnetic exchange interaction occurs with J = -31.27 cm^?1, J'= -27.26 cm^?1, and a weaker intermolecular antiferromagnetic exchange interaction occurs with zJ' = - 3.76 cm^?1. We give the d⁵-d⁵-d⁵ energy level diagram of triiron(III) complex as a function of J'/J. From the diagram we can get the total spin ST of the complex as 1/2 in the ground state.     

UNO DMRG CAS CI calculations of binuclear manganese complex Mn(IV)2O2(NHCHCO2)4: Scope and applicability of Heisenberg model

Both direct exchange and super-exchange interactions cooperate to realize inter-spin magnetic interaction in binuclear manganese complex Mn(IV)₂O₂(NHCHCO₂)₄ with a di-μ-oxo path. We revisited this spin system using DMRG CAS methods and CAS selection procedures. Our results indicate that our previous “dynamically extended spin polarization” (DE-SP) procedure for organic polyradicals and so forth does not work well. Thus, we have examined another selection procedure, the “dynamically extended super-exchange” (DE-SE) procedure. DMRG CASCI [18,18] by UB3LYP(HS)-UNO(DE-SE) can realize antiferromagnetic J values similar to experimental ones (−87 cm⁻¹). In addition, all J values between all spin states (HS[septet],IS[quintet],IS[triplet],LS[singlet])were also shown to be correct under sufficiently large M values. © 2018 Wiley Periodicals, Inc.     

Synthesis and structure of bilayered manganites based on Ca3Mn2O7 with the simultaneous substitution of calcium by lanthanum and strontium

A tetragonal (space group I4/mmm) solid solution La_2-2x (Ca_1-y Sr_y)_{1 + 2x} Mn₂O₇ based on the Raddlesden-Popper phase (n = 2), which is formed by the simultaneous substitution of calcium in Ca₃Mn₂O₇ by strontium and lanthanum, is synthesized by high-temperature annealing of La₂O₃, Mn₂O₃, CaCO₃, and SrCO₃ mixtures (1500°C, air). The concentration area of the solid solution in the scheme is a pentagon, whose corners correspond to the manganites Ca₃Mn₂O₇, Ca_0.75Sr_2.25Mn₂O₇, La_0.2Sr_2.8Mn₂O₇, La_1.6Sr_1.4Mn₂O₇, and LaCa₂Mn₂O₇.     

Synthesis,Crystal Structure and Magnetic Properties of Rb2Mn3O4

Rb₂Mn₃O₄, which is the first rubidium oxomanganates(II), has been synthesized via the azide/nitrate route from a stoichiometric mixture of the precursors RbN₃, RbNO₃, and MnO, as well as from Rb₂O and MnO, through an all solid state reaction. Its crystal structure (C2/c, Z = 4, a = 1546.9(2) pm, b = 666.22(7) pm, c = 588.06(6) pm) consists of a 3D arrangement of edge‐ and corner‐sharing MnO₄ tetrahedra with rubidium filling the space between. Magnetic susceptibility measurements indicate a magnetic phase transition at 126 K. The magnetic response as a function of temperature is complex, indicating strong, partly frustrated magnetic exchange interactions.     

über Erdalkalimetalloxocuprate,VIII Zur Kenntnis von Sr2CuO2Cl2

On Alkaline Earth Oxocuprates VIII. About Sr₂CuO₂Cl₂ Sr₂CuO₂Cl₂ was prepared and investigated by single crystal X – ray work (space group D–Immm, a = 3.975, c = 15.618 Å). Sr₂CuO₂Cl₂ is isotypic with K₂NiF₄ – compounds and shows an octahedral configuration for Cu²⁺. Cl^? occupies trans-positions of the octahedral Cu²⁺/O^2? polyhedron. A discussion with related compounds (Sr₂CuO₃ and Nd₂CuO₄) explains the observed distribution of O^2? and Cl^?.     

Linkage Isomerism and Spin Frustration in Heterometallic Rings: Synthesis,Structural Characterization,and Magnetic and EPR Spectroscopic Studies of Cr7Ni,Cr6Ni2, and Cr7Ni2 Rings Templated About Imidazolium Cations

The synthesis and structural characterization of three heterometallic rings templated about imidazolium cations is reported. The compounds are [2,4‐DiMe‐ImidH][Cr₇Ni^IIF₈(O₂CtBu)₁₆] 1 (2,4‐DiMe‐ImidH=the cation of 2,4‐dimethylimidazole), [ImidH]₂[Cr₆Ni^II₂F₈(O₂CCtBu)₁₆] 2 (ImidH=the cation of imidazole), and [1‐Bz‐ImidH]₂ [Cr₇Ni^II₂F₉(O₂CtBu)₁₈] 3 (1‐Bz‐ImidH=the cation of 1‐benzylimidazole). The structures show the formation of octagonal arrays of metals for 1 and 2 and a nonagon of metal centers for 3 . In all cases the edges of the polygon are bridged by a single fluoride and two pivalate ligands, and the position of the divalent metal centers cannot be distinguished by X‐ray diffraction. Magnetic studies combined with EPR spectroscopy allow the characterization of the magnetic states of the compounds. In each case the exchange is antiferromagnetic with a magnetic exchange parameter J≈?5.8 cm^?1, and it is not possible to differentiate the exchange between two Cr^III centers (J_CrCr) from the exchange between a Cr^III and a Ni^II center (J_CrNi). For 2 there is evidence for the presence of at least two, possibly four, linkage isomers of the heterometallic ring, caused by the presence of two divalent metal centers in the ring. The EPR spectroscopy of 3 suggests an S=1/2 ground state of the ring and that it is likely that only one linkage isomer is present.     

Magnetic properties of Cu(II) bischelate complexes with 3-imidazoline nitroxides. 2. Anab initio analysis of exchange interaction mechanisms

The mechanism responsible for the emergence of ferromagnetic exchange interactions in bischelate complexes of Cu²⁺ with enaminoketone derivatives of 3-imidazoline nitroxide CuL₂ is studied by ab initio quantum chemical methods. The parameters J_cu-L and J_L-L’ of exchange interactions between the unpaired electrons of the paramagnetic centers (Cu²⁺ ion and N-O groups of nitroxyl ligands L and L’) of these complexes were calculated in terms of the full 3x3 configuration interaction between the singlet states constructed in a basis set of molecular orbitals of unpaired electrons. It is shown that for variations of the structure of the coordination polyhedron around the Cu²⁺ ion from square planar to tetrahedral the exchange interactions between the unpaired electrons of the paramagnetic centers is ferromagnetic J_Cu-L >J_L -L’>0, which agrees with the data of magnetic measurements. The principal mechanism of exchange interactions in CuL₂ complexes is the delocalization mechanism that is due to a minor transfer of spin density from the 3d-orbitals of Cu²⁺ to the Σ-orbitals of the N-O groups of L and L’ ligands. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 5, pp. 850–856, September-October, 1997.     

A theoretical and experimental XAS study of monolayer dispersive supported CuO/γ-Al2O3 catalysts

The local structures of supported CuO/γ-Al₂O₃ monolayer dispersive catalysts with different CuO loadings have been investigated by EXAFS and multiple scattering XANES simulations. The EXAFS results show that the first nearest neighbors around the Cu atoms in the CuO/γ-Al₂O₃ catalysts are similar to that of the polycrystalline CuO powder, which is independent of the CuO loadings. Moreover, the Cu K-XANES FEFF8 calculations for CuO reveal that the monolayer-dispersed CuO species are of small distorted (CuO₄)_mⁿ⁺ clusters, which is mainly composed of a distorted CuO₆ octahedron incorporated in the surface octahedral vacant sites of the γ-Al₂O₃ support. We consider that the CuO species for the CuO/γ-Al₂O₃ catalysts with loadings of 0.4 and 0.8 mmol/100 m² are distorted (CuO₄)_mⁿ⁺ clusters composed mainly of a distorted CuO₆ octahedron incorporated in the surface octahedral vacant sites of the γ-Al₂O₃ support after calcinations at high temperature in air for a few hours. On the contrary, for the CuO/γ-Al₂O₃ with loading of 1.2 mmol/100 m², the local structure of Cu atoms in CuO/γ-Al₂O₃ is similar to that of polycrystalline CuO powder.     

Spin dimer analysis of the magnetic structures of A2V3O9 (A = Ba,Sr) and η-Na9V14O35: Importance of the V4+–O⋯O–V4+ super-superexchange interactions mediated by the O–V5+–O bridges

Spin dimer analysis was carried out for the magnetic oxides of V⁴⁺ (d¹) ions, A₂V₃O₉ (A = Ba, Sr) and η-Na₉V₁₄O₃₅, to account for their magnetic structures. After identifying the V(O_eq)₄ square planes containing the magnetic orbitals of the V⁴⁺ (d¹) ions, we analyzed the relative strengths of the various V–O_eq–V and V–O_eq⋯O_eq–V spin exchange interactions. The V–O_eq⋯O_eq–V spin exchange interactions mediated by O_eq–V⁵⁺–O_eq bridges are found to be crucial in determining the magnetic structures of A₂V₃O₉ (A = Ba, Sr) and η-Na₉V₁₄O₃₅. Our analysis suggests that η-Na₉V₁₄O₃₅ should have two different spin gaps.     

Synthese und Kristallstruktur des ersten Oxonitridoborates — Sr3[B3O3N3]

Synthesis and Crystal Structure of the First Oxonitridoborate — Sr₃[B₃O₃N₃] The cyclotri(oxonitridoborate) Sr₃[B₃O₃N₃] was synthesized at 1450 °C as coarsely crystalline colourless crystals by the reaction of SrCO₃ with poly(boron amide imide) using a radiofrequency furnace. The structure was solved by single‐crystal X‐ray diffractometry (Sr₃[B₃O₃N₃], Z = 4, P2₁/n, a = 663.16(2), b = 786.06(2), c = 1175.90(3) pm, η = 92.393(1)°, R1= 0.0441, wR2 = 0.1075, 1081 independent reflections, 110 refined parameters). Besides Sr²⁺ there are hitherto unknown cyclic [B₃O₃N₃]^6— ions (B—N 143.7(10) — 149.1(9) pm, B—O 140.5(8) — 141.4(8) pm).     

Cation‐Mediated Conversion of the State of Charge in Uranium Arene Inverted‐Sandwich Complexes

Two new arene inverted‐sandwich complexes of uranium supported by siloxide ancillary ligands [K{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 3 ) and [K₂{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 4 ) were synthesized by the reduction of the parent arene‐bridged complex [{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 2 ) with stoichiometric amounts of KC₈ yielding a rare family of inverted‐sandwich complexes in three states of charge. The structural data and computational studies of the electronic structure are in agreement with the presence of high‐valent uranium centers bridged by a reduced tetra‐anionic toluene with the best formulation being U^V–(arene^4?)–U^V, KU^IV–(arene^4?)–U^V, and K₂U^IV–(arene^4?)–U^IV for complexes 2 , 3 , and 4 respectively. The potassium cations in complexes 3 and 4 are coordinated to the siloxide ligands both in the solid state and in solution. The addition of KOTf (OTf=triflate) to the neutral compound 2 promotes its disproportionation to yield complexes 3 and 4 (depending on the stoichiometry) and the U^IV mononuclear complex [U(OSi(OtBu)₃)₃(OTf)(thf)₂] ( 5 ). This unprecedented reactivity demonstrates the key role of potassium for the stability of these complexes.