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1.
The A‐site mixed‐ammonium solid solutions of metal–organic perovskites [(NH2NH3)x(CH3NH3)1?x][Mn(HCOO)3] (x=1.00–0.67) exhibit para‐ to ferroelectric diffuse phase transitions with lowered transition temperatures from x=1.00 to 0.67. These properties are due to the decreased framework distortion and polarization in their low temperature ferroelectric phases caused by the increased CH3NH3+ concentration.  相似文献   

2.
We report the synthesis, crystal structures, and spectral, thermal, and magnetic properties of a family of metal–organic perovskite ABX3, [C(NH2)3][MII(HCOO)3], in which A=C(NH2)3 is guanidinium, B=M is a divalent metal ion (Mn, Fe, Co, Ni, Cu, or Zn), and X is the formate HCOO?. The compounds could be synthesized by either diffusion or hydrothermal methods from water or water‐rich solutions depending on the metal. The five members (Mn, Fe, Co, Ni, and Zn) are isostructural and crystallize in the orthorhombic space group Pnna, while the Cu member in Pna21. In the perovskite structures, the octahedrally coordinated metal ions are connected by the antianti formate bridges, thus forming the anionic NaCl‐type [M(HCOO)3]? frameworks, with the guanidinium in the nearly cubic cavities of the frameworks. The Jahn–Teller effect of Cu2+ results in a distorted anionic Cu–formate framework that can be regarded as Cu–formate chains through short basal Cu? O bonds linked by the long axial Cu? O bonds. These materials show higher thermal stability than other metal–organic perovskite series of [AmineH][M(HCOO)3] templated by the organic monoammonium cations (AmineH+) as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework. A magnetic study revealed that the five magnetic members (except Zn) display spin‐canted antiferromagnetism, with a Néel temperature of 8.8 (Mn), 10.0 (Fe), 14.2 (Co), 34.2 (Ni), and 4.6 K (Cu). In addition to the general spin‐canted antiferromagnetism, the Fe compound shows two isothermal transformations (a spin‐flop and a spin‐flip to the paramagnetic phase) within 50 kOe. The Co member possesses quite a large canting angle. The Cu member is a magnetic system with low dimensional character and shows slow magnetic relaxation that probably results from the domain dynamics.  相似文献   

3.
The metal ion distribution on the two metal sites of monoclinic Mn1?xCux(HCOO)2 · 2(H,D)2O mixed crystals are studied by infrared and Raman spectroscopic methods. The spectral regions 3 200–3 400 cm?1 (vOH), 2 875–2 990 cm?1 (vCH), 2 330–2 500 cm?1 (vOD of matrix isolated HDO molecules), 1 350–1 400 cm?1 (symmetric CO2 stretching modes), 570–950 cm?1 (H2O librations), and 490 cm?1 (M? O lattice modes) are mostly sensitive to the metal ions present. The frequency shifts of these bands with increasing content of copper show that Cu2+ prefers the M(1) site, coordinated by HCOO? only. The strengths of the hydrogen bonds increase on going from manganese to copper formate, due to the increased synergetic effect of Cu2+. Solubility and X-ray data of the mixed crystals are included. Irrespective of the same crystal structure, two series of mixed crystals are formed: eutonic area at 0.65 ≥ x ≥ 0.5.  相似文献   

4.
Self‐assembly of the [Mo(CN)7]4– anion and the Mn2+ ion in the aqueous solution containing ammonium formate results in a new coordination polymer, {(NH4)3[(H2O)Mn3(HCOO)][Mo(CN)7]2·4H2O}n. Single crystal X‐ray analysis revealed a very complicated three‐dimensional (3D) framework, where both the [Mo(CN)7]4– and the formate anions act as bridges between the MnII centers. Magnetic measurements revealed that this compound displays ferrimagnetic ordering below 70 K. Competing antiferromagnetic interactions between the spin carriers might lead to spin frustration and non‐linear alignment of the magnetic moments. Specifically, this compound is the first mixed [Mo(CN)7]4–/HCOO bridged molecule magnet.  相似文献   

5.
A new chromophore has been identified in copper‐doped apatite pigments having the general composition [Sr10(PO4)6(CuxOH1?x?y)2], in which x=0.1, 0.3 and y=0.01–0.42. By using X‐ray absorption spectroscopy, low‐temperature magnetization measurements, and synchrotron X‐ray powder structure refinement, it has been shown that the oxygenated compounds contain simultaneously diamagnetic Cu1+ and paramagnetic Cu3+ with S=1. Cu3+ is located at the same crystallographic position as Cu1+, being linearly coordinated by two oxygen atoms and forming the OCuO? anion. The Raman spectroscopy study of [A10(PO4)6(CuxOH1?x?y)2,], in which A=Ca, Sr, Ba, reveals resonance bands at 651–656 cm?1 assigned to the symmetric stretching vibration (ν1) of OCuO?. The strontium apatite pigment exhibits a strong paramagnetic anisotropy with an unprecedentedly large negative zero‐field splitting parameter (D) of ≈?400 cm?1. The extreme magnetic anisotropy causes slow magnetization relaxation with relaxation times (τ) up to 0.3 s at T=2 K, which relates the compounds to single‐ion magnets. At low temperature, τ is limited by a spin quantum‐tunneling, whereas at high temperature a thermally activated relaxation prevails with Ueff≈48 cm?1. Strong dependence of τ on the paramagnetic center concentration at low temperature suggests that the spin‐spin relaxation dominates in the spin quantum‐tunneling process. The compound is the first example of a d‐metal‐based single‐ion magnet with S=1, the smallest spin at which an energy barrier arises for the spin flipping.  相似文献   

6.
We report the synthesis, crystal structures, thermal and magnetic characterizations of a family of metal‐organic frameworks adopting the niccolite (NiAs) structure, [dmenH22+][M2(HCOO)62−] (dmen=N,N′‐dimethylethylenediamine; M=divalent Mn, 1Mn ; Fe, 2Fe ; Co, 3Co ; Ni, 4Ni ; Cu, 5Cu ; and Zn, 6Zn ). The compounds could be synthesized by either a diffusion method or directly mixing reactants in methanol or methanol–water mixed solvents. The five members, 1Mn , 2Fe , 3Co , 4Ni , and 6Zn are isostructural and crystallize in the trigonal space group P 1c, while 5Cu crystallizes in C2/c. In the structures, the octahedrally coordinated metal ions are connected by anti–anti formate bridges, thus forming the anionic NiAs‐type frameworks of [M2(HCOO)62−], with dmenH22+ located in the cavities of the frameworks. Owing to the Jahn–Teller effect of the Cu2+ ion, the 3D framework of 5Cu consists of zigzag Cu‐formate chains with Cu OCHO Cu connections through short basal Cu O bonds, further linked by the long axial Cu O bonds. 6Zn exhibits a phase transition probably as a result of the order–disorder transition of the dmenH22+ cation around 300 K, confirmed by differential scanning calorimetry and single crystal X‐ray diffraction patterns under different temperatures. Magnetic investigation reveals that the four magnetic members, 1Mn , 2Fe , 3Co , and 4Ni , display spin‐canted antiferromagnetism, with a Néel temperature of 8.6 K, 19.8 K, 16.4 K, and 33.7 K, respectively. The Mn, Fe, and Ni members show spin‐flop transitions below 50 kOe. 2Fe possesses a large hysteresis loop with a large coercive field of 10.8 kOe. The Cu member, 5Cu , shows overall antiferromagnetism (both inter‐ and intra‐chains) with low‐dimensional characteristics.  相似文献   

7.
Two mixed‐valent disc‐like hepta‐nuclear compounds of [FeIIFeIII6(tea)6](ClO4)2 ( 1Fe , tea = N(CH2CH2O)33?) and [MnII3MnIII4(nmdea)6(N3)6]·CH3OH ( 2Mn , nmdea = CH3N(CH2CH2O)22?) have been synthesized by the reaction of Fe(ClO4)2·6H2O with triethanolamine (H3tea) for the former and reaction of Mn(ClO4)2·6H2O with diethanolamine (H2nmdea) and NaN3 for the later, respectively. 1Fe has the cationic cluster with a planar [FeIIFeIII6] core consisting of one central FeII and six rim FeIII atoms in hexagonal arrangement. The Fe ions are linked by the oxo‐bridges from the alcohol arms in the manner of edge‐sharing of their coordination octahedra. 2Mn is a neutral cluster with a [MnII3MnIII4] core possessing one central MnII atom surrounded by six rim Mn ions, two MnII and four MnIII. The structure is similar to 1Fe but involves six terminal azido ligands, each coordinate one rim Mn ion. 1Fe showed dominant antiferromagnetic interaction within the cluster and long‐range ordering at 2.7 K. The cluster probably has a ground state of low spin of S = 5/2 or 4/2. The long‐range ordering is weak ferromagnetic, showing small hysteresis with a remnant magnetization of 0.3 Nβ and a coercive field of 40 Oe. Moreover, the isofield of lines 1Fe are far from superposition, indicating the presence of significant zero–field splitting. Ferromagnetic interactions are dominant in 2Mn . An intermediate spin ground state 25/2 is observed at low field. In high field of 50 kOe, the energetically lowest state is given by the ms = 31/2 component of the S = 31/2 multiplet due to the Zeeman effect. Despite of the large ground state, no single‐molecule magnet behavior was found above 2 K.  相似文献   

8.
The focus of this paper is on the synthesis and crystal structures of three Zn‐rich compounds with the general formula RE7Zn21+xSi2−x, where RE = Ce [x = 0.95 (1); heptacerium docosazinc silicon], Pr [x = 0.09 (1); heptapraseodymium henicosazinc disilicon], and Nd [x = 0.53 (1); heptaneodymium docosazinc silicon]. The compounds were obtained by high‐temperature reactions, using the respective elements as starting materials. The structures were determined by single‐crystal X‐ray diffraction. The title compounds crystalize in the orthorhombic space group Pbam (No. 55, Pearson symbol oP60) and are isostructural with about a dozen RE7Zn21+xTt2−x (RE = La–Nd; Tt = Ge, Sn, and Pb) compounds previously reported by our group. The results from the present refinements confirm the previously published data on RE7Zn21+xSi2−x (RE = La and Ce; x≃ 1.45) [Malik et al. (2013). Intermetallics, 36 , 118–126]. Additionally, magnetic susceptibility measurements on the corresponding bulk samples show Curie–Weiss paramagnetic behavior from 5 to 300 K, consistent with RE3+ ground states and local‐moment magnetism due to the core 4f electrons.  相似文献   

9.
Two CrIII‐MnIII heterobimetallic compounds, [Mn((R,R)‐5‐MeOSalcy)Cr(Tp)(CN)3 · 2CH3CN]n ( 1‐RR ) and [Mn((S,S)‐5‐MeOSalcy)Cr(Tp)(CN)3·2CH3CN]n ( 1‐SS ) [Salcy = N,N′‐(1,2‐cyclohexanediylethylene)bis(salicylideneiminato) dianion], were synthesized by using the tricyanometalate building block, [(Tp)Cr(CN)3] [Tp = tris(pyrazolyl) hydroborate] and chiral MnIII Schiff base precursors. Structural analyses and circular dichroism (CD) spectra revealed that 1‐RR and 1‐SS are a pair of enantiomers containing a neutral cyano‐bridged zigzag chain with (–Cr–C≡N–Mn–N≡C–)n as the repeating unit. Magnetic studies show that antiferromagnetic couplings between CrIII and MnIII ions occur by cyanide bridges. 1‐RR and 1‐SS present metamagnetic, spin‐canting, and antiferromagnetic order behaviors at low temperatures.  相似文献   

10.
The new calcium iron iridium hydrogarnet Ca3(Ir2–xFex)(FeO4)2–x(H4O4)1+x (0 ≤ x ≤ 1) was obtained by hydrothermal synthesis under strongly oxidizing alkaline conditions. The compound adopts a garnet‐like crystal structure and crystallizes in the acentric cubic space group I4 3d (no. 220) with a = 12.5396(6) Å determined at T = 100 K for a crystal with a refined composition Ca3(Ir1.4Fe0.6)(FeO4)1.4(O4H4)1.6. Iridium and iron statistically occupy the octahedrally coordinated metal position, the two crystallographically independent tetrahedral sites are partially occupied by iron. Hydroxide groups are found to cluster as hydrogarnet defects, i.e. partially substituting oxide anions around the empty tetrahedral metal sites. The presence of hydroxide ions was confirmed by infrared spectroscopy and the hydrogen content was quantified by carrier gas hot extraction; the overall composition was verified by energy dispersive X‐ray spectroscopy. The structure model is supported by 57Fe‐Mössbauer spectroscopic data evidencing different Fe sites and a magnetic ordering of the octahedral iron sublattice at room temperature. The thermal decomposition proceeds via three steps of water loss and results in Ca2Fe2O5, Fe2O3 and Ir. Mössbauer and magnetization data suggest magnetic order at ambient temperature with complex magnetic interactions.  相似文献   

11.
In this study, quasi‐cubic and hexagonal bipyramid α‐Fe2O3 polyhedrons with high‐index facets exposed were controllably synthesized by applying metal ions Zn2+ or Cu2+ as structure‐directing agents. The growth of the α‐Fe2O3 nanostructures with high‐index facets were induced by metal ions without the addition of any other surfactants. The quasi‐cubic form controlled by Zn2+ looks like a cube but has an angle of approximately 86° bound by (012), (10‐2), and (1‐12) facets, whereas the hexagonal bipyramid form controlled by Cu2+ has a sixfold axis bound by {012} facets. Magnetic measurements confirm that these two kinds of nanocrystals display shape‐ and surface‐dependent magnetic behaviors. The hexagonal bipyramid iron oxide nanocrystals show a lower Morin transition temperature of 240 K and might be spin‐canted ferromagnetically controlled at room temperature, and the ferromagnetism disappears at low temperature. The quasi‐cubic nanocrystals have a splitting between FC curve and ZFC curve from the highest experimental temperature and no Morin transformation occurs; this indicates that they would be defect ferromagnetically controlled at low temperature. The reported metal‐ion‐directing technique could provide a universal method for shape‐ and surface‐controlled synthesis of nanocrystals with high‐index facets exposed.  相似文献   

12.
Mixed‐metal sulfide Zn1?xMnxS nanorod‐assembled hierarchical hollow spheres were synthesized by a template‐free solvothermal process based on Ostwald ripening. In the reaction system, glycerol plays a key role in the formation of ZnxMn1?xS hierarchical hollow structures by a quasi‐microemulsion‐template mechanism. When applied as capacitor electrode material, the hierarchical Zn1?xMnxS hollow spheres show excellent electrochemical performance. Specifically, Zn0.25Mn0.75S hollow spheres can deliver a high specific capacitance of 664 F g?1 at a current rate of 1 A g?1, which is almost five times of that of MnS under the same conditions and higher than those of previously reported single Mn‐based compounds.  相似文献   

13.
The MnII‐based porous metal‐organic framework, [Mn3(btca)2(HCOO)(μ3‐OH)(H2O)2] · 2DMF ( 1 ) (H2btca = benzotriazole‐5‐carboxylate acid), was prepared by the solvothermal reaction of Mn(CH3COO)2 · 4H2O and H2btca, which was characterized by infrared spectroscopy, thermogravimetric analyses, and X‐ray crystallographic study. 1 exhibits 3D framework with 1D rectangle channels constructed by the strip‐shaped chains containing [Mn53‐OH)2(btca)4] pentaclusters subunits. Furthermore, the magnetic measures show that 1 exhibits weak ferromagnetic behavior at low temperature.  相似文献   

14.
A metal coordination polymer, {[Mn2Mo(CN)8(C12H8N6)(CH3CN)2(H2O)2]·2H2O}n, has been synthesized by the reaction of Mn(ClO4)2·6H2O with 3,6‐bis(pyridin‐2‐yl)‐1,2,4,5‐tetrazine (bptz) and (Bu3N)3[Mo(CN)8] at room temperature. The polymer was characterized by IR spectroscopy, elemental analysis and X‐ray diffraction, and the magnetic properties were also investigated. The X‐ray diffraction analysis reveals that the compound is a new three‐dimensional coordination polymer with a PtS‐type network. Magnetic investigation shows antiferromagnetic coupling between adjacent Mn2+ cations.  相似文献   

15.
Three 3‐amino‐1, 2, 4‐triazole (atz)‐based paramagnetic complexes, [Mn(atz)(pa)]n ( 1 ), {[Mn(atz)1.5(hip)] · H2O}n ( 2 ), and [Mn(H2O)2(atz)2(nb)2] ( 3 ) (H2pa = o‐phthalic acid, H2hip = 5‐hydroxylisophthalic acid, and Hnb = p‐nitrobenzoic acid) were prepared by introducing different carboxylate‐containing aromatic coligands, and structurally and magnetically characterized. Helical MnII‐atz and bent MnII‐pa2– chains are crosslinked by sharing the same metal sites to generate a honeycomb‐shaped framework of 1 . The undulated MnII‐atz layers constructed from 22‐member metallomacrocycles are periodically supported by ditopic hip2– ligands to lead to a pillared‐layer structure of 2 . In contrast, complex 3 is a centrosymmetric mononuclear entity, which is assembled into a three‐dimensional supramolecular network by abundant hydrogen‐bonding interactions. The structural difference of 1 – 3 is significantly due to the combinations of the flexible coordination modes adopted by the mixed atz and carboxylate groups. Weak and comparable antiferromagnetic couplings are observed in the nearest neighbors of 1 – 3 , which are cooperatively transmitted either by short carboxylate and/or atz heterobridges or by weak non‐covalent interactions.  相似文献   

16.
There have been recent reports on the formation of single‐halide perovskites, CH3NH3PbX3 (X=Cl, Br, I), by means of vapor‐assisted solution processing. Herein, the successful formation of mixed‐halide perovskites (CH3NH3PbI3?xXx) by means of a vapor‐assisted solution method at ambient atmosphere is reported. The perovskite films are synthesized by exposing PbI2 film to CH3NH3X (X=I, Br, or Cl) vapor. The prepared perovskite films have uniform surfaces with good coverage, as confirmed by SEM images. The inclusion of chlorine and bromine into the structure leads to a lower temperature and shorter reaction time for optimum perovskite film formation. In the case of CH3NH3PbI3?xClx, the optimum reaction temperature is reduced to 100 °C, and the resulting phases are CH3NH3PbI3 (with trace Cl) and CH3NH3PbCl3 with a ratio of about 2:1. In the case of CH3NH3PbI3?xBrx, single‐phase CH3NH3PbI2Br is formed in a considerably shorter reaction time than that of CH3NH3PbI3. The mesostructured perovskite solar cells based on CH3NH3PbI3 films show the best optimal power conversion efficiency of 13.5 %, whereas for CH3NH3PbI3?xClx and CH3NH3PbI3?xBrx the best recorded efficiencies are 11.6 and 10.5 %, respectively.  相似文献   

17.
The reaction of 2,3,5,6‐tetracyanopyridine (TCNPy) with V(CO)6 in CH2Cl2 forms new organic‐based magnets of V[TCNPy]x?z (CH2Cl2) (x=2, 3) composition. Analysis of the IR spectra suggests that the TCNPy is reduced and coordinated to VII sites through the nitriles. V[TCNPy]x order as ferrimagnets with 111 and 90 K Tc values for V[TCNPy]2 and V[TCNPy]3, respectively. Their respective remanent magnetizations and coercive fields are 1260 and 250 emuOe mol?1 and 9 and 6 Oe at 5 K, and they exhibit some spin‐glass behavior.  相似文献   

18.
The new clathrate Ba8–xEuxGe433 (x = 0.6) was synthesized at a pressure of 1 GPa and temperatures of up to 1220 K by means of a multi‐anvil device (Walker module) and a hydraulic 1000 ton press. X‐ray powder diffraction data indicate that the crystal structure of Ba8–xEuxGe433 (x = 0.6, space group , a = 21.2588(3) Å) corresponds to that of Ba8Ge433. Measurements of the magnetic susceptibility of Ba8–xEuxGe433 reveal Curie‐paramagnetic behaviour and prove that the electronic state of europium corresponds to 4f7, i.e., Eu2+. Electrical resistivity shows a metal‐like temperature dependence and ρ(300) ≈ 2mΩ cm for x = 0.6. Heat capacity measurements reveal an upturn of cp/T(T) below 7 K that is attributed to magnetic interaction of the europium ions.  相似文献   

19.
Solvothermal reactions of the calix[4]arene tetraacetic acid (H4CTA) with zinc nitrate in the presence of α,ω‐diaminoalkanes afford two‐dimensional metallopolycapsular networks of the formula {[Me2NH2]2[G@(Zn2(CTA)2)] ? (DMF)2 ? (H2O)4}n (G=+NH3–(CH2)n–NH3+, n=2, 3, 4; DMF=N,N‐dimethylformamide). These metallopolycapsular networks are built up of metallocapsules that consist of two CTA and two ZnII ions. Short alkanediyldiammonium (+NH3–(CH2)n–NH3+, n=2, 3, 4) guest ions are accommodated in each capsule of the metallopolycapsular network through a variety of supramolecular interactions. The thermal behaviours and the solid‐state photoluminescent properties of these complexes were also investigated.  相似文献   

20.
Metal complexes with Schiff base ligands have been suggested as potential phosphors in electroluminescent devices. In the title complex, tetrakis[6‐methyl‐2‐({[(pyridin‐2‐yl)methyl]imino}methyl)phenolato‐1:2κ8N,N′,O:O;3:2κ8N,N′,O:O]trizinc(II) hexafluoridophosphate methanol monosolvate, [Zn3(C14H13N2O)4](PF6)2·CH3OH, the ZnII cations adopt both six‐ and four‐coordinate geometries involving the N and O atoms of tetradentate 6‐methyl‐2‐({[(pyridin‐2‐yl)methyl]imino}methyl)phenolate ligands. Two terminal ZnII cations adopt distorted octahedral geometries and the central ZnII cation adopts a distorted tetrahedral geometry. The O atoms of the phenolate ligands bridge three ZnII cations, forming a dicationic trinuclear metal cluster. The title complex exhibits a strong emission at 469 nm with a quantum yield of 15.5%.  相似文献   

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