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1.
Three new cobalt borate compounds, [Co(DIEN)2][B5O6(OH)4]2 (DIEN=diethylenetriamine) (1), [B5O7(OH)3Co(TREN)] (TREN=tris(2-aminoethyl)amine) (2), and [Co2(TETA)3][B5O6(OH)4]4 (TETA=triethylenetetramine) (3) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR, elemental analysis and thermogravimetry. The structures exhibit interesting 3D supramolecular hydrogen-bonded architectures, involving the similar borate polyanion [B5O6+n(OH)4−n](n+1)−(n=0 for 1 and 3, and n=1 for 2) and the templating transition metal complexes which are generated in situ under mild solvothermal conditions. Crystal data: 1, monoclinic, space group C2/m (No. 12), , , , β=93.601(4)°, , Z=2; 2, monoclinic, P21/c (No. 14), , , , β=99.926(4)°, , Z=4; 3, triclinic, space group P-1 (No. 2), , , , α=77.009(5)°, β=80.095(2)°, γ=82.334(3)°, , Z=2.  相似文献   

2.
The crystal structures of three new intermetallic ternary compounds in the LnNiSb3 (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb3, NdNiSb3 and SmNiSb3 all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb6 octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb3), 4.6 K (NdNiSb3), and 2.9 K (SmNiSb3). Effective moments of 3.62 μB, 3.90 μB and 0.80 μB are found for PrNiSb3, NdNiSb3 and SmNiSb3, respectively, and are consistent with Pr3+ (f 2), Nd3+ (f 3), and Sm3+ (f 4).  相似文献   

3.
Dendrimer-like copolymers with two and three generations, (polystyrene)3-b-(poly(l-lactide))6 (PSt3-b-PLLA6) and PSt3-b-PLLA6-b-PSt12 have been successfully prepared using core-first method. The first step of this synthesis is the preparation of three-armed PSt by atom transfer radical polymerization (ATRP) of St using 1,1,1-tri(methylene-α-bromoisobutyryl)propane as initiator. Terminal divergence of the polymers obtained was achieved by the reaction of terminal bromines with branching agent, 2,2-dimethyl-1,3-dioxolane-4-methanol. After deprotection, the polymer with six terminal hydroxyl groups was used in the ring-opening polymerization of LLA. The dendrimer-like copolymer with PLLA as a second generation diverged continuously by the reaction of 6 terminal hydroxyl groups with branching agent, 2,2-bis(methylene-α-bromoisobutyryl)propionyl chloride. The resultant polymer with 12 terminal bromines was used as macroinitiator in the ATRP of St to produce the target dendrimer-like copolymer, PSt3-b-PLLA6-b-PSt12. The structures of polymers obtained from each step were confirmed by their 1H NMR spectra and GPC measurements. DSC results show one for the three-armed PSt, , and for the dendrimer-like copolymer with two generations, C(PSt(PLLA)2)3, and , and for the copolymer with three generations, C(PSt(PLLA(PSt)2)2)3.  相似文献   

4.
Fe[(CH3(CH2)2PO3)(H2O)] (1) and Fe[(CH3(CH2)17PO3)(H2O)] (2) were synthesized by reaction of FeCl2·6H2O and the relevant phosphonic acid in water in presence of urea and under inert atmosphere. The compounds were characterized by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy. The crystal structure of (1) was determined from X-ray single crystal diffraction studies at room temperature: monoclinic symmetry, space group P21, , , , and β=98.62(3)°. The compound is lamellar and the structure is hybrid, made of alternating inorganic and organic layers along the c direction. The inorganic layers consist of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from the water molecule, separated by bi-layers of propyl groups. A preliminary structure characterization of compound (2) suggests a similar layered structure, but with an interlayer spacing of 40.3 Å. The magnetic properties of the compounds were both studied by a dc and ac SQUID magnetometer. Fe[(CH3(CH2)2PO3)(H2O)] (1) obeys the Curie-Weiss law at temperatures above 50 K (, ), indicating a Fe +II oxidation state, a high-spin d6 (S=2) electronic configuration and an antiferromagnetic exchange couplings between the near-neighbouring Fe(II) ions. Below , Fe[(CH3(CH2)2PO3)(H2O)] exhibits a weak ferromagnetism. The critical temperature of has been determined by ac magnetic susceptibility measurements. Compound (2) shows the same paramagnetic behaviour of the iron (II) propyl derivative. The values of C and θ were found to be and −44 K, respectively, thus suggesting the presence of Fe +II ion in the S=2 spin state and antiferromagnetic interactions between Fe(II) ions at low temperatures. Zero-field and field cooled magnetic susceptibility vs. T plots do not overlap below , suggesting the presence of an ordered magnetic state. The critical temperature, TN, has been located by the peaks at from the ac susceptibility (χ′and χ″) vs. T plots. Below TN hysteresis loops recorded in the temperature region show an S-shape, while below 15 K assume an ellipsoid form. They reveal that compound (2) is a weak ferromagnet. The critical temperature TN in these layered Fe(II) alkylphosphonates is independent of the distance between the inorganic layers.  相似文献   

5.
A new layered zirconium diphosphonate fluoride, ZrF(O3PCH2)2NHCH2C6H5 has been prepared and its structure determined ab initio by X-ray powder data and refined with the Rietveld method (orthorhombic, , , , space group Pbca, , Z=8, Rwp=0.080). Both phosphonic groups of each diphosphonate building block are bonded to zirconium atoms on the same side of each layer. Benzyl groups from adjacent layers are interdigitated in the interlayer region, with probable π-π stacking interactions. The structure of the free benzylamino-N,N-bis methylphosphonic acid has been determined by single crystal X-ray data (monoclinic, space group P21, , , , β=92.930(3)°, , Z=2, R1=0.072, wR2=0.150). As in the zirconium derivative, benzyl groups from adjacent layers are interdigitated and create a regular alternation of polar and non-polar regions.  相似文献   

6.
A ferroelectric crystal (C3N2H5)5Sb2Br11 has been synthesized. The single crystal X-ray diffraction studies (at 300, 155, 138 and 121 K) show that it is built up of discrete corner-sharing bioctahedra and highly disordered imidazolium cations. The room temperature crystal structure has been determined as monoclinic, space group, P21/n with: , and and β=96.19°. The crystal undergoes three solid-solid phase transitions: ) discontinuous, continuous and discontinuous. The dielectric and pyroelectric measurements allow us to characterize the low temperature phases III and IV as ferroelectric with the Curie point at 145 K and the saturated spontaneous polarization value of the order of along the a-axis (135 K). The ferroelectric phase transition mechanism at 145 K is due to the dynamics of imidazolium cations.  相似文献   

7.
Ln3Co4Sn13 (Ln=La, Ce) have been synthesized by flux growth and characterized by single crystal X-ray diffraction. These compounds adopt the Yb3Rh4Sn13-type structure and crystallize in the cubic space group (No. 223) with Z=2. Lattice parameters at 298 K are , , and , for the La and Ce analogues, respectively. The crystal structure consists of an Sn-centered icosahedron at the origin of the unit cell, which shares faces with eight Co trigonal prisms and 12 Ln-centered cuboctahedra. Magnetization data at 0.1 T show paramagnetic behavior down to 1.8 K for Ce3Co4Sn13, with per Ce3+, while conventional type II superconductivity appears below 2.85 K in the La compound. Electrical resistivity and specific heat data for the La compound show a corresponding sharp superconducting transition at Tc∼2.85 K. The entropy and resistivity data for Ce3Co4Sn13 show the existence of the Kondo effect with a complicated semiconducting-like behavior in the resistivity data. In addition, a large enhanced specific heat coefficient at low T with a low magnetic transition temperature suggests a heavy-fermionic character for the Ce compound. Herein, the structure and physical properties of Ln3Co4Sn13 (Ln=La, Ce) are discussed.  相似文献   

8.
The new ternary transition metal telluride CrAuTe4 has been discovered through solid-state reaction of the elements. The crystal structure is solved in the monoclinic space group P2/m (No. 10) with lattice parameters , , , and β=90.604(10)°. The structure is related to that of the binary compound AuTe2, and a derivation of the structure of CrAuTe4 from AuTe2 is shown. Measurements of the thermopower, thermal conductivity, electrical resistivity, and magnetic susceptibility are presented. The compound undergoes a paramagnetic to antiferromagnetic transition at .  相似文献   

9.
α-Ca3(BN2)2 crystallizes in the cubic system (space group: ) with one type of calcium ions disordered over of equivalent (8c) positions. An ordered low-temperature phase (β-Ca3(BN2)2) was prepared and found to crystallize in the orthorhombic system (space group: Cmca) with lattice parameters: , , and . Structure refinements on the basis of X-ray powder data have revealed that orthorhombic β-Ca3(BN2)2 corresponds to an ordered super-structure of cubic α-Ca3(BN2)2. The space group Cmca assigned for β-Ca3(BN2)2 is derived from by a group-subgroup relationship.DSC measurements and temperature-dependent in situ X-ray powder diffraction studies showed reversible phase transitions between β- and α-Ca3(BN2)2 with transition temperatures between 215 and 240 °C.The structure Sr3(BN2)2 was reported isotypic with α-Ca3(BN2)2 () with one type of strontium ions being disordered over of equivalent (2c) positions. In addition, a primitive () structure has been reported for Sr3(BN2)2. Phase stability studies on Sr3(BN2)2 revealed a phase transition between a primitive and a body-centred lattice around 820 °C. The experiments showed that both previously published structures are correct and can be assigned as α-Sr3(BN2)2 (, high-temperature phase), and β-Sr3(BN2)2 (, low-temperature phase).A comparison of Ca3(BN2)2 and Sr3(BN2)2 phases reveals that the different types of cation disordering present in both of the cubic α-phases () have a directing influence on the formation of two distinct (orthorhombic and cubic) low-temperature phases.  相似文献   

10.
11.
Two compounds of formula La7A3W4O30 (with A=Nb and Ta) were prepared by solid-state reaction at 1450 and 1490 °C. They crystallize in the rhombohedric space group R-3 (No. 148), with the hexagonal parameters: , and , . The structure of the materials was analyzed from X-ray, neutron and electronic diffraction. These oxides are isostructural of the reduced molybdenum compound La7Mo7O30, which are formed of perovskite rod along [111]. An order between (Nb, Ta) and W is observed.  相似文献   

12.
Two rare-earth compounds containing selenium atoms, La(HSeO3)(SeO4) with a new open framework structure and KNd(SeO4)2 with a layered structure, have been synthesized under “sol-gel” hydrothermal conditions for the first time. Single-crystals of La(HSeO3)(SeO4) crystallize in the monoclinic system (P21, , , , β=104.91(3)°, Z=2, RAll=0.032). The structure contains puckered polyhedral layers made of LaOx (x=9,10) and SeO4 groups, which are connected via SeO3-uints to the 3D structure. The crytal structure of KNd(SeO4)2 (monoclinc, P21/c, , , , β=91.38(3)°, Z=4, RAll=0.051) contains honeycomb-like six-ring NdO9 polyhedra forming layers which are further decorated with SeO4 tetrahedra. The K+ ions occupy the interspaces of these layers and provide the charge balance.  相似文献   

13.
The thermodynamic properties of three different types of ternary oxides RFeO3(s), R3Fe5O12(s) and RFe2O4(s) (where R=Ho and Er) have been determined by calorimetric and solid-state galvanic cell methods. Heat capacities of RFeO3(s) and R3Fe5O12(s) have been determined by differential scanning calorimetry from 130 to 860 K. Heat capacity measurements from 130 to 860 K revealed λ-type anomalies for RFeO3(s) and R3Fe5O12(s) compounds which are assigned due to magnetic order-disorder transitions. The oxygen chemical potentials corresponding to the three-phase equilibria involving these ternary oxides have been determined by using solid-state electrochemical cells. The standard molar Gibbs energies of formation of RFeO3(s), R3Fe5O12(s) and RFe2O4(s) have been computed from the oxygen potential data. Based on the thermodynamic information, oxygen potential diagrams have been computed for the systems R-Fe-O (R=Ho and Er) at two different temperatures: T=1250 and 1450 K. Thermodynamic functions like , , Ho, Go, , , , , and have been generated for the compounds RFeO3(s) and R3Fe5O12(s) based on the experimental data obtained in this study and the available data in the literature.  相似文献   

14.
The crystal structures of the two oxides Bi46M8O89 (M=P, V) have been solved from single crystals X-ray data at room temperature. Bi46P8O89 crystallizes in the monoclinic symmetry (space group C2/m) with the cell parameters , , and β=112.14(3)°. The symmetry of Bi46V8O89 is also monoclinic but the space group is P21/c with the unit-cell parameters: , , and β=107.27(3)°. Both structures derive from an oxygen deficient fluorite-type structure where the Bi and M cations (M=P, V) are ordered in the framework. The structures are characterised by isolated MO4 tetrahedra (M=P, V) which contradicts the previous results. The difference between the two structures is only due to a different order of the M atoms (M=P, V) in the fluorite-type superstructure. It will be shown that some oxygen sites are partially occupied in both structures which can explain the ion conduction properties of these phases. A structural building principle will be proposed that can explain the large domain of solid solution related to the fluorite-type observed in both systems.  相似文献   

15.
The crystal structure of the low-temperature forms of Rb2KCrF6 and Rb2KGaF6 has been solved on single crystal. The symmetry is tetragonal with F4/m space group; the unit cell parameters are: , for Rb2KCrF6 at and , for Rb2KGaF6 at . The relationships between the parameters of the prototype cubic elpasolite, which is stable at high temperature, and the tetragonal superlattice of the low temperature form have been established. Considering the general formulation A2BB′F6, the cationic positions in the A and (B,B′) sublattices remain identical in the two allotropic varieties. The main originality of the structure concerns the environment of 4/5 of the potassium atoms (B sublattice) which is transformed from octahedra into pentagonal bipyramids sharing edges with adjacent B′F6 octahedra containing Cr or Ga. The displacive phase transition is simply explained by the rotation of 45° in the (a,b) plane of 1/5 of the B′F6 (B′=Cr, Ga) octahedra. The similarity of this phase transition and the transformation of perovskite into tetragonal tungsten bronze (TTB) will be discussed.  相似文献   

16.
A new Os-containing, pillared perovskite, La5Os3MnO16, has been synthesized by solid state reaction in sealed quartz tubes. This extends the crystal chemistry of these materials which had been known only for Mo and Re, previously. The crystal structure has been characterized by X-ray and neutron powder diffraction and is described in space group C-1 with parameters a=7.9648(9) Å; b=8.062(1) Å; c=10.156(2) Å, α=90.25(1)°, β=95.5(1)°; γ=89.95(2)°, for La5Os3MnO16. The compound is isostructural with the corresponding La5Re3MnO16 phase. A very short Os-Os distance of 2.50(1) Å was found in the dimeric pillaring unit, Os2O10, suggestive of a triple bond as demanded by electron counting. Nearly spin only values for the effective moment for Os5+ () and Mn2+ () were derived from magnetic susceptibility data. Evidence for magnetic transitions was seen near ∼180 and 80 K. Neutron diffraction data indicate that Tc is 170(5) K. The magnetic structure of La5Os3MnO16 at 7 K was solved revealing that Os5+ and Mn2+ form ferrimagnetically coupled layers with antiferromagnetic interlayer ordering. The ordered moments are for Mn2+ and for Os5+, which are reduced from the respective spin only values of 5.0 and . The observation of net ferrimagnetic (antiparallel) intraplanar coupling between Os5+(t2g3) and Mn2+(t2g3eg2) is interesting as it appears to contradict the Goodenough-Kanamori rules for 180° superexchange.  相似文献   

17.
18.
A second form of the literature-known layered weak ferromagnet Fe[(CH3PO3)(H2O)] has been isolated. The crystal structure determination of this new form (2) has been carried out at T=300, 200 and 130 K. It crystallizes in the orthorhombic space group Pmn21: a=5.7177(11), b=8.8093(18), , while form (1) crystallizes in the space group Pna21: a=17.58(2), b=4.814(1), . Mössbauer spectroscopy on form (2) has been performed in the temperature range 4-300 K; and, at , a drastic change in the quadrupole splitting (ΔE) and a broadening of the doublet components is noticed. But surprisingly, on cooling the crystal, no structural change is observed, which could account for the increase in ΔE. Below , 57Fe spectra transform into hyperfine splitting patterns which reveal a magnetically ordered state in agreement with the results of earlier magnetic susceptibility studies.  相似文献   

19.
The room temperature structure of Bi0.75Sr0.25MnO3 has been fitted to high-resolution synchrotron X-ray and time-of-flight neutron powder diffraction data. Constrained structural models were refined using a Pn11 supercell (, , , and α=89.894(1)°) of the underlying Pnma perovskite structure. The best-fit model evidences a 3:1 Mn3+/Mn4+charge ordering with only 30% of the ideal separation of bond valence sums. An ordered intergrowth of antiferro-orbitally ordered (LaMnO3 type) and charge and ferro-orbitally ordered (YBaMn2O6 type) blocks is observed. Off-centre Bi/Sr displacements are ferroelectrically ordered in this model.  相似文献   

20.
The linear swelling ratio α and the effective network chain length N of a series of poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels were investigated as a function of the gel preparation concentration . PDMAAm hydrogels were prepared at a fixed cross-linker ratio but at various initial monomer concentrations. It was found that α is not a monotonic function of . As is increased, α first decreases up to about and remains constant in a narrow range of , but then it increases continuously. The -dependence of α is due to the variation of the network chain length N depending on the gel preparation concentration. In the range of below 0.1, N follows the scaling relationship , while at higher concentrations, N varies only slightly with . The increase of α with N obeys the relation , as predicted by the Flory-Rehner theory.  相似文献   

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