244 research outputs found

    The dehydration of SrTeO3(H2O) - a topotactic reaction for preparation of the new metastable strontium oxotellurate(IV) phase e-SrTeO3

    Get PDF
    Microcrystalline single-phase strontium oxotellurate(IV) monohydrate, SrTeO3 (H2O), was obtained by microwave-assisted hydrothermal synthesis under alkaline conditions at 180 ◦C for 30 min. A temperature of 220 ◦C and longer reaction times led to single crystal growth of this material. The crystal structure of SrTeO3 (H2O) was determined from single crystal X-ray diffraction data: P21/c, Z = 4, a = 7.7669(5), b = 7.1739(4), c = 8.3311(5)A˚ , b = 107.210(1)◦, V = 443.42(5)A˚ 3 , 1403 structure factors, 63 parameters, R[F2>2s(F2 )] = 0.0208, wR(F2 all) = 0.0516, S = 1.031. SrTeO3 (H2O) is isotypic with the homologous BaTeO3 (H2O) and is characterised by a layered assembly parallel to (100) of edge-sharing [SrO6 (H2O)] polyhedra capped on each side of the layer by trigonal-prismatic [TeO3 ] units. The cohesion of the structure is accomplished by moderate O–H ◊ ◊ ◊ O hydrogen bonding interactions between donor water molecules and acceptor O atoms of adjacent layers. In a topochemical reaction, SrTeO3 (H2O) condensates above 150 ◦C to the metastable phase e-SrTeO3 and transforms upon further heating to d-SrTeO3 . The crystal structure of e-SrTeO3 , the fifth known polymorph of this composition, was determined from combined electron microscopy and laboratory X-ray powder diffraction studies: P21/c, Z = 4, a = 6.7759(1), b = 7.2188(1), c = 8.6773(2)A˚ , b = 126.4980(7)◦, V = 341.20(18)A˚ 3 , RFobs = 0.0166, RBobs = 0.0318, Rwp = 0.0733, Goof = 1.38. The structure of e-SrTeO3 shows the same basic set-up as SrTeO3 (H2O), but the layered arrangement of the hydrous phase transforms into a framework structure after elimination of water. The structural studies of SrTeO3 (H2O) and e-SrTeO3 are complemented by thermal analysis and vibrational spectroscopic measurements.Centro de Química Inorgánic

    Structural Phase Transitions in the Double Salts (NH<sub>4</sub>)<sub>2</sub>PO<sub>3</sub>F·NH<sub>4</sub>NO<sub>3</sub> and (NH<sub>4</sub>)<sub>2</sub><i>X</i>O<sub>4</sub>·3NH<sub>4</sub>NO<sub>3</sub> (<i>X</i> = Se, Cr)

    No full text
    In the context of investigating isostructural relationships between sulfates and monofluorophosphates, crystals of the double salts (NH4)2PO3F·NH4NO3 (AFP·AN) and (NH4)2XO4·3NH4NO3 (AX·3AN; X = Se, Cr) were grown from aqueous solutions and structurally characterized using X-ray diffraction and thermal analysis. Whereas the high-temperature forms of the two AX·3AN double salts are in fact isostructural with the sulfate analogue, AFP·AN crystallizes with a reduced amount of NH4NO3 and thus has a unique crystal structure. Both AFP·AN and the two AX·3AN compounds exhibit reversible structural phase transitions. Upon cooling, the monofluorophosphate double salt transforms from the monoclinic room-temperature polymorph (I; P21/n, Z = 4) to the intermediate triclinic polymorph (II; P1, Z = 4) that in turn transforms to the monoclinic low-temperature polymorph (III; P21/n, Z = 4). The two phase transitions (I) → (II) and (II) → (III) are characterized by a significant increase of the unit cell volumes upon cooling. The two AX·3AN double salts transform upon cooling from a disordered monoclinic crystal structure (P21, Z = 2) to a monoclinic polymorph with a doubled unit cell (P21/c, Z = 4). Such a phase transition is not observed for the sulfate analogue. All molecular moieties are fully ordered at −93 °C for the selenate double salt, whereas one of the nitrate anions remains disordered for the chromate double salt even at −173 °C. In all AFP·AN and AX·3AN crystal structures, the nitrate anions play a crucial role during the phase transitions, and an extensive network of N–H···O hydrogen-bonding interactions is responsible for the cohesion of the crystal

    Dimorphism of [Bi2O2(OH)](NO3) – the ordered Pna21 structure at 100 K

    No full text
    The re-investigation of [Bi2O2(OH)](NO3), dioxidodibismuth(III) hydroxide nitrate, on the basis of single-crystal X-ray diffraction data revealed an apparent structural phase transition of a crystal structure determined previously (space group Cmc21 at 173 K) to a crystal structure with lower symmetry (space group Pna21 at 100 K). The Cmc21 → Pna21 group–subgroup relationship between the two crystal structures is klassengleiche with index 2. In contrast to the crystal structure in Cmc21 with orientational disorder of the nitrate anion, disorder does not occur in the Pna21 structure. Apart from the disorder of the nitrate anion, the general structural set-up in the two crystal structures is very similar: [Bi2O2]2+ layers extend parallel to (001) and alternate with layers of (OH)− anions above and (NO3)− anions below the cationic layer. Whereas the (OH)− anion shows strong bonds to the BiIII cations, the (NO3)− anion weakly binds to the BiIII cations of the cationic layer. A rather weak O—H...O hydrogen-bonding interaction between the (OH)− anion and the (NO3)− anion links adjacent sheets along [001]

    The Cobalt(II) Oxidotellurate(IV) Hydroxides Co2(TeO3)(OH)2 and Co15(TeO3)14(OH)2

    No full text
    Previously unknown Co2(TeO3)(OH)2 and Co15(TeO3)14(OH)2 were obtained under mild hydrothermal reaction conditions (210 &deg;C, autogenous pressure) from alkaline solutions. Their crystal structures were determined from single-crystal X-ray diffraction data. Co2(TeO3)(OH)2 (Z = 2, P1&macr;, a = 5.8898(5), b = 5.9508(5), c = 6.8168(5) &Aring;, &alpha; = 101.539(2), &beta; = 100.036(2), &gamma; = 104.347(2)&deg;, 2120 independent reflections, 79 parameters, R[F2 &gt; 2&sigma;(F2)] = 0.017) crystallizes in a unique structure comprised of undulating 2&prop;[Co2(OH)6/3O3/3O2/2O1/1]4&minus; layers. Adjacent layers are linked by TeIV atoms along the [001] stacking direction. Co2(TeO3)(OH)2 is stable up to 450 &deg;C and decomposes under the release of water into Co6Te5O16 and CoO. Magnetic measurements of Co2(TeO3)(OH)2 showed antiferromagnetic ordering at &asymp; 70 K. The crystal structure of Co15(TeO3)14(OH)2 (Z = 3, R3&macr;, a = 11.6453(2), c = 27.3540(5) &Aring;, 3476 independent reflections, 112 parameters, R[F2 &gt; 2&sigma;(F2)] = 0.026) is isotypic with Co15(TeO3)14F2. A quantitative structural comparison revealed that the main structural difference between the two phases is connected with the replacement of F by OH, whereas the remaining part of the three-periodic network defined by [CoO6], [CoO5(OH)], [CoO5] and [TeO3] polyhedra is nearly unaffected. Consequently, the magnetic properties of the two phases are similar, namely being antiferromagnetic at low temperatures

    The Cobalt(II) Oxidotellurate(IV) Hydroxides Co<sub>2</sub>(TeO<sub>3</sub>)(OH)<sub>2</sub> and Co<sub>15</sub>(TeO<sub>3</sub>)<sub>14</sub>(OH)<sub>2</sub>

    No full text
    Previously unknown Co2(TeO3)(OH)2 and Co15(TeO3)14(OH)2 were obtained under mild hydrothermal reaction conditions (210 °C, autogenous pressure) from alkaline solutions. Their crystal structures were determined from single-crystal X-ray diffraction data. Co2(TeO3)(OH)2 (Z = 2, P1¯, a = 5.8898(5), b = 5.9508(5), c = 6.8168(5) Å, α = 101.539(2), β = 100.036(2), γ = 104.347(2)°, 2120 independent reflections, 79 parameters, R[F2 > 2σ(F2)] = 0.017) crystallizes in a unique structure comprised of undulating 2∝[Co2(OH)6/3O3/3O2/2O1/1]4− layers. Adjacent layers are linked by TeIV atoms along the [001] stacking direction. Co2(TeO3)(OH)2 is stable up to 450 °C and decomposes under the release of water into Co6Te5O16 and CoO. Magnetic measurements of Co2(TeO3)(OH)2 showed antiferromagnetic ordering at ≈ 70 K. The crystal structure of Co15(TeO3)14(OH)2 (Z = 3, R3¯, a = 11.6453(2), c = 27.3540(5) Å, 3476 independent reflections, 112 parameters, R[F2 > 2σ(F2)] = 0.026) is isotypic with Co15(TeO3)14F2. A quantitative structural comparison revealed that the main structural difference between the two phases is connected with the replacement of F by OH, whereas the remaining part of the three-periodic network defined by [CoO6], [CoO5(OH)], [CoO5] and [TeO3] polyhedra is nearly unaffected. Consequently, the magnetic properties of the two phases are similar, namely being antiferromagnetic at low temperatures

    Electroencephalographic and Cardiovascular Changes Associated with Propofol Constant Rate of Infusion Anesthesia in Young Healthy Dogs

    No full text
    This study aimed to evaluate electroencephalography (EEG) and cardiovascular changes associated with propofol constant rate of infusion (CRI) anesthesia in dogs. Six dogs were each given propofol CRI to induce different anesthetic phases including induction (1 mg/kg/min for 10 min), and decremental maintenance doses of 2.4 mg per kg per min, 1.6 mg per kg per min, and 0.8 mg per kg per minute over 45 min. Processed EEG indices including patient state index (PSI), (burst) suppression ratio (SR), and spectral edge frequency (95%) were obtained continuously until the dogs recovered to sternal recumbency. The dogs were intubated and ventilated. Cardiovascular and EEG index values were compared between anesthetic phases. The PSI, SR, mean arterial blood pressure, and subjective anesthetic depth scores were highly correlated throughout anesthetic depth changes. The PSI decreased from 85.0 ± 17.3 at awake to 66.0 ± 29.0 at induction, and then sharply reduced to 19.7 ± 23.6 during maintenance and returned to 61.5 ± 19.2 at extubation. The SR increased from 15.4 ± 30.9% at induction to 70.9 ± 39.8% during maintenance and decreased to 3.4 ± 8.9% at extubation. We concluded that EEG indices can be used to aid in tracking ongoing brain state changes during propofol anesthesia in dogs

    Crystal structure of K6[Zn(CO3)4]

    No full text
    The crystal structure of K6[Zn(CO3)4], hexapotassium tetracarbonatozincate(II), comprises four unique potassium cations (two located on a general position, and two on the twofold rotation axis of the space group C2/c) and a [Zn(CO3)4]6− anion. The ZnII atom of the latter is located on the twofold rotation axis and is surrounded in a slightly distorted tetrahedral manner by two pairs of monodentately binding carbonate groups, with Zn—O distances of 1.9554 (18) and 1.9839 (18) Å. Both carbonate groups exhibit a slight deviation from planarity, with the C atom being shifted by 0.008 (2) and 0.006 (3) Å, respectively, from the plane of the three O atoms. The coordination numbers of the potassium cations range from 6 to 8, using a threshold of 3.0 Å for K—O bonding interactions being significant. In the crystal structure, [KOx] polyhedra and [Zn(CO3)4]6− groups share O atoms to build up the framework structure

    Perioperative Brain Function Monitoring with Electroencephalography in Horses Anesthetized with Multimodal Balanced Anesthetic Protocol Subjected to Surgeries

    No full text
    This study aimed to investigate the use of electroencephalography (EEG) for detecting brain activity changes perioperatively in anesthetized horses subjected to surgery. Twelve adult horses undergoing various surgeries were evaluated after premedication with xylazine and butorphanol, induction with ketamine, midazolam, and guaifenesin, and maintenance with isoflurane. The frontal EEG electrodes were placed after the horse was intubated and mechanically ventilated. The EEG data were collected continuously from Stage (S)1—transition from induction to isoflurane maintenance, S2—during surgery, S3—early recovery before xylazine sedation (0.2 mg kg IV), and S4—recovery after xylazine sedation. The Patient State Index (PSI), (Burst) Suppression Ratio (SR), and 95% Spectral Edge Frequency (SEF95) were compared across the stages. The PSI was lowest in S2 (20.8 ± 2.6) and increased to 30.0 ± 27.7 (p = 0.005) in S3. The SR increased from S1 (5.5 ± 10.7%) to S3 (32.7 ± 33.8%, p = 0.0001). The spectral power analysis showed that S3 had a significantly higher content of delta wave activity (0.1–4 Hz) in the EEG and lower relative power in the 3 Hz to 15 Hz range when compared to S1 and S2. A similar result was observed in S4, but the lower power was in a narrower range, from 3 Hz to 7 Hz, which indicate profound central nervous system depression potentiated by xylazine, despite the cessation of isoflurane anesthesia. We concluded that the use of EEG provides clinically relevant information about perioperative brain state changes of the isoflurane-anesthetized horse

    The Family of <i>M</i><sup>II</sup><sub>3</sub>(Te<sup>IV</sup>O<sub>3</sub>)<sub>2</sub>(OH)<sub>2</sub> (<i>M</i> = Mg, Mn, Co, Ni) Compounds—Prone to Inclusion of Foreign Components into Large Hexagonal Channels

    No full text
    MII3(TeIVO3)2(OH)2 (M = Mg, Mn, Co, Ni) compounds crystallize isotypically in the hexagonal space group P63mc (No. 186) with unit-cell parameters of a ≈ 13 Å, c ≈ 5 Å. In the crystal structure, a framework with composition M3(TeO3)2(OH)1.50.5+ defines large hexagonal channels extending along [001] where the remaining OH− anions are located. Crystal-growth studies under mild hydrothermal conditions with subsequent structure analyses on basis of X-ray diffraction methods revealed that parts of other anions present in solution such as CO32−, SO42−, SeO42−, NO3−, Cl− or Br− could partly replace the OH− anions in the channels. The incorporation of such anions into the M3(TeO3)2(OH)2 structure was confirmed by energy-dispersive X-ray spectrometry (EDS) measurements and Raman spectroscopy of selected single-crystals
    corecore