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1.
J Am Chem Soc ; 2020 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-32216316

RESUMO

Understanding the electric dipole switching in multiferroic materials requires deep insight of the atomic-scale local structure evolution to reveal the ferroelectric mechanism, which remains unclear and lacks a solid experimental indicator in high-pressure prepared LiNbO3-type polar magnets. Here we report the discovery of Zn-ion splitting in LiNbO3-type Zn2FeNbO6 established by multiple diffraction techniques. The coexistence of high-temperature paraelectric-like phase in the polar Zn2FeNbO6 lattice motivated revisiting other high-pressure prepared LiNbO3-type A2BB'O6 compounds. The A-site atomic splitting (~ 1.0-1.2 Å between the split-atom pair) in B/B'- mixed Zn2FeTaO6 and O/N-mixed ZnTaO2N is verified by both powder x-ray diffraction structural refinements and high angle annular dark field scanning transmission electron microscopy images, but absent in single-B-site ZnSnO3. Theoretical calculations are in good agreement with experimental results and suggest that this kind of A-site splitting also exists in the B-site mixed Mn-analogs, Mn2FeMO6 (M = Nb, Ta) and anion-mixed MnTaO2N, where the smaller A-site splitting (~ 0.2 Å atomic displacement) is attributed to magnetic interactions and bonding between A and B cations. These findings reveal universal A-site splitting in LiNbO3-type structures with mixed multivalent B/B', or anionic sites, and the splitting-atomic displacement can be strongly suppressed by magnetic interactions and/or hybridization of valence bands between d electrons of the A- and B-site cations.

2.
J Pharm Policy Pract ; 12: 18, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31417682

RESUMO

Objectives: To describe changes in the private market for selected originators, branded generics ('similares'), and generic products during the 10 years following passage of the Brazilian Generics Law. Methods: We analyzed longitudinal data collected by IQVIA® on quarterly sales by wholesalers to retail pharmacies in Brazil from 1998 through 2010, grouped by originators, branded generics, and generic products in three therapeutic classes (antibiotics, antidiabetics, and antihypertensives). Outcomes included market share (proportion of the total private market volume), sales volume per capita, prices and number of manufacturers by group. Results: In the private market share, generics became dominant in each therapeutic class but the speed of uptake varied. Originators consistently lost most market share while branded generics varied over time. By the end of the study period, generics were the most sold product type in all classes, followed by branded generics. The number of generic manufacturers increased in all classes, while branded generics increased just after the policy but then decreased slowly through the end of 2010. For approximately 50% of the antibiotics analyzed, branded generics and generics had lower prices than originators. For antidiabetics, branded generic and generic prices were quite similar during the period analyzed. Price trends for the various subclasses of antihypertensive exhibited very different patterns over time. Conclusion: Sales of branded generics and originators decreased substantially in the three therapeutic classes analysed following the introduction of the generics policy in Brazil, but the time to market dominance of generics varied by class.

3.
Acta Crystallogr E Crystallogr Commun ; 75(Pt 4): 489-491, 2019 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-31161062

RESUMO

We report a new polymorph of acridine, C13H9N, denoted form IX, obtained as thin needles by slow evaporation of a toluene solution. The structure was solved and refined from powder X-ray data. The structures of five unsolvated forms were previously known, but this is only the second with one mol-ecule in the asymmetric unit. The melting point [differential scanning calorimetry (DSC) onset] and heat of fusion are 108.8 (3) °C and 19.2 (4) kJ mol-1, respectively.

4.
BMJ Glob Health ; 4(1): e001241, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30899565

RESUMO

Introduction: Understanding patterns of antibiotic consumption is essential to ensure access to appropriate antibiotics when needed and to minimise overuse, which can lead to antibiotic resistance. We aimed to describe changes in global antibiotic consumption between 2011 and 2015. Methods: We analysed wholesale data on total antibiotic sales and antibiotics sold as child-appropriate formulations (CAFs), stratified by country income level (low/middle-income and high-income countries (LMICs and HICs)). The volume of antibiotics sold per year was recorded for 36 LMICs and 39 HICs, measured in standard units (SU: 1 SU is equivalent to a single tablet, capsule or 5 mL ampoule/vial/oral suspension) and SU per person, overall and as CAFs. Changes over time were quantified as percentage changes and compound annual growth rates in consumption per person. Analyses were conducted separately for total sales, sales of antibiotics in the Access and Watch groups of the WHO's Essential Medicines List for children 2017, for amoxicillin and amoxicillin with clavulanic acid. Results: Antibiotic consumption increased slightly between 2011 and 2015, from 6.85×1010 SU to 7.44×1010 SU overall and from 1.66×1010 SU to 1.78×1010 SU for CAFs. However, trends differed between countries and for specific antibiotics; for example, consumption of amoxicillin as CAFs changed little in LMICs and HICs, but that of amoxicillin with clavulanic acid increased by 6.8% per year in LMICs and decreased by 1.0% per year in HICs. Conclusions: As measured in standard units in sales data, the rate of increase in global antibiotic consumption may be slowing. However, the trends appear to differ between countries and drugs. In the absence of routine surveillance of antibiotic use in many countries, these data provide important indicators of trends in consumption which should be confirmed in national and local studies of prescribing.

5.
Chemistry ; 25(7): 1752-1757, 2019 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-30286266

RESUMO

The reaction of MnII (O2 CMe)2 and NaCN or LiCN in water forms a light green insoluble material. Structural solution and Rietveld refinement of high-resolution synchrotron powder diffraction data for this unprecedented, complicated compound of previously unknown composition revealed a new alkali-free ordered structural motif with [MnII 4 (µ3 -OH)4 ]4+ cubes and octahedral [MnII (CN)6 ]4- ions interconnected in 3D by MnII -N≡C-MnII linkages. The composition is {[MnII (OH2 )3 ][MnII (OH2 )]3 }(µ3 -OH)4 ][MnII (µ-CN)2 (CN)4 ]⋅H2 O=[MnII 4 (µ3 -OH)4 (OH2 )6 ][MnII (µ-CN)2 (CN)4 ]⋅H2 O, which is further simplified to [Mn4 (OH)4 ][Mn(CN)6 ](OH2 )7 (1). 1 has four high-spin (S=5/2) MnII sites that are antiferromagnetically coupled within the cube and are antiferromagnetically coupled to six low-spin (S=1/2) octahedral [MnII (CN)6 ]4- ions. Above 40 K the magnetic susceptibility, χ(T), can be fitted to the Curie-Weiss expression, χ ∝(T-θ)-1 , with θ=-13.4 K, indicative of significant antiferromagnetic coupling and 1 orders as an antiferromagnet at Tc =7.8 K.

6.
Chemistry ; 25(17): 4373-4378, 2019 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-30499153

RESUMO

Treating deuterohemin, chloro(deuteroporphyrinato)iron(III), with a non-coordinating base in DMSO/methanol allows for the isolation of [(deuteroporphyrinato)iron(III)]2 , deuterohematin anhydride (DHA), an analogue of malaria pigment, the natural product of heme detoxification by malaria. The structure of DHA obtained from this solvent system has been solved by X-ray powder diffraction analysis and displays many similarities, yet important structural differences, to malaria pigment. Most notably, a water molecule of solvation occupies a notch created by the propionate side chains and stabilizes a markedly bent propionate ligand coordinated with a long Fe-O bond, and a carboxylate cluster associated with water molecules is generated. Together, these features account for its increased solubility and more open structure, with an increased porphyrin-porphyrin separation. The IR spectroscopic signature associated with this structure also accounts for the strong IR band at 1587 cm-1 seen for many amorphous preparations of synthetic malaria pigment, and it is proposed that stabilizing these structures may be a new objective for antimalarial drugs. The important role of the vinyl substituents in this biochemistry is further demonstrated by the structure of deuterohemin obtained by single-crystal X-ray diffraction analysis.

7.
J Am Chem Soc ; 141(2): 911-921, 2019 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-30557002

RESUMO

The size of the organic cation dictates both the composition and the extended 3-D structure for hybrid organic/inorganic Prussian blue analogues (PBAs) of A aMnII b(CN) a+2 b (A = cation) stoichiometry. Alkali PBAs are typically cubic with both MC6 and M'N6 octahedral coordination sites and the alkali cation content depends on the M and M' oxidation states. The reaction of MnII(O2CCH3)2 and A+CN- (A = NMe4, NEtMe3) forms a hydrated material of A3MnII5(CN)13 composition. A3MnII5(CN)13 forms a complex, 3-D extended structural motif with octahedral and rarely observed square pyramidal and trigonal bipyramidal MnII sites with a single layer motif of three pentagonal and one triangular fused rings. A complex pattern of MnIICN chains bridge the layers. (NMe4)3MnII5(CN)13 possesses one low-spin octahedral and four high-spin pentacoordinate MnII sites and orders as an antiferromagnet at 11 K due to the layers being bridged and antiferromagnetically coupled by the nonmagnetic cyanides. These are rare examples of intrinsic, chemically prepared and controlled artificial antiferromagnets and have the advantage of having controlled uniform spacing between the layers as they are not physically prepared via deposition methods. A3Mn5(CN)13 (A = NMe4, NEtMe3) along with [NEt4]2MnII3(CN)8, [NEt4]MnII3(CN)7, and Mn(CN)2 form stoichiometrically related A aMnII b(CN) a+2 b ( a = 0, b = 1; a = 2, b = 3; a = 1, b = 3; and a = 3, b = 5) series possessing unprecedented stoichiometries and lattice motifs. These unusual structures and stoichiometries are attributed to the very ionic nature of the high-spin N-bonded MnII ion that enables the maximization of the attractive van der Waals interactions via minimization of void space via a reduced ∠MnNC. This A aMnII b(CN) a+2 b family of compounds are referred to as being cation adaptive in which size and shape dictate both the stoichiometry and structure.

8.
Eur J Med Chem ; 162: 51-58, 2019 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-30408748

RESUMO

There is an ongoing urgent need for new targeted antibacterial compounds with novel mechanisms of action for the treatment of infections caused by bacteria that are resistant to currently available materials. Since the expression of glycosidase enzymes within bacteria is unequally distributed, glycoside derivatives of antibacterial agents offer potential as targeted prodrugs for bacterial infections. Herein we report the synthesis and characterisation of four α-D-glycopyranosides and three ß-D-glycopyranosides of the broad antibacterial agent triclosan, in generally good synthetic yields, and with excellent purities. Each glycoside was analysed to determine its ability to inhibit the growth of a wide range of Gram-negative and Gram-positive organisms, including many of clinical significance. All of the triclosan glycosides that were synthesized demonstrated antibacterial activity against many of the organisms that were examined. For example, ß-galactoside (3a) and α-arabinoside (3c) had MIC values of 0.5 µg/ml for several strains of S. aureus and S. haemolyticus. The triclosan glycosides were also generally found to be more water soluble and much more selective than the underivatized triclosan, making them ideal both for the targeted inhibition of bacterial growth and as agents for the selective recovery of bacteria from mixed cultures. In the latter case, two Bacillus strains could be identified from various strains of Bacillus and Staphylococcus after inoculation onto Nutrient Agar No. 2 with 0.25 µg/ml triclosan-α-D-glucopyranoside (3e). This glucoside may, therefore, be of use for the isolation and identification of the food-poisoning organism Bacillus cereus.


Assuntos
Antibacterianos/farmacologia , Triclosan/análogos & derivados , Antibacterianos/síntese química , Anti-Infecciosos Locais , Bactérias/efeitos dos fármacos , Infecções Bacterianas/tratamento farmacológico , Glucosídeos , Testes de Sensibilidade Microbiana , Triclosan/síntese química , Triclosan/farmacologia
9.
Malar J ; 17(1): 444, 2018 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-30497504

RESUMO

BACKGROUND: The steady supply of quality, affordable medicines is a pillar of a functioning health system. In addition to the public sector, the private, mission and not-for-profit sectors often serve a large part of the population in Africa. However, while there is generally systematic recording of public sector supply of medicines, detailed, systematic and reliable national market data including these non-public sectors are not commonly available in most countries in Africa. Understanding the total market is a missing part of the access puzzle: without this information, policy makers and health practitioners are not able to fully measure the impact of interventions, measure access to effective products, or fully evaluate the rational use of medicines. This article reports on a unique innovation which provides routine, national-level data on the total pharmaceuticals market, through a system which can be replicated elsewhere. It demonstrates how national-level market data contribute to the evidence base for policies on access to essential medicines, using the Zambian anti-malarial medicines market as a case study. METHODS: A new, routine national database on pharmaceutical market size and structure was established through a multi-partner collaboration. Information was extracted from import authorizations and allows for information on local manufacture. Data included value and volume of products as well as pack details, manufacturer and importer. The system was continually updated: data for this analysis were extracted for 6 years: 2009-2014 inclusive. Data were analysed using Microsoft Excel and validated against other sources including donor procurement data. Analysis included public and private sector markets. The policy relevance was demonstrated through analysis of four aspects of national policies on access and rational use of malaria medicines: (i) volume of product relative to disease burden; (ii) distribution by sector relative to treatment-seeking; (iii) consistency of products with respect to national policy guidelines; (iv) market concentration as a proxy for security of supply. RESULTS: The system developed provides the first accurate, systematic data on the breakdown of a national pharmaceutical market in an African context. The total value of the anti-malarials market in Zambia, including all sectors, was USD 5.5-6 million. This included 22 different molecules or combinations, produced by 56 different manufacturers, with 142 different permutations of molecule/manufacturer/strength. Such data provide a complementary mechanism to confirm key trends in malaria treatment and control in Zambia: (i) sufficient supply relative to disease burden, (ii) value and volume of the private/non-profit sector; 29%-2% of market value and 17%-2% of market volume (from 2009 to 2014), (iii) dominance of the 3 molecules recommended in the national treatment guidelines; and (iv) an evidence-base for national discussions on medicines quality, security of supply and rationale use. The system extracts information on all medicines and therefore could be used to analyse other therapeutic classes. Data have been used for several policy purposes, notably by ZAMRA to monitor the quality of products in Zambia, monitoring implementation of WHO Resolutions on artemisinin monotherapy as well as monitoring trends in product choice across sectors. CONCLUSION: Routine data are important for researchers and policy makers alike. This study shows how medicines data can be systematically gathered at national level-comprising range, volume and value in the public, private and not-for-profit sectors-to monitor more detailed trends in the market and allows triangulation of supply-side data against other sources. This systematic approach can contribute significantly to support access to medicines, monitor treatment and public health policies and create healthy markets. It can be used to monitor changes between therapeutic areas, for example the impact of improved malaria treatment on the use of antibiotics in the context of anti-microbial resistance monitoring. As data contain commercially confidential information, appropriate safeguards should be put in place to balance public health and commercial interests.


Assuntos
Antimaláricos/provisão & distribução , Bases de Dados Factuais , Uso de Medicamentos , Malária/tratamento farmacológico , Política de Saúde , Humanos , Zâmbia
11.
Pharmacoeconomics ; 36(1): 39-49, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-28914440

RESUMO

The manufacturer of olaratumab (Lartruvo®), Eli Lilly & Company Limited, submitted evidence for the clinical and cost effectiveness of this drug, in combination with doxorubicin, for untreated advanced soft tissue sarcoma (STS) not amenable to surgery or radiotherapy, as part of the National Institute for Health and Care Excellence (NICE) Single Technology Appraisal process. The Peninsula Technology Assessment Group, commissioned to act as the Evidence Review Group (ERG), critically reviewed the company's submission. Clinical effectiveness evidence for the company's analysis was derived from an open-label, randomised controlled trial, JGDG. The analysis was based on a partitioned survival model with a time horizon of 25 years, and the perspective was of the UK National Health Service (NHS) and Personal Social Services. Costs and benefits were discounted at 3.5% per year. Given the available evidence, olaratumab is likely to meet NICE's end-of-life criteria. To improve the cost effectiveness of olaratumab, the company offered a discount through a Commercial Access Agreement (CAA) with the NHS England. When the discount was applied, the mean base-case and probabilistic incremental cost-effectiveness ratios (ICERs) for olaratumab plus doxorubicin versus the standard-of-care doxorubicin were £46,076 and £47,127 per quality-adjusted life-year (QALY) gained, respectively; the probability of this treatment being cost effective at the willingness-to-pay threshold of £50,000 per QALY gained, applicable to end-of-life treatments, was 0.54. The respective ICERs from the ERG's analysis were approximately £60,000/QALY gained, and the probability of the treatment being cost effective was 0.21. In August 2017, the NICE Appraisal Committee recommended olaratumab in combination with doxorubicin for this indication for use via the UK Cancer Drugs Fund under the agreed CAA until further evidence being collected in the ongoing phase III trial-ANNOUNCE-becomes available in December 2020.


Assuntos
Protocolos de Quimioterapia Combinada Antineoplásica/administração & dosagem , Sarcoma/tratamento farmacológico , Anticorpos Monoclonais/administração & dosagem , Protocolos de Quimioterapia Combinada Antineoplásica/economia , Análise Custo-Benefício , Doxorrubicina/administração & dosagem , Humanos , Anos de Vida Ajustados por Qualidade de Vida , Ensaios Clínicos Controlados Aleatórios como Assunto , Sarcoma/economia , Avaliação da Tecnologia Biomédica/métodos
12.
Nat Commun ; 8(1): 2037, 2017 12 11.
Artigo em Inglês | MEDLINE | ID: mdl-29229914

RESUMO

Double corundum-related polar magnets are promising materials for multiferroic and magnetoelectric applications in spintronics. However, their design and synthesis is a challenge, and magnetoelectric coupling has only been observed in Ni3TeO6 among the known double corundum compounds to date. Here we address the high-pressure synthesis of a new polar and antiferromagnetic corundum derivative Mn2MnWO6, which adopts the Ni3TeO6-type structure with low temperature first-order field-induced metamagnetic phase transitions (T N = 58 K) and high spontaneous polarization (~ 63.3 µC·cm-2). The magnetostriction-polarization coupling in Mn2MnWO6 is evidenced by second harmonic generation effect, and corroborated by magnetic-field-dependent pyroresponse behavior, which together with the magnetic-field-dependent polarization and dielectric measurements, qualitatively indicate magnetoelectric coupling. Piezoresponse force microscopy imaging and spectroscopy studies on Mn2MnWO6 show switchable polarization, which motivates further exploration on magnetoelectric effect in single crystal/thin film specimens.

14.
Inorg Chem ; 55(20): 10135-10142, 2016 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-27680715

RESUMO

A novel 6H-type hexagonal perovskite Ba3(Cr0.97(1)Te0.03(1))2TeO9 was prepared at high pressure (6 GPa) and temperature (1773 K). Both transmission electron microscopy and synchrotron powder X-ray diffraction data demonstrate that Ba3(Cr0.97(1)Te0.03(1))2TeO9 crystallizes in P63/mmc with face-shared (Cr0.97(1)Te0.03(1))O6 octahedral pairs interconnected with TeO6 octahedra via corner-sharing. Structure analysis shows a mixed Cr2+/Cr3+ valence state with ∼10% Cr2+. The existence of Cr2+ in Ba3(Cr2+0.10(1)Cr3+0.87(1)Te6+0.03)2TeO9 is further evidenced by X-ray absorption near-edge spectroscopy. Magnetic properties measurements show a paramagnetic response down to 4 K and a small glassy-state curvature at low temperature. In this work, the octahedral Cr2+O6 component is stabilized in an oxide material for the first time; the expected Jahn-Teller distortion of high-spin (d4) Cr2+ is not found, which is attributed to the small proportion of Cr2+ (∼10%) and the face-sharing arrangement of CrO6 octahedral pairs, which structurally disfavor axial distortion.

15.
Inorg Chem ; 55(20): 10229-10237, 2016 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-27676324

RESUMO

New layered honeycomb tellurates, BiM(III)TeO6 (M = Cr, Mn, Fe) were synthesized and characterized. BiM(III)TeO6 (M = Cr, Fe) species crystallize in a trigonal space group, P3̅1c (No. 163), of edge-sharing M3+/Te6+O6 octahedra, which form honeycomb-like double layers in the ab plane with Bi3+ cations located between the layers. Interestingly, the structure of BiMnTeO6 is similar to those of the Cr/Fe analogues, but with monoclinic space group, P21/c (No. 14), attributed to the strong Jahn-Teller distortion of Mn3+ cations. The crystal structure of BiM(III)TeO6 is a superstructure of PbSb2O6-related materials (ABB'O6). The Cr3+ and Fe3+ cations are ordered 80% and 90%, respectively, while the Mn3+ ions are completely ordered on the B-site of the ABB'O6 structure. BiCrTeO6 shows a broad antiferromagnetic transition (AFM) at ∼17 K with a Weiss temperature (θ) of -59.85 K, while BiFeTeO6 and BiMnTeO6 show sharp AFM transitions at ∼11 K with θ of -27.56 K and at ∼9.5 K with θ of -17.57 K, respectively. These differences in the magnetic behavior are ascribed to the different concentration of magnetic nearest versus next-nearest neighbor interactions of magnetic cations due to the relative differences in the extent of M/Te ordering.

16.
Angew Chem Int Ed Engl ; 55(34): 9862-7, 2016 08 16.
Artigo em Inglês | MEDLINE | ID: mdl-27203790

RESUMO

Cationic rearrangement is a compelling strategy for producing desirable physical properties by atomic-scale manipulation. However, activating ionic diffusion typically requires high temperature, and in some cases also high pressure in bulk oxide materials. Herein, we present the cationic rearrangement in bulk Mn2 FeMoO6 at unparalleled low temperatures of 150-300 (o) C. The irreversible ionic motion at ambient pressure, as evidenced by real-time powder synchrotron X-ray and neutron diffraction, and second harmonic generation, leads to a transition from a Ni3 TeO6 -type to an ordered-ilmenite structure, and dramatic changes of the electrical and magnetic properties. This work demonstrates a remarkable cationic rearrangement, with corresponding large changes in the physical properties in a bulk oxide at unprecedented low temperatures.

17.
Inorg Chem ; 55(9): 4320-9, 2016 05 02.
Artigo em Inglês | MEDLINE | ID: mdl-27058393

RESUMO

Pb2MnTeO6, a new double perovskite, was synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction. Pb2MnTeO6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to ∼120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s(2) lone-pair electrons, together with a surprising off-centering of Mn(2+) (d(5)) magnetic cations. This strong first-order phase transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below TN ≈ 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near ∼150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb2MnTeO6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb2MnTeO6.

18.
Inorg Chem ; 55(7): 3515-29, 2016 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-27002487

RESUMO

The crystal structures of NiX2(pyz)2 (X = Cl (1), Br (2), I (3), and NCS (4)) were determined by synchrotron X-ray powder diffraction. All four compounds consist of two-dimensional (2D) square arrays self-assembled from octahedral NiN4X2 units that are bridged by pyz ligands. The 2D layered motifs displayed by 1-4 are relevant to bifluoride-bridged [Ni(HF2)(pyz)2]EF6 (E = P, Sb), which also possess the same 2D layers. In contrast, terminal X ligands occupy axial positions in 1-4 and cause a staggered packing of adjacent layers. Long-range antiferromagnetic (AFM) order occurs below 1.5 (Cl), 1.9 (Br and NCS), and 2.5 K (I) as determined by heat capacity and muon-spin relaxation. The single-ion anisotropy and g factor of 2, 3, and 4 were measured by electron-spin resonance with no evidence for zero-field splitting (ZFS) being observed. The magnetism of 1-4 spans the spectrum from quasi-two-dimensional (2D) to three-dimensional (3D) antiferromagnetism. Nearly identical results and thermodynamic features were obtained for 2 and 4 as shown by pulsed-field magnetization, magnetic susceptibility, as well as their Néel temperatures. Magnetization curves for 2 and 4 calculated by quantum Monte Carlo simulation also show excellent agreement with the pulsed-field data. Compound 3 is characterized as a 3D AFM with the interlayer interaction (J⊥) being slightly stronger than the intralayer interaction along Ni-pyz-Ni segments (J(pyz)) within the two-dimensional [Ni(pyz)2](2+) square planes. Regardless of X, J(pyz) is similar for the four compounds and is roughly 1 K.

19.
Inorg Chem ; 55(7): 3384-92, 2016 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-27002597

RESUMO

The application of pressure in solid-state synthesis provides a route for the creation of new and exciting materials. However, the onerous nature of high-pressure techniques limits their utility in materials discovery. The systematic search for novel oxynitrides-semiconductors for photocatalytic overall water splitting-is a representative case where quench high-pressure synthesis is useful and necessary in order to obtain target compounds. We utilize state of the art crystal structure prediction theory (USPEX) and in situ synchrotron-based X-ray scattering to speed up the discovery and optimization of novel compounds using high-pressure synthesis. Using this approach, two novel oxynitride phases were discovered in the GaN-Nb2O5 system. The (Nb2O5)0.84:(NbO2)0.32:(GaN)0.82 rutile structured phase was formed at 1 GPa and 900 °C and gradually transformed to a α-PbO2-related structure above 2.8 GPa and 1000 °C. The low-pressure rutile type phase was found to have a direct optical band gap of 0.84 eV and an indirect gap of 0.51 eV.

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