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1.
Nano Lett ; 2020 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-32348146

RESUMO

Because of the toxicity of lead, searching for a lead-free halide perovskite semiconducting material with comparable optical and electronic properties is of great interest. Rare-earth-based halide perovskite represents a promising class of materials for this purpose. In this work, we demonstrate the solution-phase synthesis of single-crystalline CsEuCl3 nanocrystals with a uniform size distribution centered around 15 nm. The CsEuCl3 nanocrystals have photoluminescence emission centered at 435 nm, with a full width at half-maximum of 19 nm. Furthermore, CsEuCl3 nanocrystals can be embedded in a polymer matrix that provides enhanced stability under continuous laser irradiation. Lead-free rare-earth cesium europium halide perovskite nanocrystals represent a promising candidate to replace lead halide perovskites.

2.
ACS Appl Mater Interfaces ; 11(45): 42280-42287, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31682096

RESUMO

Glass and glass-ceramic samples of metastable lithium thiophosphates with compositions of 70Li2S-30P2S5 and Li7P3S11 were controllably prepared by using a rapid assisted-microwave procedure in under 30 min. The rapid preparation times and weak coupling of the evacuated silica ampules with microwave radiation ensure minimal reactivity of the reactants and the container. The microwave-prepared samples display comparable conductivity values with more conventionally prepared (melt quenched) glass and glass-ceramic samples, on the order of 0.1 and 1 mS cm-1 at room temperature, respectively. Rietveld analysis of synchrotron X-ray diffraction data acquired with an internal standard quantitatively yields phase amounts of the glassy and amorphous components, establishing the tunable nature of the microwave preparation. X-ray photoelectron spectroscopy and Raman spectroscopy confirm the composition and the appropriate ratios of isolated and corner-sharing tetrahedra in these semicrystalline systems. Solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy resolves the seven crystallographic Li sites in the crystalline compound into three main environments. The diffusion behavior of these Li environments as obtained from pulsed-field gradient NMR methods can be separated into one slow and one fast component. The rapid and tunable approach to the preparation of high quality "Li7P3S11" samples presented here coupled with detailed structural and compositional analysis opens the door to new and promising metastable solid electrolytes.

3.
ACS Appl Mater Interfaces ; 10(8): 7208-7213, 2018 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-29457889

RESUMO

Rapid preparation utilizing assisted microwave heating permits significantly shorter preparation times for magnetocaloric compounds in the (Mn,Fe)2(P,Si) family, specifically samples of (Mn,Fe)2-δP0.5Si0.5 with starting compositions of δ = 0, 0.06, and 0.12. To fully understand the effects of processing and composition changes on structure and properties, these materials are characterized using synchrotron powder diffraction, neutron powder diffraction, electron microprobe analysis (EMPA), X-ray fluorescence (XRF), and magnetic measurements. The diffraction analysis reveals that increasing δ results in decreasing amounts of the common Heusler (Mn,Fe)3Si secondary phase. EMPA shows (Mn,Fe)2(P,Si) in all three samples to be Mn and P rich, whereas XRF demonstrates that the bulk material is Mn rich yet P deficient. Increasing δ brings the Mn/Fe and P/Si ratios closer to their starting values. Measurements of magnetic properties show an increase in saturation magnetization and ordering temperature with increasing δ, consistent with the increase in Fe and Si contents. Increasing δ also results in a decrease in thermal hysteresis and an increase in magnetic entropy change, the latter reaching values close to what have been previously reported on samples that take much longer to prepare.

4.
Chemistry ; 20(13): 3652-66, 2014 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-24615869

RESUMO

A series of 2,5-bis(arylethynyl)rhodacyclopentadienes has been prepared by a rare example of regiospecific reductive coupling of 1,4-(p-R-phenyl)-1,3-butadiynes (R=H, Me, OMe, SMe, NMe2, CF3, CO2Me, CN, NO2, -C≡C-(p-C6H4-NHex2), -C≡C-(p-C6H4-CO2Oct)) at [RhX(PMe3)4] (1) (X=-C≡C-SiMe3 (a), -C≡C-(p-C6H4-NMe2) (b), -C≡C-C≡C-(p-C6H4-NPh2) (c) or -C≡C-{p-C6H4-C≡C-(p-C6H4 -N(C6H13)2)} (d) or Me (e)), giving the 2,5-bis(arylethynyl) isomer exclusively. The rhodacyclopentadienes bearing a methyl ligand in the equatorial plane (compound 1 e) have been converted into their chloro analogues by reaction with HCl etherate. The rhodacycles thus obtained are stable to air and moisture in the solid state and the acceptor-substituted compounds are even stable to air and moisture in solution. The photophysical properties of the rhodacyclopentadienes are highly unusual in that they exhibit, exclusively, fluorescence between 500-800 nm from the S1 state, with quantum yields of Φ=0.01-0.18 and short lifetimes (τ=0.45-8.20 ns). The triplet state formation (Φ(ISC) =0.57 for 2 a) is exceptionally slow, occurring on the nanosecond timescale. This is unexpected, because the Rh atom should normally facilitate intersystem crossing within femto- to picoseconds, leading to phosphorescence from the T1 state. This work therefore highlights that in some transition-metal complexes, the heavy atom can play a more subtle role in controlling the photophysical behavior than is commonly appreciated.

5.
Chemistry ; 17(42): 11828-37, 2011 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-21901774

RESUMO

A stable trans-(alkyl)(boryl) platinum complex trans-[Pt(BCat')Me(PCy(3))(2)] (Cat'=Cat-4-tBu; Cy=cyclohexyl=C(6)H(11)) was synthesised by salt metathesis reaction of trans-[Pt(BCat')Br(PCy(3))(2)] with LiMe and was fully characterised. Investigation of the reactivity of the title compound showed complete reductive elimination of Cat'BMe at 80 °C within four weeks. This process may be accelerated by the addition of a variety of alkynes, thereby leading to the formation of the corresponding η(2) -alkyne platinum complexes, of which [Pt(η(2)-MeCCMe)(PCy(3))(2)] was characterised by X-ray crystallography. Conversion of the trans-configured title compound to a cis derivative remained unsuccessful due to an instantaneous reductive elimination process during the reaction with chelating phosphines. Treatment of trans-[Pt(BCat')Me(PCy(3))(2)] with Cat(2)B(2) led to the formation of CatBMe and Cat'BMe. In the course of further investigations into this reaction, indications for two indistinguishable reaction mechanisms were found: 1) associative formation of a six-coordinate platinum centre prior to reductive elimination and 2) σ-bond metathesis of B-B and C-Pt bonds. Mechanism 1 provides a straightforward explanation for the formation of both methylboranes. Scrambling of diboranes(4) Cat(2)B(2) and Cat'(2)B(2) in the presence of [Pt(PCy(3))(2)], fully reductive elimination of CatBMe or Cat'BMe from trans-[Pt(BCat')Me(PCy(3))(2)] in the presence of sub-stoichiometric amounts of Cat(2)B(2), and evidence for the reversibility of the oxidative addition of Cat(2)B(2) to [Pt(PCy(3))(2)] all support mechanism 2, which consists of sequential equilibria reactions. Furthermore, the solid-state molecular structure of cis-[Pt(BCat)(2)(PCy(3))(2)] and cis-[Pt(BCat')(2)(PCy(3))(2)] were investigated. The remarkably short B-B separations in both bis(boryl) complexes suggest that the two boryl ligands in each case are more loosely bound to the Pt(II) centre than in related bis(boryl) species.

7.
Chemistry ; 15(29): 7150-5, 2009 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-19544503

RESUMO

Herein we report for the first time full details on the synthesis and structural characterization of novel homodinuclear bridging cobalt and nickel borylene complexes containing bridging carbonyl ligands, an unusual coordination motif rarely before observed for homodinuclear borylene complexes. Furthermore, the homodinuclear nickel complex represents the first instance of a nickel borylene complex. Quantum chemical analyses of charge-density topology, electron localization function (ELF) and natural charges indicate the absence of direct metal-metal bonds in both the cobalt and nickel systems, in contradiction with electron counting. The topology of the Laplacian of the electron density and of the ELF around the bridging boron atom is consistent with a bis-metallo-substituted borane situation for the dicobalt system, but with a three-center-bonding borylene for the dinickel complex.

8.
Chemistry ; 15(2): 469-73, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19035616

RESUMO

Herein we report on the synthesis and structural characterization of a representative range of novel heterodinuclear bridging rhodium and iridium borylene complexes. The iridium borylene complexes feature an unusual coordination mode of the borylene ligand. Furthermore, the first instance of a heterodinuclear-bridged borylene compound containing a chromium atom in the three-membered ring is reported.

10.
J Am Chem Soc ; 130(25): 7974-83, 2008 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-18510321

RESUMO

A range of new iminoborylcomplexes of the type [L(n)M-B[triple bond]N-R], which are isoelectronic with sigma-alkynyl complexes [L(n)M-C[triple bond]C-R], was obtained by systematically varying the metal M, the coligands L, and the nitrogen bound substituent R. Selected examples include, for example, trans-[(Cy3P)2(Br)Pt(B[triple bond]N iBu)], which is characterized by a sterically less demanding N-R group or the unprecedented rhodium species cis,mer-[(Br)2(Me3P)3Rh(B[triple bond]NSiMe3)]. All compounds were fully characterized in solution by multinuclear NMR spectroscopy and, where appropriate, in the solid state by X-ray crystallography. Subsequent reactivity studies revealed that particularly the combination of smaller N-R groups with Pt-B linkages of increased stability opens up opportunities for novel reactivity patterns of this class of compounds. Within the scope of these study, we inter alia succeeded in synthesizing the unusual bridged boryl species 1,4-trans-[{(Cy3P)2(Br)Pt(B{NH iBu}NH)}2C6H4] and a complex bearing both an acetylide ligand and an iminoboryl ligand, respectively.

18.
Inorg Chem ; 45(14): 5275-7, 2006 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-16813387

RESUMO

In the present paper, we describe the first structural characterization of cymantrenyl(dihalo)borane and report on its use for the synthesis of novel cymantrenylboryl complexes.

20.
Chemistry ; 12(4): 1266-73, 2006 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-16281318

RESUMO

Reaction of [(eta5-C5H4Li)(eta7-C7H6Li)Cr]tmeda with a variety of dialkyl(dichloro)silanes in aliphatic solvents afforded the corresponding [1]silatrochrocenophanes. Structural characterization by X-ray diffraction analysis of the [1]silatrochrocenophanes bearing Me2Si, (iPr)2Si, and silacyclobutane bridges revealed tilt angles alpha of 15.56(12) degrees , 15.8(1) degrees , and 16.33(17) degrees , respectively. Analogously, a [2]silatrochrocenophane (6) was prepared in excellent yield by reaction of [(eta5-C5H4Li)(eta7-C7H6Li)Cr]tmeda with 1,2-dichloro-1,1,2,2-tetramethyldisilane. This complex also was characterized structurally and exhibited a tilt angle alpha of 2.60(15) degrees. The [1]silatrochrocenophane bearing the Me2Si bridge underwent facile and regioselective carbon-silicon bond cleavage with [Pt(PEt3)4] to give a very high yield of an oxidative addition product. The ring-opening polymerization of these novel [1]silatrochrocenophanes afforded ring-opened chromium-based polymers.

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