Here, we report our initial investigations into the coordination chemistry of symmetric diacylated thiourea ligands ((RCONH)2CS) (R = Me, Et or Ph) acting as both mono and dianionic ligands with platinum(II), palladium(II) and gold(III) metal centres. Initial investigations were centred on mixed ligand bis(triphenylphosphine) (PPh3) complexes which were prepared by reactions between cis-[PtCl2(PPh3)2] and (RCONH)2CS. A subsequent series of mixed ligand complexes from the diethyl-diacylthiourea ligand ((CH2CH2CONH)2CS) with [PtCl2(dppe)] (dppe = Ph2PCH2CH2PPh2), [PdCl2(phen)] (phen = 1,10-phenanthroline), [AuCl2(anp)] (anp = cyclometallated 2-anilinopyridyl) and [PtCl2(COD)] (COD = 1,5-cyclooctadiene) were also prepared. The complexes were characterized by a combination of common techniques (MS, NMR and SC-XRD) which determined that the ligands coordinated to the metal centres in an unexpected S,N bidentate chelate manner in all instances. The complexes showed a small degree of aqueous instability as a result of hydrolysis. Computational techniques (NCI, EDA and HS) were used to analyse complexes whose solid state structure was able to be determined crystallographically. The presence of a chalcogen bond between the thiourea sulfur and acyl oxygen atoms was revealed which dominates the molecular structure. The cyclometallated 2-anilinopyridyl gold(III) complex 1f demonstrates intermolecular dimerism in the solid state. Hirshfeld surface analysis was used to determine the percentage contribution of inherent intermolecular interactions to crystal packing and the specific contacts responsible for spatial orientations in 1a, 1b, and 1f.

AbstractThe syntheses of the tripodal tetraamine ligands 2‐(pyridin‐2‐yl)‐N,N‐bis(quinolin‐2‐ylmethyl)ethan‐1‐amine (DQPEA), N‐(pyridin‐2‐ylmethyl)‐2‐(quinolin‐2‐yl)‐N‐(2‐(quinolin‐2‐yl)ethyl)ethan‐1‐amine (DQEPMA), 2‐(pyridin‐2‐yl)‐N,N‐bis(2‐(quinolin‐2‐yl)ethyl)ethan‐1‐amine (DQEPEA), N,N‐bis(pyridin‐2‐ylmethyl)‐2‐(quinolin‐2‐yl)ethan‐1‐amine (QEDPMA), and 2‐(pyridin‐2‐yl)‐N‐(2‐(pyridin‐2‐yl)ethyl)‐N‐(2‐(quinolin‐2‐yl)ethyl)ethan‐1‐amine (QEDPEA) containing mixed quinolyl and pyridyl moieties are reported, with 2‐vinylquinoline being used to attach quinolylethyl arms to the aliphatic N atom. X‐ray crystal structures of [(Mn(DQPEA))2O2](ClO4)2 ⋅ (CH3CN)2, [Cu(DQPEA)NCCH3](ClO4)2, [Zn(DQPEA)NCCH3](ClO4)2, [Pd(DQEPEA)Cl]Cl ⋅ 11H2O are detailed, with four, five, and six‐coordination observed. In addition, the dimeric complex [(DPEA)Co(μ‐OH)3Co(DPEA)](ClO4)3 ⋅ 0.5H2O ⋅ MeCN containing the tridentate DPEA ligand formed by N‐dealkylation of QEDPEA is reported. Calculations suggest that the very short Co…Co distance of 2.5946(6) Å in this complex is unlikely to be due to a Co−Co bond.

Co(III) complexes of the N-heterocyclic carbene ligand PY4Im (PY4Im = (1,3-bis(bis(2-pyridyl)methyl)imidazol-2-ylidene)) having the general formula [(PY4Im)Co(X)](ClO4)(n) (X = NCMe; n = 3: OH-, N-3(-), NCS-, ONO-, F-; n = 2: O2CO2-, n = 1; (N-3(-))(3), n = 0) were prepared and structurally characterised. X-ray structural data are consistent with the presence of a trans influence due to the coordinated carbene carbon, and this is also supported by computational results. C-13 NMR spectra of the complexes did not display peaks corresponding to the carbene carbon, except in the case of the [(PY4Im)Co(O2CO)](+) cation, where a peak at delta = 170.21 ppm was observed. However, HMBC spectra allowed indirect determination of the chemical shifts of the carbene carbon in the remaining complexes, owing to the geometry of the PY4Im ligand. Calculated C-13 chemical shifts for the complexes showed very good agreement with the experimental values for all but the carbene carbon atoms in all cases.

In this work, a novel Orthosilicate-Orthophosphate structure phosphor K1-x(BaSr) (1+x)/2(SixP1-x)O4: Eu2+ (0 <= x <= 1) with superior quantum efficiency and excellent thermal stability was designed for the application of nextgeneration high-power white light-emitting diodes (WLEDs). The Rietveld refinement shows the isotopic cosubstitution of P5+ and K+ for Si4+ and Ba2+/Sr2+, generating a continuous change of centroid shift and crystal field splitting, further contributing to tuneable light from blue to green emission. Moreover, the excellent quantum efficiency stems from the widened bandgap and the defect-associated electron traps. Using experimental and density functional theory calculation, we confirm the potential mechanism of enhanced thermal stability, in which the co-substitution-induced crystal size mismatch brings the trapped electrons to move from defect levels to a higher energy state (conduction band) and then continue radiative transition. This work provides valuable insights into the design of other phosphors with enhanced thermal stability and quantum efficiency.

Typical Li6.75La3Zr1.75Ta0.25O12 exists as a mixture of tetragonal and cubic arrangements, but adding small amounts of Ga3+ (Li6.75-3xGaxLa3Zr1.75Ta0.25O12 x >= 0.1) resulted in a single cubic (I a-3d) phase lithium garnet oxide. Following the stabilisation of the cubic phase, the effects on lithium distributions were explored with neutron powder diffraction concerning Ga3+ content and temperature. Increasing the amount of Ga3+ reduced the amount of lithium within the structure, directly decreasing the Li 96h site occupancy and showing a minimal effect on the Li 24d site occupancy. High-temperature neutron diffraction studies revealed the migration of lithium from the Li 24d site to the Li 96h with increasing temperature. The inclusion of Ga3+ improved the total ionic conductivity over the gallium-free system. However, with increasing gallium content (x > 0.1), a negative correlation between the garnet's gallium content and total lithium ionic conductivity is observed, showing how the total amount of free lithium ions impact the system's total ionic conductivity. Though the electrolytes explored here show some limitations, the lithium-ion displacement trends with doping and temperature give us further insight into how these lithium garnet systems respond to chemical and physical change.

Typical Li6.75La3Zr1.75Ta0.25O12 exists as a mixture of tetragonal and cubic arrangements, but adding small amounts of Ga3+ (Li6.75–3xGaxLa3Zr1.75Ta0.25O12 x ≥ 0.1) resulted in a single cubic (I a-3d) phase lithium garnet oxide. Following the stabilisation of the cubic phase, the effects on lithium distributions were explored with neutron powder diffraction concerning Ga3+ content and temperature. Increasing the amount of Ga3+ reduced the amount of lithium within the structure, directly decreasing the Li 96h site occupancy and showing a minimal effect on the Li 24d site occupancy. High-temperature neutron diffraction studies revealed the migration of lithium from the Li 24d site to the Li 96h with increasing temperature. The inclusion of Ga3+ improved the total ionic conductivity over the gallium-free system. However, with increasing gallium content (x > 0.1), a negative correlation between the garnet's gallium content and total lithium ionic conductivity is observed, showing how the total amount of free lithium ions impact the system's total ionic conductivity. Though the electrolytes explored here show some limitations, the lithium-ion displacement trends with doping and temperature give us further insight into how these lithium garnet systems respond to chemical and physical change.

The discovery of phosphors with high quantum efficiency and high thermal stability is in high demand for facilitating the next generation high-power white light-emitting diodes (WLEDs). Herein, we report the design and synthesis of a high-performance blue-emitting K2Sr1.25Ba0.75(PO4)(2): Eu2+ phosphor with an excellent quantum efficiency (IQE = 96.4%) and high thermal stability (93%@200 C) via a defect engineering approach. The internal quantum efficiency was effectively enhanced through the symmetric stretching vibration of the crystal framework, preventing energy transfer loss from activator (Eu2+) to killer centers. Combining density functional theory (DFT) calculation and experimental investigation, we unravelled the intrinsic mechanism for the improvement of IQE thermal stability and proposed a model for the thermal stability enhancement. It is revealed that the induced size mismatch defects (Sr-Ba) stimulate the excited electrons to transfer from defect levels to the conduction band of the matrix. The results arising from this study demonstrate the effectiveness of the defect engineering approach for enhancing the overall performance of LED phosphors.

Lithium garnet oxides with 6.5 mol Li, such as Li6.5La3Zr15(Ta/Nb)(0.5)O-12, typically crystallise in cubic structure and exhibit excellent room-temperature ionic conductivity close to 1 mS cm(-1). However, it is challenging to densify garnet oxides. In this work, we investigated how the co-doping of tantalum (Ta) and niobium (Nb) affects the densification of pressureless sintered garnet electrolytes with compositions of Li6.5La3Zr1.5Ta(0.5-x)NbxO12, where x = 0-0.5. The highest densification (94.5% of relative density) was achieved in Li6.5La3Zr1.5Ta0.1Nb0.4O12 (TN-LLZO) when it was sintered at 1150 degrees C for 6 h. This TN-LLZO garnet electrolyte delivers an ionic conductivity of 1.04 x 10(-3) S cm(-1) (at 22 degrees C) with a low activation energy of 0.41 eV. Our findings demonstrate that the content of dopants (Ta and Nb) plays a critical role in enhancing the sintering performance of garnet ceramics at ambient pressure.

In this work, we co-doped barium (Ba) and zirconium (Zr) in a lithium garnet oxide, to improve its electrochemical properties. In the doping range of y = 0-1.0, the Li6+yLa3-yBayNbZrO12 (LLBNZO) oxides maintain a cubic crystal structure. A secondary phase of BaZrO3 emerges when y >= 0.75. The ionic conductivity of the developed garnet oxides first increases with Ba-doping in the low doping range and then decreases in the high doping range. It reaches the maximum value in Li6.5La2.5Ba0.5NbZrO12 when y = 0.5. Cyclic voltammetry shows that the garnet oxides have a wide electrochemical voltage window up to 6 V. The constant-current polarization results on the symmetric cells assembled from Li6.5La2.5Ba0.5NbZrO12 reveal that this garnet oxide is chemically stable against metallic lithium and has stable cycling performance. (C) 2021 Elsevier B.V. All rights reserved.

In this work, we investigated how the substitution of Nb in the well-established Li7La3Zr2O12 (LLZO) affects its structure and electrochemical performance. The Nb-doped solid-state electrolytes Li7-xLa3Zr2-xNbxO12 (x = 0, 0.25, 0.5, 0.75 and 1.0) were synthesized in zirconia crucibles instead of alumina, in order to eliminate the adverse influence of alumina. The stabilization of the cubic structure of the lithium garnet has been confirmed. The sintered density and ionic conductivity of the Nb-doped LLZO garnets (designated LLZNO) first increase until the Nb content reaches x = 0.5, beyond which these values decrease. We also found that exposing the synthesized garnets in humid air deteriorates ionic conductivity. The degrading mechanism relating to the exposure of the garnets is also discussed. In addition, the cycling stability of the LLZNO (x = 0.5) was assessed by cyclic voltammetry (CV) and charge/discharge cycling testing.

To enhance the ionic conductivity of lithium garnets, a co-doping strategy was adopted with both strontium and zirconium for [Formula: see text] ([Formula: see text], 0.25, 0.5, 0.75 and 1.0) (LLSNZO). By increasing the content of Sr, lithium garnet ceramics maintain cubic structure when [Formula: see text] is in the range of 0–0.75. A secondary phase of [Formula: see text] appeared in the ceramic when [Formula: see text]. We also studied the cross-section of lithium garnets with silver electrode. Results showed that the density of LLSNZO ceramics increased continuously against the increase of Sr content, while their total ionic conductivity enhanced initially and then reduced, with the maximum reached when [Formula: see text]. It is indicated that ionic conductivity of lithium garnets is not only decided by the density but also decided by the concentration and the mobility of [Formula: see text].

In this work, pressureless sintering (PLS) method was used to prepare Li7La3Zr2O12 based Al-free garnet electrolytes with the substitution of tantalum (Ta). A series of Ta-doped lithium garnets Li7-xLa3Zr2-xTaxO12 (LLZTO, x = 0, 0.25, 0.5, 0.75 and 1.0) were prepared, and the effect of Ta on the structure, densification and ionic conductivity was investigated. Both relative density and ionic conductivity of the LLZTO pellets are dependent on the content of Ta substitution, with the maximum values being reached at x = 0.5. We also studied the stability and degradation mechanism of lithium garnets (Li6.5La3Zr1.5Ta0.5O12) in humid air with relative humidity of above 70%. It is revealed that after exposure in the humid air for 4 weeks, a layer of LiOH center dot H2O was observed on the grain boundaries, which lowered its ionic conductivity considerably. In comparison, the pellet stored in a desiccator had clear surface with negligible change in the ionic conductivity.