CsCu2Sc3Te6 and CsCuY2Te4: Two new quaternary cesium copper rare-earth metal tellurides

The two new quaternary cesium copper(I) rare-earth metal(III) tellurides CsCu₂Sc₃Te₆ and CsCuY₂Te₄ were prepared at 900 °C by reacting the elements copper, scandium or yttrium and tellurium together with CsBr as flux and cesium source for fourteen days in evacuated torch-sealed silica ampoules. Both compounds crystallize in space group C2/m of the monoclinic system with unit cells of the dimensions a = 1777.63(9), b = 414.20(2), c = 1033.51(5) pm, β = 113.032(4)° for CsCu₂Sc₃Te₆ (Z = 2) and a = 3741.90(19), b = 432.73(2), c = 2087.62(11) pm, β = 107.357(4)° for CsCuY₂Te₄ (Z = 12). The crystal structure of the scandium compound contains [CuTe₄]^7? tetrahedra, which are cis-edge connected in order to build up $\underset{\mathrm{\infty }}{1}\left\{{\left[{\text{CuTe}}_{1/1}^t{\text{Te}}_{3/3}^e\right]}^{3?}\right\}$ chains, and [ScTe₆]^9? octahedra, which share edges and vertices in forming corrugated $\underset{\mathrm{\infty }}{2}\left\{{\left[{\text{Sc}}_3{\text{Te}}_6\right]}^{3?}\right\}$ layers. These layers are separated from each other by [CuTe₄]^7? tetrahedra and Cs⁺ cations in trans-face bicapped square-prismatic Te^2? coordination (CN = 10). The yttrium compound has a three-dimensional structure as well built up of [CuTe₄]^7? tetrahedra and [YTe₆]^9? octahedra. All three crystallographically independent Cu⁺ cations reside in an individual infinite $\underset{\mathrm{\infty }}{1}\left\{{\left[{\text{CuTe}}_{2/1}^t{\text{Te}}_{2/2}^v\right]}^{5?}\right\}$ chain, in which each [CuTe₄]^7? tetrahedron shares two vertices with neighbouring ones. The anionic framework $\underset{\mathrm{\infty }}{3}\left\{{\left[{\text{Y}}_2{\text{Te}}_4\right]}^{2^{?}}\right\}$ and the copper-bearing $\underset{\mathrm{\infty }}{3}\left\{{\left[{\text{CuY}}_2{\text{Te}}_4\right]}^{?}\right\}$ one consist of sixteen-membered ring channels containing three different types of Cs⁺ cations (two in each channel) with bicapped trigonal prismatic (CN = 8) and monocapped cubic Te^2? coordination (CN = 9). Thus there is no isotypy with the KCuGd₂S₄-type structure, characteristic for the lighter chalcogens (e. g. ACuM₂Ch₄; A = K–Cs, M = La–Er, Ch = S and Se).     

Photoreactivity of biologically active compounds. XIX: Excited states and free radicals from the antimalarial drug primaquine

The formation and reactivity of excited states and free radicals from primaquine, a drug used in the treatment of malaria, was studied in order to evaluate the primary photochemical reaction mechanisms. The excited primaquine triplet was not detected, but is likely to be formed with a short lifetime (<50 ns) and with a triplet energy <250 kJ/mol as the drug is an efficient quencher of the fenbufen triplet and the biphenyl triplet, and forms ${}^1{\text{O}}_2$ by laser flash photolysis $({}^{\text{PQ}}{\Phi }_{\mathrm{\Delta }}=0.025)$. Primaquine (PQ) exists as the monocation $({\text{PQH}}^{+})$ in aqueous solution at physiological pH. ${\text{PQH}}^{+}$ photoionises by a biphotonic process and also forms the monoprotonated cation radical $({\text{PQH}}^{2+\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}})$ by one electron oxidation by ${\text{HO}}^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$ (k_q = 6.6 × 10⁹ M^?1 s^?1) and ${\text{Br}}_2^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ (k_q = 4.7 × 10⁹ M^?1 s^?1) at physiological pH, detected as a long-lived transient decaying essentially by a second order process (k₂ = 7.4 × 10⁸ M^?1 s^?1). ${\text{PQH}}^{2+\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$ is scavenged by O₂, although at a limited rate (k_q = 1.0 × 10⁶ M^?1 s^?1). The reduction potential (E°) of ${\text{PQH}}^{2+\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}/{\text{PQH}}^{+}$ is < +1015 mV, as measured versus tryptophan (${\text{TRP}}^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}/\text{TRPH}$). Primaquine also forms ${\text{PQH}}^{2+\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$ at pH 2.4, by one electron oxidation by ${\text{Br}}_2^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ and proton loss (k_q = 2.7 × 10⁹ M^?1 s^?1). The non-protonated cation radical (${\text{PQ}}^{+\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$) is formed during one electron oxidation with ${\text{Br}}_2^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ at alkaline conditions (k_q = 4.2 × 10⁹ M^?1 s^?1 at pH 10.8). The estimated pK_a-value of ${\text{PQH}}^{2+\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}/{\text{PQ}}^{+\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$ is pK_a ～ 7–8. Primaquine is not a scavenger of ${\text{O}}_2^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ at physiological pH. Thus self-sensitization by ${\text{O}}_2^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ is eliminated as a degradation pathway in the photochemical reactions. Impurities in the raw material and photochemical degradation products initiate photosensitized degradation of primaquine in deuterium oxide, prevented by addition of the ${}^1{\text{O}}_2$ quencher sodium azide. Photosensitized degradation by formation of ${}^1{\text{O}}_2$ is thus important for the initial photochemical decomposition of primaquine, which also proceeds by free radical reactions. Formation of ${\text{PQH}}^{2+\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$ is expected to play an essential part in the photochemical degradation process in a neutral, aqueous medium.     

Synthesis and reactivity of (μ-η2:η2-peroxo)dicopper(II) complexes with dinucleating ligands: Hydroxylation of xylyl linker with a NIH shift

New hexadentate dinucleating ligands having a xylyl linker, X–L–R, were synthesized, where X–L–R = 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl]-2,4,6-trimethybenzene (Me₂–L–Me) and 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl]-2-fluorobenzene (H–L–F). They form dinuclear copper(I) complexes, [Cu₂(X–L–R)]²⁺ (Me₂–L–Me (1) and H–L–F (2)). The copper(I) complexes in acetone at −78 °C react with O₂ to produce intra- and intermolecular (μ-η²:η²-peroxo)dicopper(II) species depending on the concentrations of the complexes:  both complexes generate intramolecular (μ-η²:η²-peroxo)dicopper(II) species [Cu₂(O₂)(X–L–R)]²⁺ (1-O₂ and 2-O₂) at the concentrations below ∼5 mM, whereas at ∼60 mM, both complexes produce intermolecular (μ-η²:η²-peroxo)dicopper(II) species, which were confirmed by the electronic and resonance Raman spectroscopies.  The electronic spectrum of 1-O₂ in acetone at concentrations below ∼5 mM showed an absorption band at (λ_max = 442 nm, ε = 5600 M⁻¹ cm⁻¹) assignable to the ${\mathrm{\pi }}_{\sigma }^1$(O–O)-to-Cu(II) ($({\text{d}}_{x^2-y^2}+{\text{d}}_{x^2-y^2})$ component) LMCT transition in addition to an intense band attributable to the ${\mathrm{\pi }}_{\sigma }^1$(O–O)-to-Cu(II) ($({\text{d}}_{x^2-y^2}-{\text{d}}_{x^2-y^2})$ component) LMCT transition (λ_max = 359 nm, ε = 21000 M⁻¹ cm⁻¹), indicating that the (μ-η²:η²-peroxo)Cu(II)₂ core of 1-O₂ takes a butterfly structure. Decomposition of 1-O₂ resulted in hydroxylation of the 2-position of the xylyl linker with 1,2-methyl migration (NIH shift), suggesting that the hydroxylation reaction proceeds via a cationic intermediate as proposed for closely related (μ-η²:η²-peroxo)Cu(II)₂ complexes having a xylyl linker. Kinetic study of the decomposition (hydroxylation of the xylyl linker) of 1-O₂ suggests that a stereochemical effect of the methyl group in the 2-position of the xylyl linker has a significant influence on a transition state for decomposition (hydroxylation of the xylyl linker).     

Thermodynamic evaluation and optimization of the (Na2CO3 + Na2SO4 + Na2S + K2CO3 + K2SO4 + K2S) system

A critical evaluation of all phase diagram and thermodynamic data were performed for the solid and liquid phases of the (Na₂CO₃ + Na₂SO₄ + Na₂S + K₂CO₃ + K₂SO₄ + K₂S) system and optimized model parameters were obtained. The Modified Quasichemical Model in the Quadruplet Approximation was used for modelling the liquid phase. The model evaluates first- and second-nearest-neighbour short-range ordering, where the cations (Na⁺ and K⁺) are assumed to mix on a cationic sublattice, while anions $({\text{CO}}_3^{2-}\text{,}{\text{SO}}_4^{2-}\text{,}\text{and}{\text{S}}^{2-})$ are assumed to mix on an anionic sublattice. The Compound Energy Formalism was used for modelling the solid solutions of (Na, K)₂(CO₃, SO₄, S). The models can be used to predict the thermodynamic properties and phase equilibria in multicomponent heterogeneous systems. The experimental data from the literature were reproduced within experimental error limits.     

Phase relations in the system (chromium + rhodium + oxygen) and thermodynamic properties of CrRhO3

Phase relations in the system (chromium + rhodium + oxygen) at T = 1273 K have been determined by examination of equilibrated samples by optical and scanning electron microscopy, powder X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Only one ternary oxide, CrRhO₃ with rhombohedral structure ($R\overline{3}$, a = 0.5031, and c = 1.3767 nm) has been identified. Alloys and the intermetallics along the (chromium + rhodium) binary were in equilibrium with Cr₂O₃. The thermodynamic properties of the CrRhO₃ have been determined in the temperature range (900 to 1300) K by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the electrolyte. For the reaction,$\begin{array}{cc}\hfill & 1/2{\text{Cr}}_2{\text{O}}_3(\text{solid})+1/2{\text{Rh}}_2{\text{O}}_3(\text{solid})\to {\text{CrRhO}}_3(\text{solid})\text{,}\hfill \\ \hfill & \mathrm{\Delta }{G}^{°}\pm 140/(\text{J}·{\text{mol}}^{-1})=-31967+5.418(T/\text{K})\text{,}\hfill \end{array}$where Cr₂O₃ has the corundum structure and Rh₂O₃ has the orthorhombic structure. Thermodynamic properties of CrRhO₃ at T = 298.15 K have been evaluated. The compound decomposes on heating to a mixture of Cr₂O₃-rich sesquioxide solid solution, Rh, and O₂. The calculated decomposition temperatures are T = 1567 ± 5 K in pure O₂ and T = 1470 ± 5 K in air at a total pressure p^° = 0.1 MPa. The temperature-composition phase diagrams for the system (chromium + rhodium + oxygen) at different partial pressures of oxygen and an oxygen potential diagram at T = 1273 K are calculated from the thermodynamic information.