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).     

Thermodynamics of solvation of some small peptides in water at T = 298.15 K

The enthalpies of solution in water, Δ_solH_m, of some small peptides, namely the amides of five N-acetyl substituted amino acids of glycine, l-alanine, l-proline, l-valine, l-leucine and two cyclic anhydrides of glycine and l-sarcosine (diketopiperazines), were measured by isothermal calorimetry at T = (296.84, 306.89, and 316.95) K. The enthalpies of solution at infinite dilution at T = 298.15 K were derived and added to the enthalpies of sublimation, ${\mathrm{\Delta }}_{\mathrm{sub}}{H}_{\mathrm{m}}^{\circ }$, at the same temperature, to obtain the corresponding solvation enthalpies at infinite dilution, ${\mathrm{\Delta }}_{\mathrm{solv}}{H}_{\mathrm{m}}^{\infty }$. Moreover, the partial molar heat capacities at infinite dilution at T = 298.15 K, $C_{p\text{,}2}^{\infty }$, were calculated by adding molar heat capacities of solid small peptides, C_p,m(cr), to the ${\mathrm{\Delta }}_{\mathrm{sol}}{C}_{p\text{,}\mathrm{m}}^{\infty }$ values obtained from our experimental data. CH₂ group contributions, in terms of solvation enthalpy and partial molar heat capacity, were −3.2 kJ · mol⁻¹ and 89.3 J · K⁻¹ · mol⁻¹, respectively, in good agreement with the literature data. Simple additive methods were used to estimate the average molar enthalpy of solvation and partial molar heat capacity at infinite dilution for the 1/2CONH⋯CONH functional group in the small peptides. Values obtained were −46.7 kJ · mol⁻¹ for solvation enthalpy and −42.4 J · K⁻¹ · mol⁻¹ for partial molar heat capacity, significantly lower than values obtained for the CONH functional group in monofunctional model compounds.     

Heat capacity and thermodynamic functions of nano-TiO2 rutile in relation to bulk-TiO2 rutile

Several conflicting reports have suggested that the thermodynamic properties of materials change with respect to particle size. To investigate this, we have measured the constant pressure heat capacities of three 7 nm TiO₂ rutile samples containing varying amounts of surface-adsorbed water using a combination of adiabatic and semi-adiabatic calorimetric methods. These samples have a high degree of chemical, phase, and size purity determined by rigorous characterization. Molar heat capacities were measured from T = (0.5 to 320) K, and data were fitted to a sum of theoretical functions in the low temperature (T < 15 K) range, orthogonal polynomials in the mid temperature range (10 > T/K > 75), and a combination of Debye and Einstein functions in the high temperature range (T > 35 K). These fits were used to generate $\mathit{Cp}\text{,}{\text{m}}^{\circ }$, ${\mathrm{\Delta }}_0^{\text{T}}{S}_{\text{m}}^{\circ }$, ${\mathrm{\Delta }}_0^{\text{T}}{H}_{\text{m}}^{\circ }$, and ${\phi }_{\text{m}}^{\circ }$ values at selected temperatures between (0.5 and 300) K for all samples. Standard molar entropies at T = 298.15 K were calculated to be (62.066, 59.422, and 58.035) J · K⁻¹ · mol⁻¹ all with a standard uncertainty of 0.002·${\mathrm{\Delta }}_0^{\text{T}}{S}_{\text{m}}^{\circ }$ for samples TiO₂·0.361H₂O, TiO₂·0.296H₂O, and TiO₂·0.244H₂O, respectively. These and other thermodynamic values were then corrected for water content to yield bare nano-TiO₂ thermodynamic properties at T = 298.15 K, and we show that the resultant thermodynamic properties of anhydrous TiO₂ rutile nanoparticles equal those of bulk TiO₂ rutile within experimental uncertainty. Thus we show quantitatively that the difference in thermodynamic properties between bulk and nano-TiO₂ must be attributed to surface adsorbed water.     

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).     

Volumetric and acoustic study of aqueous binary mixtures of quinine hydrochloride,guanidine hydrochloride and quinic acid at different temperatures

In the present communication, we report the fundamental thermodynamic properties like volumetric and compressibility of very important bioactive compounds, viz. quinine hydrochloride, guanidine hydrochloride and quinic acid (0.01 to 0.1) mol · kg⁻¹ in water at temperatures T = (278.15, 288.15 and 298.15) K. The experimental values of density (ρ) of aqueous solutions and speed of sound (u) in aqueous solutions of the above compounds within the concentration range (0.01 to 0.1) mol · kg⁻¹ have been obtained. The apparent molar volumes (V_ϕ), and apparent molar isentropic compressibilities (κ_ϕ) of quinine hydrochloride, guanidine hydrochloride and quinic acid in water have been computed at three different temperatures. Speed of sound values have also been used to calculate the hydration number (n_H) of the solute. The temperature dependence of the apparent molar volume has been used to calculate the thermal expansion coefficient (α¹), apparent molar expansivity $(E_{\varphi }^0)$ and Hepler’s constant $\left({\partial }^2{V}_{\varphi }^0/\partial T^2\right)$. The derived parameters have been used to interpret the results in terms of (solute + solute)/(ion + ion), (solute + solvent) interactions, structure making and structure breaking tendencies of solutes in water.     

Synthesis,structure, and thermodynamics of a lanthanide coordination compound incorporating 5-nitroisophthalic acid

A lanthanide coordination compound, [Sm₃(5-nip)₄(5-Hnip)(H₂O)₇·9H₂O]_n (5-H₂nip = 5-nitroisophthalic acid), has been synthesized and characterized by elemental analysis, IR, TG-DSC, and single-crystal X-ray diffraction. Structural analysis reveals that the compound features two kinds of 1D channels with guest water molecules. TG-DSC curves show that the dehydrated product of the compound exhibits high stability up to 673 K. The enthalpy change of reaction of formation in water, ${\mathrm{\Delta }}_{\text{r}}{H}_{\text{m}}^{\theta }$(l), was determined to be (27.608 ± 0.133) kJ · mol⁻¹ at (298.15 ± 0.01) K by microcalorimetry. Based on a designed thermochemical cycle and other auxiliary thermodynamic data, the enthalpy change of reaction of formation in solid at (298.15 ± 0.01) K and the standard molar enthalpy for the compound, ${\mathrm{\Delta }}_{\text{r}}{H}_{\text{m}}^{\theta }$(s) and ${\mathrm{\Delta }}_{\text{f}}{H}_{\text{m}}^{\theta }$, were calculated to be (96.8 ± 0.8) kJ · mol⁻¹ and (−831.4 ± 16.0) kJ · mol⁻¹, respectively. In addition, thermodynamics and thermokinetics of the reaction of formation of the compound were investigated in water.