Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. V

Non-isothermal thermal studies of the dehydration of the double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues were carried out where M(I) = TI(I) and M(II) = Mg(II), Co(II), Ni(II), Cu(II) or Zn(II). Thermal parameters like activation energy, order of reaction, enthalpy change, etc. were evaluated from the analysis of TG, DTA and DTG curves. These thermal parameters were compared with those of other series, like NH₄(I), K(I), Rb(I) and Cs(I) studied earlier. On deuteration the nature of dehydration altered in the case of Tl₂Zn(SO₄)₂·6H₂O only. The thermal stability of the salt hyd discussed in relation to the salt hydrates of other series. The role of divalent cation on the thermal properties of dehydration of salt hydrates is also discussed. The order of reaction was always found unity. The values of ΔH were within ≈12–≈16 kcal mol^?1.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. III

Dehydration of double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O where M(I)Rb(I) and M(II)Mg(II), Mn(II), Co(II), Ni(II), Zn(II) and Cu(II) has been studied by derivatograph. Thermal parameters like activation energy, order of reaction, enthalpy change etc. for each step of dehydration have been evaluated from the analyses of TG, DTA and DTG curves and these parameters are compared with corresponding salt hydrates of the NH₄ and K(I) series. These double salt hydrates are deuterated and studied similarly. Activation energies for the first step of dehydration of these salt hydrates increase with the increase of second ionisation potential of the central metal except for Mg. The nature of dehydration changes in the cases of double salt hydrates of Mg(II) and Ni(II) on deuteration. The order of reaction for each case of dehydration has been found to be unity. The enthalpy change per mole of water varies from 11.4 to 17 kcal.     

Extraction-spectrophotometric determination of iron(III) by means of quinaldic acid-N-oxide

Summary A simple and sensitive method for the determination of iron(III) is described. It is based on the extraction of the yellow-coloured complex of iron with quinaldic acid-N-oxide in chloroform. The absorption maximum is at 380 nm with molar absorptivity ₃₈₀=1.03 · 10⁴. Beer's Law is obeyed over the range 0.6–6 ppm iron with relative standard deviation of +-0.3% (Sandell sensitivity 0.005 g/ml/cm²). The absorbance of the reagent blank is however high with consequent occasional disturbances, which are avoided when measured at 395 nm; molar absorptivity ₃₉₅=7.4 · 10³; effective concentration range 3–8 ppm iron with relative standard deviation +-0.5% (Sandell sensitivity 0.008g/ml/cm²). A fairly large number of common ions do not interfere. Job's method of continuous variations and Asmus method indicate a iron-reagent ratio of 13. Heterogeneous formation constant is K _D =2 · 10⁸.

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Extraktionsphotometrische Bestimmung von Eisen(III) mit Chinaldinsäure-N-oxid

Zusammenfassung Die einfache und empfindliche Bestimmung beruht auf der Extraktion des gelben Komplexes von Eisen(III) mit Chinaldinsäure-N-oxid in Chloroform. Das Absorptionsmaximum liegt bei 380 nm mit dem molaren Extinktionskoeffizient ₃₈₀=1.03 · 10⁴. Das Beersche Gesetz gilt im Bereich 0,6–6 ppm Eisen. Die relative Standardabweichung beträgt+-0,3% (Sandell-Empfindlichkeit 0,005g/ml/cm²). Die Absorption der Blindprobe ist jedoch hoch und verursacht manchmal Störungen, die beim Messen bei 395 nm vermieden werden; molarer Extinktionskoeffizient ₃₉₅= 7,4 · 10³; im Konzentrationsbereich 3–8 ppm Eisen beträgt die relative Standardabweichung+-0,5% (Sandell-Empfindlichkeit 0,008g/ml/cm²). Eine ziemlich große Zahl von Fremdionen bewirkt keine Störung. Methoden nach Job und Asmus liefern ein Verhältnis Eisen/Reagens wie 13. Die heterogene Bildungskonstante beträgt K _D =2 · 10⁸.

     

Mass spectrometry of metal compounds. Evidence of C?O cleavage in and effect of temperature on the mass spectra of chloropentacarbonylmanganese

The mass spectrum of Mn(CO)₅Cl has been studied at 70 eV and at varying inlet temperatures of 20–250°C. Like the heavier metal carbonyl derivatives, Mn(CO)₅Cl exhibits peaks due to carbido fragments. The spectrum run at 100°C shows the characteristic pattern of Mn₂(CO)₁₀ which originates from the formation and recombination of the Mn(CO)₅ radical. The spectral pattern changes further at an elevated temperature (250°C) showing the formation of Mn₂(CO)₈Cl₂. The effect of pyrolysis has been discussed.     

Dinuclear nickel(II) complexes with Schiff base ligands: syntheses, structures and bio-relevant catalytic activities

Three Ni(II) complexes of cresol-based Schiff-base ligands, namely [Ni₂(L¹)(NCS)₃(H₂O)₂], (1) [Ni₂(L²)(CH₃COO)(NCS)₂(H₂O)] (2) and [Ni₂(L³)(NCS)₃] (3), (where L¹ = 2,6-bis(N-ethylpyrrolidineiminomethyl)-4-methylphenolato, L² = 2,6-bis(N-ethylpiperidineiminomethyl)-4-methylphenolato and L³ = 2,6-bis{N-ethyl-N-(3-hydroxypropyl iminomethyl)}-4-methylphenolato), have been synthesized and structurally characterized by X-ray single-crystal diffraction in addition to routine physicochemical techniques. Density functional theory calculations have been performed to understand the nature of the electronic spectra of the complexes. Complexes 1?C3 when reacted with 4-nitrophenyl phosphate in 50:50 acetonitrile?Cwater medium promote the cleavage of the O?CP bond to form p-nitrophenol and smoothly convert 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) either in MeOH or in MeCN medium. Phosphatase- and catecholase-like activities were monitored by UV?Cvis spectrophotometry and the Michaelis?CMenten equation was applied to rationalize all the kinetic parameters. Upon treatment with urea, complexes 1 and 2 give rise to [Ni₂(L¹)(NCS)₂(NCO)(H₂O)₂] (1??) and [Ni₂(L²)(CH₃COO)(NCO)(NCS)(H₂O)] (2??) derivatives, respectively, whereas 3 remains unaltered under same reaction conditions.     

Communication: Universality of the melting curves for a wide range of interaction potentials

We demonstrate that the melting curves of various model systems of interacting particles collapse to (or are located very close to) a universal master curve on a plane of appropriately chosen scaled variables. The physics behind this universality is discussed. An equation for the emerging "universal melting curve" is proposed. The obtained results can be used to approximately predict melting of various substances in a wide range of conditions.     

N-Prolinylanthranilic acid derivatives as bifunctional organocatalysts for asymmetric aldol reactions

Several N-prolinylanthranilic acid derivatives were prepared and tested as bifunctional organocatalysts in the direct asymmetric aldol reaction of cyclohexanone with p-nitrobenzaldehyde. It was found that methyl substitution ortho to the carboxylic acid improves enantioselectivity, but substitution ortho to the anilide group does not. The catalyst derived from 2-amino-6-methylbenzoic acid was tested over a range of direct asymmetric aldol reactions and its overall performance is equal to or better than many of the known prolinamide catalysts in terms of yield, diastereoselectivity, and enantioselectivity.     

Application of an efficient multireference approach to free-base porphin and metalloporphyrins: ground, excited, and positive ion states

The improved virtual orbital-complete active space configuration interaction (IVO-CASCI) method is applied to determine the geometries of the ground state of free-base porphin and its metal derivatives, magnesium and zinc porphyrins. The vertical excitation energies and ionization potentials are computed at these optimized geometries using an IVO-based version of multireference Mo?ller-Plesset (IVO-MRMP) perturbation theory. The geometries and excitation energies obtained from the IVO-CASCI and IVO-MRMP methods agree well with experiment and with other correlated many-body methods. We also provide the ground state vibrational frequencies for free-base porphin and Mg-porphyrin. All frequencies are real in contrast to self-consistent field treatments which yield an imaginary frequency. Ground state normal mode frequencies (scaled) of free-base porphin and magnesium porphyrin from IVO-CASCI and complete active space self-consistent field methods are quite similar and are consistent with Becke-Slater-Hartree-Fock exchange and Lee-Yang-Parr correlation density functional theory calculations and with experiment. In addition, geometries are determined for low-lying excited state triplets and for positive ion states of the molecules. To our knowledge, no prior experimental and theoretical data are available for these excited state geometries of magnesium and zinc porphyrins. Given that the IVO-CASCI and IVO-MRMP computed geometries and excitation energies agree favorably with experiment and with available theoretical data, our predicted excited state geometries should be equally accurate.     

13 C NMR spectroscopy of substituted xanthones—II: 13C NMR spectral study of polyhydroxy xanthones

The ¹³C NMR chemical shifts of eleven hydroxy-, two hydroxymethoxy xanthones, and xanthone-C-glucoside, mangiferin, are presented and analyzed. Hydroxy substituent effects depending on substituent position as well as on shielded ring carbon position have been evaluated. Hydroxy substituent increments for xanthones are proposed. Effects of hydroxylation on carbonyl carbon shift and the methylation of hydroxy group and the corresponding shift increments which are of diagnostic value have been observed and discussed.     

Thermal investiongation of metal fluoberyllate hydrates and metal fluoride hydrates

The thermal decompositions of MBeF₄ · H₂O and MF₂ · x H₂O, where M = Ni(II), Co(II) or Cu(II) and x = 0–6, have been carried out using a MOM derivatograph. Dehydration takes place in multiple steps. Anhydrous fluoberyllates dissociate first to MF₂ and BeF₂ and then decompose to MO and BeO in two steps. Metal fluorides give ultimately oxyfluoride in one step. None of the intermediate hydrates is thermally stable, except CuF₂ · 2 H₂O. The probable mechanisms of thermal decomposition have been reported. Pyrolysed products are characterised by elemental analysis and X-ray powder patterns. The value of enthalpy change is reported for each decomposition step.