Proper determination of order of reactions by thermal analysis

The relationship 1– _m=1.062n ^1/1–n , well-known in non-isothermal kinetics and applied for determination of the kinetic exponentn, is not universal. A more accurate modification of the given equation is proposed in the form of a more complex function 1– _m=(n, X_m), whereX _m =E/RT _m is the dimensionless Arrhenius' criterion.     

Force constant calculations of the LAM-1 modes ofn-alkanes and their substituted α-Monohalo- and α,ω-dihalo- species in their extended zig-zag planar configurations as found in urea inclusion compounds

Force constants were determined for the C₈, C₁₀, C₁₂ and C₁₄ series ofn-alkanes C _n H_{2n + 2} using an approximate SVFF calculation and observed LAM = 1 wave numbers. In this calculation the hydrogen atoms were neglected and only the carbon backbone chain and terminal atoms were considered; this was valid since only low-frequency vibrations were under consideration. Using force constant transfer, the wavenumbers of the LAM = 1 accordion modes for the analogous -C_n H_2n + 1 X and ,-C_n H_2nX₂ species, where X = C1, Br or I were calculated. For -chloroalkanes and ,-dichloroalkanes, them = 1 accordion modes are calculated to be in the 220–130 cm^–1 and 200–120 cm^–1 regions, respectively. For the bromo- and iodo-analogues them = 1 accordion modes are calculated to be in the 200–100 cm^–1, 150–90 cm^–1 and in the 170–100, 135–80 cm^–1 regions, respectively.     

Theoretical calculations of95Mo-NMR chemical shifts for compounds [MoO4−n S n ]2−

Summary Theoretical calculation of⁹⁵Mo-NMR chemical shifts for [MoO_4–n S _n ]^2– (n=0–4) compounds is reported here for the first time on the basis of Fenske-Hall method and Sum-Over-State (SOS) perturbation theory. A systematic decrease in shielding of⁹⁵Mo nuclei with increase of number of sulfur in [MoO_4–n S _n ]^2–, which is observed experimentally, can be reasonably explained by our calculation. A good linear relationship between chemical shifts of calculation and experiment is obtained. The electronic structure and bonding in these compounds are also discussed.Supported by Nature Science Foundation of China     

Theoretical investigation of the weakly dihydrogen bonded dimers H2 − nXnAlHHArF and H2 − nXnAlHHKrF (n = 0–2; X = F, Cl)

An ab initio computational study of the properties of the dihydrogen-bonded complexes of H_{2 − n}X_nAlH (n = 0–2; X = F, Cl) with the rare gas (Rg) compounds HArF and HKrF was carried out at the MP2(full)/6-311++G(2d,2p) level of theory. For all the studied complexes, we found a low zero-point corrected binding energies. Large red shifts of the H–Rg vibrational stretching frequency in both complexes were predicted. Electrostatic interactions between the individual monomers are also predicted.     

Electron transfer in the photochemical reactions of phenothiazine with halomethanes

Photochemical transformations of phenothiazine (PTA) in solutions of halomethanes CH_nX_4–n (X = Cl, Br; n = 0, 1, 2) and in n-hexane—CH_nX_4–n mixtures under the irradiation with = 337 and 365 nm were studied. The rate constants of quenching of PTA fluorescence with halomethanes (k _q) are 4·10⁵—1.3·10¹⁰ L mol^–1 s^–1. The process occurs due to electron transfer with the C—X bond cleavage in the radical anion fragment of the primary radical ion pair. This results in the formation of the stable radical cation salt (PTA^·+X^–). The plot of k _q vs. free energy of electron transfer corresponds to the Rehm—Weller empirical equation for a one-electron process and is satisfactorily described in terms of the theory of nonradiative electron transitions in the approximation of one quantum vibration.     

Chemische Effekte des isomeren Überganges von Brom-80m in Pentamminkobalt(III)-und Bisäthylendiaminkobalt(III)-bromiden

Zusammenfassung Die chemischen Effekte des isomeren Überganges von^80mBr wurden bei Temperaturen von–78° C und–196° C an mit^80mBr markierten Proben von [Co(NH₃)₅ X]Br_3.2 nH₂O und [Co(en)₂ X _2']Br_3.1 nH₂O untersucht (X=NH₃, NCS, NO₂, OH₂, ONO, ONO₂, F, Cl, Br, I, undX'=en, NH₃, NCS, Cl, Br). Es zeigte sich, daß die Ligandenausbeute an⁸⁰Br, in den Komplexen mit abnehmender Frequenz des Maximums in der ersten Absorptionsbande des [Co(NH₃)₅ X] und des [Co(en)₂ X _2'] zunimmt. Mit anderen Worten, weniger stabile, Liganden werden leichter von Radiobrom ersetzt als Folge des isomeren Überganges in festen Komplexen.

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Chemical effects of the isomeric transition of^80mBr in pentammincobalt(III) and bisethylenediaminecobalt(III) bromides

The chemical effects of the isomeric transition of^80mBr were investigated at temperatures of–78° C and–196° C with^80mBr-labeled samples of [Co(NH₃)₅ X]Br_3.2 nH₂O and [Co(en)₂ X _2']Br_3.1 nH₂O (X=NH₃, NCS, NO₂, OH₂, ONO, ONO₂, F, Cl, Br, I, andX'=en, NH₃, NCS, Cl, Br). The ligand yield of⁸⁰Br in the complexes was found to increase with the decrease in the frequency of the maximum in the first absorption band of [Co(NH₃)₅ X] and [Co(en)₂ X _2']. In other words, less stable ligands were more easily replaced by radiobromine as a consequence of isomeric transition in solid complexes.

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Mit 1 Abbildung

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Herrn Prof. Dr.E. Broda zum 60. Geburtstag gewidmet.     

Wave-function operator calculations of the complete configuration interaction in π-systems

A simple method has been developed for the carrying out of complete configuration interaction calculations. The n-electron operator (wave-function operator) is compared with the wave-function of a 2n-electron system. An equation was obtained for this operator, which is equivalent to the complete configuration interaction (CCI). An algorithm of the calculation is described for the case of partial consideration of the transpositional symmetry of the wave-function operator. Examples are given for -calculations of the CCI for polyenes and quinoid and benzenoid hydrocarbons (up to eight sites). A method is proposed for evaluating the correlation energy in large systems without CCI using dispersion of the Hartree-Fock energy.Kharkov State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 3–11, September–October, 1990.     

Spectra and structure of small ring compounds. LIX

The Raman (3200 to 10 cm^–1) and far infrared (380 to 60 cm^–1) spectra of gaseous fluorocyclobutane,c-C₄H₇F, have been recorded. A series of Q-branches observed in both of these spectra beginning at 166 cm^–1 with successive transitions falling to lower frequencies have been assigned to the ring puckering vibrations of both the low energy equatorial and high energy axial conformers. These data have been fit to an asymmetric potential function of the form:V (cm^–1)=(1.76±0.05)10³X+(4.88±0.28)10⁴X²+(2.12 ±0.16)10³ exp(–5.66±0.41)10X² with a reduced mass function ofg ₄₄= 0.00386–0.00295X+0.03485X²+0.1228X³ +0.3459X⁴, whereX is the ring puckering coordinate. Utilizing this potential, the difference between the puckering angles for the two conformers was calculated to be 4° with the equatorial conformer having the larger value of 28°. This potential function is consistent with an energy difference between the equatorial and axial forms of 447 cm^–1 (1.28 kcal/mol) and a barrier to ring inversion from the equatorial to the axial conformation of 713 cm^–1 (2.04 kcal/mol). Experimental values for the enthalpy difference between the two conformers have been determined for both the liquid (400±30 c^–1) and gas (413±43 cm^–1) from investigations of the Raman spectra at variable temperatures. The conformational stability, enthalpy difference, structural parameters, and fundamental vibrational frequencies, which have been determined experimentally, are compared to those obtained from ab initio Hartree-Fock calculations employing the 3-21G, 6-31 G^*, and 6-31 G^** basis sets.For part LVIII, seeStruct. Chem. 1991,2, 195.Taken in part from the thesis of M. J. Lee, which has been submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree, May 1991.     

Predicting Excess Enthalpies of Ether and/or Hydrocarbon Binary Mixtures

Previous applications of the Flory–Patterson theory in the analysis of the excess molar enthalpies at 25°C for some binary mixtures composed of ethers, n-alkanes, br-alknes, and cycloalkanes are reviewed. The possibility of correlating the Flory interaction parameters X _ij in terms of the acentric factors of the components is examined. For selected ether (1) + n-alkane(2) mixtures, a set of linear relations between X ₁₂ and the acentric factors of the n-alkanes are reported.Visiting Professor on sabbatical leave from the     

Electronic spectra of the linear magnesium-containing carbon chains MgC2nH (n = 1–5): A CASPT2 study

Complete active space self-consistent-field (CASSCF) approach has been used for the geometry optimization of the X²Σ⁺ and A²Π electronic states for the linear magnesium-containing carbon chains MgC_2nH (n = 1–5). Multireference second-order perturbation theory (CASPT2) has been used to calculate the vertical excitation energies from the ground to selected seven excited states, as well as the potential energy curves of two ²Σ⁺ and two ²Π electronic states. The studies indicate that the vertical excitation energies of the A²Π ← X²Σ⁺ transition for MgC_2nH (n = 1–5) are 2.837, 2.793, 2.767, 2.714, and 2.669 eV, respectively, showing remarkable linear size dependence. Compared with the previous TD-DFT and RCCSD(T) results, our estimates for MgC_2nH (n = 1–3) are in the best agreement with the available observed data of 2.83, 2.78, and 2.74 eV, respectively. In addition, the dissociation energies in MgC_2nH (n = 1–5) are also been evaluated.     

Does the valence state index reflect the stability of neutral boron subhalide clusters?

The numbers of valence structures (NVS) and the valence state indexes (VSI) have been determined for a series of 2n framework electron clustersviz. polyhedral boron subhalides B _n X _n (n=6–12) and compared with those obtained for the parent B _n H _n ^2– dianions. The VSI does not reflect the experimental stabilities.     

Generating functions for the cage isomers of the C20n icosahedral fullerenes

The number of isomeric cages for the C_20n icosahedral fullerenes (Goldberg polyhedra), is given by the coefficient ofn ^–s in the expansion of the Dirichlet generating function (s)L[s, x(3)].When this coefficient is even, the cages occur as chiral pairs of point symmetry I; when odd, there is one structural isomer of point symmetry I _h , and the other isomers, if any, occur as chiral pairs. Asymptotic estimates are given for the number of isomers of each type.     

207Pb-NMR-Untersuchungen an Bleiorganylen

The high-resolution²⁰⁷Pb magnetic resonance spectra ofR _4–n PbX _n (R=Methyl, Ethyl;X=h₁-Cyclopentadienyl, Chloride;n=1, 2) have been studied at 16.72Mc. The²⁰⁷Pb- ·· -¹H spin-spin coupling constants for the molecules described have been obtained by analysis of the first order NMR-patterns as A_xB_yM and A_xB_yC_zM respectively. The experimental spectra have been verified by a computer simulation. The chemical shifts and coupling constants of the lead organyls investigated show similar dependences on moleculare structure as well as number and species of the substituents like analogous organotin compounds.

     

The preparation and characterisation of chromium(III) complexes of C-meso-5, 12-dimethyl-1, 4, 8, 11-tetraazacyclotetradecane (LM). Aquation and base hydrolysis kinetics ofcis- andtrans-[CrLMCl2]+

Summary The reaction of [CrCl₃(DMF)₃] with C-meso-5, 12-dimethyl-1, 4, 8, 11-tetra-azacyclotetradecane(L_M) in DMF gives a mixture ofcis-[CrL_MCl₂]Cl (ca. 90%) andtrans-[CrL_MCl₂]Cl (ca. 10%). These complexes are readily separated, as thecis-isomer is insoluble in warm methanol while thetrans-isomer is soluble. Using the dichlorocomplexes as precursors it has been possible to prepare a range ofcis-[CrL_MX₂]⁺ complexes (X=Br^–, NO ₃ ^– , N ₃ ^– , NCS^– and X₂=bidentate oxalate) and alsotrans-[CrL_MX₂]⁺ complexes (X=Br^–, H₂O or NCS^–). The spectroscopic properties and detailed stereochemistry of the complexes are discussed.The aquation and base hydrolysis kinetics ofcis- andtrans-[CrL_MCl₂]⁺ have been studied at 25° C. Base hydrolysis of thecis-complex is extremely rapid with K_OH =1.46×10⁵ dm³ mol^–1 at 25° C. This unusual reactivity appears to be associated with thetrans II stereochemistry of thesec-NH centres of the macrocycle. Base hydrolysis of thetrans complex with thetrans III chiral nitrogen stereochemistry is quite normal with k_OH =1.1 dm³ mol^–1 s^–1 at 25° C.     

Die Schwingungsspektren einiger Pentadeuterophenylphosphorverbindungen

The vibrational spectra of C₆D₅PX ₂, (C₆D₅)₂PX (X=H, Cl), (C₆D₅)₃P and of the Cyclophosphanes (PC₆H₅) _n and (PC₆D₅) _n (n=5, 6) are reported. The spectra of the phenylphosphorouscompound D (the structure beeing unknown) are given too. The C₆H₅/C₆D₅ isotopic shift data in the lower frequency-region (600–100 cm^–1) (facilitating the recognition of vibrational coupling effects) are used for vibrational assignments.

     

The OsX n Coordination Polyhedra (X = O,S, Se,Te) in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform a crystal-chemical analysis of compounds whose structures contain Os atoms surrounded by chalcogen atoms. Depending on the valence state, Os atoms bind four to seven X atoms (X = O, S, Se, Te) forming OsX _n coordination polyhedra which can be tetrahedra (n = 4), trigonal bipyramids or square pyramids (n = 5), octahedra (n = 6), or pentagonal bipyramids (n = 7). In some compounds, pairs of OsO₆ octahedra share edges to form Os–Os bonds. The influence of the Os valence state and the nature of the chalcogen atom on the composition and structure of the [Os _a X _b ] groups is discussed. On the basis of analysis of the crystal-structural data from the standpoint of the 18-electron rule, dependences of the Os–O and Os–Os bond orders on the bond lengths are proposed.     

Coordination compounds of Co(II), Ni(II) and Cu(II) with capric acid hydrazide

The reaction of aquo-ethanolic solutions of Co(II), Ni(II) and Cu(II) salts and ethanolic solution of capric acid hydrazide (L) yielded paramagnetic, high-spin bis- and tris(ligand) chelate complexes. The tris(ligand) complexes, [ML ₃]X ₂·nH₂O [M=Co(II), Ni(II);X=NO ₃ ^– , ClO ₄ ^– , 1/2SO ₄ ^2– ], have an octahedral structure formed on account of the bidentate (NO) coordination of three neutral hydrazide molecules. In the bis(ligand) complexes,ML ₂(NCS)₂ [M=Co(II), Ni(II)] and CuL ₂ X ₂·nH₂O (X=NO ₃ ^– , ClO ₄ ^– and 1/2SO ₄ ^2– ), the oxoanions and NCS^– take also part in coordination. The complexes have been characterized by elemental analysis, IR spectra, magnetic measurements, molar conductivity and TG analysis.

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Caprinsäurehydrazid-Komplexe von Co(II), Ni(II) und Cu(II)

Zusammenfassung Durch die Reaktion von wäßrig-ethanolischen Lösungen von Co(II)-, Ni(II)-und Cu(II)-Salzen mit einer ethanolischen Lösung von Caprinsäurehydrazid (L) wurden paramagnetische high-spin Bis- und Tris-Ligand-Chelatkomplexe erhalten. Tris-Ligand-Komplexe des Typs [ML ₃ X ₂·nH₂O [M=Co(II), Ni(II);X=NO ₃ ^– , ClO ₄ ^– , 1/2SO ₄ ^2– ], die eine oktaedrische Struktur besitzen, entstehen durch die Koordination von drei neutralen zweizähnigen (NO)-Hydrazidmolekülen. Bei den Bis-Ligand-KomplexenML ₂(NCS)₂ [M=Co(II), Ni(II)], sowie bei den Bis-Ligand-Komplexen CuL ₂ X ₂·nH₂O (X=NO ₃ ^– , ClO ₄ ^– , 1/2SO ₄ ^2– ) nehmen bei der Koordination außer Hydrazid auch die Säurereste teil. Die Komplexe wurden durch Elementaranalyse, IR-Spektren, magnetische Messungen, molare Leitfähigkeit und TG-Analysen charakterisiert.

     

Ab initio study of spin–orbit interaction in the ground electronic states of XH (X = C, Si, Ge and Sn) molecules

Electronic structure and spectroscopic properties for the ground electronic states of CH, SiH, GeH and SnH molecules were obtained using the multiconfigurational self-consistent field followed by spin–orbit multireference multistate perturbation theory. Spin–orbit splitting calculations for ground states of the four molecules were carried out with model core potential (MCP) and all-electron (AE) methods. MCP results are compared with corresponding AE values to estimate the accuracy of the saving cost MCP calculations. The potential energy curves, calculated for the Ω states CH(X₁²Π_1/2 and X₂²Π_3/2), SiH(X₁²Π_1/2 and X₂²Π_3/2), GeH(X₁²Π_1/2 and X₂²Π_3/2) and SnH(X₁²Π_1/2 and X₂²Π_3/2) using the MCP method, were fitted to analytical potential energy function using Murrell–Sorbie potential energy function. Based on the analytical potential energy function, force constants and spectroscopic constants for the Ω states were obtained.     

Thermodynamic Quantities and Defect Structure of La0.6Sr0.4Co1−yFeyO3−δ(y=0–0.6) from High-Temperature Coulometric Titration Experiments

The partial energies and entropies of O₂in perovskite-type oxides La_0.6Sr_0.4Co_1−yFe_yO_3−δ(y=0, 0.1, 0.25, 0.4, 0.6) were determined as a function of nonstoichiometryδby coulometric titration of oxygen in the temperature range 650–950°C. An absolute reference value ofδwas obtained by thermogravimetry in air. The nonstoichiometry at a given oxygen pressure and temperature decreases with iron contenty. At low nonstoichiometries the oxygen chemical potential decreases withδ. The observed behavior can be interpreted by assuming random distribution of oxygen vacancies, an electronic structure with both localized donor states on Fe, and a partially filled itinerant electron band, of which the density of states at the Fermi level scales with the Co content. The energy of the Fe states is close to the energy at the Fermi level in the conduction band. The observed trends of the thermodynamic quantities can be interpreted in terms of the itinerant electron model only when the iron content is small. At high values ofδthe chemical potential of O₂becomes constant, indicating partial decomposition of the perovskite phase. The maximum value ofδat which the compositions are single-phase increases with temperature.     

Metal ion complexes of 2-picolinamineN-oxide

Summary A series of cobalt(II), nickel(II) and copper(II) complexes of 2-picolinamineN-oxide, HA, has been prepared. Solids of formula [M(HA)₃](BF₄)₂ (M=cobalt(II) or nickel(II); [Cu(HA)₂]X₂ (X=BF ₄ ^– , NO ₃ ^– ); [Co(HA)₂X₂] (X=Cl^– or Br^–); [Ni(HA)₂Cl₂] and [Cu(HA)X₂] (X=Cl^– or Br^–] have been isolated and characterized by partial elemental analyses, molar conductivities, magnetic susceptibilities, DSC-TGA, and spectral methods. All complexes were found to be monomeric, and their spectral parameters are compared with those of the metal ion complexes ofN-alkyl-2-picolinamineN-oxides, 2-dialkylaminopyridineN-oxides and 2-picolinamine. The cobalt(II) and nickel(II) halide complexes spectrally show a mixture of octahedral and tetrahedral centres.