Iodostannate mit polymeren Anionen: (Me3PhN)4 [Sn3I10], [Me2HN–(CH2)2–NMe2H]2 [Sn3I10] und [Me2HN–(CH2)2–NMe2H][Sn3I8]

Iodostannates with Polymeric Anions: (Me₃PhN)₄ [Sn₃I₁₀], [Me₂HN–(CH₂)₂–NMe₂H]₂ [Sn₃I₁₀], and [Me₂HN–(CH₂)₂–NMe₂H] [Sn₃I₈] The polymeric iodostannate anions in (Me₃PhN)₄ [Sn₃I₁₀] ( 1 ) and [Me₂HN–(CH₂)₂–NMe₂H]₂ [Sn₃I₁₀] ( 2 ) consist of Sn₃I₁₂‐trioctahedra, which share four common iodine atoms with adjacent units to form infinite layers in 1 and polymeric chains in 2 . In the anion of [Me₂HN–(CH₂)₂–NMe₂H] [Sn₃I₈] ( 3 ) distorted SnI₆ octahedra sharing common edges and vertices form a two‐dimensional network. (Me₃PhN)₄ [Sn₃I₁₀] ( 1 ): Space group C2/c (No. 15), a = 2406.9(2), b = 968.26(7), c = 2651.7(2) pm, β = 111.775(9), V = 5738.9(8) · 10⁶ pm³; [Me₂HN–(CH₂)₂–NMe₂H]₂ [Sn₃I₁₀] ( 2 ): Space group P2₁/n (No. 14), a = 1187.2(1), b = 1554.4(1), c = 1188.9(1) pm, β = 116.620(8), V = 1961.4(3) · 10⁶ pm³; [Me₂HN–(CH₂)₂–NMe₂H] [Sn₃I₈] ( 3 ): Space group P2₁/c (No. 14), a = 1098.9(2), b = 803.93(7), c = 1571.5(2) pm, β = 102.96(1), V = 1352.9(2) · 10⁶ pm³.     

Lamellar Copper(I) Thiocyanate‐Based Coordination Polymers containing the Alkali Cation ligating Thiacrown Ether 1,10‐Dithia‐18‐crown‐6

The lamellar coordination polymer [(CuSCN)₂(μ‐1,10DT18C6)] (1,10DT18C6 = 1,10‐dithia‐18‐crown‐6), in which staircase‐like CuSCN double chains are bridged by thiacrown ether ligands, may be prepared in two triclinic modifications 1 a and 1 b by reaction of CuSCN with 1,10DT18C6 in respectively benzonitrile or water. Performing the reaction in acetonitrile in the presence of an equimolar quantity of KSCN leads, in contrast, to formation of the K⁺ ligating 2‐dimensional thiocyanatocuprate(I) net [{Cu₂(SCN)₃}^–] of 2 , half of whose Cu(I) atoms are connected by 1,10DT18C6 macrocycles. The potassium cations in [{K(CH₃CN)}{Cu₂(SCN)₃(μ‐1,10DT18C6)}] ( 2 ) are coordinated by all six potential donor atoms of a single thiacrown ether in addition to a thiocyanate S and an acetonitrile N atom. Under similar conditions, reaction of CuI, NaSCN and 1,10DT18C6 affords [{Na(CH₃CN)₂}{Cu₄I₄(SCN)(μ‐1,10DT18C6)}] ( 3 ), which contains distorted Cu₄I₄ cubes as characteristic molecular building units. These are bridged by thiocyanate and thiacrown ether ligands into corrugated Na⁺ ligating sheets. In the presence of divalent Ba²⁺ cations, charge compensation requirements lead to formation of discrete [Cu(SCN)₃(1,10DT18C6‐κS)]^2– anions in [Ba{Cu(SCN)₃(1,10DT18C6‐κS)}] ( 4 ).     

Synthesis and Structure of [Sn4Se11]6–, [Sn2Se52–], and [Sn3Se72–] – Model Anions for the Solventothermal Reaction Pathway to Lamellar Selenidostannates(IV)

Reaction of A₂CO₃ (A = K, Rb) with Sn and Se in an H₂O/CH₃OH mixture at 115–130°C affords the isotypic selenidostannates(IV) A₆Sn₄Se₁₁ _. xH₂O (A = K, x = 8) 1 and 2 whose discrete [Sn₄Se₁₁]^6– anions each contain two corner‐bridged ditetrahedral [Sn₂Se₆]^4– species. Similar reaction conditions with A = Cs afford Cs₂Sn₂Se₅ _. H₂O ( 3a ) and Cs₂Sn₂Se₅ ( 3b ) in which such [Sn₂Se₆]^4– building blocks are connected through common Se atoms into infinite [Sn₂Se₅^2–] chains. The [Sn₃Se₇^2–] ribbons of (Et₄N)₂Sn₃Se₇ ( 4 ), formed by treating (Et₄N)I with Sn and Se in methanol at 130°C, can be regarded as resulting from the condensation of [Sn₂Se₅^2–] chains with molecular [SnSe₄]^4– anions. The anions [Sn₄Se₁₁]^6–, [Sn₂Se₅^2–], and [Sn₃Se₇^2–] represent the products of individual reaction steps on the potential condensation pathway of [Sn₂Se₆]^4– to the lamellar selenidostannates(IV) [Sn₄Se₉^2–] or [Sn₃Se₇^2–].     

Neutral and Cationic Hexanuclear Rhenium Phosphine Clusters with μ3‐(Phosphido‐Chalcogenido), μ3‐(Arsenido‐Chalcogenido), and μ3‐(Imido or Oxo‐Chalcogenido) Hetero Ligand Shells

Reactions of dry THF/MeCN solutions of Ca[Re₆SCl(Cl^a)₆] with silylated derivatives E(SiMe₃)₂ (E = PhAs, PSiMe₃, HN, O, S) and addition of trialkylphosphine PPr₃ afford in high yields and at room temperature either the neutral clusters [Re₆SX(PPr₃)] ( 1 : X = As, 2 : X = P) or the ionic compounds [Re₆SX(PPr₃)]²⁺ · [Re₆S₆Cl₈]^2– ( 3 : X = NH, 4 : X = O, 5 : X = S). The compounds 1 – 5 were characterised by X‐ray crystal structure analysis. A di‐substitution reaction occurs on the {Re₆SCl}⁴⁺ cluster core, where the two inner μ₃‐chloro ligands Clⁱ are substituted by X (X = As, P, NH, O, S) and all six terminal chloro ligands Cl^a are exchanged by terminal PPr₃‐ligands.     

Stable γ-distonic oxonium ions: R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCHR′ĊH2CHR″ and their characteristic reaction

The γ-distonic radical ions R$ \mathop {\rm O}\limits^ + $CHR′CH₂?HR″ and their molecular ion counterparts R$ \mathop {\rm O}\limits^{{\rm + } \cdot } $CHR′CH₂CH₂R″ have been studied by isotopic labelling and collision-induced dissociation, applying a potential to the collision cell in order to separate activated from spontaneous decompositions. The stability of CH₃$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?HCH₃, C₂H₅$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?HCH₃, CH₃$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?H₂, CH₃$ \mathop {\rm O}\limits^ + $HCH₂CH₂?HCH₃ and C₂H₅$ \mathop {\rm O}\limits^ + $HCH₂CH₂?HCH₃, has been demonstrated and their characteristic decomposition, alcohol loss, identified. For all these γ-distonic ions, the 1,4-H abstraction leading to their molecular ion counterpart exhibits a primary isotope effect.     

Rearrangements of Radical Cations of [2.2]Paracyclophanes and of a bridged [14]annulene to those of pyrenes: An ESR and ENDOR study

ESR and ENDOR studies have been carried out on the radical cations obtained consecutively by reaction of trans-10b, 10c-dimethyl-10b, 10c-dihydropyrene ( 4 ) with AlCl₃ in CH₂C1₂. The primarily formed ${\bf 4}^{+ \atop \dot{}}$ rearranges at 253 K to the radical cation(s) of 1,6- ( 5a ) and/or 1,8-dimethylpyrene ( 5b ). At 323 K, the spectra of ${\bf 5a}^{+ \atop \dot{}}$/${\bf 5b}^{+ \atop \dot{}}$ are replaced by that of the highly persistent radical cation of 1,3,6,8-tetramethylpyrene ( 6 ). Surprisingly, ${\bf 6}^{+ \atop \dot{}}$ is also the only observable paramagnetic product resulting from a treatment of 4,5,7,8- ( 1 ), 4,7,13,16- ( 2 ), and 4,5,12,13-tetramethyl[2.2]paracyclophane ( 3 ) with AlCl₃ in CH₂Cl₂ at 353 K. The structures of the intermediates in the rearrangement [${\bf 1}^{+ \atop \dot{}}$, ${\bf 2}^{+ \atop \dot{}}$, ${\bf 3}^{+ \atop \dot{}}$] → ${\bf 6}^{+ \atop \dot{}}$ are discussed.     

19F-NMR-spektroskopischer Nachweis und Berechnung der statistischen Bildung der gemischten Clusteranionen [(Mo6BrCl)F]2−, n = 0 – 8

¹⁹F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo₆Br Cl )F ]^2?, n = 0 – 8 The complete system of the innersphere mixed clusters (Mo₆BrCl)⁴⁺ is formed by exchange of innersphere bound Clⁱ against outersphere bound Br^a on tempering the solid [(Mo₆Cl)Br] at 500°C for 16 h. After conversion with conc. HCl into (H₃O)₂[(Mo₆BrCl)Cl] and precipitation of the outer Cl^a with AgBF₄ in ethanol, treatment with tetrabutylammonium(TBA)fluoride yields (TBA)₂ [(Mo₆BrCl)F], a mixture of 22 different species. According to the sets of chemical equivalent fluorine atoms in total 55 ¹⁹F nmr signals are expected, which are really observed in the high resolution 1D-¹⁹F-nmr spectrum. Using increments of chemical shifts, peak intensities and multiplet structures as well as the 2D-¹⁹F/¹⁹F-COSY spectrum the complete and unambiguous assignment of all resonances is achieved. From the measured integral intensities the distribution of the different compounds is determined, revealing statistical formation of the geometrical isomers.     

CuYS2: Ein ternäres Kupfer(I)‐Yttrium(III)‐Sulfid mit Ketten {[Cu(S1)3/3(S2)1/1]3–} cis‐kantenverknüpfter [CuS4]7–‐Tetraeder

CuYS₂: A Ternary Copper(I) Yttrium(III) Sulfide with Chains {[Cu(S1)_3/3(S2)_1/1]^3–} of cis ‐Edge Connected [CuS₄]^7– Tetrahedra Pale yellow, lath‐shaped single crystals of the ternary copper(I) yttrium(III) sulfide CuYS₂ are obtained by the oxidation of equimolar mixtures of the metals (copper and yttrium) with sulfur in the molar ratio 1 : 1 : 2 within fourteen days at 900 °C in evacuated silica ampoules, while the presence of CsCl as fluxing agent promotes their growth. The crystal structure of CuYS₂ (orthorhombic, Pnma; a = 1345.3(1), b = 398.12(4), c = 629.08(6) pm, Z = 4) exhibits chains of cis‐edge linked [CuS₄]^7– tetrahedra with the composition {[Cu(S1)_3/3(S2)_1/1]^3–} running along [010] which are hexagonally bundled as closest rod packing. Charge equalization and three‐dimensional interconnection of these anionic chains occur via octahedrally coordinated Y³⁺ cations. These are forming together with the S^2– anions a network [Y(S1)_3/3(S2)_3/3]^– of vertex‐ and edge‐shared [YS₆]^9– octahedra with ramsdellite topology. The metall‐sulfur distances of the [CuS₄]^7– tetrahedra (230 (Cu–S2), 232 (Cu–S1), and 253 pm (Cu–S1′, 2 × )) cover a very broad interval, whilst these (Y–S: 267–280 pm) within the [YS₆]^9– octahedra range rather closely together.     

Darstellung,Schwingungsspektrum und Kristallstruktur von (n‐Bu4N)2[(W6Cl)F] · 2 CH2Cl2 und 19F‐NMR‐spektroskopischer Nachweis der gemischten Clusteranionen [(W6Cl)FCl]2–, n = 1–6

Synthesis, Vibrational Spectra, and Crystal Structure of ( n ‐Bu₄N)₂[(W₆Cl )F ] · 2 CH₂Cl₂ and ¹⁹F NMR Spectroscopic Evidence of the Mixed Cluster Anions [(W₆Cl )F Cl ]^2–, n = 1–6 The reaction of (n‐Bu₄N)₂[(W₆Cl)Cl] with CF₃COOH in dichloromethane gives intermediately a mixture of the cluster anions [(W₆Cl)(CF₃COO)Cl]^2–, n = 1–6. By treatment with NH₄F the outer sphere coordinated trifluoracetato ligands are easily substituted and the components of the series [(W₆Cl)FCl], n = 1–6 are formed and characterized by their distinct ¹⁹F NMR chemical shifts. An X‐ray structure determination has been performed on a single crystal of (n‐Bu₄N)₂[(W₆Cl)F] · 2 CH₂Cl₂ (orthorhombic, space group Pbca, a = 15.628(4), b = 17.656(3), c = 20.687(4) Å, Z = 4). The low temperatur IR (60 K) and Raman (20 K) spectra are assigned by normal coordinate analysis based on the molecular parameters of the X‐ray determination. The valence force constants are f_d(WW) = 1.89, f_d(WF) = 2.43 and f_d(WCl) = 0.93 mdyn/Å.     

The first normal stress difference and viscosity in shear of liquid crystalline solutions of hydroxypropylcellulose: new experimental data and theory

The constitutive equations for liquid crystalline polymers recently proposed by one of us [1] are applied here to interpret the behaviour of the shear viscosity η and the first normal stress difference N₁() measured for liquid crystalline (LC) solutions of hydroxypropylcellulose in acetic acid. N₁( ) is observed to change from positive to negative and again to positive, as the shear rate increases, at lower concentrations, in the LC phase. The -values at which N₁ changes sign depend on the molecular mass (degree of polymerization) and on the concentration. η shows a small Newtonian plateau at low shear rates and a strong shear-thinning at higher values of . The rate of decrease of η in this region shows an “hesitation” similar to one previously observed in LC solutions of poly-γ-benzyl-L-glutamate PBLG. All these observations can be rationalized within the frame-work of Martins' theory. The expressions for N₁() and η derived from this theory fit very well (quantitatively) to the experimental data and some fundamental viscoelastic parameters of the system under study are thereby obtained for the first time.     

Radical Ions of a Bishomobinaphthylene Containing two 1,6-methano[10]annulene moieties: An ESR and ENDOR study

The radical cation and the radical anion of ‘syn’-cyclobuta[1,2-c:3,4-c′]di-1,6-methano[10]annulene (‘syn’-4a,12a:6a, 10a-bishomobinaphthylene; 3 ) have been characterized by their hyperfine data. The highly resolved ESR spectrum of $ 3^{+ \atop \dot{}} $ is dominated by a triplet splitting from the outer pair of methano β-protons (H_o). In contrast, the ESR spectrum of $ 3^{- \atop \dot{}} $ is poorly resolved with the largest coupling constants arising from perimeter α-protons. The different hyperfine features of $ 3^{+ \atop \dot{}} $ and $ 3^{- \atop \dot{}} $ are rationalized by MO models. The SOMO of $ 3^{+ \atop \dot{}} $ ψ_SA(b₁), has substantial LCAO coefficients of the same sign at the bridged atoms C(1), C(6), C(11), and C(16), whereas in the SOMO of $ 3^{- \atop \dot{}} $, ψ_SS(a₁), the four atoms lie in the vertical nodal planes. The large width and the reluctance to saturation of the lines in the ESR spectrum of $ 3^{- \atop \dot{}} $ are attributed to the near-degeneracy of the lowest antibonding MO's. Due to their similar nodal properties, the SOMO's of $ 3^{- \atop \dot{}} $ and the radical anions of binaphthylene ( 4 ), 1,6-methano[10]annulene ( 1 ), and naphthalene ( 2 ) are interrelated. Moreover, because the cyclic π-systems in 3 and 1 deviate in the same way from planarity, the effect of such distortions on the coupling constants, a_Hμ, of the perimeter α-protons in $ 3^{- \atop \dot{}} $ and $ 1^{- \atop \dot{}} $ should be comparable. Indeed, on going from $ 4^{- \atop \dot{}} $ to $ 3^{- \atop \dot{}} $, the |a_Hμ| values are reduced exactaly by half as much as the corresponding values on passing from $ 2^{- \atop \dot{}} $ to $ 3^{- \atop \dot{}} $, of which the cyclic π-systems are twice contained in $ 4^{- \atop \dot{}} $ and $ 3^{- \atop \dot{}} $ respectively.     

Mechanism of the azide–bromine reaction in aqueous medium

Results on the oxidation of N by Br₂ in neutral and acid media are presented. The rate of the reaction is found to be proportional to [N] and [Br₂]. The gaseous product of oxidation is found to be pure nitrogen. The stoichiometry of the reaction is The reaction shows a positive salt effect. It is found that the addition of Br^? stabilizes the complex BrN₃, which decomposes into Br^? and N₂: The spectroscopic measurements also support the kinetic observation. The equilibrium constant K, the rate constants and the thermodynamic parameters were calculated. It is observed that H⁺ ion inhibits the reaction. The mechanism is discussed in terms of the kinetic results.     

Strukturwechselbeziehungen planarer und nichtplanarer Bis(1,2‐dithioquadratato)metallat‐Wirtsgittersysteme mit CuII‐Gastkomplexen – Struktur‐ und EPR‐Untersuchungen

Structural Interactions of Planar and Non‐planar Bis(1,2‐dithiosquarato)metalate Host Lattices with Cu^II Complexes – Structure and EPR Investigations 1,2‐Dithiosquaratometalates (M = Cu, Ni, Zn) are available by direct synthesis from metal salts with dipotassium‐1,2‐dithiosquarate. The structural influence of the planar and nonplanar host lattice systems (BzlEt₃N)₂[Cu/Ni(dtsq)₂] and (BzlEt₃N)₂[Cu/Zn(dtsq)₂] on the geometrical and electronic structure of the Cu^II guest complex [Cu(dtsq)₂]^2– is studied by EPR spectroscopy. The used host lattices (BzlEt₃N)₂[Ni(dtsq)₂] (planar) and (BzlEt₃N)₂[Zn(dtsq)₂] (tetrahedral) are characterized by X‐ray structure analysis. (BzlEt₃N)₂[Ni(dtsq)₂] crystallizes in the triclinic unit cell P1 with a = 9.1021(8) Å, b = 9.4190(8) Å, c = 11.0119(10) Å, α = 92.8560(10)°, β = 95.375(2)°, γ = 104.5180(10)° and Z = 1. (BzlEt₃N)₂[Zn(dtsq)₂] crystallizes in the monoclinic unit cell C2/c with a = 21.1299(14) Å, b = 16.6641(11) Å, c = 13.8324(9) Å, β = 123.9100(10)° and Z = 4. The g and A ^Cu tensors in the Cu/Ni system are nearly axial symmetric (g_|| = 2.122, g_⊥ = 2.028; A = –159.5 · 10^–4 cm^–1, A = –36.9 · 10^–4 cm^–1). The coordination geometry of the Cu^II guest complex in the tetrahedral Cu/Zn system is rather distorted, which is shown by the changed g and A ^Cu tensor parameters (g_|| = 2.143, g_⊥ = 2.042; A = –103.0 · 10^–4 cm^–1, A ≈ –5.0 · 10^–4 cm^–1). The spin density distribution is discussed using EHT molecular orbital calculations.     

Dibrommethylsulfoniumsalze – Darstellung und Kristallstruktur [1]

Dibromomethylsulfoniumsalts — Preparation and Crystal Structure The salts CH₃SBrA^? (A^? = SbCl, AsF) were prepared by various routes and characterized by their Ramanspectra. CH₃SBrAsF crystallized in the monoclinic space group P2₁/c with a = 770,5(4) pm, b = 942,4(12) pm, c = 1329,3(14) pm, β = 100,28(6)°, Z = 4. Distances and bond angles in the cation are as expected.     

Complex dynamical behavior in a new chemical oscillator: The chlorite–thiourea reaction in a CSTR

The reaction between chlorite ion and thiourea has been studied both in a closed (batch) system and in a flow reactor (CSTR). The principal stoichiometry is given by In batch, the reaction displays an induction period, whose length is proportional to [CS(NH₂)₂]/[ClO] [H⁺], followed by the rapid buildup and disappearance of a ClO₂ intermediate. At [ClO]/[CS(NH₂)₂] ratios between 2.5 and 3.5, a second peak in the ClO₂ absorbance is observed. In the CSTR, this iodine-free system displays simple and complex periodic oscillation, bistability, aperiodic oscillation, and birhythmicity.     

Subgroup‐chain symmetry‐adapted irreducible matrices and CG coefficients of point groups

The irreducible matrices and Clebsch–Gordan coefficients of any crystallographic point group adapted to all possible canonical subgroup chains are calculated ab initio for both single‐valued and double‐valued representations and tabulated with exact values in the form of or and with components labeled by the irrep labels of the group chain in Koster notation. The phases and ordering of the components of irreducible bases for the cubic point groups are properly chosen so that irreducible matrices for all subgroup chains of G=T_d, O, O_h obey the associated relations D(G)=D(G)D(G), i=4, 6, and the complex conjugation relation for the group T, D(T)=D(T)*. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 67–80, 1999     

The Radical Anions of 5,5′- and 6,6′-Biazulenyl

ESR. and, in part, ENDOR. studies are reported on the radical anions of 5,5′-and 6,6′-biazulenyl ( 1 and 2 , resp.), as well as on their 1, 1′, 3, 3′-tetradeuterioderivatives ( 1 -d₄ and 2 -d₄). The reduction processes of 1 and 2 leading to these radical anions (\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{\ominus \atop \dot{}}$\end{document}) and the dianions ( ) have been investigated by polarography and cyclic voltammetry. The half-wave reduction potential of 1 and the π-spin distribution in \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}}$\end{document} are consistent with the model of two weakly interacting azulene π-systems, whereas the analogous findings for 2 and \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{\ominus \atop \dot{}}$\end{document} point to a strong interaction between two such systems. This difference can be traced to the distinct inequality ∥c₆₅ ∥ « ∥ c₆₆ ∥ in the LCAO coefficients c_6μ at the centres μ=5 and 6 for the LUMO Ψ₆ of azulene.     

The radical anion of 1,2:9,10-dibenzo[2.2]paracyclophane.. An ESR,ENDOR, and TRIPLE resonance study

The radical anion of 1,2:9,10-dibenzo[2.2]paracyclophane ( 3 ) has been studied by ESR, ENDOR, and TRIPLE resonance spectroscopy under a variety of experimental conditions. The coupling constants of the eight protons in the deck-benzene rings, and of the four inner and four outer protons in the side-benzene rings are 0.234, 0.123, and 0.036 mT, respectively (solvent: 1,2-dimethoxyethane; counterion: K⁺). All three values have the same sign which is predicted to be negative. Comparison of the largest coupling constant (0.234 mT) with the corresponding value (0.297 mT) for the radical anion of the parent [2.2]paracyclophane ( 1 ) points to similar nodal properties of the singly occupied orbitals in and . Notwithstanding this similarity, seems to associate less readily than with alkali metal counterions, since tight ion pairs of with K⁺ are formed only in solvents of low solvating power. Effects of conformational changes on the ESR spectra, such as those previously observed for the radical anion of [2.2]paracyclophane-1,9-diene ( 2 ), are not apparent for in the temperature range of investigation. Hyperfine data are also reported for the radical anion of a derivative 4 which has a CH₃ substituent in one of the side-benzene rings of 3 .     

Über geordnete Perowskite mit Kationenfehlstellen. XI. Verbindungen vom Typ ABB□1/4WVIO6 ≙ ABIIB□WO24 mit AII,BII = Ba,Sr

On Ordered Perovskites with Cationic Vacancies. XI. Compounds of Type A B B □_1/4W^VIO₆ ? A B^IIB □W O₂₄ with A^II, B^II = Ba, Sr Depending on the ionic radii of the two and three valent cations in the perovskites of type ABB □_1/4W^VIO₆ ?; AB^IIB □WO₂₄ order disorder phenomena are present. The results of the x-ray and vibrational spectroscopic investigations as well as the diffuse reflectance spectra and the visible photoluminescence are reported.     

The kinetics of the reaction: Br + C3H6 ⇌ HBr + C3H5

Studies of the reaction of Br + propylene to produce HBr and allyl radical were made using VLPR (Very Low Pressure Reactor) over the range 263–363 K. Apparent bimolecular rate constants k were found to vary in an inverse manner with the initial concentration of bromine atoms introduced into the reactor. Plots of k against [Br] give straight lines whose intercepts were taken to be the true bimolecular, metathesis rate constant k₁. The reaction scheme is where k₂ ? k₁ and k_?1 [HBr] is negligibly small under our conditions. Arrhenius parameters for k₁ were assigned for linear and bent transition states and shown to give excellent fits to the observed intercepts. where θ = 2.303 RT (kcal mol^?1). The dependence of k on [Br] is accounted for in terms of the reactivity of Br* (²P_1/2) produced in the microwave discharge. The activation energy for the metathesis reaction of Br* with propylene is shown to be very small.