Phase transitions in K3AlF6

Phase transitions in the elpasolite-type K₃AlF₆ complex fluoride were investigated using differential scanning calorimetry, electron diffraction and X-ray powder diffraction. Three phase transitions were identified with critical temperatures , and . The α-K₃AlF₆ phase is stable below T₁ and crystallizes in a monoclinic unit cell with a=18.8588(2)Å, b=34.0278(2)Å, c=18.9231(1)Å, β=90.453(1)° (a=2a_c−c_c, b=4b_c, c=a_c+2c_c; a_c, b_c, c_c—the basic lattice vectors of the face-centered cubic elpasolite structure) and space group I2/a or Ia. The intermediate β phase exists only in very narrow temperature interval between T₁ and T₂. The γ polymorph is stable in the T₂<T<T₃ temperature range and has an orthorhombic unit cell with a=36.1229(6)Å, b=17.1114(3)Å, c=12.0502(3)Å (a=3a_c−3c_c, b=2b_c, c=a_c+c_c) at 250 °C and space group Fddd. Above T₃ the cubic δ polymorph forms with a_c=8.5786(4)Å at 400 °C and space group . The similarity between the K₃AlF₆ and K₃MoO₃F₃ compounds is discussed.     

Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4·3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr₄Cu₃(AsO₄)₂(AsO₃OH)₄·3H₂O (1) and Ba₂Cu₄(AsO₄)₂(AsO₃OH)₃(2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO-CuO-As₂O₅-H₂O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å³, Z=4 for 1; space group P4₂/n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å³, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu²⁺-(XO₄)³⁻ layers (X=P⁵⁺, As⁵⁺) linked by M cations (M=alkali, alkaline earth, Pb²⁺, or Ag⁺) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu₂O₈ centrosymmetric dimers crosslinked by As1φ₄ tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu₂O₈ centrosymmetric dimers of CuO₅ edge-sharing polyhedra, crosslinked by As1O₄ tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.     

Two isotypic diphosphates LiM2H3(P2O7)2 (M=Ni, Co) containing ferromagnetic zigzag MO6 chains

Two new isotypic phosphates LiNi₂H₃(P₂O₇)₂ (1) and LiCo₂H₃(P₂O₇)₂ (2) have been hydrothermally synthesized and structurally characterized by the single-crystal X-ray diffraction technique. They crystallize in the monoclinic space group C2/c with the lattice: a=10.925(2) Å, b=12.774(3) Å, c=8.8833(18) Å, β=123.20(3)° for 1 and a=10.999(2) Å, b=12.863(3) Å, c=8.9419(18) Å, β=123.00(3)° for 2. The transition metal atoms are octahedrally coordinated, whereas the lithium and phosphorus atoms are all tetrahedrally coordinated. As the lithium-induced derivatives of MH₂P₂O₇ (M=Ni, Co), 1 and 2 possess the same structure with MH₂P₂O₇ in terms of topology, comprising the MO₆ zigzag chains and P₂O₇ as the interchain groups. The magnetisms of 1 and 2 could be interpreted by adopting a quasi-one-dimensional (1D) zigzag chain model as that in their parent compounds: both 1 and 2 have ferromagnetic (FM) NiO₆/CoO₆ chains; 1 shows a FM cluster glass behavior at low temperatures, which is originated from the possible antiferromagnetic (AFM) next-nearest-neighbour intrachain interactions; 2 shows a AFM ordering at T_N=2.6 K and a metamagnetic transition at H_C=4.2 kOe at 1.8 K.     

Hydrothermal syntheses and structures of the uranyl tellurates AgUO2(HTeO5) and Pb2UO2(TeO6)

Two uranyl tellurates, AgUO₂(HTeO₅) (1) and Pb₂UO₂(TeO₆) (2), were synthesized under hydrothermal conditions and were structurally, chemically, and spectroscopically characterized. 1 crystallizes in space group Pbca, a=7.085(2) Å, b=11.986(3) Å, c=13.913(4) Å, V=1181.5(5) Å³, Z=8; 2 is in P2(1)/c, a=5.742(1) Å, b=7.789(2) Å, c=7.928(2) Å, V=90.703(2) Å³, and Z=2. These are the first structures reported for uranyl compounds containing tellurate. The U⁶⁺ cations are present as (UO₂)²⁺ uranyl ions that are coordinated by O atoms to give pentagonal and square bipyramids in compounds 1 and 2, respectively. The structural unit in 1 is a sheet consisting of chains of edge-sharing uranyl pentagonal bipyramids that are one bipyramid wide, linked through the dimers of TeO₆ octahedra. In 2, uranyl square bipyramids share each of their equatorial vertices with different TeO₆ octahedra, giving a sheet with the autunite-type topology. Sheets in 1 and 2 are connected through the low-valence cations that are located in the interlayer region. The structures of 1 and 2 are compared to those of uranyl compounds containing octahedrally coordinated cations.     

Monomeric and dimeric ruthenium thiooxalate complexes: Structures of CpRu(PPh3)2SCOCO2Me and CpRu(dppe)SCOCO2Et

The hydrosulfido complexes CpRu(L)(L′)SH react with one equivalent of O-alkyl oxalyl chlorides (ROCOCOCl) to form the corresponding O-alkylthiooxalate complexes CpRu(L)(L′)SCOCO₂R (L = L′ = PPh₃ (1), (2); L = PPh₃, L′ = CO (3); R = Me (a), Et (b)). The reactions of the hydrosulfido complexes with half equivalent of oxalyl chloride produce the bimetallic complexes [CpRu(L)(L′)SCO]₂ (L = L′ = PPh₃ (4), (5); L = PPh₃, L′ = CO (6)). The crystal structures of CpRu(PPh₃)₂SCOCO₂Me (1a) and CpRu(dppe)SCOCO₂Et (2b) are reported.     

Rhodium(I) complexes with κP coordinated ω-phosphinofunctionalized alkyl phenyl sulfide, sulfoxide and sulfone ligands and their reactions with sodium bis(trimethylsilyl)amide and Ag[BF4]

Reactions of ω-diphenylphosphinofunctionalized alkyl phenyl sulfides Ph₂P(CH₂)_nSPh (n = 1, 1a; 2, 2a; 3, 3a), sulfoxides Ph₂P(CH₂)_nS(O)Ph (n = 1, 1b; 2, 2b; 3, 3b) and sulfones Ph₂P(CH₂)_nS(O)₂Ph (n = 1, 1c; 2, 2c; 3, 3c) with dinuclear chlorido bridged rhodium(I) complexes [(RhL₂)₂(μ-Cl)₂] (L₂ = cycloocta-1.5-diene, cod, 4; bis(diphenylphosphino)ethane, dppe, 5) afforded mononuclear Rh(I) complexes of the type [RhCl{Ph₂P(CH₂)_nS(O)_xPh-κP}(cod)]¹ (n/x = 1/0, 6a; 1/1, 6b; 1/2, 6c; 2/0, 8a; 2/1, 8b; 2/2, 8c; 3/0, 10a; 3/1, 10b; 3/2, 10c) and [RhCl{Ph₂P(CH₂)_nS(O)_xPh-κP}(dppe)] (n/x = 1/0, 7a; 1/1, 7b; 1/2, 7c; 2/0, 9a; 2/1, 9b; 2/2, 9c; 3/0, 11a; 3/1, 11b; 3/2, 11c) having the P^S(O)_x ligands κP coordinated. Addition of Ag[BF₄] to complexes 6-11 in CH₂Cl₂ led with precipitation of AgCl to cationic rhodium complexes of the type [Rh{Ph₂P(CH₂)_nS(O)_xPh-κP,κS/O}L₂][BF₄] having bound the P^S(O)_x ligands bidentately in a κP,κS (13a-18a, 15b-18b) or a κP,κO (13b, 14b, 13c-18c) coordination mode. Unexpectedly, the addition of Ag[BF₄] to 6a in THF afforded the trinuclear cationic rhodium(I) complex [Rh₃(μ-Cl)(μ-Ph₂PCH₂SPh-κP:κS)₄][BF₄]₂·4THF (12·4THF) with a four-membered Rh₃Cl ring as basic framework. Addition of sodium bis(trimethylsilyl)amide to complexes 6-11 led to a selective deprotonation of the carbon atom neighbored to the S(O)_x group (α-C) yielding three different types of organorhodium complexes: a) Organorhodium intramolecular coordination compounds of the type [Rh{CH{S(O)_xPh}CH₂CH₂PPh₂-κC,κP}L₂] (22a-c, 23a-c), b) zwitterionic complexes [Rh{Ph₂PCHS(O)_xPh-κP,κS/O}L₂] having κP,κS (21a, 21b) and κP,κO (20b/c, 21c) coordinated anionic [Ph₂PCHS(O)_xPh] ligands, and c) the dinuclear rhodium(I) complex [{Rh{μ-CH(SPh)PPh₂-κC:κP}(cod)}₂] (19). All complexes were fully characterized spectroscopically and complexes 15b, 15c, 12·4THF and 19·THF additionally by X-ray diffraction analysis. DFT calculations of zwitterionic complexes gave insight into the coordination mode of the [Ph₂PCHS(O)Ph] ligand (κP,κS versus κP,κO).     

Catalytic hydrogenation of CO and CN bonds via heterolysis of H2 mediated by metal-sulfur bonds of rhodium and iridium thiolate complexes

Coordinatively unsaturated rhodium and iridium complexes having a bulky thiolate, [Cp∗M(PMe₃)(SDmp)](BAr^F₄) (1a: M = Rh; 1b: M = Ir; Dmp = 2,6-(mesityl)₂C₆H₃, Ar^F = 3,5-(CF₃)₂C₆H₃), catalyzed the hydrogenation of benzaldehyde, N-benzylideneaniline, and cyclohexanone, under 1 atm of H₂ at low temperatures. In these catalytic reactions, the M-H/S-H complexes [Cp∗M(PMe₃)(H)(HSDmp)](BAr^F₄) (2a: M = Rh; 2b: M = Ir) generated via H₂ heterolysis by 1a or 1b were suggested to transfer both M-H hydride and S-H proton to substrates. The catalytic reactions were terminated by the dissociation of H-SDmp from the metal centers of 2a and 2b that occurs at ambient temperature under H₂ atmosphere.     

Effect of π-accepting substituent on the reactivity and spectroscopic characteristics of triarylbismuthanes and triarylbismuth dihalides

Competitive chlorination of p-substituted triarylbismuthanes 1 [(p-XC₆H₄)₃Bi; a: X = OMe, c: Cl, d: CO₂Et, e: CF₃, f: CN, g: NO₂] and trimesitylbismuthane (2,4,6-Me₃C₆H₂)₃Bi 1h by sulfuryl chloride was carried out against 1b (X = H) and the effect of these substituents on the formation of triarylbismuth dichlorides 2 was studied. The relative ratios 2/2b decreased with increasing electron-withdrawing ability of the substituents (2a/2b = 53/47, 2c/2b = 33/67, 2d/2b = 35/65, 2e/2b = 29/71, 2f/2b = 16/84, 2g/2b = 0/100, 2h/2b = 46/54), indicating a lowering of reactivity of the lone pair on the bismuth atom. Pd-Catalyzed degradation of 2a-g and their difluorides 3 giving biaryls 4 was promoted by the electron-withdrawing p-substituents in the equatorial aryl groups but suppressed by the more electronegative fluorine atoms in the apical positions. This is in fairly good accord with the stability of the trigonal bipyramidal geometry. The ¹³C NMR study of 1-3 showed that the signals due to the ipso carbons (C1) attached to the bismuth atom shift downfield with increasing electron-withdrawing nature of the p-substituents. No such tendency was observed in other aromatic ring carbons. The electronic effect on the C1 atoms, similar to that on the chlorination of 1 and degradation of 2 and 3, indicates the significant participation of the C1 atoms in these reactions through the Bi-C1 bonds.     

Palladiumdichloride (ferrocenylethynyl)phosphanes and their use in Pd-catalyzed Heck-Mizoroki- and Suzuki-Miyaura carbon-carbon cross-coupling reactions

In this work the synthesis of phosphane selenides (FcCC)_nPh_3−nPSe (2a, n = 1; 2b, n = 2; 2c, n = 3; Fc = ferrocenyl, (η⁵-C₅H₄)(η⁵-C₅H₅)Fe) from (FcCC)_nPh_3−nP (1a, n = 1; 1b, n = 2; 1c, n = 3) and selenium is described to estimate the σ-donor properties of these systems by ³¹P{¹H} NMR spectroscopy. Progressive replacement of phenyl by ferrocenylethynyl causes a shielding of the phosphorus atom with increasing of the ¹J(³¹P-⁷⁷Se) coupling constants.The palladiumdichloride metal-organic complexes [((FcCC)_nPh_3−nP)₂PdCl₂] (3a, n = 1; 3b, n = 2; 3c, n = 3) have been used as (pre)catalysts in the Suzuki-Miyaura (reaction of 2-bromo-toluene (4a) and 4-bromo-acetophenone (4b), respectively, with phenyl boronic acid (5) to give 2-methyl biphenyl (6a) and 4-acetyl biphenyl (6b)) and in the Heck-Mizoroki reaction (treatment of iodobenzene (7) with tert-butyl acrylate (8) to give E-tert-butyl cinnamate (9)).The structures of molecules 1a, 1c, 2c, and 3c in the solid state were determined by single X-ray structure analysis showing that the structural parameters of these systems are unexceptional and correspond to those of related phosphanes, seleno phosphanes, and palladium dichloride complexes.     

Synthesis and structure of [C6N4H20]0.5[B5O6(OH)4]: A new organically templated pentaborate with white-light-emission

A new organically templated pentaborate [C₆N₄H₂₀]_0.5[B₅O₆(OH)₄] (1a) was prepared by reactions of triethylenetetramine (TETA) with excess boric acid in aqueous solution and characterized by elemental analysis, FTIR, TG-DTA, powder X-ray diffraction and photoluminescence spectroscopy. The structure of 1a was determined by a single-crystal X-ray diffraction. It crystallizes in the monoclinic system with space group P2(1)/c, a=9200(3) Å, b=14.121(5) Å, c=10.330(4) Å, β=91.512(4)°, V=1341.4(9) Å³, and Z=4. The luminescent properties of the compound were studied, and a green-blue luminescence occurs with an emission maximum at 507 nm upon excitation at 430 nm. The photoluminescence of 1a can be modified from green-blue to white by means of a simple heat-treatment process. The white-light-emission of sample 1c makes the pentaborate a good candidate for display and lighting applications in the white LED.     

The (phosphino)tetraphenylborate ligand in ruthenium-arene chemistry

The synthesis of a series of anionic half-sandwich ruthenium-arene complexes [E][RuCl₂(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (E = Bu₄N⁺: R = Ph, 1a, ⁱPr, 1b or Cy, 1c; E = bis(triphenylphosphine)iminium or PNP⁺: R = Ph, 1a′, ⁱPr, 1b′ or Cy, 1c′) are reported. X-ray crystallographic studies of 1a′ and 1b′ confirmed the three-legged piano-stool coordination geometry. In solution, complexes 1a-c and 1a′-c′ are proposed to form monomer-dimer equilibria as a result of chloride ligand dissociation. Complexes 1a-c and 1a′-c′ also form the formally neutral zwitterionic complexes [RuCl(L)(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (L = pyridine: R = Ph, 2a, ⁱPr, 2b or Cy, 2c; L = MeCN: R = Ph, 3a, ⁱPr, 3b or Cy, 3c) via chloride ligand abstraction using AgNO₃ or MeOTf.     

Assembly of diverse structural types of organotellurium compounds in the reactions of (4-MeO-C6H4)2TeO with pyridine carboxylic acids

The reactions of Ar₂TeO (Ar = 4-MeO-C₆H₄) with 2-, 3- and 4-pyridine carboxylic acids (LH) afforded different organotelluroxane structural types depending on the stoichiometry of the reactants and the conditions of the reaction. Ar₂Te(L)OH (1a-1c) are formed in a 1:1 reaction of Ar₂TeO with LH in the presence of water. On the other hand a 1:2 reaction under anhydrous conditions leads to the formation of Ar₂TeL₂ (2a-2c). A 2:2 reaction under anhydrous conditions affords the ditelluroxanes Ar₂Te(L)OTe(L)Ar₂ (3a-3c) while tritelluroxanes Ar₂Te(L)OTeAr₂OTe(L)Ar₂ (4a-4c) are formed in 3:2 reactions. Interestingly, 3a-3c are formed in the reaction of 2a-2c with Ar₂TeO. The former can be hydrolyzed to 1a-1c while the latter upon reaction with Ar₂TeO lead to the formation of the tritelluroxanes 4a-4c. Attempts to metalate 2a with PdCl₂(MeCN)₂ leads to a transfer of the carboxylate ligand to palladium affording Ar₂TeCl₂ and PdL₂. X-ray crystal structures of representative examples of the family of 1, 2 and 3 reveal interesting supramolecular structures and the formation of a novel [TeO]₂ structural unit. The latter results from intermolecular secondary Te?O interactions.     

Synthesis of indenes by ytterbium-catalyzed carboalkoxylation/Friedel-Crafts reaction of arylidenecyclopropanes with acetals

Ytterbium-catalyzed tandem carboalkoxylation/Friedel-Crafts reaction of arylidenecyclopropanes 1 with acetals 2 afforded the corresponding indene derivatives 3 in good to high yields. For example, in the presence of 10 mol % of Yb(OTf)₃ the reaction of 1-phenylbenzylidenecyclopropane 1a with the dimethyl acetals of benzaldehyde 2a, p-tolualdehyde 2b, and p-anisaldehyde 2c gave 1,3-diphenyl-2-(2-methoxyethyl)indene 3a, 2-(2-methoxyethyl)-3-phenyl-1-(p-tolyl)indene 3b, and 1-(p-anisyl)-2-(2-methoxyethyl)-3-phenylindene 3c in 82%, 80%, and 80% yields, respectively.     

A structure and phase analysis investigation of the “1:1” ordered A2InNbO6 perovskites (A=Ca, Sr, Ba)

The structures of the Ba₂InNbO₆, Sr₂InNbO₆ and Ca₂InNbO₆ “1:1” complex perovskites have been refined from neutron powder diffraction data. Both the A=Ca and Sr compounds occur at room temperature in P12₁/n1 (a=a_p+b_p, b=-a_p+b_p, c=2c_p) perovskite-related superstructures while the A=Ba compound occurs in the , a=2a_p, elpasolite structure type. In the case of the A=Ca compound, an extensive Ca₂[(Ca_2x/3In_1−xNb_x/3)Nb]O₆ ‘solid solution’ field spanning compositions between Ca₄Nb₂O₉ and Ca₂InNbO₆ in the CaO-InO_3/2-NbO_5/2 ternary phase diagram is shown to exist. Under the conditions of synthesis used, the ‘solid solution’ field stops just short of the ideal 1:1 Ca₂InNbO₆ composition.     

Synthesis and properties of pyrazine-pillared Ag3Mo2O4F7 and AgReO4 layered phases

The new pyrazine-pillared solids, AgReO₄(C₄H₄N₂) (I) and Ag₃Mo₂O₄F₇(C₄H₄N₂)₃ (C₄H₄N₂=pyrazine, pyz) (II), were synthesized by hydrothermal methods at 150 °C and characterized using single crystal X-ray diffraction (I—P2₁/c, No. 14, Z=4, a=7.2238(6) Å, b=7.4940(7) Å, c=15.451(1) Å, β=92.296(4)°; II—P2/n, No. 13, Z=2, a=7.6465(9) Å, b=7.1888(5) Å, c=19.142(2) Å, β=100.284(8)°), thermogravimetric analysis, UV-Vis diffuse reflectance, and photoluminescence measurements. Individual Ag(pyz) chains in I are bonded to three perrhenate ReO₄^- tetrahedra per layer, while each layer in II contains sets of three edge-shared Ag(pyz) chains (π-π stacked) that are edge-shared to four Mo₂O₄F₇^3- dimers. A relatively small interlayer spacing results from the short length of the pyrazine pillars, and which can be removed at just slightly above their preparation temperature, at >150-175 °C, to produce crystalline AgReO₄ for I, and Ag₂MoO₄ and an unidentified product for II. Both pillared solids exhibit strong orange-yellow photoemission, at 575 nm for I and 560 nm for II, arising from electronic excitations across (charge transfer) band gaps of 2.91 and 2.76 eV in each, respectively. Their structures and properties are analyzed with respect to parent ‘organic free’ silver perrhenate and molybdate solids which manifest similar photoemissions, as well as to the calculated electronic band structures.     

Structural studies of phosphor-1,1-diselenoato Mn(I) and Re(I) complexes

Mononuclear complexes of the type, M(CO)₄[Se₂P(OR)₂] (M = Mn, R = ⁱPr, 1a; Et, 1b; M = Re, R = ⁱPr, 3a; Et, 3b) can be prepared from either [-Se(Se)P(OⁱPr)₂]₂ (A) or [Se{-Se(Se)P(OEt)₂}₂] (B) with M(CO)₅Br. O,O′-dialkyl diselenophosphate ([(RO)₂PSe₂]^-, abbreviated as dsep) ligands generated from A and B act as a chelating ligand in these complexes. Upon refluxing in acetonitrile, these mononuclear complexes yield dinuclear complexes with a general formula of [M₂(CO)₆{Se₂P(OR)₂}₂] (M = Mn, R = ⁱPr, 2a; Et, 2b; M = Re, R = ⁱPr, 4a; Et, 4b). Dsep ligands display a triconnective, bimetallic bonding mode in the dinuclear compounds and this kind of connective pattern has never been identified in any phosphor-1,1-diselenoato metal complexes. Compounds 2b, 3b, and 4 are structurally characterized. Compounds 2b and 3b display weak, secondary Se?Se interactions in their lattices.     

[Cu4OCl6(DABCO)2]·0.5DABCO·4CH3OH (“MFU-5”): Modular synthesis of a zeolite-like metal-organic framework constructed from tetrahedral {Cu4OCl6} secondary building units and linear organic linkers

A novel metal-organic framework (MOF) based on a tetranuclear copper cluster and a linear organic ligand formulated as [Cu₄OCl₆(DABCO)₂]·0.5DABCO·4CH₃OH (denoted as MFU-5, MFU=Metal-Organic Framework, Ulm University; DABCO=1,4-diazabicyclo[2.2.2]octane), was prepared via solvothermal synthesis. In contrast with common MOF synthesis strategies, MFU-5 is assembled from pre-defined molecular secondary building units, i.e. {Cu₄OCl₆} moieties, which become the nodes of the coordination framework. The title compound was characterized by single crystal X-ray diffraction, variable temperature powder diffraction (VT-XRPD), thermal analysis, as well as IR- and UV/Vis spectroscopy. Crystal data for MFU-5: hexagonal, P6/mcc (no. 192), a=25.645(9), c=17.105(11) Å, V=9742(8) Å³, Z=12, 1690 structure factors, R[F²>2σ(F²)]=0.049. MFU-5 is a 3D metal-organic framework with 1D channels running along the c-axis hosting DABCO and methanol solvent molecules. The framework displays a zeolite-like structure constructed from mso cages, which represents the composite building units in the zeolites SSF, MSO and SZR. Two-fold interpenetration is observed between these building units. TG/DTA-MS and VT-XRPD characterization reveal a stepwise release of methanol and DABCO molecules upon heating, eventually resulting in a structural change into a non-porous material.     

Triphenylpyrylium salt-sensitized photoreactions of 1,4-diaryl-2,3-dioxabicyclo[2.2.2]octanes through competitive single electron-transfer pathway and proton-catalyzed pathway

2,4,6-Triphenylpyrylium tetrafluoroborate (TPPBF₄)-sensitized photoinduced electron-transfer (PET) reactions of 1,4-diaryl-2,3-dioxabicyclo[2.2.2]octanes 5 (a: Ar¹ = Ar² = p-MeOC₆H₄, b: Ar¹ = Ar² = p-MeC₆H₄, c: Ar¹ = Ar² = Ph) underwent novel fragmentation through their radical cations to give 1,4-diarylbutan-1,4-diones 6 accompanied by elimination of ethylene. On the other hand, 4-aryl-cyclohex-3-en-1-ones 7, p-substituted phenols 8, and 4-aryl-4-aryloxycyclohexanones 9 were produced through proton-catalyzed pathways when the PET reactions of 5 were performed in the absence of a certain base such as 2,6-di-tert-butylpyridine (DTBP). Particularly, the formation of 9 is consistent with the novel cationic rearrangement involving nucleophilic O-1,2-aryl shifts and C-1,4-aryl shifts.     

Structure and microstructure of the high pressure synthesised misfit layer compound [Sr2O2][CrO2]1.85

The strontium chromium oxide [Sr₂O₂][CrO₂]_1.85 misfit layer compound has been synthesised at high-pressure and high-temperature conditions. Electron diffraction patterns and high-resolution transmission electron microscopy images along [001] show the misfit character of the different layers composing the structure with a supercell along the incommensurate parameter b≈7b₁≈13b₂. The modulated crystal structure has been refined within the superspace formalism against single-crystal X-ray diffraction data, employing the (3+1)-dimensional superspace group C′nmb(0σ₂0)0 0 s. The compound has a composite structure with lattice parameters a₁=5.182(1) Å, b₁=5.411(1) Å, c₁=18.194(3) Å for the first, SrO, subsystem and the same a and c, but with b₂=2.925(1) Å for the second, CrO₂, subsystem. The layer stacking is similar to that of orthorhombic PbS(TiS₂)_1.18, but with a much stronger intersubsytem bonding in the case of the oxide. The intersubsystem lattice mismatch is mainly handled by displacement modulations of the Sr atoms, correlated with modulations of the valence, the coordination and the anisotropic displacement parameters.