Electronic structures of the boron cage molecules B4H4, B4Cl4 and B4F4

Ab initio calculations have been performed on B₄H₄, B₄Cl₄ and B₄F₄ in order to aid our understanding of the bonding in these compounds, which is presumably based on a tetrahedral boron cage. This cage has only 8 electrons and so is less than that expected on the basis of the usual framework electron counting rules. Basis sets with polarisation functions were used at the SCF, CI and CPF levels of theory to confirm that the T _d structures are indeed more stable than the D _4h ones. Davidson-Roby population analyses were able to show that many factors, including 3-centre 2-electron bonding and backbonding from the ligand to the boron cage, are of importance in determining the relative stability of the three compounds, of which B₄Cl₄ is the only one that has yet been observed experimentally.     

2-Trif luoromethyl-4H-thiochromen-4-one and 2-trif luoromethyl-4H-thiochromene-4-thione: Synthesis and reactivities

2-Trifluoromethyl-4H-thiochromene-4-thione obtained from 2-trifluoromethyl-4H-thiochromen-4-one and P₂S₅ reacts with aromatic amines, hydrazine hydrate, phenylhydrazine, and hydroxylamine at the C(4) atom of the chromene ring to give the corresponding anils, azine, hydrazones, and oxime of thiochromone. 2-Trifluoromethyl-4H-thiochromen-4-one is oxidized by hydrogen peroxide in AcOH into 4-oxo-2-trifluoromethyl-4H-thiochromene 1,1-dioxide and reduced by NaBH₄ to 2-trifluoromethyl-4H-thiochromen-4-ol or cis-2-(trifluoromethyl)thiochroman-4-ol. When treated with hydrazine hydrate, thiochromen-4-one gives 3(5)-(2-mercaptophenyl)-5(3)-trifluoromethylpyrazole. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 504–509, March, 2006.     

Reactivity of FeVO4 towards MgMoO4 in the solid-state

A compound of the formula Fe₃Mg₂Mo₂V₃O₂₀ has been obtained as a result of a reaction between FeVO₄ and MgMoO₄ taken at a molar ratio of 3:2. This compound crystallises in the monoclinic system and its unit cell parameters are the following: a=0.6971 nm, b=0.9055 nm,c=1.2542 nm, g=102.00°, Z=2. This revised version was published online in July 2006 with corrections to the Cover Date.     

UCr4C4 with filled MoNi4 type structure

The title compound was prepared by arc melting coldpressed pellets of the elemental components with subsequent annealing at both 800°C or 1100°C. UCr₄C₄ crystallizes tetragonal, space group I4/m,a=0.79363 (4) nm,c=0.30754 (3) nm,V=0.19370 nm³ withZ=2 formula units per cell. The structure was determined from single-crystal X-ray data and refined to a residual ofR=0.027 for 16 variable parameters and 279 structure factors. The positions of the metal atoms correspond to those of the MoNi₄ type structure. The carbon atoms occupy octahedral voids formed by four chromium and two adjacent uranium atoms. Chemical bonding in UCr₄C₄ and in other interstitial compounds is briefly discussed. The average valence electron number of the metal atoms is usually greater for the unfilled (host) structure than for the corresponding filled structure.Dedicated to Prof. Dr.Kurt Komarek and to Prof. Dr.Adolf Neckel on the occasion of their 60th birthdays.     

On Aliovalent Substitution on the Li Site in LiMPO4: an ­X‐ray Diffraction Study of the Systems LiMPO4–M1.5PO4 (= LixM1.5–x/2PO4; M = Ni,Co, Fe,Mn)

In this paper we report on the possibility of Li substitution by M²⁺ to various high degrees in LiMPO₄ olivine‐type compounds (M = Ni, Co, Fe, Mn), depending on the kind of transition metal M. The experimental studies were carried through by reacting stoichiometric amounts of LiM^IIPO₄ and M^II_1.5PO₄ (= M^II₃(PO₄)₂) to form compounds of composition Li_xM^II_1.5–x/2PO₄ (0 ≤ x ≤ 1). A complete solid solution over the whole range of x was found for M = Ni (together with a second order structural transition from orthorhombic to monoclinic for decreasing x), whereas far smaller degrees of dopability of the Li site were found for LiCoPO₄ and LiFePO₄ (up to compositions of approx. (Li_0.8Co_0.1)CoPO₄ and approx. (Li_0.9Fe_0.05)FeO₄. In addition, the nearly stoichiometric monoclinically distorted olivine‐type compounds with compositions (Li_0.42–0.47Co_0.29–0.265)CoPO₄ and (Li_0.14–0.16Fe_0.43–0.42)FePO₄ could be identified and are described in this article.     

Synthese und Kristallstruktur zweier Formen von Ammoniummonomolybdat (NH4)2MoO4

Synthesis and Structure of Two Forms of Ammonium Monomolybdate (NH₄)₂MoO₄ Ammonium monomolybdate (NH₄)₂MoO₄ exists in two different polymorphic forms which differ in their lattice constants and in the arrangement of the ammonium cations relative to the molybdate anions. The ammonium molybdates (NH₄)₂MoO₄(mS60)¹⁾ and (NH₄)₂MoO₄(mP60)²⁾ are synthesized by the reaction of ammonia and (NH₄)₆[Mo₇O₂₄] · 4 H₂O. (NH₄)₂MoO₄(mS60) crystallizes isostructural to the potassium compound in space group C2/m (Nr. 12) and lattice constants a = 1263.6(3), b = 652.2(1) pm, c = 776.4(2) pm and β = 117.36(1)° (V = 568.3(2) · 10⁶ pm³) containig four formula units per unit cell (R = 0.0250). (NH₄)₂MoO₄(mP60) crystallizes monoclinic in space group P2₁/n (Nr. 14) and lattice constants a = 622.8(2), b = 777.0(1) pm, c = 1118.8(4) pm and β = 98.09(2)° (V = 536.0(3) · 10⁶ pm³) (R = 0.0205). The different arrangements of the polyhedra within the unit cell is caused by hydrogen bridges. A transition point was not yet determined.     

A Convenient Route for the Synthesis of 4-Aryl- and 4-Aminopyrimidines

Summary. A series of ureidopropenenitriles were synthesised by Knoevenagel condensation of ArCOCH₂CN and HC(OEt)₃ in presence of ureas in a one pot reaction. These ureidopropenenitriles were cyclised to 4-aryl-5-cyano-3-substituted pyrimidines (in acid) or to 4-amino-5-benzoylpyrimidines (in base) in 60–70% yields. The amine pyrimidine derivatives were further converted to substituted uracils by hydrolysis with isopentyl nitrite in DMF. Alkylation of uracils furnished 1,3-dimethyluracil derivatives with DMS in alkali. All new compounds were characterised by spectral and analytical methods.     

A Novel 3D Framework Coordination Polymer based on Succinato bridged Helical Chains Connected by 4, 4' ‐ Bipyridine: [Cu(bpy)(H2O)2(C4H4O4)]?2H2O

Blue needle—shaped crystals of [Cu(bpy)(H₂O)₂(C₄H₄O₄)]· 2H₂O were obtained by slow evaporation of a methanolic aqueous solution containing a fresh Cu(C₄H₄O₄)· 2H₂O precipitate, 4, 4′—bipyridine, and ammonia. Within the complex, the six—coordinated Cu atoms are linked by bis—monodentate gauche succinate anions into chains propagating helically around the [001] axis. The chains are interconnected by 4, 4′—bipyridine ligands into a 3D framework with the crystal H₂O molecules located in the channels along the [100], [010] and [110] directions. The Cu²⁺ ions are in distorted octahedral coordination of two nitrogen and four oxygen atoms (equatorial bonds: Cu—N 1.986(5), 2.015(5)Å; Cu—O 1.950(6), 1.954(6)Å; axial bonds Cu—O: 2.524(9), 2.539(8)Å). Furthermore, the thermal and magnetic behavior of the compound will be discussed. Crystal data: hexagonal, P6₁ (no. 169), a = 11.066(2)Å, c = 24.965(5)Å, V = 2647.5(8)ų, Z = 6, R = 0.0528 and wR₂ = 0.1103 for 1426 observed reflections (F_o² > 2σ(F_o²)) out of 2170 unique reflections.     

Syntheses and structural characterizations of Fe4S4 cubane-like cluster compounds containing cycloalkylthiolate ligands

In a reaction system consisting of FeCl₂, tetrathiometallate and cycloalkylthiolate, two Fe₄S₄ cubanelike cluster compounds were obtained with the following crystallographic data: (PhCH₂NMe₃)₂ [ Fe₄S₄ (SC₅H₉)₄] (I), monoclinic space groupP2₁/c,a = 1.632 7(4),b=1.122 9(3),c = 2. 802 5(10) nm, β= 94.63(2)°, Z=4, andR= 0.074; (Et₄N)₂[F₄S4(SC₆H_lI)₄] (II), tetragod space group ,a = l.167 05(9),b = 1.167 06(2),c = 2.063 26(5) nm,Z = 2, D_obs = 1. 28 g/cm³, andR = 0. 078. The participation of cycloalkylthiolate ligand does not obviously arouse the change of the Fe₄S₄ core structure. Meanwhile, the influence of the cation on the structural symmetry of the Fe₄S₄ cluster dianion is also discussed. Project supported by the National Natural Science Foundation of China and the Climbing Program Foundation of China.     

Beiträge zur Chemie des Phosphors. 236. Über einige physikalische und chemische Eigenschaften von Diphosphan(4)

Contributions to the Chemistry of Phosphorus. 236. On Several Physical and Chemical Properties of Diphosphane(4) The density of diphosphane(4) has been measured between ?78°C and +18°C and the value d₄²⁰ = 1.014 · 0.002 extrapolated. The refractive index of P₂H₄ was determined to be n²⁰ = 1.66 ± 0.01. The surface tension at 0°C and ?50°C was measured to be σ = 34 and 42 dyn · cm^?1, respectively. In the UV absorption spectrum, gaseous P₂H₄ exhibits a broad absorption band at λ_max = 2 220 Å, in n-hexane solution, this band is shifted somewhat to shorter wave-lengths. The molar extinction coefficient was determined to be ? ≈? 900 1 · mol^?1 · cm^?1. As a result of photolytic decomposition, absorptions for PH₃ and more phosphorus-rich hydrides also occur. The solubility behavior of P₂H₄ in various organic solvents and the stabilities of the resultant solutions have been investigated. At 0°C, the solubility of diphosphane(4) in water was found to be ± 035 ± 0.003 g P₂H₄/100 g solution and that of water in diphosphane(4) to be 43.2 ± 1.6 g H₂O/100 g solution. The system diphosphane(4)/methanol also exhibits a miscibility anomaly. The IR spectra of liquid P₂H₄ and of its solutions in various solvents revealed, in accord with the results of nuclear magnetic resonance spectroscopy [7], that diphosphane(4) is practically not associated. Weak interactions through hydrogen bridging bonds occur with pyridine and methanol in which P₂H₄ serves as the proton donor and, in the latter case, also as proton acceptor. For the thermolysis of diphosphane(4), it has been found that the primary step comprises a disproportionation with inter-molecular elimination of PH₃ and formation of triphosphane(5). With further progress of the thermolysis, in dependence on the reaction conditions, mixtures of various phosphanes of differing composition are formed. Photolysis gives rise to phosphane mixtures having similar compositions. With aqueous silver salt and iodine solutions, diphosphane(4) reacts as a reducing agent; with sodium hydroxide solution, it reacts by a slow disproportionation as well as by formation and degradation of the subsequently formed polyphosphides. On reaction with triphenylmethyl, triphenylmethane and a yellow solid of varying composition are formed. The reaction of diazomethane with diphosphane(4) leads to the preferential insertion of the carbene in the P? P bond and formation of methylenebis(phosphane).     

4-Phosphoranylidene-5(4H)-oxazolones — A novel synthesis and properties

Summary 4-Phosphoranylidene-5(4H)-oxazolones (2), a hardly known class of phosphorus ylides, were readily prepared from 4-unsubstituted-5-(4H)-oxazolones (1) by treatment with Ph₃P-Br₂, Bu₃P-Br₂, Ph₃P-CCl₄, or Ph₃P-CBr₄ adducts in the presence of triethylamine in CH₂Cl₂ at room temperature in a novel, efficient one-pot procedure. The spectroscopic properties of the ylides are reported and discussed.

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4-Phosphoranyliden-5(4H)-oxazolone — Eine neue Synthese und Eigenschaften

Zusammenfassung 4-Phosphoranyliden-5(4H)-oxazolone, eine sehr wenig bekannte Gruppe der Phosphor-ylide, wurden auf einfache Weise nach einem neuen Eintopfverfahren mit guten Ausbeuten hergestellt. Als Ausgangsverbindungen wurden 4-unsubtituierte-5-(4H)-Oxazolone (1) eingesetzt, die unter der Einwirkung von Addukten wie Ph₃P-Br₂, Bu₃P-Br₂, Ph₃P-CCl₄ oder Ph₃P-CBr₄ in Anwesenheit von Triethylamin in CH₂Cl₂ bei Zimmertemperatur die Titelverbindungen liefern. Die spektroskopischen Eigenschaften der Ylide werden berichtet und diskutiert.

     

Synthesis,Crystal Structure and Reducibility of K2NiF4 Type Oxides Sm2—xSrxCuO4

K2NiF4 type compounds Sm2-xSrxCuO4(0≤x≤1.2)were prepared.Rietveld refinement of powder diffraction data shows that the crystal system of these compounds belongs to T′ type tetragonal structure of space group I4/mmm,and the addition of Sr causes a dramatic shift of the O(I) ions along the c axis from Sm(Sr) toward Cu while scarcely affecting the Cu-O(Ⅱ）bond in basal CuO4 phane.From XRD data,it can be seen that when 0.0≤x≤0.6,Sm2-xSrxCuO4 belongs to a singlephase K2NiF4 type structure,while at x≥0.7,both the free SrO phase and the CuO phase exist in these compounds.From the results of XPS and rietveld refinement,it can be seen that after replacing Sm^3 with Sr^2 of lower valence,the valence of Cu and Sm does not change apparently,and thus some defect must be formed at the oxygen ion positions and/or position A on A2BO4 to keep charge balance and to stabilize the structure.     

The Henicosaphosphide Iodides of Potassium and Rubidium,K4P21I and Rb4P21I

The novel ternary polyphosphides M₄P₂₁I (M = K, Rb) have been synthesized from the elements in single crystalline form, representing further examples for the formation of mixed crystals between simple salts and binary phosphides. They form as ruby‐red platelets and dark‐red prisms, respectively, and are only slightly sensitive to moisture and oxygen. The compounds are isotypic (Ccmm (no 63); Z = 4; oP104; K₄P₂₁I: a = 12.853Å; b = 21.795Å; c = 9.748Å; 1168 hkl, R = 0.033; Rb₄P₂₁I: a = 13.281Å; b = 21.868Å; c = 9.771Å; 777 hkl, R = 0.053) and feature corrugated 2D networks formed from two different types of polymerized P₇ units. The networks form large cavities filled by M⁺ and I^‐ ions. Zigzag chains of condensed trigonal M₆ prisms, centered by the I^‐ anions, separate the polyphosphide nets. The mean homoatomic P‐P bond length (d = 2.216Å) corresponds to a P‐P single bond. However, the individual P‐P distances vary with position and function (2.126 ‐ 2.247Å) and these are compared with those of the isolated P₂₁^‐3 anion.     

Polymorphic crystals of oxacalix[4]arene with 1,3‐alternate conformations of S4 and C2 symmetry

Calix[4]arene and oxacalix[4]arene derivatives have eight possible conformations in the up and down directions of their four aromatic rings from the mean plane of a bridged central ring, the conformations of which determine the functionality of the host frameworks. Despite being a known compound for five decades, oxacalix[4]arene, C₂₄H₁₆O₄, has not been characterized previously by crystallographic methods. It crystallizes from hexane/CH₂Cl₂ solution to give two polymorphs, i.e. prismatic and block‐shaped crystals as twisted 1,3‐alternate structures with S₄ and C₂ symmetry, respectively. These were previously suggested as the prefered stable conformations by density functional theory (DFT) calculations.     

Synthese der Silatetraphospholane (tBuP)4SiMe2, (tBuP)4SiCl2 und (tBuP)4Si(Cl)SiCl3 Molekül- und Kristallstruktur von (tBuP)4SiCl2

Synthesis of the Silatetraphospholanes (tBuP)₄SiMe₂, (tBuP)₄SiCl₂, and (tBuP)₄Si(Cl)SiCl₃ Molecular and Crystal Structure of (tBuP)₄SiCl₂ The reaction of the diphosphide K₂[(tBuP)₄] 7 with the halogenosilanes Me₂SiCl₂, SiCl₄ or Si₂Cl₆ in a molar ratio of 1:1 leads via a [4 + 1]-cyclocondensation reaction to the silatetraphospholanes (tBuP)₄SiMe₂ 1,1-dimethyl-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 1 , (tBuP)₄SiCl₂, 1,1-dichloro-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 2 , and (tBuP)₄Si(Cl)SiCl₃, 1-chloro-1-trichlorsilyl-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 3 , respectively, with the 5-membered P₄Si ring system. The reaction leading to 1 is accompanied with the formation of the by-product Me₂(Cl)-Si–(tBuP)₄–Si(Cl)Me₂ 1a (5:1), which has a chain structure. On warming to 100°C 1a decomposes to 1 and Me₂SiCl₂. The compounds 2 and 3 do not react further with an excess of 7 due to strong steric shielding of the ring Si atoms by the t-butyl groups. 1, 2 and 3 could be obtained in a pure form and characterized NMR spectroscopically; 2 was also characterized by a single crystal structure analysis. 1a was identified by NMR spectroscopy only.     

Dianionic Mononuclear Cyclo‐P4 Complexes of Zero‐Valent Molybdenum: Coordination of the Cyclo‐P4 Dianion in the Absence of Intramolecular Charge Transfer

Relative to other cyclic poly‐phosphorus species (that is, cyclo‐P_n), the planar cyclo‐P₄ group is unique in its requirement of two additional electrons to achieve aromaticity. These electrons are supplied from one or more metal centers. However, the degree of charge transfer is dependent on the nature of the metal fragment. Unique examples of dianionic mononuclear η⁴‐P₄ complexes are presented that can be viewed as the simple coordination of the [cyclo‐P₄]^2? dianion to a neutral metal fragment. Treatment of the neutral, molybdenum cyclo‐P₄ complexes Mo(η⁴‐P₄)I₂(CO)(CNAr^Dipp2)₂ and Mo(η⁴‐P₄)(CO)₂(CNAr^Dipp2)₂ with KC₈ produces the dianionic, three‐legged piano stool complexes, [Mo(η⁴‐P₄)(CO)(CNAr^Dipp2)₂]^2? and [Mo(η⁴‐P₄)(CO)₂(CNAr^Dipp2)]^2?, respectively. Structural, spectroscopic, and computational studies reveal a similarity to the classic η⁶‐benzene complex (η⁶‐C₆H₆)Mo(CO)₃ regarding the metal‐center valence state and electronic population of the planar‐cyclic ligand π system.     

4-Nitro and 4-chloro pyridine-N-oxide complexes of lanthanide perchlorates

Adducts of lanthanide perchlorates with 4-nitro and 4-chloro pyridine-Noxides (4-NPNO and 4-CPNO respectively) have been synthesised for the first time and characterised by analysis, electrolytic conductance, infrared, proton-NMR and electronic spectral data. The complexes are of the compositions Ln₂(NPNO)₁₅ (ClO₄)₆ (Ln = La, Pr, Nd and Gd), Tb(NPNO), (C1O₄)₆), Ln₂(NPNO)₁₃ (C1O₄)₆) (Ln = Dy, Ho, and Yb); Ln (CPNO)₈ (C10₄)₃) (Ln = La, Pr, Nd, Tb, Dy, Ho and Yb) and Ln(CPNO), (C1O₄)₃) (Ln = Sm and Gd). Conductivity and IR data provide evidence for the non-coordinated nature of the perchlorate groups. IR and NMR spectra suggest coordinationvia the oxygen of the N-oxide group. Electronic spectral shapes of the Nd⁺³ and Ho⁺³ complexes are interpreted in terms of eight-and seven-coordinate environments in the case of 4-NPNO complexes and eight-coordination in the case of 4-CPNO complexes. IR data indicate bridged structure in NPNO complexes of lanthanides other than Tb.     

Neues vom P4Se4

New Results on P₄Se₄ Preparation of P₄Se₄ from the elements yields always the β-modification of P₄Se₄. α-P₄Se₄ is obtained only with selenium deficient samples. However, it is also observed, when P₄Se₃ is annealed and then extracted with CS₂. The insoluble part has the X-ray pattern of α-P₄Se₄. A reversible α-β transition is not observed. MAS-³¹P-NMR investigations on solid P₄Se₄ by Eckert et al. [2] reveal P₂Se_4/2 building units, which are, in view of our results, not dimer but linked to a polymeric network. Well-crystallized samples of β-P₄Se₄ are obtained only at measuring temperatures above 573 K. The structure is of monoclinic symmetry with the space group P2₁/n (a = 114.9, b = 729.0, c = 1211.0 pm, β = 120.80°). The reaction of α-P₄Se₃I₂ with bis-(trimethyltin)selenide in CS₂ at low temperature yields molecular α-P₄Se₄, which can be detected in solution by ³¹P-NMR spectroscopy. α-P₄Se₄ has D_2d-symmetry like α-P₄S₄. It polymerizes at higher temperature. α-P₄Se₃I(SeSnMe₃) and α-P₄Se₃(SeSnMe₃)₂ were observed in the course of this reaction, too. The analogous reaction of α-P₄Se₃I₂ with bis-(trimethyltin)sulfide leads to comparable results.     

Pulse-radiolysis studies on 4-pyridinemethanol and 4-pyridinecarboxaldehyde in aqueous solutions: dimer radical anion formation in the case of 4-pyridinecarboxaldehyde

Reactions of e _aq ^– , H atom and OH radicals with 4-pyridinemethanol (4-PM) and 4-pyridinecarboxaldehyde (4-PCA) have been studied at various pH values using the pulse radiolysis technique. Reaction of e _aq ^– with 4-PM and 4-PCA leads to the formation of pyridinyl and ketyl radicals of 4-PM and 4-PCA, respectively. Ketyl radicals formed from 4-PCA react with the parent molecule to give a dimeric radical species. At pH 7, the equilibrium constant for the dimer formation was determined to be 13 500 M^-1. At pH 13 also dimer radical formation was observed. Reaction of e _aq ^– with 4-PM was found to give highly reducing pyridinyl radicals. Reaction of OH radicals with 4-PM gives a mixture of species,viz., OH adducts and radicals formed by H-atom abstraction from the –CH₂OH moiety. Radicals formed by H-atom abstraction reaction from 4-PM were found to be reducing in nature. O^– radicals were found to react with 4-PM exclusively by H-abstraction pathway.