Crystal growth, defect structure and magnetism of new Li3N-derived lithium nitridocobaltates

New nitridocobaltates Li(3-x-y)Co(x)N are revealed to contain significant Li(+) vacancies (y approximately 0.45) disordered within lithium-nitrogen planes and to exist as partially delocalised spin systems as a result of increased covalency through infinite -N-(Li,Co)-N- chains.     

Michael addition-electrophilic quenching chemistry of maleimides using dialkylzinc reagents

Michael addition-electrophilic quench reactions of N-alkyl maleimides are possible using dialkylzincs in combination with a copper catalyst and a phosphoramidite ligand. Up to 55% ee has been achieved for one example (E = H) using a chiral ligand.     

Analyticity properties and a convergent expansion for the inverse correlation length of the low-temperatured-dimensional Ising model

We show that the inverse correlation lengthm(z) of the truncated spin-spin correlation function of theZ ^d Ising model with + or — boundary conditions admits the representationm(z) = –(4d–4)ln z(1–_d1) + r(z) for smallz=e ^–, i.e., large inverse temperatures is ad-dependent analytic function atz = 0, already known in closed form ford = 1 and 2; ford = 3 b_n can be computed explicitly from a finite number of the Z^d limits of z = 0 Taylor series coefficients of the finite lattice correlation function at a finite number of points ofZ ^d.     

New mixed alkaline-earth nitridomolybdate(VI) nitride oxides with anion-ordered sub-structures

New molybdenum(VI) nitride oxides were synthesised by the reaction of strontium nitride and calcium nitride with molybdenum foil at high temperature in sealed stainless steel crucibles. The reactions yielded single crystalline products determined by X-ray diffraction to form complex structures in the triclinic space group P1(no. 2). The mixed alkaline earth compounds with composition Ca38Sr13[MoN4]12N8O3 and Ca36Sr15[MoN4]12N8O3 are isostructural with the quaternary nitride oxides Sr51[WN4]12N8O3 and Ca51[WN4]12N8O3. The structures contain isolated [MoN4](6-) tetrahedra, partially disordered alkaline earth cations and an ordered sublattice of N(3-) and O(2-) anions. Oxide anions are coordinated only to the alkaline earth metals. The title compounds are the first mixed alkaline earth metal nitride oxides.     

Mechanistic insight into the lanthanide(III) salt catalysed monoacylation of symmetrical diols from structural models

Model studies are presented that suggest the mechanism of the lanthanide(III) salt catalysed mono acylation of symmetrical diols proceeds via chelation of the diol and the anhydride to the lanthanide salt, followed by an 'intramolecular' acyl transfer.     

Oxalate-bridged complexes of dimolybdenum and ditungsten supported by pivalate ligands: ((t)BuCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)C(t)Bu)(3). Correlation of the solid-state, molecular, and electronic structures with Raman, resonance Raman, and electronic spectral data

The compounds ((t)BuCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)C(t)Bu)(3) (M(4)OXA), where M = Mo or W, are shown by analysis of powder X-ray diffraction data to have extended lattice structures wherein oxygen atoms from the oxalate and pivalate ligands of one M(4)OXA molecule are linked to metal atoms of neighboring molecules. Raman, resonance Raman, electronic absorption (2-325 K in 2-MeTHF), and emission spectra are reported, together with corresponding spectra of the mu-O(2)(13)C(13)CO(2) isotopomers. To aid in the assignment, the Raman spectra of K(2)C(2)O(4).H(2)O and K(2)(13)C(2)O(4).H(2)O have also been recorded. The visible region of the electronic spectra is dominated by intense, fully allowed MLCT transitions, M(2) delta to oxalate pi*, which show pronounced thermochromism and extensive vibronic progressions associated with the oxalate ligand at low temperatures. With excitation into these charge-transfer bands, strong resonance enhancement is seen for Raman bands assigned to the oxalate nu(1)(a(g)) and, to a lesser extent, nu(2)(a(g)) modes. Electronic structure calculations for the model compounds (HCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)CH)(3), employing density functional theory (gradient corrected and time-dependent) with the Gaussian 98 and ADF 2000 packages, predict the planar oxalate D(2h) configuration to be favored, which maximizes M(2) delta to oxalate pi* back-bonding, and indicate low barriers (<8 kcal mol(-1)) to rotation about the oxalate C-C bonds.     

Liquid chromatographic determination of nystatin in pharmaceutical preparations

A rapid, reversed-phase liquid chromatographic method was developed for the assay of nystatin in the bulk drug and a variety of dosage forms. Analysis was performed on a Symmetry C18 reversed-phase column using a mobile phase of methanol-water-dimethylformamide (DMF; 55 + 30 + 15, v/v/v), with detection by UV at 305 nm. Quantitation is based on the sum of the peak areas of the 2 major isomers of nystatin. The linearity of the assay was determined for a concentration range of 0.05 to 0.2 mg/mL (correlation coefficient > 0.999). Accuracies and precision showed good reproducibility.     

Cooperative diastereoselectivity of palladium- and platinum-promoted intramolecular [4 + 2] Diels-Alder cycloaddition reactions of 3,4-dimethyl-1-phenylphosphole

The complexes [(DMPP)2M(CH3CN2)]X2 (DMPP = 3,4-dimethyl-1-phenylphosphole; M = Pd, Pt; X = BF4-, NO3-, ClO4-) react with 2 equiv of the dienophiles N,N-dimethylacrylamide (DMAA), 2-vinylpyridine (VyPy), and diphenylvinylphosphine (DPVP) to form bis-[4 + 2] Diels-Alder cycloaddition products. The [M(DMPP)2(DMAA)2]2+ and [M(DMPP)2(VyPy)2]2+ complexes form exclusively as the cis-geometric isomers, whereas for [M(DMPP)2(DPVP)2]2+, both cis- and trans-geometric isomers are formed. The two Diels-Alder cycloadditions occur sequentially, and the absolute configuration of the first reaction influences the absolute configuration of the second. In all cases, recemic mixtures of the (R,R) and (S,S) diastereomers are formed; none of the meso (R,S) diastereomer is observed. New complexes were characterized by elemental analyses, physical properties, infrared spectroscopy, 1H, 1H(31P), 13C(1H), and 31P(1H) NMR spectroscopy, and, in most cases, X-ray crystallography.     

The thermal decomposition of dicyclopentadienyldimethyltitanium(IV)

Thermal decomposition of (C₅H₅)₂Ti(CH₃)₂ in alkane or benzene solution yields primarily methane, with only traces of ethane. Methane is produced by hydrogen abstraction from both the cyclopentadienyl rings and from the methyl groups, but never from the alkanes or benzene. A scheme of decomposition is suggested involving two paths, each with a two stage formation of methanes. A very much slower ethane formation competes with the second stage. Strong evidence exists for slow hydrogen exchange between the eyelopentadienyl rings and the methyl groups prior to significant production of ethane. Decomposition in diethyl ether yields methane, much of it arising through hydrogen abstraction from the ether. Decomposition in CCl₄ and C₂Cl₄ yields mainly methane but also some methyl chloride and ethane. Both diethyl ether and C₂Cl₄ almost block methane formation through ring attack.