Commensurability oscillations in NdBa2Cu3Oy single crystals

Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa₂ Cu₃ O_y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure.     

Determining a 'safe' high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.     

Dicarbonylcyclopentadienyltellurophenyliron complexes as ligands

The reaction of CpFe(CO)₂TePh (I) with ferricinium hexafluorophosphate as an oxidant affords ionic complex {[CpFe(CO)₂]₂(μ-TePh)}⁺PF ₆ ^? (II) with the simultaneous formation of diphenylditellurium. The decarbonylation of compound II by Me₃NO followed by the addition of complex I affords trinuclear complex {[CpFe(CO)₂(μ-TePh)]₂Fe(CO)Cp}PF₆ (III). The corresponding tetrafluoroborate (IV) is synthesized similarly. The heating of compound I with PPh₃ gives CpFe(CO)(PPh₃)TePh (V) that reacts with ionic complex [CpMn(CO)₂(NO)]PF₆ (VI) to form binuclear heterometallic ionic complex [CpFe(CO)(PPh₃)(μ-TePh)Mn(CO)(NO)Cp]PF₆ (VII). A similar reaction of Cp′Fe(CO)₂TePh (Cp′ is methylcyclopentadienyl) with compound VI affords heterometallic [Cp′Fe(CO)₂(μ-TePh)Mn(CO)(NO)Cp]PF₆ (VIII). The structures of compounds II, IV, VII, and VIII are determined by X-ray diffraction analysis (CIF files CCDC 963285, 963286, 963288, and 963289, respectively).     

Phenyltellurolate-bridged heterometallic complexes combining rhenium tricarbonyl with (dicarbonyl)(cyclopentadienyl)iron or bis(diphenylphosphino)ethaneplatinum

A reaction of CpFe(CO)₂TePh with Re(CO)₃(THF)₂Cl in THF gave the heterometallic complex [CpFe(CO)₂(μ-TePh)]₂Re(CO)₃Cl (I). Either iron atom in complex I is linked to rhenium by only one Phenyltellurolate bridge. When treated with (Dppe)Pt(TePh)₂, complex I underwent transmetalation by elimination of two CpFe(CO)₂TePh molecules followed by the formation of the heterometallic chelate complex (Dppe)Pt(μ-TePh)₂Re(CO)₃Cl (II). Complex II was also obtained in an independent way from (Dppe)Pt(TePh)₂ and Re(CO)₃(THF)₂. Structures I and II (II · MePh and II · CDCl₃) were identified by X-ray diffraction (CIF file, CCDC nos. 981467, 981468, and 981469, respectively).     

Synthesis and molecular structures of heterometallic complexes [RC5H4Fe(CO)2]2 Sn(TePh)2 and their adducts with chromium and tungsten carbonyls or with trimethylplatinum iodide

Complexes [RC₅H₄Fe(CO)₂]₂Sn(TePh)₂ (R=H, Me) containing stable heterometallic Fe−Sn−Fe fragments with two phenyltellurium groups at the tin atom were synthesized from [RC₅H₄Fe(CO)₂]₂SnCl₂ (R=H, Me) and sodium phenyltelluride and their structures were established by X-ray analysis. Their chelates with tungsten tetracarbonyl, [RC₅H₄Fe(CO)₂]₂Sn(TePh)₂[W(CO)₄] (R=Me, H), and complexes with two Cr(CO)₅ fragments or dimeric trimethylplatinum iodide were synthesized and studied by X-ray analysis. Thermal decomposition of [RC₅H₄Fe(CO)₂]₂Sn(TePh)₂ complexes and their adducts with ML fragments (ML=W(CO)₄, 2 Cr(CO)₅, (Me₃PtI)₂) into inorganic tellurides of a preset mixed-metal—chalcogenide composition was studied by differential scanning calorimetry. The temperature of complete elimination of organic fragments from methylcyclopentadienyl complexes is about 100°C lower than in the case of cyclopentadienyl analogs. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1766–1772, September, 1999.     

Synthesis,structure and magnetic properties of a trinuclear π-cyclopentadienylniobium complex containing the formate,hydroxylic and oxygen bridges

The trinuclear complex [C₅H₅NbOOCH]₃ (OH)₂ (O)₂ was prepared by heating C₅H₅Nb(CO)₃PPh₃ with anhydrous HCOOH in xylene. The niobium atoms are located at the vertices of an almost regular triangle with short Nb?Nb distance equal to 3.14». The electronic configuration of niobium is d¹. Analysis of the magnetic properties and location of the niobium atoms indicated that they bind only by the formate, hydroxylic and oxygen bridges instead of by direct NbNb bonds.     

Heterometallic iron carbonyl chalcogenide clusters containing ruthenium,rhenium, manganese,and molybdenum

The reactions of Fe₂Se₂(CO)₆ (1b) with Ru(CO)₄(C₂H₄), Mn₂(CO)₁₀, or Np"Re(CO)₂THF gave the known cluster Fe₂RuSe₂(CO)₉ (4b) and new clusters (CO)₆Fe₂Se₂Mn₂(CO)₈ (5) and Cp"Re(CO)₂Se₂Fe₂(CO)₆ (6). By successive reactions of Mo(CO)₅THF with 1b and Fe₂Te₂(CO)₆, the new heterometallic heterochalcogenide cluster Fe₂(CO)₆(₃-Se)₂Mo(CO)₂(₃-Te)₂Fe₂(CO)₆ (8) was synthesized. The structures of 4b, 5, and 6 were determined by X-ray diffraction analysis.     

Synthesis and structure of the heterotrinuclear chromium-palladium clusters (RC5H4CrCl)2-(μ3S)(μ-SCMe3)2Pd(PPh3) with ferromagnetic exchange interactions over the CrSCr system

Reactions of (RC₅H₄)₂Cr₂(SCMe₃)₂S(I, R = H; II, R = Me) with (PPh₃)₂PdCl₂ in benzene at 20°C gives trinuclear complexes (RC₅H₄)₂Cr₂Cl₂(μ₃-S)(μ-SCMe₃)₂Pd(PPh₃)(III, R = H; IV, R = Me). The structure of IV as a monobenzene solvate is established by an X-ray analysis (black-green triclinic crystals space group P$\text{1}$ with a = 11.403(4), b = 14.933(5), c = 14.131(5) Å, α = 99.13(3), β = 112.72(3), γ = 95.65(3)°, V = 2201.6 Å, Z = 2; IV·C₆H₆). The structure was solved by direct methods and refined in an anisotropic approximation to R = 0.046, R_w = 0.058 for 7643 reflections with I ? 2σ(I). In the molecule of IV metal atoms are separated by non-bonding distances (Cr … Cr 4.079(I), Cr … Pd 3.230(I) and 3.380(I) Å) but linked by the bridging tridentate sulphur atom (CrS 2.339(2) and 2.329(2), PdS 2.327(2) Å), and two SCMe₃ groups between Pd and Cr (CrS 2.396(2) and 2.403(2), PdS 2.350(2) and 2.381(2) Å, Cr?Pd 85.14(6) and 89.92(6)°). The Cl atoms are transferred from Pd to Cr atoms (CrCl 2.308(2) Å) and being terminally coordinated are in trans-positions to each other (as well as η-CH₃C₅H₄ rings) with respect to the Cr₂Pd plane. Cr atoms in III and IV exhibit ferromagnetic exchange interactions over the Cr?Cr system (+2J = 28 and 11 cm^?1, respectively).