Peak effect studies in single crystals CeRu2 and 2H-NbS2

We have studied the peak effect (PE) phenomenon in single crystals of weakly pinned superconductors CeRu₂ and 2H-NbS₂. 2H-NbS₂ is iso-structural and iso-electronic to 2H-NbSe₂, whose similarity with CeRu₂ as regards the PE representing the order-to-disorder transformation of the flux line lattice was claimed some time ago. We report on the step change in equilibrium magnetization across the peak effect in CeRu₂. We also present the vortex phase diagram of 2H-NbS₂ obtained from the magnetization data, and compare the PE phenomenon in 2H-NbS₂ and 2H-NbSe₂.     

Heterometallic palladium-copper and palladium-nickel complexes with pivalate bridges

Reactions of (α-Pic)₂Pd(OOCCMe₃)₂ (I) with dinuclear copper pivalate dihydrate and polymeric nickel bispivalate afforded the complexes (α-Pic)₂Pd(μ-OOCCMe₃)₂Cu₂(μ-OOCCMe₃)₄ (II) and Pd(μ- OOCCMe₃)₄Ni(α-Pic) (III), respectively, which were structurally characterized. The lantern dimers in complex II show no Cu···Cu bonds (Cu···Cu, 2.671(3) Å) and are united to form chains through the axial bridging pivalate groups inherited from palladium monomer I. In contrast, complex III features heterometallic palladium- nickel lanterns in which the Ni atom has an axial α-picoline ligand, while the Pd atom has no axial ligand; instead, a short Pd–Ni bond is formed (2.4976(3) Å). For triplet-state complex III and its zinc analog Pd(μ-OOCCMe₃)₄Zn(α-Pic) (IV), quantum chemical calculations and topological analysis of the electron density were performed.     

Rhenium Tris(pyrazolyl)Borate Oxothiolate Complexes: Syntheses and Structures

Russian Journal of Coordination Chemistry - The rhenium complexes TpReOCl(StBu) (I), TpReO(StBu)2 (II), and TpReO(SnC3H7)2 (III) are synthesized using two methods by analogy to the known thiophenyl...     

Synthesis,molecular structures and PMR spectra of heteronuclear niobocene derivatives containing a niobium-tin bond

Treatment of niobocene carbonylhydride, Cp₂Nb(CO)H (I), with Ph_nSnCl_4?n and Et₂SnCl₂ in THF in the presence of Et₃N leads to the respective heteronuclear complexes Cp₂Nb(CO)SnR_nCl_3?n (R = Ph, n = 3 ÷ 1 (II–IV), R = Et, n = 2 (V)). Treatment of II with HCl in ether gives Cp₂Nb(CO)SnCl₃ (VI). Complex VI and its analog (MeC₅H₄)₂Nb(CO)SnCl₃ (VIII) were prepared by an alternative synthesis using direct reaction of I or (MeC₅H₄)₂Nb(CO)H with an equimolar quantity of SnCl₄ in THF in the presence of Et₃N. Complex VI is also generated by insertion of SnCl₂ into the NbCl bond in Cp₂Nb(CO)Cl (VII). X-Ray analysis of complexes II and VIII was performed: for II, space group P2₁/n, a = 10.1021(21), b = 17.4633(32), c= 14.2473(29) Å, β = 95.578(16)°, Z = 4; for VIII, space group. P2₁/n, a= 8.9369(15), b = 13.3589(12), c = 13.9292(20) Å, β = 99.490(14)°, Z = 4. The NbSn bond in VIII (2.764(9) Å) is shorter than that in II (2.825(2) Å). In both cases the NbSn bond is significantly shorter than the sum of Nb and Sn covalent radii (1.66 + 1.40 = 3.06 Å). It is probably partly multiple in character owing to an additional interaction of the lone electron pair of the Nb^III ion (d² configuration) with the antibonding Sn orbitals. The PMR spectra of II–VI exhibit two satellites of the singlet of C₅H₅ protons because of HSn¹¹⁷ and HSn¹¹⁹ spin-spin coupling (SSC). The SSC constant correlates with the number of electronegative chlorine atoms on the Sn atom.     

Unexpected stabilization of the heterocyclic form of oxidized dithizone: Synthesis and molecular structures of chromium and tungsten 5-mercapto-2,3-diphenyltetrazolium pentacarbonyls

New chromium and tungsten pentacarbonyl complexes with 5-mercapto-2,3-diphenyltetrazole coordinated through the sulfur atom (Cr-S, 2.4655(7) Å; W-S, 2.5755(13) Å) were synthesized and structurally characterized.     

The importance of steric factors in the formation and structures of heterobinuclear wedge-like sandwich derivatives. The crystal and molecular structure of niobocenehydrido-(σ,π-cyclopentadienylidene)iron(dicarbonyl)(Nb—fe)

CpFe(CO)₂CH₃ reacts with Cp₂NbH made from Cp₂NbBH₄ and Et₃N to give Cp₂$\text{NbH(μ-C}{}_5\text{H}{}_4\text{)F}$e (III). As shown by X-ray diffraction, III contains the Cp₂NbH sandwich fragment with a 46.8° angle between the rings linked with the dicarbonyliron moiety by the NbFe bond (2.968 Å), observed for the first time, and a cyclopentadienyl bridge C₅H₄, involving the NbC. σ-bond (2.189 Å) and C₅H₄Fe π-bond (2.085 Å). A probable reaction scheme leading to III and general patterns of formation of other heterobinuclear derivatives of sandwich complexes Cp₂MLM′(L′)n are discussed. The importance of steric effects due to nonbonded interligand interactions between the M′(L′)n fragment and the sandwich system is emphasized. Increase of steric strain in the binuclear system facilitates its unusual transformations.     

Direct one-index transformations in multiconfiguration response calculations

The evaluation of gradient vectors of a general operator with one-index, double-one-index, or higher-order one-index transformed integrals is a key operation in multiconfiguration response theory calculations. We describe an integral-driven direct algorithm that carries out this operation efficiently without pretransforming the integrals. The use of this algorithm leads to a considerable reduction in disk space and timing. © 1994 by John Wiley & Sons, Inc.