An unusual reaction of terramycin with methyl iodide

An unusual fragmentation reaction was observed when terramycin is treated with MeI in acetone at room temp. The reaction proceeds with quaternization, loss of trimethylamine, fission of bonds 4a,5 and 12,12a with formation of an aldehydo-lactone derived from rings B, C and D. Additionally some transformations of this lactone are described.     

Experimental measurement and reassignment of the indium 252.134 nm line with a scanning echelle monochromator

In a recent publication it was predicted that either or both the In 252.137 nm or Co 252.136 nm transitions were misassigned. An experimental evaluation of these transitions was made with a scanning echelle monochromator system. The In 252.137 nm transition has been reassigned at 252.134 nm and the Co 252.136 nm was verified.     

A binuclear tantalum(III) complex with a bridging carboxylato ligand

Ta₂Cl₆(SMe₂)₃ reacts with one equivalent of C₄H₉CO₂Li to give a complex with a bridging carboxylate ligand, Ta₂Cl₅(O₂CC₄H₉)(SMe₂)(THF)₂. The product was isolated in two crystalline forms, 1 and 2, from a THF/hexane and benzene/hexane solvent mixture, respectively. The following are the unit cell parameters, for 1: monoclinic (P2₁/n), a = 10.537(5) Å, b = 22.015(4) Å, c = 11.663(4) Å, β = 107.80(3)°, V = 2576(3) ų, and Z = 4; for 2: monoclinic (P2₁/c), a = 15.584(4) Å, b = 15.647(4) Å, c = 11.275(3) Å, β = 106.04(5)°, V = 2642(3) ų and Z = 4. The complex is a dimer with a distorted octahedra-sharing-an-edge geometry. The TaTa distances in 1 and 2 were 2.766(1) Å and 2.779(1) Å, respectively, which is somewhat longer than in previously reported Nb(III) and Ta(III) dinuclear compounds. Diamagnetism of the complex is shown by NMR. Fenske—Hall calculations, which correctly predict an electronic transition at about 16,000 cm^?1, indicate a double TaTa bond. The observed elongation of the metalmetal bond is attributed mainly to steric crowding. The complex is the first proven low-valent Ta species with a coordinated carboxylate ion.     

σ,π-acetylido complexes via P---C bond cleavage of phosphinoacetylenes: X-ray structure of Fe2(CO)6(CCPh)(PPh2)

Solutions of Co^II salts of organic acids in primary amines absorb molecular oxygen rapidly and irreversibly forming μ-dioxygen—cobalt complexes. Thermolysis leads to a homopolar cleavage of the OO bond with subsequent radical reactions involving ligand amine. After thermolysis the capacity of oxygen uptake is reestablished (catalysis).     

Metal complexes of schiff's base derived from salicoylhydrazine and biacetylmonoxime

Biacetylmonoxime-salicoylhydrazone (BMSH) complexes of the types [Hg(BMSH)Cl₂] and [M(BMSH-H)₂], where M = Cu(II), Co(II), Ni(III), Mn(II), Zn(II), Cd(II) and UO₂(VI), have been prepared and characterized by conventional chemical and physical measurements. The IR spectra show that the ligand usually coordinates via carbonyl oxygen (CO), azomethine nitrogen (CNl) and phenolic OH with replacement of hydrogen by metal ions but acts as a bidentate molecule coordinating through (CO) and (CNl) in the Hg(II) complex. The magnetic and spectral data of the Co(II) and Ni(II) complexes support octahedral stereochemistry, whilst tetragonally distorted octahedral geometry is suggested for the Cu(II) complex.     

Synthesis and electrochemistry of cis-dioxomolybdenum(VI) complexes with tridentate Schiff base ligands containing O,N and S donor atoms

The synthesis and characterization of a number of cis-dioxomolybdenum(VI) coordination complexes involving tridentate (ONS) ligands is described. The Schiff base ligands were obtained by condensation of 5-substituted salicylaldehydes with o-aminobenzenethiol or 2-aminoethanethiol. The chemical properties of these molybdenum complexes are compared with those having tridentate ligands with the ONO donor atom set. Cyclic voltammetry was used to obtain cathodic reduction potentials (E_pc) for the irreversible reduction of the Mo(VI) complexes. Although the reductions are irreversible, trends are observed in E_pc both within each series and when different series are compared. Cathodic reduction potentials for the four series examined span the range from ?1.53 to ?1.05 V versus NHE. There are three ligand features whose effect systematically alters the Mo(VI) cathodic reduction potentials. These include (1) the X-substituent on the salicylaldehyde portion of each ligand; (2) the degree of ligand delocalization; and (3) the substitution of a sulphur donor atom for an oxygen donor atom. Each of these effects is considered separately with regard to the Mo(VI) cathodic reduction potentials and then their cumulative effect is described.     

Synthesis and NMR spectra of 2,2,2-trideuterioethylarsine and 2,2,2-trideuterioethylcyclopentaarsine

Pentakis(2,2,2-trideuterioethyl)cyclopentaarsine (PDECA) was synthesized by the reaction of 2,2,2-trideuterioethylarsine with dibenzylmercury. Variable temperature NMR spectra in C₆D₆ are interpreted in terms of fast pseudorotation. NMR and mass spectra and synthesis of 2,2,2-trideuterioethylarsine are also described.     

Potentiometric determination of the stability constants of a model (Na + K)ATPase complex

Formation constants for the binary and ternary Mn(II)-nitrilotriacetic acid (NTA) and adenosine triphosphate (ATP) which model the action of (Na⁺ + K⁺) ATPase have been determined at 25°C and I = 150 mmole dm^-3 NaCl. The results are interpreted in terms of the known stabilities of the enzyme complexes and it is concluded that metal-ion chelation of ATP alone is not enough for hydrolysis to occur. A substantial stabilisation of the ternary complex occurs, possibly through bridging sodium ions.     

The crystal structure of magnesium arsenate,Mg8.5As3O16

Single crystals of magnesium arsenate have been grown from a PbOAs₂O₅ eutectic by flux crystallization of a ceramic preparation having an initial composition of 6MgO·As₂O₅. The crystals are rhombohedral, space group $\text{R}\text{3}\text{m}$, with hexagonal unit cell parameters a = 6.0278(6) and c = 27.600(3) Å. A three-dimensional structural analysis using automatic diffractometer data has been completed and refined by full-matrix least-squares procedures to a residual R = 0.049 (R_w = 0.059) with a data-parameter ratio of 36 in the final anisotropic refinement. The structure analysis indicated that magnesium arsenate has the composition Mg_8.5As₃O₁₆ and is isostructural with the previously reported Co₈As₃O₁₆. The structure is based upon a cubic close-packed oxygen array with charge balance achieved in magnesium arsenate through partial occupancy of a unique magnesium site occurring in an arsenic-substituted MgO-type layer.     

Molar excess volumes of ternary mixtures of nonelectrolytes

Molar excess volumes V^E_ijk of methylenebromide i + pyridine j + β-picoline (k, cyclohexane (i) + pyridine (j) + β-picoline(K), benzene(i)+toluene(j)+1,2-dichloroethane(k), benzene(i) + 0-xylene(j) + 1,2-dichloroethane(k) and benzene(i) + p-xylene(j) + 1,2-dichloroethane(k) mixtures have been determined dilatometrically at 298.15 K. The data have been examined in terms of Sanchez and Lacombe theory and the graph-theoretical approach, and it is found that they are described well by the latter. Self- and cross-volume interaction coefficients V_jk, V_jjk and V_jkk, etc., have also been evaluated and the values utilised to study molecular interactions between the jth and kth molecular species in the presence of the ith in these i + j + k mixtures.     

Molar excess enthalpies of ternary mixtures of non-electrolytes

Molar excess enthalpies, H^E_ijk(T₁, x_i, x_j), for methylenebromide (i)+pyridine (j)+β-picoline (k); pyridine (i)+β-picoline (j)+cyclohexane (k); benzene (i)+toluene (j)+1,2-dichloroethane (k); benzene (i)+o-xylene (j)+1,2-dichloroethane (k); and benzene (i)+p-xylene (j)+1,2-dichloroethane (k) mixtures have been measured calorimetrically as a function of temperature and composition. The data have been analysed in terms of the Sanchez and Lacombe theory and using an approach employing the “graph theoretical” concept of connectivity parameters to characterize its pure components. It has been observed that the H^E_ijk (T, x_i, x_j) data calculated from the “graph theoretical” approach using ³ξ values based on δ^v considerations (that take into consideration the valency of individual atoms of the molecular graph constituent components) best reproduces the corresponding experimental H^E_ijk data.     

Synthese eines verbrückten π-allyl-chinolin-palladiumchlorid-komplexes

Chloro[N-3′5′-η-(4′-methylpentenyl)quinoline-2]palladium was synthesized; the NMR-spectrum of this compound is helpful in distinguishing the cis/trans-isomers of other non-bridged π-allyl-base-palladium chloride complexes.     

Distortion of the coordination polyhedron in mononuclear copper(II) complexes. Optical absorption and electron spin resonance studies on some five-coordinate copper(II) complexes

The preparation and spectral properties are reported for a series of ten mixed-ligand copper(II) complexes of the form [Cu(A)(B)_n](X), where A is acetylacetonate anion, B represents a mono- or bidentate ligand such as morpholine, piperidine, isonicotinic acid hydrazide, 2,2′-bipyridine, 1,10-phenanthroline and X is variously NO^?₃ or ClO^?₄ anion and n = 1 or 2. The coordination of the anions and ligands has been demonstrated by infrared and electronic spectral methods. Electron spin resonance spectral data show the square-pyramidal five-coordinated arrangement around copper(II) in these complexes. Parameters such as g₆, g_⊥, A₆, A_⊥, 〈g〉 and 〈A〉 calculated from electron spin resonance data in solid and solution state at room temperature as well as frozen solution indicate the presence of the unpaired electron in the d_x2_?y2 or d_z2 orbital. These results are in good agreement with electronic and photoacoustic spectral studies.     

The preparation and electrochemistry of manganese(II) complexes of an unsaturated pentadentate macrocyclic ligand

The preparation of a series of six and seven coordinate manganese(II) complexes [Mn^(II)(L)X]⁺, and [Mn^(II)(L)X₂]^2? (X = halide, water, triphenylphosphine oxide, imidazole, 1-methyl imidazole and pyridine) incorporating the pentadentate planar macrocylic ligand L is described. Cyclic voltammetry of these complexes in acetonitrile each shows a reversible one-electron reduction wave near - 1.4 V vs a Ag/AgNO₃ reference electrode. Quantitative reduction of these complexes by controlled potential electrolysis at a platinum gauze at - 1.4 V yields the corresponding one-electron reduction products which have been shown by ESR spectroscopy to be manganese(II)-ligand radical species, the electron being thought to reside on the di-imino pyridine moiety of the macrocyclic ligand. No metal reduced species could be isolated even in the presence of π-acceptor ligands such as CO or phosphines.     

Cyclobutyl neighboring group effect on the stability of bicyclo-[2.2.2]octyl bridgehead carbenium ions

Solvolysis of the novel bridgehead cyclobutyl methyl chloride

proceeds without skeletal rearrangement. Its relative rate is the first unequivocal proof for a small, but significant ability of the cyclobutyl group to stabilize an adjacent positively charged center.     

Dioxouranium(VI) complexes of some sulphur donor ligands

Complexes of uranyl chloride and uranyl nitrate of the type UO₂X₂·2L and [UO₂X₂2L′], where X = Cl or NO₃ and L = N,N′-tetramethylthiourea (TMTU); N,N′-dimethylthiourea (DMTU); monomethylthiourea (MMTU), monoethylthiourea (METU), pyridine-2-thiol (PYT) and L′ = 4,6-dimethylpyrimidine-2-thiol (PYMT), have been prepared. The complexes were characterised on the basis of IR spectroscopy and by elemental analysis. In some cases Raman spectra are also reported.     

Triethylphosphine—carbgn disulfide zwitterion as a bridging six-electron donor ligand in [Mo(CO)2(PEt3)(μ-S2CPEt3)]2; synthesis and x-ray crystal structure

The zwitterion Et₃PCS₂ reacts with Mo(CO)₆ or Mo(C₇H₈)(CO)₃ to give the dinuclear complex [Mo(CO)₂(PEt₃)(μ-S₂CPEt₃)]₂. An X-ray crystal structure determination has showed that both zwitterions coordinate one metal through an η³-S₂C linkage and the second metal through a single sulphur atom.