Geoffrey Davies

Transmetalation of tetranuclear copper complexes with tin transmetalators. Molecular structure of cis-dichloro-bis(trans-S-methyl isopropylidenehydrazinecarbodithioato)tin(IV) and consideration of transmetalation mechanisms

Tin complexes Sn(NS)2Cl2(D) and Sn(NS)4(E) (NS is monoanionic S-methyl isopropylidenehydrazinecarbodithioate) are very good transmetalators of tetranuclear copper(I) target [NCuCl]4 (I: N is N,N-diethylnicotinamide). An X-ray crystallographic study shows that D is cis-dichloro-bis(trans-S-methyl isopropylidenehydrazinecarbodithioato)tin(IV). Evidence that I reacts with 1 or 2 mol of D via strong precursors D·I and D2·I that contain NS ligands bridging tin to copper is used to discuss the transmetalation sequence. The tin-containing transmetalation products include the remarkable air-stable copper(I)-tin(IV) complex N3Cu2Sn(NS)2Cl4 obtained from the reaction of I with equimolar E.

Structural modeling in humic acids

Abstract Humic acids are important biological and environmental materials; however, to date there are no significant reports confirming the primary or secondary structure of the building blocks of humic substances. In this work, we report a complementary experimental and computational study that utilizes molecular mechanical applications and spectroscopic tools to evaluate both the primary and secondary structural features of humic acids. The identification of an amide and pronounced CD response suggests a significant secondary structure for humic acids.

Suitability of Different 13C Solid-state NMR Techniques in the Characterization of Humic Acids

Qualitative and quantitative analyses of humic acids (HAs) with five different 13C solid-state NMR techniques were assessed using HAs of various origins and locations. The NMR techniques compared are: (1) direct polarization/magic angle spinning (DP/MAS) at 13 kHz, (2) conventional cross polarization (CP)/MAS at 5 kHz, (3) ramp-CP/MAS at 8 kHz, (4) CP/total sideband suppression (TOSS) at 4.5 kHz, and (5) DP/MAS corrected by CP/spin-lattice relaxation with TOSS. The spectra from the five techniques were first compared qualitatively. Then, each spectrum was divided into eight regions for quantitative evaluation. DP/MAS spectra were used as quantitative references. Ramp-CP/MAS and CP/TOSS spectra gave consistently better results than those of the conventional CP/MAS spectra at a 13C frequency of 75 MHz, which were incorrect due to spinning sidebands. CP/MAS at low magnetic fields (22.6 and 50.6 MHz 13C frequency) indicated improved integration results but lower resolution. Correction factors calculated by comparison with DP/MAS will be useful to convert the non-quantitative peak areas in the CP/TOSS and ramp-CP/MAS spectra into more quantitative results.

Isolation of humic acid from the brown algaPilayella littoralis

A standard humic acid extraction procedure has been used to isolate dark brown organic residues from samples of the macroscopic marine brown algaPilayella littoralis. The residues are insoluble in water, but soluble at high pH, and are similar in elemental composition, ash content, UV-visible, IR, PMR and X-Ray fluorescence spectra, X-Ray diffractograms and scanning electron micrographs to residues of a humic acid isolated from municipal compost. These results indicate thatPilayella produces humic acids.

Transmetallation reactions of tetranuclear copper(II) complexes. I. Crystal and molecular structures of an intermediate and a final product of reaction of di-μ-oxo-tetra[chloro(DENC)copper(II)],(DENC = N,N-diethylnicotinamide) with [Zn(N2S2], (N2S2 = diacetyl-bis-hydrazonato-S-methyl-carboditithioate) in aprotic solvents

Abstract Di-μ-oxo-tetra[chloro(DENC)copper(II)],[(DENC)CuCl]4O2, (DENC) = N,N-diethylnicotinamide) reacts with two moles of dimeric [Zn(N2S2]2), (N2S2 = diacethyl-bis-hydrazonato-S-methyl-carbodithioate) to give 2 moles of [Cu(N2S2]2 and a variety of zinc containing products, including zinc(II) oxide. The crystal and molecular structures of the intermediate five-coordinate complex Zn(N2S2)(DENC), A, and a final product, di-μ-(N,N-diethylnicotinamide-O,N)-tetrachlorodizinc(II), B, from this interesting metal exchange reaction are reported. Although the ultimate products are the same, no intermediate analog of A is detected with monomeric tetrahedral Zn(NS)2 reactants. Complex A crystallizes in the triclinic space group P 1 with Z = 2 in a cell of dimensions a = 10.258(1), b = 10.708(1), c = 12.548(1) A, α = 107.69(1), β = 99.70(1), γ = 106.49(1)°. Complex B also crystallizes in space group P1 with Z = 2 but in a cell of dimensions a = 9.427(4), b = 14.106(6), c = 8.589(3) A, α = 120.87(3), β = 116.17(3), γ = 106.76(3)°.

SYNTHESIS, STRUCTURE AND PROPERTIES OF THE ISOMERIC DINUCLEAR COMPLEXES ((DENC)2CUX2)2 (DENC = N,N-DIETHYLNICOTINAMIDE; X = CL OR BR) AND THE KINETICS OF THEIR REACTIONS WITH DENC IN METHYLENE CHLORIDE

Abstract Tetrahalo - tetrakis - (N,N-diethylnicotinamide)dicopper(II) species [(DENC) 2 CuX 2 ] 2 (X = Cl or Br) differ in that while the chloro complex is bridged by two DENC molecules in the solid but two chloro groups in solution, the bromo complex is always bromo-bridged. These conclusions result from an X-ray structural determination of (DENC)Cl 2 Cu(DENC,DENC)CuCl 2 (DENC) and from spectroscopic comparisons. The kinetics of conversion of the respective dimers to monomeric (DENC) 3 CuX 2 species have been measured in methylene chloride solution.

Isolation of humic acid from the brown algaeAscophyllum nodosum, Fucus vesiculosus, Laminaria saccharina and the marine angiospermZostera marina

Recent discovery of humic acid (HA) in the free-living, brown algaPilayella littoralis has prompted a search for HA in other live plants. Marine algaeCodium fragile andMonostoma oxyspermum (greens),Chondrus crispus,Palmaria palmata andPolysiphonia lanosa (reds),Ascophyllum nodosum, Fucus vesiculosus andLaminaria saccharina (browns) andZostera marina (marine angiosperm) were investigated for their HA content. Only the brown algae and the marine angiosperm contained HA, which was extracted by a standard procedure augmented with necessary removal of alginic acid (where applicable). The isolated products were identified as HA by comparison of their analytical data, uv-visible, FTIR,1H NMR spectra and morphologies with those of authentic HA isolated from municipal compost.

Transmetalation: A New Route to Heteropolymetallic Molecules and Materials

Abstract The newly discovered transmetalation of polymetallic molecules by mononuclear transmetalators is an excellent source of a wide variety of related heteropolyatomic molecules and materials that cannot be obtained by other means. The systems discussed involve easily obtained reactants, stoichiometric reactions and easily separated products. Among the factors that affect specific transmetalation patterns are target structure, transmetalator identity and relative stability, redox phenomena, intramolecular ligand transfer and specific types of primary product fragmentation. A feature of reported transmetalation systems that make them excellent candidates for the production of new materials is that they are stoichiometric and flexible. Prospects for extending known systems to new targets and elements are discussed.

Transmetalation of tetranuclear copper complexes. VIII: Transmetalation of tetranuclear copper(I) complexes with a Co(NS)3 reagent

Transmetallation des complexes (DENC) 4 Cu 4 X 4 (DENC=diethylnicotinamide), par le tris(S-methyl isopropylidenehydrazinocarbodithioate)-Co(III) dans les solvants aprotiques sous N 2

The role of metal complexation in the solubility and stability of humic acid

Abstract Humic acid (HA) obtained from a variety of sources displays somewhat varied chemical composition and residual metal content. In spite of extensive purification procedures as much as 0.5% metal (by weight) can remain in the humic acid. In some cases, particularly for Cu 2+ , the metal binding appears site specific, while in others the cupric ion is less strongly bound. Furthermore, the iron content of the samples appears to be dependent on the source and purification procedure. Quantitative removal or exchange of the residual metal is expected to alter the stability and solubility properties of the HA. The treatment of highly purfied HA with Chelex® resin has afforded a material in which the amount of the so-called residual metal has been reduced by 40% or more. This reduction in metal content appears to affect solution aggregation phenomena and consequently the rate of flocculation. Metal removal depends on pre-treatment conditions of the HA sample and is highly pH and temperature dependent. These observations suggest that chemical transformations of HA at high pH and moderate temperature may affect the equilibrium state between the bound metal in HA and the metal-Chelex® complex. The apparently selective removal of metal suggests a specific role of the metal.