Robert D. Hart

The nature of soil kaolins from Indonesia and Western Australia

Purified soil kaolins from Indonesia and Western Australia were characterized using analytical TEM, XRD, TGA and chemical analysis. The Indonesian kaolins, formed from tuff, consist of a mixture of tubular kaolin crystals with relatively low Fe concentrations and platy kaolin crystals with higher Fe concentrations. Western Australian kaolins also contained tubular and platy crystals but showed no systematic relationship of crystal morphology with Fe content. The coherently scattering domain (CSD) size of the Indonesian samples (5–6 nm for 001, i.e. c axis dimension) is remarkably consistent and is approximately half of the value for the Western Australian kaolins (9.7–13.4 nm), and both are much smaller sizes than values for the reference kaolins (15.6–27.8 nm). Coherently scattering domain sizes derived from the Scherrer equation are approximately twice the values obtained from the Bertaut-Warren-Averbach Fourier method but the results show the same pattern of variation. For the Indonesian, Western Australian and reference kaolins, the N2-BET surface area ranges 59–88, 44–56 and 5–28 m2/g; the dehydroxylation temperatures range 486–499, 484–496 and 520–544°C, the mean cation exchange capacities (CEC) are 9.4, 5.0 and 3.5 meq 100 g−1 and the surface densities of charge range 0.10–0.14, 0.08–0.10 and 0.04–0.12 C/m2. The properties of the Western Australian kaolins and Indonesian kaolins differ substantially, but kaolins within each group have similar properties. These results suggest that soil kaolin properties may be characteristic of a particular pedoenvironment and that a systematic study of kaolins in different pedoenvironments is required.

The relationships between kaolinite crystal properties and the origin of materials for a Brazilian kaolin deposit.

The clay particles in a kaolin deposit from Brazil were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), analytical transmission electron microscopy (ATEM), and electron paramagnetic resonance (EPR) to examine the relationships between morphological and chemical properties of the crystals and to relate these properties to formation conditions. The XRD patterns show the dominant presence of kaolinite with minor amounts of gibbsite, illite, quartz, goethite, hematite, and anatase. ATEM observations show two discontinuities in the deposit as indicated by changes in morphology and size of the kaolinite crystals. At the base of the deposit, hexagonal platy and lath-shaped particles (mean area of 001 face = 0.26 μm2) maintain the original fabric of the parent rock which characterizes an in situ evolution. In the middle of the deposit a bimodal population of large (mean area of 001 face > 0.05 μm2) and small (mean area of 001 face < 0.05 μm2) sub-hexagonal platy kaolinite crystals occurs. This zone defines the boundary between the saprolitic kaolinite and the pedogenic kaolinite. Near the top of the profile, laths and irregular plates of kaolinite, together with sub-hexagonal particles, define two different depositional sources in the history of formation of the deposit. Crystal thickness as derived from the width of basal reflections and the Hinckley index are compatible with the morphological results, but show only one discontinuity. At the base of the deposit, kaolinite has a low- defect density whereas in the middle and at the top of the profile, kaolinite has a high-defect density. Likewise, EPR spectroscopy shows typical spectra of low-defect kaolinite for the bottom of the deposit and typical spectra of high-defect kaolinite for the other portions of the deposit. Despite the morphological changes observed through the profile, the elemental composition of individual kaolinite crystals did not show systematic variations. These results are consistent with the deposit consisting of a transported pedogenic kaolinite over saprolite consisting of in situ kaolinized phyllite.

Structual and Spectroscopic Studies on the Dimeric Complexes of Tris (2-methyphenyl) phosphine with Copper (I) Halides

1:1 adducts of the copper(I) halides, CuX (X = Cl, Br, I), with the sterically hindered ligand tris (2-methylphenyl) phospine [P(o- tol )3] have been synthesized as crystalline dihalo -bridged centrosymmetric binuclear species; six compounds have been characterized by solid-state CP-MAS n.m.r. and far-infrared spectroscopy and by room-temperature single-crystal X-ray structure determination. For X = Cl , the dimeric complex. [P(o- tol )3CuCl]2, with three-coordinate copper atoms has been obtained from acetonitrile solution. Similar dimeric complexes for X = Br and I were obtained from toluene solution, the iodide adduct incorporating cocrystallized toluene. The X = Br and I complexes crystallized from acetonitrile solution yield mixed- ligand four-coordinate copper(I) dimers, [( MeCN )P(o- tol )3CuX]2, the iodide as a 2MeCN solvate. An additional crystalline phase incorporating crystallographically independent molecules of both the three-coordinate dimer and the four-coordinate mixed- ligand dimer has also been characterized for X = Br. Solid-state 31P CP-MAS n.m.r. spectra of the complexes at B = 7.05 T show well resolved asymmetric quartets with a ∆v3/∆v1 of 1.4 for the PcuX2 complexes and 1.1-1.2 for the PcuX2N complexes; these results reflect the geometric and bonding changes in the copper coordination sphere. Far-infrared spectra of the complexes show two strong halogen-sensitive bands, with a wavenumber separation of 30-40 cm-1, which have been assigned to copper-halogen stretching modes v( CuX ), this assignment being supported by a normal coordinate analysis on the Cu2X2 core.

The role of short-range diffusion in solvent-assisted mechanochemical synthesis of metal complexes

The role of short-range diffusion in solvent-assisted mechanochemical synthesis is demonstrated in studies of a polymorphic transition and a ligand dissociation reaction involving copper(I) thiocyanate complexes.

Mechanochemical and solution synthesis, X-ray structure and IR and 31P solid state NMR spectroscopic studies of copper(I) thiocyanate adducts with bulky monodentate tertiary phosphine ligands

A number of adducts of copper(I) thiocyanate with bulky tertiary phosphine ligands, and some nitrogen-base solvates, were synthesized and structurally and spectroscopically characterised. CuSCN:PCy3 (1:2), as crystallized from pyridine, is shown by a single crystal X-ray study to be a one-dimensional polymer ...(Cy3P)2CuSCN(Cy3P)2CuSCN... (1) with the four-coordinate copper atoms linked end-on by S-SCN-N bridging thiocyanate groups. A second form (2), obtained from acetonitrile, was also identified and shown by IR and 31P CPMAS NMR spectroscopy to be mononuclear, with the magnitude of the dν(Cu) parameter measured from the 31P CPMAS and the ν(CN) value from the IR clearly establishing this compound as three-coordinate [(Cy3P)2CuNCS]. Two further CuSCN/PCy3 compounds CuSCN:PCy3 (1:1) (3), and CuSCN:PCy3:py (1:1:1) (4) were also characterized spectroscopically, with the dν(Cu) parameters indicating three- and four-coordinate copper sites, respectively. Attempts to obtain a 1:2 adduct with tri-t-butylphosphine have yielded, from pyridine, the 1:1 adduct as a dimer [(Bu(t)3P)((SCN)(NCS))Cu(PBu(t)3)] (5), while similar attempts with tri-o-tolylphosphine (from acetonitrile and pyridine (= L)) resulted in solvated 1:1:1 CuSCN:P(o-tol)3:L forms as dimeric [{(o-tol)3P}LCu((SCN)(NCS))CuL{P(o-tol)3}] (6 and 8). The solvent-free 1:1 CuSCN:P(o-tol)3 adduct (7), obtained by desolvation of 6, was characterized spectroscopically and dν(Cu) measurements from the 31P CPMAS NMR data are consistent with the decrease in coordination number of the copper atom from four (for 6) (P,N(MeCN)Cu,S,N) to three (for 7) (PCuS,N) upon loss of the acetonitrile of solvation. These results are compared with those previously reported for mononuclear and binuclear PPh3 adducts which demonstrate a clear tendency for the copper centre to remain four-coordinate. The IR spectroscopic measurements on these compounds show that bands in the far-IR spectra provide a much more definitive criterion for distinguishing between bridging and terminal bonding than does an often-used empirical rule based on ν(CN) in the mid-IR, which leads to the wrong conclusion in some cases.

Iron in soil kaolins from Indonesia and Western Australia

Abstract Soil kaolins from Indonesia and Western Australia and a range of reference kaolins were studied using Mössbauer spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and SQUID magnetometry. Mössbauer spectra indicate that the Fe within the kaolins is in the highspin Fe3+ oxidation state and that a large fraction of the Fe is present as dispersed atoms residing within the octahedral sites of the kaolinite crystal structure. The EPR spectra are typical for soil kaolins except for the absence of radiation-induced defects for the Indonesian kaolins. The Fe(I) spectra are dominant with a strong symmetric peak at g = 4.3, the presence of Fe(II) spectra is shown by a shoulder on this peak at g = 4.9 and a small phase up peak at g = 9.2. Low-temperature (5 K) magnetization (M) measurements over large field (H) sweeps (±70 kOe) yielded M(H) curves which are fitted well with Brillouin functions indicating the paramagnetic nature of the kaolins at temperatures down to 5 K. A very small remanent magnetization was detectable in the kaolins. Remanent magnetization to saturation magnetization ratios ranged from 10-4 to 10-3 for the Indonesian kaolins and were all ~10-3 for the Western Australian kaolins, indicating that at high fields the vast majority of the magnetization of the kaolins is due to paramagnetic ions. Zero-field-cooled and field-cooled magnetization measurements in small fields (500 Oe) indicate that the Indonesian kaolins are generally free from magnetically-blocked material down to a temperature of 5 K. The magnetic susceptibility of the Indonesian kaolins shows Curie Law behaviour indicating paramagnetic behaviour over all temperatures down to 5 K. Measurements on the Western Australian kaolins indicated the presence of some magnetic material that is magnetically blocked at temperatures below ~200–250 K. As a consequence, the magnetic susceptibility showed large deviations from Curie Law behaviour.

Differences in potassium forms between cutans and adjacent soil matrix in a Grey Clay Soil

Cutans are common fabric features in soil and represent foci of chemical and biological reactions. The influence of cutans on potassium forms and their transformations were investigated for a Western Australian grey clay soil. Cutans and matrix soil had similar clay mineral associations with kaolinite, smectite and illite being present, but had different chemical properties. The organic carbon content of cutans was higher than for matrix soil, while pH values and oxalate extractable/dithionate extractable iron (Feo/Fed) ratios were lower. Numerous SEM-EDS single point analyses of cutans and the plasma phase of the matrix soil indicated that the mean value of K concentration in cutans is greater than in matrix soil, and that the K concentration decreased with distance from cutan to matrix. Chemical extractions showed mean values of total K and latent exchangeable K were higher for cutans than for matrix soil, but both fixed K and exchangeable K values were the same for cutans and matrix soil. In a K adsorption/desorption experiment, 35% of K adsorbed by matrix soil could not be desorbed by 1 M NH4Ac. These results indicate that cutans are relatively enriched in K and may play an important role in determining available K and latent exchangeable K due to the special physical and chemical environments they provide in the soil.

Amorphous alumino-silicate materials in a Brazilian hydromorphic lateritic soil

Two ancient lateritic soil profiles from Brazil that are now experiencing hydromorphic conditions were investigated by chemical extractions, X-ray diffraction, differential thermal and thermogravimetric analysis, and analytical transmission electron microscopy (ATEM) to identify if the hydromorphic conditions had affected soil minerals. The soils are composed of gibbsite and kaolinite with less quartz, anatase, goethite, pedogenic chlorite, and amorphous alumino-silicate phases. These last 2 constituents occur in the middle and upper horizons of both soil profiles, together with considerable amounts of organic carbon. Analytical TEM showed that the amorphous phases enveloped corroded gibbsite and kaolinite crystals and may indicate the transformation of these minerals to amorphous phases. The amorphous phases have a similar microfabric to that of allophane and ATEM analyses of the amorphous phases gave an AlsSi atom ratio that was always >2, and commonly about 10. These atom ratios are consistent with the bulk chemical results obtained using pyrophosphate, oxalate, and dithionite extractants, but not with the theoretical ratio for allophane. The AlsSi atom ratio of the amorphous phases was related to the Al content of the mineral enveloped by the amorphous phases, i.e. gibbsite or kaolinite. This association supports the interpretation that the amorphous phases formed from the crystalline minerals. The saturated condition of the profiles, together with the high concentration of organic matter in the upper horizons, favours dissolution of the original gibbsite and kaolinite in the laterite and their transformation to amorphous alumino-silicate phases with a high Al content.

Electrochemical synthesis and structural characterization of bis(triphenylphosphine)copper(I) fluoroacetates

Bis(triphenylphosphine)copper(I) fluoroacetate complexes have been prepared by the electrochemical oxidation of copper metal in acetonitrile solutions of triphenylphosphine and mono-, di- and tri-fluoro-acetic acid respectively. Recrystallization from toluene yields unsolvated mononuclear complexes [Cu(PPh3)2(O2CCH3–nFn)], n= 1–3, which have been characterized by single-crystal X-ray crystallographic determinations. Crystals of the three complexes are isomorphous with the acetate complex (n= 0), crystallizing in the monoclinic space group P21/a with cell dimensions a≈ 18.0, b≈ 11.0 and c≈ 19.3 A and β≈ 120°. Residuals for the complexes with n= 1,2 and 3 were R= 0.077, 0.045 and 0.048 for 3677, 2789 and 3527 ‘observed’[I > 3σ(I)] reflections respectively. The bond distances Cu–P are 2.232(3), 2.222(3); 2.234(2), 2.219(2); and 2.235(2), 2.228(2)A with the corresponding P–Cu–P angles increasing from 135.0(1) to 135.8(1) to 136.7(1)°, this latter value being the largest recorded for [Cu(PPh3)2]+. The asymmetry of the co-ordination of the carboxylate group increases along the series with Cu–O distances of 2.144(6) and 2.363(7); 2.118(4), 2.465(6); and 2.113(4), 2.545(5)A for n= 1, 2 and 3 respectively. Crystallization of the difluoro- and trifluoro-acetate complexes from ethanol results in isomorphous orthorhombic Pb21a crystals (a≈ 22.2, b≈ 18.5, c≈ 9.0 A) with monodentate carboxylate and co-ordinated ethanol; the monofluoroacetate is unsolvated. For [Cu(PPh3)2(O2CCHF2)(EtOH)]R was 0.052 for 2090 ‘observed’ reflections with Cu–P 2.248(3), 2.236(3)A and P–Cu–P 120.5(1)°; Cu–O (carboxylate) is 2.074(8)A and Cu–O (ethanol) is 2.169(8)A. For [Cu(PPh3)2(O2CCF3)(EtOH)]R was 0.043 for 2350 ‘observed’ reflections, Cu–P being 2.248(2), 2.240(2)A and P–Cu–P 120.8(1)°; Cu–O (carboxylate) is 2.104(6)A and Cu–O(ethanol) is 2.160(6)A.

Anion Effects on the Structural Properties of Bis(triphenylphosphine)copper(I) Carboxylate Complexes [(PPh3)2CuO2CR]

The crystal and molecular structure of the 2 : 1 triphenylphosphine copper(I) benzoate complex [(PPh3)2CuO2CC6H5] have been determined by a room-temperature single-crystal X-ray study. The complex is isomorphous with the dithiobenzoate analogue, crystallizing in the orthorhombic space group P212121 with a 20·094(5), b 16·929(9), c 10·659(8) A, Z 4; conventional R on |F| was 0·039 for 4261 independent ‘observed’ (I > 3σ(I)) reflections. Comparison of structural data for this and other [(PPh3)2CuO2CR] complexes shows that the P–Cu–P angle and the anion coordination are dependent on both the donor strength of the anion and on steric interactions between the anion and the triphenylphosphine ligands. The structure of the analogous nitrate complex [(PPh3)2CuNO3] has also been redetermined.