Raman spectroscopy of the copper chloride minerals nantokite, eriochalcite and claringbullite - implications for copper corrosion

The application of Raman spectroscopy to the study of the copper chloride minerals nantokite, eriochalcite and claringbullite has enabled the vibrational modes for the CuCl, CuOH and CuOH2 to be determined. Nantokite is characterised by bands at 205 and 155 cm-1 attributed to the transverse and longitudinal optic vibrations. Nantokite also has an intense band at 463 cm-1, eriochalcite at 405 and 390 cm-1 and claringbullite at 511 cm-1. These bands are attributed to CuO stretching modes. Water librational bands at around 672 cm-1 for eriochalcite have been identified and hydroxyl deformation modes of claringbullite at 970, 906 and 815 cm-1 are observed. Spectra of the three minerals are so characteristically different that the minerals are readily identified by Raman spectroscopy. The minerals are often determined in copper corrosion products by X-ray diffraction. Raman spectroscopy offers a rapid, in-situ technique for the identification of these corrosion products.

Thermal analysis and hot stage Raman spectroscopy of the basic copper arsenate mineral : euchroite

The thermal analysis of euchroite shows two mass loss steps in the temperature range 100 to 105°C and 185 to 205°C. These mass loss steps are attributed to dehydration and dehydroxylation of the mineral. Hot stage Raman spectroscopy (HSRS) has been used to study the thermal stability of the mineral euchroite, a mineral involved in a complex set of equilibria between the copper hydroxy arsenates: euchroite Cu2(AsO4)(OH).3H2O → olivenite Cu2(AsO4)(OH) → strashimirite Cu8(AsO4)4(OH)4.5H2O → arhbarite Cu2Mg(AsO4)(OH)3. Hot stage Raman spectroscopy inolves the collection of Raman spectra as a function of the temperature. HSRS shows that the mineral euchroite decomposes between 125 and 175 °C with the loss of water. At 125 °C, Raman bands are observed at 858 cm-1 assigned to the ν1 AsO43- symmetric stretching vibration and 801, 822 and 871 cm-1 assigned to the ν3 AsO43- (A1) antisymmetric stretching vibration. A distinct band shift is observed upon heating to 275 °C. At 275 °C the four Raman bands are resolved at 762, 810, 837 and 862 cm-1. Further heating results in the diminution of the intensity in the Raman spectra and this is attributed to sublimation of the arsenate mineral. Hot stage Raman spectroscopy is most useful technique for studying the thermal stability of minerals especially when only very small amounts of mineral are available.

Thermogravimetric analysis and hot stage Raman spectroscopy of cubic indium hydroxide

The transition of cubic indium hydroxide to cubic indium oxide has been studied by thermogravimetric analysis complimented with hot stage Raman spectroscopy. Thermal analysis shows the transition of In(OH)3 to In2O3 occurs at 219°C. The structure and morphology of In(OH)3 synthesised using a soft chemical route at low temperatures was confirmed by X-ray diffraction and scanning electron microscopy. A topotactical relationship exists between the micro/nano-cubes of In(OH)3 and In2O3. The Raman spectrum of In(OH)3 is characterised by an intense sharp band at 309 cm-1 attributed to ν1 In-O symmetric stretching mode, bands at 1137 and 1155 cm-1 attributed to In-OH δ deformation modes, bands at 3083, 3215, 3123 and 3262 cm-1 assigned to the OH stretching vibrations. Upon thermal treatment of In(OH)3 new Raman bands are observed at 125, 295, 488 and 615 cm-1 attributed to In2O3. Changes in the structure of In(OH)3 with thermal treatment is readily followed by hot stage Raman spectroscopy.

Raman spectroscopy of gallium based hydrotalcites of formula Mg6Ga2(CO3)(OH)16•4H2O

Insight into the unique structure of hydrotalcites has been obtained using Raman spectroscopy. Gallium containing hydrotalcites of formula Mg4Ga2(CO3)(OH)12•4H2O (2:1 Ga-HT) to Mg8Ga2(CO3)(OH)20•4H2O (4:1 Ga-HT) have been successfully synthesised and characterized by X-ray diffraction and Raman spectroscopy. The d(003) spacing varied from 7.83 Å for the 2:1 hydrotalcite to 8.15 Å for the 3:1 gallium containing hydrotalcite. Raman spectroscopy complemented with selected infrared data has been used to characterise the synthesised gallium containing hydrotalcites of formula Mg6Ga2(CO3)(OH)16•4H2O. Raman bands observed at around 1046, 1048 and 1058 cm-1 were attributed to the symmetric stretching modes of the (CO32-) units. Multiple ν3 CO32- antisymmetric stretching modes are found at around 1346, 1378, 1446, 1464 and 1494 cm-1. The splitting of this mode indicates the carbonate anion is in a perturbed state. Raman bands observed at 710 and 717 cm-1 assigned to the ν4 (CO32-) modes support the concept of multiple carbonate species in the interlayer.

The effect of metamictization on the Raman spectroscopy of the uranyl titanate mineral davidite (La,Ce)(Y,U,Fe2+)(Ti,Fe3+)20(O,OH)38

Raman spectra of the uranyl titanate mineral davidite-(La) (La,Ce)(Y,U,Fe2+)(Ti,Fe3+)20(O,OH)38 were analysed and related to the mineral structure. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U-OH bending vibrations, H2O and (OH)- stretching, bending and libration modes. U-O bond lengths in uranyls and O-H…O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of davidite-(La) are in harmony with those of the uranyl oxyhydroxides. The mineral davidite-(La) is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader.

Raman spectroscopy of hydrogene-arsenate group (AsO3OH) in solid-state compounds: cobalt mineral phase burgessite Co2(H2O)4[AsO3OH]2•H2O

Raman spectrum of burgessite, Co2(H2O)4[AsO3OH]2.H2O was studied, interpreted and compared with its infrared spectrum. The stretching and bending vibrations of (AsO3) and As-OH units together with the stretching, bending and libration modes of water molecules and hydroxyl ions were assigned. The range of O-H...O hydrogen bond lengths was inferred from the Raman and infrared spectra of burgessite. The presence of (AsO3OH)2- units in the crystal structure of burgessite was proved in agreement with its recently solved crystal structure. Raman and infrared spectra of erythrite inferred from the RRUFF database are used for comparison.

Raman spectroscopy of selected borate minerals of the pinakiolite group

The Raman spectra of a series of related minerals of the pinakiolite group of minerals have been collected and the spectra related to the mineral structure. These minerals are based upon an isolated BO33- ion. The site symmetry is reduced from D3h to C1. Intense Raman bands are observed for the minerals takeuchiite, pinakiolite, fredrikssonite and azoproite at 1084, 1086, 1086 and 1086 cm-1. These bands are assigned to the ν1 BO33- symmetric stretching mode. Low intensity Raman bands are observed for the minerals at 1345, 1748; 1435, 1748; 1435, 1750; 1436, 1749 cm-1. One probable assignment is to ν3 BO33- antisymmetric stretching mode. Intense Raman bands of takeuchiite, pinakiolite, fredrikssonite and azoproite at 712 cm-1 attributed to the ν2 out-of-plane bending mode. Importantly, through the comparison of the Raman spectra, the molecular structure of borate minerals with ill-defined structures can be obtained.

Raman spectroscopy of hydrogen arsenate group (AsO3OH)2− in solid-state compounds: cobalt-containing zinc arsenate mineral, koritnigite (Zn,Co)(AsO3OH)·H2O

Raman spectra of two well-defined types of koritnigite crystals from the Jáchymov ore district, Czech Republic, were recorded and interpreted. No substantial differences were observed between both crystal types. Observed Raman bands were attributed to the (AsO3OH)2- stretching and bending vibrations, stretching and bending vibrations of water molecules and hydroxyl ions. Non-interpreted Raman spectra of koritnigite from the RRUFF database, and published infrared spectra of cobaltkoritnigite were used for comparison. The O-H...O hydrogen bond lengths in the crystal structure of koritnigite were inferred from the Raman spectra and compared with those derived from the X-ray single crystal refinement. The presence of (AsO3OH)2- units in the crystal structure of koritnigite was proved from the Raman spectra which supports the conclusions of the X-ray structure analysis.

Single crystal Raman spectroscopy of natural leiteite ZnAs2O4 and in comparison with the synthesised mineral

The oriented single crystal Raman spectrum of leiteite has been obtained and the spectra related to the structure of the mineral. The intensities of the observed bands vary according to orientation allowing them to be assigned to either Ag or Bg modes. Ag bands are generally the most intense in the CAAC spectrum, followed by ACCA, CBBC, and ABBA whereas Bg bands are generally the most intense in the CBAC followed by ABCA. The CAAC and ACCA spectra are identical, as are those obtained in the CBBC and ABBA orientations. Both cross-polarised spectra are identical. Band assignments were made with respect to bridging and non-bridging As-O bonds.

Raman spectroscopy of gallium- and zinc-based hydrotalcites

Insight into the unique structure of hydrotalcites (HTs) has been obtained using Raman spectroscopy. Gallium-contg. HTs of formula Zn4 Ga2(CO3)(OH)12 · xH2O (2:1 ZnGa-HT), Zn6 Ga2(CO3)(OH)16 · xH2O (3:1 ZnGa-HT) and Zn8 Ga2(CO3)(OH)18 · xH2O (4:1 ZnGa-HT) have been successfully synthesized and characterised by X-ray diffraction (XRD) and Raman spectroscopy. The d(003) spacing varies from 7.62 Å for the 2:1 ZnGa-HT to 7.64 Å for the 3:1 ZnGa-HT. The 4:1 ZnGa-HT showed a decrease in the d(003) spacing, compared to the 2:1 and 3:1 compds. Raman spectroscopy complemented with selected IR data has been used to characterize the synthesized gallium-contg. HTs. Raman bands obsd. at around 1050, 1060 and 1067 cm-1 are attributed to the sym. stretching modes of the (CO32-) units. Multiple ν3 (CO32-) antisym. stretching modes are found between 1350 and 1520 cm-1, confirming multiple carbonate species in the HT structure. The splitting of this mode indicates that the carbonate anion is in a perturbed state. Raman bands obsd. at 710 and 717 cm-1 and assigned to the ν4 (CO32-) modes support the concept of multiple carbonate species in the interlayer.

Single crystal Raman spectroscopy of brandholzite Mg[Sb(OH)6]2•6H2O and bottinoite Ni[Sb(OH)6]2•6H2O and the polycrystalline Raman spectrum of mopungite Na[Sb(OH)6]

The single crystal Raman spectra of minerals brandholzite and bottinoite, formula M[Sb(OH)6]2•6H2O, where M is Mg+2 and Ni+2 respectively, and the non-aligned Raman spectrum of mopungite, formula Na[Sb(OH)6], are presented for the first time. The mixed metal minerals comprise of alternating layers of [Sb(OH)6]-1 octahedra and mixed [M(H2O)6]+2 / [Sb(OH)6]-1 octahedra. Mopungite comprises hydrogen bonded layers of [Sb(OH)6]-1 octahedra linked within the layer by Na+ ions. The spectra of the three minerals were dominated by the Sb-O symmetric stretch of the [Sb(OH)6]-1 octahedron, which occurs at approximately 620 cm-1. The Raman spectrum of mopungite showed many similarities to spectra of the di-octahedral minerals informing the view that the Sb octahedra gave rise to most of the Raman bands observed, particularly below 1200 cm-1. Assignments have been proposed based on the spectral comparison between the minerals, prior literature and density field theory calculations of the vibrational spectra of the free [Sb(OH)6]-1 and [M(H2O)6]+2 octahedra by a model chemistry of B3LYP/6-31G(d) and lanl2dz for the Sb atom. The single crystal data spectra showed good mode separation, allowing the majority of the bands to be assigned a symmetry species of A or E.

Spatially offset Raman spectroscopy (SORS) for the analysis and detection of packaged pharmaceuticals and concealed drugs

Spatially offset Raman spectroscopy (SORS) is a powerful new technique for the non-invasive detection and identification of concealed substances and drugs. Here, we demonstrate the SORS technique in several scenarios that are relevant to customs screening, postal screening, drug detection and forensics applications. The examples include analysis of a multi-layered postal package to identify a concealed substance; identification of an antibiotic capsule inside its plastic blister pack; analysis of an envelope containing a powder; and identification of a drug dissolved in a clear solvent, contained in a non-transparent plastic bottle. As well as providing practical examples of SORS, the results highlight several considerations regarding the use of SORS in the field, including the advantages of different analysis geometries and the ability to tailor instrument parameters and optics to suit different types of packages and samples. We also discuss the features and benefits of SORS in relation to existing Raman techniques, including confocal microscopy, wide area illumination and the conventional backscattered Raman spectroscopy. The results will contribute to the recognition of SORS as a promising method for the rapid, chemically-specific analysis and detection of drugs and pharmaceuticals.

The application of Raman spectroscopy to the study of the uranyl mineral coconinoite Fe2Al2(UO2)2(PO4)4(SO4)(OH)2•20H2O

Raman spectra of the uranyl containing mineral coconinoite, Fe2Al2(UO2)2(PO4)4(SO4)(OH)2•20H2O, are presented and compared with the mineral’s infrared spectra. Bands connected with (UO2)2+, (PO4)3- , (SO4)2-, (OH)- and H2O stretching and bending vibrations, are assigned. Approximate U-O bond lengths in uranyl, (UO2)2+, and O-H...O hydrogen bond lengths are calculated from the wavenumbers of the U-O stretching vibrations and (OH)- and H2O stretching vibrations, respectively, and compared with published data for similar natural and synthetic compounds.

Raman spectroscopy of newberyite Mg(PO3OH)•3H2O – a cave mineral

Newberyite Mg(PO3OH)•3H2O is a mineral found in caves such as from Moorba cave, Jurien Bay, Western Australia, the Skipton Lava tubes (SW of Ballarat, Victoria, Australia) and in the Petrogale Cave (Madura , Eucla, Western Australia). Because these minerals contain oxyanions, hydroxyl units and water, the minerals lend themselves to spectroscopic analysis. Raman spectroscopy can investigate the complex paragenetic relationships existing between a number of ‘cave’ minerals. The intense sharp band at 982 cm-1 is assigned to the PO43- ν1 symmetric stretching mode. Low intensity Raman bands at 1152, 1263 and 1277 cm-1 are assigned to the PO43- ν3 antisymmetric stretching vibrations. Raman bands at 497 and 552 cm-1 are attributed to the PO43- ν4 bending modes. An intense Raman band for newberyite at 398 cm-1 with a shoulder band at 413 cm-1 is assigned to the PO43- ν2 bending modes. The values for the OH stretching vibrations provide hydrogen bond distances of 2.728Å (3267 cm-1), 2.781Å (3374cm-1), 2.868Å (3479 cm-1), and 2.918Å (3515 cm-1). Such hydrogen bond distances are typical of secondary minerals. Estimates of the hydrogen-bond distances have been made from the position of the OH stretching vibrations and show a wide range in both strong and weak bonds.