Raman spectroscopy and characterisation of α‐gallium oxyhydroxide and β‐gallium oxide nanorods

Raman spectroscopy complemented by infrared spectroscopy was used to characterise both gallium oxyhydroxide (α‐GaO(OH)) and gallium oxide (β‐Ga₂O₃) nanorods synthesised with and without the surfactants using a soft chemical methodology at low temperatures. Nano‐ to micro‐sized gallium oxyhydroxide and gallium oxide materials were characterised and analysed by both X‐ray diffraction and Raman spectroscopy. Rod‐like GaO(OH) crystals with average length of ∼2.5 µm and width of 1.5 µm were obtained. Upon thermally treating gallium oxyhydroxide GaO(OH) to 900 °C, β‐Ga₂O₃ was synthesised retaining the initial GaO(OH) morphology. Raman spectroscopy has been used to study the structure of nanorods of GaO(OH) and Ga₂O₃ crystals. Raman spectroscopy shows bands characteristic of GaO(OH) at 950 and ∼1000 cm⁻¹ attributed to Ga OH deformation modes. Bands at 261, 275, 433 and 522 cm⁻¹ are assigned to vibrational modes involving Ga OH units. Bands observed at 320, 346, 418 and 472 cm⁻¹ are assigned to the deformation modes of Ga₂O₆ octahedra. Two sharp infrared bands at 2948 and 2916 cm⁻¹ are attributed to the GaO(OH) symmetric stretching vibrations. Raman spectroscopy of Ga₂O₃ provides bands at 630, 656 and 767 cm⁻¹ which are assigned to the bending and stretching of GaO₄ units. Raman bands at 417 and 475 cm⁻¹ are attributed to the symmetric stretching modes of GaO₂ units. The Raman bands at 319 and 347 cm⁻¹ are assigned to the bending modes of GaO₂ units. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman and infrared study of phyllosilicates containing heavy metals (Sb,Bi): bismutoferrite and chapmanite

The kaolinite‐like phyllosilicate minerals bismutoferrite BiFe³⁺₂Si₂O₈(OH) and chapmanite SbFe³⁺₂Si₂O₈(OH) have been studied by Raman spectroscopy and complemented with infrared spectra. Tentatively interpreted spectra were related to their molecular structure. The antisymmetric and symmetric stretching vibrations of the Si O Si bridges, δ SiOSi and δ OSiO bending vibrations, ν (Si O_terminal)⁻ stretching vibrations, ν OH stretching vibrations of hydroxyl ions, and δ OH bending vibrations were attributed to the observed bands. Infrared bands in the range 3289–3470 cm⁻¹ and Raman bands in the range 1590–1667 cm⁻¹ were assigned to adsorbed water. O H···O hydrogen‐bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

A Raman spectroscopic study of the antimony mineral klebelsbergite Sb4O4(OH)2(SO4)

Many minerals based upon antimonite and antimonate anions remain to be studied. Most of the bands occur in the low wavenumber region, making the use of infrared spectroscopy difficult. This problem can be overcome by using Raman spectroscopy. The Raman spectra of the mineral klebelsbergite Sb₄O₄(OH)₂(SO₄) were studied and related to the structure of the mineral. The Raman band observed at 971 cm⁻¹ and a series of overlapping bands are observed at 1029, 1074, 1089, 1139 and 1142 cm⁻¹ are assigned to the SO₄²⁻ν₁ symmetric and ν₃ antisymmetric stretching modes, respectively. Two Raman bands are observed at 662 and 723 cm⁻¹, which are assigned to the Sb O ν₃ antisymmetric and ν₁ symmetric stretching modes, respectively. The intense Raman bands at 581, 604 and 611 cm⁻¹ are assigned to the ν₄ SO₄²⁻ bending modes. Two overlapping bands at 481 and 489 cm⁻¹ are assigned to the ν₂ SO₄²⁻ bending mode. Low‐intensity bands at 410, 435 and 446 cm⁻¹ may be attributed to O Sb O bending modes. The Raman band at 3435 cm⁻¹ is attributed to the O H stretching vibration of the OH units. Multiple Raman bands for both SO₄²⁻ and Sb O stretching vibrations support the concept of the non‐equivalence of these units in the klebelsbergite structure. It is proposed that the two sulfate anions are distorted to different extents in the klebelsbergite structure. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO₃OH)· 2H₂O. The mineral is characterised by an intense Raman band at 865 cm⁻¹ assigned to the ν₁ (AsO₃)²⁻ symmetric stretching mode. The equivalent IR band is found at 864 cm⁻¹. The low‐intensity Raman bands in the range from 844 to 886 cm⁻¹ provide evidence for ν₃ (AsO₃) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm⁻¹ region are attributed to ν₂ and ν₄ (AsO₃) bending modes. Prominent Raman bands at around 3187 cm⁻¹ are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm⁻¹ to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO₃OH)²⁻ units. Copyright © 2009 John Wiley & Sons, Ltd.     

Dussertite BaFe3+3(AsO4)2(OH)5—a Raman spectroscopic study of a hydroxy‐arsenate mineral

The mineral dussertite, a hydroxy‐arsenate mineral with formula BaFe³⁺₃(AsO₄)₂(OH)₅, has been studied by Raman spectroscopy complemented with infrared spectroscopy. The spectra of three minerals from different origins were investigated and proved to be quite similar, although some minor differences were observed. In the Raman spectra of the Czech dussertite, four bands are observed in the 800–950 cm⁻¹ region. The bands are assigned as follows: the band at 902 cm⁻¹ is assigned to the (AsO₄)³⁻ν₃ antisymmetric stretching mode, the one at 870 cm⁻¹ to the (AsO₄)³⁻ν₁ symmetric stretching mode, and those at 859 and 825 cm⁻¹ to the As‐OM^{2 + /3+} stretching modes and/or hydroxyl bending modes. Raman bands at 372 and 409 cm⁻¹ are attributed to the ν₂ (AsO₄)³⁻ bending mode and the two bands at 429 and 474 cm⁻¹ are assigned to the ν₄ (AsO₄)³⁻ bending mode. An intense band at 3446 cm⁻¹ in the infrared spectrum and a complex set of bands centred upon 3453 cm⁻¹ in the Raman spectrum are attributed to the stretching vibrations of the hydrogen‐bonded (OH)⁻ units and/or water units in the mineral structure. The broad infrared band at 3223 cm⁻¹ is assigned to the vibrations of hydrogen‐bonded water molecules. Raman spectroscopy identified Raman bands attributable to (AsO₄)³⁻ and (AsO₃OH)²⁻ units. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopy of the borosilicate mineral ferroaxinite

Raman spectroscopy, complemented by infrared spectroscopy, has been used to characterise the ferroaxinite minerals of the theoretical formula Ca₂Fe²⁺Al₂BSi₄O₁₅(OH), a ferrous aluminium borosilicate. The Raman spectra are complex but are subdivided into sections on the basis of the vibrating units. The Raman spectra are interpreted in terms of the addition of borate and silicate spectra. Three characteristic bands of ferroaxinite are observed at 1082, 1056 and 1025 cm⁻¹ and are attributed to BO₄ stretching vibrations. Bands at 1003, 991, 980 and 963 cm⁻¹ are assigned to SiO₄ stretching vibrations. Bands are found in these positions for each of the ferroaxinites studied. No Raman bands were found above 1100 cm⁻¹ showing that ferroaxinites contain only tetrahedral boron. The hydroxyl stretching region of ferroaxinites is characterised by a single Raman band between 3368 and 3376 cm⁻¹, the position of which is sample‐dependent. Bands for ferroaxinite at 678, 643, 618, 609, 588, 572, 546 cm⁻¹ may be attributed to the ν₄ bending modes and the three bands at 484, 444 and 428 cm⁻¹ may be attributed to the ν₂ bending modes of the (SiO₄)²⁻. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl selenite mineral marthozite Cu[(UO2)3(SeO3)2O2]·8H2O

The mineral marthozite, a uranyl selenite, has been characterised by Raman spectroscopy at 298 K. The bands at 812 and 797 cm⁻¹ were assigned to the symmetric stretching modes of the (UO₂)²⁺ and (SeO₃)²⁻ units, respectively. These values gave the calculated U O bond lengths in uranyl of 1.799 and/or 1.814 Å. Average U O bond length in uranyl is 1.795 Å, inferred from the X‐ray single crystal structure analysis of marthozite by Cooper and Hawthorne. The broad band at 869 cm⁻¹ was assigned to the ν₃ antisymmetric stretching mode of the (UO₂)²⁺ (calculated U O bond length 1.808 Å). The band at 739 cm⁻¹ was attributed to the ν₃ antisymmetric stretching vibration of the (SeO₃)²⁻ units. The ν₄ and the ν₂ vibrational modes of the (SeO₃)²⁻ units were observed at 424 and 473 cm⁻¹. Bands observed at 257, and 199 and 139 cm⁻¹ were assigned to OUO bending vibrations and lattice vibrations, respectively. O H···O hydrogen bond lengths were inferred using Libowiztky's empirical relation. The infrared spectrum of marthozite was studied for complementation. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopy of hydrogen‐arsenate group (AsO3OH) in solid‐state compounds: copper mineral phase geminite Cu(AsO3OH)·H2O from different geological environments

The participation of hydrogen‐arsenate group (AsO₃OH)²⁻ in solid‐state compounds may serve as a model example for explaining and clarifying the behaviour of As and other elements during weathering processes in natural environment. The mineral geminite, a hydrated hydrogen‐arsenate mineral of ideal formula Cu(AsO₃OH)·H₂O, has been studied by Raman and infrared spectroscopies. Two samples of geminite of different origin were investigated and the spectra proved quite similar. In the Raman spectra of geminite, six bands are observed at 741, 812, 836, 851, 859 and 885 cm⁻¹ (Salsigne, France), and 743, 813, 843, 853, 871 and 885 cm⁻¹ (Jáchymov, Czech Republic). The band at 851/853 cm⁻¹ is assigned to the ν₁ (AsO₃OH)²⁻ symmetric stretching mode; the other bands are assigned to the ν₃ (AsO₃OH)²⁻ split triply degenerate antisymmetric stretching mode. Raman bands at 309, 333, 345 and 364/310, 333 and 345 cm⁻¹ are attributed to the ν₂ (AsO₃OH)²⁻ bending mode, and a set of higher wavenumber bands (in the range 400–500 cm⁻¹) is assigned to the ν₄ (AsO₃OH)²⁻ split triply degenerate bending mode. A very complex set of overlapping bands is observed in both the Raman and infrared spectra. Raman bands are observed at 2289, 2433, 2737, 2855, 3235, 3377, 3449 and 3521/2288, 2438, 2814, 3152, 3314, 3448 and 3521 cm⁻¹. Two Raman bands at 2289 and 2433/2288 and 2438 cm⁻¹ are ascribed to the strong hydrogen bonded water molecules. The Raman bands at 3235, 3305 and 3377/3152 and 3314 cm⁻¹ may be assigned to the ν OH stretching vibrations of water molecules. Two bands at 3449 and 3521/3448 and 3521 cm⁻¹ are assigned to the OH stretching vibrations of the (AsO₃OH)²⁻ units. The lengths of the O H···O hydrogen bonds vary in the range 2.60–2.94 Å (Raman) and 2.61–3.07 Å (infrared). Two Raman and infrared bands in the region of the bending vibrations of the water molecules prove that structurally non‐equivalent water molecules are present in the crystal structure of geminite. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the mineral finnemanite Pb5(As3+O3)3Cl

The arsenite mineral finnemanite Pb₅(As³⁺ O₃)₃Cl has been studied by Raman spectroscopy. The most intense Raman band at 871 cm⁻¹ is assigned to the ν₁(AsO₃)³⁻ symmetric stretching vibration. Three Raman bands at 898, 908 and 947 cm⁻¹ are assigned to the ν₃(AsO₃)³⁻ antisymmetric stretching vibration. The observation of multiple antisymmetric stretching vibrations suggest that the (AsO₃)³⁻ units are not equivalent in the molecular structure of finnemanite. Two Raman bands at 383 and 399 cm⁻¹are assigned to the ν₂(AsO₃)³⁻ bending modes. Density functional theory enabled calculation of the position of AsO₃²⁻ symmetric stretching mode at 839 cm⁻¹, the antisymmetric stretching mode at 813 cm⁻¹ and the deformation mode at 449 cm⁻¹. Raman bands are observed at 115, 145, 162, 176, 192, 216 and 234 cm⁻¹ as well. The two most intense bands are observed at 176 and 192 cm⁻¹. These bands are assigned to PbCl stretching vibrations and result from transverse/longitudinal splitting. The bands at 145 and 162 cm⁻¹ may be assigned to Cl Pb Cl bending modes. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl mineral pseudojohannite Cu6.5[(UO2)4O4(SO4)2]2(OH)5·25H2O

Raman spectra of pseudojohannite were studied and related to the structure of the mineral. Observed bands were assigned to the stretching and bending vibrations of (UO₂)²⁺ and (SO₄)²⁻ units and of water molecules. The published formula of pseudojohannite is Cu_6.5(UO₂)₈[O₈](OH)₅[(SO₄)₄]·25H₂O. Raman bands at 805 and 810 cm⁻¹ are assigned to (UO₂)²⁺ stretching modes. The Raman bands at 1017 and 1100 cm⁻¹ are assigned to the (SO₄)²⁻ symmetric and antisymmetric stretching vibrations. The three Raman bands at 423, 465 and 496 cm⁻¹ are assigned to the (SO₄)²⁻ν₂ bending modes. The bands at 210 and 279 cm⁻¹ are assigned to the doubly degenerate ν₂ bending vibration of the (UO₂)²⁺ units. U O bond lengths in uranyl and O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the schmiederite Pb2Cu2[(OH)4|SeO3|SeO4]

Raman spectroscopy lends itself to the studies of selenites, selenates, tellurites and tellurates as well as related minerals. The mineral schmiederite Pb₂Cu₂[(OH)₄|SeO₃|SeO₄], is interesting, in that, both selenite and selenate anions occur in the structure. Raman bands of schmiederite at 1095 and 934 cm⁻¹ are assigned to the symmetric and antisymmetric mode of the (SeO₄)²⁻ anions. For selenites, the symmetric stretching mode occurs at a higher position than the antisymmetric stretching mode, as is evidenced in the Raman spectrum of schmiederite. The band at 834 cm⁻¹ is assigned to the symmetric (SeO₃)²⁻ units. The two bands at 764 and 739 cm⁻¹ are attributed to the antisymmetric (SeO₃)²⁻ units. An intense, sharp band at 398 cm⁻¹ is assigned to the ν₂ bending mode. The two bands at 1576 and 1604 cm⁻¹ are assigned to the deformation modes of the OH units. The observation of multiple OH bands supports the concept of a much distorted structure. This is based upon the four OH units coordinating the copper in a square planar structure. A single symmetric Raman band is observed at 3428 cm⁻¹ and is assigned to the symmetric stretching mode of the OH units. The observation of multiple infrared OH stretching bands supports the concept of non‐equivalent OH units in the schmiederite structure. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopy of uranopilite of different origins—implications for molecular structure

Uranopilite, [(UO₂)₆(SO₄)O₂(OH)₆(H₂O)₆](H₂O)₈, the composition of which may vary, can be understood as a complex hydrated uranyl oxyhydroxy sulfate. The structure of uranopilite from different locations has been studied by Raman spectroscopy at 298 and 77 K. A single intense band at 1009 cm⁻¹ assigned to the ν₁ (SO₄)²⁻ symmetric stretching mode shifts to higher wavenumbers at 77 K. Three low‐intensity bands are observed at 1143, 1117 and 1097 cm⁻¹. These bands are attributed to the (SO₄)²⁻ ν₃ anti‐symmetric stretching modes. Multiple bands provide evidence that the symmetry of the sulfate anion in the uranopilite structure is lowered. Three bands are observed in the region 843 to 816 cm⁻¹ in both the 298 and 77 K spectra and are attributed to the ν₁ symmetric stretching modes of the (UO₂)²⁺ units. Multiple bands prove the symmetry reduction of the UO₂ ion. Multiple OH stretching modes prove a complex arrangement of OH groupings and hydrogen bonding in the crystal structure. A series of infrared bands not observed in the Raman spectra are found at 1559, 1540, 1526 and 1511 cm⁻¹ attributed to δ UOH bending modes. U‐O bond lengths in uranyl and O H/dotbondO bond lengths are calculated and compared with those from X‐ray single crystal structure analysis. The Raman spectra of uranopilites of different origins show subtle differences, proving that the spectra are origin‐ and sample‐dependent. Hydrogen‐bonding network and its arrangement in the crystal structure play an important role in the origin and stability of uranopilite. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman spectroscopy of the nickel silicate mineral pecoraite—an analogue of chrysotile (asbestos)

The molecular structure of the mineral pecoraite, the nickel analogue of chrysotile of formula Ni₃Si₂O₅(OH)₄, was analysed by a combination of Raman and infrared spectroscopies. A comparison is made with the spectra of the minerals nepouite and chrysotile and a synthetic pecoraite. Pecoraite is characterised by OH stretching vibrations at 3645 and 3683 cm⁻¹ attributed to the inner and inner surface hydroxyl stretching vibrations. Intense infrared bands at around 3288 and 3425 cm⁻¹ are assigned to the stretching vibrations of water strongly hydrogen‐bonded to the surface of the pecoraite. The asbestos‐like mineral is characterised by SiO stretching vibrations at 979, 1075, 1128 and 1384 cm⁻¹, OSiO chain vibrations at 616 and 761 cm⁻¹ and Ni O(H) vibrations at 397 and 451 cm⁻¹. Copyright © 2008 John Wiley & Sons, Ltd.     

Transition of chromium oxyhydroxide nanomaterials to chromium oxide: a hot‐stage Raman spectroscopic study

The transition of disc‐like chromium hydroxide nanomaterials to chromium oxide nanomaterials has been studied by hot‐stage Raman spectroscopy. The structure and morphology of α‐CrO(OH) synthesised using hydrothermal treatment were confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The Raman spectrum of α‐CrO(OH) is characterised by two intense bands at 823 and 630 cm⁻¹ attributed to ν₁ Cr^III O symmetric stretching mode and the band at 1179 cm⁻¹ attributed to Cr^III OH δ deformation modes. No bands are observed above 3000 cm⁻¹. The absence of characteristic OH stretching vibrations may be due to short hydrogen bonds in the α‐CrO(OH) structure. Upon thermal treatment of α‐CrO(OH), new Raman bands are observed at 599, 542, 513, 396, 344 and 304 cm⁻¹, which are attributed to Cr₂O₃. This hot‐stage Raman study shows that the transition of α‐CrO(OH) to Cr₂O₃ occurs before 350 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectrum of decrespignyite [(Y,REE)4Cu(CO3)4Cl(OH)5·2H2O] and its relation with those of other halogenated carbonates including bastnasite,hydroxybastnasite, parisite and northupite

Raman spectroscopy complemented with infrared spectroscopy has been used to study the rare‐earth‐based mineral decrespignyite [(Y,REE)₄Cu(CO₃)₄Cl(OH)₅· 2H₂O] and the spectrum compared with the Raman spectra of a series of selected natural halogenated carbonates from different origins including bastnasite, parisite and northupite. The Raman spectrum of decrespignyite displays three bands at 1056, 1070 and 1088 cm⁻¹ attributed to the CO₃²⁻ symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of the CO₃²⁻ symmetric stretching vibration varies with the mineral composition. The Raman spectrum of decrespignyite shows bands at 1391, 1414, 1489 and 1547 cm⁻¹, whereas the Raman spectra of bastnasite, parisite and northupite show a single band at 1433, 1420 and 1554 cm⁻¹, respectively, assigned to the ν₃ (CO₃)²⁻ antisymmetric stretching mode. The observation of additional Raman bands for the ν₃ modes for some halogenated carbonates is significant in that it shows distortion of the carbonate anion in the mineral structure. Four Raman bands are observed at 791, 815, 837 and 849 cm⁻¹, which are assigned to the (CO₃)²⁻ν₂ bending modes. Raman bands are observed for decrespignyite at 694, 718 and 746 cm⁻¹ and are assigned to the (CO₃)²⁻ν₄ bending modes. Raman bands are observed for the carbonate ν₄ in‐phase bending modes at 722 cm⁻¹ for bastnasite, 736 and 684 cm⁻¹ for parisite and 714 cm⁻¹ for northupite. Multiple bands are observed in the OH stretching region for decrespignyite, bastnasite and parisite, indicating the presence of water and OH units in the mineral structure. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the magnesium‐carbonate minerals—artinite and dypingite

Magnesium minerals are important in the understanding of the concept of geosequestration. The two hydrated hydroxy magnesium‐carbonate minerals artinite and dypingite were studied by Raman spectroscopy. Intense bands are observed at 1092 cm⁻¹ for artinite and at 1120 cm⁻¹ for dypingite, attributed ν₁ symmetric stretching mode of CO₃²⁻. The ν₃ antisymmetric stretching vibrations of CO₃²⁻ are extremely weak and are observed at 1412 and 1465 cm⁻¹ for artinite and at 1366, 1447 and 1524 cm⁻¹ for dypingite. Very weak Raman bands at 790 cm⁻¹ for artinite and 800 cm⁻¹ for dypingite are assigned to the CO₃²⁻ν₂ out‐of‐plane bend. The Raman band at 700 cm⁻¹ of artinite and at 725 and 760 cm⁻¹ of dypingite are ascribed to CO₃²⁻ν₂ in‐plane bending mode. The Raman spectrum of artinite in the OH stretching region is characterised by two sets of bands: (1) an intense band at 3593 cm⁻¹ assigned to the MgOH stretching vibrations and (2) the broad profile of overlapping bands at 3030 and 3229 cm⁻¹ attributed to water stretching vibrations. X‐ray diffraction studies show that the minerals are disordered. This is reflected in the difficulty of obtaining Raman spectra of reasonable quality, and explains why the Raman spectra of these minerals have not been previously or sufficiently described. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl oxyhydroxide hydrates: becquerelite,billietite, curite,schoepite and vandendriesscheite

Raman and infrared spectra of five uranyl oxyhydroxide hydrates, becquerelite, billietite, curite, schoepite and vandendriesscheite, are reported. The observed bands are attributed to the (UO₂)²⁺ stretching and bending vibrations, U OH bending vibrations and H₂O and (OH)⁻ stretching, bending and libration modes. The U O bond lengths in uranyls and the O H···O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. They are close to the values inferred and/or predicted from the X‐ray single‐crystal structure. The complex hydrogen‐bonding network arrangement was proved in the structures of all the minerals studied. This hydrogen bonding contributes to the stability of these uranyl minerals. Copyright © 2006 John Wiley & Sons, Ltd. John Wiley & Sons, Ltd.     

Raman spectroscopic study of the selenite mineral mandarinoite Fe2Se3O9·6H2O

Selenites and tellurites may be subdivided according to formula and structure. There are five groups, based upon the formulae (a) A(XO₃), (b) A(XO₃·) xH₂O, (c) A₂(XO₃)₃·xH₂O, (d) A₂(X₂O₅) and (e) A(X₃O₈). Of the selenites, molybdomenite is an example of type (a); chalcomenite, clinochalcomenite, cobaltomenite and ahlfeldite are minerals of type (b); mandarinoite Fe₂Se₃O₉·6H₂O is an example of type (c). Raman spectroscopy has been used to characterise the mineral mandarinoite. The intense, sharp band at 814 cm⁻¹ is assigned to the symmetric stretching (Se₃O₉)⁶⁻ units. Three Raman bands observed at 695, 723 and 744 cm⁻¹ are attributed to the ν₃ (Se₃O₉)⁶⁻ anti‐symmetric stretching modes. Raman bands at 355, 398 and 474 cm⁻¹ are assigned to the ν₄ and ν₂ bending modes. Raman bands are observed at 2796, 2926, 3046, 3189 and 3507 cm⁻¹ and are assigned to OH stretching vibrations. The observation of multiple OH stretching vibrations suggests the non‐equivalence of water in the mandarinoite structure. The use of the Libowitzky empirical function provides hydrogen bond distances of 2.633(9) Å (2926 cm⁻¹), 2.660(0) Å (3046 cm⁻¹), 2.700(0) Å (3189 cm⁻¹) and 2.905(3) Å (3507 cm⁻¹). The sharp, intense band at 3507 cm⁻¹ may be due to hydroxyl units. It is probable that some of the selenite units have been replaced by hydroxyl units. Copyright © 2008 John Wiley & Sons, Ltd.     

A Raman spectroscopic study of the uranyl mineral rutherfordine—revisited

The molecular structure of the uranyl mineral rutherfordine has been investigated by the measurement of the near‐infrared (NIR) and Raman spectra and complemented with infrared spectra including their interpretation. The spectra of rutherfordine show the presence of both water and hydroxyl units in the structure as evidenced by IR bands at 3562 and 3465 cm⁻¹ (OH) and 3343, 3185 and 2980 cm⁻¹ (H₂O). Raman spectra show the presence of four sharp bands at 3511, 3460, 3329 and 3151 cm⁻¹. Corresponding molecular water bending vibrations were only observed in both Raman and infrared spectra of one of two studied rutherfordine samples. The second rutherfordine sample studied contained only hydroxyl ions in the equatorial uranyl plane and did not contain any molecular water. The infrared spectra of the (CO₃)²⁻ units in the antisymmetric stretching region show complexity with three sets of carbonate bands observed. This combined with the observation of multiple bands in the (CO₃)²⁻ bending region in both the Raman and IR spectra suggests that both monodentate and bidentate (CO₃)²⁻ units may be present in the structure. This cannot be exactly proved and inferred from the spectra; however, it is in accordance with the X‐ray crystallographic studies. Complexity is also observed in the IR spectra of (UO₂)²⁺ antisymmetric stretching region and is attributed to non‐identical UO bonds. U O bond lengths were calculated using wavenumbers of the ν₃ and ν₁ (UO₂)²⁺ and compared with data from X‐ray single crystal structure analysis of rutherfordine. Existence of solid solution having a general formula (UO₂)(CO₃)_1−x(OH)_2x.yH₂O (x, y ≥ 0) is supported in the crystal structure of rutherfordine samples studied. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Raman spectroscopic study of Mg/Al,Fe hydrotalcites with variable cationic ratios

Hydrotalcites of formula Mg₆(Al,Fe)₂(OH)₁₆(CO₃)·4H₂O formed by intercalation with the carbonate anion as a function of divalent/trivalent cationic ratio have been successfully synthesised. The XRD patterns show variation in the d‐spacing attributed to the size of the cation. Raman and infrared bands in the OH stretching region are assigned to (1) brucite layer OH stretching vibrations, (2) water stretching bands and (3) water strongly hydrogen bonded to the carbonate anion. Multiple (CO₃)²⁻ symmetric stretching bands suggest that different types of (CO₃)²⁻ exist in the hydrotalcite interlayer. Increasing the cation ratio (Mg/Al,Fe) resulted in an increase in the combined intensity of the two Raman bands at around 3600 cm⁻¹, attributed to Mg OH stretching modes, and a shift of the overall band profile to higher wavenumbers. These observations are believed to be a result of the increase in magnesium in the structure. Raman spectroscopy shows a reduction in the symmetry of the carbonate, leading to the conclusion that the anions are bonded to the brucite‐like hydroxyl surface and to the water in the interlayer. Water bending modes are identified in the infrared spectra at positions greater than 1630 cm⁻¹, indicating that water is strongly hydrogen bonded to both interlayer anions and the brucite‐like surface. Copyright © 2009 John Wiley & Sons, Ltd.