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 spectroscopic study of the multi‐anion uranyl mineral schroeckingerite

Raman spectroscopy complemented with infrared (IR) spectroscopy has been used to study the mineral schroeckingerite. The mineral is a multi‐anion mineral and has (UO₂)²⁺, (SO₄)²⁻ and (CO₃)²⁻ units in its structure, and bands attributed to these vibrating units are readily identified in the Raman spectra. Symmetric stretching modes at 815, 983 and 1092 cm⁻¹ are assigned to (UO₂)²⁺, (SO₄)²⁻ and (CO₃)²⁻ units, respectively. The antisymmetric stretching modes of (UO₂)²⁺, (SO₄)²⁻ are not observed in the Raman spectra but may be readily observed in the IR spectrum at 898 and 1180 cm⁻¹. The antisymmetric stretching mode of (CO₃)²⁻ is observed in the Raman spectrum at 1374 cm⁻¹, as is also the ν₄ (CO₃)²⁻ bending modes at 742 and 707 cm⁻¹. No ν₂ (CO₃)²⁻ bending modes are observed in the Raman spectrum of schroeckingerite. All the spectroscopic evidence points to a highly ordered structure of this mineral. Copyright © 2007 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.     

A Raman spectroscopic study of the different vanadate groups in solid‐state compounds—model case: mineral phases vésigniéite [BaCu3(VO4)2(OH)2] and volborthite [Cu3V2O7(OH)2·2H2O]

Raman spectroscopy has been used to study vanadates in the solid state. The molecular structure of the vanadate minerals vésigniéite [BaCu₃(VO₄)₂(OH)₂] and volborthite [Cu₃V₂O₇(OH)₂·2H₂O] have been studied by Raman spectroscopy and infrared spectroscopy. The spectra are related to the structure of the two minerals. The Raman spectrum of vésigniéite is characterized by two intense bands at 821 and 856 cm⁻¹ assigned to ν₁ (VO₄)³⁻ symmetric stretching modes. A series of infrared bands at 755, 787 and 899 cm⁻¹ are assigned to the ν₃ (VO₄)³⁻ antisymmetric stretching vibrational mode. Raman bands at 307 and 332 cm⁻¹ and at 466 and 511 cm⁻¹ are assigned to the ν₂ and ν₄ (VO₄)³⁻ bending modes. The Raman spectrum of volborthite is characterized by the strong band at 888 cm⁻¹, assigned to the ν₁ (VO₃) symmetric stretching vibrations. Raman bands at 858 and 749 cm⁻¹ are assigned to the ν₃ (VO₃) antisymmetric stretching vibrations; those at 814 cm⁻¹ to the ν₃ (VOV) antisymmetric vibrations; that at 508 cm⁻¹ to the ν₁ (VOV) symmetric stretching vibration and those at 442 and 476 cm⁻¹ and 347 and 308 cm⁻¹ to the ν₄ (VO₃) and ν₂ (VO₃) bending vibrations, respectively. The spectra of vésigniéite and volborthite are similar, especially in the region of skeletal vibrations, even though their crystal structures differ. Copyright © 2011 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.     

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.     

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 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 spectroscopic study of the multi‐anion mineral dixenite CuMn2+14Fe3+(AsO3)5(SiO4)2(AsO4)(OH)6

The mixed anion mineral dixenite has been studied by Raman spectroscopy, complemented with infrared spectroscopy. The Raman spectrum of dixenite shows bands at 839 and 813 cm⁻¹ assigned to the (AsO₃)³⁻ symmetric and antisymmetric stretching modes. The most intense Raman band of dixenite is the band at 526 cm⁻¹ and is assigned to the ν₂ AsO₃³⁻ bending mode. DFT calculations enabled the calculation of the position of AsO₂²⁻ symmetric stretching mode at 839 cm⁻¹, the antisymmetric stretching mode at 813 cm⁻¹, and the deformation mode at 449 cm⁻¹. The Raman bands at 1026 and 1057 cm⁻¹ are assigned to the SiO₄²⁻ symmetric stretching vibrations and those at 1349 and 1386 cm⁻¹ to the SiO₄²⁻ antisymmetric stretching vibrations. Both Raman and infrared spectra indicate the presence of water in the structure of dixenite. This brings into question the commonly accepted formula of dixenite as CuMn²⁺₁₄Fe³⁺(AsO₃)₅(SiO₄)₂(AsO₄)(OH)₆. The formula may be better written as CuMn²⁺₁₄Fe³⁺(AsO₃)₅(SiO₄)₂(AsO₄)(OH)₆·xH₂O. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the mixed anion mineral yecoraite Bi5Fe3O9(Te4+O3)(Te6+O4)2·9H2O

Tellurates are rare minerals as the tellurate anion is readily reduced to the tellurite ion. Often minerals with both tellurate and tellurite anions are found. An example of such a mineral containing tellurate and tellurite is yecoraite. Raman spectroscopy has been used to study this mineral, the exact structure of which is unknown. Two Raman bands at 796 and 808 cm⁻¹ are assigned to the ν₁(TeO₄)²⁻ symmetric and ν₃(TeO₃)²⁻ antisymmetric stretching modes and Raman bands at 699 cm⁻¹ are attributed to the ν₃(TeO₄)²⁻ antisymmetric stretching mode and the band at 690 cm⁻¹ to the ν₁(TeO₃)²⁻ symmetric stretching mode. The intense band at 465 cm⁻¹ with a shoulder at 470 cm⁻¹ is assigned the (TeO₄)²⁻ and (TeO₃)²⁻ bending modes. Prominent Raman bands are observed at 2878, 2936, 3180 and 3400 cm⁻¹. The band at 3936 cm⁻¹ appears quite distinct and the observation of multiple bands indicates the water molecules in the yecoraite structure are not equivalent. The values for the OH stretching vibrations listed provide hydrogen bond distances of 2.625 Å (2878 cm⁻¹), 2.636 Å (2936 cm⁻¹), 2.697 Å (3180 cm⁻¹) and 2.798 Å (3400 cm⁻¹). This range of hydrogen bonding contributes to the stability of the mineral. A comparison of the Raman spectra of yecoraite with that of tellurate containing minerals kuranakhite, tlapallite and xocomecatlite is made. Copyright © 2009 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 hydroxy‐arsenate‐sulfate mineral chalcophyllite Cu18Al2(AsO4)4(SO4)3(OH)24·36H2O

The mixed anion mineral chalcophyllite Cu₁₈Al₂(AsO₄)₄(SO₄)₃(OH)₂₄·36H₂O has been studied by using Raman and infrared spectroscopies. Characteristic bands associated with arsenate, sulfate and hydroxyl units are identified. Broad bands in the OH stretching region are observed and are resolved into component bands. Estimates of hydrogen bond distances were made using a Libowitzky function. Both short and long hydrogen bonds were identified. Two intense bands at 841 and ∼814 cm⁻¹ are assigned to the ν₁ (AsO₄)³⁻ symmetric stretching and ν₃ (AsO₄)³⁻ antisymmetric stretching modes. The comparatively sharp band at 980 cm⁻¹ is assigned to the ν₁ (SO₄)²⁻ symmetric stretching mode, and a broad spectral profile centred upon 1100 cm⁻¹ is attributed to the ν₃ (SO₄)²⁻ antisymmetric stretching mode. A comparison of the Raman spectra is made with other arsenate‐bearing minerals such as carminite, clinotyrolite, kankite, tilasite and pharmacosiderite. Copyright © 2010 John Wiley & Sons, Ltd.     

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 synthesized 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 characterize the synthesized gallium‐containing hydrotalcites of formula Mg₆Ga₂(CO₃)(OH)₁₆· 4H₂O. Raman bands observed at around 1046, 1048 and 1058 cm⁻¹ are 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 that 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. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Raman spectroscopic characterisation of hydrotalcites based on the formula Ca6Al2(CO3)(OH)16· 4H2O

We have successfully synthesised hydrotalcites (HTs) containing calcium, which are naturally occurring minerals. Insight into the unique structure of HTs has been obtained using a combination of X‐ray diffraction (XRD) as well as infrared and Raman spectroscopies. Calcium‐containing hydrotalcites (Ca‐HTs) of the formula Ca₄Al₂(CO₃)(OH)₁₂·4H₂O (2:1 Ca‐HT) to Ca₈Al₂(CO₃)(OH)₂₀· 4H₂O (4:1 Ca‐HT) have been successfully synthesised and characterised by XRD and Raman spectroscopy. XRD has shown that 3:1 calcium HTs have the largest interlayer distance. Raman spectroscopy complemented with selected infrared data has been used to characterise the synthesised Ca‐HTs. The Raman bands observed at around 1086 and 1077 cm⁻¹ were attributed to the ν₁ symmetric stretching modes of the (CO₃²⁻) units of calcite and carbonate intercalated into the HT interlayer. The corresponding ν₃ CO₃²⁻ antisymmetric stretching modes are found at around 1410 and 1475 cm⁻¹. Copyright © 2010 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 spectroscopic study of the magnesium carbonate mineral hydromagnesite (Mg5[(CO3)4(OH)2]· 4H2O)

Magnesium minerals are important for understanding the concept of geosequestration. One method of studying the hydrated hydroxy magnesium carbonate minerals is through vibrational spectroscopy. A combination of Raman and infrared spectroscopy has been used to study the mineral hydromagnesite. An intense band is observed at 1121 cm⁻¹, attributed to the CO₃²⁻ν₁ symmetric stretching mode. A series of infrared bands at 1387, 1413 and 1474 cm⁻¹ are assigned to the CO₃²⁻ν₃ antisymmetric stretching modes. The CO₃²⁻ν₃ antisymmetric stretching vibrations are extremely weak in the Raman spectrum and are observed at 1404, 1451, 1490 and 1520 cm⁻¹. A series of Raman bands at 708, 716, 728 and 758 cm⁻¹ are assigned to the CO₃²⁻ν₂ in‐plane bending mode. The Raman spectrum in the OH stretching region is characterized by bands at 3416, 3516 and 3447 cm⁻¹. In the infrared spectrum, a broad band is found at 2940 cm⁻¹, which is assigned to water stretching vibrations. Infrared bands at 3430, 3446, 3511, 2648 and 3685 cm⁻¹ are attributed to MgOH stretching modes. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopy of smithsonite

Raman spectroscopy at both 298 and 77 K has been used to study a series of selected natural smithsonites from different origins. An intense sharp band at 1092 cm⁻¹ is assigned to the CO₃²⁻ symmetric stretching vibration. Impurities of hydrozincite are identified by a band around 1060 cm⁻¹. An additional band at 1088 cm⁻¹ which is observed in the 298 K spectra but not in the 77 K spectra is attributed to a CO₃²⁻ hot band. Raman spectra of smithsonite show a single band in the 1405–1409 cm⁻¹ range assigned to the ν₃ (CO₃)²⁻ antisymmetric stretching mode. The observation of additional bands for the ν₃^g modes for some smithsonites is significant in that it shows distortion of the ZnO₆ octahedron. No ν₂ bending modes are observed for smithsonite. A single band at 730 cm⁻¹ is assigned to the ν₄ in phase bending mode. Multiple bands be attributed to the structural distortion are observed for the carbonate ν₄ in phase bending modes in the Raman spectrum of hydrozincite with bands at 733, 707 and 636 cm⁻¹. An intense band at 304 cm⁻¹ is attributed to the ZnO symmetric stretching vibration. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and Raman spectroscopy of indium‐based hydrotalcites of formula Mg6In2(CO3)(OH)16· 4H2O

Insight into the unique structure of layered double hydroxides has been obtained using a combination of X‐ray diffraction and Raman spectroscopy. Indium‐containing hydrotalcites of formula Mg₄In₂(CO₃)(OH)₁₂· 4H₂O [2:1 In‐LDH (layered double hydroxides)] through to Mg₈In₂(CO₃)(OH)₁₈· 4H₂O (4:1 In‐LDH) with variation in the Mg : In ratio have been successfully synthesized. The d(003) spacing varied from 7.83 Å for the 2:1 LDH to 8.15 Å for the 3:1 indium‐containing layered double hydroxide. Raman spectroscopy complemented with selected infrared data has been used to characterize the synthesized indium‐containing layered double hydroxides of formula Mg₆In₂(CO₃)(OH)₁₆· 4H₂O. Raman bands observed at around 1058, 1075 and 1115 cm⁻¹ are attributed to the symmetric stretching modes of the CO₃²⁻ units. Multiple ν₃ CO₃²⁻ antisymmetric stretching modes are found at around 1348, 1373, 1429 and 1488 cm⁻¹ in the infrared spectra. The splitting of this mode indicates that the carbonate anion is in a perturbed state. Raman bands observed at 690 and 700 cm⁻¹ assigned to the ν₄ CO₃²⁻ modes support the concept of multiple carbonate species in the interlayer. 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.     

Raman spectroscopy of gallium‐ and zinc‐based hydrotalcites

Insight into the unique structure of hydrotalcites (HTs) has been obtained using Raman spectroscopy. Gallium‐containing 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 synthesised 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 compounds. Raman spectroscopy complemented with selected infrared data has been used to characterise the synthesised gallium‐containing HTs. Raman bands observed at around 1050, 1060 and 1067 cm⁻¹ are attributed to the symmetric stretching modes of the (CO₃²⁻) units. Multiple ν₃ (CO₃²⁻) antisymmetric 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 observed at 710 and 717 cm⁻¹ and assigned to the ν₄ (CO₃²⁻) modes support the concept of multiple carbonate species in the interlayer. Copyright © 2010 John Wiley & Sons, Ltd.