Raman spectroscopic study of the arsenite minerals leiteite ZnAs2O4, reinerite Zn3(AsO3)2 and cafarsite Ca5(Ti,Fe,Mn)7(AsO3)12·4H2O

The selected arsenite minerals leiteite, reinerite and cafarsite have been studied by Raman spectroscopy. Density functional theory (DFT) calculations enabled the position of the AsO₂²⁻ symmetric stretching mode at 839 cm⁻¹, the antisymmetric stretching mode at 813 cm⁻¹ and the deformation mode at 449 cm⁻¹ to be calculated. The Raman spectrum of leiteite shows bands at 804 and 763 cm⁻¹ assigned to the As₂O₄²⁻ symmetric and antisymmetric stretching modes. The most intense Raman band of leiteite is the band at 457 cm⁻¹ and is assigned to the ν₂ As₂O₄²⁻ bending mode. A comparison of the Raman spectrum of leiteite is made with the arsenite minerals reinerite and cafarsite. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the mineral gerstleyite Na2(Sb,As)8S13·2H2O and comparison with some heavy‐metal sulfides

The mineral gerstleyite is described as a sulfosalt as opposed to a sulfide. This study focuses on the Raman spectrum of gerstleyite Na₂(Sb,As)₈S₁₃·2H₂O and makes a comparison with the Raman spectra of other common sulfides including stibnite, cinnabar and realgar. The intense Raman bands of gerstleyite at 286 and 308 cm⁻¹ are assigned to the SbS₃E antisymmetric and A₁ symmetric stretching modes of the SbS₃ units. The band at 251 cm⁻¹ is assigned to the bending mode of the SbS₃ units. The mineral stibnite also has basic structural units of Sb₂S₃ and SbS₃ pyramids with C_3v symmetry. Raman bands of stibnite Sb₂S₃ at 250, 296, 372 and 448 cm⁻¹ are assigned to Sb S stretching vibrations and the bands at 145 and 188 cm⁻¹ to S Sb S bending modes. The Raman band for cinnabar HgS at 253 cm⁻¹ fits well with the assignment of the band for gerstleyite at 251 cm⁻¹ to the S Sb S bending mode. Raman bands in similar positions are observed for realgar AsS and orpiment As₂S₃. 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.     

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.     

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 halogen‐containing carbonates

Raman spectroscopy complemented with infrared spectroscopy has been used to study a series of selected natural halogenated carbonates from different origins, including bastnasite, parisite and northupite. The position of CO₃²⁻ symmetric stretching vibration varies with the mineral composition. An additional band for northupite at 1107 cm⁻¹ is observed. Raman spectra of bastnasite, parisite and northupite show single bands at 1433, 1420 and 1554 cm⁻¹, respectively, assigned to the ν₃ (CO₃)²⁻ asymmetric 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 CaO₆ octahedron. No ν₂ Raman bending modes are observed for these minerals. The band is observed in the infrared spectra, and multiple ν₂ modes at 844 and 867 cm⁻¹ are observed for parisite. A single intense infrared band is found at 879 cm⁻¹ for northupite. Raman bands are observed forthe 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 selected bastansites and parisites, indicating the presence of water and OH units in the mineral structure. The presence of such bands brings into question the actual formula of these halogenated carbonate minerals. Copyright © 2007 John Wiley & Sons, Ltd.     

Raman microscopy of haidingerite Ca(AsO3OH)·H2O and brassite Mg(AsO3OH)·4H2O

Raman spectroscopy has been used to study the arsenate minerals haidingerite Ca(AsO₃OH)·H₂O and brassite Mg(AsO₃OH)·4H₂O. Intense Raman bands in the haidingerite spectrum observed at 745 and 855 cm⁻¹ are assigned to the (AsO₃OH)²⁻ν₃ antisymmetric stretching and ν₁ symmetric stretching vibrational modes. For brassite, two similarly assigned intense bands are found at 809 and 862 cm⁻¹. The observation of multiple Raman bands in the (AsO₃OH)²⁻ stretching and bending regions suggests that the arsenate tetrahedrons in the crystal structures of both minerals studied are strongly distorted. Broad Raman bands observed at 2842 cm⁻¹ for haidingerite and 3035 cm⁻¹ for brassite indicate strong hydrogen bonding of water molecules in the structure of these minerals. OH···O hydrogen‐bond lengths were calculated from the Raman spectra based on empirical relations. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopy of selected borate minerals of the pinakiolité group

The Raman spectra of a series of related minerals of the pinakiolité group 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 D_3h to C₁. Intense Raman bands are observed for the minerals takeuchiité, pinakiolité, fredrikssonité and azoproité 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; and 1436, 1749 cm⁻¹, respectively. One probable assignment is to ν₃ BO₃³⁻ antisymmetric stretching mode. Intense Raman bands of the studied minerals at 712 cm⁻¹ are 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. 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 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.     

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 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 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 and mid‐IR spectroscopic study of the magnesium carbonate minerals—brugnatellite and coalingite

Two hydrated hydroxy magnesium carbonate minerals brugnatellite and coalingite with a hydrotalcite‐like structure were studied by Raman spectroscopy. Intense bands are observed at 1094 cm⁻¹ for brugnatellite and at 1093 cm⁻¹ for coalingite attributed to the CO₃²⁻ν₁ symmetric stretching mode. Additional low intensity bands are observed at 1064 cm⁻¹. The existence of two symmetric stretching modes is accounted for in terms of different anion structural arrangements. Very low intensity bands at 1377 and 1451 cm⁻¹ are observed for brugnatellite, and the Raman spectrum of coalingite displays two bands at 1420 and 1465 cm⁻¹ attributed to the (CO₃)²⁻ν₃ antisymmetric stretching modes. Very low intensity bands at 792 cm⁻¹ for brugnatellite and 797 cm⁻¹ for coalingite are assigned to the CO₃²⁻ out‐of‐plane bend (ν₂). X‐ray diffraction studies by other researchers have shown that these 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. A comparison is made with the Raman spectra of other hydrated magnesium carbonate minerals. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the tellurite minerals: graemite CuTeO3·H2O and teineite CuTeO3·2H2O

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). Raman spectroscopy has been used to study the tellurite minerals teineite and graemite; both contain water as an essential element of their stability. The tellurite ion should show a maximum of six bands. The free tellurite ion will have C_3v symmetry and four modes, 2A₁ and 2 E. Raman bands for teineite at 739 and 778 cm⁻¹ and for graemite at 768 and 793 cm⁻¹ are assigned to the ν₁ (TeO₃)²⁻ symmetric stretching mode while bands at 667 and 701 cm⁻¹ for teineite and 676 and 708 cm⁻¹ for graemite are attributed to the ν₃ (TeO₃)²⁻ antisymmetric stretching mode. The intense Raman band at 509 cm⁻¹ for both teineite and graemite is assigned to the water librational mode. Raman bands for teineite at 318 and 347 cm⁻¹ are assigned to the (TeO₃)²⁻ν₂(A₁) bending mode and the two bands for teineite at 384 and 458 cm⁻¹ may be assigned to the (TeO₃)²⁻ν₄(E) bending mode. Prominent Raman bands, observed at 2286, 2854, 3040 and 3495 cm⁻¹, are attributed to OH stretching vibrations. The values for these OH stretching vibrations provide hydrogen bond distances of 2.550(6) Å (2341 cm⁻¹), 2.610(3) Å (2796 cm⁻¹) and 2.623(2) Å (2870 cm⁻¹) which are comparatively short for secondary minerals. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopic investigation of pure and ytterbium‐doped rare earth silicate crystals

Raman spectroscopy was used to study the molecular structure of a series of selected rare earth (RE) silicate crystals including Y₂SiO₅ (YSO), Lu₂SiO₅ (LSO), (Lu_0.5Y_0.5)₂SiO₅ (LYSO) and their ytterbium‐doped samples. Raman spectra show resolved bands below 500 cm⁻¹ region assigned to the modes of SiO₄ and oxygen vibrations. Multiple bands indicate the nonequivalence of the RE O bonds and the lifting of the degeneracy of the RE ion vibration. Low intensity bands below 500 cm⁻¹ are an indication of impurities. The (SiO₄)⁴⁻ tetrahedra are characterized by bands near 200 cm⁻¹ which show a separation of the components of ν₄ and ν₂, in the 500–700 cm⁻¹ region which are attributed to the distorting bending vibration and in the 880–1000 cm⁻¹ region which are attributed to the symmetric and antisymmetric stretching vibrational modes. The majority of the bands in the 300–610 cm⁻¹ region of Re₂SiO₅ were found to arise from vibrations involving both Si and RE ions, indicating that there is considerable mixing of Si displacements with Si O bending modes and RE O stretching modes. The Raman spectra of RE silicate crystals were analyzed in terms of the molecular structure of the crystals, which enabled separation of the bands attributed to distinct vibrational units. Copyright © 2007 John Wiley & Sons, Ltd.     

High‐pressure studies of the micro‐Raman spectra of iron cyanide complexes: Prussian blue (Fe4[Fe(CN)6]3), potassium ferricyanide (K3[Fe(CN)6]), and sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O)

The pressure dependences of the peaks observed in the micro‐Raman spectra of Prussian blue (Fe₄[Fe(CN)₆]₃), potassium ferricyanide (K₃[Fe(CN)₆]), and sodium nitroprusside (Na₂[Fe(CN)₅(NO)]·2H₂O) have been measured up to 5.0 GPa. The vibrational modes of Prussian blue appearing at 201 and 365 cm⁻¹ show negative dν/dP values and Grüneisen parameters and are assigned to the transverse bending modes of the Fe C N Fe linkage which can contribute to a negative thermal expansion behavior. A phase transition occurring between 2.0 and 2.8 GPa in potassium ferricyanide is shown by changes in the spectral region 150–700 cm⁻¹. In the spectra of the nitroprusside ion, there are strong interactions between the FeN stretching mode and the FeNO bending and the axial CN stretching modes. The pressure dependence of the NO stretching vibration is positive, 5.6 cm⁻¹ GPa⁻¹, in contrast to the negative behavior in the iron(II)‐meso‐tetraphenyl porphyrinate complex. Copyright © 2011 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 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.