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 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. The observed Raman bands were attributed to the (AsO₃OH)²⁻ stretching and bending vibrations as well as stretching and bending vibrations of water molecules and hydroxyl ions. The non‐interpreted Raman spectra of koritnigite from the RRUFF database and the 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. Copyright © 2010 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 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.     

A Raman spectroscopic study of bukovskýite Fe2(AsO4)(SO4)(OH)· 7H2O,a mineral phase with a significant role in arsenic migration

The Raman spectrum of bukovskýite [Fe³⁺₂(OH)(SO₄)(AsO₄)· 7H₂O] has been studied and compared with that of an amorphous gel containing specifically Fe, As and S, which is understood to be an intermediate product in the formation of bukovskýite. The observed bands are assigned to the stretching and bending vibrations of (SO₄)²⁻ and (AsO₄)³⁻ units, stretching and bending vibrations and vibrational modes of hydrogen‐bonded water molecules, stretching and bending vibrations of hydrogen‐bonded (OH)⁻ ions and Fe³⁺ (O,OH) units. The approximate range of O H···O hydrogen bond lengths was inferred from the Raman spectra. Raman spectra of crystalline bukovskýite and of the amorphous gel differ in that the bukovskýite spectrum is more complex, the observed bands are sharp and the degenerate bands of (SO₄)²⁻ and (AsO₄)³⁻ are split and more intense. Lower wavenumbers of δ H₂O bending vibrations in the spectrum of the amorphous gel may indicate the presence of weaker hydrogen bonds compared to those in bukovskýite. 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.     

A comprehensive spectroscopic study of synthetic Fe2+, Fe3+, Mg2+ and Al3+ copiapite by Raman,XRD, LIBS,MIR and vis–NIR

The identification of iron sulfates on Mars by the Mars Exploration Rovers (MERs) and the Mars Reconnaissance Orbiter emphasized the importance of studying iron sulfates in laboratory simulation experiments. The copiapite group of minerals was suggested as one of the potential iron sulfates occurring on the surface and subsurface on Mars, so it is meaningful to study their spectroscopic features, especially the spectral changes caused by cation substitutions. Four copiapite samples with cation substitutions (Fe³⁺, Al³⁺, Fe²⁺, Mg²⁺) were synthesized in our laboratory. Their identities were confirmed by powder X‐ray diffraction (XRD). Spectroscopic characterizations by Raman, mid‐IR, vis‐NIR and laser‐induced‐breakdown spectroscopy (LIBS) were conducted on those synthetic copiapite samples, as these technologies are being (and will be) used in current (and future) missions to Mars. We have found a systematic ν₁peak shift in the Raman spectra of the copiapite samples with cation substitutions, a consistent atomic ratio detection by LIBS, a set of systematic XRD line shifts representing structural change caused by the cation substitutions and a weakening of selection rules in mid‐IR spectra caused by the low site symmetry of (SO₄)²⁻ in the copiapite structures. The near‐infrared (NIR) spectra of the trivalent copiapite species show two strong diagnostic water features near 1.4 and 1.9 µm, with two additional bands near 2.0 µm. In the vis‐NIR spectra, the position of an electronic band shifts from 0.85 µm for ferricopiapite to 0.866 µm for copiapite, and this shift suggests the appearance of a Fe²⁺ electronic transition band near 0.9 µm. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopic study of synthetic reevesite and cobalt substituted reevesite (Ni,Co)6Fe2(OH)16(CO3)·4H2O

Raman spectroscopy, complemented with infrared spectroscopy of compounds equivalent to reevesite, formula (Ni,Co)₆Fe₂(OH)₁₆(CO₃)·4H₂O, with the ratio of Ni/Co ranging from 0 to 1, have been synthesised and characterised based on the molecular structure of the synthesised mineral. The combination of Raman spectroscopy with infrared spectroscopy enables an assessment of bands attributable to water stretching and brucite‐like surface hydroxyl units to be obtained. Raman spectroscopy shows a reduction in the symmetry of the carbonate anion, leading to the conclusion that the carbonate anion is bonded to the brucite‐like hydroxyl surface and to the water in the interlayer. Variation in the position of the carbonate anion stretching vibrations occurs and is dependent on the Ni/Co ratio. Water bending modes are identified in both the Raman and infrared spectra at positions greater than 1620 cm⁻¹, indicating that water is strongly hydrogen bonded to both the interlayer anions and the hydrotalcite surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the minerals diadochite and destinezite Fe3+2(PO4,SO4)2(OH)· 6H2O: implications for soil science

The two minerals diadochite and destinezite of formula Fe₂(PO₄,SO₄)₂(OH)· 6H₂O have been characterised by Raman spectroscopy and complemented with infrared spectroscopy. Both these minerals are found in soils and are identical except for their morphology. Diadochite is amorphous whereas destinezite is highly crystalline. The spectra of diadochite are broad and ill defined, whereas the spectra of destinezite are intense and well defined. Bands are assigned to phosphate and sulfate stretching and bending modes. Two symmetric stretching modes for both phosphate and sulfate support the concept of non‐equivalent phosphate and sulfate units in the mineral structure. Multiple water bending and stretching modes imply that non‐equivalent water molecules in the structure exist with different hydrogen‐bond strengths. Copyright © 2011 John Wiley & Sons, Ltd.     

反夹心化合物[E-C{5-n}H{5-n}Nn-E]+和[E-C{5-n}H{5-n}Pn-E]+(n=1，2，3; E=Al，Ga，In，Tl)的理论研究

研究了含有低价族元素的反夹心化合物[E-C_{5-n}H_{5-n}N_n-E]⁺和[E-C_{5-n}H_{5-n}P_n-E]⁺(n=1,2,3; E=Al,Ga,In,Tl)．(η5, η5) 配位的反夹心构型[E-C_{5-n}H_{5-n}N_n-E]⁺ 在能量上不稳定或不存在．而(η5,η5)配位的反夹心构型[E-C_{5-n}H_{5-n}P_n-E]⁺不但在能量上稳定, 在解离过程中也具有稳定性． 对于含有相同的E元素来说,[E-C_{5-n}H_{5-n}P_n-E]⁺的解离稳定性随着n的增加而降低;而对于确定的n来说, 含有不同E的化合物的解离能是类似的．其中[E-C₄H₄P-E]⁺的解离稳定性与已知的[E-C₅H₅-E]⁺非常相似．C_{5-n}H_{5-n}P_n与E之间的相互作用主要是离子性的． 由于在(η5,η5)配位的[E-C_{5-n}H_{5-n}N_n-E]⁺中,E和P原子上都具有孤对电子,因此该反夹心化合物可以作为多电子供体．