Benefits of near-infrared spectroscopy for characterization of selected organo-montmorillonites

The potential of near infrared (NIR) spectroscopy in characterization of organically modified clay minerals is introduced. Selected organo-clays, possibly perspective fillers in clay polymer nanocomposites, were prepared from Na-montmorillonite and different surfactants containing octylammonium chain(s), hexadecylammonium chain(s) or a benzene ring with or without a reactive double bond. Based on the stretching (ν) and bending (δ) vibrations observed in the middle IR (MIR) region, the first overtone (2νXH) and combination (ν + δ)XH modes of XH groups (X = O, C, N) are identified. The effect of larger alkylammonium cations on the vibrations of Si-O and OH bonds in montmorillonite layers is observed. The changes in the intensity of the (ν + δ)H₂O band near 5250 cm⁻¹ allows for comparison of the amount of water adsorbed on the montmorillonite surface. The water content decreases with the size of the organic cation reflecting increasing hydrophobicity of the montmorillonite surface. The NIR region shows the 2νCH₃ and 2νCH₂ bands in the 5900-5500 cm⁻¹ region, an upward shift is observed for the complex band due to 2νCH(Ar) of aromatic benzene ring. The NIR spectra are extremely useful in identification of NH₂⁺, NH⁺ and vinyl groups, which are difficult to recognize in the MIR spectra of organo-clays due to overlapping with other absorption bands. The intense bands corresponding to overtones and combination vibrations of NH₃⁺ and NH₂⁺ groups are found in the 6600-6050 cm⁻¹ and 5000-4600 cm⁻¹ regions, the (ν + δ)NH⁺ is unambiguously identified near 4750 cm⁻¹. The characteristic band assigned to 2νCH₂ in H₂CC is detected near 6130 cm⁻¹.     

Crystal structure,electrochemical and photochemical studies of the trans-[Fe(cyclam)(NO)Cl]Cl2 complex (cyclam = 1,4,8,11-tetraazacyclotetradecane)

The trans-[Fe(cyclam)(NO)Cl]Cl₂ complex was synthesized by the reaction of cis-[Fe(cyclam)Cl₂]Cl with NO gas. The X-ray structure of the complex showed that the [Fe–NO] moiety is linear, consistent with the NO⁺ character of the nitric oxide ligand. This suggestion was reinforced by the IR data, which showed the νNO at 1888 cm⁻¹. The cyclic voltammogram of the trans-[Fe(cyclam)(NO)Cl]²⁺ complex presented three electrochemical processes at −0.70, 0.08 and 0.40 V versus Ag/AgCl. The first and last redox processes are centered at the NO ligand, whereas the second is characteristic of the generated aqua species, trans-[Fe(cyclam)Cl(H₂O)]²⁺. Upon irradiation at 330 nm, pH 3.4, the title complex releases the NO moiety with the concomitant generation of the trans-[Fe(cyclam)(H₂O)Cl]⁺ complex as suggested by electronic and IR spectroscopy as well as by cyclic voltammetry technique.     

Oxygen-permeable membranes based on partially B-site substituted BaFe1−yMyO3−δ (M=Cu or Ni)

We carried out the partial substitution of the B-site in BaFeO_3−δ perovskite with divalent cations to develop novel oxygen-permeable materials. We demonstrated that the partial substitution of Cu or Ni by more than 10% resulted in the stabilization of the cubic perovskite structure even at room temperature in a highly oxygen-permeable phase, as revealed by the X-ray diffraction (XRD) analysis. The Cu substitution was more effective for the stabilization, because the introduction of Cu in the lattice more effectively made the Goldschmidt tolerance factor (t) close to 1.0. Ni- and Cu-substituted BaFeO_3−δ membranes showed higher oxygen permeabilities than their parent BaFeO_3−δ membranes particularly at lower temperatures around 600-700 °C owing to the stabilization of the cubic phase. Among the fabricated membranes, a BaFe_0.85Cu_0.15O_3−δ membrane (1.0 mm thickness) showed the highest oxygen permeation flux (1.8 cm³ min⁻¹ cm⁻² at 930 °C) under an air/He gradient. The results indicated that Cu-substituted BaFeO_3-δ is promising as a material for Co-free membranes with high oxygen permeabilities.     

The molecular structure of selected minerals of the rosasite group – An XRD,SEM and infrared spectroscopic study

Minerals in the rosasite mineral group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite have been studied by powder X-ray diffraction, scanning electron microscopy and infrared spectroscopy. X-ray diffraction shows the minerals to be complex mixtures with more than one rosasite mineral observed in each sample. SEM analysis shows the minerals to be fibrous in nature and the use of EDAX enabled the chemical composition of the minerals to be determined. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the molecular structure is similar to malachite. A comparison is made with the spectrum of malachite. The rosasite mineral group is characterised by two OH stretching vibrations at ∼3401 and 3311 cm⁻¹. Two intense bands observed at ∼1096 and 1046 cm⁻¹ are assigned to ν₁ (CO₃)²⁻ symmetric stretching vibration and the δ OH deformation mode. Multiple bands are found in the 800–900 and 650–750 cm⁻¹ regions attributed to the ν₂ and ν₄ bending modes confirming the symmetry reduction of the carbonate anion in the rosasite mineral group as C_2v or C_s. A band at ∼560 cm⁻¹ is assigned to a CuO stretching mode.     

Systematic investigation on new SrCo1−yNbyO3−δ ceramic membranes with high oxygen semi-permeability

SrCo_1−yNb_yO_3−δ (y = 0.025–0.4) were synthesized for oxygen separation application. The crystal structure, phase stability, oxygen nonstoichiometry, electrical conductivity, and oxygen permeability of the oxides were systematically investigated. Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y = 0.025–0.2. However, the further increase in niobium concentration led to the formation of impurity phase. The niobium doping concentration also had a significant effect on electrical conductivity and oxygen permeability of the membranes. SrCo_0.9Nb_0.1O_3−δ exhibited the highest electrical conductivity and oxygen permeability among the others. It reached a permeation flux of ∼2.80 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C for a 1.0-mm membrane under an air/helium oxygen gradient. The further investigation demonstrated the oxygen permeation process was mainly rate-limited by the oxygen bulk diffusion process.     

Low-dimensional compounds containing cyanido groups. XXI. Crystal structure, spectroscopic, thermal and magnetic properties of two polymorphous modifications of [Cu(men)2Pt(CN)4]n complex (men = N-methyl-1,2-diaminoethane)

Violet (1) and blue (2) polymorphous modifications of [Cu(men)₂Pt(CN)₄]_n (men = N-methyl-1,2-diaminoethane) have been prepared and investigated by IR and UV-vis spectroscopy, thermal analysis, measurement of magnetic data and X-ray structural analysis. Both modifications are formed by similar but differently packed zigzag chains, which consist of [Cu(men)₂]²⁺ moieties bridged by two trans arranged cyanido groups of [Pt(CN)₄]²⁻ units. The Cu(II) atoms in both structures are hexacoordinated by four nitrogen atoms in the equatorial plane from two molecules of bidentate men ligands with the average Cu-N(Me) and Cu-N(H₂) bond lengths of 2.046(8) and 2.008(8) Å, respectively, and by two nitrogen atoms from bridging cyanido groups in the axial positions at average distance of 2.50(7) Å. Broad nearly symmetric bands observed in the UV-vis spectra of 1 and 2 of ²B_1g → ²E_g transitions are consistent with a deformed octahedral coordination of the CuN₆ chromophoric groups. One and two ν(CN) absorption bands observed in the IR spectra of 1 and 2, respectively, are in agreement with different local symmetries of [Pt(CN)₄]²⁻ units and different Cu-N(cyanido) bond lengths in these polymorphs and are subject of discussion on the spectral-structural correlations in 1D compounds. The complexes are stable up to 238 °C when their two-stage thermal decompositions start and ending up with a mixture of CuO and metallic Pt as the most probable final thermal decomposition products. The temperature dependence of the magnetic susceptibility suggests the presence of a weak antiferromagnetic exchange coupling between Cu(II) atoms in 1, J/hc = −0.17 cm⁻¹ and in 2, J/hc = −1.3 cm⁻¹.     

Influence of the chain and layer structure of Fe(III) and In(III) aqua-pentachloro-complexes on the bending vibrations of water molecules

Studies of IR and Raman spectra of monohydrates M^I₂[M^IIICl₅(H₂O)] (where M^I=K⁺, Rb⁺, Cs⁺ and M^III=Fe³⁺, In³⁺) at 1400-1900 cm⁻¹ have been carried out. The medium intensity band, detected in the region 1580-1595 cm⁻¹ was assigned to bending vibrations of water molecules (δHOH). The shift of the δHOH band towards low wavenumbers (1580-1595 cm⁻¹) is a main sign of the water molecule interactions in the chain hydrates. Additionally in the IR and Raman spectra of these salts, the appearance of the low intensity band between 1750 and 1810 cm⁻¹ (ν_x(H₂O)) was observed. In the presented paper we also discuss the influence of M^I and M^III cations on the position and splitting of these bands.     

Aurichalcite – An SEM and Raman spectroscopic study

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise the vibrational spectrum of aurichalcite a zinc/copper hydroxy carbonate (Zn,Cu²⁺)₅(CO₃)₂(OH)₆. XRD patterns of all specimens show high orientation and indicate the presence of some impurities such as rosasite and hydrozincite. However, the diffraction patterns for all samples are well correlated to the standard reference patterns. SEM images show highly crystalline and ordered structures in the form of micron long fibres and plates. EDAX analyses indicate variations in chemical composition of Cu/Zn ratios ranging from 1/1.06 to 1/2.87. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band at 1072 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for aurichalcite at 1506, 1485 and 1337 cm⁻¹. Multiple Raman bands are observed in 800–850 cm⁻¹ and 720–750 cm⁻¹ regions and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. An intense Raman band at 1060 cm⁻¹ is attributed to the δ OH deformation mode.     

Synthesis and characterization of Zn1−xNixFe2O4 spinels prepared by a citrate precursor

Nanocrystalline single-phase samples of Zn_1−xNi_xFe₂O₄ ferrites (0<x<1) have been obtained via a soft-chemistry method based on citrate-ethylene glycol precursors, at a relatively low temperature (650 °C). The influence of the nickel and zinc contents as well as that of heat treatments were investigated by means of X-ray powder diffraction, Brunauer-Emmett-Teller (BET) surface area, scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) Spectroscopy. Higher Ni content increases the surface areas, the largest one (∼20 m²/g) being obtained for NiFe₂O₄ annealed at 650 °C for 15 h. For all compositions, the surface area decreases for prolonged annealing at 650 °C and for higher annealing temperatures. Those results were correlated to the particle size evolution; the smallest particles (∼50 nm) observed in the NiFe₂O₄ sample (650 °C, 15 h) steadily increase as Ni ions were replaced by Zn, reaching ∼100 nm in the ZnFe₂O₄ sample (650 °C, 15 h). For all the Zn_1−xNi_xFe₂O₄ samples and, whatever the heat treatments was, the FTIR spectra show two fundamental absorption bands in the range 650-400 cm⁻¹, characteristics of metal vibrations, without any superstructure stating for cation ordering. The highest ν₁-tetrahedral stretching, observed at ∼615 cm⁻¹ in NiFe₂O₄, shifts towards lower values with increasing Zn, whereas the ν₂-octahedral vibration, observed at 408 cm⁻¹ in NiFe₂O₄, moves towards higher wavenumbers, reaching 453 cm⁻¹ in ZnFe₂O₄.     

A Raman spectroscopic study of the phosphate mineral pyromorphite Pb5(PO4)3Cl

A series of selected pyromorphite minerals Pb₅(PO₄)₃Cl from different Australian localities has been studied by Raman spectroscopy complemented with selected infrared spectroscopy. The Raman spectrum of unsubstituted pyromorphite shows a single band at around 920 cm⁻¹ but for the natural minerals two bands at 919 and ∼932 cm⁻¹ attributed to the ν₁ (PO₄)³⁻ stretching vibration. The observation of multiple bands is attributed to the non-equivalence of phosphate units in the pyromorphite structure and the reduction in symmetry of the (PO₄)³⁻ units. This symmetry reduction is confirmed by the observation of multiple bands in both the ν₄ bending region (500–595 cm⁻¹) and the ν₂ bending region (350–500 cm⁻¹). The presence of isomorphic substitution of (PO₄)³⁻ by (AsO₄)³⁻ units is identified by the ν₁ symmetric stretching bands at around 824 and 851 cm⁻¹ and the ν₂ bending region around 331 and 354 cm⁻¹. Contrary to expectation Raman bands in the 3320–3700 cm⁻¹ region are observed and assigned to OH stretching bands of OH units resulting from the substitution of chloride anions in the pyromorphite structure. This study brings in to question the actual formula of natural pyromorphite as it is better represented as Pb₅(PO₄,AsO₄)₃(Cl,OH) · xH₂O.     

Investigation of the quasi-ternary system LaMnO3-LaCoO3-“LaCuO3”—I: the series La(Mn0.5Co0.5)1−xCuxO3−δ

The La(Mn_0.5Co_0.5)_1−xCu_xO_3−δ series with x=0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1 was synthesized by the Pechini method to obtain insight into the phase formation in the quasi-ternary LaMnO₃-LaCoO₃-“LaCuO₃” system caused by the instability of LaCuO₃ under ambient conditions. After sintering at 1100°C some remarkable results were obtained: LaMn_0.3Co_0.3Cu_0.4O_3−δ crystallized as a single phase in the orthorhombic perovskite structure typical of LaCuO₃. Among the synthesized compositions this compound showed the highest electrical conductivity in air at 800°C (155 S cm⁻¹) and also the highest thermal expansion coefficient (α_30−800°C=15.4×10⁻⁶ K⁻¹). The LaCuO_3−δ composition also crystallized as a single phase but in a monoclinic structure although previous investigations have shown that other phases are preferably formed after sintering at 1100°C. The electrical conductivity and thermal expansion coefficient were the lowest within the series of compositions, i.e. 9.4 S cm⁻¹ and 11.9×10⁻⁶ K⁻¹, respectively.     

Crystal structure and magnetic properties of [{Cu(cyclam)}3{Fe(CN)6}2] · 6H2O,a cyano-bridged assembly with a rope-ladder chain structure

The synthesis, crystal structure and magnetic properties of the cyano-bridged complex [{Cu(cyclam)}₃{Fe(CN)₆}₂] · 6H₂O are reported. Its structure is made up of centrosymmetric S-shaped pentanuclear [{Cu(cyclam}₃{Fe(CN)₆)}₂] units, in which three [Cu(cyclam)]²⁺ units are alternatively bridged by two trans-CN groups of [Fe(CN)₆]³⁻ anions and water molecules. The pentanuclear Fe₂Cu₃ units are held together by two complementary and very weak Fe–CN?Cu1 bonds, forming a rope-ladder chain along the c axis. The compound exhibits a ferromagnetic interaction between the Cu(II) and Fe(III) ions as a consequence of the orthogonality of their magnetic orbitals of σ and π nature, respectively. The magnetic data were fitted to the calculated magnetic susceptibility equation for a pentanuclear model, leading to the following magnetic parameters: J₁ = 9.0(3) cm⁻¹, J₂ = 3.8(4) cm⁻¹, g = 2.2, θ = −1.2 K. These results show that the interactions through the long Cu–N axial bonds are not so weak as is usually assumed.     

Synthesis and oxygen content dependent properties of hexagonal DyMnO3+δ

Oxygen deficient polycrystalline samples of hexagonal P6₃cm (space group #185) DyMnO_3+δ (δ<0) were synthesized in Ar by intentional decomposition of its perovskite phase obtained in air. The relative stability of these phases is in accord with our previous studies of the temperature and oxygen vacancy dependent tolerance factor. Thermogravimetric measurements have shown that hexagonal samples of DyMnO_3+δ (0≤δ≤0.4) exhibit unusually large excess oxygen content, which readily incorporates on heating near 300 °C in various partial-pressures of oxygen atmospheres. Neutron and synchrotron diffraction data show the presence of two new structural phases at δ≈0.25 (Hex₂) and δ≈0.40 (Hex₃). Rietveld refinements of the Hex₂ phase strongly suggest it is well modeled by the R3 space group (#146). These phases were observed to transform back to P6₃cm above ∼350 °C when material becomes stoichiometric in oxygen content (δ=0). Chemical expansion of the crystal lattice corresponding to these large changes of oxygen was found to be 3.48×10⁻² mol⁻¹. Thermal expansion of stoichiometric phases were determined to be 11.6×10⁻⁶ and 2.1×10⁻⁶ K⁻¹ for the P6₃cm and Hex₂ phases, respectively. Our measurements also indicate that the oxygen non-stoichiometry of hexagonal RMnO_3+δ materials may have important influence on their multiferroic properties.     

Experimental and quantum chemical study of pyrrole self-association through N-H?π hydrogen bonding

An FT-IR study of pyrrole self-association in CCl₄ solutions was carried out. According to the IR measurements, pyrrole forms self-associated dimeric species via N-H?π hydrogen bonding. This was also confirmed by quantum chemical calculations for pyrrole monomer and dimer at B3LYP/6-31++G(d,p) level of theory. A T-shaped minimum was located on B3LYP/6-31++G(d,p) PES of pyrrole dimer characterized with a hydrogen bond of an N-H?π type, with centers-of-mass separation of monomeric units of 4.520 Å, H?π distance of 2.475 Å, the interplanar angle between the two monomeric units being 72.9°. The anharmonic vibrational frequency shift upon dimer formation calculated on the basis of 1D DFT vibrational potentials is in excellent agreement with the experimental data (84 vs. 87 cm⁻¹). Harmonic vibrational analysis predicts somewhat smaller shift (68 cm⁻¹). On the basis of NIR spectroscopic data, anharmonicity constants for the 2ν(N-H) and 2ν(N-H?π) vibrational transitions were calculated. The orientational dynamics of monomeric and self-associated pyrrole species was studied within the framework of the transition dipole moment time correlation function formalism. The period of essentially free rotation in the condensed phase reduces from 0.05 ps for the monomeric pyrrole to 0.02 ps for the proton-donor molecule within the dimer.     

Evolution of titania nanotubes-supported WOx species by in situ thermo-Raman spectroscopy, X-ray diffraction and high resolution transmission electron microscopy

Structural evolution of WO_x species on the surface of titania nanotubes was followed by in situ thermo-Raman spectroscopy. A total of 15 wt% of W atoms were loaded on the surface of a hydroxylated titania nanotubes by impregnation with ammonium metatungstate solution and then, the sample was thermally treated in a Linkam cell at different temperatures in nitrogen flow. The band characteristic of the WO bond was observed at 962 cm⁻¹ in the dried sample, which vanished between 300 and 700 °C, and reappear again after annealing at 800 °C, along with a broad band centered at 935 cm⁻¹, attributed to the v₁ vibration of WO in tetrahedral coordination. At 900 and 1000 °C, the broad band decomposed into four bands at 923, 934, 940 and 950 cm⁻¹, corresponding to the symmetric and asymmetric vibration of WO bonds in Na₂WO₄ and Na₂W₂O₇ phases as determined by X-ray diffraction and High resolution transmission electron microscopy (HRTEM). The structure of the nanotubular support was kept at temperatures below 450 °C, thereafter, it transformed into anatase being stabilized at temperatures as high as 900 °C. At 1000 °C, anatase phase partially converted into rutile. After annealing at 1000 °C, a core-shell model material was obtained, with a shell of ca. 5 nm thickness, composed of sodium tungstate nanoclusters, and a core composed mainly of rutile TiO₂ phase.     

Spectroscopic, thermal, magnetic and structural characterization of K3VF6 prepared at room temperature

A straight forward room-temperature synthesis of V(III) containing complex fluoride K₃VF₆, using KF and vanadium(III) acetylacetonate is reported. The pale green colored powder was characterized by chemical analysis, powder X-ray diffraction; diffuse reflectance spectroscopy, infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, scanning electron microscopy, photoluminescence spectroscopy, magnetic susceptibility measurements and photoluminescence spectroscopy. The powder X-ray diffraction pattern was fitted in P2₁/n space group (monoclinic) with a = 12.106 (1) Å, b = 17.685 (0) Å, c = 11.802 (0) Å, β = 92.23° (1). Differential scanning calorimetry showed phase transitions, occurring at 158 °C and 190 °C. In the FT-IR spectrum, characteristic band for the VF₆³⁻ group was observed at 508 cm⁻¹. The bands observed in the 335-361 cm⁻¹ region and at 504 cm⁻¹ in the room temperature Raman spectrum of K₃VF₆ corresponded to the F_2g and A_1g modes, respectively. The ratio of the frequencies (F_2g/A_1g) observed in the diffuse reflectance spectrum was fitted on the Tanabe-Sugano diagram to determine the Racah parameter B value of 712 cm⁻¹. Magnetic ordering was not observed down to the lowest measured temperature of 5 K.     

Ca3−xLaxCo4O9+δ (x=0, 0.3): New cobaltite materials as cathodes for proton conducting solid oxide fuel cell

Misfit-type Ca_3−xLa_xCo₄O_9+δ (x=0, 0.3) oxides were synthesised to be evaluated as possible cathode materials for proton conducting fuel cells (PCFCs) based on BaCe_0.9Y_0.1O_3−δ (BCY10) dense ceramic electrolyte. The electrical conductivity value of Ca_2.7La_0.3Co₄O_9+δ (σ≈53 S cm^-1 at 600 °C) is in the range of usually required value for a cathode application (about 50-100 S cm^-1). In order to test the performance of each compound as cathode material, impedance measurements were carried out on Ca_3−xLa_xCo₄O_9+δ/BaCe_0.9Y_0.1O_3−δ/Ca_3−xLa_xCo₄O_9+δ symmetrical half cells over the temperature range 400-800 °C under wet air. A promising electrocatalytic activity has been observed with both compounds Ca₃Co₄O_9+δ and Ca_2.7La_0.3Co₄O_9+δ. Factually, the area specific resistance obtained was about 2.2 Ω cm² at 600 °C.     

Solute-solvent interactions in formamide and zinc chloride solutions: An investigation by Raman spectroscopy

Raman experiments of formamide and zinc chloride solutions in a wide concentration range (0.1-5.0 mol kg⁻¹) have been carried out. The spectral changes were interpreted on three different ways: (i) the rupture of the H-bonds of FA was evidenced by the trend observed in the ν_CO, δ_HNH and restricted (translation or libration) modes; (ii) the appearance of a new band in the ν_CN region (∼1338 cm⁻¹) was assigned to FA coordinated to Zn (II) through nitrogen atom; (iii) the electronic delocalization in the FA structure upon complexation provided the appearance of new features in the δ_CH and ν_CH regions. The quantitative treatment performed at the ν_CN region of FA allowed the determination of an average number of 3 FA molecules per Zn (II) in the first solvation shell. This value is supported by the appearance of features assigned to ZnCl⁺ and ZnCl₂ entities that also occupy vertices of the tetrahedron at higher salt concentrations. The present study may be useful for a better understanding on electrochemical processes employed in the production of dendritic zinc films as well as FA hydrolysis catalyzed by this metal.     

The phonon-assisted proton transfer between hydrazinium cations in (N2H5)2HMF6·2H2O (M∈{Ga, Al, Fe}) type compounds. FT IR and quantum theoretical study

FT IR spectra of a series of compounds with a general formula (N₂H₅)₂HMF₆·2H₂O (where M∈{Ga, Al, Fe}) were recorded at variable temperatures (from ∼100 to 300 K, at 10 K intervals). The appearance of the spectral region of ν(N-N) modes due to hydrazinium cations further supports the conclusions regarding the N₂H₅⁺?H⁺?N₂H₅⁺ hydrogen bond potential well based on Raman spectroscopic data [J. Raman Spectrosc. 28 (1997) 315]. The appearance of two bands corresponding to the ν(N-N) modes in the low temperature FT IR spectra that merge into one upon heating is a clear evidence of a symmetric potential well through which a phonon-assisted proton transfer (PAPT) occurs at higher temperatures. Ab initio MP2/6-311++G(2d,p) quantum chemical study of the proton transfer potential within the N₂H₅⁺?H⁺?N₂H₅⁺ cluster confirmed its double-minimum character. The first-order saddle point found on the MP2/6-311++G(2d,p) potential energy hypersurface corresponds to a centrosymmetric structure (C_2h symmetry), with the proton placed at the inversion center. The potential energy curve along the tunnelling coordinate was calculated by the intrinsic reaction coordinate (IRC) methodology, leading to an adiabatic PT barrier height of 3.94 kcal mol⁻¹ and a tunneling rate of 1.98 s⁻¹. The corresponding MP4(SDTQ)/6-311++G(2d,p)//MP2/6-311++G(2d,p) value of the adiabatic PT barrier height is 4.26 kcal mol⁻¹.     

Synthesis and vibrational spectroscopic characterisation of nickel containing aurichalcite

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise a synthetic nickel substituted aurichalcite a zinc/nickel hydroxy carbonate, (Zn²⁺, Cu²⁺, Ni²⁺)₅(CO₃)₂(OH)₆. XRD patterns show high orientation and indicate the presence of some minor impurities. The diffraction patterns for the Ni-aurichalcite are well correlated with the standard reference patterns. EDAX analyses indicate variations in chemical composition of Zn/Ni ratios of ∼20:1. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band for the Ni-aurichalcite at 1070 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for Ni-aurichalcite at 1372, 1480 and 1543 cm⁻¹. Multiple Raman bands are observed in the regions from 800 to 850 cm⁻¹ and 720 to 750 cm⁻¹, and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. This research proves that nickel containing aurichalcites can be synthesised in the laboratory thus mimicing the natural nickel containing aurichalcites.