Synthesis and characterization of (NH4)2CuBr2Cl2·2H2O crystals

Single crystals of a new compound, (NH₄)₂CuBr₂Cl₂.2H₂O, were grown from saturated aqueous solution at room temperature by slow evaporation method. The grown crystals were characterized through elemental, powder XRD, thermal and DSC analyses and FTIR and far IR spectra. The elemental analysis and the decomposition pattern formulated using the TG‐DTG studies confirm the stoichiometry of the compound. The crystallinity of the compound is confirmed from the powder XRD pattern. A preliminary single crystal X‐ray diffraction structural analysis reveals that the title compound belongs to the orthorhombic system with a = 7.7466 Å, b = 7.783 Å and c = 8.1211 Å. The low temperature DSC shows thermal anomalies at –161.1, –156.5, –152.4, –145.2, –134, –18.5, and 1.4°C during the heating run and at –4.3, –54.8, –66.1, –90.6, –109.7 and –147.2 °C during the cooling run. The thermal hysterses indicate first order phase transitions in the title compound at these temperatures. The FTIR spectra were used to assign the characteristic vibrational frequencies due to NH₄⁺, CuX₄^2– ions and other chemical bonds. The effect of substitution of two bromine atoms on the phase transitions of a closely related crystal, diammonium tetrachloro cuprate dihydrate is also discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of methylammonium tetrachlorocuprate (II) dihydrate crystals

Single crystals of methylammonium tetrachlorocuprate (II) dihydrate were obtained by slow evaporation method at room temperature. The crystals were characterized through powder XRD, thermogravimetric (TG‐DTA), low temperature DSC studies and FTIR and far IR spectra. While the powder XRD confirms the crystallinity of the compound, the TG and DTA studies confirm the formation of the compound in the stoichiometric ratio and the presence of two water molecules of crystallization. The low temperature DSC study indicates a thermal anomaly at ‐3°C. The ordering of CH₃NH₃ group at low temperature causes phase transitions in the compound. The IR spectra characterize the various chemical bonding and water molecules in the compound. Laser Raman spectral studies under progress would help understand the mechanism of phase transitions at low temperatures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and thermal characterization of methylammonium tetrachloro zincate (II) monohydrate crystals

Single crystals of methylammonium tetrachloro zincate (II) monohydrate were grown by slow evaporation of saturated aqueous solutions at room temperature. The grown crystals were colourless, bright and transparent. The crystals were characterized through elemental analysis, powder X‐ray diffraction, thermogravimetric (TG‐DTA) and low temperature differential scanning calorimetric (DSC) techniques. While the powder XRD pattern shows the crystallinity of the compound, the elemental analysis and the TG‐DTA confirm the stoichiometry of the compound. The low temperature DSC indicates first order structural phase transition at ‐8°C during heating cycle. The FTIR and far IR spectra of the compound show characteristic vibrational frequencies due to CH₃NH₃ and ZnCl₄^2‐ ions and other chemical bonds. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and thermal,phase transition and FTIR spectral characterization of tetraethylammonium tetrachlorocuprate (II) crystals

Single crystals of tetraethylammonium tetrachlorocuprate (II), [N(C₂H₅)₄]₂CuCl₄, were grown by slow evaporation method at room temperature. The crystals were characterized through powder XRD, thermogravimetric (TG‐DTA), low temperature differential scanning calorimetric (DSC) studies and FTIR spectroscopy. While the powder XRD pattern of the compound shows sharp Bragg peaks confirming the crystallinity of the compound, the TG‐DTA studies confirm formation of the compound in the stoichiometric ratio. The thermal anomalies observed in DSC curve at ‐120°C in the heating cycle and around ‐30°C in the cooling cycle indicate a first order phase transition. The phase transition was predicted to be associated with the ordering of CuCl₄^2‐ and successive long range orientation of [N(C₂H₅)₄]⁺ ions which are disordered at high temperatures. The cationic [N(C₂H₅)₄]⁺ plays a role in phase transitions at low temperatures. The sharp exothermic peak observed in high temperature DSC indicates a structural phase transition when [N(C₂H₅)₄]CuCl₃ is formed on heating the compound. The FTIR spectra of the compound characterize the various chemical bonding and water molecules adsorbed in the compound. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal,phase transition and FTIR spectroscopic studies in tetraethylammonium trichlorocadmiate crystals

Single crystals of tetraethylammonium trichlorocadmiate were grown by slow evaporation of aqueous solutions at room temperature. The bright and transparent crystals obtained were characterized through FTIR spectroscopy, thermo gravimetric (TG and DTA) and low temperature DSC analyses. A fitting decomposition pattern for the title compound was formulated based on the TG thermogram which shows a two‐stage weight loss between 300°C and 800°C. In this temperature range the DTA curve shows endothermic dips supporting the formulated decomposition pattern. The thermal anomalies observed in the low temperature DSC both during the heating and cooling cycles indicate the occurrence of the first and second order structural phase transitions in the compound. The FTIR and far IR spectra show characteristic vibration frequencies due to [N(C₂H₅)₄]⁺ and CdCl₃^‐ ions. Detailed structural analysis of the compound is under progress. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,structural and thermal studies of tetrathioureacopper(I) chloride crystals

Tetrathioureacopper(I) chloride, hereafter abbreviated as TCC, was synthesised and single crystals were obtained from saturated aqueous solution by slow evaporation (solution growth) method at room temperature. The crystals obtained are bright, colourless and transparent having well defined external faces. The grown crystals were characterized through elemental analysis, single crystal X‐ray diffraction study, thermal analysis, electron spin resonance spectroscopy and Fourier Transform infrared spectroscopy. The elemental analysis confirms the stoichiometry of the compound. The single crystal diffraction studies indicate that TCC crystallises in the tetragonal lattice and the unit cell parameters are a = b = 13.4082 Å, c = 13.8074 Å, V = 2482.29 ų, α = β = γ = 90°. Space group and the number of molecules per unit cell (Z) are found to be P4₁2₁2 and 8 respectively. The TG curve of the sample shows a prolonged decomposition from 210 to 628.3 °C, from which the decomposition pattern has been formulated. The endothermic peaks in the DTA curve indicate melting and decomposition of the compound at 165.2 and 633.8 °C respectively. An exothermic peak in high temperature DSC indicates a phase transition in the compound at 274.8 °C. Thermal anomalies observed in the low temperature DSC at –163.3, –152.0, –141.5, –108.3, 1.0 and 12.1 °C in the heating run and –157.1 and –153.9 °C in the cooling run reveal first order phase transitions in the crystal. The peaks observed at –146.2 °C in both the heating and cooling runs suggest occurrence of a second order phase transition in this compound. The IR spectroscopic data were used to assign the characteristic vibrational frequencies of various groups present in the compound. The ESR study confirms that the copper is in the +1 oxidation state in the complex. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization and structural phase transition studies in trismethylammonium pentachloro barium dihydrate single crystals

Single crystals of trismethylammonium pentachlorobarium dihydrate were grown by slow evaporation method at ambient temperature. The crystals were characterized through powder XRD, thermal, infrared and NMR spectral studies. While the powder XRD pattern confirms the crystallinity of the title compound, the TG indicates the removal of occluded and adsorbed water molecules from the crystal when it is heated up to 86 °C. The TG study also confirms the presence of two water molecules of crystallization which are dehydrated on heating the crystal between 107 °C and 150 °C. The anhydrous compound is found to be stable at least up to 900 °C. The DTA curve shows two endothermic dips corresponding to weight losses observed in the TG curve. The low temperature DSC study shows thermal anomalies during the heating and cooling cycles indicating both first and second order phase transitions. The high temperature DSC shows the stepwise dehydration indicating phase transitions at temperatures 103 °C and 145 °C. The characteristic vibrational frequencies due to methylammonium ion, BaCl₅ and other groups are assigned based on FTIR spectra. The NMR spectrum confirms the presence of protons of the methyl group and water of crystallization in the compound. In this paper, an attempt is also made to understand the effect of methyl group on the phase transitions of the compound in comparison with a closely related compound, trisammoniumpentachloro barium dihydrate. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of potassium magnesium sulphate hexahydrate crystals

Potassium magnesium sulphate hexahydrate (picromerite) was synthesized and single crystals were obtained from saturated aqueous solution by slow evaporation method at room temperature. The crystals were bright, colourless and transparent having well defined external faces. The grown crystals were characterized through Fourier Transform Infrared (FTIR) spectral studies and thermal analysis. The FTIR data were used to assign the characteristic vibrational frequencies of the various chemical bonds in the compound. The compound crystallizes in monoclinic lattice with the space group P2₁/c. The thermogravimetry (TG) indicates the removal of only two water molecules around 100 °C. A suitable decomposition pattern was formulated based on the percentage weight losses observed in TG of the compound. The results of differential thermal analysis (DTA) conform to the results of TGA. Differential scanning calorimetry (DSC) analysis carried out at high temperature suggests that the occurrence of two phase transitions in the crystal between 140 and 180 °C. When the crystal was cooled below the room temperature up to –170 °C, no thermal anomaly was observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X‐Ray Powder Diffraction,DTA and Vibrational Studies of CdNH4PO4.6H2O Crystals

Cadmium Ammonium Phosphate Hexahydrate (CAPH) is analogous to naturally occurring struvite. CAPH crystals are grown by slow evaporation technique. These crystals are characterised by X‐ray, TG‐DTA and Infra‐red studies. Powder X‐ray pattern indicates the orthorhombic crystal structure analogous to struvite. TG‐DTA analysis suggests loss of water of hydration (6H₂O) between 113 and 391°C. Later the substance melts and only Cd remains around 780 °C. Infra Red spectrum is characteristic of H₂O, PO₄^3‐ and NH₄⁺ radicals.     

Synthesis,thermal and IR spectral characterization of ammonium tetrabromocuprate (II) dihydrate crystals

Single crystals of a new compound, ammonium tetrabromocuprate (II) dihydrate were obtained by slow evaporation method. The crystals were characterized through thermogravimetric (TG), differential thermal analysis (DTA), low temperature differential scanning calorimetric (DSC) methods and infrared (IR) spectroscopic technique. While the TG study confirms the stoichiometry of the compound, the thermal hystereses in DSC indicate the occurrence of first order phase transitions in the compound at low temperatures. The FTIR spectrum of the compound characterizes the various chemical bond vibration frequencies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,spectral and thermal properties of non‐linear optical crystal ZnMg(SCN)4

Single crystals of zinc magnesium tetra thiocyanate [ZnMg(SCN)₄], a bimetallic thiocyanate complex, were grown by slow evaporation solution growth technique at room temperature. The bright, transparent and colourless crystals have well defined faces. The grown crystals were characterized through elemental analysis, powder X‐ray diffraction (XRD), thermogravimetric (TG) and differential thermal analysis (DTA), differential scanning calorimetric analysis (DSC), Fourier Transform Infra red (FTIR) and Optical studies. The elemental analysis confirms the stoichiometry of the synthesized crystals. The compound crystallizes under monoclinic structure with lattice parameters a = 10.055 Å, b = 7.44 Å, c = 6.00 Å and β = 90.113°. The TGA indicates 25 % weight loss at 205°C from which the decomposition pattern is formulated. The DSC study indicates that the crystal undergoes only first order phase transitions. The FTIR spectrum indicates among others the presence of metal‐nitrogen and metal‐sulphur bonds thus confirming the formation of the complex. The second harmonic‐generation (SHG) was confirmed by the emission of green radiation using Nd: YAG laser. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vibrational behavior of matrix‐isolated ions in Tutton compounds IV. Infrared spectroscopic study of NH4+ and SO42‐ ions included in nickel sulfates and selenates

Infrared spectra of K₂Ni(SeO₄)₂·6H₂O and (NH₄)₂Ni(SeO₄)₂·6H₂O containing SO₄^2‐ ions and those of K₂Ni(SO₄)₂·6H₂O and K₂Ni(SeO₄)₂·6H₂O containing NH₄⁺ ions are presented and discussed in the region of ν₃ and ν₁ of the sulfate ions and in the region of ν₄ of the NH₄⁺ ions, respectively. The SO₄^2‐ ions matrix‐isolated in the selenate matrices (approximately 1 mol%) exhibit three bands for ν₃ and one band for ν₁ in agreement with the low site symmetry C₁ of the host selenate ions. The NH₄⁺ guest ions included in the potassium sulfate matrix are characterized also with three bands for ν₄. However, the ammonium ions in (NH₄)₂Ni(SeO₄)₂·6H₂O as well as those included in K₂Ni(SeO₄)₂·6H₂O display four infrared bands corresponding to ν₄ due probably to some kind of disorder of the ammonium ions. The extent of energetic distortion of the isomorphously included sulfate ions as deduced from the values of Δν₃ and Δν_max is commented. The spectroscopic experiments reveal that the SO₄^2‐ guest ions are weaker distorted in the selenate matrices as compared to the same ions in the neat sulfates due to the larger unit‐cell volumes of the selenate compounds. The band positions of the water librations in the host potassium compounds are affected by the included ammonium cations. The formation of hydrogen bonds between the NH₄⁺ guest ions and the XO₄^2‐ host ions leads to a decrease in the proton acceptor capabilities of the anions and as a result the hydrogen bonds weaken on going from the neat potassium compounds to the mixed crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of simonkolleite nanodisks and their conversion into ZnO nanostructures

Simonkolleite (Zn₅(OH)₈Cl₂·2H₂O) nanodisks with a width of 40 nm have been successfully synthesized via a hydrothermal method using zinc chloride and ammonia as the starting materials. The conversion mechanisms from simonkolleite nanodisks to ZnO spindles under hydrothermal condition and to ZnO nanotablets under solid phase transformation were discussed respectively. The simonkolleite nanodisks obviously occur in hydrothermal system with the combination of a lower alkalinity, lower temperature (<363 K), a higher NH₄⁺ ions concentration and in existence of Cl^‐ anion. The morphologies, crystal phases and photoluminescence properties of as‐synthesized samples were investigated by field emission scanning electron microscopy, powder X‐ray diffractometer and fluorescence spectrophotometer. The photocatalytic activities of these as‐synthesized samples in the degradation of methyl orange have been demonstrated. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on the growth and optical characterization of Tm3+‐doped BaY2F8 single crystals

The BaY₂F₈ crystals doped with different concentrations of Tm³⁺ ions were prepared by the temperature gradient technique (TGT). X‐ray powder diffraction was applied to analyze the phase. The cracking phenomenon along (010) and (100) planes of the crystals grown by temperature gradient technique was studied on the basis of the structure of BaY₂F₈ crystals. The absorption spectra were measured and investigated in the ultraviolet‐visible and near‐infrared ranges at room temperature. Several characteristic absorption bands of Tm³⁺‐doped BaY₂F₈ crystal were observed. The emission and excitation spectra were obtained and investigated at room temperature and 12 K, showing the characteristic emission peaks of Tm³⁺ ions. The temperature dependence of Photoluminescence curve was also investigated in the range of 12–296 K. The luminescence intensity of emission bands decreased with increasing temperature, while the effective bandwidth increased. The up‐conversion spectrum excited at 650 nm was recorded and up‐conversion mechanism was analyzed in detail. The result showed the purple, green and yellow emissions corresponding to ³P₁→³F₃, ¹D₂→³H₅ and ³P₀→¹G₄ transitions, respectively.     

Structural,optical and dielectric studies on K1‐x(NH4)xH2PO4 mixed crystals grown from z‐cut seeds

Mixed crystals of K_1‐x(NH₄)_xH₂PO₄(KADP) were grown from KDP (KH₂PO₄) dominated mixed solutions with varying molar proportion of ADP (NH₄H₂PO₄) addition. It was found that, as the increase of ADP molar concentration, the growth rate along z‐axis of KADP crystal decreased rapidly. The structure of KADP crystals was investigated by powder XRD and the lattice parameter was calculated. The results showed that the lattice parameter c of KADP crystal increased with the molar concentration of ADP. The optical homogeneity of grown KADP crystals was determined with a differential phase‐shifting interferometry. Frequency dependences of the dielectric constant and dielectric loss of KADP crystals were measured at room temperature (290 K). The dielectric constants of KADP crystals were almost invariant with the increase of frequency. In the region of 10²∼10⁴Hz, the values of the dielectric loss reduced with the increase of frequency. The piezo‐resonance coupling effect still exists in KADP crystals at room temperature, but shifted to low frequency band. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of a new nonlinear optical single crystal: L‐Lysinium trifluoroacetate

Single crystals of a new L‐Lysine salt: L‐Lysinium trifluoroacetate {abbreviated as LLyTFA; [(NH₂)‐(CH₂)₄‐CH‐(NH₃)‐(COOH)]⁺ CF₃COO^‐} were grown by slow evaporation of an aqueous solution at room temperature. The grown crystals were subjected to single crystal X‐ray diffraction, FTIR and UV‐Vis‐NIR spectrum analyses. The UV‐Vis‐NIR spectrum shows that the absorption is very less in the whole of the region from ultraviolet to near IR. The Kurtz‐Perry powder SHG measurement using a Nd:YAG laser of wavelength 1064nm confirms the frequency doubling of the crystal and its powder SHG efficiency was measured as d_eff = 0.96 d_eff (KDP). (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new nonlinear optical crystal: Bi2O2(OH)(NO3)

The nonlinear optical (NLO) properties of Bi₂O₂(OH)(NO₃) crystals have been reported for the first time. Bi₂O₂(OH)(NO₃) crystals with dimensions of 1.3×1.2×0.1 mm³ have been grown by hydrothermal method, and the crystals characterized by X‐ray powder diffraction (XRD), SEM and IR. The measured second harmonic generation (SHG) effect of Bi₂O₂(OH)(NO₃) was about 7 times that of KDP. The mechanism responsible for the large SHG of Bi₂O₂(OH)(NO₃) was explained according to its structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopic and Transport Properties of (NH4)2CuCl4 · 2 H2O Single Crystal

Electron paramagnetic resonance (EPR), Optical absorption and Transport properties of (NH₄)₂CuCl₄ 2 H₂O single crystals have been studied. An anisotropic g tensor was observed with gl = 2.241 and g∥ = 2.081 by EPR method. The spin orbit coupling constant is found to be 540 cm⁻¹. The optical absorption in UV region are characterized by charge transfer band, in the visible and near infrared region at 13,333, 4,480, 4,336, and 3,998 cm⁻¹ attributed to the transitions between the (d-d) stark energy levels of the copper (II) ion in an extended octahedral crystal field. Dc electrical conductivity measurements with temperature reveal an anisotropic characteristic of a two-dimensional layered structure, and exhibits two first order structural phase transitions at about 383 K and 413 K. These transitions are attributed to loss of the two water inolecules of hydration and free rotation of NH⁺₄ ion from a state of torsional oscillation.     

Phase transitions in ammonium pyroselenite crystals

The character of the phase transitions in ammonium pyroselenite crystals, (NH₄)₂Se₂O₅ and (ND₄)₂Se₂O₅, in the high-temperature phase has been investigated. The temperature dependences of the permittivity and the angular dependences of the high-resolution ⁷⁷Se spectra in the phase-transition range have been measured. The parameters of the chemical shift tensor have been determined for ⁷⁷Se nuclei in the Se₂O₅ pyroselenite ion in the high-temperature phase and compared with the known parameters of this tensor in the low-temperature phase. Some conclusions are drawn on the character of transitions and the structure of the (Se₂O₅)²⁻ ion.     

Thermal dehydration of the double salts K2Be(XO4)2·2H2O (X = S,Se)

The thermal dehydration of the title compounds was studied by TG, DTA and DSC methods and the enthalpies of dehydration were calculated (87.6 kJ mol^–1 and 167.5 kJ mol^–1 for the sulfate and selenate compound, respectively). The larger value of ΔH_deh of K₂Be(SeO₄)₂·2H₂O is due to the stronger hydrogen bonds formed in the selenate as compared to those formed in the respective sulfate owing to the stronger proton acceptor capabilities of the SeO₄^2– ions. The enthalpies of formation (ΔH_f⁰) of the dihydrates are also calculated from the DSC measurements (– 4467.4 kJ mol^–1 and – 3447.1 kJ mol^–1 for the sulfate and selenate compound, respectively). The anhydrous double salt, K₂Be(SO₄)₂, forms tetragonal crystals with lattice parameters: a = 7.232(2) Å; c = 14.168(2) Å; V = 741.0 ų, while the anhydrous salt, K₂Be(SeO₄)₂, forms monoclinic crystals with lattice parameters: a = 9.217(3) Å; b = 10.645(3) Å; c = 8.989(2) Å; β = 108.52(4)°; V = 836.2 ų. Vibrational spectra (infrared and Raman) of both the dihydrates and the anhydrous compounds are also presented and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)