Crystal structure and thermochemical properties of phase change materials bis(1-octylammonium) tetrachlorochromate

A new crystalline complex (C₈H₁₇NH₃)₂CdCl₄(s) (abbreviated as C₈Cd(s)) is synthesized by liquid phase reaction. The crystal structure and composition of the complex are determined by single crystal X-ray diffraction, chemical analysis, and elementary analysis. It is triclinic, the space group is P-1 and Z = 2. The lattice potential energy of the title complex is calculated to be U_POT (C₈Cd(s))=978.83 kJ·mol^-1 from crystallographic data. Low-temperature heat capacities of the complex are measured by a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K. The temperature, molar enthalpy, and entropy of the phase transition for the complex are determined to be 307.3± 0.15 K, 10.15± 0.23 kJ·mol^-1, and 33.05± 0.78 J·K^-1·mol^-1 respectively for the endothermic peak. Two polynomial equations of the heat capacities each as a function of temperature are fitted by the least-square method. Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials.     

Low-temperature heat capacities and thermodynamic properties of n-undecylammonium bromide monohydrate C11H28BrNO(s)

Crystal structure of n-undecylammonium bromide monohydrate was determined by X-ray crystallography. Low-temperature heat capacities of the compound were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 390?K. Two solid–solid phase transitions were observed for the title compound. The temperatures, molar enthalpies, and entropies of the phase transitions were derived based on the analysis of heat–capacity curve. Two polynomial equations of heat capacities as a function of temperature were fitted by least-squares method. Based on the two polynomial equations, smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15?K were calculated and tabulated at 5 K intervals.     

Phase transitions and electrical conduction in thermal energy storage compound (n-C12H25NH3)2CdCl4

Differential scanning calorimetry (DSC) and differential thermal analysis (DTA) are performed for the compound (n-C₁₂H₂₅NH₃)₂CdCl₄. The ac conductivity σ_(ω,T), and the complex dielectric permittivity ?*_(ω,T) are measured as a function of temperature (100 K < T < 375 K) and at some selected frequencies (3 → 100 kHz). Two structural phase transitions are detected at T = (330 ± 1) K and T = (343 ± 1) K as minor and major transitions, respectively. The analysis of the measured electrical parameters reveals that the frequency-dependent conductivity obeys the power law, and the quantum mechanical tunneling (QMT) model is the main conduction mechanism in the low-temperature phase (LTP; phase III). The role of hydrogen bond N–H…Cl as a trigger force for phase transitions has been discussed. While the LTP is of the order–disorder type, the high-temperature phase (HTP) or phase I seems to be conformational and represents the main transition.     

Investigation on phase transitions of 1-decylammonium hydrochloride as the potential thermal energy storage material

1-Decylammonium hydrochloride was synthesized by the method of liquid phase synthesis. Chemical analysis, elemental analysis, and X-ray single crystal diffraction techniques were applied to characterize its composition and structure. Low-temperature heat capacities of the compounds were measured with a precision automated adiabatic calorimeter over the temperature range from 78 to 380?K. Three solid–solid phase transitions have been observed at the peak temperatures of 307.52?±?0.13, 325.02?±?0.19, and 327.26?±?0.07?K. The molar enthalpies and entropies of three phase transitions were determined based on the analysis of heat capacity curves. Experimental molar heat capacities were fitted to two polynomial equations of the heat capacities as a function of temperature by least square method. Smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15?K were calculated and tabulated at intervals of 5?K based on the fitted polynomials.     

1H NMR study of molecular dynamics and phase transition in (NH4)2ZnBr4

The proton second moment (M ₂) and spin-lattice relaxation time (T ₁) have been measured in (NH₄)₂ZnBr₄ in the range 77–300 K. The room-temperature spectrum shows a structure which disappears around 243 K. The signal is strong and narrow even at 77 K. Proton T ₁ shows a maximum at 263 K, caused by spin rotation interaction and decreases with decreasing temperature till 235 K, where it shows a sudden increase. Below 235 K, again it decreases and shows a slope change around 216.5 K (reported T_c ). From 216.5 K, T ₁ decreases continuously without exhibiting any minimum down to 77 K. The narrow line at 77 K, and absence of a T ₁ minimum down to 77 K indicate the possibility of quantum mechanical tunnelling in this system. Motional parameters such as activation energy and pre-exponential factor have been evaluated for the reorientational motion of the NH⁺ ₄ ion.     

Structural and dielectric properties of Pb(Li1/4Dy1/4W1/2)O3

The polycrystalline samples of Pb(Li_1/4Dy_1/4W_1/2)O₃ have been synthesized by high-temperature solid-state reaction techniques. Room temperature X-ray diffraction (XRD) studies of the compound provided preliminary structural data, and hence formation of a single phase desired material was confirmed. Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (100 Hz to 10 kHz) at room temperature (298 K) and also as a function of temperature (liquid nitrogen to 403 K) at 10 kHz suggest that the compound undergoes a ferroelectric phase transition of diffuse type.     

Dispersion of the birefringence in (CH12H25NH3)2ZnCl4 and (C12H25NH3)2ZnCl4: Co around their isotropic points

The optical dispersion of (C₁₂H₂₅NH₃)₂ZnCl₄ and (C₁₂H₂₅NH₃)₂ZnCl₄: Co is investigated by means of birefringence and optical absorption measurements in the temperature region around their isotropic points. The birefringence dispersion is analyzed in terms of a simple oscillator model based on the absorption band structure of both materials. A fairly good agreement is found between the thermal behaviour of the adjustable parameters of the oscillator model and the temperature dependence of the absorption spectra. The results suggest the existence of a structural phase transition at 315 K.     

Crystal and molecular structure of N-(p-nitrobenzylidene)-3-chloro-4-fluoroaniline

The crystal structure of N-(p-nitrobenzylidene)-3-chloro-4-fluoroaniline (II) has been determined by X-ray structure analysis. This belongs to a class of benzylidene anilines. The structure was solved by direct method. The molecular packing of the non-planar molecules are held by Van der Waals and F…H7, O…Cl, F…F and N…H interactions.     

High‐resolution Brillouin scattering and heat capacity studies of bis(guanidinium)zirconium bis(nitrilotriacetate)hydrate, [C(NH2)3]2Zr[N(CH2COO)3]2·H2O

High‐resolution micro‐Brillouin scattering and heat capacitiy studies of polar bis(guanidinium)zirconium bis(nitrilotriacetate)hydrate were performed in the temperature range 230–305 K. Strong anomalies in the Brillouin shift and the attenuation were observed near 290 K upon cooling for the sound waves corresponding to the c₂₂ elastic constant. For this elastic constant, the coupling between the order parameter and the elastic strains is linear quadratic. In case of the c₄₄ and c₆₆, the coupling is biquadratic, giving rise to an increase of these parameters below 290 K. The analysis of the acoustic anomalies and heat capacity results near 290 K revealed that they correspond to a second‐order, cell‐multiplying, displacive phase transition. The second phase transition leads to weak acoustic anomalies at approximately 284 K. Copyright © 2009 John Wiley & Sons, Ltd.     

81Br NQR Study of [NH3(CH2) n NH3]CdBr4 (n = 4 and 5) and [NH3(CH2) n NH3]ZnBr4 (n = 5 and 6)

⁸¹Br NQR frequencies and differential scanning calorimetry (DSC) were measured as a function of temperature. [NH₃(CH₂)₄ NH₃]CdBr₄ (1) and [NH₃(CH₂)₅NH₃]CdBr₄ (2) showed a doublet and quartet ⁸¹Br NQR spectrum, respectively. [NH₃(CH₂)₅NH₃]ZnBr₄ (3) and [NH₃(CH₂)₆NH₃]ZnBr₄ (4) exhibited a four-line ⁸¹Br NQR spectrum. From the NQR results, it is inferred that (1) and (2) consist of infinite two-dimensional sheets of corner-sharing CdBr₆ octahedra, whereas (3) and (4) have isolated [ZnBr₄]²⁻ tetrahedra. All of the crystals except (1) showed at least one structural phase transition above 380 K.     

Dielectric properties of Pb(Mg1/4Zn1/4Nb1/2)O11/4

Polycrystalline samples of Pb(Mg_1/4Zn_1/4Nb_1/2)O_11/4 have been synthesized by high temperature columbite precursor solid state reaction technique. Using X-ray diffraction (XRD) technique, compound formation in single phase cubic structure was observed and XRD analysis provided preliminary structural data. Detailed studies of dielectric properties of the compound reveal that this compound has high dielectric constant and diffuse phase transition in a wide range of temperatures around the Curie temperature. The charge deficiency of the compound presumably gets compensated in the high temperature columbite precursor process of sample preparation which is supported by single phasic form of the material.     

Crystal structure of di-(L-serine) phosphate monohydrate [C3O3NH7]2H3PO4H2O

The crystal structure of di-(L-serine) phosphate monohydrate [C₃O₃NH₇]₂H₃PO₄H₂O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at temperatures of 295 and 203 K. The crystal structure is refined using two sets of intensities. It is established that, in the structure, symmetrically nonequivalent molecules of L-serine occur in two forms, namely, the monoprotonated positively charged molecule CH₂(OH)CH(NH₃)⁺COOH and the zwitterion CH₂(OH)CH(NH₃)⁺COO^?, which are linked with each other and with the H₂PO ^?₄ ion through a hydrogen-bond system involving water molecules.

     

Temperature evolution of the intra-ion absorption spectra of (NH2(C2H5)2)2CoCl4 crystals in the region of their phase transitions

On the basis of spectroscopic studies of (NH₂(C₂H₅)₂)₂CoCl₄ crystals, the absorption bands corresponding to the internal electronic transitions in the Co²⁺ ion were identified. The values of the crystal field and Racah parameters were calculated. The temperature evolution of the absorption spectra of (NH₂(C₂H₅)₂)₂CoCl₄ crystals reveals the anomalies of their parameters at the points of phase transitions. The corresponding changes of the absorption spectra were discussed in terms of distortion of the metal-halogen complex. The temperature dependences of the absorption spectra of (NH₂(C₂H₅)₂)₂CoCl₄ crystals confirm the presence of the thermochromic phase transitions at 255 and 330?K.     

Optical,structural characterization and dielectric relaxation of [C2H5NH3]2ZnCl4 compound

ABSTRACT

The new organic-inorganic compound [C₂H₅NH₃]₂ZnCl₄ has been grown by the slow evaporation at room temperature. The zero-dimensional (0-D) structure for this compound was determined by the single X-ray diffraction. It crystallizes at room temperature in the non-centrosymmetric space group Pna2₁ and consists of ethylammonium cations [C₂H₅NH₃]⁺ and [ZnCl₄]^2? tetrahedra anions. That is interconnected by means of hydrogen bonding contacts N-H···Cl. The molecular geometry and vibrational frequencies of [ZnCl₄]^2? and [C₂H₅NH₃]⁺ in the ground state was calculated using density functional method (B3LYP) with 6–31G(d) and 6–311G (d,p) basis set. The optimized geometric bond lengths and bond angles, obtained by using B3LYP/6–311G (d,p), show the best agreement with the experimental data. The optical absorbance was measured in order to deduce the absorption coefficient α, optical band gap E_g. The optical band gap is determined by extrapolating the plotted graph of (αhυ)^1/2 vs. (hυ). The large value of indirect optical band gap energy indicates the insulating nature of this material. Moreover, the extinction coefficient, refractive index and the dielectric permittivity of [C₂H₅NH₃]₂ZnCl₄ compound were calculated and the results are discussed. The evolution of the dielectric loss as a function of frequency revealed a distribution of relaxation times, probably ascribed to the reorientational dynamics of alkyl chains in this compound, and then analyzed with the Cole–Cole formalism.     

Dielectric permittivity and AC conductivity investigations of the structural phase transitions in (NH3)2(CH2)7CdCl2Br2

The AC dielectric permittivity as a function of temperature (100–400 K) at different frequencies (between 80 Hz and 20 kHz) for the layered alkylene diammonium insulator containing Cd, namely, [(NH₃)₂(CH2)₇CdCl₂Br₂] has been measured. The formation of the compound was confirmed by microchemical analysis and IR absorption spectrometry. X-ray powder diffraction indicates an orthorhombic unit cell of dimensions: a = 10.219(2) Å, b = 9.168(2) Å and c = 38.694(4) Å. The AC conductivity ([sgrave]) is presented as a function of temperature and frequency. The conductivity and permittivity results indicate the presence of first-order phase transitions at 317 and 345 K. This has been confirmed by thermal analysis techniques. The activation energies were of values ranging between 0.15 and 0.62 eV depending upon the temperature range and the applied frequencies.     

Optical studies of the ferroelastic phase transitions in Rb3H(SeO4)2, (NH4)3H(SO4)2 and (NH4)3H(SeO4)2

Optical observations of growth twins and ferroelastic domains and measurements of the rotation of the optical indicatrix were carried out for Rb₃H(SeO₄)₂ and (NH₄)₃H(SO₄)₂ using an optical microscope. Taking into account the symmetry reduction from the rhombohedral (Rm) to the monoclinic phase (B2/a) the occurrence of domains and growth twins can be well described. The orientations of oblique ferroelastic walls are well determined by the spontaneous strains ^s e ₁₁ and ^s e ₂₃ at room temperature.     

Phase transitions and temperature changes of the optical absorption edge in (NH2(C2H5)2)2CoCl4 layered crystal

This work was devoted to X-ray diffraction study and investigations of temperature changes of the optical absorption edge of (NH₂(C₂H₅)₂)₂CoCl₄ crystals in the region of possible phase transitions. The X-ray powder diffraction data revealed the monoclinic phase at room temperature – space group P2/n. The cobalt atom was found to be square-plane coordinated by four chlorine atoms resulting [CoCl₄]^2– anion, which is surrounded by two DEA⁺ cations. It was shown that the low-energy tail of the absorption edge in these materials possesses an exponential shape. In the temperature range above 255?K it follows the empirical Urbach’s rule. The obtained experimental data confirmed the existence of the ferroelastic phase in (NH₂(C₂H₅)₂)₂CoCl₄ in the temperature range between 255 and 326?K. The anomalous behaviour of the investigated parameters observed at the temperatures below 255?K would be related to earlier unknown phase transitions.     

Lattice potential energy and standard molar enthalpy in the formation of 1-dodecylamine hydrobromide (1-C12H25NH3 ·Br)（s）

This paper reports that 1-dodecylamine hydrobromide (1--C₁₂H₂₅NH₃·Br)(s) has been synthesized using the liquid phase reaction method. The lattice potential energy of the compound 1--C₁₂H₂₅NH₃·Br and the ionic volume and radius of the 1--C₁₂H₂₅NH₃⁺ cation are obtained from the crystallographic data and other auxiliary thermodynamic data. The constant-volume energy of combustion of 1--C₁₂H₂₅NH₃·Br(s) is measured to be Δ_c U_m^o(1--C₁₂H₂₅NH₃·Br, s) =--(7369.03±3.28) kJ·mol^-1 by means of an RBC-II precision rotating-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of combustion of the compound is derived to be Δ_c H_m^o(1--C₁₂H₂₅NH₃·Br, s)=--(7384.52±3.28) kJ·mol ^{- 1} from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound is calculated to be Δ_f H_m^o(1--C₁₂H₂₅NH₃·Br, s)=--(1317.86±3.67) kJ·mol^-1 from the standard molar enthalpy of combustion of the title compound and other auxiliary thermodynamic quantities through a thermochemical cycle.