R.Julian C Brown

The thermodynamics of ammonium scheelites IV. Heat capacity of ammonium metaperiodate NH4IO4 from 8 to 324 K

The heat capacity of the scheelite salt ammonium metaperiodate, NH4IO4, was measured from 8 to 324 K using adiabatic calorimetry. The heat capacity against temperature curve shows an excess with a maximum around 200 K as is typical of other ammonium scheelites. A small peak in the curve near 270 K resulted from melting a saturated aqueous solution trapped in the lattice. Values of the standard molar thermodynamic quantities for NH4IO4 are presented up to 320 K. Values for Cp, mo(298.15 K)R, Δ0TSmo(298.15 K)R, and Φmo(298.15 K, 0)/R are (18.58±0.02), (23.03±0.04), and (11.20±0.02), respectively.

The thermodynamics of ammonium scheelites II. Heat capacity of deuterated ammonium perrhenate ND4ReO4 from 7.5 to 320 K

The heat capacity of the scheelite salt deuterated ammonium perrhenate ND4ReO4 was measured from 7.5 to 320 K without detection of any phase transition. An anomalous peak found between 270 and 280 K resulted from fusion of a saturated solution of D2O trapped in the lattice. Values of the standard molar thermodynamic quantities for pure ND4ReO4 are presented up to 320 K.

The thermodynamics of ammonium scheelites V. Heat capacity of deuterated ammonium metaperiodate ND4IO4 from 8 to 329 K

Abstract The heat capacity of the scheelite salt: deuterated ammonium metaperiodate, ND4IO4, was measured from 8 to 329 K using adiabatic calorimetry. The heat capacity against temperature curve shows a broad maximum with a peak around 200 K which is typical of other ammonium scheelites. A small peak in the curve around 275 K resulted from fusion of a saturated D2O salt solution trapped in the lattice. Values of the standard molar thermodynamic quantities for ND4IO4 are presented up to 330 K.

Ammonium cyanate: a DFT study of crystal structure, rotational barriers and vibrational spectrum

The crystal structure, rotational barriers and vibrational spectrum of ammonium cyanate have been studied by DFT calculations. The results show that, in the most stable structure, the ammonium ion is oriented such that each N—H bond points towards the N atoms of a cyanate anion giving rise to N—H···N hydrogen bonding, rather than N—H···O hydrogen bonding. The N—C and C—O bond lengths suggest that the structure of the anion in the crystal is best described as −N=C=O. These structural features are in agreement with recent results from neutron diffraction. At the transition state for rotation of the ammonium cation about an N—H bond, the cation is displaced and distorted from its equilibrium configuration. The barrier to the rotation of the ammonium cation about the 4 axis is found to be larger than the minimum barrier to rotation about an N—H bond, suggesting that the latter is the preferred rotational mode.

The thermodynamics of ammonium scheelites VI. An analysis of the heat capacity and ancillary values for the metaperiodates KIO4, NH4IO4, and ND4IO4

Abstract An analysis of the heat capacity of NH 4 IO 4 , ND 4 IO 4 , and KIO 4 has been carried out in which the effects of the anisotropy of the thermal expansion have been considered, an approach hitherto used successfully for the perrhenates KReO 4 , NH 4 ReO 4 , and ND 4 ReO 4 . In the ammonium scheelites, the axial expansivities are very large, but of opposite sign, and as a result the molar volume of the scheelite lattice is nearly independent of temperature. It is shown that the correction from constant stress to constant strain results in a major contribution to the heat capacity of this highly anisotropic lattice. The difference between the experimental and calculated heat capacities, referred to as ΔC p , m, is expressed as the sum of the contributions from the anisotropy and the rotational heat capacity. The results of the analysis show that the rotational contribution is much smaller than had previously been thought. However, the exact contribution of the anisotropy cannot yet be calculated because the elastic constants are not known. In calculating the heat capacity, maximum use has been made of external optical-mode frequencies derived from spectroscopic measurements.

Nitrogen-15 spin-rotation relaxation in ammonium perchlorate

Abstract The spin-lattice relaxation time has been measured for 15 N in ammonium perchlorate in the temperature range 240 to 292 K. The temperature dependence of T, suggests that spin-rotation is the dominant relaxation mechanism, and this is confirmed by calculation and by nuclear Overhauser effect measurements. The spin-rotation coupling constant for 15 NH 4 + is estimated to be 11.1 ± 0.2 kHz.

The thermodynamics of ammonium indates I. The heat capacity of the ammonium pentachloroindate monohydrate salt (NH4)2InCl5 · H2O from 8.5 to 349 K

The heat capacity of ammonium pentachloroindate monohydrate (NH4)2InCl5 · H2O was measured from 8.5 to 349 K using adiabatic calorimetry. The curve of molar heat capacity against temperature is continuous, but exhibits a small anomaly at 110 < TK < 130. Values of the standard molar thermodynamic quantities for (NH4)2InCl5 · H2O are presented up to 345 K.

The thermodynamics of ammonium indates II. The molar heat capacity of the ammonium pentabromoindate monohydrate salt (NH4)2InBr5 · H2O from 7.8 to 348 K

Abstract The molar heat capacity of ammonium pentabromoindate monohydrate (NH 4 ) 2 InBr 5 · H 2 O was measured from 7.8 to 348 K using adiabatic calorimetry. The curve of heat capacity as a function of temperature is continous. There is no sign of the phase transition predicted by Yamada and Weiss ( Ber. Bunsenges. Phys Chem. 1983 , 87, 932). Values of the standard molar thermodynamic quantities for (NH 4 ) 2 InBr 5 · H 2 O are presented to 345 K.