Hydrogen-1 nuclear magnetic resonance, differential thermal analysis, X-ray powder diffraction and electrical conductivity studies on the motion of cations, including self-diffusion in crystals of propylammonium chloride and bromide as well as their n-deuterated analogues

Abstract

H N.m.r. measurements and differential thermal analyses have been performed on solid propylammonium chloride and bromide, including their N-deuterated analogues. X-Ray powder diffraction and electrical conductivity were measured for the highest-temperature solid phase of NH,(n-C,H,)Cl. The corresponding highest-temperature solid phase of the bromide was determined. These salts have three solid phases below the respective melting temperature. In the highest-temperature phase, having a structure consisting of cation and anion layers, it was found for the chloride that the cations perform self-diffusion in two-dimensional layers. A non-linear log TI us. T1 curve observed in the room-temperature phase of propylammonium chloride and bromide could be well explained by assuming a non-Arrhenius type thermal process for the random reorientation of the cation along the cationic chain axis. The broad Tl minimum of NH,(n-C,H,)Br observed in its low-temperature phase has been assigned to two closely spaced Tl minima due to the C, reorientation of the CH, and NH; groups. Motional parameters for the above cationic motions in the three phases of the present salts have been evaluated, and the features of these motions are discussed.Hydrogen-1 N.M.R. of Solid Propylammonium Chloride and Bromide motions in the high-temperature phase, where a more disordered structure is possibly realized in consequence. To obtain detailed information about the dynamical behaviour of the cation in crystals of NH,(n-C,H,)Cl and NH,(n-C,H,)Br over a wide temperature range, the present investigation has been undertaken by examining lH n.m.r., differential thermal analysis (d.t.a.), X-ray powder diffraction and electrical conductivity. ExperimentalCrystals of NH,(n-C,H,)Cl and NH,(n-C,H,)Br were prepared by neutralizing an aqueous solution of propylamine with hydrochloric acid and hydrobromic acid, respectively, and gradually evaporating water. The crystals thus obtained were recrystallized twice from an ethanol-diethyl ether mixture. Colourless thin plates were obtained for both salts. Partially deuterated analogues, ND,(n-C,H,)Cl and ND,(n-C,H,)Br were prepared by performing repeated crystallizations of purified NH,(n-C,H,)Cl and NH,(n-C,H,)Br, respectively, from heavy water.'H N.m.r. absorptions4 and d.t.a.5 measurements were carried out using apparatus already reported. The 'H n.m.r. spin-lattice relaxation time TI was measured at the Larmor frequencies of 10.5, 20.0 and 45.5 MHz using pulsed n.m.r. spectrometers described elsewhere.'. The 'H spin-lattice relaxation time in the rotating frame Tlp was measured at 32 MHz for NH,(n-C,H,)Cl under a spin-locking radio frequency magnetic field of 3.7 G.8 The a.c. electrical conductivity of NH,(n-C,H,)Cl was determined at various temperatures using a previously reported homemade apparatusg operating at 1 kHz. The sample pellets were prepared by pressing pulverized crystals. X-ray powder diffraction patterns of NH,(n-C,H,)Cl were recorded at ca. 400 and 420 K employing a Shimadzu model VD-1 A diffractometer...

1H nuclear magnetic resonance, differential scanning calorimetry, and electrical conductivity studies on the phase transitions of pentylammonium chloride and the cationic self-diffusion in its rotator phase

“…The TI minimum can be attributed to the CH3 reorientation about the C3 axis by referring to the M2 analysis in LTSP. In fact, the fitted motional constant C agrees well with the theoretical value of 1.67 X lo9 s-2 for the CH, reorientation which was calculated using the equation given by (6) where y is the gyromagnetic ratio of the proton and the interprotonic distance r in a CH3 group was evaluated by use of the geometry employed in the M2 calculation. The fact that the observed T1 curve could be explained well by a single BPP equation implies the following.…”

“…The CH3 groups are placed in such a homogeneous crystal field that no distribution of the correlation time (21) or non-exponential T1 behavior can be observed. In the low-temperature phases of n-propyl-and nbutylammonium bromides (6,17), corresponding to LTSP of the present salt, however, we have observed unusual T1 curves explainable by considering distributions of T. This suggests the presence of microscopic inhomogeneity for the atomic arrangements in these materials.…”

“…The TI diff values determined by substituting TI , , , and T, observed at 10.5 MHz into eq. [6] are exhibited in Fig. 5.…”

Dielectric relaxation of alkyl chains in graphite oxide and n-alkylammonium halides

“…In an n-alkylammonium halide crystal, the alkyl chains are separated by 0.52 nm in the plane normal to its crystallographic C 4 axis. 1,2,27 In the nanocomposites, the chains extends in parallel to the GO layer at roughly the same distance of ∼ 0.53 nm from a chain to GO layer, but with inter-chain separation decreasing from 4.8 to 2.3 nm as the intercalated alkylammonium cations rises in concentration (Tables I and III). Even at the highest concentration the chains are much more widely separated than in a halide crystal, their coupling is therefore much weaker, leading to lower value of apparent activation energy E a * .…”

“…They undergo uniaxial rotation of the long rod-like cations and 2D self-diffusion, 1 as well as a C 3 reorientation of the CH 3 and NH + 3 groups. 2,3 As the alkylammonium halides find diverse use in surface modification through interaction between the cation of headgroup and an anion of host material, their dynamic in different environments is a key factor in designing novel materials. [5][6][7] Like graphene, Graphite oxide (GO) consists of 2D sheets, 8 retaining the layered structure of graphite, but on each layer carbon atoms randomly bond with epoxide and hydroxyl radicals on both sides.…”