A Novel Rotator Glass in Lead(II) Pentanoate: Calorimetric and Spectroscopic Study

Abstract

Lead(II) pentanoate was studied by DSC, XRD, and FTIR and solid state CP/MAS-NMR spectroscopies. A transition from the crystal to the intermediate phase, at T(ss) = 328.2 +/- 0.6 K, with delta(ss)H = 8.8 +/- 0.1 kJ x mol(-1), and a melting at T(f) = 355.6 +/- 0.3 K, with delta(f)H = 12.6 +/- 0.1 kJ x mol(-1), were observed on first heating. The thermal and structural behavior of the lead(II) pentanoate shows as a link between those of the shorter and longer members of the previously studied lead(II) alkanoate series. The optical microscopy and FTIR vs temperature studies show structural changes from the crystal to the intermediate phase and its solid state nature. Moreover, X-ray diffraction and C-13 and Pb-207 CP/MAS-NMR studies confirm the rotator nature of the intermediate phase in this compound. Two different glass states, one from the isotropic liquid and another from the rotator phase, were obtained by quenching at high and low rates, respectively. The glass transition temperatures (measured at 5 K x min(-1)) were 322.9 and 275.7K, respectively.

Theories and experimental investigations of the structural and thermotropic mesomorphic phase behaviors of metal carboxylates

“…Typically, the hydrocarbon chains in the lamellar are packed in the fully extended all-trans conformation. This was proven by a number of authors [20,27,31] on the basis of IR data as outlined in the forgoing.…”

“…Such parameters were useful in presenting a picture of the molecular and lattice packing of these compounds. Further calculations carried out by several authors [18,27,31] have shown that comparison of the d-spacing, d exp , which represents the distance between successive metal planes, and the calculated molecular…”

“…The phase behaviors of monovalent metal alkanoates have been the subject of several investigations for a number of decades, especially those of lithium, sodium, potassium, thallium and silver. In the case of lithium carboxylates, some of the most comprehensive studies have been carried out by Shoeb et al [71], Ferloni and Westrum [72], and Martinez Casado et al [27], prior to which only the crystal structure of some hydrated lithium alkanoates (lithium formate monohydrate and lithium acetate dihydrate) have been determined [27].…”

“…Though the formation of a SmA mesophase was first proposed for PbC 10 [21][22][23][24][25][26][27], it has been agreed that only a single SmC phase with fan-like texture was formed for this compound. For the shorter chain adducts, n c = 2-5, inclusive, the formation of ionic melts and various glass phases have been proposed [20,27]. For instance, on heating lead(II) pentanoate, from the room temperature crystal to the melt, two endotherms were observed at 328 and 356 K ascribed to a solid-solid phase transition followed by the isotropic melt.…”

“…Unfortunately, though highly detailed thermodynamic explanations were proposed for some compounds, the majority of these studies resulted in no molecular and lattice structure-phase behavior correlation models. However, for lead(II) [21][22][23][24][25][26][27], copper(II) [28,29], zinc(II) [30][31][32] and silver(I) [33][34][35][36] carboxylates where both crystal-crystal and mesomorphic transitions were observed in their phase sequences, a number of thermodynamic phase models were proposed. Several studies have also been carried on the thermal degradation of lead(II) [37,38] and copper(II) [39,40] carboxylates where their decomposition mechanisms, activation parameters and significant kinetic factors adduced.…”