Lead(II) alkanoates, from hexanoate to dodecanoate, have been analyzed by means of XRD, optical microscopy, DSC, FTIR, and electric spectroscopy. Four different phases have been identified, corresponding to the three thermal transitions measured by DSC:  two of them solid (crystal and “intermediate” phases), and another two fluid (neat phase and isotropic liquid). Powder crystal XRD data indicate that the samples present a bilayered structure. The analysis of the (00l) spacing dependence with temperature in the three ordered phases strongly points to the intermediate phase to be a rotator phase. Optical microscopy and FTIR versus temperature also confirm a structural change from the crystal to the intermediate phase and its solid-state nature. Electrical conductivity maps the thermal transitions of the samples and shows a high ionic conductivity in the intermediate phase, which does not depend much on the carbon chain length. The high conductivity values (3 orders of magnitude higher in comparison with that of the ordered crystal at room temperature) obtained for the intermediate phase gave a further support to the existence of a rotator mesophase in the lead(II) alkanoate series.

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.

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The mixture {x(C12H27CO2)2Pb + (1 − x)C12H27CO2H} has been investigated by differential scanning calorimetry and hot-stage polarizing-light microscopy over the whole composition range. Molecular association between the acid and the salt typical of the systems with alkaline cations is not found in the solid state. The complete phase diagram resembles those of the surfactants in water with a Krafft-like effect pointing to the formation of micellar aggregates and lyotropic phases.

During the last decades there has been a renewed interest in the study of salts with organic anion and /or cation, not only as pure substances but also their mixtures with any kind of solvents. Special attention will be given in this report to the mixtures of organic salts with organic acids. It is well known that the association of alkali alkanoates (@@soaps") and alkanoic acids into a crystalline molecular complexes ("acid soaps") of a given stoichiometry (l:l, 2:1, 3:2, etc.) generally melt incongruently. Besides these peritectic points, a lyotropic mesomorphism is also frequently found. The thallium(1) alkanoates and some acid + salt phase diagrams have been investigated recently, showing formation of only a 1:l molecular complex, which melts incongruently, and the appearance of lyotropism. On replacing thallium(1) by lead(I1) , the binary phase diagram shows completely different features. No molecular association between the acid and the salt is found in the solid state. The complete phase diagram resembles those of the surfactants in water. A Krafft-like point is found, in which the solubility of the salt increases dramatically pointing to the formation of micellar aggregates.The presence of thermotropic mesomorphism corresponds to lyotropism in that region of the phase diagram.