Lithium and Lead(II) Butyrates Binary System. Pure Compounds and an Intermediate Salt: From 2D to 3D Coordination Polymers

The binary phase diagram between lithium and lead(II) butyrates, [ x LiC 3 H 7 CO 2 + (1 − x )Pb(C 3 H 7 CO 2 ) 2 ] was determined by differential scanning calorimetry, in order to investigate the formation of intermediate salts. A complex or intermediate salt (with a 1:1 stoichiometry) was found during the solution of the phase diagram. Crystals of this salt, which melt incongruently at T fus = 443.2 K, were obtained later by crystallization. The structures of the crystal phase of both pure compounds and the intermediate salt were solved by single crystal and powder X-ray diffraction, using synchrotron radiation. Lithium and lead(II) butyrates present a monoclinic unit cell ( P 2 1 / c and P 2 1 / m, respectively). Both pure salts show a bilayered arrangement, in a structure of 2D coordination polymers, as usually metal alkanoates do. Nevertheless, the complex forms a microporous 3D ionic network (tetragonal, I 4 1 / a ), very atypical in this kind of organic salts. Binary phase diagrams are proved to be a powerful tool to detect and predict the formation of intermediate crystals.