Several complex salts of the general formula [M(II) (bipy)x(H2O)y]PbCl6 (where x=2–3, y=0–2 and M=Mn(II), Fe(II), Ni(II), Co(II), Cu(II), Zn(II), Cd(II) and Hg(II)) were synthesized and investigated
by DTA, TG and DTG. Some of the decomposition products were identified by IR spectroscopy and other methods. The compounds
decompose with the liberation of water (in the case of hydrates), chlorine (sometimes causing chlorination of organic fragments),
organic molecules (sometimes chlorinated) and sometimes hydrogen chloride. The residues comprise metal(II) chlorides and PbCl2.
Lead(II) 2,2'-bipyridine hexachloroplumba tetetrahydrate was synthesized and investigated by DTA, TG and DTG. IR spectroscopy
and other methods enabled the identification of some of the decomposition products. Comparative studies on the corresponding
chlorides: [Pb(bipy)]Cl2 and [Pb(bipy)3]Cl2, which can be considered as precursors of the hexachloroplumbate, were also undertaken. X-ray measurements enabled the tentative
determination of the crystal structure of [Pb(bipy)]Cl2. Hexachloroplumbate decomposes with the liberation of chlorine, water and organic ligands, and the process is accompanied
by the simultaneous transition of Pb(IV)→Pb(II). Chlorides release only ligands upon heating. Residues comprised always PbCl2.
Authors:P. Storoniak, M. Kabir, and J. Błażejowski
The enthalpies of formation of PbCl4, PbCl5− and PbCl62−, originating from quantum mechanics, have enabled the thermodynamic behaviour of these ions with respect to Cl-detachment
to be assessed. The stability of salts containing PbCl5− and PbCl62− as a function of the dimensions of these anions and complementary cations was studied using an approach combining the Kapustinskii-Yatsimirskii
equation with basic thermochemical relationships.
It was found that hexachloroplumbates of monovalent metal cations will not dissociate into metal chlorides and PbCl4, provided the complementary cations are suitably large in size. Hexachloroplumbates of divalent metal cations have not yet
been synthesised since no known metal cations attain the requisite large size. Such salts will not dissociate if the divalent
metal cations are able to complex suitably large electron-donating ligands. The pentachloroplumbates of both monovalent and
divalent metal cations are unstable, since no known metal cations have appropriately large ionic radii. The approach adopted
appears to be useful for the examination of the thermal behaviour, stability and reactivity of chloroplumbates.