Tribasic Lead Maleate and Lead Maleate: Synthesis and Structural and Spectroscopic Characterizations

We report on the synthesis and structure of tribasic lead maleate hemihydrate ([Pb4O3]C2H2(CO2)2·1/2H2O, TRIMAL)
and lead maleate (PbC2H2(CO2)2, PBMAL). The structure of [Pb4O3]C2H2(CO2)2·1/2H2O, solved ab initio from X-ray
powder diffraction data, consists of infinite slabs of edge-sharing OPb4 tetrahedra, of composition [Pb4O3], running
along the c axis and linked together into a three-dimensional network by tetradentate maleate anionic ligands. The
structure of PbC2H2(CO2)2, solved from single crystal diffraction data, is lamellar and contains double layers of
heptacoordinated lead atoms, bonded only to the oxygen atoms of the maleate ligands. In both compounds, lead
is in the oxidation state 2+ and the coordination polyhedra around the Pb2+ exhibit a hemidirected geometry and
are strongly distorted as a result of the lone pair of electrons. The absence of protons on the acidic portion of the
maleate moieties was confirmed by Raman spectroscopy and by 1H MAS and 1H−13C CP MAS NMR experiments.
The two compounds were further characterized using chemical and thermogravimetric analyses.