Crystal growth of lead carbonates: Influence of the medium and relationship between structure and habit

• Precursory salts form in vapour-growth of cerussite and hydrocerussite
• Dendritic forms and aggregates with pseudo-cubic morphology occur in gel growth
• Long-range chemical interactions may control the habit of crystals

The crystal-growth features of cerussite and hydrocerussite formed by two different chemical reactions are studied. With respect to the former, acid-vapour oxidation and latter carbonation of metallic lead produced a nanocrystalline precipitate for the lead carbonates. In the latter, cerussite and hydrocerusite are precipitated after mixing two mother solutions in liquid and solid porous media, forming diverse polyhedral morphologies. Crystal growth in gel medium gives rise to pseudo-cubic morphologies by the aggregation of one-micron-sized particles of cerussite. Skeletal morphologies composed of cyclically twinned crystals of cerussite also occur in gel-growth experiments. These morphologies were determined by kinetic factors, in particular by high supersaturation conditions that led to high growth rates. Kinetics also favoured the predominance of weak over strong interactions during crystal growth. The habit observed for cerussite crystals has been explained based on crystal-structure considerations and quantum-mechanical calculations. In particular, the crystal growth along the a direction in cyclically twinned crystals is explained by the binding forces between the CO32− molecular group and Pb2+, defining an uninterrupted chain of strong bonds along that direction. However, the preferred growth along the c direction observed for the cerussite crystal formed in gel media is here attributed to an intermolecular interaction through C–C bonds. The occurrence of a chemical bonding between the C atoms of the CO32− molecular groups aligned along the c direction is clearly shown by the theoretical analysis of the electron density with the quantum theory of atoms in molecules (QTAIM).