Elektrostatische Berechnungen an Karbonaten mit aplanaren Karbonatgruppen

Abstract

Abstract Madelung numbers α were computed for CaMg(CO3)2 (dolomite), Na2Mg(CO3)2 (eitelite), K2Mg(CO3)2, K2Ca(CO3)2 (buetschliite), CaCO3 (aragonite) and Na3Mg(CO3)2Cl (northupite) which all have slightly aplanar carbonate groups according to careful structure determinations. Heptapole models for the CO3 2−-complexion were used, and the distance d of the C-atom from the plane of the three O-atoms was set at d = 0.02 Å in all six compounds. Both geometrically possible orientations were taken into account. The results of our computations show that the electrostatic crystal field does not in all six cases favour the orientation of the aplanarity as determined experimentally. It is, therefore, concluded that the polarizibilities of the carbonate group and of its oxygen atoms play an important role in giving rise to this effect.