Pb2Fe2Ge2O9, the germanate analogue of the silicate mineral melanotekite

The structure of dilead(II) diiron(III) digermanium(IV) oxide, with a minor (2Fe/Mg+Ge) substitution arising from the growth conditions, has been determined using flux-grown single crystals. Interesting features of the structure include an unsymmetrical splitting of the Pb site and a strong anisotropy of the bridging O atom of the Ge2O7 group, both of which also occur in the structure of the silicate mineral melanotekite, Pb2Fe2Si2O9. These structural features can be associated with the stereoactivity of the Pb2+ lone pairs, which is found to be less pronounced in the germanate than in the silicate structure.