Crystal chemistry of new descloizite-type compounds containing mercury

Up to date the only mercury-containing phase with a descloizite-type of structure was synthetic HgZn(OH)[AsO (sub 4) ]. During phase formation studies under hydrothermal conditions, six new synthetic phases with composition HgM (super II) (OH)[AsO (sub 4) ] (M (super II) = Mg, Co, Ni, Cu) or HgM (super III) (O)[AsO (sub 4) ] (M (super III) = Mn, Fe) could be obtained. All phases adopt the descloizite-type of structure, as revealed by crystal-structure analysis using single-crystal X-ray diffraction data (space group Pnma, Z = 4, a nearly equal 7.8, b nearly equal 6.2, c nearly equal 8.6 Aa). Whereas the crystal structures of the Mg-, Co- and Ni-members show a high degree of similarity with the known Zn-member, the crystal structures of the Cu-, Mn- and Fe-members show much higher displacements of atoms relative to the Zn-member. In case of the Cu-member and to a minor extent in the Mn-member, this is ascribed to Jahn-Teller distortions of the [MO (sub 6) ] octahedra, and, in case of the Mn- and Fe-members, to missing hydrogen bonding interactions. The replacement of OH (super -) by an O (super 2-) anion in the two HgM (super III) (O)[AsO (sub 4) ] (M (super III) = Mn, Fe) structures is unprecedented for descloizite-type phases and represent rare examples where an OH (super -) --> O (super 2-) substitution does not change the adopted structure family and/or the space-group type.