Dimensional Reduction From 2D Layer to 1D Band for Germanophosphates Induced by the “Tailor Effect” of Fluoride

The “tailor effect”
of fluoride, exclusively as a terminal rather than a bridge, was applied
successfully to design low-dimensional structures in the system of
transition metal germanophosphates for the first time. Two series
of new compounds with low-dimensional structures are reported herein.
K­[MIIGe­(OH)2(H0.5PO4)2] (M = Fe, Co) possess
flat layered structures built from single chains of edge-sharing MIIO6 and GeO6 octahedra
interconnected by HPO4 tetrahedra. Their fluorinated derivatives,
K4[MIIGe2F2(OH)2­(PO4)2(HPO4)2]·2H2O (M = Fe, Co), exhibit band structures
of two four-membered ring germanium phosphate single chains sandwiched
by MIIO6 octahedra via corner-sharing. Both
of these structures contain anionic chains of the condensation of
four-membered rings built from alternating GeO4Φ2 (Φ = F, OH) octahedra and PO4 tetrahedra
via sharing common GeO4Φ2 (Φ = F,
OH) octahedra, the topology of which is the same as that of the mineral
kröhnkite [Na2Cu­(SO4)2·2H2O]. Note that the switch from the two-dimensional layered
structure to the one-dimensional band structure was performed simply
by the addition of a small amount of KF·2H2O to the
reaction mixture. This structural alteration arises from the incorporation
of one terminal F atom to the coordination sphere of Ge, which breaks
the linkage between the transition metal and germanium octahedra in
the layer to form the band structure.