Structural evolution in iron tellurates

Three new members within the iron tellurate family have been synthesized and characterized by single-crystal diffraction. Fe2Te3O9Fe2Te3O9 is orthorhombic, a=7.80240(10)Å, b=17.7501(3)Å, c=5.28050(10)Å, Z=4Z=4, space group Pnma  , final agreement factors R1=0.0261R1=0.0261(wR2=0.0688)(wR2=0.0688) for 1271 independent reflections. Fe3Te4O12Fe3Te4O12 is monoclinic, a=9.1312(2)Å, b=7.3554(2)Å, c=15.7379(3)Å, β=107.950(10)∘β=107.950(10)∘, Z=4Z=4, space group P21/cP21/c, final agreement factors R1=0.0380R1=0.0380(wR2=0.0281)(wR2=0.0281) for 3302 independent reflections. FeTe6O13FeTe6O13 is trigonal, a=b=10.16630(10)Å, c=18.9330(3)Å, Z=6Z=6, space group R3¯m, final agreement factors R1=0.0309R1=0.0309(wR2=0.0641)(wR2=0.0641) for 1264 independent reflections. Together with the four already known members of the family, Fe2TeO5Fe2TeO5, Fe2TeO6Fe2TeO6, and Fe2Te3O9Fe2Te3O9 (a dimorphic variant of the afore-mentioned structure with the same chemical formula), and Fe2Te4O11Fe2Te4O11, the iron tellurates now span from relatively Fe-rich and Te-poor to relatively Fe-poor to Te-rich compounds. The structural diversity within Fe–Te–O system is discussed in terms of the lone-pair stereochemistry of the Te4+Te4+ anion and the cross-over from Fe3+Fe3+ to mixed-valence Fe3+/Fe2+Fe3+/Fe2+ and Fe2+Fe2+ coordination polyhedra compounds.

The structures of three new iron tellurates have been determined and compared with four other iron tellurates known from the literature. The Te4+4+ lone pairs tend to align in tunnels, such as in the structure of Fe3Te4O12Fe3Te4O12.Figure optionsDownload as PowerPoint slide