Synthesis and structure of a cerium succinato-bridged ionic open framework

Abstract

Titanates occupy an important place among advanced oxide materials. After characterization of MLi2Ti6O14 compounds in the ternary oxide systems MO Li2O TiO2 (M = Sr, Ba, Pb) [1],[2], two new titanates of Sr, Li and a 3d transitionmetal, SrLiMTi4O11 (where M = Cr, Fe) were discovered. Single crystals were obtained by spontaneous nucleation using LiBO2 as flux. The SrLiCrTi4O11 structure was refined using 1491 independent reflections in orthorhombic space group Pmna, with a=13.818A, b=5.755A, c=9.901A, Z=4, R1=0.021 and wR2=0.058. The SrLiFeTi4O11 structure was refined using 5005 independent reflections in orthorhombic space group Pbcn, with a=13.878A, b=11.496A, c=19.895A, Z=16, R1=0.036 and wR2=0.105. Structures can be described by the close-packed arrangement of strontiumand oxygen atoms. The unit cell contains 6 ’’compact planes’’ perpendicular to [100] in the layer sequence ABACBC ((chc)2). Titanium, chromium or iron atoms occupy some of the created interstitial octahedral sites whereas lithium atoms are situated in tetrahedral sites. Depending on the synthesis conditions of SrLiCrTi4O11, the chromium and titanium atom distributions over the four allowed crystallographic sites are not the same. Having a similar compact-planes sequence, SrLiCrTi4O11 and SrLiFeTi4O11 structures differ in the arrangement of strontium and oxygen atoms per layer of close packing which also induces correlated variation in the Li-tetrahedra distribution.