Redetermination of Nd₂Ti₂O₇: a non-centrosymmetric structure with perovskite-type slabs

Single crystals of dineodymium(III) dititanium(IV) hepta­oxide, Nd₂Ti₂O₇, were synthesized by the flux method and found to belong to the family of compounds with perovskite-type structural motifs. The asymmetric unit contains four Nd, four Ti and 14 O-atom sites. The perovskite-type slabs are stacked parallel to (010) with a thickness corresponding to four corner-sharing TiO₆ octa­hedra. The Nd and Ti ions are displaced from the geometrical centres of respective coordin­ation polyhedra so that the net polarization occurs along the c axis. The investigated crystals were all twinned and have a halved monoclinic unit cell in comparison with the first structure determination of this compound [Scheunemann & Müller-Buschbaum (1975). J. Inorg. Nucl. Chem. 37, 2261-2263].

Ethyl 2-(4-methyl­benzo­yl)-2,3-dihydro-1H-indene-2-carboxyl­ate

The title compound, C₂₀H₂₀O₃, contains two fused rings with a quaternary carbon centre connecting p-toluoyl and eth­oxy­carbonyl groups. The dihedral angle between the fused benzene ring and the three-C-atom plane (derived from O=C—C—C=O) is 82.5 (4)°, whereas the dihedral angle between the planes of the benzene rings is 53.4 (2)°. In the crystal, molecules are linked via C—H...O_ester hydrogen bonds, forming chains propagating along [010].