Ammonolytic heating of Dion-Jacobson type layered perovskite LiLaTa2O7 produced oxynitride derivatives LiLaTa2O7-3xN2x square(x) via the substitution, 3O(2-) -> 2N(3-) + square. The nitridation level increased with raising the temperature and/or increasing the time of reaction, reaching the limit at x approximate to 0.3 by the ammonolysis at 650 degrees C for 48 h. Upon the nitridation, tetragonal pristine lattice underwent a axis expansion together with c axis contraction. Neutron Rietveld refinement of LiLaTa2O7 and LiLaTa2O7-3xN2x (x = 0.09, 0.29) revealed that the Li-centered tetrahedra are gradually compressed along the 2-fold rotation axis, with the increase of x. Solid state Li-7 nuclear magnetic resonance spectroscopy suggested that the anion vacancy resides mostly on the interlayer surface of perovskite block. As measured from the diffuse-reflectance spectroscopy, the nitridation induced marked reduction in the band gap magnitude, from 4.11 eV (x = 0) to 3.35 eV (x = 0.09) to 2.76 eV (x = 0.29). (C) 2012 Elsevier Ltd. All rights reserved.