Electronic-Structure Calculations of Cation-Ordered II-III Layered Double Hydroxides: Origin of the Distortion of the Metal-Coordination Symmetry

Cation ordering brings down the crystal symmetry and introduces distortion into the coordination polyhedra around the divalent cations. In particular, edge sharing of the differently sized [M(OH)₆] polyhedra causes a non-uniform distension of the array of hydroxy ions. The question arises as to whether this distortion has its origin in the Jahn–Teller distortion of metal coordination or a 2D “Peierls”-type distortion of the array of hydroxy ions. To address this question, DFT calculations were performed on the sulfate-intercalated [Cu–Cr], [Zn–Cr], and [Zn–Al] layered double hydroxides (LDHs). An analysis of the density of states shows that the distortion of the Cu²⁺ coordination polyhedron is due to the Jahn–Teller effect, whereas the Zn²⁺ coordination polyhedron in [Zn–Al] LDH likely suffers a “Peierls”-type distortion. In the [Zn–Cr] LDH, electronic-structure calculations do not predict any distortion in the metal coordination, which is in agreement with experimental results that show only a slight departure from ideal symmetry.