The Electronic Structure and the Chemical Bonding in NiO and La 2 NiO 4 Crystals. A Comparison with CuO and La 2 CuO 4

Modelling from quantum chemical data of the chemical bonding in NiO and La 2 NiO 4 crystals comparatively to CuO and La 2 CuO 4 , is proposed. The increase of the ionicity degree of the Ni(II)–O bonding in comparison with Cu(II)‐O bonding is observed. The covalency is low and equally distributed in the equatorial plane and apical direction in the NiO 6 octahedra in La 2 NiO 4 . As a supplementary data, which is common to La 2 CuO 4 and La 2 NiO 4 , the covalency of the apical La(III)–O bonding plays an important role in increasing the overall covalent character of the apical oxygen and triggering a further elongation of MO 6 octahedra.