Electron-density distribution in crystals of KCuF₃ with Jahn–Teller distortion

Abstract

The electron-density distribution in crystals of K+[CuFa] -has been investigated on the basis of X-ray intensity data collected by diffractometry at room temperature. The crystal has a distorted perovskite structure, containing Cu 2+ ions at pseudo-tetragonally deformed octahedral sites. On the deformation-density map, positive peaks were observed on the longest Cu-F bonds and negative peaks on the shortest Cu-F near the Cu 2+ ion. When aspherical scattering factors were used for Cu 2+ by assuming the hole of the d shell on the dx2_ y2 orbital, the difference Fourier map showed large positive peaks on the Cu-F bonds with intermediate length, though the positive and negative peaks on the longest and shortest bonds disappeared. The observed electron density is well explained if we assume that the hole occupies the orbital given by sin (tp/2)d 2 -cos (~0/2)dx2_y2. The most plausible value of cos (~0/2) after the least-squares fit was 0.976 (17). The experimental density distribution of the 3d electrons in the 3dy orbitals was obtained, revealing well the origin of the deformation-density maps.

Electron density in non-ideal metal complexes. I. Copper sulphate pentahydrate

“…The density near the Cu nucleus has a remarkable resemblance to the corresponding region of the difference map for KCuF3 shown in their Fig. 2(b) by Tanaka et al (1979). Closely similar features are observed for other Cu 2÷ complexes, which will be described in later papers in this series.…”

“…In a study of the electron density in KCuF3, Tanaka, Konishi & Marumo (1979) observed a distorted distribution. Some of the distortion can be related to differences in the lengths of the Cu-F vectors.…”

Electron-density distributions in crystals of KMnF3 and KNiF3

“…As to reflexions with very strong ELECTRON-DENSITY DISTRIBUTIONS IN KMnF a AND KNiF 3 and 0.054 and 0.070 for KNiF 3, respectively. Using the method of Becker & Coppens (1974a,b, 1975 (Tanaka, Konishi & Marumo, 1979) and KCoF 3 crystals (Kijima, Tanaka & Marumo, 1981). In order to avoid interaction of extinction parameters with scale factors and temperature factors, we introduced double scale factors, one for reflexions with sin 8/;~ <_ 0.6 A -~ and the other for reflexions with sin 0/2 > 0.6/k -~.…”

“…0.11 (7) 754 (2) 751 (3) 750 (2) 1989 (5) 1998 (7) 1992 (5) 777 (12) 795 (17) 779 (12) 3518 (21) 3472 (29) 3523 (21) 889 (15) 916 (22) 902 (15) 2336 (75) 2761 (115) 2372 (76) 937 (16) 958 (23) 951 (16) 161 (33) 216 (50) field were given by Tanaka, Konishi & Marumo (1979, 1980. The scattering factors of the Ar core and the orbital scattering factors of the 3d electrons, (J0)aa, (J2)3a and (J4 >3d were taken from International Tables for X-ray Crystallography (1974).…”

“…In previous articles on KCuF 3 (Tanaka, Konishi & Marumo, 1979, 1980 and KCoF 3 (Kijima, Tanaka & Marumo, 1981), we have found that residual density maps change drastically according to a slight variation in the assumed configurations of d electrons. Distortion of 0108-7681/83/050557-05501.50 electron distribution by the Jahn-Teller effect in KCuF 3 crystals was clearly revealed on deformation density maps.…”