Isostructurality in trivalent metal tris(benzoylacetonates)

Abstract

Isostructurality is a similarity of the spatial arrangement of molecules off different compounds in their crystal structures. A prerequisite for isostructurality of two compounds is isometry of their molecules. This is best achieved for molecules which differ only in one or few core atoms, while the surface of the molecule remains mostly unchanged [1]. A very good example of such systems are tris(diketonate) coordination compounds of trivalent metals. This was noticed as early as 1926 when has been noted that the crystal structures of trivalent metal pentane-2, 4-dionato complexes of various metals appear to be grouped in several isomorphous series [2]. If the metal atom is coordinated by asymmetrical diketonate, two different isomers (facial and meridial) are possible. Our work concentrated on compounds where trivalent metals are coordinated by 1-phenylbutane-1, 3-dionato ligands which were studied by single crystal X-ray diffraction and thermal analysis. The meridial complexes of iron(III), manganese(III), chromium(III) were already reported to be isomorphous based on their powder diffraction patterns [3]. We have shown that thay crystallize in the monoclinic system, space group P21/c. The only facial isomers which could be isolated where those of chromium(III) and cobalt(III) complexes. They were both found to crystallize in two pseudopolymorphic modifications. Pure compounds crystallize in the space group P– 1 with two molecules in the asymmetric unit. The crystal structures of the chromium and cobalt compounds are almost identical. Under same crystallization conditions, both compounds can also crystallize as hydrates. The hydrates crystallize in the space group R– 3 with 12 molecules per unit cell. The two symmetrically independent molecules in the structure differ in the mode of hydratation. As is the case with the triclinic modifications, the trigonal modifications of both chromium and cobalt compounds are almost perfectly isostructural. [1] A. Kalman, L. Parkanyi, G. Argay, Acta Cryst. (1993) B49, 1039. [2] W. T. Astbury, Proc. Roy. Soc. (1926) 28, 313. [3] R. C Fay, T. S. Piper, J. Am. Chem. Soc. (1962) 84, 2303.