Interpretation of the mechanisms of chromatographic separation on CN-silica. Part I: TLC of metal complexes

Abstract

The chromatographic behavior of four mixed tris(beta-diketonato) complexes of the type [Co(acac)(3-n)(phacphac)(n)] (n = 0-3), three (beta-ketoiminato)-Cu(II) complexes, two tris(alkylxanthato)-Co(III) complexes, and five bis(alkylxanthato)-Ni(II) complexes has been studied on thin layers of CN-silica gel with fifteen mobile phases, thirteen of which resulted in normal-phase systems. Linear relationships were established between the R, values of tris(beta-diketonato) complexes and the amount [% nu/nu] of acetone in hexane-acetone mobile phases, and between the R-M values of these complexes and the number of acac ligands substituted by phacphac ligands. The results obtained were compared with previously observed chromatographic behavior of the same substances on thin layers of silica gel and polyacrylonitrile. The corresponding separation mechanisms were also considered. It was assumed that under conditions of normal-phase chromatography with solvents of low polarity the retention behavior of complexes containing aromatic rings in the molecule is mainly determined by donor-acceptor interactions of the cyano groups of the adsorbent with the pi-electron systems of the substances being separated.