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The effect of the chelate ring size of diamine Co(III) complexes under salting-out thin-layer chromatography (TLC) conditions was investigated. For that purpose, 16 neutral and cationic complexes containing from five- to seven-membered diamine chelate rings were chromatographed on the thin layers of silica gel, cellulose and polyacrylonitrile sorbents. Six aqueous solutions of ammonium sulphate at various concentrations were used as solvent systems. In all of the instances studied, it was established that hR(F) values decrease with increasing ring size. It was also found that the R-M Values obtained were a linear function; on the one side, salt concentrations in the chromatographic solvent systems used, and on the other side the diamine chelate ring size. To explain these results, a mechanism based on hydrophobic interaction between the sorbend and sorbent is proposed. (C) 1999 Elsevier Science B.V. All rights reserved.

The effect of facial–meridional geometrical isomerism of metal complexes on their chromatographic behaviour on a thin layer of polyacrylonitrile sorbent was examined. To that purpose the three following series of complexes were chromatographed: [Co(eddp)Am], where eddp is ethylenediamine-N,N′-3-propionato ligand, Am is glycinato, alaninato, valinato, leucinato, isoleucinato or isobutyrato ligands, [CoAm 3 ], where Am is glycinato, β-alaninato, valinato or leucinato ligands as well as two pairs of isomer complexes of [Macacphac 3 ] type, where M is Co(III) or Cr(III) and acacphac is 1-phenyl-1,3-butanedionato ion. For their chromatographic separation four mono- and thirteen polycomponent solvent systems were used. In all the examined cases meridional isomers were found to exhibit higher hR F values than corresponding facial isomers. Finally, some possible separation mechanisms are discussed.

The direct synthesis of bis(alkylxanthato)nickel(II) complexes is described, consisting in the addition of nickel(II) chloride to a previously heated solution of sodium hydroxide and carbon disulphide in the corresponding alcohol. It was established that the RF values of complexes obtained with non-aqueous solvent systems increased with increasing number of carbon atoms in the xanthato ligands used, but the opposite order was found using an aqueous solvent system. There is a linear dependence between the RM values of complexes and the number of carbon atoms in the hydrophobic part of the ligands. In the former instance the proposed separation mechanism involves the formation of hydrogen bonds between strongly electronegative atoms of the ligands (O and S) and silanol groups of silica gel and in the latter a hydrophobic interaction mechanism was assumed. In this manner it was established that the previously found regularities for octahedral alkylxanthatocobalt(III) complexes can be applied also to the investigated square-planar alkylxanthatonickel(II) complexes.

Three series of tris(β-diketonato) complexes of cobalt(III), chromium(III) and ruthenium(III), in which acetylacetonato ligands were successively replaced with dibenzoylmethanato ligands, were chromatographed on silica gel thin layers and the corresponding mechanisms were considered. The RF values increased with non-aqueous and decreased with aqueous solvent systems. It was established that unmodified silica gel can be used as a sorbent for both normal- and reversed-phase chromatography of metal complexes. The earlier rule of a linear dependence between the RM values of tris(chelate) transition metal complexes and the number of substituted chelate ligands by others was extended.

Chromatographic behaviour of six anti hypertensive drugs from the class of ACE inhibitors was studied under conditions of salting-out thin-layer chromatography on silica-gel, cellulose and polyacrylonitrile (PANS) as sorbents. For this purpose, different concentrations of aqueous ammonium sulphate solutions were used as solvents. In all cases studied, it was established that hR(F) values decrease with increasing salt concentrations in the chromatographic solvent Systems used. In addition, a linear relationship of the corresponding R-M values and ammonium sulphate content in the solvent was observed. To explain these results, a separation mechanism based on hydrophobic interaction between the sorbend and sorbent is proposed.

The RF values of 78 cobalt(III) and platinum(II) complexes have been determined using solvent systems containing phenols. When the complexes were chromatographed with solvent systems containing mono- or polyhydric phenols, the trans isomers were found to exhibit higher RF values than those of the cis isomers, i.e., to display “the phenol effect”. However, by gradually decreasing the phenol content of a solvent system the phenol effect was found to disappear; in the cases of solvent systems containing small amounts of phenol, the addition of an electrolyte, or increasing its concentration, has a similar influence. The RF values of the cobalt(III) complexes increase when a five-membered ring is substituted by a six-membered one, and there is a linear relationship between the RM values and the number of substituted rings. For homologous series of cobalt(III) complexes, the RF values increase with increasing number of C atoms in the branched chain of the ligand and there is a linear relationship between the RM values and the number of C atoms in the aminocarboxylato ligand. Finally, in the cases of four pairs of diastereomeric cobalt(III) complexes, containing l-aminocarboxylato ligands,'the diastereomers having absolute configuration Λ exhibit higher RF values than those of absolute configuration Δ.

The RF values of eight pairs of facial and meridional of cobalt(III) and chromium(III) complexes have been determined by thin-layer chromatography with 21 solvent systems and by paper chromatography with 26 solvent systems. In the thin-layer chromatographic separations on silica gel the meridional isomers always exhibited higher RF values when single component solvent systems were used. On the contrary, with multicomponent solvent systems, in 30% of cases the elution order of the isomers was reversed. In paper chromatographic separations with solvent systems not containing strong acids the meridional isomers were found to exhibit higher RF values. However, when solvent systems containing strong acids were used in some cases the elution order was reversed. Possible mechanisms for the separation of those isomers are considered.