New examples of chelating triketone-like ligands that promote formation of binuclear complexes

Abstract

The present work is to investigate of binding properties of chelating triketone-like ligands, which are able to forming of binuclear complexes. The studied compounds are able to exist in cyclic or ‘close form’ (phenyl substituted or unsubstituted 2-hydroxy-2-(trifluoromethyl)chroman-4-ones) as well as in their associated ‘open form’ (phenyl substituted or unsubstituted 1,1,1-trifluoro-4-(2-hydroxyphenyl)butan-2,4-diones). In this paper there is good evidence for the compounds are being in solid in ‘close form’ (pre-ligands), whereas in basic solutions and when involved in metal ion coordination sphere they are being in ‘open form’ (ligands). Protolytic equilibria of the compounds in aqueous ethylene glycol solutions were studied. Schemes of acid-base equilibria of these compounds were proposed. Apparent ionization constants of compounds containing electron-donor and electron-acceptor substituents in the benzene ring were determined using spectrophotometric method. The binding properties of 1,1,1-trifluoro-4-(2-hydroxyphenyl)butan-2,4-dione towards Cu(II), Ni(II) and Co(II) were studied. The formation of 2:2 metal–ligand complexes was observed. X-ray analysis gives evidence the formation of complexes in which the ratio metal to ligand can be 1:2 and 2:2. Similar to β-triketones the studied ligands tends to formation of binuclear complexes with transition metal ions.