Effect of fluorine position on the coordinating ability of fluorosalicylic acids--an experimental study complemented with computations.
The complexation of 3-, 4-, and 6-fluorosalicylic acids (HL) with copper(II) was investigated in aqueous solution by pH-potentiometry combined with UV-visible spectrophotometry, and in 50 v/v % water-methanol mixture by the two-dimensional ESR simulation method. Both methods showed the formation of [CuLH(-1)] and [CuL(2)H(-2)](2-) of high stabilities, and, at low excess of ligand, the ESR-silent mixed hydroxido complex [Cu(2)L(2)H(-3)](-). Further species were also identified by the two-dimensional ESR simulation method: [CuL](+) in the acidic region, the minor dimer [Cu(2)L(2)H(-2)], and the cis and the trans isomers for [CuL(2)H(-2)](2-). The position of the fluorine atom in the aromatic ring had significant effect on the coordination abilities of the ligands, in good correlation with their reported biological activities. It was 3-fluorosalicylic acid, which formed the most stable complexes [CuLH(-1)] and [CuL(2)H(-2)](2-), while the mononuclear complexes with 6-fluorosalicylic acid were found to be the least stable. For the other ligands (including 5-fluorosalicylic acid studied recently), complexes of medium stabilities were formed. For the interpretation of these findings, ab initio and semi-empirical quantum chemical calculations were carried out for the ligand molecules, isolated and surrounded by water molecules, respectively.
Department of Physical Chemistry and Material Sciences, University of Szeged, Aradi vértanúk tere 1, H-6720 Szeged, Hungary. szabot@chem.u-szeged.hu
Terézia
T
Szabó-Plánka
Béla
B
Gyurcsik
István
I
Pálinkó
Nóra Veronika
NV
Nagy
Antal
A
Rockenbauer
Rastislav
R
Sípoš
Jozef
J
Sima
Milan
M
Melník
D003300:Copper / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005461:Fluorine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D012459:Salicylates / Q000737:chemistry*
D009942:Organometallic Compounds; D012459:Salicylates; D005461:Fluorine; C075234:5-fluorosalicylic acid; D003300:Copper