Complexation of 5-fluorosalicylic acid with copper(II): A pH-potentiometric, UV–vis spectroscopic, and electron spin resonance study by the two-dimensional simulation of spectra

The copper(II)–5-fluorosalicylic acid system was investigated in water and 50 v/v% water–methanol mixture by pH potentiometry combined with UV–vis spectrophotometry, and by the two-dimensional ESR simulation method, respectively. The data revealed that the stable paramagnetic mono- and bis(salicylato) copper(II) complexes [CuLH−1] and [CuL2H−2]2− are formed, and at low excess of ligand, the ESR-silent mixed hydroxo complex [Cu2L2H−3]− is also a major species. By the two-dimensional ESR simulation method, the species [CuL]+ in the acidic region, and the minor dimer [Cu2L2H−2] were also identified, and the cis and trans isomers of [CuL2H−2]2− were characterized. In frozen solutions, the ESR analysis revealed a slight rhombic distortion of coordination polyhedra for the latter three species.