The structure of Cu H complexes with hydroxamic acids Cu[RIN(O)--(O)CR212, where R l = Ph, R 2 = Me; R 1 = Me, R 2 = Ph, was studied by ESR spectroscopy. In toluene solutions and low-temperature glasses, the complexes exist as two forms, which were identified as c/s-and trans-isomers. The proportions of the isomers were determined.Key words: copper(n) complexes, hydroxamic acids, ESR, HFS, isomerism.Study of cis--trans-isomedsm of coordination compounds has played an important role in the development of A. Werner's coordination theory. I,z However, the interest in the study of the properties of cis-and transisomers still has not attenuated. 3,4cis--trans-lsomerism is usually related to those complex compounds, whose coordination sphere contains atoms of two different sorts, for example, [O, N], [O, SI, [N, Sl, etc. This work deals with an ESR study of the structures of coordination compounds of copper(n) with hydroxamic acids; the coordination sphere in these complexes consists of atoms of only one sort (oxygen).The ESR spectra of compounds 1 and 2 recorded in toluene solutions at room temperature have been tentatively discussed previously)
ExperimentalThe complexes were prepared by a known procedure, s Compound I. A solution of copper acetate monohydrate (1.32 g) in 60 mL of water was added dropwise with stirring to a solution of C-methyI-N-phenylhydroxamic acid (2 g) in 60 mL of dioxane. This gave a yellow-green solution, whose pH was brought to 7 by adding an aqueous solution of KOH. Then the solution was concentrated, the resulting crystalline precipitate was dissolved in chloroform, and the solution was ESR spectra were recorded on a Radiopan SE/X-2542 radiospectrometer operating at 9.45 GHz. The magnetic field was calibrated with a nuclear magnetometer using the DPPH radical as the standard. The spectra were processed on a PC using a previously described procedure. 7To narrow the lines in the ESR spectra, solutions of compounds 1 and 2 were freed from O 2 by bubbling At. To facilitate interpretation of the ESR spectra, the 63Cu isotope was employed in the synthesis of compounds I and 2 (enrichment 99.8%).The experimental spectra were subjected to computer processing by minimization of the error functional7:Here lexp are the experimental intensities of ESR signals recorded as arrays of points with a constant step of the magnetic field I4"; li t are theoretical intensities found for the same H values as the sum of the derivatives of the Lorentz and Gauss functions centered around the resonance H values; N is the number of points.During minimization, the values of g-factors, HFS constants at the 63Cu nucleus, and the widths of resonance lines were varied. The line width was specified by the expression where m I is the projection of the nuclear spin in the direction of the external magnetic field, t~ is the term taking into account all the broadening effects identical for all the HFS lines. The 13 coefficient is defined as the product of the g-teusor and the tensor of hyperfine coupling (HFC). The y coeffi...
