Isomerism of copper(II) coordination compounds with hydroxamic acids

Abstract

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...

EPR spectra and structures of dinuclear copper(II) complexes with acyldihydrazones of benzenedicarboxylic acids

“…The EPR spectra of stable organic radicals in copper com plexes with chelate ligands were observed many times, and several explanations were given for their appear ance. [30][31][32][33][34] The intensity of the EPR spectra of radicals strongly depends, first, on the meta or para arrangement of the substituents and, second, on the nature of the sub stituents R.…”

Synthesis and characterization of hydroxamic acid N,3-dihydroxy-2-naphthamide and its copper (II) complex per keto/enol forms and rare earth flotation

“…As occurs with HAs in general, both SHA and H2O5 contain four primary active electronegative groups, which can potentially participate in coordination chemistry. Through a tautomerization mechanism, it is extremely likely that they resonate between the amide and imidic forms [22] . For the imidic form, the Pauling standardization of electronegativity was used to show that the most electronegative atom in the HA structure is the nitrogen with a value of 4.03, whereas the oxygen in the N-OH group calculated to be 3.69, the imidic OH group was determined at 3.85, and the phenolic OH group was found to be 3.80.…”

Structure of N-substituted copper(II) hydroxamates in crystalline state and frozen solution

“…Two monomeric species, presumably, cis and trans isomers, were detected by electron paramagnetic reso nance (EPR) in solutions at room temperature [3]. In addition to the monomeric species, the [CuL 2 ] 2 dimer can be detected under cooling of solution in a low temperature glass [4].…”