G. M. Larin

ESR study of weak exchange interactions in binuclear copper(ii) complexes with 2-hydroxyacetophenone acyldihydrazones

The binuclear copper(ii) complexes with 2-hydroxyacetophenone acyldihydrazones (H4L) Cu2L·2Py were studied by ESR spectroscopy. In these complexes, the coordination polyhedra are linked via the polymethylene chain containing from one to five units. In the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids, weak spin-spin exchange interactions occur between the paramagnetic centers. An increase in the length of the polymethylene chain to five units hinders exchange interactions, and the ESR spectrum of the corresponding complex has a signal typical of monomeric copper(ii) complexes.

EPR study of weak exchange interactions in binuclear copper(ii) complexes with salicylaldehyde acyldihydrazones

The binuclear CuII complexes with bis(salicylidene)hydrazones of dicarboxylic acids and their analogs (H4L) of composition [Cu2L·2Py] in which the coordination polyhedra are linked by a polymethylene chain containing from one to eight CH2 units were studied by EPR spectroscopy. Weak antiferromagnetic spin-spin exchange interactions between two CuII atoms were found in the complexes based on hydrazones of malonic, succinic, glutaric, and adipic acids. These exchange interactions are manifested in the EPR spectra of liquid solutions as seven-line hyperfine signals from two equivalent CuII atoms with the hyperfine coupling constant aCu ≈ 40·10–4 cm–1. The exchange ceases as the length of the polymetylene chain increases to five-eight units and the EPR spectra show a four-line signal with aCu ≈ 80·10–4 cm–1 typical of mononuclear complexes.

Molecular structures and ESR spectra of copper(II) complexes with 2-hydroxypropiophenone acyldihydrazones

The dinuclear copper(ii) complexes with 2-hydroxypropiophenone acyldihydrazones (H4L) having the composition [Cu2L·mPy], where the L ligand contains the polymethylene chain with different lengths (from two to five units), were synthesized and studied. The crystal and molecular structures of the 2-hydroxypropiophenone adipoylhydrazone complex [Cu2L·4Py]·Py were established by X-ray diffraction analysis. Copper atoms are 8.212 Å distant from each other, and their nearest environment has the tetragonal pyramidal geometry. The ESR spectra of solutions of the complexes based on acyldihydrazones of succinic, glutaric, and adipic acids contain seven HFS lines with the constant ∼40·10–4 cm–1 from two equivalent copper atoms. The spectra were interpreted as a result of the spin-spin exchange interaction of two unpaired electrons. An increase in the polymethylene chain length to five units prevents exchange interactions. The ESR spectrum of the complex with acyldihydrazone of pimelic acid contains a signal of four HFS lines with aCu = 73.4·10–4 cm–1, which is typical of mononuclear copper(ii) complexes.

ESR spectra of copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones

ESR spectra of binuclear copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones (H4L) [Cu2L·2Py], in which the coordination polyhedra are linked by the polymethylene chain with different lengths (from one to five units), were studied. The spectra of the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids exhibit weak exchange interactions between the paramagnetic sites. These interactions induce seven HFS lines from two equivalent copper nuclei with the constant ∼40·10–4 cm–1 in the ESR spectra of liquid solutions. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of the complex based on heptadioic acyldihydrazone contains the signal of four HFS lines with the constant ∼72·10–4 cm–1, which is common for the copper(ii) monomeric compounds.

Isomerism of copper(II) coordination compounds with hydroxamic acids

The structure of CuII complexes with hydroxamic acids Cu[R1N(O)−(O)CR2]2, where R1=Ph, R2=Me; R1=Me, R2=Ph, was studied by ESR spectroscopy. In toluene solutions and low-temperature glasses, the complexes exist as two forms, which were identified ascis-andtrans-isomers. The proportions of the isomers were determined.

Influence of conjugated π bonds in equatorial ligands on the electron structure of low-spin complexes of Co(II)

Conclusions1.The authors have investigated the ESR spectra of two low-spin complexes of Co(II) with Schiff bases in low-temperature glasses and magnetically dilute powders, and have found that in both complexes the unpaired electron is localized on the dyz orbitals.2.The experimental results for these complexes, and for similar ones investigated previously, are interpreted by means of a theoretical model based on the crystal field, the interelectron repulsion, and the spin-orbit interaction, without invoking the theory of perturbations.3.The authors suggest a model which explains the splitting of the Orbitals dxz, dyz in the square complexes on the basis of the effect of π conjugation in the chelating ligands.

ESR study of weak exchange interactions in binuclear copper(ii) complexes with acyldihydrazones of fluorinated β-diketones

A series of binuclear copper(ii) complexes with acyldihydrazones of aliphatic dicarboxylic acids (from malonic to adipic) and fluorinated β-diketones (trifluoro- and hexafluoroacetylacetone) of composition Cu2L·2Py (H4L is acyldihydrazone) were studied by ESR spectroscopy. The ESR spectra of solutions of complexes with trifluoroacetylacetone acyldihydrazones have an isotropic signal with a seven-line hyperfine structure from two equivalent copper nuclei (g = 2.112, aCu = (39—40)·10–4 cm–1), which is indicative of weak exchange interactions between the paramagnetic centers due to spin density delocalization through a chain of the σ-bonds of the polymethylene bridge. On going to hexafluoroacetylacetone derivatives, the coupling is suppressed and the ESR spectra of solutions of such complexes show a signal with a four-line hyperfine structure (g = 2.121—2.131, aCu = (55—63)·10–4 cm–1) typical of mononuclear copper complexes.

Anomalous line broadening in the ESR spectra of copper(ii) dithizonate

The structure of the copper(ii) complex with dithizone (H2Dz) was studied by ESR spectroscopy. The lines of the ESR spectra of the Cu(HDz)2 complex in solutions are so broad that the superhyperfine structure (SHFS) from the ligand atoms is unobservable and even the hyperfine structure (HFS) from the copper nuclei is poorly resolved. In polycrystalline magnetically dilute powders with the ratio Ni(HDz)2 : Cu(HDz)2 = 60 : 1, the SHFS from the N atoms is well resolved in both perpendicular and parallel orientations. The copper(ii) complex with dithizone has a square-planar structure in both liquid solutions and Ni(HDz)2 matrix. Reasons for the unusual linewidths in the ESR spectra of Cu(HDz)2 are discussed.

Synthesis and study of binuclear vanadyl complexes with acyldihydrazones of salicylaldehyde and dicarboxylic acids

The binuclear vanadyl(ii) complexes [(VO)2·2Py·2EtOH]·mH2O with acyldihydrazones of salicylaldehyde (H4L) and dicarboxylic acids were synthesized and studied. In these complexes, two chelate vanadyl(ii) complexes with the tridentate bicyclic ligands are linked to each other by the polymethylene bridges —(CH2)n— of different lengths varying from one to four units. The ESR spectra of solutions of these complexes, unlike those of analogous copper(ii) complexes, have an isotropic signal with an eight-line hyperfine structure (g = 1.972, aV = 93·10–4 cm–1) typical of monomeric vanadyl complexes, which indicates that no exchange interactions occur between the paramagnetic centers through the polymethylene chain.

Mutual influence of metals and ligands in the complex formation of oxo anions of d-elements with chelating ligands

The complex-formation processes between ions of d-elements having multiple M=O bonds with bidentate monoanions, mainly 1,1-ditiolates, are considered. The data of ESR spectroscopy and X-ray diffration analysis for this type of complexes are analyzed. Owing to the strongtrans-effect of the M=O group, M-ligand valence bonds are not formed in thetrans-position to the M=O group, and only donor-acceptor M-ligand bonds are realized. The valence M-ligand bonds can arise only in the equatorial plane, incis-positions with thespect to the multiple M=O bond.