Copper(II) bis(hexafluoroacetylacetonate) complexes with 2-(2-methyltetrazolyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 1-oxides

An efficient procedure was developed for the synthesis of alkyltetrazolyl-substituted nitronyl nitroxides (L ¹ and L ²). These compounds were used to prepare the first alkyltetrazolyl-substituted imino nitroxides (L ³ and L ⁴). The molecular structures of L ³ and L ⁴ were confirmed by X-ray diffraction. Investigation of the products prepared by the reaction of copper(II) bis(hexafluoroacetylacetonate), Cu(hfac)₂, with nitroxides made it possible to divide ligands L ¹—L ⁴ into two groups. The reactions of spin-labeled tetrazoles L ¹—L ³ with Cu(hfac)₂ afford the heterospin complexes Cu(hfac)₂L₂, whereas L ⁴ serves as a bidentate ligand in the Cu(hfac)₂ L ⁴ complex. In the solid Cu(hfac)₂L₂ complexes, antiferromagnetic exchange interactions between the unpaired electrons of the nitroxide fragments of the adjacent molecules prevail, due to which μ_eff decreases with decreasing temperature, and the spins of nitroxides are completely compensated at 5–10 K. The Cu(hfac)₂ L ⁴ complex displays strong intramolecular ferromagnetic coupling, due to which μ_eff at room temperature is close to 2.9 μ_B. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 64–70, January, 2006.     

Peculiarities of NMR spectra of heterospin complexes

Experimental investigation and theoretical simulation of the unusual phenomenon of multiple broadening and narrowing of NMR signals due to the temperature variation of a solution of the stereochemically non-rigid heterospin Ni²⁺ complex with stable nitroxide were performed. The investigation of the temperature dependence of the NMR signals of stereochemically non-rigid heterospin systems can be used for choosing conditions for growing heterospin single crystals containing molecules in a definite conformation.     

Crystal structure and magnetic properties of the octahedral complexes of Ni(II) with 3-imidazoline nitroxides

This paper reports on our studies of the crystal structures and magnetic properties of five mixed-ligand octahedral complexes of Ni(II) with 3-imidazoline nitroxides Ni(RL)₂X₂, where RL are deprotonated enaminoketone derivatives of 3-imidazoline nitroxide with different substituents R (CF₃, Ph) in the side chain, and X is pyridine, dimethylsulfoxide, or semi-phenanthroline. It is established that this type of heterospin system is characterized by an intramolecular exchange interaction parameter (J) of an order of 10 cm⁻¹. Substitution of the N-donor diamagnetic pyridine or phenanthroline by the O-donor dimethylsulfoxide in the coordination sphere of the metal decreases J by 2–3 cm⁻³. A transition from trans-to cis-coordination of the enaminoketone ligands and variation of the R substituent in the chelate ring do not affect the value of J. Deceased. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 5, pp. 901–916, September–October, 1998. This work was supported by INTAS grant No. 94-3508 and RFFR grants No. 96-03-33738 and 96-03-32229.     

Complexes of metals with paramagnetic 3-Imidazoline schiff bases

Methods for the synthesis of intracomplex bischelates CuL₂, NiL₂, CoL₂, and the mixed- ligand complex NiL₂y₂, where L is a deprotonated derivative of the stable nitroxide 4- (2′- hydroxyphenyl)- 2,2,5,5tetramethyl- 3- imidazoline- 1-oxyl, were developed. In the solid state, the compounds have a molecular structure. The most significant difference in the structure of ML₂ molecules lies in the values of the angle between the chelate rings (56.9‡ for CuL₂, 78.8‡ for CoL₂, and 0‡ for NiL₂. In complexes with paramagnetic metal ions, the intramolecular exchange interactions are ferromagnetic in character and are close in the order of magnitude (5.7 cm^{− 1} for CuL₂ and 6.8 cm⁻ for NiL₂Py₂) to the values for complexes with deprotonated enaminoketone derivatives of 3- imidazoline. The NiL₂ molecules, having a square coordination of the central atom, are biradicals with antiferromagnetic exchange interactions between the unpaired electrons of nitroxyl groups (− 3.6 cm⁻). The transformation of NiL₂ into NiL₂Py₂ leads to a transition of Ni(II) from the low- to high- spin state and to ferromagnetic exchange between the unpaired electrons of the paramagnetic centers. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 4, pp. 750–761, July–August, 1997.     

Magnetic isotope effect of tin and isotope exchange in the reactions of organotin compounds

Conclusions Magnetic isotope effects from tin are not observed during the isotope analysis of the products from reactions involving trimethylstannyl radicals. One of the possible reasons for this is the demonstrated presence of degenerate exchange processes between the initial compounds and the products during the reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2207–2211, October, 1985.     

Magneto-structural correlations in layered polymeric molecular ferromagnets based on Ni(II) and Co(II) complexes with 3-imidazoline nitroxide radicals and methanol with different substituents in the metal cycle

We report on the synthesis, structure, and magnetic properties of Ni(II) and Co(II) complexes with deprotonated enaminoketone derivatives of 3-imidazoline nitroxide radicals and methanol, ML₂(CH₃OH)₂. The complexes differ in substituents in the γ-position of the donor enaminoketone group (Cl, H, CH₃). When the substituents are varied, the magnetic behavior of these exchange clusters and their capability for three-dimensional ordering of magnetic moments at 5–7 K are not altered, and the arrangement of polymer layers remains constant. However, such variation of substituents is very important for the chemistry of these compounds. Thus the accepting ability of the central atom is reduced by substitution of the hydrogen atom by the methyl group but enhanced by substitution of halogen for hydrogen in the side chain of the enaminoketone. This favors a magnetic phase transition to a ferromagnetic state. The results obtained in this work are important for the chemical design of molecular ferromagnets based on metal bischelates with paramagnetic ligands. International Tomography Center, Siberian Branch, Russian Academy of Sciences. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences. Novosibirsk State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 4, pp. 76–90, July–August, 1994. Translated by L. Smolina