Regiospecificity in the Exchange Coupling of the Spins of Copper(II) Ion Coordinated with the Ring Nitrogen Atoms and N-tert-Butylaminoxyl Radical Attached as a Substituent on the Pyridine and N-Phenylimidazole Rings

Abstract

Complexes of bis(hexafluoroacetylacetonato)copper(II) [Cu(hfac)(2)] ligated with 3- and 4-(N-oxyl-tert-butylamino)pyridines (3NOPy and 4NOPy) and N-{3- and 4-(N-oxyl-tert-butylamino)phenyl}imidazoles (3NOIm and 4NOIm) were prepared. The 1:2 complexes [Cu(hfac)(2)(3NOPy and 4NOPy)(2)] have hexacoordinated octahedral structures in which the two pyridyl nitrogen atoms are coordinated to the copper(II) ions in the trans configuration. The 1:1 complex [Cu(hfac)(2)(4NOPy)] has a distorted pentacoordinated pseudo-head-to-tail cyclic dimer structure in which the oxygen atom of the aminoxyl group of one complex is situated at a distance of 2.79 Å from the copper ion of the other complex. The magnetic properties of these and two other complexes, [Cu(hfac)(2)(3NOIm and 4NOIm)(2)], were investigated using a SQUID susceptometer. Temperature dependence studies of the chi(mol)Tvalues of [Cu(hfac)(2)(4NOPy)(2)] revealed that the two aminoxyl radicals interact ferromagnetically with the copper(II) ion (S = (1)/(2)) with an exchange parameter J/k(B) = 60.4 +/- 3.3 K to produce a quartet ground state (S = (3)/(2)). On the other hand, the chi(mol)T value of the isomeric [Cu(hfac)(2)(3NOPy)(2)] was nearly constant at 0.5 emu K mol(-)(1) in the temperature range 5-300 K. A rectangular four-spin model was fitted to the chi(mol)T vs T plot for complex [Cu(hfac)(2)(4NOPy)] to give J/k(B) = 58.6 and 58.5 K. Similarly, the J values for [Cu(hfac)(2)(3NOIm and 4NOIm)(2)] were negative and positive, respectively, but their absolute J values were too small to determine in both cases.

Broken symmetry approach and density functional theory calculations for heterospin system consisting of copper(II) and aminoxyl radicals

“…All the results from these two types of calculations (UDFT and UHF) indicate that complex 1 has positive DE, which indicates that, this complex have ferromagnetic character (see Fig. 4) in good agreement with the experiments [17]. Although the magnitude of DE value significantly depends on calculation methods, both UDFT and UHF methods indicate that complex 1 is regarded as stable high-spin complex.…”

“…Thus, the optimized structure could not reproduce well the experimental results [10, [26][27][28][29][30]. Therefore, all the structures used in this work derived from the experimental geometries [17]. Figs.…”

“…The hfac and pyridyl ligands are essentially planar. One-dimensional compounds of hfac metal complexes with dipyridyl ligands or with other ligand have been reported [15,17,18,[31][32][33][34]. …”

“…In our target system the total spin S = 3/2 and BS state (SÀ1) = 1/2. Based on expression (4) (from the original experimental paper [17]) J 2 is very small and can be ignored. Therefore, we concentrated on calculating J 1 values.…”

“…1) consisting of organic radicals and transition metal ions have been studied theoretically by using BS approach. On the other hand, the magnetic properties of diradicals contain heteroatoms and metal-radical heterospin systems had been extensively studied experimentally [14,[17][18][19][20][21].…”