Molecular Structures and Magnetic Properties of the Mixed-Ligand Complexes of Bis(hexafluoroacetylacetonato)manganese(II), -copper(II), and -zinc(II) with 4,4‘-Bis(N-tert-butyl-N-oxylamino)-2,2‘-bipyridine. Isosceles Triangular Hetero-Three-Spin Systems Consisting of Aminoxyls and Metal Ions

Abstract

4,4'-Bis(N-tert-butyloxylamino)-2,2'-bipyridine (4) and its 1:1 complexes with bis(hexafluoroacetylacetonato)manganese(II), -copper(II), and -zinc(II) were prepared. An X-ray structure analysis of free ligand 4 reveals that the molecule has a trans conformation with Ci symmetry and the aminoxyl radical center has a short contact of 2.36 A with one of the neighboring molecules. The three 1:1 complexes have mutually similar molecular structures in which the 2,2'-bipyridine moiety has a cis conformation and serves as a bidentate ligand and coordination geometry around the metal atom is a distorted octahedron. The EPR experiments for free ligand 4 and [Zn(hfac)2.4] in frozen solution suggested that the exchange couplings between the two aminoxyls (R) through the 2,2'-bipyridine rings are antiferromagnetic with JR-R/kB = -19.3 +/- 0.5 and -24.3 +/- 0.4 K, respectively. Isosceles triangular three-spin models were applied to the 1:1 magnetic metal complexes to give JR-M/kB = -19.1 +/- 0.2 K and JR-R/kB = -32.9 +/- 0.3 K for [Mn(hfac)2.4] and JR-M/kB = +73 +/- 18 K and JR-R/kB = -24.5 +/- 6.5 K for [Cu(hfac)2.4].

Structures and magnetic properties of two new heterospin complexes involving nitroxide radicals and oxamido-bridged copper(II)

“…The magnetic interaction between Cu(II) and nitroxide radical ligands through the pyridine ring is weakly anti-ferromagnetic [20]. This is in agreement with the following: (1) the nitrogen atom of the pyridine ring lies on the basal plane of the Cu(II) and (2) according to the spin polarization mechanism, the nitrogen atom of the pyridine ring has small spin density.…”

X-ray Crystallography and Magnetic Studies of a Stable Macrocyclic Tetranitroxide. Intramolecular Dimer of Nitroxides in a Constrained Geometry of the Upper Rim of Calix[4]arene

“…It is well-known that intermolecular π-dimerization of nitroxides and other stable radicals may lead to relatively strong antiferromagnetic couplings. 6 We envision that intramolecular dimers of stable di-and polynitroxides, with a conformationally restricted macrocyclic backbone, may provide novel aCUs. Such coupling units are essential for effective approaches to polymerbased organic magnets.…”

Ruthenium Carbon-Rich Group as a Redox-Switchable Metal Coupling Unit in Linear Trinuclear Complexes

“…2 and 4 cm −1 for nitronyl nitroxide and verdazyl radicals, respectively. In order to understand the magnetic behavior of such redoxactive assemblies through the rationalization of the different interactions that can exist in such compounds, we further designed new mono-and binuclear metal acetylide complexes [(Ph−CC−) 2−n Ru(dppe) 2 (−CC-bipyM(hfac) 2 ) n ] (n = 1, 2; M = Cu II , Mn II ; bipy = 2,2′-bipyridin-5-yl) bearing inorganic radicals (Scheme 1) 74 (i) to set up a new magnetic coupling and (ii) to achieve the redox modulation/creation of exchange interactions between the different elements of those assemblies. Note that the ruthenium acetylide system displays a sufficiently low oxidation potential (E°= 0.5 V vs SCE) to avoid oxidations of Cu II and Mn II centers, 75 and that this 2,2′-bipyridin-5-yl positioning was chosen because 4-yl positioning would create a spin frustration between Mn/Cu and Ru spin carriers and annihilate a probable polarization mechanism magnetic coupling (Ovchinnikov rule).…”

“…In order to understand the magnetic behavior of such redox-active assemblies through the rationalization of the different interactions that can exist in such compounds, we further designed new mono- and binuclear metal acetylide complexes [(Ph–CC−) 2– n Ru­(dppe) 2 (−CC-bipyM­(hfac) 2 ) n ] ( n = 1, 2; M = Cu II , Mn II ; bipy = 2,2′-bipyridin-5-yl) bearing inorganic radicals (Scheme ) (i) to set up a new magnetic coupling and (ii) to achieve the redox modulation/creation of exchange interactions between the different elements of those assemblies. Note that the ruthenium acetylide system displays a sufficiently low oxidation potential ( E ° = 0.5 V vs SCE) to avoid oxidations of Cu II and Mn II centers, and that this 2,2′-bipyridin-5-yl positioning was chosen because 4-yl positioning would create a spin frustration between Mn/Cu and Ru spin carriers and annihilate a probable polarization mechanism magnetic coupling (Ovchinnikov rule).…”