Delocalization mechanism of ferromagnetic exchange interactions in complexes of copper(II) with nitroxyl radicals

Structural and Magnetic Studies of Copper(II) and Zinc(II) Coordination Complexes Containing Nitroxide Radicals as Chelating Ligands

“…Hence, the direct exchange term J dir only gives a very small positive value. On the other hand, in spite of the smallness of the delocalization ρ z 2, the large intra-atomic [31] In the present complexes 1a and 1b the nitroxide groups are axially coordinated to the Cu II ion. However, the determined exchange parameter is antiferromagnetic (J exp Ϸ 80 cm -1 ), which is contrary to the expected ferromagnetic interaction in axially coordinated Cu II -nitroxide complexes.…”

“…According to Musin and coworkers, [31] the strong antiferromagnetic coupling (J Ϸ -500 cm -1 ) [3] in equatorially coordinated Cu II -nitroxide complexes can be explained by the above-mentioned direct exchange interaction J dir . The third term of J(3d x 2 -y 2, π*) in Equation (5) becomes dominant due to the large overlap integral S Ϸ 10 -1 (J dir Ϸ -500 cm -1 ).…”

Copper(II)-Nitroxide Based Spin-Transition Like Species

“…While at room temperature axial coordination of the nitroxide ligand occurs for both metal centers, at 50 K one observes an equatorial ligation of the nitroxide ligand to the intracyclic copper(lI) ion (Cu2) which suggests that decrease of X.T between 140 and 70 K has to be found in the change of coordination geometry of the intracyclic metal ion (Cu2). Indeed, if as mentioned a weak metal-ligand ferromagnetic coupling is expected for the room temperature geometry, in contrast, equatorial binding is known to result in strong spin pairing [23][24][25]. Thus, at low temperature each intracyclic copper ion is strongly coupled with a nitroxide ligand such that only the two extracyclic metal ions are observed.…”

“…In Nitronyl Nitroxide eomplexes where the ligand is eoordinated by the nitroxyl oxygen atom to an octahedral or square pyramidal metal ion, the same mies apply [23,24]: i) When the ligand is equatorially bound [10,[25][26][27], the metal-nitroxide magnetie interaction is antiferromagnetie and large (12JI > 500 em-l). ii) When the eoordination of the ligand is axial [9][10][11][12]23], the interaction is ferromagnetic and weak (2J < 100 em-l).…”

Interplay between lattice, orbital, and magnetic degrees of freedom in the chain-polymer Cu(II) breathing crystals

“…The first attempt to understand the nature of the spin exchange in the clusters containing the Cu atoms and a stable nitroxyl radical was performed rather long ago by Musin et al 16 The authors provided a detail quantumchemical analysis of the possible mechanisms of the exchange interaction in the magnetic fragmentsĊu(II)· · ·O-Ṅ < (or >Ṅ-O· · ·Ċu(II)· · ·O-Ṅ<) of bischelating complexes of Cu(II) with nitroxyl radicals. The drawback of this and some other [17][18][19][20] treatments was in the consideration of an isolated fragment rather than the crystal as a whole.…”