%0 Generic
%A Okazawa, Atsushi
%A Hashizume, Daisuke
%A Ishida, Takayuki
%D 2010
%T Ferro- and Antiferromagnetic Coupling Switch Accompanied by Twist Deformation around the Copper(II) and Nitroxide Coordination Bond
%U https://acs.figshare.com/articles/dataset/Ferro_and_Antiferromagnetic_Coupling_Switch_Accompanied_by_Twist_Deformation_around_the_Copper_II_and_Nitroxide_Coordination_Bond/2739034
%R 10.1021/ja102163d.s002
%2 https://acs.figshare.com/ndownloader/files/4416115
%K BF
%K oxygen atoms
%K copper ion
%K temperature ranges
%K 2 pyNO
%K chelate plane
%K nitroxide oxygen atom
%K oxygen atom
%K phase transition
%K anion ligand
%K 64 K
%K Cu
%K Magnetic study
%K Twist Deformation
%K orthogonal arrangement
%K Pbca space group
%X Two novel copper(II) complexes with tert-butyl 2-pyridyl nitroxide (2pyNO•), [Cu2+(2pyNO−)(2pyNO•)]2(BF4−)2 (1·BF4) and [Cu2+(2pyNO−)(2pyNO•)]2(ClO4−)2 (1·ClO4), were prepared and structurally characterized. They contained mixed-valent ligands from 2pyNO, whose oxygen atoms were located at equatorial positions of the copper ion. The [Cu2+(2pyNO−)(2pyNO•)] unit was dimerized by μ-oxo bridges of the anion ligand, giving a zigzag linear spin system involving four paramagnetic S = 1/2 centers. The two compounds are isomorphous in an orthorhombic Pbca space group. Magnetic study revealed that 1·ClO4 showed ferromagnetic copper−radical coupling in all temperature ranges investigated here. On the other hand, 1·BF4 exhibited a structural phase transition at 64 K, where the magnetic susceptibility was drastically dropped on cooling. The copper−radical magnetic couplings were characterized as ferro- and antiferromagnetic for the high- and low-temperature phases, respectively. The crystallographic analysis clarified that the nitroxide oxygen atom remained at the equatorial position throughout the single-crystal-to-single-crystal phase transition, while the previously known spin-transition-like copper−radical compounds showed conversion of the roles of equatorial and axial positions. The orthogonal arrangement between the copper dσ and nitroxide π* orbitals is essential for the ferromagnetic coupling, and a slight dislocation of the radical oxygen atom from the chelate plane leads to violation of the orthogonal orbital arrangement, giving a practically diamagnetic low-temperature phase.
%I ACS Publications