%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