Study on the construction of photoresponsive single-molecule magnets in frozen solutions

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For the construction of monometallic single-molecule magnets (SMMs), We proposed to use the heterospin systems consisting of the 2p organic spins and the 3d metal ions. In our heterospin systems, pyridine ligands carrying mono-, di-, and tricarbene (S=2/2,4/2, and 6/2, respectively) and high-spin Co(II) ions, CoCl_2 and Co(p-tolsal)_2, were employed as the 2p organic spins and the 3d metal ions, respectively. Various combinations of two components, diazo-pyridine ligands and Co(II) ions, in solutions were mixed in appropriate ratios. To avoid the intermolecular magnetic interaction, the frozen solution conditions were used as the samples for SQUID measurements. The ac and dc magnetic susceptibility measurements for six samples of the complexes were carried out before and after irradiation. In ac magnetic susceptibility measurements after irradiation of six samples, the in-phase and out-of phase components (χ' and χ", respectively) with the applying frequency dependence were observed, indicating that the cobalt complexes have slow magnetic relaxations. The values of the activation barriers, U_<eff>, for flipping the spin were estimated to be 40- 93 K for the six complexes. In the dc field dependence of magnetization at 1.9 K, relatively large hysteresis loops with coercive force, H_c=7-10 kOe for the six complexes were observed. Obtained values of U_<eff>, τ_0, and H_c, for all six complexes were summarized together with those for the related complexes. In this work, we successfully prepared the monometallic single-molecule magnets in frozen solution. Furthermore, by changing the S values of the complexes systematically, it was concluded that the activation barrier, U_<eff>, for flipping the spin and the relaxation time due to the resonant quantum tunneling effect increased and decreased, respectively, with increasing S value of the complex.