Structural and Magnetic Study of O₂ Molecules Arranged along a Channel in a Flexible Single-Crystal Host Family

We report the magnetic behaviors of O2 molecules, which aligned in the channels of four types of single-crystal adsorbents, [M2(bza)4(pyz)]n (bza = benzoate; pyz = pyrazine; M = RhII (1a) and CuII (1b)) and [M2(bza)4(2-mpyz)]n (2-mpyz = 2-methylpyrazine; M = RhII (2a) and CuII (2b)). The X-ray single-crystal structures at various temperatures from 10 to 298 K were determined for O2-included crystals of 1a and 2a. All adsorbed O2 molecules exhibited abnormal magnetic phases above 4 T in the temperature range around 55−105 K. The magnetic behaviors of adsorbed O2 molecules between four inclusions were discussed. The existence of the metastable state, which was also suggested by hysteresis on the M−H curves, was revealed by analysis of the time course of the magnetization. Considering that the abnormal magnetic behavior occurred at relatively high temperatures and a low magnetic field, it was suggested that these behaviors were induced because of the changes of magnetic interaction of included O2 aggregates involving transformation which is supported by the surrounding of the channels of the single-crystal hosts under the applied magnetic field.