Solvent exchange caused reversible variations in color, magnetic properties, and the Faraday spectra Of Co-1.5(II)[Cr-III(CN)(6)].7.5H(2)O (1) prepared in water. Compound 1 turned from peach to deep blue, which was due to a change in the coordination geometry on Coll ion from six-coordinate pseudo-octahedral (OhCoII) to four-coordinate pseudo-tetrahedral (TdCoII) geometries, when it was immersed in EtOH. The confirmed formula for the deep blue powder was Co-1.5(III)[Cr-III(CN)(6)].2.5H(2)O.2.0EtOH. The magnetic properties also changed; that is, the magnetic critical temperature, saturation magnetization, and coercive field went from 25 to 18 K, from 7.0 to 5.5 mu(B), and from 240 to 120 G, respectively. This solvatomagnetism is because the ferromagnetic magnetic coupling between OhCOII (S = 3/2) and Cr-III (S = 3/2) is replaced by the antiferromagnetic coupling between TdCoII (S = 3/2) and Cr-III (S = 3/2). Accompanying the solvatochromism and solvatomagnetism, the Faraday spectra drastically changed. The Faraday ellipticity (FE) spectrum of 1 had a distorted dispersive peak (A), which is due to the T-4(1g) --> T-4(1g), T-2(1g) transitions of OhCOII ion, around 480 nm, but the FE spectra of 2 showed a new dispersive-shaped band (B) at 580 rim. The observed B band was assigned to the (4)A(2) --> T-4(2) transition of the TdCoII ion. The Faraday spectra were well reproduced by a simulation that considers the ligand field splitting, spin-orbital coupling, and the ferromagnetic ordering. These solvatochromic effects were repeatedly observed.