Structure of cyano-bridged Eu(III)-Co(III) bimetallic assembly and its application to photophysical verification of photomagnetic phenomenon

New crystal structure of Eu(DMF)₄(H₂O) ₃Co(CN)₆•H₂O (DMF = N,N′- dimethylformamide) (Eu-Co) has been determined to be monoclinic, P2(1)/n, a = 19.796(12) Å, b = 8.862(11) Å, c = 17.525(10) Å, β = 96.26(5)°, V = 3056(5) ų, Z = 4. The Eu(III) ion adopts an antiprismatic eight-coordination and forms a cyano bridge with r(Eu-N) = 2.496(7) Å and Θ(Eu-N-C) = 165.7(7)° to the Co(III) ion. The complex exhibits some common features with the Eu-Fe complex. Diffuse reflectance electronic spectra and magnetic susceptibility of Eu-Cr, Eu-Mn, Eu-Fe, and Eu-Co complexes were compared. By substituting the metal ions, both electronic and structural features affected the charge transfer bands and superexchange interactions concerning cyanide ligands. In addition, only Eu-Co exhibited ⁵ D ₀ → ⁷ F ₂ and ⁵ D ₀ → ⁷ F ₁ luminescence bands at 16300 cm^-1 and 16900 cm^-1, respectively at 298 K (λ_ex = 360 nm (27000 cm^-1)), because quenching by cyano-bridged ions did not prevent Eu(III) ion from exhibiting emission. Thus, only Eu-Co may be suitable for verification of an assumption of mechanism concerning drastic photoinduced magnetic changes for Nd-Fe. Merely small decrease of magnetization was observed for Eu-Co after UV light irradiation at 2.0 K. This result was attributed to slight structural changes around cyano bridges without transitions of spin states.