Magnetic Properties of Iron(III) Complexes with Photoisomerizable Ligands

New spin-crossover Iron(III) complexes [Fe(salten)(trans-stpy)]BPh4·(CH3)2CO·0.5H2O 1 and [Fe(salten)(cis-stpy)]BPh42 with cis-trans photoisomerizable ligands have been synthesized and characterized, where trans-stpy is trans-4-styrylpyridine and cis-stpy cis-4-styrylpyridine, and salten denotes bis(3-salicylideneaminopropyl)amine, which is a quinquedentate Schiff base derived from the condensation of salicylaldehyde and di(3-aminopropyl)amine. The data of the variable-temperature magnetic susceptibility measurements for the complexes show that 1 and 2 exhibit spin-crossover phenomena in a solid. The spin-state transition temperature of 1 is lower than that of 2. The temperature dependencies of the Mössbauer spectra for the complexes also provide evidence that spin-state transitions between the high- and low-spin states take place, and that the rates of the spin interexchange at 298 K are faster than the inverse of the lifetime (1×10-7 s) of the Mössbauer nucleus. A temperature dependence of the UV-visible spectra suggesting spin-equilibrium in acetonitrile solution was obtained. The X-ray diffraction structures of single crystals of 1 and 2 were determined. Crystal data for 1: C60H61N4O3.5FeB, space group P1 (#2), Z = 2, a = 14.83(1), b = 17.98(1), c = 11.31(2) Å, α = 103.71(8), β = 110.60(8), γ = 94.31(7)°, V = 2702(5) Å3, R = 14.0%, Rw = 17.2%. Crystal data for 2: C57H54N4O2FeB, space group P21/n (#14), Z = 4, a = 14.823(9), b = 17.417(7), c = 18.37(1) Å, β = 95.331(8)°, V = 4722(3) Å3. The coordination cores of both complexes have trans coordination in oxygen atoms. Although light irradiation to 1 in acetonitrile brings about isomerization from trans- to cis- of styrylpyridine, the change in the spin-state of the complexes is not clear.