A cyanide-bridged FeII/FeIII mixed-valence chain exhibiting spin transition in the Fe(II) sites

A cyanide-bridged {FeIII2FeII}n one-dimensional chain {[Fe(Tp)(CN)3]2Fe(btb)}n (1) (Tp = hydrotris(pyrazolyl)borate, btb = 1,4-(1H-1,2,4-triazole)butane) has been synthesized via the hydrothermal reaction of Li[Fe(Tp)(CN)3], btb, and FeII(ClO4)2·6H2O at 120 °C. Single-crystal X-ray analysis reveals that compound 1 is an isolated neutral mixed-valence {FeIII2FeII}n double-zigzag chain with each [FeIII(Tp)(CN)3]− unit connecting with two Fe(II) centres via two of its three CN− groups in the cis-positions, and two triazole groups from btb coordinated with Fe(II) ion in its axial positions. Single-crystal data obtained at different temperature together with magnetic data indicate that complex 1 exhibits thermal induced spin transition in the Fe(II) sites with T1/2 ≈ 165 K. Additionally, light-induced excited spin-state trapping (LIESST) of 1 was also observed at low temperature.