Persistent Bidirectional Optical Switching in the 2D High-Spin Polymer {[Fe(bbtr)₃](BF₄)₂}_∞

In the covalently linked 2D coordination network {[Fe­(bbtr)₃]­(BF₄)₂}_∞, bbtr = 1,4-di­(1,2,3-triazol-1-yl)­butane, the iron­(II) centers stay in the high-spin (HS) state down to 10 K. They can, however, be quantitatively converted to the low-spin (LS) state by irradiating into the near-IR spin allowed ⁵dd band and back again by irradiating into the visible ¹dd band. The compound shows true light-induced bistability below 100 K, thus, having the potential for persistent bidirectional optical switching at elevated temperatures.