Light-induced spin-state switching in the mixed crystal series of the 2D coordination network {[Zn1-xFex(bbtr)3](BF4)2}∞: optical spectroscopy and cooperative effects.

Depending on the iron(ii) concentration, the mixed crystals of {[Zn1-xFex(bbtr)3](BF4)2}∞, bbtr = 1,4-di(1,2,3-triazol-1-yl)butane, 0.01 ≤ x ≤ 1, show macroscopic light-induced bistability between the high-spin and the low-spin state. In the highly diluted system with x = 0.