Abstract
Materials capable of sensing volatile guests at room temperature by an easily monitored set of outputs are of great appeal for development as chemical sensors of small volatile organics and toxic gases. Herein the dinuclear iron(II) complex, [Fe-2(II)(L)(2)(CH3CN)(4)](BF4)(4)center dot 2CH(3)CN (1) [L=4-(4-methylphenyl)-3-(3-pyridazinyl)-5-pyridyl-4H-1,2,4-triazole], is shown to undergo reversible single-crystal-to-single-crystal (SCSC) transformations upon exposure to vapors of different guests: 1 (MeCN)(sic)2 (EtOH)-> 3 (H2O)(sic)1 (MeCN). Whilst 1 and 2 remain dimetallic, SCSC to 3 involves conversion to a 1D polymeric chain (due to a change in L bridging mode), which, remarkably, can undergo SCSC de-polymerization, reforming dimetallic 1. Additionally, SC-XRD studies of two ordered transient forms, 1TF3 and 2TF3, confirm that guest exchange occurs by diffusion of the new guests into the nonporous lattices as the old guests leave. These reversible SCSC events also induce color and magnetic responses. Indeed dark red 1 is spin crossover active (T-1/2 down arrow 356 K; T-1/2 up arrow 369 K), whilst orange 2 and yellow 3 remain high spin.