Reversible Guest Binding in a Non-Porous FeII Coordination Polymer Host Toggles Spin Crossover

Journal article, 2015

Formation of either a dimetallic compound or a 1D coordination polymer of adiponitrile adducts of [Fe(bpte)]2+ (bpte=[1,2-bis(pyridin-2-ylmethyl)thio]ethane) can be controlled by the choice of counteranion. The iron(II) atoms of the bis(adiponitrile)-bridged dimeric complex [Fe2(bpte)2(μ2-(NC(CH2)4CN)2](SbF6)4 (2) are low spin at room temperature, as are those in the polymeric adiponitrile-linked acetone solvate polymer {[Fe(bpte)(μ2-NC(CH2)4CN)](BPh4)2 Me2CO} (3Me2CO). On heating 3Me2CO to 80°C, the acetone is abruptly removed with an accompanying purple to dull lavender colour change corresponding to a conversion to a high-spin compound. Cooling reveals that the desolvate 3 shows hysteretic and abrupt spin crossover (SCO) S=0虠S=2 behaviour centred at 205K. Non-porous 3 can reversibly absorb one equivalent of acetone per iron centre to regenerate the same crystalline phase of 3Me2CO concurrently reinstating a low-spin state.