Tuning the spin-crossover behaviour of a hydrogen-accepting porous coordination polymer by hydrogen-donating guests

A Hoffman-like coordination polymer with appreciable porosity and uncoordinated pyridyl groups, namely, [Fe(2,5-bpp){Au(CN)2}2]⋅x Solv (2,5-bpp = 2,5-bis(pyrid-4-yl)pyridine; Solv = solvent), was synthesised and characterised. A series of fascinating spin-crossover behaviours with abrupt, stepwise and hysteretic features were obtained by exchange with a range of protic solvents (ethanol, n-propanol, isopropyl alcohol, sec-butanol and isobutanol). Guest-host hydrogen-bonding interactions involving the H-accepting site of the framework are primarily responsible for the pronounced cooperativity of these spin-crossover behaviours. Meanwhile, the tunable critical temperatures over a range of about 130 K are presumably attributable to a certain degree of competition between internal pressure and local electronic influences of solvents.