Tunable cooperativity in a spin-crossover Hoffman-like metal–organic framework material by aromatic guests

Abstract

A spin-crossover Hoffman-like metal–organic framework, [Fe(dpb){Au(CN)₂}₂]·nSolv (dpb = 1,4-di(pyridin-4-yl)benzene; nSolv = 1.5DMF·0.3EtOH·0.2C₆H₁₂), is prepared and presents appreciable porosity. By introducing different aromatic guest molecules (benzene, naphthalene, anthracene, and ferrocene) and carbon disulfide into this framework, the spin-crossover cooperativity is dramatically modulated. The thermal hysteresis width is tuned from 0 K to 73 K by replacing the original solvents with naphthalene in the 1D channel. DFT calculations are carried out to evaluate the optimized positions of guests and offer an insight into the relationship between spin-crossover cooperativity and host–guest interaction. As a result, significant π⋯π stacking interactions (or S⋯Au contact) between the host framework and aromatic guest molecules (or CS₂) are responsible for the strong cooperativity.