Guest-Induced Multistep to Single-Step Spin-Crossover Switching in a 2-D Hofmann-Like Framework with an Amide-Appended Ligand

A detailed study of the two-dimensional (2-D) Hofmann-like framework [Fe(furpy)(2)Pd(CN)(4)]center dot nG (furpy: N-(pyridin-4-yl)furan-2-carboxamide, G = H2O,EtOH (A center dot H2O,Et), and H2O (A center dot H2O)) is presented, including the structural and spin-crossover (SCO) implications of subtle guest modification. This 2-D framework is characterized by undulating Hofmann layers and an array of interlayer spacing environments-this is a strategic approach that we achieve by the inclusion of a ligand with multiple host-host and host-guest interaction sites. Variable-temperature magnetic susceptibility studies reveal an asymmetric multistep SCO for A center dot H2O,Et and an abrupt single-step SCO for A center dot H2O with an upshift in transition temperature of similar to 75 K. Single-crystal analyses show a primitive orthorhombic symmetry for A center dot H2O,Et characterized by a unique Fe-II center-the multistep SCO character is attributed to local ligand orientation. Counterintuitively, A center dot H2O shows a triclinic symmetry with two inequivalent Fe-II centers that undergo a cooperative single-step high-spin (HS)-to-low-spin (LS) transition. We conduct detailed structure-function analyses to understand how the guest ethanol influences the delicate balance between framework communication and, therefore, the local structure and spill-state transition mechanism.