Exploiting Pressure To Induce a "Guest-Blocked" Spin Transition in a Framework Material

A new functionalized 1,2,4-triazole ligand, 4-[(E)-2-(5-methyl-2-thienyl)vinyl]-1,2,4-triazole (thiome), was prepared to assess the broad applicability of strategically producing multistep spin transitions in two-dimensional Hofmann-type materials of the type [(FePd)-Pd-II(CN)(4)(R-1,2,4-trz)2]center dot nH(2)O (R-1,2,4-trz = a 4-functionalized 1,2,4-triazole ligand). A variety of structural and magnetic investigations on the resultant framework material [(FePd)-Pd-II-(CN)(4)(thiome)(2)]center dot 2H(2)O (A center dot 2H(2)O) reveal that a high-spin (HS) to low-spin (LS) transition is inhibited in A center dot 2H(2)O due to a combination of guest and ligand steric bulk effects. The water molecules can be reversibly removed with retention of the porous host framework and result in the emergence of an abrupt and hysteretic one-step spin transition due to the removal of guest internal pressure. A spin transition can, furthermore, be induced in A center dot 2H(2)O (00.68 GPa) under hydrostatic pressure, as evidenced by variable-pressure structure and magnetic studies, resulting in a two-step spin transition at ambient temperatures at 0.68 GPa. The presence of a two-step spin crossover (SCO) in A center dot 2H(2)O under hydrostatic pressure compared to a one-step SCO in A at ambient pressure is discussed in terms of the relative ability of each phase to accommodate mixed HS/LS states according to differing lattice flexibilities.