Thermal- and light-induced spin crossover in a guest-dependent dinuclear iron(II) system

We previously reported the dinuclear material [Fe-2(II)(ddpp)(2)-(NCS)(4)]center dot 4CH(2)Cl(2) (1 center dot 4CH(2)Cl(2); ddpp = 2,5-di(2 ,2 -dipyridylamino)pyridine) and its partially desolvated analogue (1 center dot CH2Cl2), which undergo two- and One-step spin-crossover (SCO) transitions, respectively. Here, we manipulate the type and degree of solvation in this system and find that either a one- or two-step spin transition can be specifically targeted. The chloroform clathrate 1 center dot 4CHCl(3) undergoes a relatively abrupt one-step SCO, in which the two equivalent Fe-II sites within the dinuclear molecule crossover simultaneously. Partial desolvation of 1 center dot 4CHCl(3) to form 1 center dot 3CHCl(3) and 1 center dot CHCl3 Occurs through single-crystal-to-single-crystal processes (monoclinic C2/c to P2(1)/n to P2(1)/n) in which the two equivalent Fe-II sites become inequivalent sites within the dinuclear Molecule Of each phase. Both 1 center dot 3CHCl(3) and 1 center dot CHCl3 undergo One-step Spin transitions, with the former having a significantly higher SCO temperature than 1 center dot 4CHCl(3) and the latter, and each has a broader SCO transition than 1 center dot 4CHCl(3), attributable to the overlap of two SCO steps in each case. Further magnetic manipulation call be carried Out oil these materials through reversibly resolvating the partially desolvated material with chloroform 10 produce the original one-step SCO. or with dichloromethane to produce a two-step SCO reminiscent of that seen for 1 center dot 4CH(2)Cl(2). Furthermore, we investigate the light-induced excited spin state trapping (LIESST) effect oil 1 center dot 4CH(2)Cl(2) and 1 center dot CH2Cl2 and observe partial LIESST activity for the former and no activity for the latter.