Drastic effect of lattice propionitrile molecules on the spin-transition temperature of a 2,2'-dipyridylamino/s-triazine-based iron(II) complex

Reaction of iron(II) selenocyanate (obtained from Fe(ClO4)2 and KNCSe) with 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(pentafluorophenoxy)-(1,3,5)triazine (L1F) in propionitrile produces the compound [Fe(L1F)2(NCSe)2].2CH3CH2CN (1NCSe.2PrCN), which shows spin-crossover (SCO) properties characterized by a T1/2 of 283 K and a ?T80 (i.e., temperature range within which 80% of the transition considered occurs) of about 65 K. Upon air exposure, 1NCSe.2PrCN gradually converts to a new SCO species that exhibits different properties, as reflected by T1/2 = 220 K and ?T80 = 70 K. Various characterization techniques, namely, IR spectroscopy, thermogravimetric analysis, and thermodiffractometric studies, reveal that the new phase is obtained through the loss of the lattice propionitrile molecules within several days upon air exposure or several hours upon heating above 390 K.