Influence of supramolecular bonding contacts on the spin crossover behaviour of iron(II) complexes from 2,2 '-dipyridylamino/s-triazine ligands

Reactions of the related ligands 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(phenoxy)-(1,3,5)triazine (L1) and 2-(N, N-bis(2-pyridyl) amino)-4,6-bis(pentafluorophenoxy)-(1,3,5) triazine (L1(F)) with iron(II) thiocyanate produced two spin-crossover coordination compounds with distinct cooperative behaviours. trans-[Fe-(L1)(2)(NCS)(2)]center dot 2CH(2)Cl(2) (1) displays a very gradual transition centred at T 1/2 = 233 K, characterized by a Delta T-80 (namely the temperature range within which 80% of the transition considered occurs) of 90 K, while that of fluorinated trans-[Fe(L1(F))(2)(NCS)(2)]center dot 2CH(3)CN (3) is significantly more abrupt (and centred at T 1/2 = 238 K), with a Delta T-80 of 50 K, resulting from supramolecular contacts induced by the fluorinated phenol groups. The coordination compound equivalent to 1 with selenocyanate anions, namely trans-[Fe-(L1)(2)(NCSe)(2)]center dot 4CH(2)Cl(2)center dot 4CH(3)OH (2), also exhibits SCO properties centred at T 1/2 = 238 K, but the transition is very gradual (Delta T-80 = 150 K). Light-induced excited spin-state trapping (LIESST) is effective although incomplete for 2 and 3, while it is complete with a T-LIESST of 58 K for 1.