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

Abstract

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^FF) with iron(II) thiocyanate produced two spin-crossover coordination compounds with distinct cooperative behaviours. trans-[Fe(L1)₂(NCS)₂]·2CH₂Cl₂ (1) displays a very gradual transition centred at T½ = 233 K, characterized by a ΔT₈₀ (namely the temperature range within which 80% of the transition considered occurs) of 90 K, while that of fluorinated trans-[Fe(L1^FF)₂(NCS)₂]·2CH₃CN (3) is significantly more abrupt (and centred at T½ = 238 K), with a ΔT₈₀ 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]·4CH₂Cl₂·4CH₃OH (2), also exhibits SCO properties centred at T½ = 238 K, but the transition is very gradual (ΔT₈₀ = 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.