Discrete Fe^II spin-crossover complexes of 2,2′-dipyridylamino-substituted s-triazine ligands with phenoxo, cyanophenoxo and dibenzylamino functionalities

Four 2,2′-dipyridylamino-s-triazine-substituted ligands, each of which incorporate different aromatic substituents (phenoxo, 4-CN-phenoxo and benzylamino) with different degrees of bulk and flexibility, have been formed and incorporated into a number of mononuclear Fe^II complexes of type trans-[Fe^II(L)₂(NCX)₂]·solvent (in which X = S, Se and BH₃). These ligands were designed to promote π-π stacking between complexes. The complexes reported have been comprehensively characterised using single-crystal diffraction techniques in combination with magnetic susceptibility measurements. Light-induced excited spin-state trapping (LIESST) measurements have been performed on selected complexes. Light irradiation has shown the occurrence of a reversible photoswitching process at low temperature. New mononuclear spin-crossover compounds of type trans-[Fe^II(NCX)₂(L)₂]·solvent have been synthesised and structurally characterised. The L ligands are chelated to Fe by dipyridylamine groups and have aromatic substituents on the central triazine ring that influence cooperativity effects monitored by magnetic and light-induced excited-state spin trapping (LIESST) measurements.