Effect of Methoxy Ligand-Substituent and NCE Coligands in Tuning T1/2 of Coordinatively Elastic Fe(II) Spin Crossover Complexes

We report the multistep synthesis of a thiadiazole based ligand (LOMe-Nap) with a methoxy substituent in the six-position of the naphthalene ring, along with the corresponding iron(II) [FeII(LOMe-Nap)2(NCE)2] 1–3 (E = S, Se, and BH3) complexes. We also report the synthesis of the [FeII(LNap)2(NCBH3)2] (4) complex with the previously reported LNap ligand. The complexes obtained were characterized by single crystal X-ray crystallography and SQUID magnetometry in all four cases (1–4). Complex 1 shows a weak thermally induced excited spin state trapping (TIESST) effect up to about 60 K. The effects of the methoxy ligand substituent in altering the noncovalent intramolecular π–π interaction are discussed, as well as the tuning of the switching temperature (T1/2) by the choice of NCE. The S < Se < BH3 series is established in both families of compounds.