In air a spin crossover active iron(ii) complex of amine/NCBH3− ligands is converted to a low spin complex of imine/CN− ligands†
Abstract
Two new mononuclear FeII complexes, [FeL1(NCBH3)2] (1) and [FeL2(CN)2]·3H2O (2) (L1 = N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine, L2 = N-(2-pyridylmethyl)-N′-(2-pyridylmethylene)-1,2-ethanediamine) were synthesized from the same starting solution under different atmospheric conditions. Complex 1 was isolated under an N2 atmosphere with an expected molecular structure, namely a tetradentate L1 ligand and two NCBH3− co-ligands wrapping an iron(II) ion. It exhibits a gradual spin crossover centered around 355 K, as confirmed by X-ray crystallography, magnetic, DSC and Mössbauer studies. Complex 2 was isolated in the presence of air. One of the secondary amine groups in L1 undergoes an in situ oxidative dehydrogenation, forming a new monoimine asymmetric ligand L2. Besides, a CN− co-ligand is also in situ generated from NCBH3− during the reaction. The strong ligand field strength imposed by CN− and L2 stabilizes 2 in the LS state. Solvent water molecules in complex 2 are hydrogen bonded into a well-defined 1D water chain. 2 shows a proton conductivity of 8.9 × 10−5 S cm−1 at 55 °C and 95% relative humidity.