Heteroleptic Iron(II) Spin-Crossover Complexes Based on a 2,6-Bis(pyrazol-1-yl)pyridine-type Ligand Functionalized with a Carboxylic Acid.

Two new heteroleptic complexes Fe(1bppCOOH)(3bpp-bph)·solv (, solv = various solvents; 1bppCOOH = 2,6-bis(1-pyrazol-1-yl)isonicotinic acid; 3bpp-bph = 2,6-bis(5-([1,1'-biphenyl]-4-yl)-1-pyrazol-3-yl)pyridine) and Fe(1bppCOOH)(1bppCOOEt)·0.5MeCO (, 1bppCOOEt = ethyl 2,6-bis(1-pyrazol-1-yl)isonicotinate) were designed and prepared. The heteroleptic compound was obtained by the combination of stoichiometric amounts of Fe(ClO), 1bppCOOH, and 3bpp-bph, and it was designed to fine-tune the spin crossover (SCO) properties with respect to the previously reported homoleptic compound Fe(1bppCOOH). Indeed, the introduction of a new substituted 3bpp ligand induces a weaker ligand field in addition to promoting the formation of π···π and C-H···π intermolecular interactions through the biphenyl groups. For the desolvated counterpart , this results in a shift of the SCO curve toward room temperature and the observation of a 13 K hysteresis width. Besides, compound , which represents the first example of a heteroleptic complex containing two 1bpp tridentate ligands, stabilizes the LS state at room temperature confirming the same trend observed for the corresponding homoleptic compounds. Interestingly, both and heteroleptic complexes exhibit photoswitchable properties when irradiating with a 523 nm laser at 10 K. Preliminary characterization of the deposited complexes on native SiO by X-ray absorption measurements suggests oxidation and decomposition of the complexes.