Local structure of spin-crossover complex studied by x-ray absorption spectroscopy: nature of photo-induced phase

Abstract

In-situ x-ray absorption spectroscopy (XAS) was used to probe the local structure of photo-induced phase of Fe(II) spin-crossover complex. High-quality XAS data under photo-excitation were obtained for fine powder specimen using a novel pixel array detector (PAD). It was demonstrated that the technique can x-ray probe opaque specimen with high sensitivity (requiring less than 10−3 g) which is irradiated with visible photons. We find that the nearly octahedral ligand coordination (Oh) of FeN6 cluster undergoes a significant expansion upon the diamagnetic (S = 0) ↔ paramagnetic (S = 2) transformation induced by laser light (532 nm), at much lower temperature than the critical temperature of thermally induced phase transition. Indication of symmetry breaking was observed in the distorted ligand molecules, in contrast to the relaxed undistorted structure in the thermally induced high spin phase.