Spin‐Crossover in a Dinuclear Iron(II) Complex on Highly Oriented Pyrolytic Graphite: An X‐Ray Absorption Spectroscopy Study

The spin-crossover (SCO) properties of the dinuclear complex <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mo>[</mml:mo> <mml:msub><mml:mrow><mml:mo>{</mml:mo> <mml:mtext>Fe</mml:mtext> <mml:msub> <mml:mrow><mml:mrow><mml:mo>(</mml:mo> <mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>B</mml:mi> <mml:msub><mml:mrow><mml:mo>(</mml:mo> <mml:mtext>pz</mml:mtext> <mml:mo>)</mml:mo></mml:mrow> <mml:mn>2</mml:mn></mml:msub> <mml:mo>)</mml:mo></mml:mrow> </mml:mrow> <mml:mn>2</mml:mn></mml:msub> <mml:mo>}</mml:mo></mml:mrow> <mml:mn>2</mml:mn></mml:msub> <mml:mi>μ</mml:mi> <mml:mo>-</mml:mo> <mml:mo>(</mml:mo> <mml:msub><mml:mrow><mml:mtext>ac(bipy)</mml:mtext></mml:mrow> <mml:mn>2</mml:mn></mml:msub> <mml:mo>)</mml:mo> <mml:mo>]</mml:mo></mml:mrow> <mml:annotation>$\left[\right. \left{\right. \text{Fe} \left(\left(\right. \left(\text{H}\right)_{2} \text{B} \left(\left(\right. \text{pz} \left.\right)\right)_{2} \left.\right)\right)_{2} \left(\left.\right}\right)_{2} \mu - \left(\right. \left(\text{ac(bipy)}\right)_{2} \left.\right) \left]\right.$</mml:annotation></mml:semantics> </mml:math> are studied as (sub)-monolayer and thin film deposited by an ultrahigh vacuum liquid-jet deposition technique on highly oriented pyrolytic graphite (HOPG) by X-ray absorption spectroscopy. A comparison of the SCO properties of thin films and a dropcast sample indicates that the spin-switching probability of the thin films is limited due to substrate-molecule interactions. The maximum percentage of molecules in the low-spin (LS) state observed for 0.7 and 1.8 monolayers (ML) is ≈43% at a temperature of 80 K in comparison to the dropcast sample where ≈66% of the complex is in the LS state. The similar switching properties of the dropcast sample as of a bulk powder sample confirm that the SCO properties are not affected by the presence of solvent necessary for deposition. The soft-X-ray-induced excited spin-state trapping (SOXIESST) effect is pronounced in all samples, although the light-induced high-spin (HS) fraction of the dropcast and the thin-film samples on HOPG is higher as compared to the HS fraction attained by SOXIESST, which confirms the sensitivity of the complex to light.