6 research outputs found
Effect of ligand methylation on the spin-switching properties of surface-supported spin-crossover molecules
X-ray absorption spectroscopy investigations of the spin-state switching of spin-crossover (SCO) complexes adsorbed on a highly-oriented pyrolytic graphite (HOPG) surface have shown so far that HOPG is a promising candidate to realize applications such as spintronic devices because of the stability of SCO complexes on HOPG and the possibility of highly efficient thermal and light-induced spin-state switching. Herein, we present the spin switching of several Fe(II) SCO complexes adsorbed on an HOPG surface with particular emphasis on the thermally induced spin transition behaviour with respect to different structural modifications. The complexes of the type [Fe(bpz)2(L)] (bpz  =  dihydrobis(pyrazolyl)borate, L  =  1,10-phenanthroline, 2,2'-bipyridine) and their methylated derivatives exhibit SCO in the solid state with some differences regarding cooperative effects. However, in the vacuum-deposited thick films on quartz, complete and more gradual spin transition behavior is observable via UV/vis spectroscopy. In contrast to that, all complexes show large differences upon direct contact with HOPG. Whereas the unmodified complexes show thermal and light-induced SCO, the addition of e.g. two or four methyl groups leads to a partial or a complete loss of the SCO on the surface. The angle-dependent measurement of the N K-edge compared to calculations indicates that the complete SCO and HS-locked molecules on the surface exhibit a similar preferential orientation, whereas complexes undergoing an incomplete SCO exhibit a random orientation on the surface. These results are discussed in the light of molecule-substrate interactions
Soft-x-ray-induced spin-state switching of an adsorbed Fe(II) spin-crossover complex
For probing the nature of spin-state switching in spin-crossover molecules
adsorbed on surfaces, x-ray absorption spectroscopy has emerged as a powerful
tool due to its high sensitivity and element selectivity in tracing even
subtle electronic, magnetic, or chemical changes. However, the x-rays itself
can induce a spin transition and might have unwanted influence while
investigating the effect of other stimuli such as temperature or light, or of
the surface, on the spin switching behaviour. Herein, we present the spin
switching of an Fe(II) complex adsorbed on a highly oriented pyrolytic
graphite surface with particular emphasis on the x-ray-induced switching. For
a submonolayer coverage, the complex undergoes a complete and reversible
temperature- and light-induced spin transition. The spin states are switched
both ways by x-rays at 5 K, i.e. from the high-spin state to the low-spin
state or vice versa, depending on the relative amount of each species.
Furthermore, we quantify the fraction of molecules undergoing soft x-ray-
induced photochemistry, a process which results in an irreversible low-spin
state component, for a particular exposure time. This can be greatly
suppressed by reducing the beam intensity
Evolution of cooperativity in the spin transition of an iron(II) complex on a graphite surface
Cooperative effects determine the spin-state bistability of spin-crossover molecules (SCMs). Herein, the ultimate scale limit at which cooperative spin switching becomes effective is investigated in a complex [Fe(H2B(pz)(2))(2)(bipy)] deposited on a highly oriented pyrolytic graphite surface, using x-ray absorption spectroscopy. This system exhibits a complete thermal- and light-induced spin transition at thicknesses ranging from submonolayers to multilayers. On increasing the coverage from 0.35(4) to 10(1) monolayers, the width of the temperature-induced spin transition curve narrows significantly, evidencing the buildup of cooperative effects. While the molecules at the submonolayers exhibit an apparent anticooperative behavior, the multilayers starting from a double-layer exhibit a distinctly cooperative spin switching, with a free-molecule-like behavior indicated at around a monolayer. These observations will serve as useful guidelines in designing SCM-based devices