Vacuum-Evaporable Spin-Crossover Complexes in Direct Contact with a Solid Surface: Bismuth versus Gold

Abstract

To investigate the ability for spin-state switching of spin-crossover (SCO) complexes adsorbed to solid substrates, the SCO complex [Fe(H 2 B(pz) 2 ) 2 (phenme 4 )] (pz = pyrazole, phenme 4 = 3,4,7,8-tetramethyl-1,10-phenanthroline) is prepared. The new complex is investigated by magnetic susceptibility measurements and Mößbauer spectroscopy in the solid state and by temperature-dependent UV/vis spectroscopy in a thin film deposited by physical vapor deposition (PVD) on quartz glass. Thermal- and light-induced SCO is observed in the bulk and the film on glass. Submonolayers of this complex obtained by PVD are studied by temperature-dependent near-edge X-ray absorption fine structure (NEXAFS) on Au(111) as well as Bi(111) and by scanning tunneling microscopy (STM) on Au(111). NEXAFS shows thermal- and light-induced spin-state switching of the complex on Bi(111), however, with a large temperature-independent high-spin fraction (∼50%). On the other hand, combined evidence from NEXAFS and STM indicates that on Au(111) the complex dissociates into [Fe(H 2 B(pz) 2 ) 2 ] and phenme 4 . Similar observations are made with the parent complex [Fe(H 2 B(pz) 2 ) 2 (phen)], which on Bi(111) stays intact and exhibits thermal-induced as well as light-induced SCO, but on Au(111) dissociates into [Fe(H 2 B(pz) 2 ) 2 ] and phen.