For the investigation of spin crossover (SCO) complexes by x-ray absorption spectroscopy (XAS) measurements in the tender to hard x-ray regime, a transmission heating cell has been developed. Some SCO complexes show a spin transition at certain temperatures above room temperature (RT). To measure a reliable hysteresis curve, high temperature stability (preferably <0.5 °C) as well as minimal overheating of the setpoint temperatures (<1 °C) has been achieved. The cell is designed for use in our von Hámos XAS laboratory spectrometer. The SCO complex [Fe(bzimpy)2](ClO4)2 · 0.25H2O was investigated as a first proof-of-principle experiment. In situ measurements up to 250 °C were carried out, showing the characteristic spin transition of the SCO complex during heating. Further XAS measurements were conducted at beamline BL10 of the DELTA storage ring, which demonstrated the feasibility of in situ measurements during a continuous temperature ramp with our heating cell. The current temperature limit of the cell is 500 °C when used in vacuum. Hence, the cell can also be used for other sample systems, such as thermoelectric materials, which are frequently investigated in this temperature regime.

Two iron(III) spin crossover complexes [Fe(⁵Cl-L)(NCS)] (1) and [Fe(⁵Cl-L)(NCSe)] (2) were synthesized with the pentadentate Schiff base ligand ⁵Cl-L and thiocyanato and selenocyanato as coligands. ⁵Cl-L, as an asymmetric {N₃O₂} donor Schiff base, was synthesized by a condensation reaction of 5-chlorosalicyladehyde using the asymmetric N-(2-aminoethyl)-1,3-propanediamine. The complexes exhibited a spin crossover at 280 (1) and 293 K (2), respectively, and were subjected to electron spin resonance (ESR) and Mössbauer spectroscopy at 77, 295 and 325 K. Ab initio CASSCF calculations followed by the NEVPT2 method were applied for predicting the g-tensor components as well as Mössbauer parameters.