Zero-field, temperature-dependent Fe Mössbauer spectra were recorded for the as-synthesized sample 5e and for the annealed sample 5e * between 80 K and 300 K in the cooling and heating mode to follow the spin crossover and to confirm the changes observed in the magnetic measurements upon annealing. Selected spectra are given in Figure . Further temperature-dependent Mössbauer spectra and the summary of the Mössbauer parameters obtained from the fits are given in Figure and Table . The as-synthesized sample shows two doublets at 300 K, where the majority species (85%) represents an iron(II) HS species corresponding to the formed iron(II) CP [FeL(bipy)]n inside the dBCP. The minority species shows characteristic Mössbauer parameters (δ = 0.39 mm s -1 , ΔEQ = 1.01 mm s -1 ) for an iron(II) LS species, which was detected before and can be assigned to the iron(II) complex [FeL] coordinated to two vinyl pyridine units of the coordination polymer, i.e. [FeL(VP)2]. Upon cooling of the sample in the spectrometer, the area of the doublet corresponding to the iron(II) LS species increased and the residual iron(II) HS fraction was lowered to 44% at 80 K, which is in good agreement with the residual HS fraction of the magnetic measurement of 51% at 80 K. After thermal annealing, the measurement procedure was repeated. Interestingly, for the annealed sample 5e* the iron(II) LS species [FeL(VP)2] disappeared due to the recrystallization of the coordination polymer and only one iron(II) HS doublet is observed at 300 K. Thus the Mössbauer spectra confirm the changes observed in the magnetic measurements and the T-dependent PXRD patterns. Upon cooling below 215 K (in the spin crossover region), the iron(II) HS fraction of the annealed sample is constantly lower than for the as-synthesized sample 5e at the same temperature. At 80 K, the iron(II) HS fraction of sample 5e * was decreased to 30%. In Table , the γHS values of 5e and 5e* obtained by magnetic susceptibility measurements and Mössbauer spectroscopy are compared. The systematically lower γHS values of the annealed sample obtained by SQUID magnetometry can be explained by the different annealing environments for the two measurements (see SI).