In line with the results from Mössbauer spectroscopy, all samples are predominantly in the iron(II) HS state at room temperature with MT values between 3.2 cm 3 K mol -1 and 3.3 cm 3 K mol -1 . For the as-synthesized samples (black curve in Figure and in the SI), the MT values at 50 K are surprisingly very similar between 1.8 cm 3 K mol -1 and 1.6 cm 3 K mol -1 , thus approximately 50% of the iron centers are involved in the SCO (HS = 0.5), independent of the particle size, complex loading and synthesis conditions (excess of bipy). With increasing particle size (samples 1 to 5) and improved synthesis conditions (c, d to e) the curve progression is slightly more abrupt, but apparently it does not influence the completeness of the spin crossover. .