Following the initial particle morphology assessment, we examined the crystalline structure of Class I, Class II, and bulk-synthesized particles using powder X-ray diffraction (PXRD) at room temperature (Figure ). While both systems exhibit low crystallinity, comparing Class I and II particles with bulk [Fe(Htrz)₂(trz)]BF₄ (pure polymorph I) reveals notable differences. In bulk samples, there is an almost defined double peak and a well-defined triple peak at 2θ ≈ 11° and 25°, respectively. In contrast, Class I particles display a single peak and a less distinct triple peak within the same 2θ range, suggesting that they crystallize as a mixture of polymorphs I and II, with polymorph II as the predominant phase. Conversely, Class II particles show a welldefined double peak and triple peak in the 2θ range, though the peak ratio for the double peak differs significantly from that of the bulk sample. This observation indicates a mixture of polymorphs I and II, with polymorph I as the major component in Class II particles. The occurrence of mixed-phase [Fe(Htrz)₂(trz)]BF₄ is not novel and has been observed to arise when the material is downscaled under conditions that differ significantly from the original synthetic methods used for bulk production, as reported by others. The magnetic properties of Class I and II particles were determined using temperaturedependent magnetic susceptibility measurements (Table and Figure ). Both Class I and II particles show slightly different magnetic behaviors in the χT vs T measurements (χ being the mass paramagnetic susceptibility) after the first heating/cooling cycle. While both Class I and II particles display abrupt hysteretic thermal transitions, their SCO switching temperature, T1/2, in the heating and cooling modes are slightly shifted and the HS fraction at low temperature is higher for Class I particles. Moreover, the hysteresis width (ΔT) varies between the two classes, measuring 25 K for Class I and 29 K for Class II, compared to a ΔT of 40 K observed for bulk [Fe(Htrz)₂(trz)]BF₄ (Figure ). We associate all these differences in magnetism to the different mixture of polymorphs found in the particles, as similar behaviors have been observed in other mixed phase [Fe(Htrz)2(trz)]BF4 compounds. Furthermore, the magnetic behavior of Class I and II particles, which is intermediate between that of [Fe(Htrz)₂(trz)]BF₄ polymorphs I and II, further supports our hypothesis regarding the formation of mixed-phase compounds.