Low-temperature heat capacity of polynuclear Fe(HTrz)3(B10H10)·H2O (I) and trinuclear [Fe3(PrTrz)6(ReO4)4(H2O)2](ReO4)2 (II) spin crossover coordination compounds was measured in 80–300 K temperature range using a vacuum adiabatic calorimeter. For
I, an anomaly of heat capacity with a maximum at Ttrs=234.5 K (heating mode) was observed, ΔtrsH=10.1±0.2 kJ mol−1 ΔtrsS=43.0±0.8 J mol− K−1. For II, a smooth anomaly between 150 and 230 K was found, ΔtrsH=2.5±0.25 kJ mol−1 ΔtrsS=13.6±1.4 J mol− K−1. Anomalies observed in both compounds correspond to 1A1⇔5T2 spin transition.