Structural data for fifteen complexes of Fe(III) of a general formula [FeL5X], with pentadentate Schiff-base ligands L5 and unidentate coligands X−, were subjected to a statistical analysis. The multivariate methods such as Pearson correlation, cluster analysis and principal component analysis split the data into two clusters depending upon the low-spin and/or high-spin state of the complex at the temperature of the X-ray experiment. Some of these complexes exhibit a thermally induced spin crossover. The numerical analysis of the magnetic susceptibility and magnetization data for an enlarged set of Fe(III) spin crossover systems yields the enthalpy ΔH and entropy ΔS of the transition along with the transition temperature T1/2 and the solid state cooperativeness. The thermodynamic data show a mutual relationship manifesting itself by linear ΔS vs ΔH and T1/2vs ΔH correlations.