Continuous spin-crossover transformation is exhibited by the solvates of the composition [Fe(3-EtO-SalAPA)2]ClO4.S (where 3-EtO-SalAPA is the monoanionic Schiff base derived from 3-ethoxysalicylaldehyde and N-(3-aminopropyl)aziridine and S is C6H5F, C6H5Cl, C6H5Br, C6H5I or o-C6H4Cl2). Their gradual nature of spin-state interconversion is evidenced by the variable-temp. magnetic susceptibility and EPR data. Only a single quadrupole-split doublet is seen in the Moessbauer spectra for all solvates in the temperature range of 110-300 K. Thus, all complexes interconvert spin states slower than the EPR time scale (~10-10 s) but faster than the 57Fe Moessbauer time scale (~10-7 s). As the size of the solvate mol. S increases from C6H5F to o-C6H4Cl2 along the preceding sequence, the Tc value estimated from the meff vs. T curve of the corresponding solvate trends towards the lower temperature A linear relationship was observed between the mol. vols. of the monohalogenated benzene and the Tc values of the corresponding solvates, with the only exception being the chlorobenzene analog. This anomaly is attributed to a first-order phase transition occurred around 185 K, which coincides with the Tc value of this solvate.

Key words: X-RAY DIFFRACTION ANALYSIS, IRON COMPLEX, DIFFERENTIAL SCANNING CALORIMETRY, VARIABILITY, TRANSITION METAL COMPLEX, ELECTRON SPIN RESONANCE, SCHIFF BASE, SPIN, MAGNETIZATION, MAGNETISM