• Spin crossover;
  • Polymorphism;
  • Iron;
  • Magnetic properties;
  • Solvent effects


A water-containing iron(III) complex, [FeIII(SalEen)2]ClO4·0.5H2O [1, SalEen = N-ethyl-N-(2-aminoethyl)salicylaldiminate], and an unsolvated complex, [FeIII(SalEen)2]ClO4 (2), are synthesized and structurally characterized. Complex 1 crystallizes in a polar orthorhombic space group Fdd2, whereas 2 crystallizes in a monoclinic space group P21/c. The presence or absence of water molecules results in different molecular packings, which give rise to different magnetic properties. The temperature dependent magnetic measurements show very gradual spin transitions for both 1 and 2; the iron(III) center is in the high-spin (HS) state with S = 5/2 at 350 K and is in the low-spin (LS) state with S = 1/2 below 30 K for 1 (T1/2 = 155 K) and at 120 K for 2 (T1/2 = 230 K). The crystal structures of the HS and LS states for both 1 and 2 are characterized. In addition, the structure of 1 at 150 K is also investigated. The Fe–N and Fe–O bond lengths are 0.14 and 0.03 Å shorter in the LS state than those in the HS state. The octahedral distortion in the iron(III) coordination geometry, expressed as Σ and Θ parameters, is slightly larger in the HS than in the LS state.