Iron(III) complexes with pentadentate Schiff-base ligands: Influence of crystal packing change and pseudohalido coligand variations on spin crossover

Two novel iron(III) complexes involving pentadentate Schiff-base ligands, [Fe(LBr)(L1)], show temperature induced incomplete spin crossover of a gradual nature. While for the L1 = NCSe− coligand the transition temperature (326 K or 317 K) lies above room temperature, the N3− coligand causes its drop down to 143 K or 140 K (two values were obtained by different models). This shift is associated with a significant decrease of the enthalpy of the transition from about ΔH = 6.1 kJ mol−1 to ca. ΔH = 1.7 kJ mol−1, while the entropy of the transition is about ΔS = 19 J K−1 mol−1 and ΔS = 12 J K−1 mol−1, respectively. Two analogous complexes with Cl− and NCS− coligands remain high-spin over the whole temperature range.

Two novel iron(III) complexes involving pentadentate Schiff-base ligands, [FeLBr(X)], show a temperature induced incomplete spin crossover of the gradual nature. While for the X = NCSe− coligand the transition temperature lies about 320 K, the N3− coligand causes its drop to about 141 K. Two analogous complexes with Cl− and NCS− coligands are high-spin.Figure optionsDownload as PowerPoint slide