Synthesis and Mössbauer Spectroscopy Studies on the Spin States of tris (2‐Pyridylimine) Iron(ii) Complexes

Some new tris (2‐pyridylimine) complexes of iron(II) such as FeL 3 X 2 (L = substituted imine ligand, 2‐py‐CR 1 =NR 2 , where R 1 or R 2 =H, CH 3 (Me) and C 4 H 5 (Ph), X=ClO 4 − or NCS − , have been synthesized and their electronic structures in the solid state examined by magnetic measurement and 57 Fe Mössbauer spectroscopic studies. All the perchlorate complexes FeL 3 (ClO 4 ) 2 are low‐spin electronic ground state of Fe(II). The dithiocyanato‐complexes, FeL 3 (NCS) 2 ; the spin states of Fe(II) are dependent on substituent R 1 and R 2 . The two complexes Fe(2‐py‐CH=NH) 3 (NCS) 2 and Fe(2‐py‐CPh=NH) 3 (NCS) 2 are spin‐intermediate (S=1) and Fe(2‐py‐CH=NPh) 3 (NCS) 2 shows a thermally inducing spin transition of 5 T⇄ 1 A 1 , whereas the other derivatives remain a low‐spin (S=0, 1 A 1 ) ground state of Fe(II) at three temperatures of 298, 202 and 78 K .