Preparation and Magnetic Properties of Iron(3+) Spin-Crossover Complexes Bearing a Thiophene Substituent: Toward Multifunctional Metallopolymers

The synthesis of a new 3-ethynylthienyl-substituted QsalH ligand
(QsalH is the short form for N-(8-quinolyl)salicylaldimine)
(ThEQsalH 3), and the preparation, electronic, and magnetic
properties of three homoleptic and cationic iron(3+) complexes containing
this ligand with PF6− 4,
SCN− 5, and ClO4− 6 counteranions are reported. In all three complexes
a spin-crossover is observed in the solid state by variable temperature
magnetic susceptibility measurements and Mössbauer spectroscopy,
indicating that the synthetic modification of the QsalH ligand has
not significantly altered the electronics at the metal center. This
includes the observation of a very rare S = 5/2 to
3/2 spin-crossover in a non-porphyrin iron(3+) complex 5. The molecular structure and magnetic properties of an unusual iron(2+)
complex 7 generated by reduction of complex 6 serendipitously during a recrystallization attempt in aerobic acetone
solution is also reported. Complexes 4−6 feature iron(3+) reduction and oxidation of the thiophene ring at
potentials of approximately −0.7 and +1.2 V (vs Fc), respectively.