Mixed-valence {FeII2FeIII4} hexanuclear complexes with thermally induced Fe(III) spin-crossover behavior.

Cyano-bridged mixed-valence {Fe 6 } hexanuclear complexes {[Tp 4-Me Fe II (CN) 3 ] 2 [Fe III (Tpa)] 2 [Fe III (OR)(Tpa)] 2 }·6ClO 4 · S (Tp 4-Me = tri(4-methyl-pyrazol-1-yl)borate, Tpa = tris(2-pyridylmethyl)amine; R = -CH 3 , S = 8MeOH 1, R = -C 2 H 5 , S = 6EtOH 2) have been obtained by building the units of [Tp 4-Me Fe(CN) 3 ] - and [Fe(Tpa)] 2+ in methanol and ethanol, respectively. Complex 1 exhibited single-crystal-to-single-crystal (SCSC) transformation to give {[Tp 4-Me Fe II (CN) 3 ] 2 [Fe III (Tpa)] 2 [Fe III (OH)(Tpa)] 2 }·6ClO 4 ·8H 2 O (3) in water. Detailed analysis of the coordination environment of the Fe III centers on the square lattice and magnetic susceptibility measurements of all the complexes confirmed their Fe 3+ spin-crossover (SCO) properties ( T 1/2 = 178 K, 1; 185 K, 2; 208 K, 3).