Structural diversity in iron(II) complexes of 2,6-di(pyrazol-1-yl)pyridine and 2,6-di(3-methylpyrazol-1-yl)pyridine

The syntheses, magnetochemistry and crystallography of [Fe(L-1)(2)]I-0.5[I-3](1.5) (1), [Fe(L-1)(2)][Co(C2B9H11)(2)](2) (2) and [Fe(L-2)(2)][SbF6](2) (3) (L-1 = 2,6-di(pyrazol-1-yl)pyridine; L-2 = 2,6-di(3-methylpyrazol-1-yl)-pyridine) are described. Compounds 1 and 3 are high-spin between 5-300 K. For 1, this reflects a novel variation of an angular Jahn-Teller distortion at the iron centre, which traps the molecule in its high-spin state. No such distortion is present in 3; rather, the high-spin nature of this compound may reflect ligand conformational strain caused by an intermolecular steric contact in the crystal lattice. Compound 2 exhibits a gradual high -> low spin transition upon cooling with T-1/2 = 318 +/- 3 K, that is only 50% complete. This reflects the presence of two distinct, equally populated iron environments in the solid. One of these unique iron centres adopts the same angular structural distortion shown by 1 and so is trapped in its high-spin state, while the other, which undergoes the spin-crossover, has a more regular coordination geometry. In contrast with 3, the solvated salts [Fe(L-2)(2)][BF4](2)center dot 4CH(3)CN and[Fe(L-2)(2)][ClO4](2)center dot(CH3)(2)CO both undergo gradual thermal spin-transitions centred at 175 +/- 3 K.