Unusual Fe9 and Fe18 structural types from the use of 2,6-pyridinedimethanol in Fe(III) cluster chemistry.

The syntheses, crystal structures and magnetochemical characterization are reported for two new Fe(III) complexes Fe(18)O(6)(OH)(8)(pdm)(10)(pdmH)(4)(H(2)O)(4)(10) (3) and Fe(9)O(4)(OH)(2)(O(2)CMe)(10)(pdm)(pdmH)(4) (4). They were synthesized from the use of the potentially O,N,O tridentate chelate, 2,6-pyridinedimethanol (pdmH(2)), in the presence or absence of carboxylate groups. Octadecanuclear complex 3 was obtained during reactivity studies on previously-reported Fe(8)O(3)(OEt)(pdm)(4)(pdmH)(4)(EtOH)(2)(5) (2), the latter undergoing hydrolysis to 3 on recrystallization from undried MeCN. The reaction of pdmH(2) with preformed Fe(3)O(O(2)CMe)(6)(py)(3) in CH(2)Cl(2) gave enneanuclear complex 4. Both complexes 3 and 4 are unprecedented structural types. The core of 3 comprises a central [Fe(4)O(6)] defective-dicubane attached on either side to a [Fe(7)O(11)] unit, which can be described as two [Fe(4)(μ(4)-O)] tetrahedra fused at a common Fe atom. The core of 4 can be considered as four vertex-fused triangular [Fe(3)(μ(3)-O)] units. Variable-temperature (T) and -field (H) solid-state dc and ac magnetization (M) studies were carried out on complexes 3 and 4 in the 1.8-300 K range. Analysis of the obtained data revealed that complexes 3 and 4 possess an S = 4 and S = 5/2 ground state spin, respectively.