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

ABSTRACT

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)](ClO(4))(10) (3) and [Fe(9)O(4)(OH)(2)(O(2)CMe)(10)(pdm)(pdmH)(4)](NO(3)) (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)](ClO(4))(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)](NO(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.