New hexanuclear and dodecanuclear Fe(III) clusters with carboxylate and alkoxide-based ligands from cluster aggregation reactions

Abstract

The syntheses, structures and magnetic properties are reported of three new iron(III) clusters [Fe 6(μ 3-O) 2(O 2CH 2)(O 2CCH 2Bu t ) 12(py) 2] ( 1), [Fe 6(μ 3-O) 2(O 2CCH 2Cl) 6(moe) 6](NO 3) 2 ( 2) and [Fe 12(μ 3-O) 8(μ-OMe) 2(O 2CPh) 12(pam) 6] ( 3). Complex 1 was synthesised from the reaction of [Fe 3O(O 2CCH 2Bu t ) 6(H 2O) 3](O 2CCH 2Bu t ) with pyridine in MeCN. Complex 2 was prepared by treatment of [Fe 3O(O 2CCH 2Cl) 6(H 2O) 3](O 2CCH 2Cl) and Fe(NO 3) 3 with methoxyethanol (moeH) in MeCN, and complex 3 was obtained from the reaction of [Fe 3O(O 2CPh) 6(H 2O) 3](O 2CPh), syn-2-pyridinealdoxime (pamH) and NaOMe in MeCN. All three compounds can be structurally described as representing different ways of linking or fusing oxide-centered [Fe 3(μ 3-O)] 7+ triangular units. Thus, the Fe 6 core of 1 comprises two such units bridged at one of their edges to give a twisted boat conformation, whereas the Fe 6 core of the cation of 2 comprises two [Fe 3(μ 3-O)] 7+ units face-to-face in a staggered manner to give an Fe 6 octahedron. The more complicated Fe 12 core of 3 contains a central Fe 6 unit that can be described in various ways, one of which is as four edge-sharing [Fe 3(μ 3-O)] 7+ triangular units and two additional [Fe 3(μ 3-O)] 7+ units attached to the flanks. One particular additional point of interest in 1 is the occurrence of a rare methanediolate group formed in situ and bound in an unusual μ 4-bridging mode. Variable-temperature solid-state magnetic susceptibility studies on complexes 1– 3 in the temperature range 5.00–300 K reveal that the complexes all possess S = 0 ground state spins, consistent with the expected antiferromagnetic exchange interactions between the constituent iron(III) ions.