Preparation and characterization of CrIII, MnII, FeII, CoII and NiII complexes of a hexaazadithiophenolate macrocycle

Abstract

The ligating properties of the 24-membered macrocyclic dinucleating hexaazadithiophenolate ligand (L^Me)²⁻ towards the transition metal ions Cr^II, Mn^II, Fe^II, Co^II, Ni^II and Zn^II have been examined. It is demonstrated that this ligand forms an isostructural series of bioctahedral [(L^Me)M^II₂(OAc)]⁺ complexes with Mn^II (2), Fe^II (3), Co^II (4), Ni^II (5) and Zn^II (6). The reaction of (L^Me)²⁻ with two equivalents of CrCl₂ and NaOAc followed by air-oxidation produced the complex [(L^Me)Cr^IIIH₂(OAc)]²⁺ (1), which is the first example for a mononuclear complex of (L^Me)²⁻. Complexes 2–6 contain a central N₃M^II(μ-SR)₂(μ-OAc)M^IIN₃ core with an exogenous acetate bridge. The Cr^III ion in 1 is bonded to three N and two S atoms of (L^Me)²⁻ and an O atom of a monodentate acetate coligand. In 2–6 there is a consistent decrease in the deviations of the bond angles from the ideal octahedral values such that the coordination polyhedra in the dinickel complex 5 are more regular than in the dimanganese compound 2. The temperature dependent magnetic susceptibility measurements reveal the magnetic exchange interactions in the [(L^Me)M^II₂(OAc)]⁺ cations to be relatively weak. Intramolecular antiferromagnetic exchange interactions are present in the Mn^II₂, Fe^II₂ and Co^II₂ complexes where J = −5.1, −10.6 and ∼−2.0 cm⁻¹ (H = −2JS₁S₂). In contrast, in the dinickel complex 5 a ferromagnetic exchange interaction is present with J = +6.4 cm⁻¹. An explanation for this difference is qualitatively discussed in terms of the bonding differences.