Synthesis,Structure and Magnetic Properties of a Cyclic Heterotetranuclear Co3Fe Complex of 2-Mercaptophenol (H2mp) with tri-n-Butylphosphine Participation

Neutral heterotetranuclear complex Co₃Fe(mp)₄(Hmp)(PBuⁿ₃)₃ 2 (PBuⁿ₃ = tri-n-butylphosphine) of 2-mercaptophenol (H₂mp) was synthesized in a molar ratio of CoCl₂:FeCl₃:H₂mp:NaOMe:PBuⁿ₃ = 0.75:0.25:1:2:1 under anaerobic conditions. It represents partially Fe^III-substituted form of the asymmetric mixed-valence tetracobalt complex Co₄(mp)₄(Hmp)(PBuⁿ₃)₃ (1). 2 crystallizes in the triclinic space group Pl?, with a = 12.373(2) Å, b = 15.677(3) Å, c = 20.571(4) Å, α = 93.59(3)° β = 93.45(3)° γ = 112.30(3)°, V = 3669 ų, and Z = 2. The molecule exhibits a cyclic skeleton of Co₃FeS₄O₃ with two doubly μ₂-S bridges, one doubly μ₂-O bridge, and one singly μ₂-O bridge. The four mp^2? ligands display two different modes, O_bS_b-T and O_tS_b, while the monoanion Hmp^? is only terminally chelated to Fe³⁺ ion in HO_tS_t fashion (b stands for bridge, t for terminal, and T for trinuclear). The three Co centers are located in approximately square-based pyramidal environments, and the Fe atom in distorted trigonal bipyramidal geometry. Three types of main fragment ions were observed in the FAB mass spectrum of 2. The dissociation of the fragments follows the order: PBuⁿ₃ first, then Hmp and mp ligands. Moreover, the dissociation of Fe(Hmp) is first, followed by Co(mp) and Co(mp)₂, according with the fact that Fe(Hmp) is only loosely bonded. Variable-temperature magnetic susceptibility measurements showed that 2 exhibits weak magnetic exchange interactions.