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 FeIII‐substituted form of the asymmetric mixed‐valence tetracobalt complex Co4(mp)4(Hmp)(PBun3)3 (1). 2 crystallizes in the triclinic space group Pl̄, 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 Å3, 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 mp2− ligands display two different modes, ObSb‐T and OtSb, while the monoanion Hmp− is only terminally chelated to Fe3+ ion in HOtSt 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.