A series of [Co(Mabiq)Cl2-n] (n = 0, 1, 2) compounds and evidence for the elusive bimetallic form

The synthesis and characterization of a series of cobalt compounds, coordinated by the redox active macrocyclic biquinazoline ligand, Mabiq (2-4:6-8-bis(3,3,4,4-tetramethyldihydropyrrolo)-10-15-(2,2′-biquinazolino)-[15]-1,3,5,8,10,14-hexaene-1,3,7,9,11,14-N6), is presented. The series includes the monometallic Co(Mabiq)Cl2 (1), Co(Mabiq)Cl (2), and Co(Mabiq) (4), with formal metal oxidation states of +3 → +1. A binuclear cobaltous compound, Co2(Mabiq)Cl3 (3), also was obtained, providing the first evidence for the ability of the Mabiq ligand to coordinate two metal ions. The electronic structures of the paramagnetic 2 and 3 were examined by EPR spectroscopy and magnetic susceptibility studies. The CoII ion that resides in the N4-macrocylic cavity of 2 and 3 adopts a low spin S = 1/2 configuration. The bypirimidine functionality in 3 additionally coordinates a high-spin, S = 3/2 cobaltous ion in a tetrahedral environment. The two metal ions in 3 are weakly coupled by magnetometry. The square planar, low-valent 4 offers one of a limited number of examples of structurally characterized N4-macrocyclic CoI compounds. Spectroscopic and DFT computational data suggest that a CoII(Mabiq•) description may be a reasonable alternative to the CoI formalism for this compound