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-N-6], is presented. The series includes the monometallic Co(Mabiq)Cl-2 (1), Co(Mabiq)Cl (2), and Co(Mabiq) (4), with formal metal oxidation states of 3+ > 1+. A binuclear cobaltous compound, Co-2(Mabiq)Cl-3 (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 electron paramagnetic resonance spectroscopy and magnetic susceptibility studies. The Co-II ion that resides in the N-4-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 wealdy coupled by magnetometry. The square-planar, low-valent 4 offers one of a limited number of examples of structurally characterized N-4-macrocyclic Co-I compounds. Spectroscopic and density functional theory computational data suggest that a Co-II(Mabiq(center dot)) description may be a reasonable alternative to the Co-I formalism for this compound.