Spectroscopic and solid-state evaluations of tetra-aza macrocyclic cobalt complexes with parallels to the classic cobalt(II) chloride equilibrium

Abstract

The Co(III) complex of 3,6,9,15-tetra-azabicyclo[9.3.1]penta-deca-1,11,13-triene (L1) has been synthesized in DMF and isolated as a blue solid (1) ([L1CoIIIClX]n+, X = Cl− or DMF, n = 1 or 2). Complex 1 exhibits solution behavior similar to the classic cobalt(II) chloride equilibrium. When 1 is dissolved in water, the solution is pink and this complex exists as 1a, which consists of a cobalt(III) bound to L1 and two cis-chlorides with a perchlorate counter-ion to balance the complex charge ([L1CoIIICl2][ClO4]). In contrast, when 1 is dissolved in DMF or other organic solvents the solution is blue and is observed as 1b. The 1b complex salt contains two cobalt centers. One cobalt(III) is bound to L1, Cl−, and DMF. Charge balance is accomplished by the second cobalt center: [CoIICl4]2−, thus making 1b (L1CoIIICl(DMF)][CoIICl4]). This equilibrium was confirmed using UV–visible spectroscopy, EPR, and X-ray crystallography.