Coordination environment variations in multinuclear trigonal bipyramid Co(II) complexes bearing tetradentate sulfonamide N-donors and phenoxazinone synthase activities

Abstract

Most documented investigations deploying transition metal complexes as phenoxazinone synthase models only report one or two complexes, which limits understanding of structure-property correlations between varying compositions as well as the coordination environments of the active site changes and the biomimetic activities. In efforts to systematically investigate changes in the vicinity of cobalt(II), five new complexes of two tripod N,N′,N″-(nitrilotris(ethane-2,1-diyl))tris(benzenesulfonamide) ligand derivatives (1 and 2) were self-assembled with incorporation of Na+, K+ or Cs+ as bridging counter cations. All the complexes were structurally analysed and found to possess distorted trigonal bipyramid cobalt(II) centres such that an easily displaceable water molecule always occupy one of the axial positions. While ligand 1 forms (Na[Co1.w]E)n as a 1D coordination polymer, ligand 2 forms the dimeric complexes (Na[Co2.w]M)2, (Na[Co2.w])2, (K[Co2.w]A)2 and (Cs[Co2.w]M2,w2)2. Continuous Shape Measurement (CShM) calculations were carried out to analyse distortions of the obtained trigonal bipyramid geometries. The high turnover numbers of 584 h−1 for (Na[Co2.w])2, 564 h−1 for (Cs[Co2.w]M2.w2)2, 543 h−1 for (K[Co2.w]A)2 and 446 h−1 for (Na[Co2.w]M)2 represent attractive level of phenoxazinone mimicking capacity relative to literature data for mononuclear cobalt(II) complexes. It was concluded that the release of free cobalt(II) anions [Co1.w]− or [Co2.w]− via dissociations of the multinuclear complexes is necessary for the phenoxazinone synthase mimicking activities to occur and that the incorporated group I metal ions possess no influence on the observed mimicking activities. The trigonal bipyramid coordination environments of the anionic chelates [Co1.w]− or [Co2.w]− yielded better outcomes than their previously reported vacant octahedral (vOC-5, C4v) complex analogues.