Synthesis and characterization of trivalent tribridged dicobalt complexes incorporating alkoxide, aqua-hydroxide, acetate and phosphate ligating groups

Two dinuclear trivalent cobalt complexes viz. [Co2(P1–O)(AcO)(H2O)(OH)](ClO4)3, (1) and [Co2(P1–O)(AcO)(DPP)](ClO4)3, (2), where P1–O=N,N′,N″,N‴-tetrakis(2-methylpyridyl)-2-hydroxy-1,3-diaminopropaneP1–O=N,N′,N″,N‴-tetrakis(2-methylpyridyl)-2-hydroxy-1,3-diaminopropane, AcO = acetate and DPP = diphenyl phosphate, containing three intervening bridges between the two cobalt(III) centers have been synthesized and characterized. Complex 1 was formed by the reaction of a divalent dicobalt complex [Co2(P1–O)(AcO)](ClO4)2 with hydrogen peroxide. The X-ray crystallographic analysis shows that 1 contains a μ-acetato–μ-aqua-hydroxo–μ-alkoxo–dicobalt(III) core comprised of two distorted octahedral Co sites. Complex 2 also has two six-coordinated cobalt(III) ions with N3O3 set of donor atoms derived from the binucleating ligand, P1–OH and the oxygen atoms of acetate (OAc) and diphenyl phosphate (DPP) groups, rendering octahedral geometry around each cobalt(III). The distance between the two cobalt(III) sites in the complexes 1 and 2 is 3.38 and 3.35 Å, respectively that are close to the M…M distance in dinuclear metalloenzymes. Complexes 1 and 2 are also characterized by conventional spectroscopic methods such as UV–Vis, FT-IR, 1H, 13C and 31P NMR and ESI-MS spectroscopic methods.

Graphical abstractTwo dinuclear trivalent cobalt complexes viz. [Co2(P1–O)(AcO)(H2O)(OH)](ClO4)3, (1) and [Co2(P1–O)(AcO)(DPP)](ClO4)3, (2) have been synthesized and characterized. Complex 1 was formed by the hydrogen peroxide reactivity of a divalent dicobalt complex [Co2(P1–O−)(AcO−)](ClO4)2. The X-ray crystallographic analysis shows that 1 contains a μ-acetato–μ-aqua-hydroxo–μ-alkoxo–dicobalt(III) core comprised of two distorted octahedral Co sites. Complex 2 also has three intervening bridges, μ-acetato–μ-diphenyl phosphato–μ-alkoxo between the cobalt(III) ions with distorted octahedral geometry. The distance between the two cobalt(III) sites in the complexes 1 and 2 is 3.38 and 3.35 Å, respectively that are close to the M…M distance in dinuclear hydrolases.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A pair of dicobalt(III) complexes containing an acetate or phosphate bridge are synthesized. ► X-ray structure of both reveals distorted octahedral geometry around Co(III). ► The complexes are characterized in the solution state by conventional spectroscopic methods. ► 1H NMR reveals the low spin nature of Co(III), as expected.