The dominance of sulfate over two organic ligands in the solvothermal assembly of an undecanuclear cobaltous cluster: crystallography and mass spectrometry

Abstract

An unexpected dominance of the coordination affinity of the sulfate anion over those of two organic chelating ligands, (1-methyl-1H-benzo[d]imidazol-2-yl)methanol (Hmbm) and pyridin-2-ylmethanamine (pma), was observed during the study of the solvothermal assembly of [Co₁₁(mbm)₆(pma)₂(SO₄)₈(H₂O)₆(CH₃OH)₆]·5CH₃OH (1), from CoSO₄·7H₂O at 100 °C in methanol. ESI-MS of solutions at different periods of the assembly reveal a hierarchical sequence, [Co₁] → [Co₂] → [Co₃] → [Co₄] → [Co₅] → [Co₉], where the lower nuclearity species are richer in Co²⁺ and SO₄²⁻ before the inclusion of more mbm ligands at the last step. Its crystal structure consists of an almost symmetrical wheel of nine cobalt atoms, [Co₉(mbm)₆(SO₄)₈(H₂O)₆] in edge-sharing octahedral coordination arranged in triangles with two peripheral dangling [Co(pma)(CH₃OH)₃]. The sulfate ions exhibit three different coordination modes, two in μ₆-, two in μ₃- and four as μ₂-bridging. Its thermal, optical and magnetic properties are also reported.