A homovalent coordination cluster, [CoII10(OH)2(bda)6(ib)6] (1), featuring a nearly planar, hexagonal {Co10} array composed of ten edge-sharing {Co3(µ3-O)} triangles, forms in a nearly quantitative reaction as solvothermal decomposition product of the heterovalent pentanuclear precursor [CoII3CoIII2(Hbda)2(bda)2(ib)6] (ib: isobutyrate; H2bda: N-butyldiethanolamine) in DMSO. 1 crystallizes in the triclinic space group P-1 (a = 7.4200(15) Å, b = 9.773 (2) Å, c = 11.601(2) Å, α = 105.38(3)°, β = 106.32(3)°, γ = 93.38(3)°). The use of the {CoII3CoIII2} precursor, in combination with autogenous pressure, was found to be crucial for the condensation process yielding 1, which cannot be obtained by analogous reactions of the ligands and CoII salts in DMSO. Magnetic ac and dc susceptibility data of 1 reveal dominant ferromagnetic exchange interactions, but no slow magnetization relaxation.