A homovalent, planar cobalt(II)-based and decanuclear coordination cluster [CoII10(OH)2(bda)6(ib)6] (1) has been obtained by a facile solvothermal reaction of a heterovalent pentanuclear precursor [CoII3CoIII2(Hbda)2(bda)2(ib)6], which is crucial for the synthesis of compound 1, as it can not be obtained by simple heating of the ligands and the cobalt(II) salt in DMSO.