The complex, [Mn6O2(OOCCMe3)(10)(HOO-CCMe3)(3)(py)], has a hexanuclear structure with a Mn6O2 core. This complex crystallizes in the monoclinic space group P2(1)/n with a = 17.757(5) angstrom, b = 27.413(5) angstrom, c = 22.348(5) angstrom, beta = 90.233(5)degrees, V = 9,040(4) angstrom(3) and Z = 4. It contains a [Mn6O2](10+) core that can be described as two edge-sharing Mn-4 tetrahedra at the centre of each of which tetrahedron lies a mu(4)-O2- ion. All Mn atoms are six-coordinate and possess distorted octahedral geometry. Mn-4 exhibits butterfly arrangement with both mu(4)-O atoms on the same side of the molecule. The complex is mixed-valence ((Mn4Mn2III)-Mn-II), and the Mn-III centers are assigned as the two central metal ions bridged by two O2- ions.