The reaction of MnCl 2 ·4H 2 O, H 8 L (2,2′-bis- p - t Bu-calix4arene) and NEt 3 in a dmf/MeOH solvent mixture results in the formation of a mixed valent decametallic cluster of formula Mn II 6 Mn III 4 (L) 2 (μ 3 -OH) 4 (μ-OH) 4 (MeOH) 4 (dmf) 4 (MeCN) 2 ·MeCN ( 3 ). Complex 3 crystallises in the monoclinic space group P 2 1 / n with the asymmetric unit comprising half of the compound. Structure solution reveals that the bis-calix4arene ligands are arranged such that one TBC4 moiety in each has undergone inversion in order to accommodate a Mn III 4 Mn II 6 metallic skeleton that describes three vertex-sharing Mn III 2 Mn II 2 butterflies. The structure is closely related to the species Mn III 6 Mn II 4 (L) 2 (μ 3 -O) 2 (μ 3 -OH) 2 (μ-OMe) 4 (H 2 O) 4 (dmf) 8 ·4dmf ( 4 ), the major difference being the oxidation level of the Mn ions in the core of the compound. DFT calculations on the full structures reveal that replacing the Mn III ions in 4 for Mn II ions in 3 results in a significant decrease in the magnitude of some antiferromagnetic exchange contributions, a switch from ferromagnetic to antiferromagnetic in others, and the loss of significant spin frustration. Isolation of structurally related Mn III 4 Mn II 6 and Mn III 6 Mn II 4 clusters using the 2,2′-bis- p - t Bu-calix4arene ligand framework reveals significant differences in magnetic exchange interactions and spin frustration effects.