Table . List of DFT calculated exchange interactions, J1-6, for compounds 3 and 4 together with pertinent structural information describing the bond distances and angles in each pairwise interaction. OL refers to the calix [4]arene O-atoms. The grey shaded rows highlight the exchange interactions, J1, J2 and J5, directly affected by the change in oxidation state of the two central Mn ions. For complex 4, the J values are found to be in a much larger range, with both ferro-and antiferromagnetic exchange being observed (+4.1 ≤ J ≤ -40.4 cm -1 ). J1, between two central Mn III ions connected by two µ3-OH bridges, is the largest antiferromagnetic exchange present due to the small Mn-O-Mn angles (97.6°) and short Mn-O (1.92 Å) and Mn-Mn (2.88 Å) distances. The large J value has been confirmed through calculations on a dinuclear model complex adapted from the X-ray structure (Fig. ). We note that the JT axes of the two Mn III ions are oriented parallel to the bridging ligands, which can be classified as a type I structure based on detailed studies of the dinuclear {Mn III 2(OR)2} motif. In this class of interactions, a large JAF contribution and a negligible JF contribution are expected, leading to strong antiferromagnetic coupling, as observed here. J2 is ferromagnetic in nature, mediated between Mn II and Mn III ions via a single µ2-OR bridge with a short Mn-O distance (2.03 Å) and a large Mn-O-Mn angle (122.8°). Interestingly, although J3 (Mn II -OH-Mn II ) is mediated via similar bridging angles and distances as that seen for J2, it is weakly antiferromagnetic in nature, highlighting the important role played by the oxidation state of the Mn ion in controlling the sign and magnitude of the exchange. J3, J4 and J6 are much more weakly antiferromagnetic in comparison to J1 due to the larger Mn-O/Mn distances and larger Mn-O-Mn angles present, just as they are in 3. J5, between two Mn III ions bridged by a µ3-O ion and a µ2-OR group, is weakly ferromagnetic in nature. J5 can be classified as a type II {Mn III 2(OR)2} unit in which the JT axes of the Mn III ions are oriented parallel to each other and lying along µ-oxo bridge. This leads to borderline ferro/antiferromagnetic coupling dictated by Mn-O-Mn angle and Mn-O distances. The highly frustrated nature of the interactions in complex 4 precludes the identification of an isolated spin ground state.