XRD-quality crystals of metallocavitand 8 were obtained as a water adduct (8•H2O), upon the crystallization of this complex from DCM under an ambient atmosphere. The refined structure clearly shows a single Mn(II) ion rigidly fixed at the bottom of the molecular cavity, with a water molecule completing the octahedral configuration around the metal center (Figure ). The Mn-N and Mn-O bonds of 2.185Å and 2.o71Å (in av.), respectively, are typical of high-spin Mn(II) systems. In fact, the unintentional occurrence of the water molecule in this structure proved quite fortunate, as the Mn-OH2O bond length of 2.191Å in this compound provided us with an excellent point of reference for comparison with the Mn-O bonds in Mn(IV)=O and Mn(III)-OH complexes 9 and 10, respectively (vide infra).