This report describes the synthesis and characterization of a series of novel biscapped and monocapped tris( dioxime) Mn(II) complexes [Mn(dioxime)(3)(BR)(2)] and [Mn(dioxime)(3)BR](+) (dioxime = cyclohexanedione dioxime (CDOH2) and 1,2-dimethylglyoxyl dioxime (DMGH(2)); R = Me, n-Bu, and Ph). All tris( dioxime) Mn(II) complexes have been characterized by elemental analysis, IR, UV/vis, cyclic voltammetry, ESI-MS, and, in the cases of [Mn(CDOH)(3)BPh] OH center dot CHCl3 and [Mn(CDO)(CDOH)(2)(BBu(OC2H5))(2)], X-ray crystallography. It was found that biscapped Mn(II) complexes [Mn(dioxime)(3)(BR)(2)] are not stable in the presence of water and readily hydrolyze to form monocapped cationic complexes [M( dioxime)(3)BR](+). This instability is most likely caused by mismatch between the size of Mn(II) and the coordination cavity of the biscapped tris( dioxime) ligands. In contrast, monocapped cationic complexes [M(dioxime)(3)BR](+) are very stable in aqueous solution even in the presence of PDTA (1,2-diaminopropane-N, N, N', N'-tetraacetic acid) because of the kinetic inertness imposed by the monocapped tris( dioxime) chelators that are able to completely "wrap" Mn(II) into their N-6 coordination cavity. [Mn(CDO)(3)BPh] OH has a distorted trigonal prismatic coordination geometry, with the Mn( II) being bonded by six imine-N donors. The hydroxyl groups from three dioxime chelating arms form very strong intramolecular hydrogen bonds with the hydroxide counterion so that the structure of [Mn(CDOH)(3)BPh] OH can be considered as being the clathrochelate with the hydroxide counterion as a "cap".