The macropolyhedral [B19H22](-) monoanion 1 and the dianion [B19H21](2-) 2 are synthesized in consistent 86-92% yields by the reaction of [PSH](+)[syn-B18H21](-) with BH3(SMe2) in 1,2-Cl2C2H4 at 72 degrees C. ['PS' is an abbreviation for 'Proton Sponge', 1,8-bis-(dimethylamino)naphthalene 'PSH' is its protonated derivative.] The molecular structures of 1 and 2 were elucidated as their [PS{BH2}](+) and [PS{BH2}](2+) salts la and 2a by single-crystal X-ray diffraction studies, in which all atoms were located, and supported by mass spectrometric analyses together with calculations of the cluster molecular geometries (ab ignitio and/or DFT) and of B-11 chemical shifts based on GIAO-DFT shielding tensors Acidification of dianion 2 with CF3COOH in acetonitrile, H2SO4 in dichloromethane, or aqueous HCl results in the clean formation of the monoanion B19H22]- 1 Conversely, shaking a concentrated acetonitrile solution of 1 in 0.5 M aqueous NaOH cleanly yields the [B19H21](2) dianion 2 Reaction of a dichloromethane solution of 1 with a 36% aqueous solution of HCHO in the presence of H2SO4 quantitatively converts 1 at room temperature to a 1:1 mixture of the syn- and anti-isomers of B18H22. This cluster dismantling process is the first example of a syn- to anti-B18H22 isomer conversion.