The compounds K2Mn3(H2O)(6)[Mo(CN)(7)](2). 6H(2)O and Mn-2(H2O)(5)Mo(CN)(7). nH(2)O (alpha phase, n = 4; beta phase, n = 4.75) have been synthesized in the form of well shaped single crystals by slow diffusion of aqueous solutions containing [Mo(CN)(7)]K-2. 2H(2)O and [Mn(H2O)(6)](NO3), respectively. The first compound has been obtained in the presence of an excess of K+ ions. The crystal structures have been determined. K2Mn3(H2O)(6)[Mo(CN)(7)](2). 6H(2)O is two-dimensional, and Mn-2(H2O)(5)Mo(CN)(7). nH(2)O (alpha and beta phases) are three-dimensional. The magnetic properties have been studied in great detail through single crystal magnetic measurements, and the magnetic phase diagrams have been determined. The three compounds exhibit a long-range ferromagnetic ordering along with a field-induced spin reorientation. Furthermore, the last two compounds show an additional magnetically ordered state which disappears when applying a sufficiently large magnetic field. The magnetic properties have been found to be dramatically modified when the non-coordinated water molecules are released. For instance, T-c is shifted from 39 to 72 K for K2Mn3(H2O)(6)[Mo(CN)(7)](2). 6H(2)O, and a pronounced coercivity is observed after partial dehydration.