The new transition-metal oxothiostannate [Ni(cyclen)-(H2O)(2)](4)[Sn10S20O4]center dot similar to 13H(2)O (1) was prepared under hydrothermal conditions using Na4SnS4 center dot 14H(2)O as the precursor in the presence of [Ni(cyclen)(H2O)(2)](ClO4)(2)center dot H2O. Compound 1 comprises the [Sn10S20O4](8-) anion constructed by the T3-type supertetrahedron [Sn10S20] and the [Sn10O4] anti-T2 cluster. Channels host the H2O molecules, and the sample can be reversibly dehydrated and rehydrated without significantly affecting the crystallinity of the material. Sn-119 NMR spectroscopy of an aqueous solution of Na4SnS4 center dot 14H(2)O evidences that between 25 and 120 degrees C only [SnS4](4-) and [Sn2S6](4-) anions are present. In further experiments, hints were found that the formation of tin oxosulfide ions depends on the Ni2+-centered complexes. Compound 1 exhibits promising photocatalytic properties for the visible-light-driven hydrogen evolution reaction, with 18.7 mmol.g(-1) H-2 being evolved after 3 h.