In situ transformations of selenidostannate frameworks in ionic liquids (ILs) were initiated by treatment of the starting phase K₂[Sn ₂Se₅] and the consecutive reaction products by means of temperature increase and/or amine addition. Along the reaction pathway, the framework dimensionalities of the five involved selenidostannate anions develop from 3D to 1D and back, both in top-down and bottom-up style. Addition of ethane-1,2-diamine (en) led to the reversion of the 2D→1D step from 2D-{[Sn₂₄Se₅₆]^16-} to 1D-{[Sn ₆Se₁₄]^4-}. As rationalized by DFT investigations, the 2D anion is thermodynamically favored. Photoconductivity measurements reveal that all samples show Schottky contact behavior with absolute thresholds below 10 V. One of the samples exhibits conductive states within the energy range of visible photons. New dimensions: Three selenidostannate phases yielded from complex transformation pathways in ionic liquids include (in part reversible) dimensionality changes of the anionic Sn/Se substructures (see figure). As rationalized by DFT investigations, the transformations are provoked by competing influences of temperature and amine addition (DMMP=2,6-dimethylmorpholine, en=ethane-1,2-diamine).