The novel uranyl sulfate templated by protonated guanidinium molecules was obtained from aqueous solution under ambient conditions. Its crystal structure was determined by the single crystal X-ray diffraction analysis and evaluated using a topological approach and information-based complexity calculations. The Se-for-S substitution resulted in a symmetry breaking (from orthorhombic in sulfate to monoclinic in selenate) due to the rearrangement of oxygen atoms, so the resulting symmetry is a consequence of interplay between the template-substructure interactions and size of the tetrahedral cation.