The K3Sb4BO13 (KSBO) material undergoes an uncommon symmetry increase upon cooling, from triclinic symmetry at room temperature to monoclinic symmetry at low temperature. The first-order phase transition is accompanied by shrinkage of the unit cell, resulting in the transformation of every pair of head-to-tail triangular BO3 groups into one B2O6 unit featuring unique edge-sharing BO4 tetrahedra. This is the first material with B2O6 units formed through temperature lowering and exhibiting a B–O anionic framework composed uniquely of isolated edge-sharing BO4 tetrahedra. Several techniques including single-crystal X-ray diffraction experiments, Raman and 11B magic-angle-spinning NMR spectroscopies, and, for the first time, B K-edge electron energy loss spectroscopy were used to evidence the rare and discrete B2O6 units. The complete transformation of BO3 units into B2O6 units makes the KSBO compound the perfect candidate to extract information about B2O6 units whose signal can be unambiguously assigned.