The crystal structure of Na 3B 7O 12 and Na 2Tl 2B 10O 17 was determined by the single crystal X-ray diffraction method. The first one crystallizes in the triclinic system, space group P-1, with the following unit cell parameters: a=6.638(2) Å, b=8.249(3) Å, c=8.836(3) Å, α=95.875(5)°, β=100.680(4)°, γ=99.688(4)°; V=464.2(2) Å 3; Z=2. The crystal structure was solved from 1982 reflections until R 1=0.0293. It exhibits a three-dimensional framework built up from BO 3 triangles (▵) and BO 4 tetrahedra (T). Three kinds of borate groups can be considered: B 3O 7 and B 3O 8 rings and BO 3 triangle; the shorthand notation of the fundamental building block (FBB) existing in this compound is: 7: ∞ 3 [(3: 2▵+T)+(3: ▵+2T)+(1: ▵)]. The second borate Na 2Tl 2B 10O 17 crystallizes in the monoclinic system, space group C2/ c, with a=21.711(10) Å, b=6.446(3) Å, c=10.952(5) Å, β=105.897(8)°; V=1474.0(1) Å 3; Z=4. The crystal structure was solved from 1884 reflections until R 1=0.0387. It consists of a two-dimensional network of sharing corners BO 3 triangles and BO 4 tetrahedra forming B 5O 11 double rings, leading to the FBB: 10: ∞ 2 2[(5: 3▵+2T)]. These two new borates were compared with the compounds M 3B 7O 12 (M=Li, Rb, Cs; B/M=2.33) and AgSrB 7O 12, and Cs 2Na 2B 10O 17 and Cs 2K 2B 10O 17 (M 2M′ 2B 10O 17, M and M′ monovalent elements; B/(M+M′)=2.5). The latter are isotype and isostructural of Na 2Tl 2B 10O 17. Na 3B 7O 12 is isotype and isostructural of Li 3B 7O 12; the three-dimensional structure of these two heptaborates is different from the two-dimensional structures of AgSrB 7O 12, Rb 3B 7O 12 and Cs 3B 7O 12, which contain different FBBs with 7, 14 and 63 boron atoms, respectively.