Three new cobalt borate compounds, [Co(DIEN) 2 ][B 5 O 6 (OH) 4 ] 2 (DIEN=diethylenetriamine) (1), [B 5 O 7 (OH) 3 Co(TREN)] (TREN=tris(2-aminoethyl)amine) (2), and [Co 2 (TETA) 3 ][B 5 O 6 (OH) 4 ] 4 (TETA=triethylenetetramine) (3) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR, elemental analysis and thermogravimetry. The structures exhibit interesting 3D supramolecular hydrogen-bonded architectures, involving the similar borate polyanion [B 5 O 6+ n (OH) 4− n ] (n+1)− (n=0 for 1 and 3, and n=1 for 2) and the templating transition metal complexes which are generated in situ under mild solvothermal conditions. Crystal data: 1, monoclinic, space group C2/m (No. 12), a=15.2372(3)Å, b=11.5987(2)Å, c=8.4163(3)Å, β=93.601(4)°, V=1484.49(7)Å3, Z=2; 2, monoclinic, P2 1 /c (No. 14), a=8.9881(3)Å, b=20.7648(5)Å, c=9.3681(2)Å, β=99.926(4)°, V=1722.25(8)Å3, Z=4; 3, triclinic, space group P-1 (No. 2), a=12.3717(4)Å, b=12.9653(8)Å, c=19.0925(3)Å, α=77.009(5)°, β=80.095(2)°, γ=82.334(3)°, V=2925.3(2)Å3, Z=2.