The organically templated pentaborate [C10N2H9][B5O6(OH)4]·H3BO3·H2O (1a) was synthesized by boric acid and 4, 4′-bipyridine in aqueous solution and characterized by single-crystal X-ray diffraction, elemental analysis, FTIR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and photoluminescence spectroscopy. The compound crystallizes in the triclinic system with space group P (a = 9.196(3) Å, b = 9.822(3) Å, c = 12.113(3) Å, α = 66.243(3)°, β = 76.998(3)°, γ = 75.067(3)°, V = 958.4(5) Å3, and Z = 2). The polyanions form a novel 3D supramolecular network with three kinds of channels by extensive hydrogen bonds. The title compound shows a UV photoluminescence with an emission maximum at 372 nm upon excitation at 248 nm, and the photoluminescence can be modified from UV to blue by means of a simple heat-treatment process. The pentaborate could be a promising blue component for possible application in the white LED.