Colorless block crystals of the title compound are prepared by addition of boric acid to a solution of 4,4′‐bipyridine in water (90 °C, 68% yield).

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Synthesis, Crystal Structure, and Variable-Temperature-Luminescent Property of the Organically Templated Pentaborate [C10N2H9][B5O6(OH)4]·H3BO3·H2O. -Colorless block crystals of the title compound are prepared by addition of boric acid to a solution of 4,4'-bipyridine in water (90°C, 68% yield). The compound crystallizes in the triclinic space group P1 with Z = 2 (single crystal XRD). The structure contains monoprotonated bipyridinium cations, [B 5 O 6 (OH) 4 ]anions, and H 3 BO 3 and H 2 O molecules. The bicyclic [B5O6(OH)4]groups form a three-dimensional supramolecular network with three kinds of channels by extensive hydrogen bonds. The compound exhibits UV photoluminescence with an emission maximum at 372 nm upon excitation at 249 nm. The photoluminescence can be modified from UV to blue by a simple heat-treatment process. The novel pentaborate is a promising blue component for possible application in white light emitting diodes. -(YANG*, Y.; FU, D.; LI, G.; ZHANG, Y.; Z. Anorg. Allg. Chem. 639 (2013) 5, 722-727, http://dx.