Bis(2,6-diaminopyridinium) bis(hydrogen oxalate) monohydrate

Al-Dajani, Mohammad T. M.; Talaat, Jamal; Shamsuddin, Shaharum; Hemamalini, Madhukar; Fun, Hoong‐Kun

doi:10.1107/s1600536811004119

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“…In addition, N–H···N and N–H···π hydrogen bonds interconnect the molecules in a zigzag fashion, leading to a complex three-dimentional (3D) network . This typical hydrogen-bonding interaction is observed in 2,6-DAP complexes with other molecules. − Furthermore, the ability of the pyridine nitrogen to accept protons is high compared with the one substituted with an electron-donating amino group because of its strong basicity . The anion precursor for the title salt is phosphoric acid, which has three hydrogen-bond donor sites and one hydrogen-bond acceptor site.…”

Section: Introductionmentioning

confidence: 99%

Fluorescence Properties Reinforced by Proton Transfer in the Salt 2,6-Diaminopyridinium Dihydrogen Phosphate

et al. 2014

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Luminescent materials have many interesting applications, but it remains difficult to control the luminescence of organic materials and in particular to retain the same luminescence in solution and in the solid state, a property of interest for various imaging applications. In the present work, the fluorescent properties of the salt of 2,6-diaminopyridinium with dihydrogen phosphate have been explored. As a result of proton transfer from phosphoric acid to the pyridine nitrogen and the stabilizing effect of the two primary amines at the positions ortho to the pyridine nitrogen, the band gap between the HOMO and the LUMO is considerably diminished in comparison with that in 2,6-diaminopyridine. This is confirmed by a red shift in its absorption spectrum. Because protonation is retained in aqueous solution, the dissolved 2,6-diaminopyridinium dihydrogen phosphate salt retains a similar fluorescent spectrum as in the solid state. The crystals have been studied by single-crystal X-ray diffraction; FTIR, Raman, UV-vis-NIR, and luminescence spectroscopy; HOMO-LUMO calculations using DFT; and thermal analysis. The compound provides an example of a supramolecular motif that controls the crystal structure and the luminescence properties. In addition, the crystal exhibits negligible thermal expansion over a temperature interval of 150 °C. In short, 2,6-diaminopyridinium dihydrogen phosphate is an interesting compound for the design of luminescent devices.

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