Design, synthesis and noncentrosymmetric solid state organization of three novel pyridylphosphonic acids?

CrystEngComm Pub Date: 2011-03-15 DOI: 10.1039/C1CE05140G

Abstract

Three pyridylphosphonic acids, 3-pyridylphosphonic acid 1, 5-(dihydroxyphosphoryl)nicotinic acid 2, and 3,5-pyridinediyldiphosphonic acid 3, were synthesized and structurally investigated by solid state FT-IR and single crystal X-ray diffraction methods. All compounds appear in zwitterionic forms in the solid state with a proton transferred from the phosphonic group toward the pyridine N-atom. Strong hydrogen-bond interactions O–H?O and N–H?O organize the molecules of the compounds into polar three-dimensional networks. The crystal structures are additionally stabilized via weaker C–H?O hydrogen bonds and π?π or C[double bond, length as m-dash]O?π interactions. Powder second harmonic generation and solution NMR spectra were measured as well. The NMR spectra revealed that the double bonds of the functional groups (P[double bond, length as m-dash]O and C[double bond, length as m-dash]O), although differently oriented versus the Npy atom, are coplanar with the aromatic rings in all stable, low energy conformers of compounds 1–3 in solution. In crystals, however, the P[double bond, length as m-dash]O bonds are tilted toward the ring by 10.77(7)° in 1, 70.42(8)° in 2 and by 43.97(7)° and 6.56(8)° in 3. All three compounds exhibit moderate powder SHG efficiencies compared to that of urea.

Graphical abstract: Design, synthesis and noncentrosymmetric solid state organization of three novel pyridylphosphonic acids
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