Hydrogen-bonded frameworks of two new tridentate betaine derivatives tri-(4-carboxypyridinium-ethyl)-amine: Syntheses, crystal structures and thermal stabilities

• A flexible tridentate betaine derivative is synthesized and characterized by EA, 1H NMR, IR.
• Double-ladder and honeycomb molecular frameworks are constructed by normal and weak(CHN/O) hydrogen bonds.
• OHπ interaction is observed in the X-ray crystal structure.

A tridentate betaine derivative, tri-(4-carboxypridinium-ethyl)-amine N[CH2CH2(C5H4N+)COO−]3 (L) has been synthesized. Crystallization of this compound in HClO4/H2O and DMF/H2O yields single crystals of (L·3H+)·3ClO4−·2H2O (1) and L·2H2O (2) suitable for single crystal X-ray diffraction analysis, respectively. The results indicate that 1 crystallizes in space group P1¯ with a = 7.681(3) Å, b = 13.523(4) Å, c = 17.147(5) Å, α = 68.86(1) °, β = 86.83(2) °, γ = 80.49(1) °, and Z = 2. 2 crystallizes in space group Pbca with a = 15.397(2) Å, b = 10.616(4) Å, c = 27.728(6) Å, α = 90°, β = 90°, γ = 90°, and Z = 8. Analysis of the crystals and molecular structures of 1 and 2 indicates that the flexible titled compound is a versatile candidate in constructing various hydrogen bonded molecular frameworks due to the existence of the α-H atoms of pyridinium rings and naked carboxylate groups.

The existence of positively-charged nitrogen atoms and electron-withdrawing carboxylate groups makes the α-hydrogen atoms more acidic and enable them to form various weak hydrogen bonds.Figure optionsDownload as PowerPoint slide