l-Arginine trifluoroacetate salt bridges in its solid state compound: The low-temperature three dimensional structural determination of l-arginine bis(trifluoroacetate) crystal and its vibrational spectral analysis

Structural varieties of l-arginine trifluoroacetate (abbreviated as LATF) and l-arginine bis(trifluoroacetate), LABTF, in the solid state compounds were observed and analyzed by the nuclear magnetic resonance (NMR) spectroscopy. The guanidinium–carboxylate interaction plays an important role involving in the crystal structure construction. Conformational changes of l-Arg+ and l-Arg2+ cations result from the intrinsic structural difference by hydrogen bonding and electrostatic interactions. The low-temperature structure of its crystalline salt, l-arginine bis(trifluoroacetate), was determined to describe the hydrogen bonding interactions. In comparison with the crystal structure at room temperature, the low-temperature l-Arg2+ cations present tiny conformational difference and the rotational disorder of CF3 group disappears. FT-IR and Raman spectra were investigated and hydrogen bonding interactions were analyzed on the basis of its vibrational spectra. Results indicate that this type interaction is greatly contributive to the structural features and vibrational spectral properties.

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► Conformational varieties of l-Arg+ and l-Arg2+ cations in l-arginine trifluoroacetate compounds were observed.
► Low-temperature structure of l-arginine bis(trifluoroacetate) was firstly determined and compared with that at room temperature.
► Theoretical IR and Raman spectra of LABTF were modeled, and the theoretical infrared absorption edge is coincident with the experimental value.