Raman, DRIFT and ATR-IR spectra, corrosion inhibition, DFT and solid-state calculations of 4-amino-3-choloro-2,5,6-trifluoropyridine

Abstract

The Raman spectrum (3700-100 cm−1) of 4-Amino-3-choloro-2,5,6-trifluoro-pyridine (ACTFP; C5H2ClF3N2) has been recorded in the solid phase using 514.5 nm (green) and 785 nm (red) lasers to trace relative intensity changes. Moreover, the ATR-IR (4000-500 cm−1) and DRIFT (4000–400 cm−1) spectra of the solid were also recorded. Nine structures were suggested for ACTFP based on amino-imino tautomerism in addition to suggested conformers as a result of amino group internal rotation. DFT-B3LYP calculations at basis sets up to 6–311++G(d,p) favor the non-planaramino form (S-1; C1 symmetry), possessing the least energy with real vibrational frequencies. Based on X-ray single crystals and owing to the observed four stretches for NH2 moiety, the presence of two molecules per unit cell (a dimer molecule) is also investigated using both Gaussian B3LYP/at 6-31G(d) and CASTEP solid state computations. Reliable vibrational assignments were proposed herein based on estimated wavenumbers, normal coordinate analyses (NCA), potential energy distributions (PEDs) and de-convoluted spectra. Nevertheless, the NCA were found to be extensively mixed, all C–F and C–Cl fundamentals were confidently allocated herein, however were not considered in earlier published data of similar molecules. Moreover, frontier molecular orbitals (HOMO and LUMO) and atomic charge distributions (NPA and ESP) were also predicted for ACTFP to examine its efficiency as a corrosion inhibitor.