Raman, infrared and NMR spectra, vibrational assignments and quantum mechanical calculations of centrosymmetric 3,6-Dicholoro-1,2,4,5-tetrazine

Abstract The Raman spectrum (2000−100 cm −1 ) of 3,6-Dicholoro-1,2,4,5-tetrazine (DCTZ, C 2 N 4 Cl 2 ) in solid phase has been recorded. Moreover, the mid-IR (2000–400 cm −1 ) and ATR-IR (2000-480 cm −1 ), 13 C (0–200 ppm) and 15 N (0–440 ppm) NMR spectra were recorded. Initially, optimization followed by frequency calculations were carried out for DCTZ restricted to C i and D 2h point groups to work out the least energy conformer with real frequencies. DFT(B3LYP) and MP2(full) computations utilizing 6-31G(d) and 6–311++G(d,p) basis sets favor C i symmetry conformer by 781/598 cm −1 (9.3/7.2 kjmol −1 ) and 745/698 cm −1 (8.9/8.3 kjmol −1 ). The simulated spectra are well compiled to the experimentally recorded IR, Raman, 13 C and 15 N regardless of few coincident vibrational frequencies that belong to D 2 h symmetry conformer. Thus, we have carried out additional CASTEP solid state optimization for one molecule per unit cell (C i symmetry) employing Materials Studio using DFT-PBE method. Similar calculations were completed for D 2 h molecular symmetry for one molecule and repeated molecules per unit cell in which C i symmetry is favored by 341 cm −1 (4.1 kjmol −1 ). It is worth mentioning that computations for both C i and D 2h conformers produce real vibrational frequencies . Assisted by normal coordinate analysis, potential energy distributions (PEDs), complete and confident vibrational assignments are provided herein for C i conformer. The results are conferred herein are compared with comparable molecules whenever applicable.