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, C2N4Cl2) in solid phase has been recorded. Moreover, the mid-IR (2000–400 cm−1) and ATR-IR (2000-480 cm−1), 13C (0–200 ppm) and 15N (0–440 ppm) NMR spectra were recorded. Initially, optimization followed by frequency calculations were carried out for DCTZ restricted to Ci and D2h 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 Ci 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, 13C and 15N regardless of few coincident vibrational frequencies that belong to D2h symmetry conformer. Thus, we have carried out additional CASTEP solid state optimization for one molecule per unit cell (Ci symmetry) employing Materials Studio using DFT-PBE method. Similar calculations were completed for D2h molecular symmetry for one molecule and repeated molecules per unit cell in which Ci symmetry is favored by 341 cm−1 (4.1 kjmol−1). It is worth mentioning that computations for both Ci and D2h conformers produce real vibrational frequencies. Assisted by normal coordinate analysis, potential energy distributions (PEDs), complete and confident vibrational assignments are provided herein for Ci conformer. The results are conferred herein are compared with comparable molecules whenever applicable.