Bromazepam: Crystal structure, spectroscopic and quantum chemical calculations

In the present study, comprehensive experimental and quantum chemical calculations on 7-bromo-1,3-dihydro-5-(2-pyridyl)-2H-1,4-benzodiazepin-2-one (Bromazepam) were carried out using X-ray single crystal analysis, FT IR, 1H NMR and UV/vis. Bromazepam crystallizes in monoclinic crystal system of P21/a group with a = 10.3224(5) Å, b = 15.8882(5) Å, c = 8.1627(3) Å and β = 106.848 (12)° and forms an infinite chain structure with a trans-zigzag type in the solid state along the crystallographic axis “a” through N6…HC13 intermolecular hydrogen bond with a distance of 2.584 Å Optimized geometrical structures, and harmonic vibrational frequencies were investigated by DFT(B3LYP) and HF methods. TD-DFT calculations were performed to assign the experimental electronic transitions. The chemical shift of the ionizable NH should be described by the cluster model rather than using the default polarizable continuum model (PCM). The bond lengths calculated by HF/LANL2DZ functional agree well with the crystal data specifically by using the combined basis sets in the optimization process.

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