Crystal structures of mirtazapine molecular salts

Abstract

A few molecular salts of the anti-depressant drug R/S-Mirtazapine with organic carboxylic acids, its HCl salt, and Mirtazapine hemihydrate were crystallized and characterized by X-ray diffraction, IR and Raman spectroscopy, and thermal analysis. Whereas Mirtazapine base sublimed above ambient conditions its molecular salts do not show any sublimation even at elevated temperatures. Crystal structure analysis showed that proton transfer in the hemiadipate salt occurs contrary to the ΔpK_a rule. A strong ionic two-point synthon of N⁺–H⋯O⁻ and C–H⋯O⁻hydrogen bonds is a recurring motif in Mirtazapinium carboxylate crystal structures.