Study in the Solid State, Framework Energy and Crystal Structure by X-ray Diffraction Techniques of Cetirizine and Levocetirizine Dihydrochloride Used As Antihistamines

Cetirizine dihydrochloride and levocetirizine are antihistamines of second-generation that block histamine receptors H1, are widely used to treat allergic symptoms.These compounds belong to the class of antihistamines piperazine type and like other secondgeneration antihistamines, are considered non-sedating [1].The crystal structure of cetirizine dihydrochloride has been solved and refined using X-ray powder diffraction data and optimized using Density Functional Theory (DFT) techniques.The cetirizine dihydrochloride Fig. 1, crystallized in a monoclinic system and space group P21/n (Nº 14) with parameters a=13,6663(3) Å, b=7,0978(7) Å, c=23,8311(1) Å, β=102, 488(3)°, V=2251,06 Å 3 and Z=4.On the other hand, the levocetirizine dihydrochloride Fig. 1, crystallized in a monoclinic system and space group P21 (Nº 4) with parameters a=13,5450(7) Å, b=7,0719(9) Å, c=24,0527(2) Å, β=98, 159(3)°, V=2280,65 Å 3 and Z=2.In both crystalline structures there are multiple hydrogen bonds intra and inter molecular, πinteractions and hydrogen-π interactions.The molecular packing and crystal energy are dominated by Van der Waals attractions according to Hirshfeld surfaces.Finally, the crystal structure was optimized with DFT and all non-H bond distances and angles were subjected to restraints, based on a Mercury Mogul Geometry Check of each molecule.A search in the Cambridge Structural Database (CSD) [2] confirmed the absence of reports for the crystal structure of cetirizine dihydrochloride and levocetirizine.However, there are several reports of cetirizine dihydrochloride and levocetirizine in the PDF-4/Organics database [3] contains four entries PDF 00- 058-1973, 00-058-1974 and 00-058-1975, corresponding to unindexed patterns about cetirizine dihydrochloride, dextrocetirizine dihydrochloride and levocetirizine dihydrochloride, respectively; PDF 00-066-1627 corresponding an experimental pattern for cetirizine dihydrochloride, according to this report, it crystallizes in a monoclinic cell with parameters a=24.1256(7)Å, b=7.07588(7)Å, c=13.5196(4)Å β=98.0028(28)° and V=2285.45Å 3 in space group P21/n (Nº14).Figure 1.Cetirizine dihydrochloride crystal structure show π-interactions (left); Levocetirizine dihydrochloride crystal structure with two independent crystallographic molecules (right).