(2-Azoniaethyl)guanidinium dichloride – A promising phase-matchable NLO material employing a simple hydrogen bond acceptor in its structure

• Molecular crystals for NLO based on guanidine derivatives are discussed.
• Promising material – AEGCl – was prepared and characterised.
• Crystal packing of AEGCl is discussed within group of closely related materials.
• SHG efficiency and phase matching was studied for polycrystalline AEGCl.

(2-Azoniaethyl)guanidinium dichloride (AEGCl), a salt of a functional guanidine derivative, was prepared and characterised by single-crystal and powder X-ray diffraction analysis, elemental analysis and by NMR, UV–Vis and vibrational spectroscopy. The crystal structure of AEGCl, which crystallises with the symmetry of the chiral space group P21, is built up via simple and multicentred NH⋯Cl hydrogen bonds and further supported by CH⋯Cl contacts. The compound is thermally robust and exhibits promising NLO properties with powder SHG efficiency better than potassium dihydrogen phosphate. In contrast, (2-azoniaethyl)guanidinium salts with inorganic oxoanions such as (2-azoniaethyl)guanidinium dinitrate and diperchlorate, synthesised for a comparison, form centrosymmetric crystal assemblies having several structurally independent “molecules” in their structures.

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