▎ 摘　　要

2-[(2-Ammonioethyl)amino]acetate dihydrate, better known as N-(2-aminoethyl)glycine dihydrate, C(4)H(10)N(2)O(2)center dot 2H(2)O, (I), crystallizes as a three-dimensional hydrogen-bonded network. Amino acid molecules form layers in the ac plane separated by layers of water molecules, which form a hydrogen-bonded two-dimensional net composed of fused six-membered rings having boat conformations. The crystal structure of the corresponding hydroiodide salt, namely 2-[(2-ammonioethyl)ammonio]acetate iodide, C(4)H(11)N(2)O(2) +center dot I-, (II), has also been determined. The structure of (II) does not accommodate any solvent water molecules, and displays stacks of amino acid molecules parallel to the a axis, with iodide ions located in channels, resulting in an overall three-dimensional hydrogen-bonded network structure. N-(2-Aminoethyl)glycine is a molecule of considerable biological interest, since its polyamide derivative forms the backbone in the DNA mimic peptide nucleic acid (PNA).