l-2-Nitrimino-1,3-diazepane-4-carboxylic acid monohydrate

The cyclic form of l-nitro-arginine, C(6)H(10)N(4)O(4), crystallizes with two independent mol-ecules in the asymmetric unit. According to the geometrical parameters, similar in both mol-ecules, the structure corresponds to that of l-2-nitrimino-1,3-diazepane-4-carboxylic acid; there are, however, conformational differences between the independent molecules, one of them being close to a twisted chair while the other might be described as a rather flattened boat. All six active H atoms in the two molecules are involved in hydrogen bonds, two of which are intra-molecular and four inter-molecular, forming an infinite chain of mol-ecules along the b axis.