Potassium l-2-nitrimino-1,3-diazepane-4-carboxyl-ate monohydrate.

The title compound, K(+)·C(6)H(9)N(4)O(4) (-)·H(2)O, crystallizes with the K atoms located on special positions related by pseudocentres of symmetry. Each K atom is coordinated by six O-atom donors. The N and water H atoms are involved in inter- and intra-molecular N-H⋯O, N-H⋯N and O-H⋯O hydrogen bonding.

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

The title compound, C(6)H(10)N(4)O(4)·H(2)O, crystallizes with two independent formula units in the asymmetric unit, their geometric parameters being quite similar. The conformations of the 1,3-diazepane rings are also similar and close to a twist-boat. All ten O- and N-bound H atoms are involved in hydrogen bonds, two of which are intra- and eight inter-molecular linking crystallographically independent mol-ecules, into a three-dimensional hydrogen-bonded network.

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

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.

l-Argininium ethyl sulfate.

The title compound, C(6)H(15)N(4)O(2) (+)·C(2)H(5)O(4)S(-), exhibits nonlinear optical properties. An extensive hydrogen-bonding network [N⋯O = 2.786 (4)-3.