Diaqua-bis-(hydrogen tartrato)cobalt(II) dihydrate.

The title complex, [Co(C(4)H(5)O(6))(2)(H(2)O)(2)]·2H(2)O, contains a Co(II) ion, two single deprotonated tartrate anions, two coordinated water mol-ecules and two lattice water mol-ecules. The coordination geometry of the Co(II) ion is a distorted octa-hedron with two O atoms from two coordinated water mol-ecules occupying cis positions in the equatorial plane and four O atoms from two hydrogen tartrate ions occupying the remaining positions. In the crystal, inter-molecular O-H⋯O hydrogen bonds link the mol-ecules into a three-dimensional network.

Diaqua-bis-(5-carb-oxy-1H-imidazole-4-carboxyl-ato-κN,O)iron(II).

In the title compound, [Fe(C(5)H(3)N(2)O(4))(2)(H(2)O)(2)], the Fe(II) ion lies on an inversion centre and is coordinated by two N and two O atoms from two 5-carb-oxy-1H-imidazole-4-carboxyl-ate ligands and two water mol-ecules in a distorted octa-hedral geometry. An intra-molecular O-H⋯O hydrogen bond occurs. In the crystal, inter-molecular N-H⋯O and O-H⋯O hydrogen bonds form a three-dimensional network, which consolidates the packing.

5-Carb-oxy-2-isopropyl-1H-imidazol-3-ium-4-carboxyl-ate monohydrate.

In the title compound, C(8)H(10)N(2)O(4)·H(2)O, the imidazole N atom is protonated and one of the carboxyl-ate groups is deprotoned, forming a zwitterion. An intra-molecular O-H⋯O hydrogen bond occurs. The crystal structure is stabilized by inter-molecular N-H⋯O and O-H⋯O hydrogen bonds. In addition, inter-molecular N-H⋯O and O-H⋯O hydrogen bonds link the mol-ecules into two-dimensional networks parallel to (10[Formula: see text]).