6-Methyl-nicotinic acid.

All non-H atoms of the title compound, C(7)H(7)NO(2), are nearly coplaner, the r.m.s. deviation being 0.0087 Å. In the crystal, the partially overlapped arrangement and the face-to-face distance of 3.466 (17) Šbetween parallel pyridine rings of neighboring mol-ecules indicates the existence of π-π stacking. Inter-molecular O-H⋯N hydrogen bonding and weak C-H⋯O hydrogen bonding are present in the crystal structure.

Dichlorido[bis-(2-ethyl-5-methyl-1H-imidazol-4-yl-κN)methane]-cobalt(II) monohydrate.

In the title compound, [CoCl(2)(C(13)H(20)N(4))]·H(2)O, the Co(II) atom lies on a mirror plane and is four-coordinated by two N atoms of the imidazole ligand and two Cl atoms in a distorted tetra-hedral arrangement. The water mol-ecule participates in the formation of hydrogen bonds, resulting in a three dimensional network involving the Cl atoms and the NH groups. The terminal C atom of the ethyl group is disordered over two sites of equal occupancy.

Aqua-[bis-(2-ethyl-5-methyl-1H-imidazol-4-yl-κN)methane]-oxalatocopper(II) dihydrate.

In the title compound, [Cu(C(2)O(4))(C(13)H(20)N(4))(H(2)O)]·2H(2)O, the Cu(II) atom exhibits a distorted square-pyramidal geometry with the two N atoms of the imidazole ligand and the two O atoms of the oxalate ligand forming the basal plane, while the O atom of the coordinated water mol-ecule is in an apical position. The Cu(II) atom is shifted 0.232 (2) Šout of the basal plane toward the water mol-ecule. The asymmetric unit is completed by two solvent water mol-ecules. These water mol-ecules participate in the formation of an intricate three-dimensionnal network of hydrogen bonds involving the coordinated water mol-ecule and the NH groups.

Bis[bis-(2-ethyl-5-methyl-1H-imidazol-4-yl-κN)methane](nitrato-κO,O')nickel(II) nitrate.

In the title compound, [Ni(NO(3))(C(13)H(20)N(4))(2)]NO(3), the Ni(II) ion shows a distorted octa-hedral geometry formed by four N atoms from two bis-(2-ethyl-5-methyl-1H-imidazol-4-yl)methane ligands and two O atoms from a chelating nitrate anion. Three ethyl groups in the complex cation and the O atoms of the uncoordinated nitrate anion are disordered over two sets of positions [occupancy ratios of 0.52 (3):0.48 (3) and 0.63 (3):0.37 (3), respectively]. In the crystal, inter-molecular N-H⋯O hydrogen bonds connect the complex cations into a zigzag chain along [010] and further N-H⋯O hydrogen bonds between the chains and the uncoordinated nitrate anions lead to layers parallel to (100).