Diaquabis(pyrimidine-2-carboxylic acid-κ2 N,O)cobalt(II) dichloride

In the title salt, [Co(C5H4N2O2)2(H2O)2]Cl2, the CoII ion is located on an inversion center. It is chelated by two neutral pyrimidine-2-carboxylic acid molecules and is coordinated by two water molecules in an octahedral coordination geometry. The cations and anions are linked via O—H⋯Cl hydrogen bonds into a layer structure; an intramolecular O—H⋯N hydrogen bond connects the carboxylic acid group to the pyrimidine N atom.

In the title salt, [Co(C 5 H 4 N 2 O 2 ) 2 (H 2 O) 2 ]Cl 2 , the Co II ion is located on an inversion center. It is chelated by two neutral pyrimidine-2-carboxylic acid molecules and is coordinated by two water molecules in an octahedral coordination geometry. The cations and anions are linked via O-HÁ Á ÁCl hydrogen bonds into a layer structure; an intramolecular O-HÁ Á ÁN hydrogen bond connects the carboxylic acid group to the pyrimidine N atom.
The work was supported by the ZIJIN project of Zhejiang University, China.

Comment
As part of our ongoing investigation on the nature of aromatic stacking (Cheng et al., 2000;Wu et al., 2003), the title Co II compound has recently been prepared and its crystal structure is presented here.
The molecular structure of the title compound is shown in Fig. 1. The crystal of the title compound consists of complex cations and Clanions. The Co II located on an inversion center is coordinated by two neutral pyrimidine-2-carboxylic acid and two water molecules with an octahedral geometry ( Table 1). The Clanions link with the complex cations via O-H···Cl hydrogen bonding (Table 2 and Fig. 1). The charge balance indicates that the pyrimidine-2-carboxylic acid is a neutral ligand but not an anion; and the significant difference in C-O bond distances (Table 1) also suggests that the carboxyl group is not deprotonated. This is obviously owing to the acidified solution environment in the preparation of the compound (see _publ_section_exptl_prep). The intra-molecular O-H···N hydrogen bonding exsits between the carboxyl group and adjacent pyrimidine-N atom (Fig. 1). Thus the pyrimidine-2-carboxylic acid can not play a role of bridge ligand in this structure, contrast to that found in pyrimidine-2-carboxylate complex of Co(II) reported previously (Rodriquez-Dieguez et al., 2007).
π-π stacking is not observed in this crystal structure, which is different from the situation in a related Cu II complex with pyrimidine-2-carboxylate (Zhang et al., 2008). It may be due to extensive hydrogen bonding network involving coordinated water molecules and counter Clanions.
Experimental 2-Cyanopyrimidine (0.19 g, 1.8 mmol), CoCl 2 .6(H 2 O) (0.24 g, 1 mmol) were dissolved in a mixture solution of water (15 ml) and ethanol (5 ml), then hydrochloric acid solution (3 ml, 37%) was added into the solution. The solution was refluxed for 5 h. Single crystals of the title compound were obtained after about one month.

Refinement
Hydroxy and water H atoms were located in a difference Fourier map and refined as riding in as-found relative positions, with U iso (H) = 1.5U eq (O). Other H atoms were placed in calculated positions with C-H = 0.93 Å and refined in riding mode with U iso (H) = 1.2U eq (C).