Potassium 2-(N-hydroxycarbamoyl)acetate monohydrate

The crystal structure of the title compound, K+·C3H4NO4 −·H2O, consists of potassium cations, monoanions of 2-carboxyacetohydroxamic acid [namely 2-(N-hydroxycarbamoyl)acetate] and solvent water molecules. The elements of the structure are united in a three-dimensional network by numerous K⋯O coordinate bonds and O—H⋯O and N—H⋯O hydrogen bonds. The coordination sphere of the K+ ions may be described as a distorted double capped octahedron. Bond lengths and angles are similar to those in related compounds.

The crystal structure of the title compound, K + ÁC 3 H 4 NO 4 À Á-H 2 O, consists of potassium cations, monoanions of 2-carboxyacetohydroxamic acid [namely 2-(N-hydroxycarbamoyl)acetate] and solvent water molecules. The elements of the structure are united in a three-dimensional network by numerous KÁ Á ÁO coordinate bonds and O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. The coordination sphere of the K + ions may be described as a distorted double capped octahedron. Bond lengths and angles are similar to those in related compounds.

Comment
Hydroxamic acids represent an important class of chelating agents and enzyme inhibitors (Kaczka et al., 1962;Hershko et al., 1992;Ghio et al., 1992;Shao et al., 2004). In recent years hydroxamic acids have also been widely used in coordination chemistry as versatile bridging ligands able to produce multinuclear compounds containing a large number of metal ions, such as metallacrowns (Bodwin et al., 2001;Cutland-Van Noord et al., 2002). Recently we reported that 2-carboxyacetohydroxamic acid is an efficient ligand for obtaining 12-metallacrown-4 complexes with copper(II) ions which can be used as pentanuclear building blocks for preparation of one-dimensional coordination polymers .
The present investigation is aimed at the study of the molecular structure of the title compound (I) which is a suitable ligand for preparation of polynuclear complexes and coordination polymers.  Table 1).
The residue of 2-carboxyacetohydroxamic acid is a monoanion bearing the deprotonated carboxylic group with the hydroxamic function remaining protonated. The anion exhibits C-O, N-O, C-N bond lengths which are typical for carboxylic and hydroxamic groups (Wörl et al., 2005. The conformation of monoanion of 2-carboxyacetohydroxamic acid is significantly non-planar due to the presence of the flexible C-CH 2 -C moiety uniting two planar hydroxamic and carboxylic fragments. The mentioned groups are disposed nearly perpendicularly; the dihedral angle between their planes is equal to 86.37 (5) o .
The potassium cation exhibits coordination number 8, and its coordination polyhedron can be considered as severely distorted double capped octahedron. Its coordination environment is formed by two solvate water molecules and six oxygen atoms of monoanion of 2-carboxyacetohydroxamic acid belonging to the deprotonated carboxylic groups (O(1)) and both oxygen atoms of the hydroxamic functions(O(3) and O(4)) belonging to the different translational anions. Each potassium cation has in its coordination sphere the oxygen atoms belonging to five different translational monoanions of 2-carboxyacetohydroxamic acid. The K-O bond lengths lie in the range 2.711 (1) -3.058 (1) Å which is normal for potassium cations (Świątek-Kozłowska et al., 2000;Mokhir et al., 2002).

Refinement
The O-H and N-H H atoms were located from the difference Fourier map and refined isotropically. The methylene H atoms were positioned geometrically and were constrained to ride on their parent atoms, with C-H = 0.975-0.98 Å, and U iso = 1.2 U eq (parent atom). Fig. 1. A view of compound (I), with displacement ellipsoids shown at the 50% probability level. H atoms are drawn as spheres of arbitrary radii. The hydrogen bonding is shown by dashed lines [symmetry codes: (i) 1 + x, y, z; (ii) x, 1.5 -y, -1/2 + z; (iii) 1 + x, 1.5 -y, 1/2 + z; (iv)1 -x, 1 -y, -z; (v) 1 -x, -1/2 + y, 1/2 -z].   Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Figures
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )