Crystal structure of catena-poly[[[aqualithium(I)]-μ-pyrimidine-2-carboxylato-κ4 N 1,O 2:N 3,O 2′] hemihydrate]

In this one-dimensional coordination polymer, four symmetry-independent Li(C5H3N2O2)(H2O) units form molecular ribbons running along the unit-cell c-axis direction. Within each ribbon, the ligand molecule, acting in a μ2-mode, bridges two adjacent Li cations using both its N,O-bonding sites.


Chemical context
The pyrimidine-2-carboxylato ligand exhibits rich versatility when applied to the synthesis of functional materials, resulting in structures with interesting structural and magnetic properties. Zeolite-type structures have been reported for Cd II coordination polymers with this ligand (Sava et al., 2008;Zhang et al., 2008a). A variety of polymeric molecular patterns have been observed in the structures of a number of divalent metal complexes with the title ligand, for example: Mn II Zhang et al., 2008b); Fe II and Co II (Rodríguez-Dié guez et al., 2007;Zhao & Liu, 2010); Ca II (Zhang et al., 2008b); Cu II (Suá rez-Varela et al., 2008). Polymeric molecular patterns were also found in two Li I structures with the pyrimidine-2-carboxylato ligand (Starosta & Leciejewicz, 2011, 2012. Interesting hexanuclear, wheelshaped nickel cationic complexes with the pyrimidine-2carboxylato ligand, encapsulating ClO 4 À or BF 4 À anions have been synthesized (Colacio et al., 2009). Structures built of monomeric molecules have been also reported in an Ag I complex by Kokunov & Gorbunova (2007) and in a Cu II complex by Suá rez-Varela et al. (2008) and Zhang et al. (2008c).
In the course of our studies of coordination modes of lithium complexes with diazine carboxylates, a third lithium complex with the title ligand has recently been synthesized. Fragments of two molecular ribbons in the structure of the title compound, showing the atom labels and 50% probability displacement ellipsoids for the non-H atoms. [Symmetry codes: (i) x, y, z + 1; (ii) x, y, z À 1.] Symmetry code: (i) x; y; z À 1.

Figure 2
The packing of molecular ribbons in the structure of the title compound as viewed down the ribbon direction (the crystallographic c axis). For clarity, H atoms are not shown.
as donors and carboxylate O atoms belonging to adjacent ribbons as acceptors are also observed.

Related complexes
The title compound is the third Li complex with the pyrimidine-2-carboxylate ligand reported so far. In one of these complexes (Starosta & Leciejewicz, 2011), molecular ribbons composed of Li cations bridged by the bidentate carboxylate groups and bridged by bidentate nitrate anions form molecular layers. An interesting feature is the absence of any N,O chelating bonding to the metal ion. The structural motif in the remaining complex (Starosta & Leciejewicz, 2012) consists of a molecular chain similar to that in the title compound. In this structure, the chains are bridged by pairs of aqua-coordinated Li ions inter-connected by an aqua O atom. The tetrahedral coordination of each of these Li cations is completed by two carboxylate O atoms acting in a bidentate mode and donated by the ligands belonging to adjacent chains. The charge of the resulting cationic ribbon is compensated by the interspersed chloride anions.

Synthesis and crystallization
50 ml of an aqueous solution containing 1 mmol of pyrimidine-2-carbonitrile and 5 mmol of LiOH was boiled under reflux for 20 h with constant stirring. After cooling to room temperature, the solution was filtered and titrated with 0.1 N acetic acid until the pH reached ca 6.5, then stirred at 320 K for 3 h and left to evaporate slowly at room temperature. The residue was redissolved in a 1:1 ethanol-water mixture and left to crystallize at room temperature. After a few days, blockshaped single crystal of the title compound were extracted, washed with cold methanol and dried in the air.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms bonded to pyridine-ring C atoms were placed at calculated positions with C-H = 0.93 Å and treated as riding on the parent atoms with U iso (H) = 1.2U eq (C). The H atoms of water molecules were found from the Fourier map and refined isotropically.    (Agilent, 2014); program(s) used to solve structure: SHELXS2014 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2008); molecular graphics: SHELXL2014 (Sheldrick, 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2008).

Special details
Experimental. Absorption correction: Agilent (2014). Clark & Reid (1995). Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by R.C. Clark & J.S. Reid. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. 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 R-factors(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.