Poly[tri-μ-aqua-diaqua-μ-phosphonoformato-cobalt(II)sodium]

The title complex, [CoNa(CO5P)(H2O)5]n, was obtained by reacting sodium phosphonoformate with cobalt nitrate. The complex contains cobalt(II) and sodium ions, which are bridged by the O atoms of two aqua ligands. The CoII ion is octahedrally coordinated by three phosphonoformato ligands (one bi- and the other monodentate) and by two O atoms from the bridging aqua ligands. The sodium cation is hexacoordinated by six O atoms from four bridging and two terminal aqua ligands. The complex molecules are linked to give a three-dimensional structure by phosphonoformate ligands bridging CoII atoms and water molecules establishing cobalt–sodium bridges. O—H⋯O hydrogen bonding between the aqua ligands and all O atoms of the phosphonoformato ligand and neighbouring aqua ligands help to consolidate the packing.

The title complex, [CoNa(CO 5 P)(H 2 O) 5 ] n , was obtained by reacting sodium phosphonoformate with cobalt nitrate. The complex contains cobalt(II) and sodium ions, which are bridged by the O atoms of two aqua ligands. The Co II ion is octahedrally coordinated by three phosphonoformato ligands (one bi-and the other monodentate) and by two O atoms from the bridging aqua ligands. The sodium cation is hexacoordinated by six O atoms from four bridging and two terminal aqua ligands. The complex molecules are linked to give a three-dimensional structure by phosphonoformate ligands bridging Co II atoms and water molecules establishing cobalt-sodium bridges. O-HÁ Á ÁO hydrogen bonding between the aqua ligands and all O atoms of the phosphonoformato ligand and neighbouring aqua ligands help to consolidate the packing.  Galanski et al. (2003); Margiotta et al. (2007); Mesri et al. (1996).  Table 1 Hydrogen-bond geometry (Å , ).

Xu-Jian Luo and Xiu-Qing Zhang Comment
Organophosphates have been widely used in medicinal chemistry and life science. They play an important role in life processes of substance transportation and energy transformation, and are also important for biological substances, such as ATP, DNA, RNA, etc. Bisphosphonates (BPs) are metabolically stable analogues of pyrophosphates. They have a very high affinity to calcium ions and therefore show a very strong inhibitory effect on osteoclastic resorption. They are used as therapeutic agents for several bone-related diseases. Foscarnet and phosphonoacetic acid are known to inhibit viral DNA polymerase, inhibit the replication of herpes viruses, and also inhibit retroviruses (Mesri et al., 1996). Recently, several bifunctional metal-phosphonate complexes have been explored (Galanski et al., 2003;Margiotta et al., 2007;Xue et al., 2010;Torres Martin de Rosales et al., 2009).
The molecular structure of the title compound is shown in Fig. 1. Each Co(II) ion is in an octahedral environment coordinated by two O atoms (O1, O4) from a chelating phosphonoformate ligand, two O atoms (O6, O7) from two bridging water molecules and two O atoms (O2A, O3B) from two other phosphonoformates. Similarly, the Na(I) ion is coordinated by four O atoms (O6, O7, O8, O9) from four bridging water molecules and two O atoms (O9C, O10) from two terminal water ligands. The complex is linked to 3-D structure by phosphonoformate ligands bridging cobalt atoms and water molecules establishing cobalt sodium bridges (Fig. 2).

Experimental
An aqueous solution (15 ml) of Co(NO 3 ) 2 × 6 H 2 O (0.145 g, 0.5 mmol) was added dropwisely to an aqueous solution (15 ml) of sodium phosphonoformate (0.180 g, 0.6 mmol) at 323 K. The resulting mixture was refluxed for 3 h, and then the aqueous solution was allowed to cool down to room temperature. Pink block shaped crystals suitable for X-ray single diffraction analysis were harvested by slow evaporation (yield, 65%).

Refinement
H atoms of the water molecules were located in a difference Fourier map and refined, with O-H distances restrained to 0.82 Å.

Computing details
Data collection: CrystalClear (Rigaku, 1999); cell refinement: CrystalClear (Rigaku, 1999); data reduction: CrystalStructure (Rigaku/MSC & Rigaku, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).   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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq