Poly[[diaquabis[μ4-5-nitroisophthalato-κ4 O 1:O 1:O 3:O 3′]bis[μ3-pyridine-4-carboxylato-κ3 O:O′:N]tricobalt(II)] tetrahydrate]

The title compound, {[Co3(C6H4NO2)2(C8H3NO6)2(H2O)2]·4H2O}n, exhibits a two-dimensional layer-like structure in which the CoII ions exhibit two kinds of coordination geometries. One nearly octahedral CoII ion with crystallographic inversion symmetry is coordinated to six carboxylate O atoms from four bridging 5-nitroisophthalate (NIPH) ligands and two isonicotinate (IN) anions, while the other type of CoII ion binds with one N atom and one carboxylate O atom from two IN anions, two carboxylate O atoms from two different NIPH anions and one ligated water molecule, displaying a distorted square-pyramidal coordination geometry. Three adjacent CoII ions are bridged by six carboxylate groups from four NIPH ligands and two IN anions to form a linear trinuclear secondary building unit (SBU). Every trinuclear SBU is linked to its nearest neighbours in the ab plane, resulting in a two-dimensional layer-like structure perpendicular to the c axis. Along the a-axis direction neighbouring molecules are connected through carboxylate and pyridyl units of the IN anions, along the b axis through carboxylate groups of the NIPH ligands. The H atoms of one free water molecule are disordered in the crystal in a 1:1 ratio. Typical O—H⋯O hydrogen bonds are observed in the lattice, which include the following contacts: (a) between coordinated water molecules and carboxylate O atoms of the NIPH anions, (b) between lattice water molecules and carboxylate O atoms of the NIPH anions, and (c) between coordinated and lattice water molecules. These intermolecular hydrogen bonds connect the two-dimensional layers to form a three-dimensional supramolecular structure.


Experimental
Crystal data [Co 3 (C 6 H 4 Table 1 Hydrogen-bond geometry (Å , ). Over the past decades, rational design and construction of metal coordination polymers with aromatic carboxylates have become an attractive area in coordination and supramolecular chemistry, due to the fascinating network topologies they exhibit (Natarajan & Mahata, 2009) and due to industrially focused applications in gas storage, adsorption and separation (Ma et al., 2009), nonlinear optical devices (Zang et al., 2006), and fluorescence (Jiang et al., 2010), etc. Due to versatile coordination modes and easy formation of secondary building units, 5-nitroisophthalate (NIPH) has been widely employed to construct coordination polymers (Chen et al., 2010;Du et al., 2008;Sun et al., 2010).
Most cobalt complexes with 5-nitroisophthalate (NIPH) and aromatic N-donor coligands (pyridine, bipyridine, and imidazole) possess low-dimensional structure characteristics, namely, ladder, loop-like chain, zigzag chain, layer, and grid, etc (Chen et al., 2006;Du et al., 2008;Luo et al., 2003). Cobalt complexes based on NIPH ligand and other carboxylates have been less developed . In this work, we selected isonicotinic acid (HIN) as the coligand based on the following considerations: (1) it possesses the bifunctional bridging groups with both oxygen and nitrogen donors as a potential linkers and (2) it can adopt various coordination modes in high-dimensional heterometallic frameworks (Amo-Ochoa et al., 2010). Herein, synthesis and crystal structure of a new cobalt compound is presented, which was prepared by hydrothermal reaction of Co(CH 3 COO) 2 .4 H 2 O with 5-nitroisophthalic acid and isonicotinic acid.
The title compound exhibits a two-dimensional layer-like framework. As illustrated in Fig.1 can be seen as four-connected nodes and the organic ligands (the NIPH and IN anions) act as two-connected rods. On the basis of this simplification, this two-dimensional structure can be described as a (4,4)-topological network.
There are multiple O-H···O hydrogen bonds in the complex, which include the following types of contacts: (a) between coordinated water molecule and carboxylate oxygen atoms of the NIPH anions [O···O, 2.820 (3)  In summary, a new (4, 4)-two-dimensional layer-like polynuclear Co II coordination polymer was constructed by hydrothermal reaction between Co(II) ions and mixed carboxylate ligands, which is further extended to a three-dimensional supramolecular network through intermolecular hydrogen bonding. (w).

Refinement
The disordered hydrogen atoms (H3W and H4W) of lattice water molecule O2W are, due to a close contact of O2W with one of its symmetry equivalent counterparts across an inversion center, disordered in a 1:1 mode in the crystal. In one of the alternative orientations O2W is hydrogen bonding via H3WB to O2W ii and via H4WB to both O2 v and O5 vi . In the other orientation, with O2W acting as the acceptor of a hydrogen bond from O2W ii , the water molecule hydrogen bonds via H3WA and H3WB to O6 vi and O2 v (see Table 1 for symmetry operators). All hydrogen atoms of water molecules were located in electron difference density Fourier maps. The disordered hydrogen atoms (H3W and H4W) of lattice water molecule O2W were refined in a 1:1 disordered mode with O-H distance restraints of 0.85 (2) Å, and H···H

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. All H atoms are drawn as spheres of arbitrary radii.

tetrahydrate]
Crystal data  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.