Poly[[diaquadi-μ-dicyanamido-nickel(II)] bis(pyridinium-4-olate)]

The title compound, {[Ni(C2N3)2(H2O)2]·2C5H5NO}n, is a centrosymmetric two-dimensional coordination polymer with a layer (4,4) network structure. The asymmetric unit is compossed of an NiII atom, which sits on an inversion center, a μ-1,5-bridging dicyanamide anion, a water molecule, and a free 4-hydroxypyridine molecule present in the zwitterionic pyridinium-4-olate form. The NiII atom is coordinated in a slightly distorted N4O2 octahedral geometry by four bridging dicyanamide ligands and two trans water molecules. In the crystal, the two-dimensional networks are linked via N—H⋯O and O—H⋯O hydrogen bonds, forming a three-dimensional network.

The title compound, {[Ni(C 2 N 3 ) 2 (H 2 O) 2 ]Á2C 5 H 5 NO} n , is a centrosymmetric two-dimensional coordination polymer with a layer (4,4) network structure. The asymmetric unit is compossed of an Ni II atom, which sits on an inversion center, a -1,5-bridging dicyanamide anion, a water molecule, and a free 4-hydroxypyridine molecule present in the zwitterionic pyridinium-4-olate form. The Ni II atom is coordinated in a slightly distorted N 4 O 2 octahedral geometry by four bridging dicyanamide ligands and two trans water molecules. In the crystal, the two-dimensional networks are linked via N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, forming a threedimensional network.

Poly[[diaquadi-µ-dicyanamido-nickel(II)] bis(pyridinium-4-olate)]
Ling-Ling Zheng S1. Comment In recent years, coordination polymers involving dicyanamide (dca, N(CN) 2 ) have attracted a great deal of attention, not only for their interesting extended architectures but also for their magnetic properties, especially compounds in the M(dca) 2 series (Manson et al., 1998;Batten et al., 1998;Manson et al., 2001). The introduction of coligands has led to dramatic modifications of the crystal structures and magnetic properties (Batten et al., 2003;Miller et al., 2001). When 4hydroxypyridine was used as a coligand, the title complex was obtained.
In the crystal structure, the µ-1,5 dca ligand links neighboring Ni II atoms, forming a two-dimensional (4,4) network ( Fig. 2). This resembles the situation in [Mn(dca) 2 (4-cyanopyridine) 2 ] n (Dalai et al., 2002) and [Co 2 (dca) 4 (4-cyanopyridine) 4 ] n (Du et al., 2006), but the structures are not isomorphous and here the co-ligands are coordinated to the metal atoms. However, as in the title compound, the layer-like structures are linked through hydrogen bonding interactions. In the title compound this involves the water molecules and the pyridinium-4-olate groups (Table 1).

S2. Experimental
To a methanol solution (20 mL) of nickel nitrate (0.145 g, 0.5 mmol) and 4-hydroxypyridine (0.095 g, 1.0 mmol), a water solution (5 ml) of dca (0.089 g, 1.0 mmol) was added slowly with stirring over 30 min at rt. The clear solution obtained was filtered and the filtrate left to evaporated at rt. After a few days, green single crystals were obtained (yield: 5%).

S3. Refinement
The NH and water H-atoms were located in difference electron-density maps and freely refined: N-H = 0.858 (16)   A view of the octahedral coordination geometry of the nickel(II) atom in the title compound. The coligand, present in the 4-pyridium-olate form, has been omitted for clarity. Displacement ellipsoids are shown at the 50% probability level.

Figure 2
A partial view of the two-dimensional (4,4) network in the title compound.

Poly[[diaquadi-µ-dicyanamido-nickel(II)] bis(pyridinium-4-olate)]
Crystal data [Ni(C 2  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 Ni1