Di-μ-sulfato-bis[diaqua(1H-imidazo[4,5-f][1,10]phenanthroline)nickel(II)] dihydrate

In the title compound, [Ni2(SO4)2(C13H8N4)2(H2O)4]·2H2O, the complete dimeric complex is generated by an inversion center. The NiII atoms are octahedrally coordinated by two N atoms from one 1H-imidazo[4,5-f][1,10]phenanthroline (IP) ligand and two O atoms from two adjacent sulfate ions forming the equatorial plane, with two coordinated water molecules in the axial sites. Both of the sulfate ions act as bidentate-bridging ligands connecting the two NiII ions, thus generating a binuclear complex. In the crystal structure, O—H⋯O and O—H⋯N hydrogen bonds involving the coordinated and uncoordinated water molecules and N—H⋯O links lead to the formation of a two-dimensional sheet structure developing parallel to (010). Weak π–π stacking interactions [centroid–centroid separation = 3.613 (2) Å] between the IP ligands also occur.

In the title compound, [Ni 2 (SO 4 ) 2 (C 13 H 8 N 4 ) 2 (H 2 O) 4 ]Á2H 2 O, the complete dimeric complex is generated by an inversion center. The Ni II atoms are octahedrally coordinated by two N atoms from one 1H-imidazo[4,5-f][1,10]phenanthroline (IP) ligand and two O atoms from two adjacent sulfate ions forming the equatorial plane, with two coordinated water molecules in the axial sites. Both of the sulfate ions act as bidentate-bridging ligands connecting the two Ni II ions, thus generating a binuclear complex. In the crystal structure, O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds involving the coordinated and uncoordinated water molecules and N-HÁ Á ÁO links lead to the formation of a two-dimensional sheet structure developing parallel to (010). Weakstacking interactions [centroid-centroid separation = 3.613 (2) Å ] between the IP ligands also occur.

Di
The center of the dimeric complex is located on an inversion center. Each Ni II atom is octahedrally coordinated by two N atoms from one IP ligand and two oxygen atoms from two adjacent sulfate ions forming the equatorial plane, whereas axial positions are occupied by two oxygen atoms of coordinated water molecules ( Figure 1). Taking account of these two irregular bond angles [168.06 (11)° for O3-Ni-N1 and 172.06 (12)° for O1W-Ni-O2W], the geometry of copper center is best described as a distorted octahedron (Table 1). The distances of Ni-N and Ni-O bonds are similar to those of related complexes (An et al., 2007;Xu et al., 2003). Both of sulfates taking as bidentated-bridging mode connect Ni II ions, generating a binuclear complex. The separation of Ni-Ni distance is 5.16 (6) Å, which is markedly shorter than the corresponding Ni-Ni distance of 6.132 (4)Å in Ni II analog (Gu et al., 2004). Each IP molecule only binds to Ni II center via two nitrogen atoms from two pyridine rings. The IP ligand does not show any abnormal characteristic, with its four bound rings being basically coplanar. One type of π-π stacking interaction between pyridine and imidazole ring from two adjacent IP ligands. The centroid to centroid distances for the further π-π stacking interaction is 3.613 (2)Å [symmetry code = x, -y, z -1/2], thus indicating weak π-π stacking interaction (Fig. 2).
Intramolecular hydrogen bonds between coordinated water molecules and oxygen atoms from sulfate ions may contribute to its stability (Table 2). Fruthermore, the linking agent is the extensive hydrogen-bonding network involving all the available water molecules and, together with some N atoms of the organic ligand, resulting in the formation of a two-dimensionnal network ( Figure 2). For example, the lattice water molecule (O3W) is hydrogen bonded to the O2 and O4 atoms of two related sulfates groups, so generating a R 4 2 (8) motif (Bernstein et al., 1995) (Figure 2).

S2. Experimental
IP (0.031 g, 0.18 mmol) and NiSO 4 (0.28 g, 0.11 mmol) were added to acetonitrile (15 ml), the mixture was heated for ten hours under reflux conditions. The resultant solution was then filtered to give a pure solution which was infiltrated by diethyl ether freely in a closed vessel: three weeks later, green blocks of (I) were collected.

Figure 1
View of (I) with displacement ellipsoids drawn at the 30% probability level.  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.