catena-Poly[[[diaqua(di-2-pyridylamine-κ2 N,N′)nickel(II)]-μ-fumarato-κ2 O 1:O 4] tetrahydrate]

In the crystal structure of the title compound, {[Ni(C4H2O4)(C10H9N3)(H2O)2]·4H2O}n, zigzag chains are built up from cis-[Ni(dpya)(H2O)2]2+ cations (dpya is di-2-pyridylamine) linked by bis-monodentate coordinated bridging fumarate ligands. The NiII atom is coordinated by one chelating dpya ligand, two aqua ligands in trans positions and two monodentate fumarate ligands in cis positions in the form of a deformed octahedron. The water molecules, O atoms of the fumarate carboxylate groups and the amine group of the dpya ligand are involved in an extended network of intra- and intermolecular O—H⋯O hydrogen bonds. Moreover, π–π interactions between the pyridine rings of the dpya ligand contribute to the stability of the structure. Two of the five uncoordinated water molecules are half-occupied.

In the crystal structure of the title compound, { [Ni(C 4 H 2 O 4 )-(C 10 H 9 N 3 )(H 2 O) 2 ]Á4H 2 O} n , zigzag chains are built up from cis-[Ni(dpya)(H 2 O) 2 ] 2+ cations (dpya is di-2-pyridylamine) linked by bis-monodentate coordinated bridging fumarate ligands. The Ni II atom is coordinated by one chelating dpya ligand, two aqua ligands in trans positions and two monodentate fumarate ligands in cis positions in the form of a deformed octahedron. The water molecules, O atoms of the fumarate carboxylate groups and the amine group of the dpya ligand are involved in an extended network of intra-and intermolecular O-HÁ Á ÁO hydrogen bonds. Moreover,interactions between the pyridine rings of the dpya ligand contribute to the stability of the structure. Two of the five uncoordinated water molecules are half-occupied.
The heteroleptic coordination sphere of the Ni II atom beside two fumarato ligands is completed by one bidentate chelate bonded dpya ligand and two aqua ligands placed in trans positions ( Fig. 1). As can be seen from the values of the bond angles (Table 2), the octahedron around the Ni II atom is somewhat deformed. The mean Ni-N bond lengths is 2.059 (3) (Lu et al., 2001) and [Ni(fumarate) (Xie et al., 2003).
The geometric parameters associated with dpya and aqua ligands are normal [Lu et al., 2001;Huang et al., 2006]. There are five general crystallographically distinct positions in the unit cell occupied by not coordinated water molecules. Among these two positions (O8 and O9) are partially occupied with s.o.f. put to half as required by proximity of symmetry (-1) related positions of O8 and proximity of the O9 water oxygen to O8, respectively. The water molecules along with the not coordinated oxygen atoms from carboxylate groups are involved in hydrogen bonds of the O-H···O type; some of these HBs are intramolecular (Fig. 2, Table 3). In the hydrogen bonding system is involved also the dpyaligand through N-H···O type hydrogen bond (Fig. 2, Table 3). Between pairs of dpya ligands π-π interactions operate which further stabilize the structure (Fig. 3). The Cg1···Cg2 i distance (symmetry code (i) -x, 0.5+y, 0.5-z, where Cg1 and Cg2 are centroids of the rings (N1/C1-C5) and (N2/C6-C10), respectively) between the aromatic rings is 3.723 (1) Å; these interactions links the {Ni(dpya)} units into layers lying in the bc plane.

Experimental
With the exception of dpya, which was of purum quality, the other reagents were of analytical grade and all were used without further purification. The title complex was prepared using the following procedure. An aqueous solution of supplementary materials sup-2 Ni(CH 3 COO) 2 .4H 2 O(248 mg, 1 mmol in 30 cm 3 H 2 O) and a solution of 171 mg (1 mmol) dpya ligand in 40 cm 3 of EtOH (96 %vv) were mixed firstly. To the formed azure hot (90 °C) solution solid fumaric acid (116 mg, 1 mmol) and aqueous solution of NaOH (2 cm 3 , 1 M) were added successively and the reaction mixture was stirred 60 minutes at 90 °C. The formed blue solution was left to evaporate slowly at room temperature. Within a week, in one of several reaction attempts, few blue plates of the title compound appeared. One crystal was picked off for X-ray structure analysis. After disturbing the mother liquor immediate jellification started which prevented isolation of further crystals.

Figures
Crystal data [Ni(C 4

Special details
Experimental. Absorption correction: a grid of 8 x 8 x 8 = 512 sampling points was used 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.