catena-Poly[[[diaquanickel(II)]-di-l- glycine] dichloride]

In the polymeric title complex, {[Ni(C2H5NO2)2(H2O)2]Cl2}n, the Ni atom lies on an inversion center and is in a distorted octahedral NiO6 configuration, with four carboxylate O atoms from four zwitterionic glycine molecules forming the equatorial plane and two water O atoms occupying the axial positions. The Cl counterions lie in the interstices. The Ni complexes are linked into polymeric sheets parallel to the bc plane. These sheets are then further connected into a threedimensional network by O—H O, O—H Cl and N— H Cl hydrogen bonds, together with weak C—H O interactions.


Experimental
Crystal data [Ni(C 2 H 5

catena-Poly[[[diaquanickel(II)]-di-µ-glycine] dichloride]
Cynn Dee Ch'ng, Siang Guan Teoh, Suchada Chantrapromma, Hoong-Kun Fun and Siu Mun Goh S1. Comment Nickel plays versatile and sometimes controversial roles in living systems as the biological effects of nickel are closely related to their chemical nature (Lancaster, 1998). Nickel complexes have been the subject of intense study in recent years mostly due to their biological significance such as antitumor and antibacterial activities (Matkar et al., 2006, Kasuga et al., 2001. Several nickel complexes have been found to inhibit proliferation of diverse cancer cells (Ferrari et al., 2002;Liang et al., 2004, Matkar et al., 2006. Based on the significant biological role played by nickel complexes, we have synthesized several nickel complexes and herein, we report the preparation and crystal structure of the title complex (Fleck & Bohatý, 2005).
In the molecular structure of the polymeric title complex, {[Ni(C 2 H 5 NO 2 ) 2 (H 2 O) 2 ]Cl 2 } n ( Fig. 1), the Ni II lies on an inversion center and has an NiO 6 coordination environment. The coordination sphere of the Ni II ion is a slightly distorted octahedron consisting of the O 4 coordination plane of the four glycine zwitterions (coordinating through one carboxylic O atom from each glycine zwitterion) and the two axially bound water molecules. The Ni-O(glycine) distances [Ni1-O1 = 2.0398 (7) Å and Ni1-O2 = 2.0753 (7) Å] and Ni-O(water) distances [2.0413 (8) Å] are quite similar to those observed in another closely related Ni II complex which are in the range 2.033 (2)-2.086 (2) Å (Fleck & Bohatý, 2005) and are also similar to the Ni-O distances observed in ionic compounds (Shannon, 1976). Other bond lengths and angles observed in the structure are also normal (Allen et al., 1987). In the glycine zwitterion, the carboxylate group is slightly twisted from the C1/C2/N1 plane with torsion angles O2-C1-C2-N1 = 167.23 (9) (Table 1) into polymeric sheets along the [010] direction (Fig. 3). These sheets are furthered connect to the interstial Clions by O-H···Cl and N-H···Cl hydrogen bonds to the water molecules and amino groups, respectively forming a three-dimensional network ( Table 1). The crystal is stabilized by O-H···O, O-H···Cl and N-H···Cl hydrogen bonds, together with weak C-H···Cl interactions (Table 1).

S2. Experimental
The title complex was synthesized by heating under reflux a 1:2 molar mixture of nickel(II) chloride hexahydrate, NiCl 2 .6H 2 O (0.2377 g, 1 mmol) and glycine (0.1503 g, 2 mmol) in water (30 ml) for 3 h. A green transparent solution was obtained and allowed to cool to room temperature. Green single crystals of the title complex suitable for X-ray structure determination were obtained after a few days of evaporation. Mp. 442-443 K.

S3. Refinement
H atoms were located in difference maps and refined isotropically. The highest residual electron density peak is located at 1.74 Å from O1W and the deepest hole is located at 0.72 Å from Ni1.

catena-Poly[[[diaquanickel(II)]-di-µ-glycine] dichloride]
Crystal data [Ni(C 2 H 5  Special details Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.