Tetraquabis(5-fluorosaccharinato)nickel(II)

In the centrosymmetric title complex, [Ni(C7H3FNO3S)2(H2O)4], the NiII atom exhibits a slightly distorted trans-NiN2O4 octahedral coordination. The nitrogen donors are provided by two 5-fluorosaccharinate ligands and the oxygen donors are provided by four water molecules. The crystal structure features O—H⋯O and bifurcated O—H⋯(F,O) hydrogen bonds, the latter involving the F atom of the 5-fluorosaccharinate ligand.

In the centrosymmetric title complex, [Ni(C 7
The choice of fluorinated saccharinates stems from the novel types of interactions in which carbon bound fluorine may participate (Plenio, 1997). Our initial studies have led to the preparation of the title nickel complex (I) that contains 5-fluorosaccharinate (5-fsacch) as an anionic ligand.
The crystal structure of (I) consists of monomeric Ni(5-fsacch) 2 (H 2 O) 4 molecular units, as shown in Figure 1. The Ni II atom, which lies on an inversion center, is octahedrally coordinated by a pair of trans N atoms from two equivalent 5-fsacch ligands, and by four O atoms from two pairs that contain equivalent water molecules ( Table 1).
The average Ni-N and Ni-O bond distances in (I) are 2.086 Å (1) and 2.076 (2) Å, respectively. By comparison to a similar structure, in (I) the average Ni-N distance is shorter whereas the average Ni-O distance is longer than their corresponding values in the previously reported nickel saccharinate complex, namely Ni(sacch) 2 (H 2 O) 4 .2(H 2 O) (II) (sacch = saccharinate) (Haider et al., 1983). In (II) the average Ni-N distance is 2.154 (1) Å, while the average Ni-O distance is 2.069 (2) Å. All angles in (I) are normal and are comparable to their corresponding values in (II).
The crystal structure in (I) features extensive hydrogen bonding (Table 2) in which both the carbonyl and sulfonyl O atoms of 5-fsacch, as well its carbon bound fluorine, act as hydrogen bond acceptors for the water H atoms, as shown in Fig. 2. This hydrogen bonding scheme is different from that of (II) for two major reasons. First, there is the presence of the previously mentioned C-F···H hydrogen bonding in (I) that is obviously absent in (II). Second, in (II) there exists hydrogen bonding involving lattice water molecules, which because of their absence in (I) precludes such interactions.

Experimental
All chemicals and solvents were purchased from commercial sources and used without further purification. The synthesis of sodium 5-fluorosaccharinate will be described elsewhere. A 10 ml solution of sodium 5-fluorosaccharinate (0.10 mmol) was added dropwise to a 10.0 ml solution of nickel(II) chloride tetrahydrate (0.050 mmol). Light blue, block-like crystals of (I) were formed in about three weeks by slow evaporation after the solution volume was reduced to 5.0 ml under ambient conditions.

Refinement
Hydrogen atoms bonded to carbon were placed in geometrically idealized positions and included as riding atoms with refined isotropic displacement parameters. The water H atoms were located in difference maps and refined freely.

Tetraquabis(5-fluorosaccharinato)nickel(II)
Crystal data [Ni(C 7  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 Rfactors(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.