Tris(oxamide dioxime-κ2 N,N′)nickel(II) sulfate pentahydrate

The asymmetric unit of the title compound, [Ni(C2H6N4O2)3]SO4·5H2O, contains two complex cations, two sulfate anions and ten lattice water molecules. In both independent cations, the central NiII ion adopts a distorted octahedral coordination involving six imino N atoms of three bidentate oxamide dioxime ligands. The bulk structure is achieved by a three-dimensional network of O—H⋯O and N—H⋯O hydrogen bonds which interlink the ionic partners and some water molecules in such a manner that the lattice framework thus formed defines channels parallel to [100]. The other water molecules are lodged inside these channels. Two of the ten water molecules in the asymmetric unit are disordered over three sites, in 0.356 (3):0.324 (5):0.320 (5) and 0.247 (3):0.293 (6):0.460 (6) occupancy ratios, and one O atom of a sulfate ion is also disordered over two sites, with occupancies of 0.621 (5) and 0.379 (5).

The asymmetric unit of the title compound, [Ni(C 2 H 6 N 4 O 2 ) 3 ]-SO 4 Á5H 2 O, contains two complex cations, two sulfate anions and ten lattice water molecules. In both independent cations, the central Ni II ion adopts a distorted octahedral coordination involving six imino N atoms of three bidentate oxamide dioxime ligands. The bulk structure is achieved by a threedimensional network of O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds which interlink the ionic partners and some water molecules in such a manner that the lattice framework thus formed defines channels parallel to [100]. The other water molecules are lodged inside these channels. Two of the ten water molecules in the asymmetric unit are disordered over three sites, in 0.356 (3):0.324 (5):0.320 (5) and 0.247 (3):0.293 (6):0.460 (6) occupancy ratios, and one O atom of a sulfate ion is also disordered over two sites, with occupancies of 0.621 (5) and 0.379 (5).
shown to be one of the few well documented examples of solid materials containing water cluster patterns of category T according to the classification of Infantes & Motherwell (2002). Most importantly, such nano-channelled frameworks enclosing infinite water tapes or water filaments (Martin et al., 2007) provide excellent template systems to probe the feasibility of the fascinating prospect of one dimensional proton conduction in solids (one-dimensional-PCS) (Bélombé et al., 2006(Bélombé et al., , 2007Rashid et al., 2001;Akutsu-Sato et al., 2005). Herein we report the crystal structure of the title compound, (I), as yet another example of a closely related solid material encapsulating water cluster patterns that fit into the Infantes-Motherwell classification. Fig. 1 depicts the ionic constituents of (I). The helical pseudo-octahedral coordination geometry of the complex cation, [Ni(H 2 oxado) 3 ] 2+ (H 2 oxado iso xamide dioxime), is similar to the usual chiral geometries, and the bond lengths and angles compare within experimental error with those reported previously (Endres & Jannack, 1980;Bélombé et al., 2006). The asymmetric unit of (I) contains two complex cations, two sulfate anions and ten lattice water molecules. The skeletal lattice framework of (I) is constructed by the ionic partners, and by those of the crystal waters (dubbed "skeletal" waters), all of which are held together by a three-dimensional network of O-H···O and N-H···O hydrogen bonds as shown in Fig. 2. It is obvious from this figure that the major part of the crystal waters is concentrated along the elliptic nanochannels (ca 4.68 Å wide and 14.61 Å long). These "central" water molecules are linked via hydrogen bonds (Table 1)   In other words, these lattice components are ordered along the stacking direction strictly in an eclipsed sequence relative to one another, hence leading to an unusually short spacing of 2.0 Å between the O atoms of neighboring water molecules.
The geometric parameters within the coordination spheres of the crystallographically independent [Ni(H 2 oxado) 3 ] 2+ complexes are closely comparable. So are also those of the sulfate ions, despite the fact that one O atom, viz. O2, in the SO 4 2ion, is disordered (apparently along the bonding axis) over two sites. This disorder, obviously, leads to the observation of the two bond lengths, S2-O2A = 1.678 (7) Å and S2-O2B = 1.446 (4) Å, with an average of S2-O2 =1.562 Å.
As shown in Fig. 2, four of the twenty crystal waters in the unit cell of (I) are lodged inside the "walls" of the host or skeletal lattice, and are involved in O-H···O bridgings with the O atoms of the SO 4 2ions or with the -OH groups of the oxamide dioxime ligands. Hence, these water molecules (O1w and O3w) are called "skeletal" waters. The molecules sup-2 of water containing the atoms O2W, O4W, O5W and O6W are positioned at the periphery of the channel walls, due to their involvement in hydrogen bonding with the "external" O atoms of the sulfate ions and with the amino groups of the organic ligands. They are, therefore, termed "peripheral" waters. Some of the water molecules containing the atoms O7W, O8W, O9W and O10W are lodged around the central axes of the lattice channels and dubbed "central" waters form together with the "skeletal" water molecules discrete linear pentamers and involve the disordered molecules mentioned above. All the water molecules in this structure lie with their molecular planes parallel to the bc plane, i.e. perpendicular to the [100] stacking direction. Within separate stacks, however, the group orientations of these molecules with respect to the improper axis of rotation (2) are different.
It is worth noting finally, that compound (I) represents a highly promising precursor system in the context of our ongoing metathetic syntheses of nanochannelled metal organic frameworks (MOFs) conceived as potential one dimensional proton conducting solids (one-dimensional-PCS) (Bélombé et al., 2006(Bélombé et al., , 2007.

Experimental
Commercial NiSO 4 .6H 2 O and freshly prepared oxamide dioxime (Ephraim, 1889;Nenwa, 2004) were mixed together in a ratio of 0.53 g (2 mmol): 0.71 g (6 mmol) and dissolved in warm H 2 O (323 K, 40 ml) acidified with 1 drop of concentrated H 2 SO 4 . The resulting indigo-blue solution was stirred for 2 h and filtered. The filtrate collected in an open dish was evaporated completely over a few days in a hood. Prismatic violet crystals were deposited, contaminated with a slight amount of starting NiSO 4 which was washed off with H 2 O (3 ml) and separated by filtration. After drying for 48 h between filter papers at ambient temperature, 1.1 g (~92% yield) of crystalline material was obtained and used for X-ray analysis.

Refinement
One of the sulfate O atoms, O2, is disordered over two positions (O2A and O2B), with refined occupancies of 0.621 (5) and 0.379 (5). Two water molecules are disordered over three sites ( and refined as riding on their parent atoms, with U iso (H) = 1.2U eq (N) and 1.5U eq (O). The highest peak and deepest hole in the final difference map are 1.47 Å from atom O12W and 1.45 Å from S1, respectively. The H atoms on the disordered water molecules could not be located.

Special details
Geometry. All e.s. 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.