Diaquabis(1,1,4-trimethylthiosemicarbazide)- nickel(II) dinitrate

The determination of the crystal structure of the title compound, [Ni(C4H11N3S)(2)(H2O)(2)](NO3)(2), reveals a distorted octahedral geometry around the Ni centre, which lies on an inversion centre, with water molecules occupying the axial positions. Hydrogen bonding is observed between the 1,1,4-trimethylthiosenticarbazide NH groups and the nitrate anions, and also between the coordinated water molecules and the anions.


Comment
The title compound, (I), was formed as part of our investigations into the crystal engineering of nickel bis(thiosemicarbazide) dicarboxylates, in which the Ni-containing cations and dicarboxylate anions are linked through chargeaugmented hydrogen bonds (Allen et al., 1999;Burrows et al., 2000Burrows et al., , 2004)).
The asymmetric unit in (I) consists of a nickel(II) centre, to which is co-ordinated one 1,1,4-trimethylthiosemicarbazide ligand, via the S and dimethylamine N atoms, and one water molecule.A nitrate anion completes the asymmetric unit.The remainder of the molecular unit is generated by transformation through a crystallographic inversion centre, on which the metal is located.The structure of (I) is shown in Fig. 1.
The geometry around the Ni centre is distorted octahedral, with bond angles ranging from 82.95 (3) to 97.05 (3) .Each nitrate anion forms hydrogen bonds to three separate Ni II species.The presence of parallel N-H donors (D) on the 1,1,4-trimethylthiosemicarbazide ligand and parallel O acceptors (A) on the nitrates facilitates the formation of DD:AA interactions, graph set R 2 2 (8) (Etter, 1990), which link the cations and anions.Each of the remaining AA faces of the nitrates is involved in a single O-HÁ Á ÁO interaction with coordinated water molecules The combination of the DD:AA hydrogen bonds with one such O-HÁ Á ÁO interaction results in the formation of 'slipped' hydrogen-bonded chains along the crystallographic a axis, as illustrated in Fig. 2. Within the chains are hydrogenbonded rings of graph set R 2 4 (16).The 'slipped' description of these chains is relative to chains observed in networks formed from reactions with linear dicarboxylates, such as fumarate or terephthalate, where the cations are linked solely via DD:AA interactions to the anion carboxylate groups (Allen et al., 1999;Burrows et al., 2004).The formation of the three-dimensional structure is faciliated by the second O-HÁ Á ÁO interaction, graph set R 5 6 (23), illustrated in Fig. 3. Thus all of the hydrogenbond donors are satisfied.By contrast, not all of the hydrogenbond acceptors available to the O atoms of the nitrate anion are utilized, O2 being the only atom to form two interactions, with atoms H3 and H4B.In the cases of atoms O1 and O3, only one hydrogen bond is formed.Details of the hydrogen bonding are given in Table 1.

Experimental
Equimolar aqueous solutions of bis(1,1,4-trimethylthiosemicarbazide)nickel(II) nitrate (Burrows et al, 2004) and the sodium salt of either succinic or itaconic acid were allowed to evaporate slowly over a period of two weeks.In both cases, the formation of green crystals of (I) resulted.Analysis by single-crystal X-ray diffraction revealed the identity of the products and confirmed that the dicarboxylate was not incorporated into the crystalline material in either case.

Data collection
Nonius KappaCCD area-detector diffractometer ' and !scans Absorption correction: multi-scan (Blessing, 1995) T min = 0.697, T max = 0.697 15 566 measured reflections 2317 independent reflections 2203 reflections with I > 2(I) The positions of the water, amino and amido H atoms were located in a difference map and refined isotropically, subject to a distance restraint of 0.89 (2) A ˚. H atoms on all C atoms were included in calculated positions, constrained to an ideal geometry with C-H distances of 0.98 A ˚and with U iso (H) = 1.5U eq (C).Each group was allowed to rotate freely about its C-N bond.
The EPSRC is thanked for funding.

Special details
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.

Figure 1 A
Figure 1 A view of the molecule of (I), showing the atom-labelling scheme.Displacement ellipsoids are drawn at the 30% probability level and H atoms are represented by small spheres.[Symmetry code: (i) x + 1, y + 1, z + 1.]

Figure 3
Figure 3Hydrogen-bond interactions (dashed lines) in the formation of the R 5 6 (23) graph set.