Tris(1,10-phenanthroline-κ2 N,N′)nickel(II) hexaoxido-μ-peroxido-disulfate(VI) N,N-dimethylformamide disolvate monohydrate

The asymmetric unit of the title complex, [Ni(C12H8N2)3]S2O8·2C3H7NO·H2O, consists of a complex [Ni(phen)3]2+ cation and one isolated pds anion, with two DMF molecules and one water molecule as solvates (where phen is 1,10-phenanthroline, pds is the hexaoxido-μ-peroxoido-disulfate dianion and DMF is dimethylformamide). The [Ni(phen)3]2+ cation is regular, with an almost ideal NiII bond-valence sum of 2.07 v.u. The group, as well as the water solvent molecule, are well behaved in terms of crystallographic order, but the remaining three molecules in the structure display different kinds of disorder, viz. the two DMF molecules mimic a twofold splitting and the pds anion has both S atoms clamped at well-determined positions but with a not-too-well-defined central part. These peculiar behaviours are a consequence of the hydrogen-bonding interactions: the outermost SO3 parts of the pds anion are heavily connected to the complex cations via C—H⋯O hydrogen bonding, generating an [Ni(phen)3]pds network and providing for the stability of the terminal pds sites. Also, the water solvent molecule is strongly bound to the structure (being a donor of two strong bonds and an acceptor of one) and is accordingly perfectly ordered. The peroxide O atoms in the pds middle region, instead, appear as much less restrained into their sites, which may explain their tendency to disorder. The cation–anion network leaves large embedded holes, amounting to about 28% of the total crystal volume, which are occupied by the DMF molecules. The latter are weakly interacting with the rest of the structure, which renders them much more labile and, accordingly, prone to disorder.

The asymmetric unit of the title complex, [Ni(C 12 H 8 N 2 ) 3 ]-S 2 O 8 Á2C 3 H 7 NOÁH 2 O, consists of a complex [Ni(phen) 3 ] 2+ cation and one isolated pds anion, with two DMF molecules and one water molecule as solvates (where phen is 1,10phenanthroline, pds is the hexaoxido--peroxoido-disulfate dianion and DMF is dimethylformamide). The [Ni(phen) 3 ] 2+ cation is regular, with an almost ideal Ni II bond-valence sum of 2.07 v.u. The group, as well as the water solvent molecule, are well behaved in terms of crystallographic order, but the remaining three molecules in the structure display different kinds of disorder, viz. the two DMF molecules mimic a twofold splitting and the pds anion has both S atoms clamped at well-determined positions but with a not-too-well-defined central part. These peculiar behaviours are a consequence of the hydrogen-bonding interactions: the outermost SO 3 parts of the pds anion are heavily connected to the complex cations via C-HÁ Á ÁO hydrogen bonding, generating an [Ni(phen) 3 ]pds network and providing for the stability of the terminal pds sites. Also, the water solvent molecule is strongly bound to the structure (being a donor of two strong bonds and an acceptor of one) and is accordingly perfectly ordered. The peroxide O atoms in the pds middle region, instead, appear as much less restrained into their sites, which may explain their tendency to disorder. The cation-anion network leaves large embedded holes, amounting to about 28% of the total crystal volume, which are occupied by the DMF molecules. The latter are weakly interacting with the rest of the structure, which renders them much more labile and, accordingly, prone to disorder.

N,N-dimethylformamide disolvate monohydrate Miguel Angel Harvey, Sebastián Suarez, Fabio Doctorovich and Ricardo Baggio Comment
The binding behavior of peroxodisulfate (pds) towards a number of transition metal metal cations (Cd(II), Hg(II), Cu(II), Mn(III), Zn(II), Ag(II)) has been well documentated in the literature Youngme et al., 2007;Manson et al., 2009., Blackman et al., 1991Harrison et al., 1980;Harvey et al., 2011, and references therein) but its rather elusive character as a ligand has also been evidenced in many other structures where the anion wouldn't coordinate, thus acting as a balancing counterion or, in occasions, just as a neutral co-crystallization agent in the form of peroxodisulfuric acid. Among the cations being reluctant towards pds coordination it must be mentioned the case of Cd (Harvey et al., 2005); Co(III) (Singh et al., 2009); Zn(II) (Harvey et al., 2004), Cu(II) (Youngme et al., 2008), Mn(IV) (Baffert et al., 2009), and even the more stringent case of Ni, of which no crystal structure with pds had been reported up to date: in particular, all our previous experiments aimed to produce such a complex had so far been unsuccessful. Therefore, we present herein the first Ni II -pds structure, where the anion did not enter into the Ni II coordination sphere The asymmetric unit of the complex consists of a globular [Ni(phen) 3 ] 2+ nucleus (Fig 1a), one isolated pds anion, two DMF and one water molecules as solvates.
The [Ni(phen) 3 ] 2+ cationic centre is absolutely regular and does not differ from the more than 100 similar groups which appear in the v5.33 version of the CSD (Allen, 2002). The Bond Valence Sum for the Ni II cation in the title compound (Brown and Altermatt, 1985) is almost ideal (2.07 v.u.), and the regularity in the NiN 6 coordination sphere is shown by the tight range of similar parameters (d(Ni-N): 2.087 (3)-2.100 (3)Å; N-Ni-N cis angles: 79.04 (12)-79.71 (12)° (chelating); 92.79 (12)-96.46 (12)° (non-chelating); N-Ni-N trans angles: 172.06 (12)-170.20 (12)°), but it can perhaps be best assessed by the geometric disposition of the three Bond Valence Vectors associated to the three chelating phen ligands (for details, see Harvey et al., 2006) which define an absolute planar array (sum of internal angles: 360.00°), and a theoretical (almost nil) resultant vector ( 0.017 v.u.). The cationic group as well as the water solvate are well behaved in terms of crystallographic order, but the remaining three groups in the structure display different kinds of disorder, as explained in detail in the refinement section, the two DMF mimicking different kinds of two-fold splitting (Figs. 1c,1d) with occupation factors of 0.546 (12)/0.454 (12) and 0.520 (12)/0.480 (12), respectively. In the case of pds this occurs in a more complicated fashion, having both S's "clamped" at two well determined positions (Fig 1b) and a not-so-welldefined central part (Occupation for O4,O5:0.641 (3)).
These peculiar behaviours may be better understood by inspection of Table 1 stable [Ni(phen) 3 ]-pds network and acting as a clamp for the terminal SO 3 groups. The oxygens in the pds middle region, instead, are much less restrained to their sites, and this could explain some tendency to disorder. Similar mobility restrictions apply to the water solvate, donor of two strong bonds (Table 1, entries 1 and 2) and acceptor of one (3rd entry). On the other hand, the above cationic-anionic network leaves large embedded holes (about 28% of the total crystal volume, as calculated by PLATON, Spek, 2009). These holes are occupied by the DMF molecules (in light tracing in Fig   2). Analysis of the acceptors in Table 1 and inspection of Figure 2 reaveals that they hardly interact with the rest of the structure, being thus labile and, accordingly, prone to disorder.

Experimental
The title compound was prepared by adding DMF to a solid, equimolar mixture of [Ni(CH 3 COO) 2 ].4H 2 O, K 2 S 2 O 8 and phen.H 2 O in such a way that phen final concentration was 0.500 M. Crystals suitable for X-ray diffraction developed in a few hours.

Refinement
All C-H atoms were found in a difference map, but treated differently in refinement. Those attached to C were further idealized and finally allowed to ride. CH 3 groups were also free to rotate. Water H's were refined with restrained d(O-H).

In all cases displacement parameters were taken as
A rather peculiar characteristic of the structure was its having the two DMF solvates as well as the pds anion disordered, all of them in different ways: in both DMF molecules the disorder mimics a two fold symmetry, with the pseudo two fold axis by force passing throuh the central N; in the case of moieties E (D) this occurs with the pseudo diad being perpendicular (parallel) to one of the to the two C(methyl)-N lines, Fig 1c (1d).
The case of the pds anion was not that clear cut, but interesting anyway: the molecule occupies in the crystal several, slightly offset positons, all of them with the S atoms "clamped" in the S1, S2 reported coordinates (No "ghosts" in their neighbourhood). The central oxygens O4 and O5, instead, presented a clear splitting which needed to be included in the model in order to have a proper refinement. The coresponding outermost minoritarian oxygens, however, could not be clearly disclosed and have to be accordingly disregarded. To compensate for this fact, atoms O1-O3, O6-O8 were given full occupancy. This procedure, fulfilled with some restraints in metrics and in displacement factors, allowed to reduce the R factor by more ~10%, and the s.u.'s for the O4, O5 coordinates in ~30%.

Computing details
Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009     Special details 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.