3,5-Dimethyl-1-(4-nitrobenzyl)pyridinium bis(benzene-1,2-dithiolato-κ2 S,S′)nickelate(III)

The asymmetric unit of the title compound, (C14H15N2O2)[Ni(C6H4S2)2], contains one cation and two halves of two centrosymmetric crystallographically independent anions. In the anions, the NiIII atoms are coordinated by four S atoms in a distorted square-planar geometry. In the cation, the dihedral angle between the pyridine and benzene rings is 88.66 (17)°. In the crystal, anions and cations interact through C—H⋯S and C—H⋯O hydrogen bonds.


Guang-Xiang Liu Comment
Metal complexes of 1,2-dithiolate ligands have been intensively studied because of their novel properties and applications in the areas of molecular conducting, magnetic materials, nonlinear optics, and others (Robertson et al., 2002;Kato, 2004). Over the last decade, a large number of new dithiolene ligands and resultant complexes have been prepared to optimize the molecular properties in an effort to prepare novel and advanced material, whose molecular arrangement can be sensitively affected by strong and directional noncovalent interactions (Cassoux, 1999;Canadell, 1999;Akutagawa & Nakamura, 2000). Although the closed-shell cations make no contribution to the conductivity and magnetism, their size and shapes play a predominant role in influencing the crystal structure and consequently, in altering the electronic and magnetic properties. Recently, using benzylpyridinium derivatives ([RBzPy] + ) as the counter cation of [M(mnt) 2 ] -(M = Ni, Pd, and Pt; mnt 2-= maleonitriledithiolate), a series of ion-pair complexes with segregated columnar stacks of cations and anions have been reported (Ren et al., 2002(Ren et al., , 2008. The quasi-one-dimensional magnetic nature of these complexes was attributed to intermolecular π orbital interactions within the anionic columns. Furthermore, for some complexes, spin-Peierls-like transition was observed (Ren et al., 2004). More presently, we are devoted to our research interesting on the molecular magnets self-assembled from [Ni(bdt) 2 ]ion (bdt is benzene-1,2-dithiolato) due to its molecular and electronic structure resembling [Ni(mnt) 2 ]ion, which is expected to obtain new series of molecular magnets with peculiar magnetic phase transition via incorporating the benzylpyridinium derivatives into the [Ni(bdt) 2 ]spin system. We report herein the synthesis and crystal structure of the title compound, a new ion-pair complex.
As shown in Fig. 1, the asymmetric unit of the title complex contains two different, independent halves of centrosymmetric [Ni(bdt) 2 ]anions and one [NO 2 BzPy(CH 3 ) 2 ] + cation. The nickel atoms are each coordinated by four sulphur atoms in square-planar geometry. As for the Ni1-containing unit, the Ni1-S1 and Ni1-S2 distances are 2.1419 (11) and 2.1490 (10) Å, respectively. These values are in agreement with those reported for an analogous [Ni(bdt) 2 ]complex (Liu et al., 2007). The S-Ni-S bond angle within the five-member ring is 91.77 (4)°, which is slightly larger than that observed in the complex with substituent groups on benzene rings (Liu et al., 2007). There exists a dihedral angle of 5.36 (6)° between the C 6 S 2 and NiS 2 planes, with atom Ni1 deviating 0.165 (5) Å from the C 6 S 2 plane.
In the Ni2-containing unit, the Ni-S bonds range 2.1425 (11) to 2.1474 (11) Å and the S-Ni-S bond angle within the five member ring is 91.56 (4)°, which is in agreement with that of the Ni1-containing unit. The Ni2 atom deviates by 0.017 Å from the C 6 S 2 plane and the dihedral angle between the C 6 S 2 and NiS 2 planes is 1.12 (4)°. The independent C 6 S 2 planes are nearly perpendicular to each other forming a dihedral angle of 78.33 (8)°. In the cation, the dihedral angles formed by the N2/C19/C16 reference plane are 65.68 (14)° for the phenyl ring and 48.66 (15)° for the pyridine ring, respectively. The phenyl ring and the pyridine ring make a dihedral angle of 88.66 (17) anions and cations. Conversely, the Ni1-containing units stack in side-by-side fashion in which the anions with uniform spaced arrangements form one-dimensional chains along the a axis. The shortest separation between adjacent Ni(III) ions is 7.611 (14)Å. In the crystal (Fig. 2), anions and cation are held together via C-H···O and C-H···S hydrogen bonding interactions (Table 1).

Experimental
Under argon atmosphere at room temperature, benzene-1,2-dithiol (284 mg, 2 mmol) was added to a solution of sodium metal (92 mg, 4 mmol) in 25 ml of absolute methanol. A solution of NiCl 2 .6H 2 O (240 mg, 1 mmol) in methanol was added, resulting in the formation of a muddy red-brown color. Following this, 1-(4-nitrobenzyl)-3,5-dimethylpyridinium bromide (646 mg, 2 mmol) was added, and the mixture allowed to stand with stirring for 1 h and then stirred for 24 h in air. The colour of the mixture gradually turned green, indicating oxidation from a dianionic species to the more stable monoanionic form. The precipitate was washed with absolute methanol and ether and then dried. The crude product was recrystallized twice from methylene chloride to give black needles in ~61% yield.

Refinement
H atoms were positioned geometrically, with C-H = 0.93, 0.97 and 0.96 Å for aromatic, methylene and methyl H atoms, respectively, and constrained to ride on their parent atoms, with U iso (H) = xU eq (C), where x = 1.5 for methyl H and 1.2 for all other H atoms.  The asymmetric unit of the title complex, with displacement ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Atoms marked with suffixes A and B are related to those with no suffixes by the symmetry codes (1-x, 2-y, 1-z) and (1-x, 2-y, -z) respectively.  Packing diagram of the title complex viewed along the a axis. Hydrogen bonds are shown as dashed lines.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq