Crystal structure of bis(1-hexyl-N,N-dimethylpyridinium) bis(maleonitriledithiolato)nickelate(II)

In the title salt, the1-hexyl-N,N-dimethylpyridinium cations possess an extended chain conformation, while the bis(maleonitriledithiolato)nicklate(II) complex anion has a square-planar NiS4 geometry comprising four S-donor atoms from two bidentate chelate comprising maleonitriledithiolate ligands, with the Ni2+ cation lying on a crystallographic mirror plane. The crystal has a layered structure consisting of alternating cations and anions.

The asymmetric unit of the title compound, (C 13 H 23 N 2 ) 2 [Ni(C 4 N 2 S 2 ) 2 ], consists of a 1-hexyl-N,N-dimethylpyridinium cation and one half of a [Ni(mnt) 2 ] 2À dianion (mnt 2À = maleonitriledithiolate) in which the Ni 2+ cation lies on a crystallographic inversion centre. The square-planar coordination about Ni 2+ comprises four S atoms from two bidentate chelate mnt 2À ligands [Ni-S = 2.1791 (9) and 2.1810 (8) Å , and S-Ni-S bite angle = 91.93 (3) ]. The hydrocarbon chains of cations show trans-planar conformations and lie approximately parallel to the long molecular axis of the [Ni(mnt) 2 ] 2À anions, giving stacks along the c axis. The anions and cations form layers lying parallel to the bc plane. Only weak C-HÁ Á ÁNi and C-HÁ Á Á associations are present in the crystal packing.

Chemical context
Molecular solids based on transition metal dithiolene complexes have attracted much interest in recent years, not only regarding fundamental research of magnetic interactions and magneto-structural correlations but also in the development of new functional-molecule-based materials (Robertson & Cronin, 2002). Much work has been performed in molecular solids based on M[dithiolene] 2 complexes because of their application as building blocks in molecular-based materials showing magnetic, superconducting and optical properties (Nishijo et al., 2000;Ni et al., 2004, Ren et al., 2004. In our previous studies, we have investigated the effect of the introduction of mobile organic cations into the rigid [Ni(mnt) 2 ] 2À spin system and created some multi-functional compounds (Yu et al., 2012(Yu et al., , 2013Duan et al., 2011). In order to further explore the correlation between the structural features of the counter-cations and the stacking patterns of the anions as well as their physical properties, we have designed and synthesized the soft 1-hexyl-N,N-dimethylpyridinium cation and combined it with the [Ni(mnt) 2 ] 2À dianion, giving the title compound, (C 13 H 23 N 2 ) 2 [Ni(C 4 N 2 S 2 ) 2 ], (I), and the crystal structure is reported herein.
The hydrocarbon chain of the cation is slightly disrupted close to the pyridyl ring in the completely trans-planar conformation, with a chain to pyridyl ring dihedral angle of 83.03 (19) . The direction of the hydrocarbon chains is approximately parallel to the long molecular axis of the anions, with a dihedral angle between the molecular plane of the hydrocarbon chain and that of the anion (defined by S1,S2,S2 i ,S1 i ) of 10.76 (18) [symmetry code: (i) Àx + 1, Ày, Àz]. Between the cation and anion there is a novel Ni1Á Á ÁH-C17 ii interaction (HÁ Á ÁNi = 2.72 Å ) (Fig. 2) [symmetry code: (ii) Àx + 1, Ày + 1, Àz].

Supramolecular features
In the crystal of (I), both the anions and cations form layers lying parallel to the bc plane (Figs. 2 and 3). In the anion layer, two neighboring [Ni(mnt) 2 ] 2À anions are associated via sideto-side stacking with typical interatomic separations of 8.713 (1) Å (Ni1Á Á ÁNi1 ii ), and 6.218 (3) Å (S1Á Á ÁS2 ii ). The cations are arranged into bilayers, also lying parallel to the ab plane. In each layer, the cations exhibit an antiparallel arrangement. The cation and anion layers stack alternately, forming columns which extend along c (Fig. 4).

Database survey
In the structures of [Ni(mnt)  The atom-numbering scheme in the molecular structure of (I), showing the cation and the centrosymmetric dianion, with displacement ellipsoids drawn at the 30% probability level. [Symmetry code: (i) Àx + 1, Ày, Àz.]

Synthesis and crystallization
Disodium maleonitriledithiolate (2.0 mmol) and nickel(II) chloride hexahydrate (1.0 mmol) were mixed with stirring in water (20 mL) at room temperature. Subsequently, a solution of 1-hexyl-N,N-dimethylpyridinium iodide (1.0 mmol) in methanol (10 mL) was added to the mixture and the red precipitate that was immediately formed was filtered off and washed with methanol. The crude product was recrystallized in acetone (20 mL) to give red block-shaped crystals which were used in the X-ray analysis.

Figure 3
Alternating anion and cation layers, which lie parallel to the crystallographic ab plane.

(I)
Crystal data (C 13 H 23 N 2 ) 2 [Ni(C 4  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.28 e Å −3 Δρ min = −0.47 e Å −3 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. 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 > 2sigma(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.