Bis[tris(pyridin-2-yl)amine]iron(II) tris(dicyanomethylidene)methanediide

Both ions in the title compound lie across centres of inversion, with the anion being statistically disordered.

In the title compound, [Fe{(C 5 H 4 N) 3 N} 2 ][C{C(CN) 2 } 3 ], both ions lie across centres of inversion, with the anion being statistically disordered over two sets of atomic sites having equal occupancy. The cation and anion have approximate 3 and 32 symmetry, respectively, and the Fe-N bond lengths indicate low-spin Fe II . A combination of two-centre C-HÁ Á ÁN and three-centre C-HÁ Á Á(N) 2 hydrogen bonds link the ions into complex sheets. Several low-occupancy water molecules are present, whose H atoms could not be located: accordingly, the reflection data were subjected to the SQUEEZE procedure [Spek (2015). Acta Cryst. C71, 9-18].

Structure description
As a consequence of their ability to link metal ions in a variety of different ways, polynitrile anions, either functioning alone or in combination with neutral co-ligands, provide opportunities for the generation of molecular architectures with varying dimensions and topologies (Miyazaki et al., 2003;Benmansour et al., 2007Benmansour et al., , 2008Benmansour et al., , 2012Atmani et al., 2008;Yuste et al., 2009). The presence of other potential donor groups such as those derived from -OH, -SH or -NH 2 , together with their rigidity and electronic delocalization, mean that polynitrile anions can also lead to new bistable materials (Benmansour et al., 2010;Setifi et al., 2009Setifi et al., , 2014Pittala et al., 2017). As a part of our continuing study of the structural and magnetic properties of iron(II) complexes containing both polynitrile and polypyridyl units (Setifi et al., 2013(Setifi et al., , 2017(Setifi et al., , 2018a, we data reports report here the molecular and supramolecular structure of a new compound based on tri(2-pyridyl)amine (tpa) as ligand and the tris(dicyanomethylene)methanediide dianion (tcpd 2À ) as the counter-ion.
The structure consists of a [Fe((C 5 H 4 N) 3 N) 2 ] 2+ cation containing six-coordinate Fe in an octahedral coordination environment and a [C(C(CN) 2 ) 3 ] 2À anion (Fig. 1). In addition, there are also partial-occupancy water molecules present, but these could not be structurally characterized in a satisfactory manner. The cation lies across a centre of inversion ( 1 2 , 1 2 , 1 2 ) with the unique ligand coordinated in a tripodal fashion, such that the point symmetry of the cation approximates very closely to S 6 (3). The Fe-N distances lie in the range 1.981 (3)-1.997 (3) Å . This is typical for six-coordinate low-spin Fe II complexes, whereas Fe-N distances in analogous high-spin Fe II complexes are typically observed at around 2.15 Å (Orpen et al., 1989). The trigonal anion is disordered across another centre of inversion ( 1 2 , 1, 0). The geometry at the central atom C4 is exactly planar, but the three independent C(CN) 2 groups are twisted out of this plane, making dihedral angles with it of 26.2 (9), 27.7 (13) and 29.3 (9) , so that the point symmetry of the anion approximates very closely to D 3 (32). The anion is chiral, but the inversion symmetry confirms that equal numbers of the two enantiomeric conformations are present.
Within the selected asymmetric unit, the cation is linked to both orientations of the disordered anion by one two-centre C-HÁ Á ÁN hydrogen bond and one three-centre C-HÁ Á Á(N) 2 hydrogen bond (Table 1), forming an ion pair. An additional further three-centre system links these ion pairs into complex sheets lying parallel to (100) (Fig. 2): within this sheet, each anion site is occupied by one of the two possible orientations of the anion, and these orientations are distributed at random throughout the structure such that equal numbers of the two exist in the crystal as a whole.

Synthesis and crystallization
The title compound was synthesized solvothermally under autogenous pressure using a mixture of iron(II) sulfate heptahydrate (28 mg, 0.1 mmol), tri(2-pyridyl)amine (31 mg, 0.1 mmol) and dipotassium tris(dicycanomethylene)methanediide (28 mg, 0.1 mmol) in water-ethanol (3:1 v/v, 20 ml). The mixture was sealed in a Teflon-lined autoclave and held at 423 K for 3 d, and then cooled to ambient temperature at a rate of 10 K per hour (yield 45%). Red needles of the title complex suitable for single-crystal X-ray diffraction were selected directly from the synthesized product.

Figure 2
Part of the crystal structure showing the formation of a hydrogen-bonded sheet lying parallel to (100). Hydrogen bonds are drawn as dashed lines and, for the sake of clarity, H atoms not involved in the motif shown have been omitted. Each anion site is occupied by one of the two possible orientations of the anion, distributed at random.

Figure 1
The structure of the two ionic components, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. The anion is disordered across a centre of inversion and the atoms marked 'a 0 or 'b 0 are at the symmetry positions (1 À x, 1 À y, 1 À z) and (1 À x, 2 À y, Àz), respectively. distances in the anion to values of 1.42 (2) and 1.16 (2) Å , respectively, while the 1,3 non-bonded CÁ Á ÁN distances were restrained to 2.58 (4) Å . Conventional refinement then indicated the presence of several low-occupancy water molecules, whose H atoms could not be located: accordingly, the reflection data were subjected to the SQUEEZE procedure (Spek, 2015), which indicated a void volume of 149 Å 3 centred at the origin, and a total of 11 electrons per unit cell in addition to those of the ionic components.

Funding information
FS gratefully acknowledges the Algerian MESRS (Ministé re de l'Enseignement Supé rieur et de la Recherche Scientifique), the DGRSDT (Direction Gé né rale de la Recherche Scientifique et du Dé veloppement Technologique), as well as the Université Ferhat Abbas Sé tif 1 for financial support.

data-2
IUCrData (2020). 5, x201278 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.