Crystal structure and Hirshfeld surface analysis of hexakis(μ-benzoato-κ2 O:O′)bis(pyridine-3-carbonitrile-κN 1)trizinc(II)

The asymmetric unit of the title complex contains one half of the complex molecule, one and a half ZnII cations, three benzoate (Bnz) and one pyridine-3-carbonitrile (CPy) molecule; the Bnz anions act as bidentate ligands through the carboxylate O atoms, while the Cpy anion acts as a monodentate N(pyridine)-bonding ligand. The complete centrosymmetric trinuclear complex thus comprises a linear array of three ZnII cations. In the crystal, the Bnz anions link to the Cpy N atoms via weak C—H⋯N hydrogen bonds, forming a two-dimensional network. The Hirshfeld surface analysis confirms the role of H-atom contacts in establishing the packing.


Chemical context
The structure-function-coordination relationships of the arylcarboxylate ion in Zn II complexes of benzoic acid derivatives change depending on the nature and position of the substituent groups on the benzene ring, the nature of the additional ligand molecule or solvent, and the pH and temperature of synthesis (Shnulin et al., 1981). When pyridine and its derivatives are used instead of water molecules, the structure is completely different (Catterick et al., 1974). The solid-state structures of anhydrous Zinc(II) carboxylates include one-dimensional, two-dimensional and three-dimensional polymeric motifs of different types, while discrete monomeric complexes with octahedral or tetrahedral coordination geometry are found if water or other donor molecules are coordinated to Zn (Usubaliev et al., 1992). The structure determination of the title compound, (I), a trinuclear zinc complex with six benzoate anions and two neutral pyridine-3-carbonitrile ligands, was undertaken in order to compare the results obtained with those reported previously. In this context, we synthesized the Zn II -containing title compound, hexa(-benzoato-2 O,O 0 )bis(pyridine-3-carbonitrile-N)trizinc(II), [Zn 3 (C 7 H 5 O 2 ) 6 (C 6 H 4 N 2 ) 2 ], and report herein its crystal and molecular structures as well as a Hirshfeld surface analysis. ISSN 2056-9890

Structural commentary
The molecular structure of the title complex (I) is formed by a centrosymmetric array of three Zn II cations, which are coordinated by six benzoate anions and two neutral pyridine-3-carbonitrile ligands. The middle Zn II cation occupies a special position and lies on a crystallographic inversion centre. The benzoate anions act as bidentate ligands, bridging two pairs of Zn II cations. The pyridine-3-carbonitrile ligands are monodentately coordinated through the pyridine N atoms (Fig. 1).

Figure 1
The molecular structure of the title complex with the atom-numbering scheme. Unlabelled atoms are related to labelled ones by the symmetry operation (1 À x, 2 À y, 1 À z). Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity. distance of 3.850 (4) Å ] help to consolidate a three-dimensional architecture.

Hirshfeld surface analysis
Visualization and exploration of intermolecular close contacts of a structure is invaluable, and this can be achieved using the Hirshfeld surface (HS) (Hirshfeld, 1977). HS analysis may be carried out to investigate the locations of atomsÁ Á Áatom short contacts with potential to form hydrogen bonds andstacking interactions.
In the HS with d norm (Fig. 3), the white surface indicates contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distant contact) than the van der Waals radii, respectively. The bright-red spot appearing near Cpy-N2 indicates its role as the respective donor and/or 1968 Hö kelek et al. View of the three-dimensional Hirshfeld surface of the title complex plotted over d norm in the range À0.0957 to 1.6461 a.u.

Figure 4
View of the three-dimensional Hirshfeld surface of the title complex plotted over electrostatic potential energy in the range À1.7824 to 9.8050 a.u. The hydrogen-bond donors and acceptors are viewed as blue and red regions around the atoms corresponding to positive and negative potentials, respectively.

Figure 2
Part of the crystal structure. Weak C-H Bnz Á Á ÁN Cpy (Bnz = benzoate and Cpy = pyridine-3-carbonitrile) hydrogen bonds are shown as dashed lines. H atoms not involved in these interactions have been omitted for clarity.

Figure 5
Hirshfeld surface of the title complex plotted over shape-index. acceptor in the dominant C-HÁ Á ÁN hydrogen bond; it also appears as blue and/or red regions, respectively, corresponding to positive or negative potentials on the HS mapped over electrostatic potential (Fig. 4). The shape-index of the HS is a tool to visualize thestacking by the presence of adjacent red and/or blue triangles; if there are no adjacent red and/or blue triangles, then there are nointeractions. Fig. 5 clearly suggests that there areinteractions in (I).
The overall two-dimensional fingerprint plot, Fig. 6a, and those delineated into HÁ Á ÁC/CÁ Á ÁH, HÁ Á ÁN/NÁ Á ÁH and CÁ Á ÁC contacts are illustrated in Fig. 6 b-d, respectively, together with their relative contributions to the Hirshfeld surface. The widely scattered points of high density are due to the C-HÁ Á Á interactions in the crystal, resulting in the fingerprint plot delineated into HÁ Á ÁC/CÁ Á ÁH contacts with 21.2% contribution to the HS, Fig. 6b. In the fingerprint plot delineated into HÁ Á ÁN / NÁ Á ÁH contacts, the 12.9% contribution to the HS arises from the C-HÁ Á ÁN hydrogen bonding and is viewed as a pair of spikes with the tip at d e + d i $2.6 Å in Fig. 6c. Finally, the CÁ Á ÁC contacts assigned to short interatomic CÁ Á ÁC contacts andstacking interactions with    9.7% contribution to the HS appear as an arrow-shaped distribution of points in Fig. 6d, with the vertex at d e = d i $1.65 Å . The Hirshfeld surface representations with the function d norm plotted onto the surface are shown for the HÁ Á ÁN/NÁ Á ÁH and CÁ Á ÁC interactions in Fig. 7a and b, respectively.
The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the packing. The crystal packing is dominated by van der Waals interactions and hydrogen bonding.

Synthesis and crystallization
The title compound was prepared by the reaction of ZnSO 4 Á7H 2 O (1.44 g, 5 mmol) in H 2 O (25 ml) and pyridine-3carbonitrile (1.04 g, 10 mmol) in water (25 ml) with sodium benzoate (1.44 g, 10 mmol) in water (100 ml) at room temperature. The mixture was filtered and set aside to crystallize at ambient temperature for several days, giving colourless single crystals (yield: 1.55 g, 82%).

Hexakis(µ-benzoato-κ 2 O:O′)bis(pyridine-3-carbonitrile-κN 1 )trizinc(II)
Crystal data  [1966][1967][1968][1969][1970] Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0033 (2) 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.