Crystal structure of {(S)-1-phenyl-N,N-bis[(pyridin-2-yl)methyl]ethanamine-κ3 N,N′,N′′}bis(thiocyanato-κN)zinc from synchrotron data

The ZnII ion in the title compound shows a distorted square-pyramidal coordination geometry with three N atoms of the chiral S-ppme ligand and two N atoms of the thiocyanate anions. In the crystal, molecules are connected by hydrogen bonds and π–π interactions, forming a two-dimensional supramolecular network parallel to the bc plane.


Chemical context
Recently, the preparation of new polyamines or their derivatives have attracted increasing attention in organic chemistry, pharmaceutical chemistry and materials science because they can easily interact with metal ions and form stable multifunctional compounds with various applications in magnetic materials, sorption materials, as well as fluorescent substances (Lodeiro & Pina, 2009;Nowicka et al., 2011;Yao et al., 2015). For instance, metal complexes with cyclam or azamacrocyclic ligands have been synthesized and investigated for selective adsorption of CO 2 over N 2 gases (Huang et al., 2013). In particular, chiral derivatives based on polyamine ligands can easily form chiral metal complexes with interesting properties, such as chiral recognition or as asymmetric catalysts. For example, the chiral two-dimensional coordination polymer, [Ni(L R,R )] 3 [C 6 H 3 (COO) 3 ] 2 Á12H 2 OÁCH 3 CN {L R,R is 1,8-bis-[(R)--methylbenzyl]-1,3,6,8,10,13-hexaazacyclotetradecane}, showed an efficient chiral recognition for rac-1,1 0 -bi-2-naphthol (Ryoo et al., 2010). Moreover, a chiral iron(III) complex containing binol derivatives exhibited high enantioselectivity and high yield for the enantiopure -amino alcohols (Tak et al., 2016). Nevertheless, only a few of these complexes have been reported and characterized because the preparation of these complexes remains a major challenge in synthetic chemistry and materials science (Gu et al., 2016). The thiocyanate ion is a versatile anion which can bridge to metal ions through the S or N atom, thus allowing the assembly of supramolecular compounds (Nawrot et al., 2016). We report here the preparation and crystal structure of a chiral zinc complex constructed from the versatile tridentate chiral ligand (S)-1-phenyl-N,N-bis[(pyridin-2-yl)methyl]ethanamine (S-ppme) and the thiocyanate ion, namely [Zn(NCS) 2 (S-ppme)]. ISSN 2056-9890

Structural commentary
A view of the molecular structure of the title compound is shown in Fig. 1. The coordination environment of the Zn II ion can be described as distorted square pyramidal. The Zn II ion is coordinated by three N atoms from the chiral S-ppme ligand and by two N atoms of thiocyanate ions. The thiocyanate ions coordinate through the N atoms in cis positions with respect to each other and are trans to the phenyl group of the chiral S-ppme ligand. The coordinating thiocyanate ions are linear but slightly bent in relation to the Zn II ion [N4-C21-S1 = 179.9 (1) , N5-C22-S2 = 178.5 (4) , Zn1-N4-C21 = 171.6 (4) and Zn1-N5-C22 = 170.3 (4) ]. The bond angle between the thiocyanate ions is 101.43 (2) . The average N C and C-S bond lengths of the thiocyanate ions are 1.158 (4) and 1.629 (6) Å , respectively, which implies that both thiocyanate ions are not delocalized. The former is very similar to the C N triple-bond length, while the latter is slightly shorter than reported C-S single-bond length (Hashem et al., 2014). The pyridine rings of the S-ppme ligand are twisted with respect to each other. The average Zn-N S-ppme and Zn-N NCS bond lengths are 2.183 (2) and 1.986 (2) Å , respectively. The bond angles around the Zn II ion range from 73.99 (1) to 156.01 (1) .

Supramolecular features
The thiocyanate ligands form intermolecular C-HÁ Á ÁS hydrogen bonds with adjacent pyridine groups of the chiral S-ppme ligand, giving rise to a sheet structure parallel to the ac plane ( Fig. 2 and Table 1) (Steed & Atwood, 2009). In the sheet, adjacent C8-C12/N3 pyridine rings of chiral S-ppme ligands are also linked through a face-to-faceinteraction, with a centroid-centroid distance of 3.482 (1) Å and a dihedral angle of 2.947 (1) . A view of the molecular structure of the title compound, showing the atom-labelling scheme, with displacement ellipsoids drawn at the 50% probability.

Figure 2
A view of the crystal-packing structure for the title compound, showing the C-HÁ Á ÁS hydrogen bonds (sky-blue dashed lines) andinteractions (black dashed lines). Table 1 Hydrogen-bond geometry (Å , ).
ligand (Rowthu et al., 2011;Woo et al., 2011) for which syntheses, magnetic properties and crystal structures have been reported.

Synthesis and crystallization
The chiral S-ppme ligand was prepared according to a slight modification of the method of Rowthu et al. (2011). A methanol solution (5 mL) of KNCS (0.078 g, 0.80 mmol) was added slowly to a methanol solution (15 mL

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.