Crystal structure and Hirshfeld surface analysis of ((S,S)-2,2′-{[(1,2-diphenylethane-1,2-diyl)bis[(azaniumylylidene)methanylylidene]}bis(6-methoxyphenolato))trinitratosamarium(III)

The asymmetric unit of the title mononuclear ten-coordinated samarium chiral Schiff base complex prepared from o-vanillin, (1S,2S)-(−)-1,2-diphenylethylenediamine and samarium nitrate hexahydrate contains two crystallographically independent molecules.


Chemical context
Lanthanide metal complexes can have attractive functions such as magnetism and fluorescence when synthesized with properly designed ligands (Yao et al., 2019;Lin et al., 2009). In recent years, lanthanide complexes that act as single-molecule magnets (SMM) have received much attention (Then et al., 2015). In these complexes, distortion of the coordination geometry is an important factor for magnetic anisotropy and for the resulting SMM properties. However, the coordination chemistry of lanthanides is complicated, and it is necessary to prepare complexes with coordination environments suitable for the required properties. On the other hand, salen ligands are known to form stable chelate complexes with many metals (Cozzi et al., 2004). By incorporating a substituent group into salen ligands, it is possible to easily add more coordination sites and optical functionality such as the antenna effect that depend on intermolecular interactions and arrangements. Hence, functional lanthanide salen complexes have attracted attention (Ren et al., 2016). Accurate data such as bond angles and the geometry of coordination sites obtained based on crystal structure analysis and Hirshfeld surface analysis will be useful for the molecular design of new lanthanide and salen complexes. In this study, we prepared a new Sm III -salen complex and report herein on its crystal structure and Hirshfeld surface analysis.

Structural commentary
The title Sm III complex crystallizes in the monoclinic space group C2. The asymmetric unit contains two crystallographically independent molecules. This distorted prismatic ISSN 2056-9890 [SmO 10 ] complex consists of three bidentate nitrate ions and two pairs of phenolate and methoxy groups of the salen ligand, which is slightly distorted from planar.
The bond distances between the metal center and ligating atoms range from 2.333 (5) to 2.373 (4) Å for the phenolato oxygen atoms, and from 2.606 (5) to 2.621 (6) Å for methoxy oxygen atoms. The bond lengths between the metal center and the nitrate oxygen atoms range from 2.475 (5) to 2.633 (5) Å , showing more flexibility than those of the Schiff base ligand. In the Schiff base ligand, the imine moieties are protonated to form iminium cations, but the C N bond lengths remain close to those of normal imine bonds at 1.287 (8) and 1.30 (1) Å .
Intramolecular hydrogen bonds occur between the iminium protons and the phenolic oxygen atoms, with lengths of 1.71-1.89 Å (Table 1, Fig. 1). The bond distances and angles in the ligand are similar to those of analogous complexes (Hayashi et al., 2013).

Figure 1
View of the two independent complex molecules of the title compound, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. Intramolecular hydrogen bonds are shown as dashed lines. All non-H atoms should be labelled Hirshfeld surfaces and fingerprint plots (McKinnon et al., 2004) were calculated using CrystalExplorer17.5 (Turner et al., 2017). Hydrogen bonds are strong interactions and they are indicated as red dots on the surface (Fig. 2) or two sharp spikes in the fingerprint plot (Fig. 3). 'Wings' in the fingerprint plots and diagonal plots at 1.8 Å are regarded as a characteristic feature potentially resulting from aromatic rings (Spackman et al., 2002)The contributions to the Hirshfeld surface are HÁ Á ÁH (33.5%), OÁ Á ÁH (34.1%) and CÁ Á ÁH (21.7%) contacts.

Synthesis and crystallization
(1S,2S)-(À)-1,2-Diphenylethylenediamine (0.100 g, 0.471 mmol) and o-vanillin (0.143 g, 0.940 mmol) were dissolved in ethanol (30 mL) and the resulting mixture was stirred at 313 K for 1 h to afford a yellow solution. To this solution, samarium nitrate hexahydrate (0.208 g, 0.468 mmol) was added and it was stirred at 313 K for 2 h. A yellow precipitate appeared immediately. The precipitate was filtered and washed with ethanol and hexane. The title compound      (Sheldrick, 2008).

((S,S)-2,2′-{(1,2-diphenylethane-1,2-diyl)bis[(azaniumylylidene)methanylylidene]}bis(6methoxyphenolato))trinitratosamarium(III)
Crystal data  (9) 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.