{N-[1-(2-Oxidophenyl)ethylidene]-dl-alaninato}(pentane-1,5-diyl)silicon(IV)

The coordination geometry of the pentacoordinated SiIV atom in the title complex is a distorted trigonal bipyramid.

The title Si IV complex, C 16 H 21 NO 3 Si, is built up by a tridentate dinegative Schiff base ligand bound to a silacyclohexane unit.The coordination geometry of the pentacoordinated Si IV atom is a distorted trigonal bipyramid.The presence of the silacyclohexane ring in the complex leads to an unusual coordination geometry of the Si IV atom with the N atom from the Schiff base ligand and an alkyl-C atom in apical positions of the trigonal bipyramid.There is a disorder of the methyl group at the imine bond with two orientations resolved for the H atoms [major orientation = 0.55 (3)].In the crystal, C-H� � �O interactions are found within corrugated layers of molecules parallel to the ab plane.

Structure description
Schiff base ligands with additional O donor ligands are suitable ligands to generate pentacoordinated Si IV complexes (Wagler et al., 2014).The Schiff base N-[1-(2-hydroxyphenyl)ethylidene]-dl-alanine has been utilized previously for the preparation of a Cu II complex (Zhao et al., 2008).The Cu II atom of this complex is coordinated to the tridentate Schiff base ligand and the bidentate bis(3,5-dimethylpyrazol-1-yl)methane ligand.This Schiff base ligand has not yet been used for the generation of silicon complexes.Schiff base ligands derived from salicyl aldehyde (Warncke et al., 2012), o-hydroxyacetophenone (Bo ¨hme et al., 2006) and naphthyl aldehyde (Schwarzer et al., 2018) have been used for the preparation of related Si IV complexes.
The title compound, C 16 H 21 NO 3 Si, crystallizes with one molecule in the asymmetric unit (Fig. 1).The Schiff base ligand is formally dinegatively charged and coordinates the Si IV atom via the phenoxy-O1, imine-N1 and carboxyl-O2 atoms.The Si IV atom is part of a silacyclohexane ring and is bound therein via the C12 and C16 atoms.The coordination geometry of this pentacoordinate Si IV complex was analyzed with the parameter � (Addison et al., 1984).The largest bond angle � and the second largest angle � at the Si IV atom are used to calculate this parameter with � = (� À �)/60 � .A value of � = 0 indicates a perfect square pyramid, whereas a value of � = 1 indicates a perfect trigonal bipyramid.In the complex under investigation the largest angle at the Si IV atom is C16-Si1-N1 with 167.09 (8) � .The second largest angle is O1-Si1-O2 with 123.53 ( 7) � (see Table 1).This leads to a parameter � = 0.73, which corresponds to a distorted trigonal bipyramid.The apical positions are represented by N1 and C16, while the atoms O1, O2 and C12 are the atoms in the trigonal plane.Silicon complexes with tridentate O,N,O 0 -Schiff base ligands and two alkyl groups form mainly distorted trigonal bipyramidal geometries in the solid state (Schwarzer et al., 2018;Bo ¨hme & Fels, 2023a,b).The apical positions of the coordination polyhedron are usually occupied by the two O atoms of the Schiff base, when there are two single alkyl groups bound to the Si IV atom.Having N and C atoms in apical positions has so far only been observed in the case of a silacyclobutane derivative (Schwarzer et al., 2018).The silacyclohexane ring in the complex under investigation leads to a similar coordination geometry as in the silacyclobutane derivative.

Synthesis and crystallization
The sodium salt of the Schiff base ligand was prepared from 2-hydroxyacetophenone and alanine according to a literature procedure (Fels, 2015).To a solution of 1.12 g (4.89 mmol) sodium{N-[1-(2-hydroxyphenyl)ethylidene]-dl-alaninate} in 30 ml of dry THF was added 0.64 g (6.36 mmol) triethylamine, which led to a yellow suspension.The ClSiMe 3 (1.27g, 11.74 mmol) precursor was added with a syringe via a septum.A white precipitate of triethylammonium chloride formed during stirring at 50 � C for 1 h.The triethylammonium chloride was filtered off and the residue was washed with 10 ml THF.The filtrate was reduced in a vacuum and was carefully freed from volatile components at 90 � C in a vacuum.The remaining pale-yellow liquid was dissolved in 20 ml of THF.1,1-Dichlorosilacyclohexane (0.71 g, 4.18 mmol) was diluted with 5 ml of THF and added with a syringe to the solution.A paleyellow suspension formed.This suspension was stirred for 20 days at room temperature.Filtration of the suspension gave a pale-yellow solution, which was reduced in a vacuum to a gray-brown solid.Recrystallization from the mixed solvents of chloroform (8 ml) and n-hexane (5 ml) yielded pale-yellow crystals suitable for crystal structure analysis, yield: 0.57 g (45%), m.p. = 435 K.

Figure 1
A view of the molecular structure of the title compound, with the atomlabeling scheme.Displacement ellipsoids are drawn at the 50% probability level.

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.

Table 3
Experimental details.