Crystal structure and Hirshfeld surface analysis of the anionic tetrakis-complex of lanthanum(III) NMe4LaL 4 with the CAPh-ligand dimethyl (2,2,2-trichloroacetyl)phosphoramidate

A crystal structure of the anionic tetrakis-complex of lanthanum(III) NMe4LaL 4 with the CAPh-ligand dimethyl (2,2,2-trichloroacetyl)phosphoramidate is reported and discussed.


Structural commentary
The title compound (C 4 H 12 N)[La(C 4 H 6 Cl 3 NO 4 P) 4 ] crystallizes in the monoclinic crystal system with two molecules in the unit cell. Both the cation and the anion have crystallographically-imposed C 2 symmetry with atoms La1 and N3 located on the twofold axis. The molecular structure of the complex is shown in Fig. 1. In the complex, the La 3+ ion has a triangular dodecahedral coordination environment formed by the eight O atoms of the bidentate CAPh ligands and the N(CH 3 ) 4 + unit acts as the counter-ion (Fig. 1) (2) and 1.459 (2) Å (Amirkhanov et al., 2014). The C-O and P-O bonds of the ligand in the complex are longer than those in the neutral ligand (HL), indicating greater C O and P O double-bond character in HL than in NMe 4 LaL 4 . The C-N and P-N bonds, with lengths in the ranges 1.291 (6)-1.292 (6) and 1.598 (4)-1.602 (5) Å , respectively, in NMe 4 LaL 4 are shorter compared to those in the free ligand, in which the reported C-N bond length is 1.347 (2) Å and P-N is 1.676 (1) Å (Amirkhanov et al., 1995).

Supramolecular features
There are no classical hydrogen bonds in the crystal structure of the title compound, although the complexes are linked via numerous weak C-HÁ Á ÁO and ClÁ Á ÁCl intermolecular inter-actions (Table 1). In particular, the PO and OCH 3 groups of the ligands are involved in the formation of interactions with the hydrogen atoms of the tetramethylammonium cation, linking the complex anion and the counter-ion in a chain along the b-axis direction. The Cl12AÁ Á ÁCl12A ii [symmetry code (ii): Àx, Ày + 1, Àz + 1] interactions, at 3.475 (12) Å , are only 0.03 Å less than the sum of the van der Waals radii but definitely below the maximum separation (4.0 Å ) considered to represent at least weak, attractive ClÁ Á ÁCl interactions (Capdevila-Cortada et al., 2016). These serve to connect neighbouring chains. The crystal packing of the title compound is shown in Fig. 2.

Hirshfeld surface analysis and fingerprint plots
To visualize the intermolecular interactions in the title compound, the Hirshfeld surface and its corresponding twodimensional fingerprint plots (Spackman et al., 2009) were calculated using CrystalExplorer17 (Turner et al., 2017). There are several light-red spots on the d norm surface (Fig. 3), which correspond to OÁ Á ÁH/HÁ Á ÁO contacts. They are located near the oxygen atoms of the ligand PO groups and the hydrogen atoms of the tetramethylammonium cation. Thus, the strongest contacts in the crystal of the title compound exist between the NMe 4 + cation and the complex anion. The two-dimensional fingerprint plots show distances from the Hirshfeld surface to the nearest exterior atom (d e plots) and from an interior atom to the surface (d i plots), specify atomÁ Á Áatom contacts in a crystal and provide a quantitative idea of the types of intermolecular contacts experienced by molecules. An analysis of the fingerprint plots (  Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) Àx þ 1 2 ; y þ 1; Àz þ 3 2 .

Figure 2
The crystal packing of the title compound viewed along the b-axis direction.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 25% probability level. Hydrogen atoms are omitted for clarity [Symmetry code: (i) Àx + 1 2 , y, Àz + 1 2 ).

Synthesis and crystallization
The 1 H NMR spectrum of a solution of the title compound in DMSO-d 6 was recorded on a Varian 400 NMR spectrometer at room temperature. The infrared (IR) spectrum was recorded on a Perkin-Elmer BX-II Bruker spectrometer using a KBr pellet.
Preparation of NMe 4 LaL 4. LaCl 3 Á7H 2 O (0.0371 g, 0.1 mmol) in the presence of HC(OC 2 H 5 ) 3 (0.14 ml, 0.7 mmol) as dehydrating agent was dissolved in 2-propanol under heating. In a separate flask, NaL (0.1122 g, 0.4 mmol) was dissolved in acetone and NMe 4 Cl (0.0121 g, 0.11 mmol) was added under stirring and heating. The two mixtures were combined and boiled for a minute, then cooled to room temperature. A white precipitate of NaCl was formed and was filtered off and the filtrate left in a flask in a desiccator over CaCl 2 . After two days, colourless crystals suitable for X-ray diffraction studies were obtained. The crystals were filtered off, washed with 2-propanol and dried in air.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were placed in calculated positions and refined with a riding model: C-H = 0.96 Å with U iso (H) = 1.5U eq (C).
The structure exhibits disorder of the Cl atoms of one CCl 3 substituent. All Cl-C bond distances were restrained to be similar to each other (within a standard deviation of 0.005 Å ) with a target value of 1.745 Å . U ij values of the disordered chlorine atoms were restrained to be similar to each other (within a standard deviation of 0.02 Å 2 ). The disorder ratio is 50 to 50. SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Tetramethylammonium tetrakis{2,2,2-trichloro-1-[(dimethoxyphosphoryl)imino]ethanolato}lanthanum(III)
Crystal data (C 4  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.92 e Å −3 Δρ min = −0.91 e Å −3 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.