Crystal structure of pentakis(ethylenediamine-κ2 N,N′)lanthanum(III) trichloride–ethylenediamine–dichloromethane (1/1/1)

The crystal structure of the title compound consists of a ten-coordinate lanthanum(III) cation chelated by five ethylenediamine ligands. This complex co-crystallized with one molecule of ethylenediamine and three chloride anions.

We report here the crystal structure of a ten-coordinate lanthanum(III) metal coordinated by five bidentate ethylenediamine ligands, [La(C 2 H 8 N 2 ) 5 ]Cl 3 Á-C 2 H 8 N 2 ÁCH 2 Cl 2 . One free ethylenediamine molecule and three Cl À anions are also located in the asymmetric unit. The overall structure is held together by an extensive hydrogen-bonding network between the Cl À anions and the NH groups on the metal-bound ethylenediamine ligands. The free ethylenediamine molecule is held in an ordered position by additional hydrogen bonds involving both the chlorides and -NH groups on the metal-bound ligands. One highly disordered molecule of dichloromethane is located on an inversion center; however, all attempts to model this disorder were unsuccessful. The electron density in this space was removed using the BYPASS procedure [van der Sluis & Spek (1990). Acta Cryst. A46, 194-201].

Chemical context
The coordination chemistry of rare earth elements has impact in the areas of nuclear power, light-emitting diodes, medical imaging agents, and fluorescent sensors. The geometry of this ten-coordinate lanthanum(III) structure is of interest to researchers developing high denticity ligands for lanthanides and actinides.

Structural commentary
The asymmetric unit of the title compound contains one La III ion chelated by five ethylenediamine molecules, one unbound ethylenediamine molecule, and three chloride ions (Fig. 1). The coordination geometry of the La 3+ ion resembles a distorted bicapped square antiprism [range of La-N bond lengths = 2.715 (3)-2.876 (3) Å ]. Interestingly, all three Cl À ions and the free ethylenediamine molecule are involved in an extensive hydrogen-bonding network that acts to rigidify the three-dimensional structure within the crystal lattice (see Figs. 2 and 3, and Table 1).
Each asymmetric unit contains one small void that lies on an inversion center (see the Supramolecular features and Refinement sections for more discussion on the contents and treatment of this void).

Supramolecular features
Six La 3+ -containing complex cations and twelve Cl À anions are arranged in a rough hexagon in the bc plane (Fig. 2). The center of this hexagon contains two free ethylenediamine molecules involved in extensive hydrogen bonding with the Cl À ions and bound -NH groups of the lanthanum complex. The relatively non-polar portion of the free ethylenediamine molecules face the interior of the hexagon, which creates a void that resembles the shape of the chair conformation of cyclohexane. There are two of these voids per unit cell (see Refinement section) each located about an inversion center and likely containing one highly disordered dichloromethane molecule.
A view of the packing down the a axis ( Fig. 3) reveals that the lanthanum complexes are arranged into a honeycomb-like lattice. Each side of the lanthanum complex supramolecular hexagon is shared with a neighboring hexagon and held together with extensive hydrogen-bonding interactions (Table 1).

Database survey
Related structures involving a lanthanum(III) ion coordinated by three or more ethylenediamine ligands have been reported by Jia et al. (2005Jia et al. ( , 2006, Feng et al. (2009)   The asymmetric unit of the title crystal structure, showing displacement ellipsoids at the 50% probability level. H atoms have been omitted for clarity. Color codes: black C, blue N, purple La, light blue Cl.

Figure 3
The extended hydrogen-bonding network forming a honeycomb-like network, viewed down the a axis. H atoms not involved in a hydrogen bond have been omitted for clarity. Hydrogen bonds are shown as red dashed lines. Color codes as in Fig. 1.

Synthesis and crystallization
Crystals suitable for X-ray diffraction studies were serendipitously grown from the vapor diffusion of a 3:1 ethylenediamine-dichloromethane solution into a saturated solution of the lanthanum(III)-ligand complex previously reported by our group (Sartain et al., 2014) in acetonitrile.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were placed in calculated positions and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C,N) for methylene and amino groups. In the free ethylenediamine molecule, N-H distances were restrained to 0.9 Å using DFIX instructions in SHELXL (Sheldrick, 2008). If these hydrogens were left unrestrained, the result was bond lengths that were outside accepted values.

Special details
Experimental. Absorption correction: SADABS-2012/1 (Bruker, 2012) was used for absorption correction. wR2(int) was 0.0852 before and 0.0598 after correction. The Ratio of minimum to maximum transmission is 0.8603. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.