Synthesis and crystal structure of 4-(2-ammonioethyl)morpholin-4-ium dichloridodiiodidocadmate/chloridotriiodidocadmate (0.90/0.10)

The crystal structure of a new inorganic–organic hybrid material, (C6H16N2O)[CdCl1.90I2.10], consists of 4-(2-ammonioethyl)morpholin-4-ium cations and dichloridodiiodidocadmate/chloridotriiodidocadmate (0.90/0.10) anions connected by hydrogen bonds into a three-dimensional network.


Chemical context
Inorganic-organic hybrid materials are crystalline materials in which the organic and inorganic moieties are connected via covalent, ionic or hydrogen bonds inside the structures. These materials provide the opportunity to combine intended properties of both the organic and inorganic components when they are self-assembled in the solid state. For instance, inorganic metal halides may be associated with functionalized organic molecules (carboxylic acids, amides or amines) to produce two different types of hybrid materials, both of which are of technological interest. When the organic molecules coordinate to the metal ions of the metal halides, the resulting products are called coordination polymers or coordination compounds. The coordination polymers may be related to compounds with metal-organic framework (MOF) structures. These MOF materials have been studied intensively due to their intriguing structures and their potentially interesting properties, including high porosity, structural flexibility, nonlinear optical behaviour or magnetic properties (Mitzi et al., 2001).
Once the moieties are combined as perhalidometalate anions and organic cations, the resulting products are called ionic organic-inorganic hybrid materials. These materials frequently conserve the properties of the individual parts, i.e. the organic component may add structural diversity and optical properties (fluorescence and luminescence), while the inorganic component potentially contributes to mechanical ISSN 2056-9890 resistance, thermal stability, electric properties (conductor, semiconductor, insulator) or magnetic properties (Ciurtin et al., 2001). Well-tested applications of these ionic hybrids include light-emitting diodes (LEDs) (Ciurtin et al., 2001). Moreover, in these materials, the crystal packing is ensured by Coulombic interactions and hydrogen bonds. These noncovalent weak forces of N-HÁ Á Áhalide-metal play a vital role in supramolecular chemistry and continue to attract much attention. As a contribution to the investigation of the above materials, we report here the crystal structure of one such compound, (C 6 H 16 N 2 O)[CdCl 1.90 I 2.10 ], formed from the reaction of 4-(2-aminoethyl)morpholine and cadmium iodide in hydrochloric acid.

Structural commentary
The asymmetric unit of the title hybrid salt, (C 6 (Fig. 1), both occupying general positions in the unit cell. Each Cd II atom is tetracoordinate in a distorted tetrahedral environment defined by two Cl atoms and two I atoms in 90% of the cases and by one Cl atom and three I atoms in the remaining 10%. The disorder involves only one halogen site and implicates the statistical presence of the Cl1 and I3 atoms. The partial presence of iodine in this site reflects a small increase of the Cd-Cl1 bond length when compared with Cd-Cl2 [2.5919 (11) and 2.5148 (11) Å , respectively]. The other Cd-Cl and Cd-I bond lengths are in agreement with the values reported in the literature (Sato et al., 1986;Ishihara et al., 2000). The average distortion of the [CdCl 1.90 I 2.10 ] 2À anion from the ideal tetrahedral conformation can be confirmed by the values of the two largest angles around the Cd II atom [115.28 (2) and 120.96 (4) ]. These two angles can also be used to calculate the 4 structural parameter introduced by Yang et al. (2007) for complexes with coordination number four (CN = 4) to quantify this distortion. This parameter is defined as 4 = [360 À ( + )]/(360 À 2), where and are the two greatest valence angles around the central atom and = 109.5 is the ideal tetrahedral angle. 4 can range from 1 to 0, passing from an ideal tetrahedral to a perfect square-planar conformation. The 4 value of the present structure is 0.87, indicative of a distorted tetrahedral environment. The bond angles involving the Cd II atom range between 94.15 (3) and 120.95 (4) . The lower value, significantly smaller than all the other bond angles, is observed for The asymmetric unit of the title compound, with displacement ellipsoids drawn at the 50% probability level. Table 1 Hydrogen-bond geometry (Å , ).  (3) 149 (4) Symmetry codes: (i) x; Ày þ 1 2 ; z À 1 2 ; (ii) Àx þ 2; y À 1 2 ; Àz þ 1 2 .

Figure 2
Packing diagram of the title compound viewed approximately along the a axis, showing the three-dimensional hydrogen-bonding network (dashed lines). Only the hydrogen bonds formed when the disordered halogen site is occupied by the Cl atom (i.e. the predominant situation) are reported for clarity.
the Cl1-Cd-Cl2 angle. This distortion is too large to be attributed uniquely to the structural disorder involving the Cl1 site and suggests the involvement of the Cl atoms in a complex system of N-HÁ Á ÁCl hydrogen bonds as being responsible of the phenomenon.

Supramolecular features
As depicted in Fig. 1, the organic entity is double protonated at both the N atoms (N1 and N2) to ensure charge balance. In connectivity terms, the cations are linked by intermolecular N-HÁ Á ÁO hydrogen bonds involving one of the ammonium H atoms, leading to a C(6) chain motif, with the corrugated chains extending parallel to the c axis. The [CdCl 1.90 I 2.10 ] 2À anions lie between the chains to maximize the electrostatic interactions and are connected with the organic cations via N-HÁ Á ÁCl and C-HÁ Á ÁCl1(I3) hydrogen bonds (Table 1). These hydrogen bonds develop in the ab plane, leading to the formation of a three-dimensional network structure (Fig. 2). The analysis of the N-HÁ Á ÁCl distances, varying between 2.38 and 2.40 Å , shows that they are much shorter than the sum of the van der Waals radii, indicating a rather strong character of these hydrogen bonds.  (El Glaoui et al., 2008;Lamshö ft et al., 2011), in which the Zn II atom is coordinated by four Cl atoms in a slightly distorted tetrahedral environment ( 4 = 0.93). In spite of a common symmetry and of a certain similitude in the unit-cell parameters, this and the title compound are not isotypic. Due to a major efficency in the hydrogenbond formation, the [ZnCl 4 ] 2À anions interact in a different way with the cations, building layers parallel to the ac plane and not, as in the title compound, a three-dimensional network structure. Calculation of the index geometry for fourcoordinated atoms, 4 , shows that the distortion of the tetrahalidocadmate unit in the present compound ( 4 = 0.87) is not only larger than that observed in the previously mentioned [ZnCl 4 ] 2À analogue, but also than the one of the [ZnI 2 Cl 2 ] 2À unit ( 4 = 0.95) in the salt with N-methyl-1,3,5-triaza-7phosphaadamantane (Smolenski et al., 2009). This confirms the involvement of the Cl atoms in a complex system of strong N-HÁ Á ÁCl hydrogen bonds at the origin of tetrahedral distortion observed in the present case.
An aqueous solution of 4-(2-aminoethyl)morpholine was added dropwise to a mixture of CdI 2 and HCl in a minimum amount of water (20 ml). After stirring for a period of 4 h, the resulting solution was placed in a Petri dish and allowed to evaporate slowly at room temperature. Single crystals of the title compound, suitable for X-ray diffraction analysis, were obtained after several days (yield $78%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. One halogen site was found to be statistically occupied by Cl and I atoms (Cl1 and I3). The siteoccupancy factors were refined by assuming full site occupancy and by using the same coordinates and anisotropic displacement parameters for both atoms. The N-bound morpholinium H atom was located in a difference Fourier map and refined freely. All other H were placed geometrically and refined as riding, with N-H = 0.89 Å and C-H = 0.97 Å . The  Computer programs: APEX2 and SAINT (Bruker, 2008), SHELXT (Sheldrick, 2015a), SHELXL2014 (Sheldrick, 2015b), ORTEP-3 (Farrugia, 2012) and SCHAKAL (Keller, 1999).
isotropic displacement parameters of the ammonium H atoms were refined freely, whereas the remaining ones were refined with U iso (H) = 1.2U eq (C). A rotating model was used for the ammonium group.

4-(2-Ammonioethyl)morpholin-4-ium dichloridodiiodidocadmate/chloridotriiodidocadmate (0.90/0.10)
Crystal data (C 6  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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )