Synthesis and crystal structure of 4-(2-ammonio-eth-yl)morpholin-4-ium di-chlorido-diiodido-cadmate/chlorido-tri-iodido-cadmate (0.90/0.10).

The crystal structure of the title compound, (C6H16N2O)[CdCl1.90I2.10], a new organic-inorganic hybrid salt synthesized in the form of single crystals, consists of discrete statistically distributed di-chlorido-diiodido-cadmate/chlorido-tri-iodido-cadmate anions (occupancy ratio 0.90:0.10) and 4-(2-ammonio-eth-yl)morpholin-4-ium cations, [NH3(CH2)2NH(CH2)4O]2+. The cations are linked by inter-molecular N-H⋯O hydrogen bonds, forming corrugated chains extending parallel to the c axis. The [CdCl1.90I2.10]2- tetra-halidocadmate anions lie between the chains to maximize the electrostatic inter-actions and are connected with the organic cations via N-H⋯Cl and C-H⋯Cl(I) hydrogen bonds developing in the ab plane and leading to the formation of a three-dimensional network structure. The tetra-coordinate CdII atom has a distorted tetra-hedral conformation, with a τ4 index of 0.87.

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 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 n class="Chemical">hydrogen bonds. These non-covalent weak forces of N—H⋯halide–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, (C6H16N2O)[CdCl1.90I2.10], 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, (C6H16N2O)[CdCl1.90I2.10], contains one [NH3(CH2)2NH(CH2)4O]2+ cation and one tetra­halidocadmate anion with average composition [CdCl1.90I2.10]2− (Fig. 1 ▸), both occupying general positions in the unit cell. Each CdII 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 [CdCl1.90I2.10]2− anion from the ideal tetra­hedral conformation can be confirmed by the values of the two largest angles around the CdII atom [115.28 (2) and 120.96 (4)°]. These two angles can also be used to calculate the τ4 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 τ4 = [360 − (α + β)]/(360 − 2θ), where α and β are the two greatest valence angles around the central atom and θ = 109.5° is the ideal tetra­hedral angle. τ4 can range from 1 to 0, passing from an ideal tetra­hedral to a perfect square-planar conformation. The τ4 value of the present structure is 0.87, indicative of a distorted tetra­hedral environment. The bond angles involving the CdII 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 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—H⋯Cl hydrogen bonds as being responsible of the phenomenon.

Figure 1

The asymmetric unit of the title compound, with displacement ellipsoids drawn at the 50% probability level.

In the organic entity, the morpholine ring adopts a typical chair confirmation and all the geometrical features agree with those found in 4-(2-ammonio­eth­yl)morpholin-4-ium tetra­chlorido­zincate (El Glaoui et al., 2008 ▸; Lamshöft et al., 2011 ▸).

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—H⋯O 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 [CdCl1.90I2.10]2− anions lie between the chains to maximize the electrostatic inter­actions and are connected with the organic cations via N—H⋯Cl and C—H⋯Cl1(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—H⋯Cl 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.

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H2N⋯O1i	0.89	2.01	2.894 (4)	172
N2—H3N⋯Cl2	0.89	2.40	3.279 (4)	168
N2—H4N⋯Cl1ii	0.89	2.39	3.221 (4)	156
C2—H2A⋯I3	0.97	2.98	3.637 (4)	126
C6—H6A⋯Cl1	0.97	2.73	3.577 (4)	146
C6—H6A⋯I3	0.97	2.73	3.577 (4)	146
N1—H1N⋯Cl2	0.89 (5)	2.38 (5)	3.180 (3)	149 (4)

Symmetry codes: (i) ; (ii) .

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.

Database survey

A search of the Cambridge Structural Database (Version 5.37; last update February 2016; Groom et al., 2016 ▸) for related compounds showed the appearance of the zinc analogue of formula (C6H16N2O)[n class="Chemical">ZnCl4] (El Glaoui et al., 2008 ▸; Lamshöft et al., 2011 ▸), in which the ZnII atom is coordinated by four Cl atoms in a slightly distorted tetra­hedral environment (τ4 = 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 hydrogen-bond formation, the [ZnCl4]2− 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 four-coordinated atoms, τ4, shows that the distortion of the tetra­halidocadmate unit in the present compound (τ4 = 0.87) is not only larger than that observed in the previously mentioned [ZnCl4]2− analogue, but also than the one of the [ZnI2Cl2]2− unit (τ4 = 0.95) in the salt with N-methyl-1,3,5-tri­aza-7-phospha­adamantane (Smolenski et al., 2009 ▸). This confirms the involvement of the Cl atoms in a complex system of strong N—H⋯Cl hydrogen bonds at the origin of tetra­hedral distortion observed in the present case.

Synthesis and crystallization

Crystals of (C6H16N2O)[CdCl1.90I2.10] were prepared starting from CdI2 (purity 99%, Sigma–Aldrich), 4-(2-aminioeth­yl)morpholine (purity 99%, Sigma–Aldrich) and HCl (37% w/w), weighted in stoichiometric amounts conforming to the idealized equation:

NH2(CH2)2N(CH2)4O + CdI2 + 2HCl → [NH3(CH2)2NH(CH2)4O]CdCl2I2.

An aqueous solution of 4-(2-amino­eth­yl)morpholine was added dropwise to a mixture of CdI2 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 n class="Disease">I atoms (Cl1 and I3). The site-occupancy 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 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.

Table 2

Experimental details

Crystal data
Chemical formula	(C6H16N2O2)[CdCl1.90I2.10]
M r	578.68
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	294
a, b, c (Å)	6.7773 (14), 13.870 (3), 16.104 (3)
β (°)	93.788 (3)
V (Å3)	1510.5 (5)
Z	4
Radiation type	Mo Kα
μ (mm−1)	6.06
Crystal size (mm)	0.37 × 0.22 × 0.20
Data collection
Diffractometer	Bruker SMART CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2008 ▸)
T min, T max	0.218, 0.415
No. of measured, independent and observed [I > 2σ(I)] reflections	16802, 2879, 2626
R int	0.033
(sin θ/λ)max (Å−1)	0.611
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.024, 0.055, 1.09
No. of reflections	2879
No. of parameters	136
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	1.09, −0.82

Computer programs: APEX2 and SAINT (Bruker, 2008 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL2014 (Sheldrick, 2015b ▸), ORTEP-3 (Farrugia, 2012 ▸) and SCHAKAL (Keller, 1999 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989016013967/wm5315sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016013967/wm5315Isup2.hkl

CCDC reference: 1501997

Additional supporting information: crystallographic information; 3D view; checkCIF report

(C6H16N2O2)[CdCl1.90I2.10]	F(000) = 1063
Mr = 578.68	Dx = 2.545 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 6.7773 (14) Å	Cell parameters from 386 reflections
b = 13.870 (3) Å	θ = 8.5–19.7°
c = 16.104 (3) Å	µ = 6.06 mm−1
β = 93.788 (3)°	T = 294 K
V = 1510.5 (5) Å3	Prism, colourless
Z = 4	0.37 × 0.22 × 0.20 mm

Bruker SMART CCD diffractometer	2626 reflections with I > 2σ(I)
ω scan	Rint = 0.033
Absorption correction: multi-scan (SADABS; Bruker, 2008)	θmax = 25.7°, θmin = 1.9°
Tmin = 0.218, Tmax = 0.415	h = −8→8
16802 measured reflections	k = −16→16
2879 independent reflections	l = −19→19

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.024	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.055	w = 1/[σ2(Fo2) + (0.0208P)2 + 2.0157P] where P = (Fo2 + 2Fc2)/3
S = 1.09	(Δ/σ)max < 0.001
2879 reflections	Δρmax = 1.09 e Å−3
136 parameters	Δρmin = −0.82 e Å−3

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.

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cd1	0.58963 (4)	0.38807 (2)	0.25555 (2)	0.03751 (9)
I1	0.42207 (4)	0.42832 (2)	0.10184 (2)	0.04982 (10)
I2	0.50580 (4)	0.51493 (2)	0.37657 (2)	0.05043 (10)
Cl1	0.96790 (13)	0.38224 (6)	0.24065 (6)	0.0529 (4)	0.8977 (19)
I3	0.96790 (13)	0.38224 (6)	0.24065 (6)	0.0529 (4)	0.1023 (19)
Cl2	0.57453 (14)	0.22097 (7)	0.31540 (7)	0.0399 (2)
O1	0.9564 (4)	0.3339 (2)	0.55915 (17)	0.0457 (7)
N1	0.9882 (5)	0.2064 (2)	0.41993 (19)	0.0305 (7)
N2	0.9358 (5)	0.1077 (3)	0.2309 (2)	0.0431 (9)
H2N	0.9550	0.1249	0.1788	0.067 (16)*
H3N	0.8266	0.1357	0.2470	0.059 (15)*
H4N	0.9228	0.0439	0.2335	0.14 (3)*
C1	1.0431 (6)	0.3661 (3)	0.4858 (3)	0.0417 (10)
H1A	1.1421	0.4147	0.5005	0.050*
H1B	0.9420	0.3953	0.4484	0.050*
C2	1.1375 (6)	0.2838 (3)	0.4422 (2)	0.0364 (9)
H2A	1.1931	0.3074	0.3921	0.044*
H2B	1.2443	0.2572	0.4782	0.044*
C3	0.8898 (6)	0.1772 (3)	0.4971 (3)	0.0423 (10)
H3A	0.9854	0.1458	0.5357	0.051*
H3B	0.7846	0.1316	0.4826	0.051*
C4	0.8059 (7)	0.2645 (3)	0.5379 (3)	0.0478 (11)
H4A	0.7052	0.2936	0.5003	0.057*
H4B	0.7440	0.2449	0.5878	0.057*
C5	1.0752 (6)	0.1214 (3)	0.3779 (3)	0.0391 (9)
H5A	0.9875	0.0666	0.3823	0.047*
H5B	1.2006	0.1052	0.4071	0.047*
C6	1.1085 (6)	0.1385 (3)	0.2867 (2)	0.0362 (9)
H6A	1.1331	0.2065	0.2780	0.043*
H6B	1.2248	0.1031	0.2722	0.043*
H1N	0.894 (7)	0.232 (3)	0.386 (3)	0.041 (12)*

	U11	U22	U33	U12	U13	U23
Cd1	0.03783 (17)	0.04165 (17)	0.03285 (16)	0.00247 (13)	0.00088 (12)	0.00227 (12)
I1	0.04754 (18)	0.0661 (2)	0.03486 (16)	0.01088 (14)	−0.00489 (12)	0.00216 (13)
I2	0.05227 (18)	0.0630 (2)	0.03538 (16)	0.01156 (14)	−0.00161 (13)	−0.00926 (13)
Cl1	0.0452 (6)	0.0470 (6)	0.0661 (7)	−0.0028 (4)	0.0006 (4)	0.0049 (4)
I3	0.0452 (6)	0.0470 (6)	0.0661 (7)	−0.0028 (4)	0.0006 (4)	0.0049 (4)
Cl2	0.0285 (5)	0.0382 (5)	0.0524 (6)	−0.0018 (4)	−0.0011 (4)	0.0063 (4)
O1	0.0485 (17)	0.0536 (18)	0.0356 (16)	−0.0092 (14)	0.0067 (13)	−0.0116 (14)
N1	0.0276 (16)	0.0342 (17)	0.0291 (16)	0.0006 (13)	−0.0026 (13)	−0.0022 (13)
N2	0.038 (2)	0.059 (3)	0.032 (2)	0.0007 (17)	0.0003 (15)	−0.0022 (17)
C1	0.045 (2)	0.043 (2)	0.037 (2)	−0.0047 (19)	0.0025 (19)	−0.0054 (18)
C2	0.032 (2)	0.043 (2)	0.034 (2)	−0.0068 (17)	0.0018 (16)	−0.0048 (17)
C3	0.044 (2)	0.047 (2)	0.037 (2)	−0.0093 (19)	0.0056 (18)	−0.0011 (19)
C4	0.043 (2)	0.060 (3)	0.042 (2)	−0.011 (2)	0.0130 (19)	−0.012 (2)
C5	0.041 (2)	0.035 (2)	0.041 (2)	0.0066 (18)	−0.0019 (18)	−0.0040 (17)
C6	0.031 (2)	0.038 (2)	0.040 (2)	−0.0025 (16)	0.0036 (17)	−0.0096 (18)

Cd1—Cl2	2.5148 (11)	C1—H1A	0.9700
Cd1—Cl1	2.5919 (11)	C1—H1B	0.9700
Cd1—I1	2.7124 (6)	C2—H2A	0.9700
Cd1—I2	2.7135 (5)	C2—H2B	0.9700
O1—C1	1.425 (5)	C3—C4	1.507 (6)
O1—C4	1.428 (5)	C3—H3A	0.9700
N1—C5	1.499 (5)	C3—H3B	0.9700
N1—C2	1.503 (5)	C4—H4A	0.9700
N1—C3	1.505 (5)	C4—H4B	0.9700
N1—H1N	0.89 (5)	C5—C6	1.521 (6)
N2—C6	1.490 (5)	C5—H5A	0.9700
N2—H2N	0.8900	C5—H5B	0.9700
N2—H3N	0.8900	C6—H6A	0.9700
N2—H4N	0.8900	C6—H6B	0.9700
C1—C2	1.504 (6)
Cl2—Cd1—Cl1	94.15 (3)	N1—C2—H2B	109.5
Cl2—Cd1—I1	120.95 (3)	C1—C2—H2B	109.5
Cl1—Cd1—I1	106.20 (3)	H2A—C2—H2B	108.1
Cl2—Cd1—I2	107.85 (3)	N1—C3—C4	110.1 (3)
Cl1—Cd1—I2	110.00 (2)	N1—C3—H3A	109.6
I1—Cd1—I2	115.280 (18)	C4—C3—H3A	109.6
C1—O1—C4	109.8 (3)	N1—C3—H3B	109.6
C5—N1—C2	113.0 (3)	C4—C3—H3B	109.6
C5—N1—C3	111.7 (3)	H3A—C3—H3B	108.2
C2—N1—C3	108.9 (3)	O1—C4—C3	111.3 (3)
C5—N1—H1N	108 (3)	O1—C4—H4A	109.4
C2—N1—H1N	108 (3)	C3—C4—H4A	109.4
C3—N1—H1N	106 (3)	O1—C4—H4B	109.4
C6—N2—H2N	109.5	C3—C4—H4B	109.4
C6—N2—H3N	109.5	H4A—C4—H4B	108.0
H2N—N2—H3N	109.5	N1—C5—C6	113.7 (3)
C6—N2—H4N	109.5	N1—C5—H5A	108.8
H2N—N2—H4N	109.5	C6—C5—H5A	108.8
H3N—N2—H4N	109.5	N1—C5—H5B	108.8
O1—C1—C2	111.2 (3)	C6—C5—H5B	108.8
O1—C1—H1A	109.4	H5A—C5—H5B	107.7
C2—C1—H1A	109.4	N2—C6—C5	112.2 (3)
O1—C1—H1B	109.4	N2—C6—H6A	109.2
C2—C1—H1B	109.4	C5—C6—H6A	109.2
H1A—C1—H1B	108.0	N2—C6—H6B	109.2
N1—C2—C1	110.7 (3)	C5—C6—H6B	109.2
N1—C2—H2A	109.5	H6A—C6—H6B	107.9
C1—C2—H2A	109.5

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2N···O1i	0.89	2.01	2.894 (4)	172
N2—H3N···Cl2	0.89	2.40	3.279 (4)	168
N2—H4N···Cl1ii	0.89	2.39	3.221 (4)	156
C2—H2A···I3	0.97	2.98	3.637 (4)	126
C6—H6A···Cl1	0.97	2.73	3.577 (4)	146
C6—H6A···I3	0.97	2.73	3.577 (4)	146
N1—H1N···Cl2	0.89 (5)	2.38 (5)	3.180 (3)	149 (4)