Synthesis, Crystal Structure, DFT Theoretical Calculationand Physico-Chemical Characterization of a New Complex Material (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O

Abstract

The chemical preparation, crystal structure, Hirshfeld surface analysis and spectroscopic characterization of the novel cadmium (II) 2,5-dichloro-p-phenylendiaminium decachlorotricadmate(II) hexahydrate complex, (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O, has been reported. The atomic arrangement can be described as built up by an anionic framework, formed by edge-sharing [CdCl₆]²⁻ octahedra in linear polymeric chains spreading along the a-axis, while the organic cations surround these latters. The inspection of the Hirshfeld surface analysis helps to discuss the strength of hydrogen bonds and to quantify the inter-contacts, which reveal that H…Cl/Cl…H (38.9%), H…H (13.9%), and Cd…Cl/Cl…Cd (12.4%) are the main interactions that govern the crystal packing of the studied structure. SEM/EDXwas carried out and the powder XRD confirmed the good crystallinity of the material. FT-IR and the DFT calculation reveal the good correlation between the experimental and the theoretical wavenumbers. The HOMO-LUMO energy gap was used to predict the electric conductivity of the compound. Finally, the thermal TGA/DTA analysis shows stability until 380 K.

1. Introduction

In recent years, great efforts have been developed for hybrid materials. In fact, the idea behind these types of materials is to optimize both organic and inorganic components on the molecular scale and the expected material takes advantage of organic (such as polymerizable and mesomorphism) and inorganic moieties (such as conductivity), where their properties are strongly dependent on their structures [1,2,3,4,5,6,7].

The approach is based on the identification of the hydrogen bond acceptor sites, as their sites with the hydrogen bond donors have the potential to afford organized crystalline arrays in different dimensions [8,9,10]. In fact, amines are commonly selected as potential hydrogen bonding donors and metal halides are particularly considered as strong hydrogen bond acceptors. Particularly, 2,5-dichloro-p-phenylendiamine is an organic molecule which contains two amino groups on the aromatic ring. It is a good template presenting both rigidity and flexibility and is also rarely studied. The non-planarity and the stabilization of the amine is the result of a balance between two opposing forces: the conjugation of the nitrogen lone pair with the aromatic ring [11]. This latter is a very useful in several fields such as microelectronics and electromagnetic sensors, due to the high environmental stability, and controllable electrical conductivity [12,13,14]. However, it should be emphasized that solid-state structures arise from a balance of intermolecular forces. Although stronger forces may dominate, weaker forces (donor-acceptor interactions, and dispersion forces) are also important and may lead together to the development of the three-dimensional network [9].The association of protonated organic cations and metallic-based moieties, either anions or polyatomic clusters, led to a remarkable diversity of assemblies. As metal halides, halocadmates(II) have received considerable attention thanks to their polymorphic behavior, electronic configuration, and lattice location. Moreover, their structural diversity is the key issue in semiconductor physics, supramolecular studies, and bioinorganic studies [15,16,17,18].

The principal goal of this work is to give detailed information about the anionic polymeric part of the considered compound with respect to its physicochemical properties. Thus, in order to examine the interactions inside the supramolecular arrangement, it is important to study their quantitative measurements.

2. Experimental

2.1. Elaboration of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O

The studied compound (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O was prepared by an acid-base reaction between HCl, cadmium chloride and 2,5-dichloro-p-phenylenediaminein in a stoichiometric amount 3:2.

A 5.5 g of CdCl₂ (3 × 10⁻² mol) was mixed with HCl (purity 37%) and neutralized by 2 × 10⁻² mol of 2,5-dichloro-p-phenylenediamine (3.5 g, purity 97%) dissolved in ethanol.

After three weeks, colorless plate crystals adequate for XRD study were obtained with dimensions of 0.4 × 0.15 × 0.15 mm³.

The chemical reaction scheme is:

3CdCl₂ + 2C₆H₈Cl₂N₂ + 4HCl + 4H₂O→(C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O

The elemental analysis technique is used in order to determine the proposed formula: C (12.43%/12.45%); H (2.41%/2.44%); N (4.83%/4.84%) (exp/theor).

2.2. Charactrisation

2.2.1. X-ray Powder Diffraction (XRPD) Analysis

PXRD pattern was recorded using a Siemens D 5000 diffractometer (λ = 1.542 Å) with 2θ in the range 5–50°.

2.2.2. X-ray Single-Crystal Structural Analysis

The X-ray diffraction data were collected at 150 K using a Rigaku AFC system equipped with graphitmonochromatedMoKα radiation. The absorption corrections were made with the help of the Rigaku/MSC Crystal clear package [19]. The structure was solved by a dual space method with the Olex 2 program and refined by successive differential Fourier syntheses and performed on F² by a full matrix least squares procedure using the Olex2.refine program [20,21].

The structure of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O was developed in the centrosymmetric space group P$\overline{1}$. The drawings were made with Diamond2.0 [22] and the structural graphics of the asymmetric unit were created with Mercury 3.8 [23].

2.2.3. Morphologies and EDX Analysis

SEM micrographs were observed on JEOL-6610LV electron microscope at an acceleration voltage of 20 kV, with a magnification of 500× and 1500×, coupled with Oxford X-Max microanalysis system EDX.

2.2.4. Spectroscopic Measurements

The (FT-IR) spectrum was registeredusing a NICOLET IR 200 between 4000 and 500 cm⁻¹.

2.2.5. Thermal Study

The TGA/DTA was performed with a PYRIS 1TG machine on 12.772 mg with a scanning rate of 5 Kmin⁻¹ under a dynamic argon atmosphere from 300 to 1100 K.

2.2.6. DFT Calculation

Theoretical calculations were made on the two organic ligands and on the Cd₃Cl₁₃ group as defined in the asymmetric unit. All calculationswere made using the DFT/B3LYP/LanL2DZ basis set for all atoms. The software used is Gaussian A-09, except for the boundary orbital calculations for which Gaussian-98was used. The results were analyzed with Molekel (border orbitals and MEP), Gauss-Sum (IR and orbital distribution (DOS)) and Molden (preparation of files, analysis of optimizations and spectra) softwares.

3. Results and Discussion

3.1. SEM Morphologies and EDX Analysis

SEM/EDX is a technique that has been used to observe the size, morphology and to determine the elemental composition of the crystal. Figure 1a shows the surface morphology of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O. As it can be seen, the surface is uniformly made by an assembly of fine particles with a stick form.

Figure 1. SEM images of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O for a magnification 500 times (left) and 1500 times (right) (a). EDX spectrum in the zone of high contrast (b).

Additionally, in order to verify the elements present in the studied material, the EDX profile has been recorded and is shown in Figure 1b. The spectrum confirms the presence of Cd, Cl, N, C, and O in the target material.

3.2. X-ray Powder Diffraction (XRPD) Analysis

Figure 2 compares the XRPD pattern of the compound (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O with those generated from the single-crystal data. The overlaid simulated XRDP closely resembles the experimental pattern at the majority of the positions of the peaks.

Figure 2. Theoretical and experimental XRPD of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

3.3. Crystal Structure Description

The asymmetric unit consists of two halves of (C₆H₈Cl₂N₂)²⁺, three water molecules and one half of [Cd₃Cl₁₀]⁴⁻ anion, formed by cadmium atom Cd(1) located on an inversion center at (0,0,1/2) and Cd(2)(Figure 3). It is worth noting that the water molecules O10 are disordered equally over two positions with a molar ratio of 0.5:0.5 (O10A and O10B). The crystal data and the experimental parameters used for the intensity data collection are reported in Table 1. Selected bonds and angles are listed in Table 2; Table 3.

Figure 3. ORTEP representation of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

Table 1. Crystallographic Details.

Crystal Data
Chemical formula	Cd3Cl10·2(C6H8Cl2N2)·6(H2O)
Mr	1157.95
Crystal system, space group	Triclinic, P$\overline{1}$
Temperature (K)	150
a, b, c (Å)	6.784 (4), 9.552 (6), 13.592 (9)
α, β, γ (°)	102.247 (9), 92.665 (11), 97.160 (7)
V (Å3)	851.6 (9)
Z	1
Radiation type	Mo Kα
µ (mm−1)	2.99
Crystal size (mm)	0.4 × 0.15 × 0.15
Data Collection
Diffractometer	Rigaku Mercury
Absorption correction:	Multi-scan
Tmin, Tmax	0.421, 0.638
No. of measured, independent and observed [F2 > 2.0σ(F2)] reflections	9842, 3887, 3357
Rint	0.071
(sin θ/λ)max (Å−1)	0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S	0.041, 0.100, 1.11
No. of reflections	3887
No. of parameters	198
No. of restraints	5
Δρmax, Δρmin (e Å−3)	0.99, −1.57
CCDC No	2061865

Table 2. Distances and angles of Cd₃Cl₁₀ in (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

Distances (Å) in [Cd(1)Cl6]2−		Distances (Å) in [Cd(2)Cl6]2−
Cd1—Cl3	2.6998 (16)	Cd2—Cl3iii	2.6480 (17)
Cd1—Cl3i	2.6998 (16)	Cd2—Cl3	2.8180 (16)
Cd1—Cl4ii	2.6125 (17)	Cd2—Cl4	2.6471 (16)
Cd1—Cl4iii	2.6125 (17)	Cd2—Cl5	2.6506 (16)
Cd1—Cl5i	2.5857 (15)	Cd2—Cl6	2.5269 (15)
Cd1—Cl5	2.5857 (15)	Cd2—Cl7	2.5681 (16)
Angles (°) in [Cd3Cl10]4−
Cl3—Cd1—Cl3i	180.0	Cl4—Cd2—Cl3	91.58 (3)
Cl4ii—Cd1—Cl3	95.52 (3)	Cl4—Cd2—Cl3iii	84.83 (3)
Cl4iii—Cd1—Cl3i	95.52 (3)	Cl5—Cd2—Cl3	82.78 (3)
Cl4ii—Cd1—Cl3i	84.48 (3)	Cl5—Cd2—Cl3iii	89.82 (3)
Cl4iii—Cd1—Cl3	84.48 (3)	Cl5—Cd2—Cl4	172.55 (3)
Cl4iii—Cd1—Cl4ii	180.0	Cl6—Cd2—Cl3	84.46 (3)
Cl5—Cd1—Cl3i	93.63 (3)	Cl6—Cd2—Cl3iii	168.21 (3)
Cl5—Cd1—Cl3	86.37 (3)	Cl6—Cd2—Cl4	90.00 (3)
Cl5i—Cd1—Cl3i	86.37 (3)	Cl6—Cd2—Cl5	94.27 (3)
Cl5i—Cd1—Cl3	93.63 (3)	Cl7—Cd2—Cl3	172.96 (3)
Cl5—Cd1—Cl4ii	89.73 (3)	Cl7—Cd2—Cl3iii	94.57 (3)
Cl5i—Cd1—Cl4iii	89.73 (3)	Cl7—Cd2—Cl4	95.40 (3)
Cl5—Cd1—Cl4iii	90.27 (3)	Cl7—Cd2—Cl5	90.18 (3)
Cl5i—Cd1—Cl4ii	90.27 (3)	Cl7—Cd2—Cl6	96.47 (3)
Cl5i—Cd1—Cl5	180.0	Cd2—Cl3—Cd1i	91.97 (3)
Cd2—Cl4—Cd1vi	96.39 (3)	Cd2iii—Cl3—Cd1i	94.30 (3)
Cd2—Cl5—Cd1i		98.57 (3)

Symmetrycodes: (i) −x+2, −y, −z+1; (ii) x+1, y, z; (iii) −x+1, −y, −z+1; (vi) x−1, y, z.

Table 3. Geometric feature of (C₆H₈Cl₂N₂)²⁺ in (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

Distances (Å) in (C6H8Cl2N2)2+
Cl8—C18	1.727 (4)	Cl9—C20	1.731 (4)
N13—C17	1.477 (5)	N14—C15	1.452 (5)
C17—C18	1.388 (5)	C15—C16	1.393 (5)
C17—C19	1.376 (5)	C15—C20	1.395 (6)
C18—C19	1.388 (5)	C16—C20	1.385 (6)
Angles (°) in (C6H8Cl2N2)2+
C18—C17—N13	120.7 (3)	C16—C15—N14	120.0 (4)
C19—C17—N13	118.0 (3)	C20—C15—N14	120.6 (3)
C19—C17—C18	121.1 (4)	C20—C15—C16	119.4 (4)
C17—C18—Cl8	120.4 (3)	C20—C16—C15	119.4 (4)
C19—C18—Cl8	120.1 (3)	C15—C20—Cl9	118.8 (3)
C19—C18—C17	119.4 (4)	C16—C20—Cl9	120.0 (3)
C18—C19—C17	119.5 (3)	C16—C20—C15	121.2 (4)

The crystal packing is formed by a polymeric chains of [Cd₃Cl₁₀]_n⁴ⁿ⁻ anions propagating parallel to the a-axis (Figure 4). These chains, located at z = ½, are made by edge-sharing CdCl₆ octahedra, where the [C₆H₈Cl₂N₂]²⁺ and H₂O are inserted between these chains.

Figure 4. View of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O along the $\overrightarrow{b}$ direction.

The stability and cohesion of the atomic arrangement are made via a large number of hydrogen bonds between the cations and the inorganic polymeric chains: N14–H13C…Cl6, N13–H13B…Cl5, N13–H13A…Cl6 and N13–H13B…O11 hydrogen bonds (Table 4).

Table 4. H-bond characteristic (Å, º).

D-H…A	D-H	H…A	D…A	D-H…A
N14—H14a…O11vii	0.88 (3)	1.88 (3)	2.768 (5)	178 (3)
N14—H14c…O12viii	0.88 (3)	1.99 (3)	2.851 (5)	164 (2)
N13—H13b…O11vi	0.97 (4)	2.01 (4)	2.946 (6)	162 (4)
N14—H14b…Cl6ix	0.99 (2)	2.19 (4)	3.118 (5)	156 (6)
N13—H13a…Cl5i	0.98 (6)	2.66 (5)	3.200 (5)	115 (3)
N13—H13a…Cl6v	0.98 (6)	2.35 (5)	3.139 (4)	138 (4)
O11—H11b…O12ii	0.93 (5)	1.80 (5)	2.728 (4)	174 (5)
O12—H12b…O10A	0.90 (6)	1.93 (6)	2.817 (15)	174 (6)
O12—H12b…O10Biii	0.90 (6)	2.03 (6)	2.878 (14)	157 (6)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x+1, y, z; (iii) −x+1, −y+1, −z+1; (v) x+1, y, z; (vi) −x+1, −y, −z+1, (vii) x, y, z+1; (viii) x−1, y, z+1; (ix) −x, −y+1, −z+2.

For the inorganic entity, two types of cadmium chloride octahedral are observed: Cd(1)Cl₆ and Cd(2)Cl₆, which give rise to a polymeric chain of [Cd₃Cl₁₀]_n⁴ⁿ⁻ along the b-axis. Figure 5 shows that the Cd(1)Cl₆ octahedron shares one bridging chlorine atoms (Cl(4) and Cl(3)) with the Cd(2)Cl₆ ocathedra, generated by a symmetric center, share one bridging chlorine atoms (Cl(3) and Cl(3′)). Moreover, the bond length and angles vary with the environment around the Cl atoms. The value of the Cd-Cl bond lengths are in the range 2.527–2.818 Å. The average bridging Cd-Cl distances, of 2.6695 Å, are longer than the terminal ones, equal to 2.5936 Å, and the Cl-Cd-Cl bond angles vary from 168.21 to 180° [24,25,26,27,28]. These distortionsare most likely caused by the interaction of the NH₃⁺ groups with the chloride pairs that affect the distortion of the CdCl₆ units via Cd²⁺ lone pair.

Figure 5. The [Cd₃Cl₁₀]⁴⁻ trimer coordination.

The average values of the distortion parameters of the [CdCl₆]²⁻ octahedra were calculated using Equations (1) and (2), respectively:

$$\mathrm{ID}(\mathrm{Cd}-\mathrm{Cl})={\sum }_{\mathrm{i}=1}^{\mathrm{n}1}\frac{\left|\mathrm{di}-\mathrm{dm}\right|}{\mathrm{n}1\mathrm{dm}},$$

(1)

$$\mathrm{ID}(\mathrm{Cl}-\mathrm{Cd}-\mathrm{Cl})={\sum }_{\mathrm{i}=1}^{\mathrm{n}2}\frac{\left|\mathrm{ai}-\mathrm{am}\right|}{\mathrm{n}2\mathrm{am}},$$

(2)

where d is the (Cd-Cl) distance, a is the (Cl-Cd-Cl) angle, m is the average value, n1 = 6 and n2 = 12. The value of the distortion indices were ID(Cd-Cl) = 0.044 and ID(Cl-Cd-Cl) = 0.0026 for Cd(1)Cl₆ and ID(Cd-Cl) = 0.063 and ID(Cl-Cd-Cl) = 0.0026 for Cd(2)Cl₆. These low values highlight the distorted octahedron geometry of the metal.

On the other hand, the organic part of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O is made by two crystallographic independent [C₆H₈Cl₂N₂]²⁺ dictations. The cations containing C17, C18 and C19 carbon atoms (molecule A) are located at (0,0,0), while those formed by C15, C16 and C20 (molecule B) carbon atoms are located over the inversion center at (1/2,1/2,0) and are linked to the water molecules via N-H…O and O-H…O hydrogen bonds to form ribbons extending along the c-axis and located at y = ½ (Figure 6). It is worth mentioning that all organic molecules are parallel to each other and are stacked in an offset manner, but there is nevertheless a degree of π-π overlap between adjacent rings since the distance between two organic cations corresponds to a unit cell, equal to 6.784(4), while the interaction C-Cl…π could be considered since the shortest distance between the centroid of the ring and chloride atom is 3.504 Å [29,30].

Figure 6. Perspectiveviewof (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

The main geometrical characteristics of these entities, grouped in Table 3, agree with that found in the literature [31,32,33,34].

3.4. Hirshfeld Surface

(HS) analysis was carried out for decoding and quantifying the intermolecular contributions in the solid material using Crystal Explorer 17.5 [35]. The 2D fingerprint plots are used to highlight a particular atom pain in close contact [36].

The calculation of enrichment ratio for a pair of elements (X, Y) E_XY is given in the reference [37], as shown in Table 5.

Table 5. Hirshfeld contact surfaces and enrichment ratios for (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

Atoms	H	Cl	C	Cd	O
Surface%	35.65	39.4	13.45	6.3	1.5
O	2.8	0	0	0	0
Cd	0.04	2.49	0	0	0
C	0.14	0.72	4.9	0	0
Cl	1.38	0.63	0.72	2.49	0
H	1.09	1.38	0.14	0.04	2.8

Figure 7a shows the d_norm surface for 2,5-dichloro-p-phenylendiaminium decachlorotricadmate (II) hexahydrate. Herein, the red spots are attributed to the N-H…O and O-H…O hydrogen bonds. However, the small flat regions delineated by the blue outline in the surface mapped with curvedness indicate the absence of π…π stacking interactions in the structure. In addition, there is no evidence of the adjacent red and blue triangles on the shape index surface (Figure 7b,c).

Figure 7. The HS mapped with d_norm (a). Shape index (b) and curvedness (c) for the title compound.

Figure 8 contains the percentages of the different interactions. The 2D fingerprint plot reveals that H…Cl/Cl…H contacts are the most encountered interactions and their relative contribution reaches 38.9%, as shown in Figure 9a, due to the abundance of chloride and hydrogen on the molecular surface (%S_Cl = 39.4% and % S_H = 35.65%) with an enrichment ratio E_HCl = 1.38. Indeed, the structure cohesion is ensured by three N-H…Cl hydrogen bonds (Table 4). The H…H contact represent 13.9% (Figure 9b). The Cd…Cl/Cl…Cdis around 12.4% (Figure 9c) with an enrichment ratio E_CdCl = 2.49, followed by Cl…Cl 9.9% (Figure 9d) and C…C 8.9% (Figure 9e). The Cl…Cl intermolecular interactions are marked by a low amount of enrichment ratio E_ClCl = 0.63 due to the electrostatic repulsion between two charges of the same sign. The C…C contacts have the most enrichment value, E_CC = 4.9, due to the accumulation of aromatic nuclei in the crystalline packing S_C = 13.45%. Other interconnects, such as C…Cl/Cl…C 7.7% (Figure 9f), H…C/C…H 1.4% (Figure 9h) and Cd…H/H…Cd 0.2% (Figure 9i) contributes less to the surface. The C…Cl, H…C and Cd…H interactions are; E_CCl = 0.72, E_HC = 0.14 and E_CdH = 0.04. The low enrichment ratio value reveals that pairs tend to avoid contact with each other. Finally, the percentage of H…O/H…O intermolecular interactions is around 3% (Figure 9g) and they are over-represented (E_HO = 2.8). Indeed, there are three N-H…O and three O-H…O hydrogen bonds in the structure (Table 4).

Figure 8. Contacts in (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O crystals.

Figure 9. Fingerprint plots showing contribution from different contact. (a) H…Cl/Cl…H, (b) H…H, (c) Cd…Cl/Cl…Cd, (d) Cl…Cl, (e) C…C, (f) C…Cl/Cl…C, (g) O…H/H…O, (h) H…C/C…H, (i) Cd…H/H…Cd.

3.5. Infrared Spectral Studies

The FT-IR was used to verify the functional groups in the synthesized material and their vibrational behavior. Figure 10 display the FT-IR spectrum of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O. Since all bands originating from the vibration of the anions are observed below 400 cm⁻¹, the vibrational spectrum is only due to the cation [38].

Figure 10. Infrared absorption spectrum of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

The bands at high-frequency domain can be attributed to the N-H, O-H and C-H stretching vibrations. The assignment and the deduction of these bands are based on similar reported results [39,40].

Indeed, the bands observed at 3572 cm⁻¹, 3528 cm⁻¹, and 3496 cm⁻¹ are attributed to υ_(O-H) of water molecules confirmed by DFT computations with the frequency at 3498 cm⁻¹ and 3420 cm⁻¹. However, the two bands at 3347 and 3401 cm⁻¹ are assigned to the stretching vibrations of the N-H group. The DFT calculation predicted these modes in the range 3159 and 3134 cm⁻¹. As matter of fact, hydrogen bonding interactions influence the frequency as well as the intensity and the width of these vibrations. As for the C-H stretching bands, they are assigned generally between 3000 and 2800 cm⁻¹ and are visible by DFT computation at 2970 and 3185 cm⁻¹. Moreover, the band between 1590 and 1480 cm⁻¹ corresponds to δ_(N-H) and δ_(O-H) deformation vibrations. This vibration is well observed by DFT calculations by a large band at 1485 cm⁻¹.

Furthermore, the vibration band located 1406 cm⁻¹ is assigned to the υ_(C=C) aromatic ring stretching vibrations, this vibration is well-observed by the DFT calculation and was found at 1421 cm⁻¹. The vibration at 1103 cm⁻¹ corresponds to aromatic C-H in plan bending mode and it is confirmed by DFT calculations at 1080 cm⁻¹. Moreover, the band at 817 cm⁻¹ corresponds to the out of plan bending of the benzene ring, which is consistent with the proposed tetra-substituted benzene ring. The vibration bands between 1292 cm⁻¹ and 1172 cm⁻¹ are attributed to valence vibrations of υ_(C-N), DFT calculations predicted this mode at 1350 cm⁻¹ and at 1250 cm⁻¹. Additionally, the C-Cl stretching frequencies are seen at 875 cm⁻¹. However, the ρ_(C-H) and ω_(N-H) vibrations bands appear at 650 cm⁻¹ and 500 cm⁻¹ as weak bands, and this was calculated to be found in the region 1000 to 500 cm⁻¹ and they are weakly visible.

The DFT-IR spectrum and the experimental spectrum, given in Figure 10, are very similar. In Figure 11 a nice straight-line correlation was observed. It is worth considering that when comparing both experimental and theoretical results, the theoretically predicted parameters were calculated in a simulated water phase, and this latter is so far from the experimental environment. Subsequently, small deviations should not be surprising. Even so, the results demonstrate a good agreement, which is well-confirmed by the correlation (R² = 0.987) that is mostly achieved in the fingerprint region.

Figure 11. Calculated vs. experimental wavenumbers of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

3.6. Quantum Mechanical Study of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O

The HOMO and LUMO molecular orbitals were determined (Figure 12). As it can be seen, the HOMO-LUMO energy difference is very small, around 0.2 eV, which seems to indicate a weak stability. The HOMO is localizedon the inorganic part of the system, while the LUMO islocated on the organic and the inorganic parts, which will lead to electronic transfers from one to the other. The (DOS)energy is represented in Figure 13.

Figure 12. Frontier molecular orbitals in (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

Figure 13. The DOS spectrum of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

3.7. Molecular Electrosatatic Ootential (MEP) Analysis

The MEP map is used to identify the active sites of a given molecule. For this reason, MEP mapped surface of this compound is shown in Figure 14. As it can be seen, the electrostatic potential maps are colour-coded and are subdivided into many regions. The blue and red colours indicate the positive and negative potentials, respectively. The inorganic part is negative, while the organic entity is positive. These results agree with Mulliken charges (Table 6).

Figure 14. MEP surface of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

Table 6. Mulliken charge distribution in (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

Atom	Mulliken Charge
C1	1.331123
C2	−4.737247
C3	−1.070936
H(C3)	0.206980
C4	−1.443429
C5	0.547071
C6	1.649255
H(C6)	0.271790
Cl7	−0.075264
Cl9	0.262067
N8	1.487065
H(N8)	0.380289 0.392109 0.403416
N10	−1.070241
H(N10)	0.523128 0.497461 0.479144
Cd	1.202720 1.335296 1.175898
Cl	−0.680423 −0.919000 −0.747317 −0.452354 −0.606892 −0.576617 −0.534910 −0.845237 −0.556969 −0.728453 −0.787878 −0.596435 −0.715207

3.8. Mulliken Population Analysis of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O

The Mulliken charge distribution of all atoms is shown in Table 6. The underlined atoms are those that are interacting in the Cd₃Cl₁₃ + Ligand 2 system. The transfer occurs to the para atoms of those where the interaction takes place (carbon 2 and other nitrogen). The atoms of the organic molecule are numbered as depicted in Figure 15.

Figure 15. The atoms numbering of the organic molecule.

For the Cd₃Cl₁₃anion, the cadmium ions have positive charges, while all chlorine atoms have negative charges. For the organic cations, Cl7 has a negative charge of −0.075, while Cl9 has a positive charge of 0.262. The nitrogen atoms N8 have a positive charge of 1.487, while the N10 has a negative charge of −1.070. The carbon atoms C1, C5 and C6 have positive charges, while C2, C3 and C4 have negative charges. It is worth noting that hydrogen atoms in the range 0.206–0.523 carry a positive charge.

3.9. Thermal Analysis

Thermal analysis is one of the most useful methods of analysis in collecting both physical and chemical information. For this reason, we chose (TG/DTA), the most used technique of thermal analysis in providing information about the bonding of components within the sample. The TGA and DTA measurements, in the range 200–1200 K, are depicted in Figure 16.

Figure 16. TGA/DTA curves of (C₆H₈Cl₂N₂)₂[Cd₃Cl₁₀]·6H₂O.

The first peak in the DTA curve occurred at 380 K with ΔH = 994.99 J.g⁻¹, corresponding to the complete dehydration of the compound. It is accompanied by a weight loss observed in the TGA curve equal to 7.78% (calculated weight loss: 7.79%). While the three endothermic peaks observed in the DTA curve at 452, 535, and 600 K correspond to the decomposition of the organic matrix with a total experimental weight loss equal to 30.94% and calculated weight loss: 30.92%. Then, the DTA curve presents a sharp endothermic peak, centered at 919 K, corresponding to the degradation of the inorganic group (exp.loss: 59.60%/thero. loss: 59.74%). At the end of the experience, the obtained solid is a black residuethat represents1.68% of the initial mass.

4. Conclusions

A new hybrid material of cadmium with 2,5-dichloro-p-phenylenediamine has been synthesized in an aqueous solution at room temperature. XRD analysis shows that 2,5-dichloro-p-phenylendiaminium decachlorotricadmate(II) hexahydrate crystallizes in the triclinic crystal system P$\overline{1}$, the different entities are held together by columbic attraction and multiple hydrogen bonds to form a three-dimensional network. The Hirshfeld surface analysis and the 2D fingerprint plots were performed and highlight that Van der Waal forces exert an important role on the stabilization in the crystal structure. Scanning electronic microscopy (SEM) was carried out and the EDX spectrum of the title compound revealed the presence of all non-hydrogen atoms. The powder XRD is in agreementwith single-crystal. Structural and spectroscopic proprieties were investigated by FT-IR spectroscopy as well as by DFT calculation. The MEP map defines the nucleophile and the electrophile sites. The HOMO-LUMO energy gap proposes a good electric conductivity. Finally, the thermal stability is proved by TGA/DTA thermal analysis.