I. INTRODUCTION
The synthesis and structural studies of novel family of complexes MeX 2-2(NH2-PhY) (Baldovino-Pantaleón et al., Reference Baldovino-Pantaleón, Morales-Morales, Hernández-Ortega, Toscano and Valdés-Martinez2007; Rademeyer, Reference Rademeyer2004), where Me—transition metal; X—I, Br, Cl; Ph—phenyl radical; and Y—H or Cl, were undertaken to understand the principles guiding the construction of complex compounds and their multidimensional architecture. General structural scheme for this kind of complexes is shown in Figure 1a. Complexes with similar chemical structure are investigated due to their similarity to cisplatin; c i s-Pt(NH3)2Cl2 [Figure 1b], a compound which belongs to very important group of anticancer drugs (Thorn et al., Reference Thorn, Willet and Twamley2006).
The aim of our study is to replace Pt by other transition metals (e.g., Cd or Zn), Cl by other halogen atoms, and NH3 by aromatic amines, to synthesize new compounds, and next to investigate their structural and other properties by many techniques including powder diffraction.
Some properties of these compounds, such as low solubility in water, imply a possibility of their applications in removing of toxic pollutants, for instance, cadmium or zinc salts and aromatic amines. Such compounds can also be used as a storage media for amines or cadmium compounds. Their application in crystal engineering (hybrid inorganic-organic materials with structures based on fragments of CdI2 layers or blocs with rotational polymorphism) seems also quite interesting.
In this paper we present results of first part of our studies for compounds with general formula CdI2-2(NH2-PhY). Results of further investigations will be subject of subsequent publications (Dobija et al., in press).
II. SYNTHESIS
To obtain a series of aniline derivative complexes, aniline or chloroanilines were mixed with water (10 ml) and 2-propanol (5 ml) and slowly (drop wisely) added to warm solution of CdI2 (1.83 g, 0.005 mol) in water (15 ml). To obtain CdI2⋅2[NH2–C6H5] 0.93 g (0.01 mol) of aniline was used whereas for syntheses bis(2-chloroaniline) diiodidecadmium(II), bis(3-chloroaniline) diiodidecadmium(II), and bis(4-chloroaniline) diiodidecadmium(II) hemi(4-chloroanilate), 2-, 3-, and 4-chloroaniline (1.27 g, 0.01 mol) were used, respectively. After one day obtained white precipitates were filtered off, washed with the mixture of water (12 ml) and 2-propanol (4 ml), and dried in air. Before the X-ray powder diffraction measurements the samples were thoroughly powdered.
Figure 1. Structural scheme of complexes of formula CdI2-2(NH2-PhY) (a) and cisplatin (b).
TABLE I. Crystallographic data of the investigated compounds.
a Determined by chemical analysis or single-crystal studies.
b Smith and Snyder, Reference Smith and Snyder1979.
c de Wolff, Reference de Wolff1968.
II. EXPERIMENTAL
Powder diffraction data were collected on a Philips X-pert PRO MPD diffractometer equipped with a X’celerator detector. The measurements were performed at room temperature, 2θ range from 5° to 90° 2θ, converted with 0.02° step. Other experimental details were as follows: radiation type—Cu K α (1.541 87 Å) at 40 kV, 30 mA; fixed divergence slit ½, receiving slit of 0.1. Peak positions were determined by use of the second derivative method using program written by Sonneveld and Visser (Reference Sonneveld and Visser1975); unit-cell parameters were determined using indexing programs of the PROSZKI package (Łasocha and Lewiński, Reference Łasocha and Lewiński1994). High-temperature studies were carried out in air, on a Philips X-pert PRO MPD diffractometer, using XRK camera (Anthon Paar). Annealing temperatures of the samples were as follow: 25, 100, 200, 300, and 400 °C.
IV. RESULTS AND DISCUSSION
A. Powder diffraction
Crystallographic data for the investigated compounds are shown in Table I. The first two compounds {1, 2} crystallize in the monoclinic crystal system with space group C2/c and the last two {3 and 4} in the triclinic crystal system with space group P-1. Unit-cell parameters for the compounds {1, 2, and 4} were confirmed by structural studies on single-crystal samples. Complete structural data will be the subject of further publications, diffraction data are listed in Tables II – V. Compound {3} crystallizes only in the form of very fine powder, which makes it impossible to carry out classical structural single-crystal studies. At the same time, the small number of strong diffraction lines makes indexing problem extremely difficult. Obtaining reliable unit-cell parameters is also hampered because of a dominant zone problem. We used all indexing programs (Łasocha and Lewiński, Reference Łasocha and Lewiński1994) to obtain solutions based on two periods: 14.183(1) Å, 7.0278(1) Å, and 98.25(1)°, while the third one is determined with lower reliability. Among dozens of plausible solutions we have selected one with the volume enabling accommodation in the unit-cell two formal molecules. To check lattice parameters for this compound additional efforts such as structural studies or recrystallization are necessary. Such studies as we mentioned above are in progress.
Compound {4} seems to be a very interesting sample. Despite of many attempts (synthesis with various amounts of the reactants) the compound with a formula CdI2-2(NH2-Ph)⋅1/2(NH2-PhCl) was always obtained. Excess of amine is likely to stabilize the structure; it is also the reason for lower density in comparison to other compounds {1, 2, and 3}.
B. High-temperature X-ray diffraction
The obtained compounds become very unstable with increasing temperature. All the compounds decompose at temperature about 200 °C (Figures 2 – 5). Cadmium iodide is the final main product of thermal decomposition of the investigated compounds, PDF-4+ 00-033-0239 or PDF-4+ 01-089-3192 (ICDD, Reference Kabekkodu2009). In the temperature of 400 °C, melting of the CdI2 samples is observed and all diffraction lines disappear. The compound {4} also decomposes in a similar way, and structural changes connected with the loss of excess of amine were not observed (Figure 5). Compounds {1} and {3} appeared to be the most unstable (Figures 2 and 4). Lines from cadmium iodide appear in temperature of 100 °C, and the pure CdI2 phase is observed in temperature of 200 °C. In the case of compounds {2} and {4} additional peaks (not listed on above mentioned PDF cards) are observed even in the temperatures above 200 °C. These maxima can be partially attributed to other polytypic modifications of cadmium iodide (Figures 3 and 5).
TABLE II. X-ray diffraction data of CdI2⋅2[NH2–C6H5] {1}.
TABLE III. X-ray diffraction data of CdI2⋅2[NH2–C6H4Cl] {2}
TABLE IV. X-ray diffraction data of CdI2⋅2[NH2–C6H4Cl] {3}. Two lines (2θ,d,I): 30.537, 2.927 54, 0.5 and 37.782 00, 2.381 17, 0.25% were not indexed.
TABLE V. X-ray diffraction data of {CdI2⋅2[NH2–C6H4Cl]}1/2NH2–C6H4Cl {4}.
Figure 2. Powder diffraction patterns of CdI2⋅2[NH2–C6H5] {1} in various temperatures.
Figure 3. Powder diffraction patterns of CdI2⋅2[NH2–C6H4Cl] {2} in various temperatures.
Figure 4. The X-ray patterns of the compound CdI2⋅2[NH2–C6H4Cl] {3} in various temperatures.
Figure 5. The powder diffraction patterns of the compound {CdI2⋅2[NH2–C6H4Cl]}1/2NH2–C6H4Cl {4} in various temperatures.
V. CONCLUSION
Four new complexes of cadmium iodide with aniline and its derivatives were obtained. Crystallographic parameters (e.g., a, b, c, α, β, γ, Z, D x, and space group) of these compounds were determined, and stability of these compounds as a function of increased temperature was examined. More detailed crystal structure studies, tests for the presence of rotational polymorphism, and initial pharmaceutical investigations will be the subject of our further research. The investigations were carried out due to the fact that obtained compounds can be of interest in environmental chemistry to remove or neutralize cadmium ion contaminants. In controlled conditions, these compounds may also serve as depository of amines or heavy atoms.
ACKNOWLEDGMENT
Support by ICCD Grant in Aid program is kindly acknowledged.
