Elsevier

Journal of Molecular Structure

Volume 1156, 15 March 2018, Pages 235-242
Journal of Molecular Structure

2D polymeric cadmium(II) complexes containing 1,3-imidazolidine-2-thione (Imt) ligand, [Cd(Imt)(H2O)2(SO4)]n and [Cd(Imt)2(N3)2]n

https://doi.org/10.1016/j.molstruc.2017.11.067Get rights and content

Highlights

  • Crystal structures of [Cd(Imt)(H2O)2(SO4)]n (1) and [Cd(Imt)2(N3)2]n (2); Imt = 1,3-imidazolidine-2-thione.

  • Compounds 1 and 2 exist as 2D polymers.

  • Polymers are formed by μ3-SO4 and μ(1,3) azide groups in 1 and 2 respectively.

Abstract

The present study aims at preparing and carrying out the structural investigation of two polymeric cadmium(II) complexes of imidazolidine-2-thione (Imt) based on sulfate or azide ions, [Cd(Imt)(H2O)2(SO4)]n (1) and [Cd(Imt)2(N3)2]n (2). The structures of the complexes were determined by single crystal X-ray analysis. Both compounds, 1 and 2 crystallize in the form of 2D coordination polymers and the cadmium(II) ion is six-coordinate having a distorted octahedral geometry in each compound. In 1, the metal ion is bonded to one sulfur atom of Imt and five oxygen atoms with two from water and three of bridging sulfate ions. In 2, the cadmium coordination sphere is completed by two Imt molecules binding through the sulfur atoms and four nitrogen atoms of bridging azide ions. The crystal structures are stabilized by intra and intermolecular hydrogen bonding interactions. The complexes were also characterized by IR and NMR spectroscopy and the spectroscopic data is consistent with the binding of the ligands.

Introduction

Cadmium(II) is known to form a wide variety of 1:1 to 1:4 complexes with thiones (L), with the structural arrangements generally based on tetrahedral and octahedral coordination environments. The 1:1 complexes [1], [2], [3], [4] for example, [Cd(Tu)(H2O)2(SO4)]n [2] and [Cd(MeImt)(SeCN)2]n [4] (MeImt = N-methylimidazolidine-2-thione) usually exist in the polymeric form. The structures of the 1:2 complexes such as, [Cd(Tu)2X2] [5], [Cd(Dmtu)2X2] [6], [7], [Cd(Tmtu)2X2] [8], [9], [10] or [Cd(Imt)2X2] [11], [12] (X = Cl, Br, I) are the most common and often consist of discrete monomeric molecules with a tetrahedrally [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21] (or octahedrally [22], [23]) coordinated Cd(II) ion. In some cases, polymeric species are formed through bridging sulfur or nitrogen atoms [21], [24], [25], [26], [27], [28], [29], e.g., [Cd(Metu)2(SCN)2]n [24] and [Cd(Imt)2(SCN)2]n [25]. The 1:3 compounds are rare. The crystal structure of [Cd(Tu)3(SO4)] shows that the molecule is a dimer, and the coordination around the metal atom is intermediate between square pyramidal and trigonal bipyramidal [30]. Another such compound is known in the form of a co-crystal of [Cd(Tu)2(H2O)4]SO4 and [Cd(Tu)3(H2O)3]SO4 [31]. The complexes with a Cd:thione ratio of 1:4 may be ionic or nonionic. In the ionic complexes like [Cd(2-mercaptopyridine)4](NO3)2 [32] or [Cd(Diaz)4]SO4 (Diaz = 1,3-diazinane-2-thione) [33], the Cd(II) atom possesses a tetrahedral environment. The molecular species for instance, [Cd(Diaz)4Cl2] [34] display a distorted octahedral geometry around the metal ion [29], [34], [35]. These structural studies show that thioureas or thiones coordinate to cadmium(II) via the sulfur atom. We have reported earlier the crystal structures of several cadmium(II) complexes of heterocyclic thiones [4], [5], [6], [7], [8], [9], [10], [14], [15], [16], [17], [23], [24], [33], [34], [35]. To investigate further about the structural aspects of such complexes, we report in this work the spectroscopic data and X-ray structures of two new 2D polymeric cadmium(II) complexes of imidazolidine-2-thione (Imt), [Cd(Imt)(H2O)2(SO4)]n (1) and [Cd(Imt)2(N3)2]n (2). The main goal of the present study is to exploit the effect of binding flexibility of sulfate and azide ions for the preparation of Cd-Imt polymers.

Section snippets

Materials

Cadmium sulfate (CdSO4·8/3H2O) and NaN3 were obtained from Merck Chemical Company, Germany. Imidazolidine-2-thione was prepared according to the method reported in the literature [36].

Synthesis of [Cd(Imt)(H2O)2(SO4)]n (1) and [Cd(Imt)2(N3)2] (2)

Complex 1 was prepared by adding 0.10 g (1.0 mmol) Imt in 15 mL methanol to an aqueous solution (5 mL) of cadmium sulfate (0.26 g, 1.0 mmol) and stirring the mixture for 30 min. Mixing resulted in a colorless solution. The clear solution was kept at room temperature for crystallization. As a result, a white

X-ray structure studies

The molecular structure of compound 1 is illustrated in Fig. 1. Selected bond angles and distances are given in Table 2. The compound crystallizes in Pbca space group in the form of a 2D polymer comprising of [Cd(Imt)(H2O)2(SO4)] units (Fig. 2). The 2D wavy network is characterized by 12-membered ring motifs [CdOSO]3, where the cadmium ion is hexa-coordinate as [Cd(Imt)(OH2)2(OSO3)3]. It is bonded to two water molecules in a cis position, the sulfur atom of the terminal imidazolidine-2-thione

Conclusion

This paper describes the synthesis and structural characterization of two cadmium(II) complexes of 1,3-imidazolidine-2-thione (Imt), [Cd(Imt)(H2O)2(SO4)]n (1) and [Cd(Imt)2(N3)2]n (2). The X-ray structures of the complexes show that both of them exist in the form of two dimensional polymers with each cadmium atom being octahedrally coordinated. The polymers are assembled through triply-bridging sulfate and doubly-bridging, μ(1,3) azide ions in case of 1 and 2 respectively. The 2D polymers are

Acknowledgement

The Deanship of Scientific Research, Prince Sattam bin Abdulaziz University, Al-Kharj, Saudi Arabia is gratefully acknowledged for supporting this work through Project No. 2016/01/6822.

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