Elsevier

Polyhedron

Volume 29, Issue 7, 10 May 2010, Pages 1815-1821
Polyhedron

An unprecedented coordination mode of the orotate ligand in novel polynuclear cadmium(II)–orotate complexes

https://doi.org/10.1016/j.poly.2010.02.037Get rights and content

Abstract

Two novel carboxylate-bridged Cd(II)–orotate polynuclear complexes with 2-(2-ethylamino)pyridine (2-etapy), [Cd(μ-HOr)(2-etapy)]n (1), and N,N-diethylethylenediamine (N,N-eten) ligands, {[Cd(μ-HOr)(H2O)(N,N-eten)]·H2O}n (2) (H3Or = orotic acid), have been synthesized and characterized by TGA–evolved gas analysis (TGA–EGA), IR spectroscopy and single crystal X-ray diffraction techniques. The orotate ligand acts as a bridging ligand with two different coordination modes, showing an unprecedented tetradentate coordination mode. The HOr ligand simultaneously chelates Cd(II) ions through the carboxylate oxygen, deprotonated pyrimidine nitrogen atoms and carboxyl oxygen atoms as a tetradentate ligand in 1. In complex 2, the HOr ligand bridges two Cd(II) ions through the carboxylate oxygen and deprotonated pyrimidine nitrogen atoms and oxygen atom of a carboxylate group of a neighbouring complex unit. Three-dimensional (3D) supramolecular structures are generated by hydrogen-bonding, and π···π and C–H···π interactions between the closest chains in both complexes.

Graphical abstract

We have successfully synthesized the polynuclear cadmium(II)–orotate complexes Cd(μ-HOr)(2-etapy)]n and {[Cd(μ-HOr)(H2O)(N,N-eten)]·H2O}n. In the complexes, the orotate ligand exhibits a new coordination mode in addition to the 23 different modes so far crystallographically characterized.

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Introduction

The design and synthesis of coordination polymers has received much attention in recent years because of their interesting molecular topologies and potential applications in catalysis, non-linear optics, sensors, gas storage and magnetism [1], [2], [3], [4], [5]. Heterocyclic carboxylates such as pyrazine, pyridine, pyrazole and imidazole carboxylic acids have been used in the construction of supramolecular coordination polymers [6], [7], [8], [9], [10], [11], [12]. 2,6-Dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid (orotic acid, vitamin B13, H3Or) is one of such interesting ligands and has been widely studied in recent years as a polyfunctional ligand because of its significance in the biosynthesis of pyrimidine bases [13], [14], and antitumor activity displays for Ni(II), Pt(II) and Pd(II) complexes [15], [16]. Furthermore, the deprotonated orotates (H2Or and HOr2−) are widely used ligands for the construction of coordination polymers due to their versatile bridging modes, such as monodentate, bidentate, tridentate bridging and mixed chelating-bridging [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [15], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53], [54], [55], [56], [57] (Scheme 1). On the other hand, polynuclear Cd(II) complexes have attracted extensive interest in recent years because they possess photoluminescent properties [58], [59]. However, the coordination chemistry and structural properties of cadmium(II) polymers based on the orotate ligand have not been reported to date. Recently, we have reported the first mononuclear Cd(II)–orotate complexes along with their crystal structures, [Cd(HOr)2(enH)2] and [24] mer-[Cd(HOr)(H2O)QX]·2H2O [25], where the orotate ligands act as bidentate ligands. In the present paper, we described the syntheses, spectroscopic and thermal properties, and crystal structures of two novel coordination polymers of Cd(II)–orotate with 2-(2-ethylamino)pyridine and N,N-diethylethylenediamine ligands, [Cd(μ-HOr)(2-etapy)]n (1) and {[Cd(μ-HOr)(H2O)(N,N-eten)]·H2O}n (2), showing an unprecedented coordination mode for the orate ligand.

Section snippets

Materials and measurements

All chemicals used were analytical reagent grade and were commercially purchased. IR spectra were obtained with a Perkin Elmer 100 FT-IR spectrometer using KBr pellets in the 4000–400 cm1 range. A Perkin Elmer Diamond TG/DTA Thermal Analyzer was used to record simultaneous TG, DTG and DTA curves in a static air atmosphere at a heating rate of 10 °C/min in the temperature range 40–700 °C using platinum crucibles. TGA–EGA measurements were performed in Pt crucibles under a static air atmosphere at

Synthesis

The aim of this work was to study the effects of aliphatic and aromatic amine derivatives as co-ligands on the coordination mode of orotate in mixed-ligand complexes. Previous observations showed that a second ligand in the coordination sphere of orotate complexes could produce N- or O-coordination of the orotate anion, as observed in [Pt(PEt3)2(2,6-dap)(N-HL)] [28], [Cu(H2Or)(PPh3)2] [29], [Mn(HOr)(bipy)(H2O)]n [50] and recently in {[Cu(μ-HOr)(ba)2]}n [66]. The reaction of different amine

Conclusions

We have successfully synthesized the two polynuclear cadmium(II)–orotate complexes, [Cd(μ-HOr)(2-etapy)]n (1) and {[Cd(μ-HOr)(H2O)(N,N-eten)]·H2O}n (2). In the complexes, the orotate ligand exhibits a new coordination mode in addition to the twenty three different modes so far crystallographically characterized.

Acknowledgement

This work was supported by the Eskişehir Osmangazi University by project No. 200819042.

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