Coordination complexes and polymers from the initial application of phenyl-2-pyridyl ketone azine in mercury chemistry
Graphical abstract
The initial use of phenyl-2-pyridyl ketone azine in mercury chemistry afforded a series of neutral monomeric and dimeric HgII coordination compounds and polymers. The synthesis of different products is dependent upon the identity of the ancillary ligands present in the reaction mixture, namely halides and pseudo-halides. All products were characterized using X-ray crystallography, thermal analyses, and fluorescence studies.
Introduction
Mercury and its compounds [1], [2], [3], [4], [5], [6], [7], [8] are of immense importance in chemistry and related disciplines due to their potential applications in the paper industry and as preservatives, paints, cosmetics, fluorescent lamps, sensors and mercury batteries [9], [10], [11], [12]. Exploiting the diversity in coordination geometries around this 5d10 ion, different coordination frameworks may be accessed using a variety of organic ligands along with different inorganic/organic bridging units [1], [13], [14]. The coordination behavior of azines as organic spacers has spawned great interest in recent years due to the ease of their syntheses, their chelating abilities, and the various denticities; additionally, subtle steric and/or electronic control on their frameworks has proven to lead to different monometallic and homo- or heterobimetallic complexes with interesting properties [15], [16], [17]. Halides [1], [14](b), [14](c), [18], [19], thiocyanates, ambidentate pseudohalides [13](a), [14](a), [20], [21], and nitrites [22] are suitable terminal/bridging groups in mercury chemistry, and in combination with organic ligands often result in different molecular frameworks and crystalline networks through their versatile ligation modes and different non-covalent forces [23], [24].
The ligand of choice for this work was phenyl-2-pyridyl ketone azine (L; Scheme 1). This ligand has previously afforded a small suite of products, including mono and/or dinuclear Cu, Ag, Ni, Zn, Co (all 3d metals) and Ag (4d metal) complexes [25]; however, there is no report of 5d metal complexes with L. Thus, we ventured to study the coordination behavior of this ligand in HgII, and explore its coordination chemistry with a 5d metal ion. This work also focuses on the metal ion and its coordination geometry; along these lines we were particularly interested to investigate the synthesis of various complexes, and also structurally characterize the resulting products. Subtle changes to these geometries were also to be probed in this systematic study, and as such we varied the anionic terminal/bridging ancillary ligands (halides, pseudohalides, etc.). Finally, the chromophore qualities of the resulting systems were of interest, and as such we were able to investigate the fluorescence properties of the resulting compounds. Therefore, herein we report the successful syntheses, X-ray crystallography, thermal behavior, and luminescence properties of three mononuclear compounds [Hg(L)Cl2] (1), [Hg(L)Br2] (2) and [Hg(L)(NO2)2] (3), one dinuclear compound [Hg2(μ-L)(SCN)4] (4) and one 1D coordination polymer [Hg(L)(μ-I2)HgI2]n (5), all incorporating the aforementioned phenyl-2-pyridyl ketone azine ligand.
Section snippets
Materials and measurements
The Schiff base, phenyl-2-pyridyl ketone azine (L) was prepared following the reported method as described elsewhere [15] and used without further purification. All other reagents and solvents used for the syntheses and analyses were commercially available and used as received. FT-IR spectra were recorded on a Bruker Tensor 27 FT-IR spectrometer. Microanalyses were performed using a Heraeus CHN-O-Rapid analyzer. Melting points were measured on an Electrothermal 9100 apparatus and are
Synthesis and spectroscopic results
The apparatus used in this work is shown in Fig. 1, and consists of a glass tube fitted with a side branched arm, which forms an angle of ∼45° with the main reaction tube. The HgII salts are typically added to the main reaction tube, and the ligand is added as a methanolic solution (0.5 mmol of the ligand L in 25 ml of methanol). Alternately, all solid reactants may be added to the main reaction tube and neat methanol (25 ml) is added to fill the apparatus. Then, the main reaction tube is sealed
Conclusions
In summary, a series of new luminous mercury(II) coordination complexes of different nuclearities were isolated from the use of a versatile Schiff base ligand, namely phenyl-2-pyridyl ketone azine, combined with various anionic co-ligands such as chloride, bromide, iodide, nitrite and thiocyanate. Structural analyses reveal an interesting variation in the coordination behavior of the ligand system from bidentate to tridentate chelating, to binucleating bis(bidentate) coordination modes. This is
Acknowledgments
We are grateful to the University of Tabriz Research Council for the financial support of this research. BKG thanks the CSIR, New Delhi, India for financial support. KB is grateful to CSIR New Delhi, India for fellowship. Finally, CL acknowledges the Cottrell College Science Award (CCSA) sponsored by the Research Corporation for Science Advancement, for the financial support.
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