Synthesis, crystal structure, thermal and luminescence properties of CuX(2,3-dimethylpyrazine) (X = Cl, Br, I) coordination polymers

Abstract

Three new coordination polymers based on CuI and 2,3-dimethylpyrazine (2,3-dmpyz) were prepared, structurally characterized and investigated for their thermal and luminescence properties. In the ligand rich 2:3 compound [(CuI)2(2,3-dmpyz)3] (CuI)2 dimers are found, which are connected by the N-donor ligands into chains, whereas in the structure of the 1:1 intermediate [(CuI)(2,3-dmpyz)] (CuI)4 tetramers are found, which are also connected into chains. The crystal structure of the ligand deficient 2:1 compound [(CuI)2(2,3-dmpyz)] is built up of CuI double chains, which are connected by the 2,3-dmpyz ligands into layers. Thermal decomposition of results in its direct transformation into the ligand deficient compound , without the formation of the 1:1 compound as an intermediate. A similar thermal reactivity is found for compound , which transforms into on heating. Stirring of a crystalline suspension of pure or in acetonitrile, always leads to a transformation into the ligand deficient compound indicating that compound is the most stable of all the coordination polymers, whereas compounds and are metastable. The luminescence properties of the CuCl and CuI coordination polymers were investigated at 298 and 77K. It was observed that the emission maxima strongly depends on the nature of the halide atom and the composition and structure of the coordination polymers. In addition, several of these compounds show luminescence thermochromism. These results are compared with those obtained for the previously reported CuCl and CuBr(2,3-dimethylpyrazine) coordination polymers.

Pyrazine-bridged copper(I) iodide coordination polymers: Control of chain separation through ligand design

“…The aromatic rings of the stacked ligands are coplanar with the quinoxaline rings overlapping, in such a way that the fused benzene ring of one overlaps the fused pyrazine of another with an inter-layer separation of 3.376(3) Å , a centroid-to-centroid distance of 3.90(1) Å and a ''slippage'' [18] of 0.36(1) Å . This structure is similar to that formed by the reaction of copper(I) bromide with quinoxaline [4]. However, in that case the quinoxaline rings bridge the copper atoms through both ring nitrogens, leading to a structure in which the copper halide ladders are much closer together.…”

“…Pyrazines, which are well-known bridging ligands [2], have been used for this purpose. For example, X-ray crystal structures have been reported of copper(I) iodide ladders bridged by methylpyrazine [3], 2,3-dimethylpyrazine [4] and quinoxaline [5], in which adjacent ladders are separated by approximately 7 Å . In a similar complex with a 2,2 0 -dimethyl-4,4 0 -bipyrimidine bridge this separation is extended to 11 Å [6].…”

Cu(I) hybrid inorganic–organic materials with intriguing stimuli responsive and optoelectronic properties

“…Upon cooling to 77 K a red shift in the emission bands was observed for 16-19 suggesting that also metalcentered or metal-metal "bond" to ligand charge transfer excited states should be taken into account. Differently, for 20 with significant cuprophilic interactions, a "classical" thermochromism was observed (a blue shift from 664 nm at room temperature to 462 nm at 77 K (2,3-dmpyz)], 24 (2,3-dmpyz = 2,3-dimethylpyrazine), obtained by reaction of CuX (X=Cl, I) with the N-donor ligand [40]. A dependence on the nature of the halide atom was found in the room temperature solid state emission spectra, with maxima at 544-560 nm for the iodine-containing polymers and at 621-631nm for the chlorine ones.…”

A Rational Route to Coordination Polymers with Condensed Networks and Cooperative Magnetic Properties

“…However, even if some of these compounds exhibit interesting properties like luminescence or thermoluminescence one important property is missing because they are all diamagnetic. [48,59,67] This is a pity because the preparation of coordination polymers that show cooperative magnetic properties is still a major challenge in the field. In this context it is noted that 1D and 2D coordination compounds that show a slow relaxation of the magnetization like e.g.…”