Synthesis, crystal structures and investigations on the thermal properties of new CuBr(2-ethylpyrazine) coordination polymers

The new 3:2 coordination polymer catena[Cu3Br3 (mu(2)-2-ethylpyrazine-N,N')(2)] (I) was prepared by the reaction of CuBr with 2-ethylpyrazine in acetonitrile at room temperature. Its crystal structure consists of Cu3Br3 rings which are connected by the 2-ethylpyrazine ligands to chains. The 2:1 compound poly[Cu2Br2(mu(2)-2-ethylpyrazine-N,N')] (II) was only obtained phase pure if the reaction was performed at 100 degreesC. In this compound CuBr single chains occur, which are connected to sheets by the 2-ethylpyrazine ligands. If compound I is heated it decomposes in two separate steps as shown by thermogravimetry (TG), differential thermoanalysis (DTA) and mass spectroscopy (MS). Ex situ and temperature dependent in situ X-ray powder diffraction experiments prove that in the first step the 2:1 coordination polymer II has formed as the phase pure compound which decomposes to CuBr in the second step. From heating rate dependent TG measurements there is no hint for the occurrence of additional intermediates during the thermal decomposition reaction.