Synthesis, crystal structure and thermal properties of silver(I) bromide ethylenediamine coordination polymers

Reaction of silver(I) bromide with ethylenediamine (en) leads to the formation of the 1:1 compound poly[AgBr(μ2-en-N,N′)] (I). In the crystal structure the silver atoms of AgBr dimers are connected to two bridging bromine atoms and two nitrogen atoms of different en ligands. The dimers are thus connected by the ligands into layers via μ-N,N′ coordination. In the 2:1 coordination polymer poly[(AgBr) 2(μ2-en-N,N′)] (II) a three-dimensional AgBr substructure occur which consists of helical AgBr chains that are connected via peripheral Ag-Br contacts into a three-dimensional network that contains large channels. The en ligands are situated in these channels bridging the Ag atoms. From solution this compound cannot be obtained as a pure phase, since compound I is always formed as the major phase. On heating the 1:1 compound I in a thermobalance the sample mass decreases slowly and several mass steps are observed, which are not fully resolved. If the reaction is stopped at 230°C, pure AgBr has formed. At 115°C only traces of compound II are found. The major phase consists of an as yet unidentified ligand poor compound.