Influence of water on the structure and magnetic properties of a copper bromide coordination compound with 3-amino-4-ethoxycarbonylpyrazole

The influence of water on a polynuclear [CuL₂Br₂]_n (1) copper bromide compound with 3-amino-4-ethoxycarbonylpyrazole (L) is investigated. The abundance of water in solution results in the formation of three new complexes with drastically different coordination units: polynuclear {[CuL₄Br]Br}_n·nH₂O (2) and two mononuclear polymorphs [CuL₄Br₂]·2H₂O (monoclinic-3, triclinic-4). The crystal structures are determined for all three complexes. Complex 2 has a weak (≪1 cm^-1) superexchange interaction between copper ions and bromide ions. Complexes 3 and 4 have no exchange interaction. It is found that the two polynuclear complexes may transform into each other through dissolution followed by recrystallization under certain conditions.