Synthesis, decomposition studies and crystal structure of a three-dimensional CuCN network structure with protonated N-methylethanolamine as the guest cation

Abstract

The compound poly[2-hydroxy-N-methylethan-1-aminium [μ₃-cyanido-κ³C:C:N-di-μ-cyanido-κ⁴C:N-dicuprate(I)]], {(C₃H₁₀NO)[Cu₂(CN)₃]}_n or [meoenH]Cu₂(CN)₃, crystallizes in the tetragonal space group P4₃. The structure consists of a three-dimensional (3D) anionic Cu^ICN network with noncoordinated protonated N-methylethanolamine cations providing charge neutrality. Pairs of cuprophilic Cu atoms are bridged by the C atoms of μ₃-cyanide ligands, which link these units into a 4₃ spiral along the c axis. The spirals are linked together into a 3D anionic network by the two other cyanide groups. The cationic moieties are linked into their own 4₃ spiral via N-H...O and O-H...O hydrogen bonds, and the cations interact with the 3D network via an unusual pair of N-H...N hydrogen bonds to one of the μ₂-cyanide groups. Thermogravimetric analysis indicates an initial loss of the base cation and one cyanide as HCN at temperatures in the range 130-250 °C to form CuCN. We show how loss of a specific cyanide group from the 3D CuCN structure could form the linear CuCN structure. Further heating leaves a residue of elemental copper, isolated as the oxide.

Keywords: 3D network; copper cyanide; crystal structure; cuprophilic interaction; decomposition study; ethanolamine; spiral configuration; thermogravimetric analysis.