Ammonium salts of carbamoyldicyanomethanide, C(CN)2(CONH2)−: Effects of hydrogen-bonding cations on anionic networks

Abstract

A series of five salts of carboamoyldicyanomethanide, C(CN)₂(CONH₂)⁻cdm, have been synthesised and structurally characterised using different cations; ammonium (1), methylammonium (2), dimethylammonium (3), trimethylammonium (4) and tetramethylammonium (5). These organic salts vary in the degree of hydrogen-bonding interactions that the cation can partake in with minimal change in the size of the cation. The structure of 1 shows the NH₄ cation involved in extensive hydrogen bonding to the cdm anions to form a 3D network with minimal interaction between anions and the disruption of previously observed supramolecular synthons that occur between cdm anions. In contrast to this the structure of 5 contains no hydrogen-bonding between cations and anions and leads to the formation of a corrugated sheet containing only interactions between neighbouring anions. The intermediate cases involving the MeH₃N⁺ (2), Me₂H₂N⁺ (3) and Me₃HN⁺ (4) cations, display a 2D hydrogen bonded sheet in the case of 2 and 1D chains in the structures of 3 and 4. The structure of a larger tetraalkylammonium salt, (Et₃MeN)cdm (6) contains a similar sheet network to that of the Me₄N⁺ compound with subtle changes due to the increase in size of the counter cation. The role of the steric bulk of the counter-cation has been further investigated by the synthesis of the benzyltrimethylammonium salt of cdm (7) in which the anions form a previously observed 1D chain motif and are well separated due to the bulk of the cation.