Destabilisation of a dual-synthon hydrogen bonding motif by packing effects and competing hydrogen bond donors

Abstract

Several Cu^II complexes of carbamoyldicyanomethanide (cdm, C(CN)₂(CONH₂)⁻) with various bidentate co-ligands have been prepared and characterised to examine the persistence of a previously observed dual-synthon ‘heterotape’ hydrogen-bonding motif that incorporates both amide and nitrile functionalities. Using 2,2′-bipyridine or 1,10-phenanthroline as co-ligands yields dimeric complexes of the form [Cu(cdm)Cl(L)]₂·2MeOH (L = 2,2′-bipy 1 or 1,10-phen 2). However, the bridging species in these two dimers are different; μ₂ chloride bridging in the bipyridine dimer and η¹(N):η¹(N′) cdm bridging in the phenanthroline complex. The subtle change in co-ligand prompts a change in the bridging mode that prevents the desired motif from forming in the phenanthroline structure, an effect that appears to arise from the greater π-stacking of the phenanthroline groups. The dimeric complex [Cu(cdm)(acac)(H₂O)]₂3 and the monomeric complexes [Cu(cdm)₂(NH₂(CH₂)₃NH₂)] 4 and [Mn(cdm)Cl(1,10-phen)₂] 5 also fail to display the expected tape motif, although other complicated hydrogen bonding is present, and their structures are discussed.