Werner clathrates with enhanced hydrogen bonding functionality. (1st May 2019) - Wicht, Merrill M.
Graphical abstract: The robustness of the frameworks formed by hostH1, Ni(NCS)2 (nicotinamide)4 when crystallised with alcohol guests was compared with that of the same host with carbonyl guests. In all structures with alcohols, amide tetramers are formed between the neighbouring hosts and the guests are hydrogen bonding to the thiocyanate. In case of carbonyl guests, similar interactions are formed between the hosts but the lack of hydrogen bond formation between the host and the guest leads to less efficient enclathration of the guests. Competition experiment revealed that the nicotinamide based host discriminates towards 1-butanol and 4-methylcyclohexanol. The hostH2, Ni(NCS)2 (isonicotinamide)4 showed the formation of less predictable hydrogen bonded frameworks in its inclusion compounds. In the mixed ligand complex, H3, Ni(NCS)2 (nicotinamide)2 (isonicotinamide)2, the nicotinamide ligands hydrogen bonded in a similar manner seen in structures ofH1 and formed amide tetramers, whereas the isonicotinamide ligands formed a variety of discrete hydrogen bonds with neighbouring molecules. Abstract: The role of hydrogen bonding to generate molecular frameworks for selective enclathration of selected, closely related alcohols, carbonyls and water by three Ni(II) isothiocyanate based Werner hosts was scrutinized and their generation of crystal structures elucidated. Structures of host:guest compounds ofH1, Ni(NCS)2 (nicotinamide)4, with five alcohols were compared with five guests with carbonyl functionalities. In both cases, host columns formed by interaction via hydrogen bonded amide tetramers. However, the hydrogen bond between the guest alcohol functional group and thiocyanato sulphur showed a more robust structure than those with intercalated carbonyl guests found in layers between sheets of host molecular bands. A predictable framework ofH1 host led to architectures with analogous patterns. Physical properties differed according to their hydrogen bonding capabilities. Selectivity was achieved for the separation of a pair of alcohols (1-butanol and 2-pentanol) and a pair of carbonyls (3- and 4-methylcyclohexanone), both difficult to separate due to similar physical properties. The positive discrimination characteristics of hostH1 towards one of a pair of alcohols and carbonyl isomers have given possibilities for future industrial prospects. HostH2, Ni(NCS)2 (isonicotinamide)4, presented three different tubulate packing arrangements, with the guests (H2 O, ethanol and self-included ligand isonicotinamide) occupying channels in the structure. Hydrogen bonding between host carbonyl oxygens and amides formed molecular frameworks into which the guest was included. Mixed-ligand hostH3, Ni(NCS)2 (nicotinamide)2 (isonicotinamide)2 with inclusion of water and methanol, confirmed our findings of hydrogen bonded frameworks with the two different ligands inH1 andH2 ; nicotinamide ligands formed amide tetramers, whereas the isonicotinamide ligands formed a variety of discrete hydrogen bonds with neighbouring molecules. The host networks formed porous materials for inclusion, giving the advantage of 'tunability', and pores with different size and nature available to accommodate guest molecules and to separate isomers.