Complex phase behaviour and structural transformations of metal-organic frameworks with mixed rigid and flexible bridging ligands

Two new heteroleptic metal-organic framework materials show strong adsorption of H2 and ethanol. [Co2(L1)(bdc)2], where L1 = N1,N4-bis(4-pyridinylmethyl)-2,5-dimethylbenzene-1,4-diamine and bdc is benzene-1,4-dicarboxylate, has a twofold interpenetrating pillared layer structure with pcu topology. It has a stepped, hysteretic EtOH adsorption that can be related to complicated phase and structural transformation behaviour that occurs on de-solvation and re-solvation, including major conformational changes to the geometry of the flexible L1 ligand. [Co2(L1)(bpdc)2], where bpdc = biphenyl-4,4’-dicarboxylate, has a unique six-connected self-catenating framework structure. Solvation changes occur without significant structural change and a partially-hydrolysed material binds its own decomposition products as guests.