A Highly Flexible Metal-Organic Framework Constructed from Asymmetric Flexible Linkers and Heptanuclear Zinc Carboxylate Secondary Building Units and its Anisotropic Dynamic Responses Exhibited During Guest Removal and Single Crystal Coordinated Solvent Exchange
A new porous and flexible metal-organic framework (MOF) has been synthesised from the flexible asymmetric linker N-(4-Carboxyphenyl)succinamate (CSA) and heptanuclear zinc oxo-clusters of formula [Zn7O2(Carboxylate)10DMF2] involving two coordinated terminal DMF ligands. The structural response of this MOF to the removal or exchange of its guest molecules has been probed using a combination of experimental and computational approaches. The topology of the material, involving double linker connections in the a and b directions and single linker connections along the c axis, is shown to be key in the materials anisotropic response. The a and b directions remain locked during guest removal, while the c axis linker undergoes large changes significantly reducing the material’s void space. The changes to the c axis linker involve a combination of a hinge motion on the linker’s rigid side and conformational rearrangements on its flexible end, which were probed in detail during this process despite the presence of crystallographic disorder along this axis which prevented accurate characterisation by experimental methods alone. While inactive during guest removal, the flexible ends of the a and b axis linkers are observed to play a prominent role during DMF to DMSO solvent exchange, facilitating the exchange reaction arising in the cluster.