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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.