[Co₂(ppca)₂(H₂O)(V₄O₁₂)_0.5]: A Framework Material Exhibiting Reversible Shrinkage and Expansion through a Single‐Crystal‐to‐Single‐Crystal Transformation Involving a Change in the Cobalt Coordination Environment

Shrinkage factor: The ligand ppca (4-(pyridin-4-yl)pyridine-2-carboxylic acid) has enabled the synthesis of a new 3D framework material, [{[Co2(ppca)2(H2O)(V4O12)0.5]⋅3.62 H2O}n], which exhibits so-called “dynamic structural changes”. Temperature changes lead to the reversible removal of guest molecules and/or ligands (e.g. H2O) bound to the framework with a concomitant reversible structure change (see scheme).