Unusual and Tunable Negative Linear Compressibility in the Metal–Organic Framework MFM-133(M) (M = Zr, Hf)

High-pressure single-crystal X-ray structural analyses of isostructural MFM-133(M) (M = Zr, Hf) of flu topology and incorporating the tetracarboxylate ligand TCHB4– [H4TCHB = 3,3′,5,5′-tetrakis(4-carboxyphenyl)-2,2′,4,4′,6,6′-hexamethyl-1,1′-biphenyl] and {M6(μ3-OH)8(OH)8(COO)8} clusters confirm negative linear compressibility (NLC) behavior along the c axis. This occurs via a three-dimensional wine-rack NLC mechanism leading to distortion of the octahedral cage toward a more elongated polyhedron under static compression. Despite the isomorphous nature of these two structures, MFM-133(Hf) shows a higher degree of NLC than the Zr(IV) analogue. Thus, for the first time, we demonstrate here that the NLC property can be effectively tuned in a framework material by simply varying the inorganic component of the frameworks without changing the network topology and structure.