Our current research on metal-organic frameworks (MOFs) focuses primarily on their physical properties, including their mechanical, optical, magnetic, ferroelectric and electronic behaviour.  In the area of mechanical properties we have worked extensively on the amorphization of MOFs [1], as well as on the impact of hydrogen bonding on the Young’s modulus and hardness of perovskite-related MOFs [2].  I shall discuss several cases of phase transitions that depend heavily on framework flexibility.  These include the transition from a porous to a dense framework at 160K in the Zeolitic Imadazolate Framework, ZIF-₄, which is accompanied by a decrease in volume of ~23% [3].  A second example involves a reversible, pressure-induced phase transition in a dense rare-earth formate, which shows the breaking and making of bonds during a transition that is accompanied by a 10% change in volume [4].  We shall also discuss the semiconducting hybrid perovskite, CH₃NH₃Pbl₃, which shows a transition due to hydrogen bond ordering on cooling below 160 K [5].  Finally we shall explore chemical transformations that depend on flexibility, such as the topochemical dehalogenation of a copper trithiocyanurate framework that is accompanied by a change from an insulating crystalline phase to an amorphous semiconductor [6], and an insulator to proton conductor transition that is driven by hydration [7].

1. T.D. Bennett and A.K. Cheetham, Acc. Chem. Res. 47, 1555 (2014)

2. W. Li, E.G. Bithell, P.T. Barton, Z. Lin, A. Thirumurugan, S. Henke, H.H.-M. Yeung, M.T. Wharmby, C.J. Howard and A.K. Cheetham, J. Am. Chem. Soc. 136, 7801 (2014)

3. M.T. Wharmby, S. Henke, T.D. Bennett, Y. Yue, C. Mellot-Draznieks, and A.K. Cheetham, Angew. Chem. Intl. Ed. 54, 6447 (2015)

4. E.C. Spencer, M.S.R.N. Kiran, Wei Li, U. Ramamurty, N.L. Ross and A.K. Cheetham, Angew. Chem. Intl. Ed. 53, 5583 (2014)

5. J.-H. Lee, N.C. Bristowe, P.D. Bristowe, and A.K. Cheetham, Chem. Comm. 51, 6434  (2015)

6. S. Tominaka, T. Suga, T.D. Bennett and A.K. Cheetham, Chem. Sci. 6, 1465 (2015)

7. S. Tominaka, F.X. Coudert, T.D. Dao, T. Nagao and A.K. Cheetham, J. Am. Chem. Soc. 137, 6428 (2015)