Flexibility Transition and Guest-Driven Reconstruction in a Ferroelastic Metal–Organic Framework
S J Hunt, M J Cliffe, J A Hill, A B Cairns, N P Funnell and A L Goodwin
Cryst Eng Comm 17, 361-369 (2015)

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The metal–organic framework copper(I) tricyanomethanide, Cu(tcm), undergoes a ferroelastic transition on cooling below Tf = 240 K. Thermal expansion measurements reveal an order-of-magnitude variation in framework flexibility across Tf. The low-temperature phase α-Cu(tcm) exhibits colossal positive and negative thermal expansion that is the strongest ever reported for a framework material. On exposure to acetonitrile, Cu(tcm) undergoes a reconstructive solid-phase transition to acetonitrilo- copper(I) tricyanomethanide. This transition can be reversed by heating under vacuum. Infrared spectroscopy measurements are sensitive to the phase change, suggesting that Cu(tcm) may find application in solid-phase acetonitrile sensing.