Homologous Critical Behavior in the Molecular Frameworks Zn(CN)2 AND Cd(imidazolate)2

Ines E. Collings (1) , A. B. Cairns (1) , A. L. Thompson (1) , J. E. Parker (2) , C. C. Tang (2) , M.G. Tucker (3) , Jadna Catafesta (4, 5) , Claire Levelut (4) , Julien Haines (5) , Vladimir Dmitriev (6, 7) , Philip Pattison (8) , A. L. Goodwin (1)

1 Univ Oxford, Inorgan Chem Lab, Dept Chem, Oxford OX1 3QR
2 DIAMOND Light source
3 RAL - STFC Rutherford Appleton Laboratory
4 L2C - Laboratoire Charles Coulomb
5 ICGM ICMMM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier
6 ESRF - European Synchrotron Radiation Facility
7 Swiss Norwegian Beamlines
8 EPFL - Ecole Polytechnique Fédérale de Lausanne

Using a combination of single-crystal and powder X-ray diffraction measurements, we study temperature- and pressure-driven structural distortions in zinc(II) cyanide (Zn(CN)(2)) and cadmium(II) imidazolate (Cd(im)(2)), two molecular frameworks with the anticuprite topology. Under a hydrostatic pressure of 1.52 GPa, Zn(CN)(2) undergoes a first-order displacive phase transition to an orthorhombic phase, with the corresponding atomic displacements characterized by correlated collective tilts of pairs of Zn-centered tetrahedra. This displacement pattern sheds light on the mechanism of negative thermal expansion in ambient-pressure Zn(CN)(2). We find that the fundamental mechanical response exhibited by Zn(CN)(2) is mirrored in the temperature-dependent behavior of Cd(im)(2). Our results suggest that the thermodynamics of molecular frameworks may be governed by considerations of packing efficiency while also depending on dynamic instabilities of the underlying framework topology.

Domaines: Matériaux

Ines E. Collings, A. B. Cairns, A. L. Thompson, J. E. Parker, C. C. Tang, et al.. Homologous Critical Behavior in the Molecular Frameworks Zn(CN)2 AND Cd(imidazolate)2. Journal of the American Chemical Society, 2013, 135, pp.7610. ⟨10.1021/ja401268g⟩. ⟨hal-00903668⟩