Homologous critical behavior in the molecular frameworks Zn(CN)(2) and Cd(imidazolate)(2)

Journal article

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.

Authors: Collings, I; Cairns, A; Thompson, A; Parker, J; Tang, C

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: Journal of the American Chemical Society
• Volume: 135
• Issue: 20
• Pages: 7610–7620
• Publication date: 2013-01-01
• Edition: Accepted Manuscript
• DOI: 10.1021/ja401268g
• EISSN: 1520-5126
• ISSN: 0002-7863
• Language: English
• Keywords: critical behaviour; phase transition; cadmium imidazolate; variable-temperature; variable-pressure; Zinc cyanide
• Subjects: Solid state chemistry; Crystallography; Inorganic chemistry; Structural chemistry