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Uniaxial negative thermal expansion and metallophilicity in Cu3[Co(CN)6]

DOI: 10.1016/j.jssc.2017.10.009 DOI Help

Authors: Adam Sapnik (University of Oxford) , H. L. B. Bostroem (University of Oxford) , X. Liu (Nanjing University of Aeronautics and Astronautics) , C. S. Coates (University of Oxford) , A. R. Overy (University of Oxford; Diamond Light Source) , E. M. Reynolds (University of Oxford) , A. Tkatchenko (University of Luxembourg) , A. L. Goodwin (University of Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Solid State Chemistry

State: Published (Approved)
Published: October 2017
Diamond Proposal Number(s): 13284

Abstract: We report the synthesis and structural characterisation of the molecular framework copper(I) hexacyanocobaltate(III), Cu3[Co(CN)6] , which we find to be isostructural to H3[Co(CN)6] and the colossal negative thermal expansion material Ag3[Co|rm(CN)6] . Using synchrotron X-ray powder diffraction measurements, we find strong positive and negative thermal expansion behaviour respectively perpendicular and parallel to the trigonal crystal axis: αa=25.4(5)MK−1 and αc=−43.5(8)MK−1 . These opposing effects collectively result in a volume expansivity αV=7.4(11)MK−1 that is remarkably small for an anisotropic molecular framework. This thermal response is discussed in the context of the behaviour of the analogous H- and Ag-containing systems. We make use of density-functional theory with many-body dispersion interactions (DFT+MBD) to demonstrate that Cu …Cu metallophilic (‘cuprophilic’) interactions are significantly weaker in Cu3[Co(CN)6] than Ag …Ag interactions in Ag3[Co|rm(CN)6] , but that this lowering of energy scale counterintuitively translates to a more moderate—rather than enhanced—degree of structural flexibility. The same conclusion is drawn from consideration of a simple GULP model, which we also present here. Our results demonstrate that strong interactions can actually be exploited in the design of ultra-responsive materials if those interactions are set up to act in tension.

Journal Keywords: Negative thermal expansion; Framework materials; Metallophilic interactions

Subject Areas: Chemistry, Materials

Instruments: I11-High Resolution Powder Diffraction

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