Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010
Dec 16, 2015
Ag3[Co(CN)6]: Giant Positive and Negative Thermal Expansion
Elizabeth A. ClarkMaterials 286GMay 26, 2010
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Thermal Expansion: A result of Anharmonicity in Bond Vibrations
http://www.ami.ac.uk/courses/topics/0197_cte/images/ch_cte_imga.gif
• Thermal expansion occurs in most materials because of the anharmonicity of the bond vibrations
•The bond length increases as temperature increases
r r
3
Negative Thermal Expansion due to Transverse Vibrations
α ≈ -9x10-6 /K
ZrO6 OctahedraZrW2O8
J. S. O. Evans et al., Chem. Mater., 8 [12], 2809–2823
4
Ag3[Co(CN)6]: Structure
A.L. Goodwin et al., Science, 319, 794-797
Cobalt sits in carbon octahedra. Planes of silver sit between the octahedra, and are connected by nitrogen.
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P3 1mRhombahedral
6
Ag3[Co(CN)6]: Connectivity
Ag+ ions sit on the vertices of a Kagome lattice
Argentophilicity – weak Ag-Ag interactions, (In case of Au-Au, similar in strength to hydrogen bonds)
AgAg ≈ 3.4Å
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Ag3[Co(CN)6]: Colossal Thermal Expansion/Contraction
130x10-6/K < αa < 150x10-6/K-120x10-6/K < αc < -130x10-6/K
αAg…Co ≈ 0/KA.L. Goodwin et al., Science, 319, 794-797
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Argentophilic Interactions Drive Colossal PTE/NTE
A.L. Goodwin et al., Science, 319, 794-797
A: Lattice enthalpy from density functional calculations ()
B: Mean partial phonon frequencies: CN Δ Co Ag
9A.L. Goodwin et al., J. Am. Chem. Soc., 130 [30], 9660-9661
Argentophilic Interactions Drive Colossal PTE/NTE
10J.L. Korčok, M.J. Katz, D.B. Leznoff, J. Am. Chem. Soc., 131, 4866-4871
Strength of Metallophilic Interactions Affect Thermal Expansion