Rational design of materials with extreme negative compressibility: Selective soft-mode frustration in KMn[Ag(CN)2]3
A B Cairns, A L Thompson, M G Tucker, J Haines and A L Goodwin
J Am Chem Soc 134, 4454–4456 (2012)
The final authors’ version of this article is available open access via. the Oxford Research Archive.
We show that KMn[Ag(CN)2]3 exhibits the strongest negative linear compressibility (NLC) effect over the largest pressure range yet observed. Variable pressure neutron powder diffraction measurements reveal that its crystal lattice expands along the c axis of its trigonal cell under increasing hydrostatic pressure, while contracting along the a axis. This corresponds to a “wine-rack”-like mechanism for NLC that we find also results in anisotropic negative thermal expansion (NTE) in the same material. Inclusion of extra-framework K+ counterions has minimal effect on framework flexibility (and hence the magnitude of NTE/NLC) but selectively frustrates the soft phonon modes responsible for destroying NLC in the related material Ag3[Co(CN)6].