QUANTUM THERMAL EXPANSION

Hydrogen bonding transition and isotope-dependent negative thermal expansion in H3Co(CN)6
D A Keen, M T Dove, J S O Evans, A L Goodwin, L Peters and M G Tucker
J Phys: Condens Matt 22, 404202 (2010)

We investigate the structures of H3Co(CN)6 and D3Co(CN)6 and their temperature dependence using a combination of advanced neutron and x-ray diffraction techniques. Lattice parameter refinements show marked temperature- and isotope-dependent effects in the thermal expansion behaviour. Reverse Monte Carlo modelling of neutron total scattering data characterizes the distribution of D atom positions in the deuterated compound; analysis of these distributions reveals that the two N–H/D bonds become increasingly different with increasing temperature, suggesting a mechanism for the observed thermal expansion anomalies. We discuss these results in the context of the previous crystallographic, spectroscopic and theoretical results for H3Co(CN)6 and ‘super-short’ \mathrm {N}{\cdots }\mathrm {H}{\cdots }\mathrm {N} systems in general.

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