Pressure-induced Bond Symmetrization in HgNCN
ORAL
Abstract
Mercury carbodiimide (HgNCN) exhibits two distinct crystalline polymorphs which host
distinct mesomeric forms of the [NCN] 2- anion [1]. In traditional wet synthesis, neutral
pH conditions produce the cyanamide, featuring one single and one triple C-N bond
[\chemfig{N~C-N}] 2- . In contrast, alkaline environments stabilize the carbodiimide form of
the ion, characterized by two double C-N bonds [\chemfig{N=C=N}] 2- . The two
polymorphs are separated by such a high energy barrier that conversion between the
two essentially requires the synthesis to be restarted from scratch. Here we use density
functional theory to show that, in contrast to wet chemical methods, mechanochemical
methods (oriented stress) allow for independent control of the crystal structure and the
form of the [NCN] 2- anion. Our calculations reveal that changes in the [NCN] 2- bonding
arrangement results in an insulator-to-metal transition. Our results show a novel
mechanochemical approach to tuning mesomeric effects in the solid-state, expanding
the accessible phase space beyond the limits of traditional synthesis techniques.
[1] X. Liu et al. Inorg. Chem. 2002, 41, 16, 4259–4265
distinct mesomeric forms of the [NCN] 2- anion [1]. In traditional wet synthesis, neutral
pH conditions produce the cyanamide, featuring one single and one triple C-N bond
[\chemfig{N~C-N}] 2- . In contrast, alkaline environments stabilize the carbodiimide form of
the ion, characterized by two double C-N bonds [\chemfig{N=C=N}] 2- . The two
polymorphs are separated by such a high energy barrier that conversion between the
two essentially requires the synthesis to be restarted from scratch. Here we use density
functional theory to show that, in contrast to wet chemical methods, mechanochemical
methods (oriented stress) allow for independent control of the crystal structure and the
form of the [NCN] 2- anion. Our calculations reveal that changes in the [NCN] 2- bonding
arrangement results in an insulator-to-metal transition. Our results show a novel
mechanochemical approach to tuning mesomeric effects in the solid-state, expanding
the accessible phase space beyond the limits of traditional synthesis techniques.
[1] X. Liu et al. Inorg. Chem. 2002, 41, 16, 4259–4265
*This work was supported by the National Science Foundation (NSF) Center for the Mechanical Control of Chemistry (CMCC), CHE-2303044. The CMCC is part of the Centers for Chemical Innovation Program.
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Presenters
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Dawson Smith
- Northwestern University