Density Functional Studies Revealing Anomalous Lattice Behavior in Metal Cyanide, AgC₈N₅

Abstract

We have investigated anomalous lattice behavior of metal organic framework compound AgC8N5on application of pressure and temperature using ab-initio density functional theory calculations. The van der Waals dispersion interactions are found to play an important role in structural optimization and stabilization of this compound. Our ab-initio calculations show negative linear compressibility (NLC) along the c-axis of the unit cell. The ab-initio lattice dynamics as well as the molecular dynamics simulations show large negative thermal expansion (NTE) along the c-axis. The mechanism of NLC and NTE along the c-axis of the structure is governed by the dynamics of Ag atoms in the a-b plane. The NLC along the c-axis drives the NTE along that direction.

Phonons and Anomalous Lattice Behavior in KMnAg3(CN)6 and KNiAu3(CN)6: Inelastic Neutron Scattering and First-Principles Calculations

“…MOF show very large NTE coefficient and large compressibilities due to their highly anisotropic and flexible structures. The MOF exhibiting NLC along particular crystal direction are often found to show NTE along the same direction with similar mechanism 5,9,11 .…”

“…A combination of polyhedral units of metal ions coupled to organic linkages gives rise to MOF compounds which exhibit interesting lattice behavior [9][10][11] . The flexibility, porous nature and anisotropic bonding give rise to the interesting mechanism of negative linear compressibility (NLC), NTE as well as phase transitions in MOF's when exposed to varying temperature-pressure environments 5,9,11 . Different mechanisms responsible for NTE behaviour in metal inorganic and metal organic framework structures give rise to difference in magnitude of thermal expansion coefficients in these compounds 9,12 .…”

“…This type of structural flexibility has been identified in some metal organic framework structures (MOF) [5][6][7][8] . A combination of polyhedral units of metal ions coupled to organic linkages gives rise to MOF compounds which exhibit interesting lattice behavior [9][10][11] . The flexibility, porous nature and anisotropic bonding give rise to the interesting mechanism of negative linear compressibility (NLC), NTE as well as phase transitions in MOF's when exposed to varying temperature-pressure environments 5,9,11 .…”

“…12−14 The flexibility, porous nature, and anisotropic bonding give rise to the interesting mechanism of negative linear compressibility (NLC), NTE, and phase transitions in MOFs when exposed to varying temperature−pressure environments. 8,12,14 Different mechanisms responsible for NTE behavior in metal−inorganic and metal−organic framework structures give rise to difference in magnitude of thermal expansion coefficients in these compounds. 12,15 Among the compounds exhibiting large anisotropic NTE, MOFs often show large NTE as well as NLC due to their highly anisotropic and flexible structures.…”

“…The MOFs exhibiting NLC along a particular crystal direction are often found to show NTE along the same direction with a similar mechanism. 8,12,14 Earlier, we measured the phonon spectra of MCN (M = Ag, Au, and Cu) 13 and ZnAu 2 (CN) 4 12 and Zn(CN) 2 16,17 compounds. These MCN compounds resemble a onedimensional structure.…”