A first-principles study of pressure-induced phase transformation in a rare-earth formate framework

Abstract

Among the panoply of exciting properties that metal-organic frameworks (MOFs) exhibit, fully reversible pressure-induced phase transformations (PIPTs) are particularly interesting as they intrinsically relate to the flexibility of MOFs. Recently, a number of MOFs have been reported to exhibit this feature, which is attributed to bond rearrangement with applied pressure. However, the experimental assessment of whether a given MOF exhibits PIPT or not requires sophisticated instruments as well as detailed structural investigations. Can we capture such low pressure transformations through simulations is the question we seek to answer in this paper. For this, we have performed first-principles calculations based on the density functional theory, on a MOF, [tmenH2][Y(HCOO)4]2 (tmenH2(2+) = N,N,N',N'-tetramethylethylenediammonium). The estimated lattice constants for both the parent and product phases of the PIPT agree well with the earlier experimental results available for the same MOF with erbium. Importantly, the results confirm the observed PIPT, and thus provide theoretical corroborative evidence for the experimental findings. Our calculations offer insights into the energetics involved and reveal that the less dense phase is energetically more stable than the denser phase. From detailed analyses of the two phases, we correlate the changes in bonding and electronic structure across the PIPT with elastic and electronic conduction behavior that can be verified experimentally, to develop a deeper understanding of the PIPT in MOFs.

Phase Transitions and Coexistence of Magnetic and Electric Orders in the Methylhydrazinium Metal Formate Frameworks

“…In order to better understand the structure–property relationship in this family of compounds, it is important to search for frameworks templated by novel protonated amines and study such compounds in a broad temperature range. Recently, pressure is emerging as another important parameter that can help to understand properties of these materials. − For instance, it has been shown that pressure may enhance ferroelectric properties or lead to novel phases with potentially useful properties, which are not accessible at ambient conditions …”

Metal–organic frameworks under pressure

“…5). 94,95 The coordination number of the M 3þ ion is unchanged in the process. A similar mechanism operates in CoCl 2 bpp [bpp ¼ 1,3-bis(4-pyridyl)propane], as Cl À ligands switch to bridging Co centers in the high-pressure phase.…”

Temperature- and pressure-dependent studies of niccolite-type formate frameworks of [NH3(CH2)4NH3][M2(HCOO)6] (M = Zn, Co, Fe)

“…High-pressure data of MOFs are of great interest since they provide information on pressure dependence of intermolecular interactions, stability of the structure and the properties of highpressure polymorphs that may have significantly different properties from the parent phase. 10,18,35,36 High-pressure data are therefore important for future technological applications and understanding the structure-property relationship for this crystal.…”