Efficient and tunable one-dimensional charge transport in layered lanthanide metal–organic frameworks

Abstract

The emergence of electrically conductive metal-organic frameworks (MOFs) has been one of the most exciting, if somewhat paradoxical, developments in porous materials, and has already led to applications as varied as chemical sensing and electrical energy storage. The most conductive MOFs are those made from organic ligands and square-planar transition metal ions connected into two-dimensional (2D) sheets that stack in a similar manner to the graphene sheets in graphite. Their electrical properties are thought to depend critically on the covalency of the metal-ligand bond. Much less importance is given to charge transport normal to the 2D sheets, not least because there is little synthetic opportunity to control their stacking sequence or distance. Here, we report exquisite control over the stacking sequence and distance in a series of materials made from 2D sheets of organic ligands connected in the third dimension by infinite lanthanide-oxygen chains. Contrary to transition metal MOFs, efficient charge transport leading to conductivity values of up to 0.5 S/cm in the lanthanide materials occurs primarily normal to the 2D sheets. We further show that the smaller lanthanides Yb 3+ and Ho 3+ enforce a shorter stacking distance of only 3.002(6) Å and afford consistently higher conductivity than the larger lanthanides Nd 3+ and La 3+ , which distend the sheets up to 3.068(2) Å. This first systematic study of structure-function relationships in layered conductive MOFs is enabled by the high degree of crystallinity afforded by the relatively ionic lanthanide-ligand bonds. These results demonstrate that increasing the covalency of the metal-ligand bond is not the only viable path to achieve record conductivity in 2D MOFs, and that the interactions of the organic ligands alone can produce efficient charge transport pathways.

Robust Atomistic Modeling of Materials, Organometallic, and Biochemical Systems

“…Theidea of ageneral GFN-type FF is inspired by the latest developments in the field of SQM methods,n amely the evolution of GFN1-, GFN2, and especially GNF0-xTB [25] methods,where the latest key ingredient was the introduction of ac lassical electronegativity-equilibrium (EEQ) atomiccharge model [26,27] for the description of pairwise interatomic electrostatic interactions.T his allowed to truncate the fundamental expansion of the DFT energy E [1]i nt erms of electron-density fluctuations d1 after the first-order term, leading to an on-self-consistent method which employs classical atomic charges.GFN-FF introduces approximations to the remaining quantum-mechanical terms in GFN0-xTB by replacing most of the extended-Hückel-type theory (EHT) for covalent bonding by classical bond, angle,a nd torsion terms.T oh ighlight the ancestry from the xTB methods,t he similarities and differences between FF and QM methods are illustrated in Figure 2.…”

Robust Atomistic Modeling of Materials, Organometallic, and Biochemical Systems

“…Concepts for designing molecules with desired (bio)chemical activities or physical properties have become state-of-theart in experimental chemistry. [1,2] Molecular size and complexity has no boundaries and the elemental composition is versatile. [3] Within the last decades,t he field of theoretical chemistry has evolved into an indispensable part of chemistry and has proven to be an important companion of the experiment.…”

Autogenous Production and Stabilization of Highly Loaded Sub‐Nanometric Particles within Multishell Hollow Metal–Organic Frameworks and Their Utilization for High Performance in Li–O2 Batteries

“…Accordingly, there were many great efforts to utilize MOFs as materials for preparing various shaped structures with advanced functionalities. [ 11–16 ] In this work, we develop multilayer MOFs with alternating stable and decomposable layers for the autogenous production and stabilization of SNPs in scalable mass loadings. Interestingly, we also show that the single water molecule transfer throughout multilayer MOFs plays a very important role to activate the autogenous synthesis of SNPs.…”