Coexistence of open and closed gallery spaces in intercalation compounds

TL;DR

This study investigates how macrocyclic molecules intercalate between MoS2 layers, revealing coexistence of open and closed gallery spaces, with the fraction of open spaces increasing with macrocycle loading, affecting the stacking and properties of the compounds.

Contribution

It demonstrates the coexistence of open and closed gallery spaces in MoS2 intercalation compounds and models their distribution using X-ray scattering and TEM data.

Findings

Open and closed gallery spaces coexist at less than full monolayer loading.

The fraction of open spaces increases with macrocycle loading.

Layer stacking remains consistent with random lateral shifts.

Abstract

A series of molybdenum disulfide intercalation compounds was prepared to study the effect of varying loadings of the samples with intercalated molecules. The molecules, (5,7,7,12,14,14-hexamethyl-1,4,8,11- tetraazacyclotetradeca-4,11-diene) macrocycles, occupy the gallery spaces between the MoS2 layers in a single layer. The samples were characterized by thermogravimetry, wide angle X-ray scattering, scanning electron microscopy and transmission electron microscopy (TEM). TEM images reveal the layer stacking as the filling of the gallery spaces with macrocycles increases gradually up to one monolayer per gallery space. Fourier transforms of these images are in excellent agreement with the X-ray scattering of the bulk compound. X-ray scattering by these compounds was simulated by evaluating the Debye sum for weighted averages of model particles that have sequences of open and closed gallery spaces. Open and closed gallery spaces coexist in the samples with less than one monolayer of intercalated molecules per gallery space. The fraction of open gallery spaces increases with macrocycle loading, from zero for restacked MoS2 without macrocycles to one for a fully intercalated compound. The sequence of open and closed spaces is approximately random, and the MoS2 layers stack with the same orientation but with random lateral shifts. The binding enthalpy of the macrocycles in the gallery spaces is about 14 meV.