# Two problematic structures: partial residual electron density in a crown ether and cages with 4 metal centers and 8 disordered anions

## TL;DR

The paper discusses two unresolved crystal structures involving a crown ether and a metal-containing cage, both with problematic electron density and disorder.

## Contribution

The paper presents two problematic crystal structures that highlight challenges in modeling residual electron density and disorder.

## Key findings

- A Ni complex with Cs cations and 18-Crown-6 shows residual electron density in the crown ether cavity, likely due to a water molecule with partial occupancy.
- A cage with 4 metal centers and 8 disordered anions was analyzed, but the disorder could not be refined satisfactorily due to poor data quality.
- The author chose not to publish the structures due to unsatisfactory refinement results.

## Abstract

I will discuss two problematic structures. I have decided not to publish these structures because I am not satisfied with the refinement, but I think they are worth discussing.

The first structure is a Ni complex with Cs cations, 18-Crown-6, and residual electron density in one of the crown ether’s cavity. The residual electron density could be due to a cation or more likely a water molecule with partial occupancy, but it could not be successfully modeled.

The second structure is a large cage with 4 metal centers and 8 disordered anions. The data quality is not very good, and the anions are highly disordered. Disorder could be modeled, but the resulting structure has poor refinement parameters.