# Intercalation of Neutral Guests in Pillared Salt Cocrystals of 5-Ureidosalyclic Acid

## TL;DR

This paper explores how 5-ureidosalyclic acid forms pillared salt cocrystals with various solvents and how these structures can incorporate guest molecules.

## Contribution

The study introduces a new design concept for intercalated materials using charged, planar layers with exposed counterions.

## Key findings

- 5-ureidosalyclic acid forms pillared salt inclusion complexes with different solvents.
- The 5-USA anion can act as a bidentate ligand for manganese(III), forming solvated inclusion complex anions.
- The morpholinium salt solvate adopts a trans isomer form, while others adopt a cis isomer form.

## Abstract

The salts of 5-ureidosalyclic
acid (5-USA) form a range
of pillared
salt inclusion complexes from basic solvents, namely, triethylamine,
piperidine, morpholine, and 4-ethylpyridine. The triethylamine derivative
is unsolvated, while the other salts include 1–3 solvent molecules
of formula XH+(5-USA-H)−·nX (X = morpholine, n = 1, 2, and 3 (2a – 2c); X = 4-ethylpyridine, n = 1 (3) and X = piperidine, n = 2.5 (4)). The morpholine salt expands the layered
structure to include 1, 2, or 3 guests. The 5-USA anion can also act
as a bidentate ligand for manganese(III), again forming highly solvated
inclusion complex anions [Mn(5-USA-H)2(Solv)2]−. When interacting strongly with the countercation,
the 5-USA anions adopt an unusual cis carboxylate
isomer form, whereas the morpholinium salt solvate (H-morpholine)[Mn(5-USA-H)2(morpholine)2]·2(morpholine) (5c) is trans. The soft, plastic crystals of this complex
gradually desolvate, losing channel morpholine and ultimately spontaneously
recrystallizing as the 5-USA salt dimorpholine inclusion complex 2b. The complex hydrogen-bonded, pillared 5-USA salts illustrate
a design concept for intercalated materials of forming charged, planar
layers that leave the charge-balancing counterion exposed, such that
interlayer guest species must be incorporated to effectively solvate
the charged moieties.

Crystals of
a urea−salicylic acid derivative form
charged, planar layers that leave the counterion exposed causing incorporation
of further interlayer guests. One such layered cocrystal crystallizes
from desolvation and deliquescence of plastic crystals of a manganese
complex of the urea−salicylic acid ligand.