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43466-AC10
Intercalative Investigation of Hydrogen-Bonded Clay Mimics

Alicia M. Beatty, Mississippi State University

1. Intercalation into hydrogen-bonded organic clay mimics:

Experimental parameters:

• Starting materials: Crystalline materials having hydrogen-bonded dicarboxylic acid-based layers and primary amine-based inter-layer components. R-groups between layers in the host solids are benzyls and alkyls.

• Intercalation attempts made via heating and sonication of the starting materials in non-polar solvents (dry toluene, dry hexane, to prevent dissolution of starting solids) in the presence of a guest (1:10 guest:solvent by volume or by weight).

• Guests molecules ranged from the neat solvents to halobenzenes, nitrobenzenes, xylenes, longer chain alkanes up to hexadecane, and long chain alchohols.

Results:

• No intercalation was observed for the organic hydrogen-bonded solids. Solids gave identical TGA and XRD patterns before and after the experiments.

• Particle sizes were reduced significantly upon sonication, indicating that exfoliation of the layers may occur during sonication.

Conclusions: Sonication is the best method to use to investigate intercalation in these systems. Our conclusions from all of the iterations of experiments conducted using the original organic clay mimic crystalline structures (built from 3,5 PzDCA with primary amines or from 3,5 Pyridine dicarboxylic acid and diamines) are that the lattice forces in these crystals are too strong to allow intercalation of small molecules between layers. Exfoliation may be occurring, and can be investigated in the future using SEM/TEM to look at solids before and after sonication.

Communication of results: Because these are essentially negative results, they will likely not be reported as stand-alone results but will be discussed briefly in the paper generated from the results in section 2 (vide infra).

2. Intercalation into inorganic/organic hybrid hydrogen-bonded clay mimics:

Experimental parameters:

• Starting materials: Crystalline materials formed from hydrogen bonded metal-containing dicarboxylic acids and primary amine-based inter-layer components. R-groups between layers in the host solids are benzyls and alkyls.

• Intercalation attempts were made via heating and sonication of the starting materials in non-polar solvents (dry toluene, dry hexane, to prevent dissolution of starting solids) in the presence of a guest (1:10 guest:solvent by volume or by weight). Times ranged from 3 hours to 24 hours sonication and heating.

• Guests molecules ranged from the neat solvents to halobenzenes, nitrobenzenes, xylenes, longer chain alkanes up to hexadecane, and long chain alchohols. In later experiments we used pyridine and substituted pyridines as “guest” molecules to replace axial ligands on the metal-based dicarboxylic acids.

• Solids were obtained by filtering then washing with dry solvent to remove and surface adherence of guest molecules.

Results:

• No intercalation was observed for simple alkanes and aryls. Solids gave identical TGA and XRD patterns before and after the experiments.

• Intercalation was observed using pyridine and substituted pyridines:

o TGAs showed increased weight loss at lower temperatures due to replacement of H2O with pyridine-based ligands.

o Powder XRD showed either broadening of the (001) peak (which measures inter-layer spacing) or an extra peak at lower 2-theta (indicating an increase in peak spacing)

o Color change observed

Conclusions: Sonication is the best method to use to investigate intercalation in these systems. Only the pyridine-based lewis bases could be used as intercalants, probably because the intermolecular forces using hydrophobic “guests” weren't strong enough to keep these molecules between layers. Exfoliation may be occurring, and can be investigated in the future using SEM/TEM to look at solids before and after sonication.

Communication of results: The successful intercalations in these studies are very significant, as we have demonstrated that close-packed hydrogen-bonded solids can remain intact during guest exchange/uptake. The manuscript reporting these results is in draft form, but will be sent in for review in 2008.

3. Synthesis of guest-containing inorganic/organic hybrid clay mimics.

Experimental parameters:

Rather than benzylamine starting materials (in conjunction with the previously used metal-containing dicarboxylic acids vide supra), phenylethylamine starting materials were used to synthesize the layered solids. (This means ONE extra CH2 unit exists between the amine and the aryl group, which adds some flexibility to the R groups between layers).

Results:

• The same hydrogen bonded layer as those in section 2 was observed. However, single crystal X-ray showed presence of guest molecules for several structures. Guests were identified as solvent molecules.

• A second set of structures showed ability to dynamically lose and re-uptake axial water ligands. Ability to maintain stable coordinatively-unsaturated intermediates depended on having oxygen-containing substituents on amine starting materials, and Copper(II) was the only metal for which these stable intermediates were observed.

Conclusions:

a. The flexible phenylethylamine components in inorganic/organic hybrid clay mimics allow incorporation of guests, as shown by single crystal X-ray.

b. Copper(II)-containing dicarboxylic acid starting materials show dynamic ligand loss and re-uptake in our clay mimic solids, as evidenced by powder XRD.

Communication of results: These results a. and b. will be communicated in two separate papers, both of which are in draft forms.

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