2016 URF Poster

Functional Materials Based on Metal Complexes

Presenters: Bailey Bouley, Colton D’Ambra, Huy Lam, Jason RossResearch Educator: Dr. Lauren DePue

Faculty Professors: Dr. Richard Jones, and Dr. Bradley Holliday3D-Structure

Funding and Support

Conclusion

Publications by the Functional Materials Stream1) Chan, C.; Yang, X.; Jones, R. A; Holliday, B. J.; Stanley, J. M. “{μ-6,6’-Dimeth-Oxy-2,2'-[butane-1,4-Diylbis(nitrilo-Methyl-Idyne)]diphenolato-1:2κO,O,O,O:O,N,N',O}tris-(nitrato-

1κO,O')copper(II)gadolinium(III)” Acta Crystallogr. Sect. E. Struct. Rep. 2010, 66, m576–7.

2) Liao, A.; Yang, X.; Stanley, J. M.; Jones, R. A.; Holliday, B. J. “Synthesis and Crystal Structure of a New Heterotrinuclear Schiff-Base Zn–Gd Complex.” J. Chem. Crystallogr. 2010, 40, 1060–1064.

3) Stanley, J. M.; Chan, C. K.; Yang, X.; Jones, R. A.; Holliday, B. J. “Synthesis, X-Ray Crystal Structure and Photophysical Properties of tris(dibenzoylmethanido)(1,10-phenanthroline)samarium(III).”

Polyhedron 2010, 29, 2511–2515.

4) Yang, X.; Chan, C.; Lam, D.; Schipper, D.; Stanley, J. M.; Chen, X.; Jones, R. A; Holliday, B. J.; Wong, W.-K.; Chen, S. “Anion-Dependent Construction of Two Hexanuclear 3d-4f Complexes with a

Flexible Schiff Base Ligand”. Dalton Trans. 2012, 41, 11449–11453.

5) Yang, X.; Lam, D.; Chan, C.; Stanley, J. M.; Jones, R. A; Holliday, B. J.; Wong, W.-K. “Construction of 1-D 4f and 3d-4f Coordination Polymers with Flexible Schiff Base Ligands.” Dalton Trans.

2011, 40, 9795–9801.

6) Yang, X.; Schipper, D.; Jones, R. A; Lytwak, L. A; Holliday, B. J.; Huang, S. “Anion-Dependent Self-Assembly of near-Infrared Luminescent 24- and 32-Metal Cd-Ln Complexes with Drum-like

Architectures.” J. Am. Chem. Soc. 2013, 135, 8468–8471.

7) Yang, X.; Schipper, D.; Liao, A.; Stanley, J. M.; Jones, R. A.; Holliday, B. J. “Anion Dependent Self-Assembly of Luminescent Zn–Ln (Eu and Tb) Salen Complexes.” Polyhedron 2013, 52, 165–169.

8) Yang, X.; Schipper, D.; Zhang, L.; Yang, K.; Huang, S.; Jiang, J.; Su, C.; Jones, R. A. “Anion dependent self-assembly of 56-metal Cd–Ln nanoclusters with enhanced near-infrared luminescence

properties.” Nanoscale. 2014, 6, 10569.

9) Jones, R. A.; Gnanam, A. J.; Arambula, J. F.; Jones, J. N.; Swaminathan, J.; Yang, X.; Schipper, D.; Hall, J. W.; DePue, L. J.; Dieye, Y.; et al. “Lanthanide nano-drums: a new class of molecular

nanoparticles for potential biomedical applications.” Faraday Discuss. 2014, 175, 241–255.

10) Brown, K. A.; Yang, X.; Schipper, D.; Hall, J. W.; DePue, L. J.; Gnanam, A. J.; Arambula, J. F.; Jones, J. N.; Swaminathan, J.; Dieye, Y.; et al. “A self-assembling lanthanide molecular nanoparticle for

optical imaging.” Dalt. Trans. 2015, 44 (6), 2667–2675.”

X-ray Crystallography

Coordination of Ligands to Lanthanides

Synthesis of Schiff Base Ligands

Introduction to our Research

The coordination of a ligand to a lanthanide begins by selecting the appropriate reagents for the desired result. Using Hard/Soft

Acid/Base Theory it is established that lanthanides bind well to ligands containing oxygen and nitrogen. Most of the lanthanide

metals luminesce at specific wavelengths in either the visible or near-infrared region. Others have different applications, such as

gadolinium whose magnetic properties allow it to act as a contrast agent during an MRI scan. Selecting the appropriate ligand

depends on the functional groups as well. Most ligands used have derivatives with an added bromine that can substitute other

functional groups. The ligand chosen also affects the crystal structure, so the ligand can be chosen based on a desired structure.

General Procedure:

1. Dissolve lanthanide salt in desired solvents.

2. Add ligand to the solution.

3. Reflux ligand for 45-60 minutes.

4. Allow solution to cool.

5. Filter solution to remove solid impurities.

6. Pipette solution into test tubes.

7. Put test tubes in a jar filled with diethyl ether.

8. Using Slow Vapor Diffusion, wait until formation of crystals.

The typical solvents used are ethanol and toluene because the complexes are soluble in ethanol, but not toluene, so this reduces the

overall solubility, promoting crystallization. The general procedure can be modified for different ligands based on what has worked

in the past. For example, letting the solution sit for a couple of days before filtering sometimes causes complexes to crystallize

directly in the round bottom flask. Additional reagents can be added to the reaction flask to attempt the formation of a multi-nuclear

coordination compound.

The jars create an environment that allows slow vapor diffusion to form crystals. The highly volatile diethyl ether slowly diffuses

into the test tubes mixing together and forming a new solution. The complexes are insoluble with diethyl ether, so they will be

supersaturated in the solution after the diethyl ether enters. If the complex can find a nucleation site in the test tube (i.e. a

microscopic scratch on the side), crystallization will begin. If there are no nucleation sites, the complex will precipitate out. The

diethyl ether enters the test tubes slowly allowing for the crystals to form in high enough quality to allow their structure to be found

via X-ray crystallography.

Figure 4. Lanthanide metals luminesce at specific wavelengths in narrow bands

primarily in the visible or NIR spectrum. The specific wavelength allows the

lanthanide metals to be found when they attach to something, creating uses in fields

such as cancer diagnosis.

Figure 7. Reaction set-up for typical synthesis.

Figure 2. Luminescent lanthanide containing

compounds under UV lamp (Sm – pink; Tb – green;

Eu – red).

Figure 3a & 3b. Growing

crystals via slow vapor

diffusion.

Ligand Synthesis

Lanthanide Coordination

Crystal GrowthX-ray

Crystallography

Group

Imine synthesis begins by combining the amine and aldehyde components in a round bottom flask

containing ethanol as a solvent. The solutions are refluxed on medium heat and high stir for 1-2

hours to ensure progression of the reactions. After the refluxes are complete, the solutions were

left to cool to room temperature to promote precipitation.

Figure 6. Sample vanillin derivatives used as aldehydes and sample amines used in synthesizing Schiff base ligands.

Figure 8. Synthesis of bidentate and monodentate Schiff-based ligands from vanillin

derivatives and amines.

Single crystal X-ray diffraction is a valuable tool in determining the structures of complexes synthesized in the

functional materials lab. As the name implies, a single crystal is required for analysis and must be free of cracks,

twinning, and other deformities. After initial screening under a microscope with polarized light, a single crystal may be

mounted onto a loop for diffraction.

Once the crystal is mounted and centered a beam of X-rays is directed at the center of the crystal. This initial beam is used to

determine if the crystal is of sufficient quality to continue diffraction. If the crystal is acceptable, the diffraction continues and

data is collected as the crystal is rotated on its loop. Depending on the specific machine being used, an initial crude structure is

given and the software Olex2 is then used to refine the structure in preparation for publication.

Figure 5. Crystal structure of the complex that results from the

coordination of a lanthanide metal to the Schiff base ligand composed

of o-vanillin and o-phenyldiamine. The oxygen atoms of the ligand

donate their electron pairs to make a bond coordinate bond with the

ligand.

If a significant amount of the ligand formed a solid, the solution

was filtered via vacuum filtration and the imine collected. For many

of the monodentate ligands however, they are liquids at room

temperature and had to be stored as either a molar solution in

ethanol or as a pure liquid. Some ligands that were solid at room

temperature but soluble in ethanol and were rotary evaporated to

remove the ethanol to recover the imine.

After the products were isolated, NMR samples were run to show the absence of the aldehyde and

amine peaks and the presence of the imine peaks, indicating the success of the reaction.

Figure 1. The lanthanide luminesces through the antenna effect. Light

is absorbed by the ligand and transfers energy to the lanthanide, causing

it to enter an excited state. The lanthanide then relaxes and releases

light through luminescence.

Lanthanide complexes have many applications due to their spectroscopic, magnetic and luminescent properties.

These applications include: (1) detecting tumors under a UV light and observing whether the area contains a

luminescent lanthanide; (2) multiple variations of Gd(III) chelates are used in MRI as contrasting agents; (3) and

lanthanides are prevelant in OLED television displays due to these sharp, strong lanthanide emissions. These

luminescent properties would not be possible without the use of organic ligands on lanthanide ions to provide stability

and utilize the Antennae Effect.

The organic ligands absorb UV light and transfer the energy to

lanthanide ion. Once the lanthanide ion is excited by the ligand,

it releases the energy in a narrow light emission that depends on

the lanthanide ion in the complex. The experiments conducted

used organic Schiff base salen-type ligands with lanthanide

ions, transition metal ions, or both to make interesting metal

complexes. Single crystal X-ray crystallography determines the

structure of the complexes, which can then be further studied

for other useful properties.

Figure 9. Examples of the crystal structures that results from the ligand reacted in certain conditions: (a) The pictured

ligand reacted with Nd(NO3)3 to form a neodymium compound containing two ligands bound via the oxygens; (b) The

pictured ligand reacted with Cd(OAc)2 and Nd(OAc)3 to form a barrel-shaped structure containing 12 ligands and 8

neodymium atoms.

Figure 10. X-ray quality crystals are removed from test tubes and collected in oil to prevent the solvent from drying out.

They’re then placed on a loop in preparation for X-ray diffractometry. Once the X-ray diffraction data is collected, the

structure can usually be deciphered.

Further research will consist primarily of synthesizing more ligands and metal complexes. Additional characterization of the

metal complexes will be done involving fluorimetry, IR spectroscopy, and NMR spectroscopy. Fluorimetry of the metal

complexes will determine the quantum yield. Knowledge of this helps determine if the complexes will be good candidates for

applications utilizing their luminescence.

Some of the ligands synthesized will contain a bromine functional group which will allow a number of substitutions to occur in

order to functionalize the complex. Once substituted, the metal complexes can find potential uses as contrast reagents, NMR

shift reagents, or as biomarkers. The ring structure shown in Figure 10 shows promise as a biomarker due to the high number of

lanthanide metals and lack of toxic cadmium as in the barrel structures. The high number of lanthanides increases the chances of

the lanthanide centers reaching the targeted area as well as causing the targeted area to luminesce brighter once subjected to UV

light.

Figure 11. Example of MRI taken without contrast

agent (left) and with a Gd complex as a contrast

agent (right).

Figure 12. Example of the effect of a Eu NMR shift reagent on n-pentanol. The

overlapping peaks shown in (a) are separated enough to be distinguished in (b).