Examining the Construction of Potential Coordination Polymers

with Aromatic N-oxides of

Mercury(II)

Michael Tran, Will Lynch and Cliff Padgett

Department of Chemistry and Physics

Armstrong Student Scholars Symposium

April 21, 2016

Coordination Polymers & N-oxides

• Supramolecular chemistry is a growing field of

interest

• Unique topologies and potential applications

• Applications such as gas storage, ion exchange

processes for remediation, heterogeneous

catalysis

• N-oxides: Variability of construction allows for

multiple binding modes and investigation of steric

and electronic effects

• Solid State Sciences, 2011, 13, 1692-1700.

Example Binding Modes of Aromatic N-oxides

Single Crystal X-ray Crystallography

General Synthetic Scheme

Pyridine N-oxide / HgBr2

Bond Length (Å)

Hg1 – O1 2.673

Hg1 – Br1 2.445

Hg1 – Br2 2.459

Bond Angle (°)

Br1 – Hg1 – Br2 159.38

Br1 – Hg1 – O1 96.62

Br2 – Hg1 – O1 89.10

Pyridine N-oxide / HgBr2

Coordination Polymer

Zig-Zag 1-D Polymer with N-oxide Bridges

2 terminal bromides per Hg

Hg:N-oxide 1:1

3-Picoline N-oxide / HgBr2

Bond Length (Å)

Hg1 – O1 2.702

Hg1 – Br1 2.435

Hg1 – Br2 2.448

Bond Angle (°)

Br1 – Hg1 – Br2 160.05

Br1 – Hg1 – O1 98.41

Br2 – Hg1 – O1 88.58

3-Picoline N-oxide / HgBr2

Coordination Polymer

Zig-Zag 1-D Polymer with N-oxide Bridges

2 terminal bromides per Hg

Hg:N-oxide 1:1

4-Picoline N-oxide / HgBr2

Bond Length (Å)

Hg1 – O1 2.542

Hg1 – Br1 2.462

Hg1 – Br2 2.449

Bond Angle (°)

Br1 – Hg1 – Br2 163.88

Br1 – Hg1 – O1 92.73

Br2 – Hg1 – O1 95.81

4-Picoline N-oxide / HgBr2

Coordination Polymer

Braided Polymer with Br- and N-oxide Bridges

1 bridging bromide, 1 terminal bromide per Hg

Hg:N-oxide 1:1

4-Methoxypyridine N-oxide / HgBr2

Bond Length (Å)

Hg1 – O1 2.531

Hg1 – Br1 2.462

Hg1 – Br2 2.445

Bond Angle (°)

Br1 – Hg1 – Br2 167.66

Br1 – Hg1 – O1 85.95

Br2 – Hg1 – O1 94.82

4-Methoxypyridine N-oxide / HgBr2

Coordination Polymer

Braided Polymer with Br- and N-oxide Bridges

1 bridging bromide, 1 terminal bromide per Hg

Hg:N-oxide 1:1

Quinoline N-oxide / HgBr2

Bond Length (Å)

Hg1 – O1 2.408

Hg1 – Br1 2.450

Hg1 – Br2 2.460

Bond Angle (°)

Br1 – Hg1 – Br2 157.20

Br1 – Hg1 – O1 101.43

Br2 – Hg1 – O1 101.23

Quinoline N-oxide / HgBr2

Coordination Polymer

Braided Polymer with Alternating Br- and N-oxide Bridges

1 bridging bromide, 1 terminal bromide per Hg

Hg:N-oxide 1:1

Isoquinoline N-oxide / HgBr2

Bond Length (Å)

Hg1 – O1 2.768

Hg1 – Br1 2.438

Hg1 – Br2 2.447

Bond Angle (°)

Br1 – Hg1 – Br2 160.11

Br1 – Hg1 – O1 96.56

Br2 – Hg1 – O1 90.01

Isoquinoline N-oxide / HgBr2

Coordination Polymer

1-D Polymer with N-oxide Bridges

2 terminal bromides

Hg:N-oxide 1:1

6-Methoxyquinoline N-oxide / HgBr2

Bond Length (Å)

Hg1 – O1 2.630

Hg2 – O1 2.491

Hg1 – Br1 2.438

Hg1 – Br2 2.429

Hg2 – Br3 2.455

Bond Angle (°)

Br1 – Hg1 – Br2 178.35

Br1 – Hg1 – O1 88.27

Br2 – Hg1 – O1 93.36

Br3 – Hg2 – O1 96.09

6-Methoxyquinoline N-oxide / HgBr2

Coordination Polymer

Double Braided Polymer with Br- and N-oxide Bridges

1 bridging bromide, 1 terminal bromide per Hg

Hg:N-oxide 2:1

2,2’-Dypyridyl N,N’-dioxide / HgBr2

Bond Length (Å)

Hg1 – O1 2.472

Hg1 – O2 2.459

Hg1 – Br1 2.474

Hg1 – Br2 2.474

Bond Angle (°)

Br1 – Hg1 – Br2 158.30

Br1 – Hg1 – O1 104.97

O1 – Hg1 – O2 71.90

Br2 – Hg1 – O2 99.95

2,2’-Dypyridyl N,N’-dioxide / HgBr2

Monomer Bidentate Chelate

Monomer with π-π StackingHg:N-oxide 1:1

2,2’-Dypyridyl N,N’-dioxide / HgCl2

Bond Length (Å)

Hg1 – O1 2.458

Hg1 – O2 2.472

Hg1 – Cl1 2.334

Hg1 – Cl2 2.339

Bond Angle (°)

Cl1 – Hg1 – Cl2 161.45

Cl1 – Hg1 – O1 103.63

O1 – Hg1 – O2 70.97

Cl2 – Hg1 – O2 99.02

2,2’-Dypyridyl N,N’-dioxide / HgCl2Monomer Bidentate Chelate

Monomer with π-π StackingHg:N-oxide 1:1

Data Summary

Compound Hg-O (Å)

Hg-Br (Å)

Br-Hg-Br (°) Hg : N-oxide

Description

PNO 2.67 2.45 160 1:1 Zig-Zag N-oxide Bridge

3MePNO 2.70 2.44 160 1:1 Zig-Zag N-oxide Bridge

4MePNO 2.54 2.46 164 1:1 Braided Br- & N-oxide

Bridges

4MeOPNO 2.51 2.46 168 1:1 Braided Br- & N-oxide

Bridges

QNO 2.41 2.45 157 1:1 Braided Br- & N-oxide

Bridges

iQNO 2.77 2.44 160 1:1 Zig-Zag N-oxide Bridge

6MeOQNO 2.63,

2.49

2.44 178 2:1 Double Braided Br- & N-

oxide Bridges

2,2’-DPNO 2.46 2.47 158 1:1 Chelate Monomer

2,2’-DPNO 2.46 2.33* 161 1:1 Chelate Monomer

* Chloride

Conclusions

•N-oxide monomeric ligands are effective ligands

for forming O-Hg-O coordination polymers

•Bromide is capable of serving as both bridge and

terminal ligands in these systems

•N-oxide ligands with chelate ligand

environments for monomers

• For PNO substituted N-oxides, the Hg-O bond

length follows a general Hammett trend

•The bulkier the ligand the more “sophisticated” the

polymeric chain

•The polymers form with a general organic (π-π)

stacking layer and a inorganic layer