By Ha Ra Yi

Inductive and Steric Influence Effects and Sterics between Ruthenium and Iron

N

N

N

NN

N

MII

Br

Br

Background Information

NN

N

R Substituentsincrease in

electron donationR

-CH3

-OCH3

-Br

-H

-Cl

-N

-COOH

The size of the ligand field splitting determines the ground state electronic configuration (high-spin vs lowspin) as well as the energy difference between the high-spin/low-spin states of a particular octahedral compound.

-Bromine was used as the substituent attached to Terpyridine.-The radius of bromine is larger than chlorine, but not a electron withdrawing.

No substituents, expressed octahedral geometry

Tri-Dentate meaning it “bites” in three placesBis-Bromo Terpyridine because of the 2 binding locations

Atomic Radius:Br 94pm (picometer)Ru178pmFe156pm

Research Questions:• To what extent can the inductive properties

(electron-donating/withdrawing) of substituents influence the redox potential of the metal complex?

• How does Bromo-Terpyridine interact with the metal centers of Ruthenium and Iron?

• Because of the large radius of the Ruthenium it will bind closely to the ligands versus Iron, and will have a larger inductive effect.

• There will be more steric hindrance with iron than ruthenium because of the atomic radius of Bromine.

Hypothesis

(Based on literature)Experimental Process

Dried Nitrogen(Desiccator)

pyridinium 1-[2-oxo-2-(2 pyridinyl)ethyl] iodide 0.988grams weighed out

2-bromo-6-(3’-dimethylammonio-1’-oxopropyl)-pyridine chloride1.004grams weighed out

ammonium acetate 4.368grams weighed outMethanol~ 30mL poured

All reactants were poured into a 100mL round bottom flask and refluxed for 4 Hours

Overall reaction yielded 1.233grams of 6-bromo-2, 2’: 6’, 2”-terpyridine

DI water was used to fill up to 140mL mark for filtrate

Filter adapter set up to being filtration through frit

00.20.40.60.811.21.41.6

-0.0000006

-0.0000004

-0.0000002

0

0.0000002

0.0000004

0.0000006

0.0000008

0.000001

0.0000012

0.0000014

Base Line

Base Line

Potential (Volts)

Curr

ent

µA

Contamination on working electrode

00.20.40.60.811.21.4

-0.000015

-0.00001

-0.000005

0

0.000005

0.00001

0.000015

0.00002

Ruthenium Vs Iron Br-Terpy complex

Fe_Br-Tpy

Potential (volts)

Curr

ent

µAResults:

Comparison:

Ru-Br Terpy VS Iron-Br Terpy

• Ruthenium curve did not indicate a difference in spin state

• The Electron withdrawing group has less inductive effect which could be from the atomic radius of ruthenium

• It has more of a chance to pull of an electron from the outer most electron cloud (d-orbital)

• Indicates a low-spin state mixture (Showing slight reduction)

• The inductive effect is more prevalent due to bromine and irons smaller atomic radius

• The removal of electron density from the metal would explain the left shift

Reduction

Oxidation

00.20.40.60.811.21.4

-0.000015

-0.00001

-0.000005

0

0.000005

0.00001

0.000015

0.00002

Ruthenium Bromo-terpy VS Ruthenium terpy

Ru_TerpyRu_Br-Terpy

Potential (Volts)

Curr

ent

µA

Results:Substituent VS With Substituent

Comparison

• Bromine created an inductive effect on the metal.

• The metal was oxidized more so with bromine than without

• The size of ruthenium with bromine shows steric and explains the right shift

• There is more electron density richness on the metal

• The bromine promotes more oxidation and reduction to occur

• Without bromine the curve is shifted to the left, which indicates the removal of electron density from the metal.

• Since there is not a substituent, the electron density on the metal would have to determined from the metal and its atomic radius

• The shift of the curve to the right explains how tightly the ligand is binded to the metal, and it expresses a tightly covalent bond between the metal and the ligand

Results:Substituent VS With Substituent

Comparison

• Bromine - inductive effect on metal

• The metal was oxidized more so with bromine than without

• The size of ruthenium with bromine shows steric and explains the right shift

• There is more electron density richness on the metal

• The bromine promotes more oxidation and reduction to occur

• Without bromine the curve is shifted to the left, which indicates the removal of electron density from the metal.

• Since there is not a substituent, the electron density on the metal would have to determined from the metal and its atomic radius

• The shift of the curve to the right explains how tightly the ligand is binded to the metal, and it expresses a tightly covalent bond between the metal and the ligand

00.20.40.60.811.21.41.6

-1.00E-05

-5.00E-06

-5.08E-21

5.00E-06

1.00E-05

1.50E-05

Potential (Volts)

Curr

ent (

Amps

)

CH3-Terpy

Terpy

Br-Terpy

Evan’s MethodNMR Spectrum will show two

TMS signals due to experiencing different magnetic fields. One

signal will be from the reference tube and the other signal from

the outer tube. The peak distance (Hertz) is dependent on

both the number of unpaired electrons and concentration of

the paramagnetic solute.

North

South

Reference NMR Tube:1% TMS in d6-Acetone

Outer NMR Tube:1% TMS in d6-Acetone,& ParaMagnetic Solute

Using Evans Method

[Fe(Terpy)2]2+ Meff = 0.0 B.M. (Snet = 0.0)

[Fe(Me-Terpy)2]2+ Meff = 1.6 B.M. (Snet = 0.45)

[Fe(Br-Terpy)2]2+ Meff = 3.2 B.M. (Snet = 1.31)

• Not enough time to synthesize ligand with wanted substituents • Could not Purify by Column Chromatography• Percent yield was too small to react with Transition Metals

• Methoxy(OCH3) substituent

• Reflux for bromo-terpyridine took too long

Problems Encountered:

0.036g/ 0.102g = 35% yield of 6-methoxy-2, 2’: 6’, 2”-terpyridine But, 0.009g of 6-methoxy-2, 2’: 6’, 2”-terpyridine needed for synthesis