1. The development of anion-sensing systems is of considerable
current interest because of biological, environmental and
pharmaceutical concerns. Anions play important roles in biological
systems and medicine, pollutant anions are responsible for
environmental problems such as the eutrophication of rivers, and
the food industry constantly verifies the tolerable level of anions in
our food.
Can voltammetric measurements be used to selectively detect
specific anions in solution? To answer this we are examining the
redox properties of known ion-binding Re complexes via cyclic
voltammetry in the presence of different anions. If the anions can be
detected by electrochemical means, we will attempt to produce ion-
selective electrodes by adhering the Re complexes to polymers
affixed to the electrode surface. The potential benefit is greater
sensitivity, selectivity, and/or stability of the sensor.
Challenges related to developing ion sensing systems:
• Charge/size ratio
• pH sensitivity
• Size/geometry
Current (Field) Techniques
• Colorimetric, fast, simple
• No complex equipment
Drawbacks
• Metal not reusable (high formation constants)
• Color & turbidity dependent
Previous Work
Ion Selective Redox Chemistry:
Polymer Modified Rhenium Complex Electrodes
Nigel Rambhujun1, Susan Young1, William Vining2
1Hartwick College, Oneonta, NY 2State University of New York at Oneonta, NY
Acknowledgements
References
Techniques
• Cyclic voltammetry
• Controlled potential (bulk)
electrolysis
• Spectroelectrochemistry
• Polymer modification of
electrode surfaces
Transition metal complex ions can effectively sense anions due to
the combined properties of the metal-anion system:
1. Metals are usually positively charged and effectively bind anions
through both electrostatic and covalent interactions.
2. The color of the complex ion can vary with the nature of the
ligands.
3. Metal complexes exist in a wide variety of geometries, which can
accommodate anions of different shapes.
4. The molecular structure is tunable and can be chemically
modified to exhibit greater selectivity in binding a specific anion.
5. Complexes can undergo redox reactions due to multiple
accessible oxidation states, giving them measurable
electrochemical properties.
Introduction
Compound 2:
rhenium(I) diimine
tricarbonyl complex
• Metal-ligand reaction
• Naked eye change
Methods
Spectroelectrochemistry Cell (Pine)
• PF6
–
• ClO4
–
Previous research1 has studied the anion recognition properties of
dinuclear rhenium(I) diimine tricarbonyl complexes by luminescence
and UV-Vis spectroscopic methods. In this study, using a
mononuclear rhenium(I) complex, we hope to translate the
spectroscopic changes observed to electrochemical changes that
can be detected using cyclic voltammetry.
Results
Future Work
• Department of Chemistry, Hartwick College &
Department of Chemistry, State University of
New York at Oneonta for providing the funding
for my project
• Dr. Maurice Odago, SUNY Oneonta, for
providing the rhenium complex ions and free
(uncomplexed) ligands, and for helpful advice.
1. M.O. Odago, A.E. Hoffman, R.L. Carpenter,
D. Chi Tak Tse, S.S. Sun, A. J. Lees, Inorg.
Chim. Acta. 374 (2011) 558
2. P.T. Kissinger, W.R. Heineman, Journ. Chem.
Ed., 60:9 (1983) 702
3. A. Ramdass, V. Sathish, M. Ve;ayudham, P.
Thanasekaran, K.L Lu, S. Rajagopal, Inorg.
Chem. Comm. 35 (2013) 186
Conclusions
• Identify the nature of the different
reductive and oxidative waves
observed: compound 2 showed four
irreversible oxidative waves and four
irreversible reductive waves. At least
one of each appears to be ligand-based.
• Produce ion selective electrodes by
adhering 2 or other similar compounds
to polymers affixed to the electrode
surface.
• The color change observed with
cyanide results from an interaction with
the ligand in 2.
• Cyanide binding to the complex was
observed electrochemically: the cyanide
ion passivates oxidation of 2.
• Comparison with the acetate ion shows
that the ion binding is not simply an
acid-base reaction with 1.
• The chemical changes following bulk
reduction of 2 in the presence of
cyanide appears to be a one-step
process, whereas that following
reduction of 2 in the absence of cyanide
appears to be at least a two-step
process.
Isosbestic point
at 410nm
Anions Tested
as N(t-Bu)4
+ salts
• CN–
• CH3COO–
Re compound with CN-
Free ligand with CN-
Re compound with CN-
Re compound with CH3COO-
Fig. 1: CV of 2, showing four irreversible
oxidative waves and four irreversible
reductive waves. (At least one of each
appears to be ligand-based.)
Fig. 2: CV of 2 in the presence of
ClO4
– (The scan is very similar to the
CV of 2.)
Fig. 3: CV of 2 in the presence of
CN–. (Cyanide appears to passivate
the oxidation of the Re compound.)
Fig. 4: UV-Vis spectra of 1 and 2 in the presence
of CN–. (The free ligand in the presence of cyanide
has the same band, ~450 nm, as the Re complex
in the presence of cyanide.)
Fig. 5: UV-Vis spectra of 2 in the presence of
CN– and CH3COO–. (The difference suggests
that CN– is interacting with 2 and not simply
acting as a weak base.)
Fig. 6: UV-Vis spectra of a controlled potential
electrolysis of 2 at –600 mV. (The process
appears to occur in at least two steps.)
Fig. 7: UV-Vis spectra of a controlled potential
electrolysis of 2 at –600 mV in the presence of
cyanide. (This appears to be a one-step process.)
1
2
3
Compound 1:
free ligand