Chemistry Reference
In-Depth Information
Table 7.2
(
Continued
)
Sample and
device
requirements
Method
Outcome expected
X-Ray absorption fine-edge
spectroscopy (EXAFS) and
X-ray absorption near-edge
spectroscopy (XANES)
Solids or solutions; analysis of
metals in biological samples
possible.
X-ray diffractometer /
synchrotron.
Information on the
environment around the
metal; type and number of
donor groups and metal
bond distances.
Emission spectroscopy
Gaseous, liquid, solid or
(preferably) solution of
complex.
Fluorescence
spectrophotometer.
Luminescence or
phosphorescence behaviour
of complexes; information
on electronic structure.
Microwave spectroscopy
Gaseous sample with a dipole
moment necessary.
Microwave spectrometer.
Some structural information,
including bond distances
for very simple molecular
species.
Photoelectron spectroscopy
Solid or gaseous samples.
PES spectrophotometer.
Information on molecular
environment and donor
type.
Mass spectrometry (MS)
A liquid or solid of reasonable
volatility, or a gaseous
sample.
Quadrupole or time-of-flight
(TOF) mass spectrometer.
Molecular mass. Compound
characterization from
fragmentation pattern.
Tandem techniques (general)
Where two (or even more)
instruments or
methodologies are joined
together to allow for
expansion of the analysis and
collected information.
Enhanced information
through the combination of
methods. Detection of
short-lived species can be
achieved.
Tandem techniques (example):
Electrospray ionization mass
spectrometry (ESI-MS)
Aqueous solution of a complex
(some other solvents may be
used).
Tandem ESI-MS instrument.
Molecular mass of ionic
compounds. Possible
identification of solution
species.
Where a coordination complex is isolable as a solid, and particularly as a crystalline solid,
additional methods are available to assign structure (Table 7.3), up to a detailed picture
of the three-dimensional structure including accurate bond distances and angles obtained
by diffraction methods. Where non-crystalline samples or solids deposited on surfaces are
obtained, alternate methods can probe structure. Deliberate formation of extended solids
of particular shapes defined by the way metal ions and selected ligand components self-
assemble is the realm of materials science, an area of exceptional growth and promise that
is taking coordination chemistry into new frontiers. An array of different physical methods
is now available for investigation of such species.
The fact that metal ions in complexes often have the ability to undergo oxidation and/or
reduction, with the resultant complexes having distinctly different properties as a result of
the change in the metal d-electron set, means that techniques able to probe these processes
have developed (Table 7.4). In coordination chemistry, the technique of cyclic voltammetry
(sometimes called 'electrochemical spectroscopy' because of its capacity to rapidly probe
behaviour in different oxidation states in simple solution experiments) is now commonly
employed. Thermodynamic properties, such as reaction enthalpy and complex stability
