The variety of functionalities and
porous structures inherent to
metal-organic frameworks (MOFs) together with the facile tunability
of their properties makes these materials suitable for a wide range
of existing and emerging applications. Many of these applications
are based on processes involving interaction of MOFs with guest molecules.
To optimize a certain process or successfully design a new one, a
thorough knowledge is required about the physicochemical characteristics
of materials and the mechanisms of their interaction with guest molecules.
To obtain such important information, various complementary analytical
techniques are applied, among which vibrational spectroscopy (IR and
Raman) plays an important role and is indispensable in many cases.
In this review, we critically examine the reported applications of
IR and Raman spectroscopies as powerful tools for initial characterization
of MOF materials and for studying processes of their interaction with
various gases. Both the advantages and the limitations of the technique
are considered, and the cases where IR or Raman spectroscopy is preferable
are highlighted. Peculiarities of MOFs interaction with specific gases
and some inconsistent band assignments are also emphasized. Summarizing
the broad analytical possibilities of the IR and Raman spectroscopies,
we conclude that it can be applied in combinations with other techniques
to explicitly establish the structure, properties, and reactivity
of MOFs.
The state of the accessible copper ions in a Cu-basolite C300 sample (copper benzene-1,3,5-tricarboxylate) was studied by CO as an IR probe molecule. Low temperature CO adsorption on a sample activated at 473 K results in a series of carbonyl bands. Three intense sharp bands at 2141, 2128 and 2123 cm(-1) are very sensitive to the CO equilibrium pressure and are associated with CO polarized by the aromatic ring. Three bands, at ca. 2192, 2178 and 2148 cm(-1) are assigned to three different kinds of monocarbonyl species. At high CO coverage, the principal carbonyls (2178 cm(-1)) are converted into polycarbonyls. A band at 2125 cm(-1) (resistant to evacuation) is associated with Cu(+) ions on small CuO particles. Experiments on (12)CO-(13)CO adsorption revealed lack of vibrational coupling and also showed that the bands at 2192 and 2148 cm(-1), although changing almost in concert, were due to individual species. Sample activated at 373 K does not contain copper oxide, which indicates that activation at higher temperatures, 473 K, leads to some irreversible changes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.