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Fig. 3 Pictorial representation of intrazeolitic [Cu(CO)2]1 complexes
formed at RT inside the ZSM-5 channels. The zeolitic framework has
been represented with sticks while the sphere representation has been
adopted for both Cu1 cations and CO molecules. This model is in
agreement with the experimental IR, XANES and EXAFS results
summarized in this work.
data collected on different Cu1-exchanged zeolites supported
this thesis.8,24
The same experimental set-up has been used here but the
EXAFS spectra have been collected at room temperature.
Under these conditions, from IR and microcalorimetric data
the formation of [Cu(CO)2]1 complexes is inferred. The results
are illustrated in Fig. 2 where the calculated and experimental
EXAFS signal together with the partial contributions of the
different 2 body (g2 single scattering) and 3 body (g3 multiple
scattering) configurations are compared. Being the solvation
power of two CO molecules less important than that of three,
the presence of a contribution from the zeolitic framework has
been necessary to reproduce the experimental spectrum (top
curve in Fig. 2), consisting in 2.3 0.3 oxygen atoms located at
2.11 0.03 Å. The number of framework oxygen neighbours
is in good agreement with that found before the CO dosage
(2.5 0.3, see above) while the Cu(I)–OF distance has been
considerably stretched (þ0.11 0.03 Å) with respect to the
zeolite in vacuo. Concerning the scattering due to the carbonyl
ligands, our EXAFS study results in a number of coordinated
CO molecules of 1.8 0.3, being so in agreement with the
[Cu(CO)2]1 stoichiometry suggested by IR, see Fig. 1a and
refs. 6–10 and microcalorimetry.9,10 The Cu–C distance obtained for the [Cu(CO)2]1 complex is 1.88 0.02 Å, the C–O
distance (1.12 0.03 Å) is in good agreement with the gasphase value (1.128 Å) and the Cu–C–O bond angle is linear
within the error bars (170 101), in agreement with indirect IR
evidences (vide supra).
Parallel IR and XANES experiments (Fig. 1) indicate that
intrazeolitic [Cu(CO)2]1 complexes are in C2v symmetry. A
pictorial representation of intrazeolitic [Cu(CO)2]1 complexes
formed at RT inside the ZSM-5 channels is reported in Fig. 3.
An Increase of the Cu–C distance of 0.05 Å by moving from
[Cu(CO)2]1 (this work) to [Cu(CO)3]1 (see ref. 6) complexes is
expected to accommodate a third CO ligand in the first coordination shell of copper. The experimentally obtained Cu–C
with advanced quantum mechanical methods:25 Lupinetti
et al.25a (1.891 Å), Ramprasad et al.25b (1.900 Å) and Sodupe
et al.25c (1.969 Å). The loss of framework oxygen coordination
by Cu(I) upon CO coordination has recently been observed in
the ab initio study of the group of Nachtigall.11e,26 on several
cationic sites in both MFI and FER frameworks, where also
an almost linear geometry has been found: 1711 r Cu–C–O
r 1791.
that the phenomenon can actually be followed in situ by
EXAFS and XANES spectroscopies when the appropriate
experimental set-up is available.18
The number of coordinated CO molecules obtained by EXAFS data analysis (1.8 0.3) is in good agreement with the
[Cu(CO)2]1 stoichiometry suggested by IR and testified by
microcalorimetric experiments.9,10 The Cu–C distance obtained
for the [Cu(CO)2]1 complex is 1.88 0.02 Å, with a C–O
distance (1.12 0.03 Å). The increase of the Cu–C distance of
0.05 Å observed by moving from [Cu(CO)2]1 to [Cu(CO)3]1
complexes is a consequence of the local rearrangement needed
to accommodate a third CO ligand in the first coordination
shell of copper. EXAFS determined that the Cu–C–O bond
angle is linear within the error bars (170 101), while IR and
XANES indicate that intrazeolitic [Cu(CO)2]1 complexes are
in C2v symmetry. The experimental values reported here are in
good agreement with the values obtained with advanced
quantum mechanical methods.
Acknowledgements
Luciana Capello thanks the INFM grant for her stage at the
ESRF during her Thesis degree in Materials Science. The cell
used for performing in situ XANES/EXAFS measurements has
been realized in collaboration with the GILDA beamline and
INFM OGG in Grenoble (F. Danca, F. La Manna and R.
Felici) and supported by INFM PURS project. The scientists
and technicians of BM8 (GILDA) of the ESRF are gratefully
acknowledged for their fundamental support during data
acquisition. We are indebted to Profs. G. Spoto, S. Boridga
and A. Zecchina (University of Torino) and with Prof. V. Bolis
(University of Piemonte Orientale) for fruitful discussions.
References
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8
9
10
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4. Conclusions
In this work we complete the X-ray absorption study of
[Cu(CO)n]1 complexes formed at RT inside ZSM-5 channels
by reporting the structure of the [Cu(CO)2]1 adducts. It
represents the natural complement of the investigation of the
[Cu(CO)3]1 complexes, performed at liquid nitrogen temperature and reported elsewhere.6 The picture emerging from the
two combined works is that the temperature and pCO can be
readily used as thermodynamic parameters to tune the nuclearity of [Cu(CO)n]1 adducts hosted inside ZSM-5 channels and
12
13
This journal is & The Owner Societies 2005
(a) E. I. Solomon, U. M. Sundaram and T. E. Machonkin, Chem.
Rev., 1996, 96, 2563; (b) R. H. Holm, P. Kennepohl and E. I.
Solomon, Chem. Rev., 1996, 96, 2239; (c) S. Ferguson-Miller and
G. T. Babcock, Chem. Rev., 1996, 96, 2889.
K. Klier, Langmuir, 1988, 4, 13.
M. Iwamoto and H. Hamada, Catal. Today, 1991, 10, 57.
Following the convention introduced by Iwamoto, a 100% exchange is reached when a Cu21 ion is introduced for each two
monovalent counterions, i.e., for each two Al31 ions of the
framework.
C. Prestipino, G. Berlier, F. X. Llabrés i Xamena, G. Spoto,
S. Bordiga, A. Zecchina, G. Turnes Palomino, T. Yamamoto and
C. Lamberti, Chem. Phys. Lett., 2002, 363, 389.
C. Lamberti, G. Turnes Palomino, S. Bordiga, G. Berlier, F.
D’Acapito and A. Zecchina, Angew. Chem. Int. Ed., 2000, 39,
2138.
C. Lamberti, S. Bordiga, M. Salvalaggio, G. Spoto, A. Zecchina,
F. Geobaldo, G. Vlaic and M. Bellatreccia, J. Phys. Chem. B,
1997, 101, 344, and refs. therein.
A. Zecchina, S. Bordiga, G. Turnes Palomino, D. Scarano, C.
Lamberti and M. Salvalaggio, J. Phys. Chem. B, 1999, 103, 3833.
V. Bolis, S. Maggiorini, L. Meda, F. D’Acapito, G. Turnes
Palomino, S. Bordiga and C. Lamberti, J. Chem. Phys., 2000,
113, 9248.
V. Bolis, A. Barbaglia, S. Bordiga, C. Lamberti and A. Zecchina,
J. Phys. Chem. B, 2004, 108, 9970.
(a) L. Rodriguez-Santiago, M. Sierka, V. Branchadell, M. Sodupe
and J. Sauer, J. Am. Chem. Soc., 1998, 120, 1545; (b) D. Nachtigallova, P. Nachtigall, M. Sierka and J. Sauer, Phys. Chem. Chem.
Phys., 1999, 1, 2019; (c) D. Nachtigallova, P. Nachtigall and J.
Sauer, Phys. Chem. Chem. Phys., 2001, 3, 1552; (d) P. Nachtigall,
M. Davidova and D. Nachtigallova, J. Phys. Chem. B, 2001, 105,
3510; (e) M. Davidova, D. Nachtigallova, R. Bulanek and
P. Nachtigall, J. Phys. Chem. B, 2003, 107, 2327.
Y. Kuroda, T. Okamoto, R. Kumashiro, Y. Yoshikawa and
M. Nagao, Chem. Commun., 2002, 1758.
X. Solans-Monfort, V. Branchadell, M. Sodupe, C. M. ZicovichWilson, E. Gribov, G. Spoto, C. Busco and P. Ugliengo, J. Phys.
Chem. B, 2004, 108, 8278.
Phys. Chem. Chem. Phys., 2005, 7, 1743–1746
1745