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Copper Atom-Dihydrogen Matrix Photochemistry; An ESR FTIR UV-VIS Absorption Spectroscopic and Kinetic Study.

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activity of photoexcited metal atoms.
This manuscript is
to be cited as
Angew. Chem. Suppl.
Dieses Manuskriptist
zu zitieren als
Angew. Chem. Suppl.
addition to those mentioned above, include BCtiVatlOn of the
C-H bonds (but not the C-C bond) of ethane /5/, and abstraction of oxygen atoms from molecular oxygen to form CUO,CU(~~)
0 Varlag Chemie GmbH, D4940 Weinheim, 1982
and O3 /6/.
Copper Atom-Dihydrogen Matrix Photochemistry;i
Other photochemical
reactions of copper atoms in low temperature matrices, in
An ESR, PTIR, W - Y I S Absorption
The uv-visible absorption spectrum obtained for copper
atoms isolated in Kr/H2 matrices at 12 K (Cu/Kr/H2 =
1/1o4/1O3) closely resembled that observed L7a,7b/ for the
Spectroscopic and Kinetic Study
case of pure Kr matrices, although the effects caused by
310 nm photoexcitation of the entrapped copper atoms
Oeoffrey A. Ozin.* Steven A. Mitchell
(h2P + 42S) were markedly different for the pure Kr and
Kr/H2 = 10/1 cases.
Jamie Garcia Prieto
Photoinduced diffusion and dimerization
of the copper atoms /7a,7b/
the pure Kr matrices,
was observed in the case of
where the loss of copper atoms
was characterized by approximately second order kinetics in
the photolysis time, consistent with the occurrence of the
bimolecular dimerization reaction: 2Cu
Cu2. However, in
the case of the Kr/H2 = 10/1 matrices the photolnduced decay
of copper atoms was much faster, and was characterized by
-first order kinetics
in the photolysis time, as would be
expected for a reaction of the type Cu + H2
Professor G.A.
Ozin, Dr. S.A. Mitchell, Lash Miller
where H2 is in great excess. Furthermore. the photodecay
Chemistry Laboratories, 80 St. George St., University of
rates for Cu atoms in Kr/H2 = 10/1 and Kr/D2
10/1 matrices
Toronto, Toronto, Ontario, Canada M5S 1Al
were found to be identical within experimental error.
Dr. J. Garcia Prieto, Instituto Mexican0 del Petroleo,
minimal growth of Cu2 was observed under these conditions.
Av. Clen Metros, No.152, Mexico, 14.D.F.,
- 785
- 787 -
In a recent report /1/ we described the reaction of
photoexcited copper atoms (320 nm) with methane in
For our experimental arrangement (450 W Xe lamp, Oriel model
7240 monochromator with a 20 nm band pass and fibre optics
the half
solid methane mhtrices at 12 K, which was shown by uv-
attachment for in situ sample illumination
visible, IR and ESR studies to involve insertion of the cop-
life of the copper atoms for 310 nm irradiation was found to
per atom into a C-H bond of methane to fbrm the stable (at
be approximately 18 minutes.
12 K) intermediate species CH CuH, which decomposes via se-
condary photolysis (320 nm) to yield CH +CuH (predominantly)
Direct evidence for a chemical reaction involving photoexcited copper atoms and molecular hydrogen was obtained
or CH3Cu+H. Similar photochemical reactions involving me-
by means of In situ ESR and PTIR studies / 8 / of Cu/Kr/H2
thane and several transition metal atomic species have been
matrices. Flgure 1 shows ESR spectra obtained for matrices
described by Billups &
containing copper atoms and 10% H2, D2 or HD diluted in Kr.
/2/. In this communication we
wish to report for the first time that photoexcited copper
In each case the freshly deposited matrix showed only the
atoms are similarly reactive with respect to molecular hy-
known /9a/ spectrum of copper atoms, and no H or D atoms.
drogen. although the detailed energetics and dynamics ln-
The high field doublet associated with 63Cu and 65Cu atoms
volved in the Cu
H2 and Cu t CH4 photochemical reactions
are likely to be different.
Future studies may demonstrate
is reproduced in Figure 1 for matrices containing the various isotopic hydrogen molecules. It Is notable that the
that these kinds of matrix reactions may be considered to
structure on either side of the major resonance lines does
be the condensed phase 2P or 2D analogues of the well known
not show a dependence on the Isotopic composition of the
gas phase reactions involving the first excited singlet
hydrogen diluent. It is probable that this structure o r i -
and triplet (3PJ) states of the group IIB metal atoms
with hydrogen and alkanes /3.4/.
As we demonstrate in this
ginates from inhomogeneous broadening effects due to the
occurrence of multiple trapping sites for the copper atoms
report, in situ ESR and FTIR spectroscopy provide very con-
in these Kr/H2, D, or HD = 10/i matrices /9b/.
venient and sensitive techniques for detecting reactive in-
toexcitation of the entrapped copper atoms caused decay of
310 nm pho-
termediates and products formed in low temperature matrices
the copper atom resonance lines with the concurrent appear-
by excited state metal atom reactions with closed shell
ance and rapid growth of resonance l i n ~ / l O /due to H and/or
molecules. Thus it appears that the matrix technique has
D atoms, as shown in Figure 1. No lines attributable to
considerable potential as a means of investigating the re-
copper oxidation state I1 species such as. H-Cu-H, were
- 7aa -
Figure 1: Left side ESR spectra (Varian E4, 9.278 GHz)
exothermicity of the product channels and the identity of
showing the high field doublet associated with
the reactant metal excited state. Careful consideration of
6 5 ~ uand 6 3 ~ uatoms isolated in freshly deposited
the possible complicating effects of the surrounding matrix
Kr/H2. D2, and HD (10/1) matrices at 12 K (see
on the detailed cage energetics and dynamics of condensed
text). Right side
Spectra showing the presence
phase metal atom photosensitization reactions involving H2
of H and D atoms in the various matrices after =
(or any other reagent) will be required in future mechanis-
1 hr. photolysis at 310 nm. No H or D atoms were
tic investigations of these systems.
detected prior to the photolysis treatment.
The appearance of CuH as a product of the photochemical
reaction of copper atoms with H2 was detected by FTIR stu-
dies, as illustrated in Figure 2 and Table I.
- 709
changes in the CuH region as a result of 310 nm
photolysis of Cu/Kr/H2 = 1/104/103 matrices at
ducts CH CuH and C2H5CuH were detected, as well as their
major secondary photolysis products CH tCuH and C2H5tCuH
respectively /1,5/. It is interesting to note that in the
12 K, corrected for baseline slope arising from
thin-layer interference effects. A) Spectrum for
freshly deposited matrix; B,C) Spectra for 90 min.
case of the Kr/HD matrices there was a pronounced intramole-
and 270 min. irradiations at 310 nm, respectively.
cular isotope effect on the production of H or D atoms. As
Table I:
shown in Figure lC, H atoms were favored over D atoms by a
identical copper atom photodecay rates in Kr/H2 and Kr/D2
Figure 2: FTIR spectra (Nicolet 8000) showing spectral
observed in these experiments, in contrast to similar studies with CH4 and C2H6 in which the primary insertion pro-
factor of approximately 2. These isotope effects and the
10/1 rratrices are similar in both direction and magnitude to
Infrared Frequencies Observed for Cu Atom Photoreactions in Kr/H2, D2, and HD Matrices at 12 K
( cm-l )/a/
As signmen t
those found for the reactions of 'P~,~, Cd /4c/ and Hg /4d/
1907, 1388
atoms with HD, H2 and D2 in the gas phase. These reactions
1869, 1348
are known to produce the metal hydride and H atoms, and have
1852, 1336
been postulated to occur by a direct insertion
- dissocia-
838, 622
H/D /c/
tion mechanism involving side-on attack of molecular hydro~~
gen by the excited metal atom /lU.However, great caution
In the region 2000-500 Cm-l
needs to be exercised in attempts to extrapolate the results
Copper monohydride species (see text)
for gaseous 2Po,1 Cd and Hg atoms to the present study of
Interstitial H(D) atoms (reference 11)
rare gas isolated Cu atoms. To be able to make definitive
mechanistic statements on the Cu/H2 system, as well as
Absorption bands due to the cage vibrational mode of in-
meaningful comparisons with other metal atomic reagents, one
terstitial H lor D) atoms /12/ Mere also observed in these
will have to establish the reactant electronic State and the
experiments (see Table I). In addition to the strong CuH
influence (if any) of the matrix support. This is because it
stretching mode /1,13/ at 1852 cm-',
is well documented /4/ that interpretation of isotope
observed at slightly higher frequencies, as shown in Figure
effects in these kinds of systems, depends critically on the
2. The origin of these vCuH bands iswncertain. although the
- 790
weaker vCuH bands were
observed doublet vCuH/vCuD isotopic splitting patterns
a) Breckenridge, W.H.;
(Table I) definitely implicate a copper mIn-hydride species
Renlund, A.M.,
J. Phys. Chem.
b) Breckenridge, W.H.;
Renlund, A.M.
whlch should display well resolved triplet vHCuH/uHCuD/wDCuD
83, (1974), 303.
bid, 82, (1978),
isotopic structure. The occurrence of a secondary trapping
J. Chem. SOC. Farad. Trans. 2, E,(1972), 289
site effect for CuH could account for the band labelled I1
(and references cited therein).
copper c-hydride molecule
in all cases rather than a
in Figure 2, but this explanation seems unsatisfactory for
from the major vCuH band of CuH. An
ciated with a dicopper monohydride species, formed by a re+
Garcia-Prieto, J., Angew.
Ozin, G.A.;
Mitchell, S.A.;
Garcia-Prieto, J., J. Phys.
a) Ozin, G.A.;
Mitchell, S.A.;
Garcia-Prieto, J., J.
Phys. Chem. (in press), (1981).
This seems a reasonable
Elitchell, S.A.;
d) Callear, A.B.;
Chem. submitted for publlcation, 1981.
interesting possibility is that this uCuH band I is asso-
action of the type Cu + CuH
Chem. Int. Ed., (in press).
the vCuH band labelled I, in view of the rather large frequency shift (55 em-')
Ozin, G . A . ;
c) Breckenridge, W.H.;
b) Ozin, G.A.;
possibility in view of the known /7a,7b/ photoinduced dif-
H.; McIntosh, D.; Mitchell, S.; Norman, Jr., J.G.;
fusion behavior of copper atoms in rare gas matrices. How-
Noodleman. L., J. Am. Chem. SOC., =,(1979),
ever, detailed copper concentration and isotopic substitu-
8. Experimental details of our in situ fibre optics matrix
tion studies will be required to establish this assignment
photochemical assembly, suitable for ESR, FT-IR and
for band I.
W - V I S absorption spectroscopic and kinetic studies,
will be described in a forthcoming publication (Ozin,
The photochemical reaction of copper atoms with molecu-
lar hydrogen in Kr matrices can be written as follows:
H2 t hv (310 nm) + CuH t H.
We find no evidence for
logous to the CH CuH and C2H5CuH species identified in the
Cu t CH4 and Cu t C2H6 photochemical reactions respectively
An alternative explanantion for the origin of the fine
of an exchange coupled,next-nearest neighbour Cu...Cu
dimer, analogous to the situation for the matrix en-
tity of the reactive electronic state of the copper atoms
trapped H atom-methyl radical complex, W. Gordy and R.
Morehouse, Phys. Rev.,
photoexcitation of copper atoms in rare gas matrices is
m, (1966).
- 795 -
- 793 -
followed by efficient P'4
structure could be that ofa triplet state ESR resonance
Finally, there is an ambiguity regarding the iden-
in these reactions, since it is known /?a,7b/ that h2p
McLeod, D. Jr., J. Chem. Phys.,z,
formation of a copper dihydride H4u-H intermediate, ana-
Mitchell, S.A.; Garcia-Prieto, J.).
Kasai, P.H.;
10. Bhattacharya, D.; Wang, H-Y.; Willard, J.E., J. Phys.
32D3/2,5/2 nonradiative tran-
as, (1981).
1310; Iwasaki, M.; Muto, J.;
sitions. Reactions involving the 2P and 2D3/2 levels with
Torlyama, K.; Nunome. K; Fukaya, M.,
hydrogen are expected to be exothermic or nearly thermo-
1328 (and references cited therein).
neutral, respectively. We hope to report a more detailed
study of the energetics, dynamics and electronic state
5, (1981),
A non-statistical preference for CuD+H over CuHtD in the
reaction of 320 nm photoexcited Cu atoms with HD argues
correlations involved in these and related condensed phase
in favour of a short lived transition state complex /4/.
metal atom photosensitization reactions in the near future.
Moreover, because the quenching rates observed for 320
nm photoexcited Cu atoms by €I2 and D2 are comparable,
The generous financial assistance of the Natural Scien-
yet the product channels with HD are non-statistica1,it
ces and Engineering Research Council of Canada's Operating,
is evident that the attack geometry of Cu on H2 is side-
Major Equipment (Nicolet 8000 FTIR) and Strategic Energy
on. The weakening of the H-H bond and ultimately its
Programmes is greatly appreciated:
rupture can be considered to arise from the synergistic
(S.A.M.) also acknow-
ledges the NSERC and Noranda for graduate scholarships at
transfer of cu atom p-electron density into the
the earlier and latter stages of his work. (J.G.P.)
antibonding orbital of H2, simultaneous with the delo-
the Instituto Mexican0 del Petrdleo for financial support
calization of
of his research during his leave of absence at the
the vacant s-orbital of the Cu atom.
University of Toronto.
bending motion for HCuD in which momentum is conserved,
Billups, W.E.;
Mitchell, S.A.;
Konarski, M.M.;
Pitts, J.N.,
Hauge. R.H.;
J. Am. Chem. Soc.,~.(1980).
Calvert, J.G.;
bonding electron density from H2 into
Thus in a single
one can qualitatively understand how some 2/3 of the
Ozin, G.A.; McIntosh, D.F.;
Prieto. J., J. Am. Chem. Soc.
kinetic energy of the transition state complex can be
imparted to the H-atom and 1/3 to the D-atom, leading to
a product distribution of approximately 2:l for H:D in
the reaction of Cu atoms with HD,aS observed in practice.
"Photochemistry"; Wiley:
New York, (19661, Chapter 2 .
- 794 -
- 796
1 2 . Bondybey, V.E.;
Pimentel. G . C . ,
J. Chem. Phys..56,(1972)
Recently we demonstrated t h a t 320nm resonance e x c i t a t i o n
13. Wright, R.B.;
of copper atoms C U ( ~ P ) + C U ( ~iSn) t h e presence or methane a t
Bates, J.K.;
Inorg. C h e m . , x ,
12K, causes h i g h l y e f f i c i e n t and s e l e c t i v e i n s e r t i o n of t h e
(1978) ,2275.
Cu atom i n t o a CH bond of CH4 t o form CH CuH as t h e primary
The a c t i v a t i o n energy and quantum y i e l d
photoproduct /l/.
Received January (7, 1982 /S 76a S/
f o r t h e chemical quenching of C U ( ~ P by
) CH,, have Since been
e s t a b l i s h e d t o be c l o s e t o zero and u n i t y r e s p e c t i v e l y /2/.
S i m i l a r experiments with e t h a n e have a l s o r e v e a l e d s e l e c t i v e
CH bcnd a c t i v a t i o n chemistry t o y i e l d C2H5CuH l e a v i n g t h e CC
bond untouched /3/.
I n both of t h e s e c a s e s , a secondary
p h o t o l y s i s channel ( i n v o l v i n g RCuH absorbing around 350nm)
l e d t o competitive fragmentation of t h e i n s e r t i o n product t o
y i e l d as t h e major p r o d u c t s CH tCuH and C2H5+CuH with only
t r a c e a m u n t s of CH3Cu+H and C H Cu+H r e s p e c t i v e l y ( s e l e c 2 5
t i v i t y r a t i o approximately 99:l /1,2,3/).
I n t h e c a s e of
p h o t o e x c i t e d C U ( ~ P )i n t h e presence of H a ,
only CuHtH photo-
p r o d u c t s were d e t e c t e d at 12K with no evidence f o r t h e r e a c t i v e d i h y d r i d e i n t e r m e d i a t e HCuH /4/. I n r a r e g a s
on t h e o t h e r hand, c ~ ( ’ P ) undergoes an e f f i c i e n t n o n - r a d i a t l v e
r e l a x a t i o n p r o c e s s t o t h e l o w l y i n g CU(’DI state, which by
v i r t u e of t h e e l e c t r o n i c t o v i b r a t i o n a l energy t r a n s f e r
l o c a l l y t o the surrounding matrix
cage, coupled w i t h t h e long l i v e d n a t u r e of t h e C U ( ~ D s) t a t e
( n o t e 2D+2S i s p a r i t y f o r b i d d e n ) , p e r m i t s p h o t o d i f f u s i o n and
e x c i t e d s t a t e r e a c t i v e encounters with o t h e r immobilized
ground S t a t e Cu(’S)
i n t h e m a t r i x according t o :
797 -
Dieses Manuskript ist
zu zitieren als
Angew. Chem. Suppl.
This manuscript is
to be cited as
Angew. Chem. Suppl.
t o y i e l d Cu2 i n
t h e e x c i t e d A-state (Wlgner-Witmer s e p a r a t e d atom-molecule
c o r r e l a t i o n r u l e s ) which can ‘be d e t e o t e d by w e l l r e s o l v e d ,
s t r u c t u r e d A-state emission around 400-42Onm / 5 / . Relevant
a l s o t o t h e p r e s e n t s t u d y is t h e o b s e r v a t i o n t h a t photoe x c i t a t i o n of t h e 8 - s t a t e of Cu2 i n r a r e g a s m a t r i c e s (370-
0 Valag Chamie GmbH, 0-8940 Weirhim. t882
400nm) r e s u l t s I n a cage-asslsted fragmentation-recombination
;.:ethane A c t i v a t i o n By Photoexcited Dlcopper Molecules
p r o c e s s ( r e c a l l t h a t both t h e A and 8-states of Cu2 are
bound i n t h e gas phase /6/) as seen by C U ( ~ D )s t a t e emission
(around 750 and 870nm f o r t h e 2 ~ 3 / 2 and 2 ~ 5 / 2 terms r e s -
p e c t i v e l y /5/) w i t h a concomitant small (approximately 10%)
Geoffrey A. Ozin*, Steven A. M i t c h e l l
and Jamie Carsla-
b u t r e p r o d u c i b l e n e t p h o t o d i s s o c i a t i v e y i e l d /7/
according t o :
Because t h e Cu(%) s t a t e cannot be d i r e c t l y p o p u l a t e d from
C U ( ~ S )in a b s o r p t i o n ( d i p o l e f o r b i d d e n p r o c e s s ) y e t i t can be
i n d i r e c t l y prepared by Cu2(B)+Cu2(X) e x c i t a t i o n , coupled with
t h e o b s e r v a t i o n t h a t t h i s kind of low energy e l e c t r o n i c t r a n s i t i o n g e n e r a l l y r e d - s h i f t s with i n c r e a s i n g c l u s t e r n u c l e a r i t y
i n t h e s i z e range n = 2
6 (350 t o 600nm) /4,8/, l e a d $ one
t o e n q u i r e whether CH or CC bonds i n completely s a t u r a t e d hy* P r a f e s s o r G.A.
Ozin and Dr. S.A. M i t c h e l l , Lash Miller
Czernical L a b o r a t o r i e s , 80 S t . George S t . , U n i v e r s i t y of
T x o n t o , Toronto, Ontario, Canada, M5S 1 A l
C.-. J. OarCia-Prieto,
I n s t i t u t o Nexicano d e l PetrGleo, Av.
Cisn Metros, No.152, Mexico, 14.D.F.
drocarbons can b e s e l e c t i v e l y a c t i v a t e d u s i n g p h o t o e x c i t e d ,
low n u c l e a r i t y metal c l u s t e r s . Experiments of t h i s t y p e a r e
novel and could y i e l d c o n s i d e r a b l e fundamental i n f o r m a t i o n
r e l e v a n t t o t h e r a p i d l y developing f i e l d of heterogeneous
p h o t o c a t a l y s i s employing oxide and z e o l i t e s u p p o r t e d m e t a l
c l u s t e r s /9/.
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photochemistry, vis, spectroscopy, matrix, esr, ftir, stud, atom, kinetics, coppel, absorption, dihydrogen
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