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Fourier Transform Far Infrared Spectroscopy of Ligand Free Metal Clusters; Matrix Effects on the Molecular Geometry of Trichromium Cr3.

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reac;::,
?OE:
Dieses Manuskript ist
This manuscript is
to be cited as
Angew. Chem. Suppl.
1983, 92- 113
zu zitieren als
Angew. Chem. Suppl.
7983, 92-1 13
0 Verldg Chernte GrnbH, D-6940 Wemheim. 1983
0121 -4277:83/020! 0092SO9.50~0
:~:ai?eC
:rx
s Z t i d LeS
'ilsratimal speczrosc
typpc f o r n a t - r i x i s o l a t e d m e t 3 1 t r l a t . 3 n i C s a n d h i g h e r
o f th:s
p r e s e c t l y a r o c n t t o Ranan a n d r e s c n a n c e ? a m a n
m e t a l c:usters
o b s e r v a c i c n s o f :+Gt h e s e m e t h o d s a!cne
;a,',
l,', 4:
sb4 a,nc:
PS.,
2:.
I4
9.
.
..v'hile
c a n ~n f o r t u n a t e c i r c w , s t a ~ ~ ce s~ tsa b l l s n
such as ,
c l u s t e r g e o m e t r y , s r k , i g n i t ~ e s c a n a r i s e ,'7-;0,,
t h o s e r e l a t i n g t o s c a t . t e r 1 r . q f r o m 3r r e s o n a n c e e c h a n c e r n e n t b?
o n l y c e r t a i n T r t a l ~ s o t o p c m e r sa n d ' o r s t r u c t u r a l i s o m e r s , ar.8
"on-obser'Jaticn
3f
n a n c e Raman b a n d s ,
OL'
c;eoffro.: 7;.
il71?*,
Wdrk D .
a c c e s s t.o t h e comg!imer.tary
Gdkcr,
Uouqlas F.
i n a c t i v e or w e a k l y a c t l r e Randn o r r e s c some of . w h i c h
S t ~ v c nA .
Witchell and
cir . r r n l j C e c : a r i f : e d
by
i o w f r e q c e n c y ~ n f r a r e ds ? e c t r o s -
copic data.
McIntosh
c o r n u n i c a t l o n , w e w i s h t o r e p o r t t.he
t h i s srelim,ioar:i
:r.
f i r s : i ? . f r ~ r e dj p e c t r o s c c p i c d a t a for a " l i T a - d - : r e e "
i ~ i i t t : i c , -.+ze;; ;r3 : r x c 3 i : i z e ~ i n sol;:
f c c u s e s a t t e n t i o n on s o : e c u l a r
~ e t a l
:-r 2 7 5 ::e
&:.Lc:~
s t r u c t u r e and s u p f o r t
Ln:er-
aCti3ns.
were r e c o r d e d w i t h a : : i c o i e :
Spec:ra
20CSi:
r a p i d sca.-.nir.g FT-I? s p e c t . r o m e t e r e q s i p p e d .d:th
r.ign v a c u u m ,
B
6 . Z i ~~ y i a r
( 3 * = :3'
b e a n s p l i t t e r and t r y g l y c i n e s u l p h a t e d e t e c t o r
- 7
Ozln, D r . M.D. Bakci- a n d D r . D . F .
*i'rofrt:t;or [;.A.
Idsh M i l
6C S : .
:,.I-
C ~ C P I C L~a ~k r a t o r l e s , I : n l v ~ r s l t o~f ~ T c r o n t o ,
t i i t c h e l l , C h v n l s t r y D i v i s i o n , N a t i o n a l Rcsearcll
Cc:incil
C::nada,
-
92
me t a 1 c l a st e rs
c a n t c a t a l y t i c s y s t e m s i n u s e toda:,
chemica:
I xmob 1 1 i z e d
? h e :!esire
/l/.
t o en-
s i z e , s t r u c t u r e a n d s u p p o r t d e p e n d e n c e of t h e
t r a n s f o r n a t i o n s t h a t o c c u r on m e t a l c l - s t e r
h e t e r c 5 e r . e ~c~a ~t a l y s t s . h a s s t : n u l a r e d
based
o v e r t h e past. decade
a flood S r e s e a r c n aimed a t understandinq t n e chemrcai and
p > . . j s i c a 1 ? r o p e r t i e s o f small, w e l l d e f : n e d
in t h e as a n d c o n d e n s e d ;?.ases
'2,.
s ~ m p : e i e t a l i x e r s has ~ r o w n
n e t z i cicsters
Xhi;e
:are
o v e r :he
5 a t a 51r
;;ljt
Ce,*
:,ears,
1;er:i i i t t i e is know e x p e r i x e n t a l l ; ;
ters.
S p e c t r z s c o p i c a n d s t r u c t u r a l i n f o r n a t i o n on t h e s e
e ~ u i t i m e t i l ~ c : ~ c . u l e is
s x e e d e 3 'or
fcr h i g h e r c i u s -
ab i n i t l o v o l e c u l a r t.r-
j i t a l t 3 e c r e t i c i i c s t o t e a t t h e i r predict;ccs.
:rack
cherris..s i l l :
:.a+?
vity.'seiec:ivity
I-teractions / 3 1 .
iiith t h i s knowledge,
a T r e a t e r o p p o r t c n i t y :c f i n e r u m a c t i ? a t t e r n s oc c l u s t e r 3 a s e d c a t a i y s t s : 4 , .
Ligand-free n e t a l c i u s r e r s ;mobillzed
s o L i d s ':ia.;e
i n rare 58s
ESR. YC3,
a b s o r p t i o n and
and E Y S S / S / .
emission,
Yossbauer,
C n l y r e c e n t l y , h a v e Raman,
;?.terf;rc;rdns
hours.
F o u r t.0 s i x t e e n hocr
94
-
a n d arqor. or. x e n o n w e r e p e r f o r m e d i n s i t 3
lilt3
a s:l:ctir!
helium r e f r i g e r a t i o n u n i t .
Mechanical v i b r a t i o n :ctrrference
from t h e Displex system w a s n;nlmized
,with 4-pole
by e i e c t r o n l c f i i t e r i n q
nutterwoth hi5h pdss and l o w ?ass n o i s e L ~ l t e r s
b u i l t i n t o t h e s p e c t - r o n e t - e r ? a c k a g e r e s u l t i n q ~n '.i:.?a:
tllrned o f f .
T h e o p t i c a ; t r a i n t h r o u c h t.he I R ce:;
iccluces
t w o 3 m t h i c k p o l y e t h y l e n e wi?,dc~ds p l x s t h e cen:ra:
lnvr t h i c k
s i l i c o n window r e s u l t i n g i n a t o t a l t r a n s n i s s i o n ,>f a b o u t 109.
r e f e r e n c e , a n d s p e c t r a r e c n r d e d t h u s were st-ored f o r s c t s e q u e n t r a t i o r n g a g a i n s t t h e s p e c t r a of t h e m a t r i x .
I n f r e s h l y Zeposi ted
Cr,'Ar
ar.d C r ' 9 e Z c n 2 e n s a : e i
u n d e r c o n d i t i o n s w h i c n a z s c o n d u c i v e :o
Cr,
=
C r 2 and C r j n u t n o t h i g h e r c l u s t e r s . I l l .
:.'lo5
t o :;lo"
-
prepared
ice z o . : s c ~ a : - ~ r . cf
at. I ~ K ; , c h r 3 n i L r - c ? . r o r r ; ' x
L2/ [ C r l r a r e g a s
stretcnir..;
d e f o r m a t i o c a l n o d e s were o b s e r v e d i n Lhe f r e q c e n c : ,
2r.d
ri.??e
3 5 0 - 9 5 cm-'.
From
d
c l o s e e x a m i n a t i o n of
t h e far I R spectra
eyer
a
r a n g e o f d e p o s i t i o n , ?eta1 c o n c e n t r a t i o n a n d t h e r n a ? a n n e a l i n g
conditions.
f o r b o t h A r and X e s o l i d s a s r e p r e s e n t 2 t i v e mat-
C r j m o l e c u l e c a n b e i d e n t i f i e d a s l i s t e d i n T a b l e 1..
93
as a
When t h e s i l i c o n 'window was a t 1ZK t h i s p a t h ~ 3 :sed
s
n i q u e s been added t o t h i s impressi*,e L i s t /6/.
-
to
n o i s e r a t i o s o n l y 2 t o 3 times w o r s e t h d n w i t h t h e D153;i.x
rices
d i r e c t s t r . ; c c ~ r a l i n f o r m a t i o n for m a t r i x e n t r a p p e d g u e s t s 1s
1s
c o d e p c s i t l o n s o f c ? r 3 ~ , i u nd t c r s
resonacce Pman acd reicnance flcorescence spectroscopic tech-
In g e n e r a l ,
en-
The s p e c t r a a r e
window c o o l e d t o 12K b y a n A i r P r o d u c t s D l s p l r x c l o s e d c::cle
been s t u d i e d by a n a r r a y of s p e c t r o s c o p i c m e t h o d s
includin~; cv-visible
UPS,
2500 co-added
Gf
shown e x a c t l y a s t h e y were p l o t t e d a n d t b e r e s o ? u : l o n
the
e v o l u t i c r . o f c l u s t e r p r o p e r t i e s i r o n a t o m t o ml:i m e r a l a n d
e v a l u a t e neta;-s,pport
transfomation
-
o n h i c h s u r f a c e a r e a s x p p o r t s a r e by f a r t h e m o s t s l g n l f l -
:he
four:er
T h e s p e c t r a shown i n t h e f i g u r e s a r e t h e r e s u l t
-
i l i q n l j . d :s?e r s e d t r a p , s i t i o n
gir:eer
of
4 cn-'.
Canada.
S u s a o x Drive, O c t , i w a ,
cnHz i . w a t t i .
c o m p a s s i n g a n e a s d z e m e n t t l x e o f 2 11'2
rqe S t . , T o r o n c o , O n t a r i o , MSS l n l , C a n a d 3
<:c~c
n r . S.A.
HzIntosh,
( F i q u r e s 1 . 2 ) , v i b r a t i o n a l modes o f t h e sa:rix
isolated
I t is
c l e a r f r o m t h e s e d a t a t h a t d i f f e r e n t isomers of C r j e x i s t
-
95
-
A
A
I
1
:
25 L 1"
-
Figure 1:
96
-
-
FT far IR absorption spectra
"lY
98 -
for Cr/Xe = 5/104
C
deposited at 12X and annealed at the temperatures
indicated.Spikes and baseline irregularities seen
in Figures 1 and 2 near the high frequency cuto f f of the 6.25" mylar beamsplitter are associated
with incomplete filtering of the Displex mechanical
vibrations.
Peak to peak noise at 200
=
0.6%.
Figure 2;
FT f d r abburption I R spectra f u r CK/AK ratios of
(A)
'L
l/IO3 (B)
Ic
2.5/10'
( C ) 2, 1/10' deposited
at 1 2 K and annealed at the temperatures indicated
I'i,dk t o ~ ~ , di i o
k ibe
-
97
-
-
dt
99 -
?Oi.
'!"-I
=
0.5%.
an2 re;ati'-e
wr.ose ~ c l e : . ~ ? ? :;rc?e:r:.
icn-'
f'i-
3604
to s a m p l e p r e p a r a t i o c and s o s t t r e a t : T e n t .
tremely se.ns;tive
~ r ana::-s-s
.
: s ~ c e . ? r r a c i a n s are
cf a l a r q e c o l l e c t i o n of C r
KO
1
f a r I? d a t a y i e l d s
3 2 0 -1
,
t h e v i b r a t r o r a l f r e q x e n c i e s for e a c h o b s e r v e d t o r n of C r 3 a s
listed
>/ '\\
*i)
T a b l e 1.
280 -
Our r e s u l r s i n d i c a t e c h a t t h e ? r e f e r r e d s t r u c t u r e 0 5 C r 3
for a p a r t i c - l a r cb.oice o f e x p e r i m e n t a l u a r a n e t e r s
e n c e d by b n e t n e r i t i s p r c d c c e d ? - r i n g
of t h e ::1-
220
deposition process or f r o m 5iffllslon scntrolied
Thu5 f o r exa;r.ple,
ir. f r e s h l : ,
x/
/'/
-
r'i/
210
the aqglsireratisn events
-
c a n be a s c r i b e d
t.0
the s;ngle
matrizes
-rser...ed
t h e 3tne:
C X - ~s
113x5. :.?.Ls
same Z r .
s;es:-.s
r . 1 ~a~f t e r a n n e a l i n g cc .icy
1s
;x.%',
'\
~
Cr
>~
'?\
120 -
.Ar
In
'27.
'
140 -
I?. a c t l v e 3 ' v i b -
r a t r o n a ? n c d e c f c - e Djh e q u i l a t e r a l t r i a n q u l a r fo:n.
a r o u n d ,Lj
IW -
shows a s i n g l e b r o a d band c e n t r e d a r o u n d 2 1 0 c 3 - l
( I ' i q u r e 1: vk:ch
100
80
( F i g u r e 2 ) . i.anea-
-
1:ng
t?.e 1,:s . n a t r i c e s c o c t a i n i n : ; t L e D j h
-!31(
- however.
c 3 25-
f3
11. I n dr nat:Lces,
and
40 -
20 -
t e preferred i n freshly de;ositel
a s we;;
ter~ln::o
7Cr
\\
?2
a s 25K
60
-
-
'\
60
larger anqle C r j noie-
g e n e r a t e s C r j w i t n a n g i e s ~n L i e r a n g e 6 0 - 9 0 "
a r c u n d L 2 C m :Pic-re
cules ter.C
of C r 3
for:
Jl
,:,.
180 -
d e p o s L t e l :<a x a t r i c e s
',,'\
a t 123. C r ,
'3
'
200 - .:\,~
of t k e c o n -
n u c l e a y i o n r e a c t i o n s i n d u c e d by t h e r m a l a r . n e a l ; n g
?er.sate.
26D
influ-
IS
'
\>\ 1,:L
.\,
330 -
I00
80
100 -
102
-
t h e fsra and d i s t r i b u t i o n o f i m n o b i l i z e d C r 3 c l u s -
:.aried
co thks i c c o u n t of
ters.
C o n s i d e r i n g for e x a m p l e , t r i s u b s t i t u t i o n a i v a c a n c y Cr
primary,
traps
(of w h i c h f o u r t y p e s e x l s t i n t h e f c c l a t t i c e s o f
ing
?
fr,
riz,
I10
i10
'$0
I60
-
cte c h ~ ~ q
~ne t?.e a n q l e
and i n t e r a c t i o n ,
oC.
frr,
The
:12j.
force constants, describ-
2 r Z 3and t h e i r i n t e r a c t i o n ,
were h e i d c o n s t a n t f o r
r a r e g a s s o l i d s h a v i n c a n g l e s of 1 8 0 " . 120-, 90° a n d 6 0 " w i t h
a l l angles
1
a t 1.00 a n d 0 . 0 5 mdyne/A, r e s p e c t l v e l y , w h i l e t h e
r e l a t i v e a b u n d a n c e s o f 1 : 4 : 2 : 2 r e s p e c t i v e l y ) i t seems t h a t
primary, f ;
,
and i n t e r a c t i o n , f r i , f o r c e c o n s t a n t s , d e s c r l b -
i t is n o t o n l y t h e number a n d d i m e n s i o n o f t k s e t r a p s ,
that
Ir13 a n d its i n t e r a c t r o n s ' x i c h
ing
i rlZ a n d 1 r J 3 , v e r e v a r i e d
have a d e c i s i v e i n f l u e n c e o n t h e C r 3 c l u s t e r d i s t r i b u t i o n
a c c o r d i n g - t o t!>e f o r m u l a e a i v e n I n f o o t n o t e c o f T a b l e 1.
f o r a p a r t i c u l a r preparation, but a l s o t h e s h o r t range i n t e r -
a e s i d e s assisti:.?
a c t i o r s S e t w e e n C r j a n 2 t h e rare g a s c a a e a s w e l l a s w l t h
s t r u c t u r a l f o r n s o f C r 3 a n d al.':ng
surrounding c5romi'm g u e s t s .
c a l c u l a t i o n s e s t a b l i s h th.at t h e c o n t r i S u t : o n
Cr/Ar
-
For example,
i n low d i s p e r s i o n
from
m a t r i c e s ( F i g u r e 2 R ) t h e f a r IH S a n d s o f C r
1,'lO'
a r e f o u n d t o be c o n s i d e r a b l y b r o a d e r t h a n t h o s e o b s e r v e d i n
h i g h dispersion C r / X r
-
1/10'
matrices (Figure 2C).
On d e -
cr3
w i t h t h e i d e n t i f i c a t i o n of t h e d i f f e r e n t
v;brational
isotopomers is i n t h e r a n g e 8 - 1 0
s t r e t c h i n g modes a n d 2 - 8 cm-'
: F i g u r e 3 a n d T a b l e 1).
for the
assignxcrt;,
these
t o t ? e band w i d t h
cm-l
for ,1 a n d
v3
v 2 d e f o r m a t i o n mode
F u r t h e r m o r e , t h e far 19 d a t a f o r t h e
p o s i t i o n , t n e C r 3 s p e c t r a under t h s fomer c o n d i t i o n s , d e p i c t
Djh
..r3 'wit?. 5 e n d a n g i e s z e t t h e 2 r e s e r . c e of s t r u c t u r a l fqLn-.s o f '.
of b a n d s o s l t l c n a n d band s h a p e , i n d i c a t i n g c , ? a t > h x o n a n d / o r
ween 100-150'.
v i b r o n i c c o u p l i n g c o n t r i b u t i o n s t o t h e b a n d w r d t h s of C r
In t h i s context, n o m a l coordinate c a l c u l a t i o n s
f o r C r 3 as a f u n c t i o r . o f bend a n g l e
J
from 60-163'
proved t o be
form of C r
i n A r and Y e a r e v i r t u a l l : ,
c o m p a r a b l e a:tnocgh
i d e n t i c a l :n
terms
3 are
not necessarily negligibie i n rhese a a t -
p a r t i c u l a r l g v a l u a b l e f o r u n r a v e l l i n s t h e i s c n e r i c and iso-
rices.
t o p i c c o n t r i b u t i o n s t c t h e o b s e r v e d C r 3 C a r I?
bands :Figure
t h e p r s n o u n c e d b a n d w i d t h s o f t h e f a r I R a b s o r p c r o n s of Cr..
3 and T a b l e 1 ) .
i n A r u n d e r low 3 l s p e r s : n n
The c a l c u l a t i o n s 'dera p e r f o r m e d u s l n c t h e
One c a n t h e r e f o r e 5eq;n
t o u n d e r s t a n d t h e o r i g r n of
cnndirions
tern5 of contributions
W i l s o n G F m a t r i x s e t h o d /la/ w i t h i n .which t h e b a s i s s e t was
assurned t o c o n t a i r . o n l y t h r e e " b o n d - s t r e t c h i n ? "
e o u s e f f e c t s , a s " e l ? a s from a d i s t i l b u t i o n o f s t r u c t u r a l
ordlnates,
1. r12, C r Z 3 a n d
C r13.
internal
CO-
T h e bcnd d l s t a n c e s d 1 2
a n d d 2 3 w e r e h e l d f i x e d a t 2 . 3 6 A a n d t h e d13 d i s t a n c e was
101
-
v i b r o n i c c o u p l i n q , innomogen-
isomers. w i t h bend a n g l e s of i 0 0 - 1 5 0 "
i n quench condensed
filns, r h r c h c o l l a p s e t o 5 0 - 8 0 "
a n q l e :some:s
ling a t 4 0 R .
-
and/or
:?
from i s o t o p o a e r s , :honon
i n ccntrast,
--
snal:
on a n n e 6 -
the high dispersion conditicns
103 -
f o r C r 3 i n .ir t e x d t 3 f a v c d r n a r r o w e r sand w i c t n s a n d b e t t e r
r e s o l v e d far IR s p e c t r a w h i c h p e r m i t a c i e a r e r i d e n t i f i c a t z o n
of i n d i v i d u a l C r 3 c l u s t e r g u e s t s w i t h bend a n g l e s from 60°
through t o a t l e a s t 130".
*- I" *- "
*"U"
Ur;der t h e s e c o n d i t i o n s t h e C r 3
i s o m e r s w i t h l a r g e r a n g l e s 130-130" a p p e a r t o be f a v o u r e d on
seem
d e p o s i t i o n a t 1 2 K w h i l s t t h e s m a l l e r a n u l e forms 6 0 - 9 0 "
t o b e p r e f e r r e d i n 40K a n n e a l e d f i l m s .
P r i o r t o t h i s f a r Ix s t u d y , t h e e x ? e r i m e n t a l
information
p e r t a i n i n g t o C r 3 c o n s i s t e d of Its i d e n t i f i c a t i o n i n rare g a s
0
10
--7
0
3
0
0
Y.
m
m
c
m
0
m a t r i c e s by u v - v i s i b l e
N
"
b-
N
a b s o r p t i o n s p e c t r o s c c p y ,ill,'.
Cpeci-
f i c a l l y t h i s i n v o l v e d a n a l y s i s of t h e r n e t a l c o n c e n t r 3 t i c n ,
N
p h o t o a g g r e g a t i o n and t h e n a l c h a r a c t e r i s t i c s of a n e l e c t r o n i c
t r a n s i t i o n a t 477-479
nm r n i c h was a s s o c i a t e d . # i t > pr 3'
"ul-
~
--
t i p l e t r a p p i n g s i t e e f f e c t s fsr - - 3
were s u s p e c t e d a t the
t i m e /ll/ w h i c h f r o m t h e r e s u l t s o f t h e p r e s e n t s t - d y c o z l d
be s e m a n t i c s f a r C r 3 i s o n e r i c forxs.
The c a l c u l a t e d str'Jc-
e n e r g i e s f 3 r C r 3 u s i n g e x ~ e n d e dX h c i e l
m o l e c u l a r o r b i t a l n e t h o d s i n d i c a t e t h a t t h e D3h
fora
1s
ferred o v e r t h e l i n e a r f o m by aboi;t 11 :kcal/atom.xe:e
?re/13/
a l t h o u g h t h e r e s u l t s of t h e a r e s e n t s t c d y s u g g e s t t h a t t h e
e n e r g y d i f f e r e r c e s s e p a r a t i n g i s o m e r s of C r 3 c o u l d be c o n s i 0
N
d e r a b l y less a n d p r o b a b l y of t h e o r d e r o f t h e van d e r waais
i n t e r a c t i o n s w i t h rare g a s a t a m s , of 2 - 5
noteworthy t h a t
-
104
17
106
-
-
:nvol:-i?c
I t is
-
anC K r nrzrices Z K 1ZK z n l y
C r 2nd VC 5 ~ o - s1.7 .AT
one s p e c i e s
k c a l xo1e-l.
b i m e t a l l i c p h o t o a g g r e g a t i o n experi:en:s
. . b e d i f f e r e n t i a t e d f o r e a c h of t h e mixed
CCUIC
trirners C r Y o / C r N o 2
2-
/ll/.
t h e s e f r i a t m i c b:,eta
This observation i n p i l e s t h a t
c cl-sters
e i t h e r 5 r v e t?.ree
bonds
o r a r e fl-xional sr t h a t a l l i s s c e z s e b s c r b ir. a v e r y n a r r c w
e c e z g y ranoe c c m - , a r a b l e t= :he
out to be a v : h r o r . i c z l l y
ang;e,
x i d t t zf :he
.m /Ill,
t z o n i c b a n d s a t :?:,':9a
aczive,
cbserved e l e c -
f o r x of C r j t u r n s
jn
z~uxionale c u i l a t e z a l trii f t h e 2-
-1
t h e r . i t s f a r I?. s ? e c t r c s c o p y x - l l h a v e t o be d e s c r i b e d
x i t 5 - n t i e f r m e w c r k zf v i 3 z s 1 i c
o r y a s <iscussed
ra:her
t2ax vLSraticnal
the-
f 3 r li3 ,/14,' and o b s e r v e < by esr s ? e c z r o s c s p ) -
f o r K 3 /l5/.
.
.
In s'uxnary, chis s r s c y 2enonstrates fcr tke f r r s :
-
105
-
- 107
-
tile
References:
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108 -
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It i s evident t>at the Cr,
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shallow
surface
potential
internal coordinate
energy
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5.
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110 -
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properties of a supported metal cluster / 1 7 / .
Trans. I,
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Acknowledgements:
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