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The Raman spectrum of zirconium (IV) tetrahydroborate
INORG.
NUCL.
CHEM.
LETTERS
Voi.
7,
pp.
857-859,
1971.
Pergamon
Press.
Printed in Great Britain.
THE RAMAN SPECTRUM OF ZIRCONIUM (IV) TETRAHYDROBORATE B.E. Smith
and
B.D. James
Department of Chemistry, U n i v e r s i t y of Queensland, St. Lucia, Brisbane, Qld.
4067. A u s t r a l i a .
( R e c e i ~ d 27 May 1971)
I t has been f i r m l y established via X-ray and electron diffraction studies ( I , 2) that the zircon.ium (IV) tetrahydroborate molecule contains a tetrahedral ZrB4 "skeleton z:, singl e B-H terminal bonds along the Zr-B axes and t r i p J e hydrogen bridges between the central zirconium and each boron atom. The vapor phase infrared spectrum of this compound was i n i t i a l l y interpreted on the assumption that the molecule contained double hydrogen bridges (3) analogous to diborane (4) and aluminum tetrahydroborate (5). The i n t e r p r e t a t i o n of the v i b r a t i o n a l spectra of the doubly bridged aluminum tetrahydroborate (6, 7) was considerably aided by the Vibrational treatment of the simpler diborane molecule.*
For the unique t r i p l e
'
hydrogen bridge system in zirconium tetrahydroborate, however, there is no corresponding simple analogue and any treatment of the v i b r a t i o n a l spectra must accordingly suffer.
In order to assist reinterpretation of the infrared
spectrum in terms of the t r i p l e bridge model, the complementary Raman spectrum was studied. Experimental Zirconium tetrahydroborate was obtained by metathesis of ZrCl 4 and LIBH4 according to the method of Reid et at (9) and p u r i f i e d by t r a p - t o - t r a p distillation
on a vacuum l i n e (10).
Relevant references are given in Ref. 8. 857
858
ZIRCONIUM (IV) TETRAHYDROBORATE
Vol. 7 , No. 9
The spectra were recorded from an a p p r o x i m a te l y 2.5M s o l u t i o n in benzene using a Perkin-Elmer LR-]
instrument.
(He/Ne laser source, 632.8 rim, 8mW). Benzene
was refluxed and distilled over calcium hydride prior to use.
Results and Discussion The Raman spectrum of zirconium tetrahydroborate
is given below
(in cm-l): 2570
m
p
2215 (sh)vw 2180
m
p
2125 (sh)vw 1285
s
p
1077
w
dp
549
vs p
216
s
dp
Is = strong, m = medium, w = weak, v = very, sh = shoulder, p = polarized, dp = depolarized]. For a T d molecular symmetry, 4A l + 5E + 9T 2 modes are Raman active. Accordingly, just four polarized lines have been observed and are readily assigned.
The band at 2570 cm -l is a B-H terminal stretch;
a bridge expansion;
that at 2180 cm -l
that at 1285 cm -l a symmetric* bridge stretch;
one at 549 cm -l the Zr-B skeletal stretch. inthe doubly bridged diborane molecule (ll).
and the
All these modes have counterparts The' strong depolarized line at
216 cm -1 may be assigned to a Zr-B skeletal deformation or alternatively it may be a low-frequency bridge mode. spectrum, that at I077 cm
-I
Of the remaining three weak bands in the
apparently has no coincidence in the infrared
spectrum (3), where only T 2 modes are active, and hence it may be an E mode. The lines at 2215 cm -l and 2125 cm -l lie in the region of bridge expansion and stretching vibrations
*
(6, 7).
An in-phase motion of the hydrogen atoms symmetric with respect to ~he Zr-B C 3 axis.
Vol. 7, No. 9
ZIRCONDIUM (IV) TETRAHYDROIBORATE
859
Acknowledgments This work is supported by the Australian Research Grants Committee. B.E.S. acknowledges the receipt of a Commonwealth Postgraduate Award. References
I.
P.H. Bird and M.R. Churchill, Chem. Communs., 403, (1967).
2.
V. Plato and K. Hedberg, Inorg. Chem., l_~0, 590, (1971).
3.
B.D. James, R.K. Nanda and M.G.H. Wallbridge, J. Chem. Soc. A, 182, (|966)
4.
L.S. Bartell and B.L. Carroll, J. Chem. Phys., 42, I135, (1965).
5.
A. Almenningen, G. Gundersen and A. Haaland, Acta. Chem. Scand., 2_2.2, 328 (1968).
6.
W.C. Price, J. Chem. Phys., 17, IO44, (1949).
7.
A.R. Emery and R.C. Taylor, Spectrochlm. Acta, l__66, 1455, (1960).
8.
I. Freund and R.S. Halford, J. Chem. Phys., 433, 3795, (1965).
9.
W.E. Reid, J.M. Bish and A. Brenner, J. Electrochem. Soc., I04 , 21, (1957).
lO.
N. Davies, D. Saunders and M.G.H. Wailbrldge, J. Chem. Soc., A, 2915, (1970).
II.
R.P. Bell and H.C. Longuet-Higgins, Proc. Roy. Soc. (London), Series A, 183, 357, (1945).
NUCL.
CHEM.
LETTERS
Voi.
7,
pp.
857-859,
1971.
Pergamon
Press.
Printed in Great Britain.
THE RAMAN SPECTRUM OF ZIRCONIUM (IV) TETRAHYDROBORATE B.E. Smith
and
B.D. James
Department of Chemistry, U n i v e r s i t y of Queensland, St. Lucia, Brisbane, Qld.
4067. A u s t r a l i a .
( R e c e i ~ d 27 May 1971)
I t has been f i r m l y established via X-ray and electron diffraction studies ( I , 2) that the zircon.ium (IV) tetrahydroborate molecule contains a tetrahedral ZrB4 "skeleton z:, singl e B-H terminal bonds along the Zr-B axes and t r i p J e hydrogen bridges between the central zirconium and each boron atom. The vapor phase infrared spectrum of this compound was i n i t i a l l y interpreted on the assumption that the molecule contained double hydrogen bridges (3) analogous to diborane (4) and aluminum tetrahydroborate (5). The i n t e r p r e t a t i o n of the v i b r a t i o n a l spectra of the doubly bridged aluminum tetrahydroborate (6, 7) was considerably aided by the Vibrational treatment of the simpler diborane molecule.*
For the unique t r i p l e
'
hydrogen bridge system in zirconium tetrahydroborate, however, there is no corresponding simple analogue and any treatment of the v i b r a t i o n a l spectra must accordingly suffer.
In order to assist reinterpretation of the infrared
spectrum in terms of the t r i p l e bridge model, the complementary Raman spectrum was studied. Experimental Zirconium tetrahydroborate was obtained by metathesis of ZrCl 4 and LIBH4 according to the method of Reid et at (9) and p u r i f i e d by t r a p - t o - t r a p distillation
on a vacuum l i n e (10).
Relevant references are given in Ref. 8. 857
858
ZIRCONIUM (IV) TETRAHYDROBORATE
Vol. 7 , No. 9
The spectra were recorded from an a p p r o x i m a te l y 2.5M s o l u t i o n in benzene using a Perkin-Elmer LR-]
instrument.
(He/Ne laser source, 632.8 rim, 8mW). Benzene
was refluxed and distilled over calcium hydride prior to use.
Results and Discussion The Raman spectrum of zirconium tetrahydroborate
is given below
(in cm-l): 2570
m
p
2215 (sh)vw 2180
m
p
2125 (sh)vw 1285
s
p
1077
w
dp
549
vs p
216
s
dp
Is = strong, m = medium, w = weak, v = very, sh = shoulder, p = polarized, dp = depolarized]. For a T d molecular symmetry, 4A l + 5E + 9T 2 modes are Raman active. Accordingly, just four polarized lines have been observed and are readily assigned.
The band at 2570 cm -l is a B-H terminal stretch;
a bridge expansion;
that at 2180 cm -l
that at 1285 cm -l a symmetric* bridge stretch;
one at 549 cm -l the Zr-B skeletal stretch. inthe doubly bridged diborane molecule (ll).
and the
All these modes have counterparts The' strong depolarized line at
216 cm -1 may be assigned to a Zr-B skeletal deformation or alternatively it may be a low-frequency bridge mode. spectrum, that at I077 cm
-I
Of the remaining three weak bands in the
apparently has no coincidence in the infrared
spectrum (3), where only T 2 modes are active, and hence it may be an E mode. The lines at 2215 cm -l and 2125 cm -l lie in the region of bridge expansion and stretching vibrations
*
(6, 7).
An in-phase motion of the hydrogen atoms symmetric with respect to ~he Zr-B C 3 axis.
Vol. 7, No. 9
ZIRCONDIUM (IV) TETRAHYDROIBORATE
859
Acknowledgments This work is supported by the Australian Research Grants Committee. B.E.S. acknowledges the receipt of a Commonwealth Postgraduate Award. References
I.
P.H. Bird and M.R. Churchill, Chem. Communs., 403, (1967).
2.
V. Plato and K. Hedberg, Inorg. Chem., l_~0, 590, (1971).
3.
B.D. James, R.K. Nanda and M.G.H. Wallbridge, J. Chem. Soc. A, 182, (|966)
4.
L.S. Bartell and B.L. Carroll, J. Chem. Phys., 42, I135, (1965).
5.
A. Almenningen, G. Gundersen and A. Haaland, Acta. Chem. Scand., 2_2.2, 328 (1968).
6.
W.C. Price, J. Chem. Phys., 17, IO44, (1949).
7.
A.R. Emery and R.C. Taylor, Spectrochlm. Acta, l__66, 1455, (1960).
8.
I. Freund and R.S. Halford, J. Chem. Phys., 433, 3795, (1965).
9.
W.E. Reid, J.M. Bish and A. Brenner, J. Electrochem. Soc., I04 , 21, (1957).
lO.
N. Davies, D. Saunders and M.G.H. Wailbrldge, J. Chem. Soc., A, 2915, (1970).
II.
R.P. Bell and H.C. Longuet-Higgins, Proc. Roy. Soc. (London), Series A, 183, 357, (1945).