Infrared spectra, structure, and bonding of the GeH3-CrH, HGe≡MoH3, and HGe≡WH3 molecules in solid neon and argon

Article abstract of DOI:10.1021/ic800552s

Laser ablated chromium, molybdenum, and tungsten atoms react with germane during condensation in excess noble gases. The chromium reaction stopped at the germyl metal hydride, molybdenum gave some hydride but mostly germylidyne, and tungsten reacted spontaneously to give only the germylidyne species. These molecules were identified by isotopic shifts, density-functional theory product energy and frequency calculations, and comparison to the analogous methane and silane reaction products. Effective bond orders for the HGe≡MoH ₃ and HGe≡WH₃ molecules are 2.82 and 2.87 using the B3LYP density functional, and are slightly lower than their silicon and carbon analogues. Our calculated Ge≡M triple bond lengths for these simple trihydride complexes are 0.05 to 0.10 A shorter than those measured for larger group 6 organometallic complexes.

Full text of DOI:10.1021/ic800552s

Inorg. Chem. 2008, 47, 8159-8166
Infrared Spectra, Structure, and Bonding of the GeH3sCrH, HGetMoH3,
and HGetWH3 Molecules in Solid Neon and Argon
Xuefeng Wang and Lester Andrews*
Department of Chemistry, UniVersity of Virginia, P.O. Box 400319,
CharlottesVille, Virginia 22904-4319
Received March 27, 2008
Laser ablated chromium, molybdenum, and tungsten atoms react with germane during condensation in excess
noble gases. The chromium reaction stopped at the germyl metal hydride, molybdenum gave some hydride but
mostly germylidyne, and tungsten reacted spontaneously to give only the germylidyne species. These molecules
were identified by isotopic shifts, density-functional theory product energy and frequency calculations, and comparison
to the analogous methane and silane reaction products. Effective bond orders for the HGetMoH3 and HGetWH3
molecules are 2.82 and 2.87 using the B3LYP density functional, and are slightly lower than their silicon and
carbon analogues. Our calculated GetM triple bond lengths for these simple trihydride complexes are 0.05 to
0.10 Å shorter than those measured for larger group 6 organometallic complexes.
Introduction
Laser-ablated metal atoms have been employed in our
laboratory to react with small molecules and form simple
compounds of particular interest for their chemical bond-
ing.10-12 Such is the case for the simplest group 6 methyli-
dyne molecules HCtMoH3 and HCtWH3, which are major
products of the methane activation reaction whereas only
CH3-CrH is formed with the lightest member of the family.
The chemistry of group 6 metals (Cr, Mo, W) reveals an
interesting trend. Because different d orbitals participate in
bonding, the tungsten and molybdenum compounds favor
high oxidation states while chromium counterparts form low
oxidation states. For example group 6 metal atoms react with
H2O2 to give high oxidation state H2WO2 and H2MoO2, and
low oxidation state Cr(OH)2, respectively.13 In addition
tungsten and molybdenum atoms react with H2 in solid neon
to produce trigonal prismatic C3V hexahydride, WH6, and
MoH6, while only the dihydride complex, CrH2(H2)2 is
obtained for chromium.14 Of particular interest to the present
Carbon is well-known for yielding multiple bonds,1,2 and
a large number of organometallic complexes containing
carbon-metal double and triple bonds are known, particu-
larly the alkylidene and alkylidyne complexes of group 6
metals.3,4 However, heavier members of the carbon family
are less effective in multiple bonding. As a result only one
silylyne complex with Mo-Si triple bond character5 and
several examples of germylyne group 6 metal complexes
have been reported by the Power and Filippou groups.6-9
* To whom correspondence should be addressed. E-mail: lsa@
virginia.edu.
(1) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; Wiley: New York, 1999.
(2) Massey, A. G. Main Group Chemistry, 2nd ed.; John Wiley and Sons:
New York, 2000.
(3) McLain, S. J.; Wood, C. D.; Messerle, L. W.; Schrock, R. R.;
Hollander, F. J.; Youngs, W. J.; Churchill, M. R. J. Am. Chem. Soc.
1978, 100, 5962; (carbyne synthesis)
(4) (a) Schrock, R. R. Chem. ReV. 2002, 102, 145. (b) Herndon, J. W.
Coord. Chem. ReV. 2004, 248, 3. (c) Herndon, J. W. Coord. Chem.
ReV. 2005, 24, 999. (d) Herndon, J. W. Coord. Chem. ReV. 2006, 250,
1889.
(10) Cho, H.-G.; Andrews, L. J. Am. Chem. Soc 2005, 127, 8226; (Mo +
CH4)
(11) Cho, H.-G.; Andrews, L.; Marsden, C. Inorg. Chem. 2005, 44, 7634;
(Cr, W + CH4)
(12) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040; and
references therein (Review article)
(5) Mork, B. V.; Tilley, T. D. Angew. Chem. 2003, 115, 371.
(6) Simons, R. S.; Power, P. P. J. Am. Chem. Soc. 1996, 118, 11966.
(7) Pu, L.; Twamley, B.; Haubrich, S. T.; Olmstead, M. M.; Mork, B. V.;
Simons, R. S.; Power, P. P. J. Am. Chem. Soc. 2000, 122, 650.
(8) Filippou, A. C.; Philippopoulos, A. I.; Portius, P.; Neumann, D. U.
Angew. Chem. 2000, 112, 2881.
(13) Wang, X.; Andrews, L. J. Phys. Chem. A 2006, 110, 10409; (M +
H2O2)
(14) (a) Wang, X.; Andrews, L. J. Am. Chem. Soc. 2002, 124, 5636; (WH6).
(b) Wang, X.; Andrews, L. J. Phys. Chem. A 2003, 107, 570; (Cr +
H2). (c) Wang, X.; Andrews, L. J. Phys. Chem. A 2005, 109, 9021;
(Mo + H2)
(9) (a) Filippou, A. C.; Portius, P.; Philippopoulos, A. I. Organometallics
2002, 21, 653. (b) Balazs, G.; Gregoriades, L. J.; Scheer, M.
Organometallics 2007, 26, 3058.
10.1021/ic800552s CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 18, 2008 8159
Published on Web 08/12/2008

Wang and Andrews
Figure 1. Infrared spectra for the Cr, Mo, and W atom and GeH4 reaction products in the 2000-1640 and 840-760 cm-1 regions in solid argon at 4 K.
(a) W + GeH4 deposition for 60 min, (b) after annealing to 20 K, (c) after >470 nm irradiation, (d) after annealing to 30 K. (e) Mo + GeH4 deposition for
60 min, (f) after annealing to 20 K, (g) after >380 nm irradiation, (h) after annealing to 30 K. (i) Cr + GeH4 deposition for 60 min, (j) annealing to 20 K,
(k) after >470 nm irradiation, (l) after annealing to 30 K. Bands labeled “c” are common to different metals and thus not due to a unique metal reaction
product.
investigation, silane activation by group 6 metals gave the
SiH3-MH hydride for Cr and Mo and the HSitMH3
silylidyne for Mo and W.15
We present here a matrix infrared spectroscopic study of
laser-ablated Cr, Mo, and W atom reactions with GeH4 in
solid argon and neon. The most interesting new products,
HGetMoH3 and HGetWH3, are isoelectronic to the above
silylidynes and the methane reaction product methylidynes
HCtMoH3 and HCtWH3.10-12
orbital (NBO)18,23 analysis was also done to explore the
bonding in new germylidyne molecules.
Results and Discussion
Infrared spectra of products formed in the reactions of
laser-ablated chromium, molybdenum, and tungsten atoms
with GeH4 in excess argon and neon during condensation at
4 K will be presented in turn. DFT calculations were
performed to support the identifications of new reaction
products. Common species, such as GeHx intermediates,
hydrogen species, and metal oxides have been identified in
previous papers.24-26
Infrared Spectra. Figure 1 compares spectra of reaction
products for three group 6 metal atoms and germane in argon,
and the product absorptions are listed in Tables 1 and 2. In
this manner common bands can be identified and eliminated
from consideration for new metal reaction products. For
example GeH2 and GeH are produced24b at 1839 and 1813
cm-1 in all laser ablated metal experiments with germane.
Experimental and Computational Methods. Matrix
isolation experiments involving laser-ablated Cr, Mo and W
atom reactions with small molecules and germane (Mathe-
son) reactions with ozone in excess argon have been
described in previous papers.13-17 The Nd:YAG laser
fundamental (1064 nm, 10 Hz repetition rate with 10 ns pulse
width) was focused onto a rotating metal target (Johnson
Matthey), which gave a bright plume spreading uniformly
to the 4 K CsI window. The metal targets were polished to
remove the oxide coatings and immediately placed in the
vacuum chamber. The laser energy was varied about 10-20
mJ/pulse. Fourier transform infrared spectroscopy (FTIR)
spectra were recorded at 0.5 cm-1 resolution on a Nicolet
750 with 0.1 cm-1 measurement accuracy using an MCTB
detector. Isotopic samples (GeD4 and GeHxD4-x (x ) 0-4))
were prepared as described, and the sample was frozen and
degassed before use.16 Matrix samples were annealed at
different temperatures, and selected samples were subjected
to photolysis by a medium pressure mercury arc lamp
(Philips, 175W, globe removed) and glass filters.
Complementary density-functional theory (DFT) calcula-
tions were performed using the Gaussian 03 program,18 the
B3LYP and BPW91 density functionals, 6-311+G(3df,3pd)
basis set for hydrogen and germanium atoms, and SDD for
the metal atoms.19-22 All of the geometrical parameters were
fully optimized, and the optimized geometry was confirmed
by vibrational analysis. Harmonic vibrational frequencies
were calculated analytically with zero-point energy included
for the determination of reaction energies. Natural bond
(15) Wang, X.; Andrews, L. J. Am. Chem. Soc. 2008, 130, 6766; (Cr, Mo,
W and SiH4)
(16) Withnall, R.; Andrews, L. J. Phys. Chem. 1990, 94, 2351; (GeH4)
(17) (a) Andrews, L. Chem. Soc. ReV. 2004, 33, 123. (b) Andrews, L.;
Citra, A. Chem. ReV. 2002, 102, 885.
(18) Kudin, K. N., et al. Gaussian 03, Revision D.01; Gaussian, Inc.:
Pittsburgh, PA, 2004.
(19) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
Y.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(20) Perdew, J. P.; Burke, K.; Wang, Y. Phys. ReV. B 1996, 54, 16533;
and references therein.
(21) Frisch, M. J.; Pople, J. A.; Binkley, J. S. J. Chem. Phys. 1984, 80,
3265.
(22) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta. 1990, 77, 123.
(23) (a) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
83, 735. (b) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. ReV
1988, 88, 899.
(24) (a) Smith, G. R.; Guillory, W. A. J. Chem. Phys. 1972, 76, 3208;
(photolysis of GeH4). (b) Wang, X.; Andrews, L.; Kushto, G. P. J.
Phys. Chem. A 2002, 106, 5809; (Ge + H2 )
(25) (a) Wight, C. A.; Ault, B. S.; Andrews, L. J. Chem. Phys. 1976, 65,
1244. (b) Milligan, D. E.; Jacox, M. E. J. Mol. Spectrosc. 1973, 46,
460; (ArnH+)
(26) Bare, W. D.; Souter, P. F.; Andrews, L. J. Phys. Chem. A 1998, 102,
8279; (metal oxides)
8160 Inorganic Chemistry, Vol. 47, No. 18, 2008

GeH3sCrH, HGetMoH3, and HGetWH3
5
Table 1. Observed and Calculated Fundamental Frequencies of the GeH3sCrH Germyl Metal Hydride in the Ground A′ Electronic State with the Cs
Structurea
GeH3sCrH
GeD3sCrD
approximate description
obs
calc(L)
int
calc(W)
int
obs
calc(L)
int
calc(W)
int
Ge-H str, a′′
Ge-H str, a′
1996
2090
2085
2059
1713
884
881
781
437
343
281
219
84
144
127
144
185
38
40
356
84
0
28
2
78
2059
2050
2016
1701
852
845
749
411
321
256
218
88
123
111
116
133
33
33
288
82
0
25
4
61
1440
1490
1483
1463
1224
628
626
561
325
248
220
194
60
73
70
69
96
19
20
182
43
0
1468
1459
1432
1215
605
6101
538
308
232
214
179
63
62
60
57
69
16
16
147
41
0
Ge-H str, a′
1944
1404
1194
Cr-H str, a′′
GeH2 bend, a′
GeH2 bend, a′
GeH3 def, a′
HCrGe bend, a′′
GeH2 rock, a′′
HCr,GeH3 rock, a′
Cr-Ge str, a′
HCrGe def, a′′
1656b
781b
covered
1
15
41
0
16
33
a Frequencies and intensities are in cm-1 and km/mol. Observed in an argon matrix. Frequencies and intensities computed with B3LYP/6-311++G(3df,3pd)
in the harmonic approximation using the SDD core potential and basis set for Cr noted (L) and using BPW91 noted (W). Symmetry notations are based on
b
the Cs structure. Neon matrix values 1677 and 792 cm-1
.
1
Table 2. Observed and Calculated Fundamental Frequencies of HGetMoH3 and HGetWH3 Complexes in the Ground A1 Electronic States with the
C3V Structuresa
HGetMoH3
calc
DGetMoD3
calc
HGetWH3
calc
DGetWD3
calc
approx. mode description
obs
int
obs
int
obs
int
obs
int
Ge-H str, a1
M-H str, e
M-H str, a1
MH2 bend, e
MH2 def, e
MH3 def, a1
GetM str, a1
HGeM def, e
2079 63
1482 33
2107 42
1502
22
1804.8b 1895 247 × 2 1292.3c
1352 125 × 2 1894.0d 1951 204 × 2 maskedf 1386.7 103 × 2
1801.0b 1891 218
maskedc 1337 109
1887.5d 1961 222
maskedf 1387.3 111
853
587
535
371
305
36 × 2
605
424
429
339
218
17 × 2
32 × 2
11
16
7 × 2
829
529
578e
347e
326
29 × 2
588
379
14 × 2
61 × 2
48
33 × 2
51
17 × 2
20
429d
331d
235
6
3
7
13 × 2
6 × 2
3 × 2
a Frequencies and intensities are in cm-1 and km/mol. Observed in an argon matrix. Frequencies and intensities computed with B3LYP/6-311++G(3df,3pd)
in the harmonic approximation using the SDD core potential and basis set for Mo and W. Calculations using the BPW91 functional gave similar frequencies.
b
The mode symmetry notations are based on the C3V structure. Neon matrix band positions 1827.3, 1822.5 cm-1
.
c Neon matrix band positions masked by
methane impurity. d Neon matrix band positions 1917.4, 1911.2 cm-1 e These nondegenerate modes are mixed internal coordinates. f Argon matrix counterpart
.
masked by a common band, but neon matrix position is 1373.5 cm-1. The 1340 cm-1 band in the GeHxD4-x experiment is close to this band position for
the all-D species.
A unique chromium product is formed on >470 nm
irradiation and includes bands at 1996, 1968, 1944, 1656,
and 781 cm-1. A possible molybdenum counterpart gives a
weak shoulder absorption at 1751 cm-1 on a broad 1741
cm-1 band that is common to all metals and a new 790 cm-1
band. The major molybdenum product increases on annealing
to 20 and 30 K, on >380 and >290 nm irradiation and gives
rise to sharp bands at 1804.8 and 1801.0 cm-1. The tungsten
product is masked by a common germane combination band
on sample deposition, which decreases to reveal sharp new
product absorptions at 1894.0 and 1887.5 cm-1 with a 1:2
relative intensity. These bands increase on >470 nm irradia-
tion, and also on annealing to 30 K so this reaction appears
to be spontaneous. Recall that recent silane reactions gave
similar bands at 1806.2 and 1802.1 cm-1 for Mo and at
1894.9 and 1887.8 cm-1 for W with the same reversed 2:1
and 1:2 relative intensity pattern.15
The reaction with GeD4 in excess argon gave the 1194.1
cm-1 counterpart of the chromium product with H/D
frequency ratio 1.387 for a Cr-H stretching mode and two
weaker bands at 1440 and 1404 cm-1. The Mo counterparts
for this product were not observed. The major Mo product
also increased on near uv irradiation at 1292.3 and 1284.0
cm-1 (Figure 2) and defined 1.397 and 1.403 H/D ratios for
two different Mo-H stretching modes. Unfortunately the W
product counterparts were covered by precursor combination
bands. However, the W reaction with mixed isotopic
GeHxD4-x sample gave new peaks at 1894, 1890, 1888, and
1340 cm-1. The mixed isotopic precursor and Mo produced
new peaks at almost the same positions, 1804 and 1292 cm-1,
as the pure isotopic precursors.
In solid neon the stronger chromium product bands were
observed at 1677.3 and 792.1 cm-1, which are shown in
Figure S1 (Supporting Information), and the deuterium
counterpart of the former was observed at 1209 cm-1. Figure
3 compares the neon matrix spectra for the Mo and W
reactions: the common GeH2 and GeH bands were observed
at 1862.5 and 1831.5 cm-1. The sharp major W product is
observed at 1917.4 and 1911.2 cm-1 and the sharp major
Mo product at 1827.3 and 1822.5 cm-1. With GeD4, the W
product gave a single absorption at 1373.5 cm-1.
Calculations. Following our investigation of group 6 metal
reactions with methane, which progressed through insertion
followed by hydrogen transfer,10-12 calculations were done
for the series of products GeH3-MH, GeH2dMH2,
HGetMH3, and the bridged species Ge(H)dMH3. The
energy profile is shown in Figure 4. As for the methane and
silane reactions, the global minimum energy species for
chromium is the first insertion product GeH3-CrH, and the
energies of subsequent H-transfer species are significantly
higher. With Mo the initial GeH3-MoH intermediate is low
in energy, the germylidene is 8 kcal/mol higher, the ger-
mylidyne is 4 kcal/mol higher, but the bridged species is 8
kcal/mol lower. However for tungsten, the product energy
Inorganic Chemistry, Vol. 47, No. 18, 2008 8161

Wang and Andrews
Figure 2. Infrared spectra for the Cr, Mo, and W atom and GeD4 reaction products in the 1450-1180 cm-1 region in solid argon at 4 K. (a) W + GeD4
deposition for 60 min, (b) after annealing to 20 K, (c) after >470 nm irradiation, (d) after annealing to 30 K. (e) Mo + GeD4 deposition for 60 min, (f) after
annealing to 20 K, (g) after >470 nm irradiation, (h) after annealing to 30 K. (i) Cr + GeD4 deposition for 60 min, (j) annealing to 20 K, (k) after >470
nm irradiation, (l) after annealing to 30 K.
is about 70 cm-1 lower than the SiH3 analogue, which are
in agreement with calculations. Two corresponding Ge-D
modes were observed at 1440 and 1404 cm-1 in solid argon
(Figure 2, c denotes bands common to all experiments), and
the H/D ratios, 1.385, for these bands are near that for
germane itself, 1.387. The Cr-H stretching mode is,
however, higher by 10 cm-1 in the germane species following
the increase in the Cr-H stretching mode from CH3-CrH
to SiH3-CrH. The deuterium counterpart is found at 1194
cm-1 for the Cr-D stretching mode, and the H/D ratio for
the present Cr-H stretching mode, 1.387, is near this ratio
for the silicon, 1.386, and carbon, 1.385, species.11,15 The
unique identifying mode for this molecule is the symmetric
GeH3 deformation (umbrella mode), which is observed spot
on the calculated value at 781 cm-1 (Table 1, Figure 1).
Figure 3. Infrared spectra for the Mo and W atom and GeH4 reaction
products in the 1940-1800 cm-1 region in solid neon at 4 K. (a) W +
Correlation between strong calculated and observed frequen-
GeH4 deposition for 60 min, (b) after annealing to 8 K, (c) after >470
cies supports the identification of GeH3-CrH following the
observation of the silicon analogue.15 We observe only two
of the three computed Ge-H stretching modes: according
to our calculations, the third mode may not be resolved from
the observed higher frequency band.
GeH3-MoH. Weak new absorptions were observed at
1751 and 790 cm-1 on sample deposition with molybdenum
in excess argon. The band labeled “c” is common to all metal
experiments with germane. These bands relate with the
strongest calculated frequencies for the molybdenum hydride
counterpart (Table S1, Supporting Information), but the
weaker Ge-H stretching modes and deuterium counterparts
were not observed. These bands were not observed in solid
neon. This evidence supports a tentative identification of the
GeH3-MoH species, but most of this reaction product
continues to other species during relaxation of the laser-
ablated Mo atom reaction product with germane.
nm irradiation, (d) after >380 nm irradiation, (e) after annealing to 10
K. (f) Mo + GeH4 deposition for 60 min, (g) after annealing to 8 K, (h)
after >470 nm irradiation, (i) after >380 nm irradiation, (j)after
annealing to 10 K.
decreases steadily with the number of hydrogen atoms
transferred to the metal center, and the bridged trihydride
species is the global minimum. We also performed intrinsic
reaction coordinate calculations18 to locate the transition state
between the singlet state HGetMH3 and Ge(H)dMH3
molecules and found such an intermediate with one imagi-
nary H-Ge-M bending frequency for each (i611 and i507)
and 14 and 11 kcal/mol higher energy than the germylidyne
species for M ) Mo and W, respectively. Product structures
calculated for each metal are illustrated in Figure 5.
GeH3-CrH. New absorptions appeared at 1996, 1944,
1656, and 781 cm-1 on >470 nm irradiation and sharpened
on annealing in experiments with chromium (Figure 1). Only
the two strongest and lowest of these were observed in solid
neon, at 1677 and 792 cm-1 (Figure S1, Supporting Informa-
tion). Similar absorptions were assigned to SiH3-CrH
molecules in our silane investigation.15 The Ge-H stretching
modes are about 100 cm-1 lower than the corresponding
Si-H modes, and the very strong GeH3 deformation mode
HGetMH3 (M ) W, Mo). The new 1804.8, 1801.0 cm-1
2:1 relative intensity pair of bands in the Mo experiment
are slightly lower than a similar pair at 1806.2, 1802.1 cm-1
using silane15 and a single band at 1830 cm-1 in the methane
reaction.10 These bands shifted to 1292.3 and 1284.0 cm-1
8162 Inorganic Chemistry, Vol. 47, No. 18, 2008

GeH3sCrH, HGetMoH3, and HGetWH3
Figure 4. Energy profiles for group 6 metal atom and germane reaction products computed at the B3LYP level of theory.
Figure 5. Optimized structures for products of group 6 metal and germane reaction. Parameters, bond lengths in angstroms, and angles in degrees, given
for B3LYP, BPW91.
with deuterium substitution and gave 1.397 and 1.403 H/D
isotopic frequency ratios. Neon matrix counterparts were
observed at 1827.3 and 1822.5 cm-1 for the hydrogen
species. Likewise, the 1894.0, 1887.5 cm-1 1:2 relative
intensity pair of bands in the W experiment are also lower
than the corresponding 1894.9, 1887.8 cm-1 pair with silane
and the 1907, 1896 cm-1 set from the methane reaction. The
neon matrix counterparts at 1917.4, 1911.2 cm-1 shift on
deuterium substitution into a single band at 1373.5 cm-1,
which gives 1.396 and 1.392 H/D ratios for the two modes.
We note that the present new neon matrix bands are just
2-3 cm-1 below the values observed for MoH4 and WH4,
respectively, with comparable H/D isotopic frequency ratios,
1.390 and 1.387, which verifies the observation of new
Mo-H and W-H stretching modes.14 Although the deute-
rium product is masked in solid argon with GeD4, the mixed
precursor has a window at the appropriate place, and we
observe the strong deuterium counterpart at 1341 cm-1,
which gives the H/D frequency ratio 1.412. Furthermore, the
1894, 1890, 1888 cm-1 band profile shows that two or more
H atoms are bonded to the W center.
Our calculations for harmonic symmetric and antisym-
metric W-H stretching modes for HGetWH3 (Table 2) find
1.413 and 1.407 H/D ratios, respectively, which support
assignment of the two above bands to symmetric and
antisymmetric W-H stretching modes as the symmetric
mode involves less metal and more hydrogen motion for an
obtuse angle between the equivalent W-H bonds.
Inorganic Chemistry, Vol. 47, No. 18, 2008 8163

Wang and Andrews
Table 3. Calculated Fundamental Frequencies for the Bridged
Ge(H)dMoH3 and Ge(H)dWH3 Germylidene Complexesa
We have also calculated (B3LYP) a triplet state butterfly-
structured product Ge(H)2WH2, which has the same energy
as singlet HGetWH3, but the calculated W-H stretching
frequencies 1800 cm-1 (287 km/mol) and 1968 cm-1 (102
km/mol) do not correlate with our observed germylidyne
frequencies. In addition, the analogous triplet state butterfly-
structured Si(H)2WH2 product is 1 kcal/mol higher in energy
than singlet HSitWH3. The calculated W-H stretching
frequencies 1806 cm-1 (284 km/mol) and 1964 cm-1 (101
km/mol) for this butterfly structure do not match our observed
silylidyne frequencies.15
Frequencies calculated with the BPW91 functional are
slightly lower (Table S2, Supporting Information), and they
correlate well with the B3LYP values, which substantiates
the application of DFT to support vibrational assignments
for these molecules.27,28
A close correlation between argon and neon matrix
frequencies is expected as the less polarizable neon matrix
host interacts less with the guest molecule than the more
polarizable argon matrix,29 and the 21-24 cm-1 differences
(1.2%) observed here are appropriate for the vibration of
metal hydrides with polar bonds.14
Reaction Mechanisms. The reaction of chromium, mo-
lybdenum, or tungsten atoms with GeH4 gives the straight-
forward inserted metal hydride GeH3-MH, which is trapped
in the cold argon matrix for M ) Cr, and some for M )
Mo, but most continues further to HGetMoH3 and with
tungsten all goes to the lower energy HGetWH3 final
product. This is consistent with the product energy profile
(Figure 4), which shows that the metal hydride is the only
plausible product for chromium, one possibility for molyb-
denum, and most unlikely for tungsten. Remember that
annealing increases the HGetMoH3 and HGetWH3 prod-
ucts,
Ge(H)dMoH3
Ge(H)dWH3
approximate description
calc
int
calc
int
M-H str, a′
M-H str, a′′
M-H str, a′
M-(H) str, a′
(H)-Ge str, a′
MH2 bend, a′
MH2 rock, a′′
MH2 twist, a′′
M-H def, a′′
Ge-M str, a′
M-H def, a′
MH2 tors, a′′
1906
1904
1811
1754
1015
904
833
719
598
452
249
131
16
101
5
1966
1960
1902
1717
1219
874
860
674
594
436
124
213
150
10
11
8
34
31
32
53
7
2
90
19
72
45
9
345
337
297
264
21
8
a Ground states 1A′. Frequencies and intensities are in cm-1 and km/
mol computed with B3LYP/6-311++G(3df,3pd) in the harmonic ap-
proximation using the SDD core potential and basis set for Mo and W.
Symmetry notations are based on the Cs structure. Calculations with the
BPW91 density functional gave similar frequencies.
The assignments to HGetWH3 and HGetMoH3 follow
those for HSitWH3 and HSitMoH3 and are based on
B3LYP harmonic frequency calculations.15 For HGetMoH3
we find a strong degenerate Mo-H antisymmetric mode at
1895 cm-1 and a half as strong Mo-H symmetric mode at
1891 cm-1 (Table 2), and we observe only two bands at
1804.8 and 1801.0 cm-1 with 2:1 relative intensity (frequen-
cies overestimated by 5.0%). In addition the strong band is
25 cm-1 lower than the strong band for HCtMoH3 and the
calculated value for HGetMoH3 is 16 cm-1 lower than the
calculated value for the methylidyne. However, the calculated
value for the bridged species is only 5 cm-1 lower (Table
3), which is not as good agreement by 11 cm-1, and the
bridged species has an observable bridge bond stretching
mode predicted 150 cm-1 lower, but this band is not
observed. Hence, our 1804.8 and 1801.0 cm-1 bands are best
assigned to the HGetMoH3 germylidyne, which is separated
from the lower energy bridged species by a 14 kcal/mol
higher energy transition state.
M + GeH4 f GeH3-MH f GeH2dMH2 f HGetMH3
(1)
which shows that reaction 1 is spontaneous for Mo and W
atoms to give the final germylidyne product. Here, however,
we are able to trap very little GeH3-MoH in solid argon
and no GeH3-WH, GeH2dMoH2, and GeH2dWH2 inter-
mediates as the reaction goes on to the more stable final
products.30 We were not able to trap any GeH3-MoH in
the more slowly condensing solid neon matrix at 4 K. In the
silicon case, both SiH3-MoH and HSitMoH3 are preserved
as major products.15 Finally, on the basis of reaction energies,
HGetWH3 is more stable than HGetMoH3 as reaction 1
is 64 kcal/mol exothermic for W and 13 kcal/mol exothermic
for Mo, computed at the B3LYP level of theory.
For the HGetWH3 molecule our calculation predicted a
strong degenerate W-H antisymmetric mode at 1961 cm-1
and a half as-strong W-H symmetric mode at 1951 cm-1,
and the two predictions are in very good agreement with
the 1894.0 and 1887.5 cm-1 experimental values (overesti-
mated by 3.5% and 3.3%). The two bands are observed 13
and 8 cm-1 lower than the corresponding bands for
HCtWH3, and our calculation predicts them 10 and 9 cm-1
lower. For the bridged species, the two higher modes are
predicted to fall 5 and 0 cm-1 lower than for the methylidyne,
and a comparable bridge bond stretching mode at 58 cm-1
lower. Hence, the two higher bands for the bridged species
are not predicted as accurately as those for the germylidyne,
but the clincher is the absence of the observable bridged
stretching mode. The unobserved lower energy bridged
species is separated from HGetWH3 by an 11 kcal/mol
higher energy transition state. The new peaks observed with
the GeHxDx-4 reagent are in agreement with our calculations
for the HGetMHD2 and DGetMH2D species, but these
band positions are not sufficiently unique to rule out the
bridged species in their own right.
Structure and Bonding. The structures calculated for the
three products of each group 6 metal atom reaction are
collected in Figure 5. The three germyl metal hydrides have
Cs structures comparable to those found for the methyl metal
(27) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502.
(28) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 3937.
(29) Jacox, M. E. Chem. Phys. 1994, 189, 149.
(30) We would not be able to detect GeH3-WH, even if it were trapped, as
the two strongest infrared absorptions (Table S1) are likely to be
masked by germane precursor and product bands.
8164 Inorganic Chemistry, Vol. 47, No. 18, 2008

GeH3sCrH, HGetMoH3, and HGetWH3
hydrides,10,11 and the silyl metal hydrides,15 but of course,
the GesM single bonds are longer than their silicon and
carbon analogues. The calculated GesM single bond lengths
range from 2.561 Å for Cr to 2.610 Å for Mo to 2.604 Å
for the W compound, and they compare favorably to 2.590
Å and 2.681 Å values measured for Cr and W germylene
complexes.7 These open structures for germyl metal hydrides
are in contrast to the butterfly hydrogen-bridged structure
observed and calculated for Ge2H2.31,32
One of the most interesting comparisons with carbon is
for the methylidene, silylidene,15 and germylidene species.
First, our computed GedMo double-bond length 2.406 Å
and GedW double-bond length 2.407 Å are near the median
for the values computed for single bonds above and triple
bonds below. Second, the computed GeH2dMoH2 and the
GeH2dWH2 structures have a plane of symmetry, the two
Ge-H bonds and the two M-H bonds are equivalent, and
therefore no agostic distortion results. Agostic distortion was
found for CH2dMoH2 at the B3LYP and even more at the
CASPT2 level of theory10,33 and for CH2dWH2 using
CCSD.11 It appears that the H bonded to Ge is too far away
from the metal center for any interaction that can lead to
distortion of these germylidene molecules. And third, notice
that the dimensions for the three group 6 metal germylidenes
are nearly the same.
Table 4. Natural Orbital Occupation Numbers for the HEtMH3 (E )
C, Si, Ge, M ) Mo, W) Molecules and the Resulting EBOa
molecule
σ
π
σ*
π*
EBO
HCtMoH3 (L)
HCtMoH3 (W)
HCtWH3 (L)
1.96
1.96
1.98
1.98
1.93
1.92
1.96
1.95
1.91
1.90
1.94
1.93
3.94
3.97
3.97
3.95
3.87
3.90
3.88
3.91
3.87
3.90
3.88
3.91
0.07
0.07
0.05
0.05
0.08
0.09
0.04
0.05
0.08
0.09
0.05
0.06
0.04
0.04
0.04
0.04
0.05
0.04
0.04
0.04
0.04
0.04
0.04
0.04
2.89
2.90
2.91
2.92
2.83
2.84
2.88
2.89
2.82
2.83
2.87
2.87
HCtWH3 (W)
HSitMoH3 (L)
HSitMoH3 (W)
HSitWH3 (L)
HSitWH3 (W)
HGetMoH3 (L)
HGetMoH3 (W)
HGetWH3 (L)
HGetWH3 (W)
a Values for π orbitals summed over both components. (L) denotes the
B3LYP functional and (W) the BPW91 functional.
Our calculated HGetMoH3 and HGetWH3 structures
have C3V symmetry, the same as their silicon and carbon
analogues.10-12,15 Our computed GetMo bond length of
2.213 Å may be compared to 2.271 Å and 2.318 Å values
measured recently for germylyne complexes,6,9 and our 2.238
Å GetW computation may be considered with regard to
2.293 Å and 2.302 Å measurements for tungsten germy-
lynes.9 However, if our B3LYP calculation provides an
accurate representation, the present simple trihydrido metal
germylidyne complexes may have stronger triple bonds than
the larger ligand stabilized complexes. Although we did not
observe HGetCrH3, our calculated bond length of 2.094 Å
is also shorter than the 2.167 Å value reported for the GetCr
bond in a representative organometallic complex.7 Finally,
our B3LYP calculated GetM (M ) Cr, Mo, W) triple bond
lengths are 4, 3, and 2% shorter than these bond distances
from the addition of tabulated triple bond covalent radii,34
which is acceptable agreement considering the differences
in these approaches.
The effective bond orders (EBOs) can be calculated from
the orbital occupancies, namely total bonding minus total
antibonding divided by two. The occupancies and EBOs are
compared in Table 4 for methylidynes, silylidynes, and
germylidynes of Mo and W. Notice that the EBO decreases
more from C to Si than from Si to Ge, as the larger valence
orbitals are less effective at bonding, and that the EBOs are
slightly higher for W than corresponding Mo species. All
Figure 6. Highest occupied molecular orbitals (HOMOs) for triple bonds
in the HGetMoH3 and HGetWH3 molecules calculated with B3LYP/
SDD/6-311++G(3df,3pd). Isoelectronic density level is 0.03 e/au3.
are effectively triple bonds. The bonding sigma and pi
molecular orbitals illustrated in Figure 6 for HGetMoH3
and HGetWH3 are almost the same to the eye. They may
be compared to the analogous molecular orbitals for the
silylidynes,15 which are slightly more compact as expected.
It is also significant that the germylidynes HGetMH3 are
polarized similarly to the silylidynes and quite differently
from the methylidynes.15 Natural charges are compared in
Table S3, Supporting Information. This polarization affects
the Ge-H bond and reduces the s character (40.7%) with
the balance (59.3%) in the sigma Ge-W bond whereas the
C-H bond has more s character (45.3%) with the remainder
(54.5%) in the sigma C-W bond. In these molecules the pi
bonds are valence np-tungsten 5d, as summarized in Table
S2, Supporting Information.
(31) Palagyi, Z.; Schaefer, H. F., III; Kapuy, E. J. Am. Chem. Soc. 1993,
115, 6901.
It is also interesting to compare the product energy profile
for methane reactions11 with the products from germane
(Figure 4). The chromium insertion product is the global
minimum energy species for both reactions. With molybde-
(32) Ricca, A.; Bauschlicher, C. W., Jr J. Phys. Chem. A 1999, 103, 11121.
(33) Roos, B. O.; Lindh, R. H.; Cho, H.-G.; Andrews, L. J. Phys. Chem.
A 2007, 111, 6420; (theoretical study of CH2)MH2 complexes)
(34) Pyykko¨, P.; Riedel, S.; Patzschke, M. Chem.sEur. J. 2005, 11, 3511;
(triple bond covalent radii)
Inorganic Chemistry, Vol. 47, No. 18, 2008 8165

Wang and Andrews
num, all products are closer in energy but the insertion
product is lowest for methane and germane (except for the
bridged species). With tungsten, the strength of the W-H
bond contributes to promote maximum hydrogen transfer and
make the triple bonded species the global minimum for both
precursors (again except for the bridged species).
HGetMoH3 and HGetWH3 molecules contain fully de-
veloped triple bonds with effective bond orders of 2.82 and
2.87 using the B3LYP density functional, which are slightly
lower than their silicon and carbon analogues. Finally, our
calculated triple bond lengths for these simple Mo and W
trihydride germylidyne complexes are 0.05 to 0.10 Å shorter
than those measured for larger ligand-stabilized organome-
tallic complexes.
Conclusions
Reactions of laser ablated chromium, molybdenum, and
tungsten atoms with germane during condensation in excess
argon start with the GeH3-MH insertion product, which is
trapped for Cr, some for Mo, but most continues to
HGetMoH3, and all is believed to rearrange to lower energy
HGetWH3 for W. The subject molecules were isolated in
solid argon and neon and identified by isotopic shifts and
DFT frequency and structure calculations. The intermediate
GeH2dMoH2 and the GeH2dWH2 structures have a plane
of symmetry, and therefore no agostic distortion. The simple
Acknowledgment. We gratefully acknowledge financial
support from NSF Grant CHE 03-52487 and NCSA Grant
CHE07-0004N to L.A.
Supporting Information Available: Tables S1, S2, and S3
comparing calculated frequencies and molecular properties and
Figure S1 of neon matrix spectra for the chromium reaction with
germane. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC800552S
8166 Inorganic Chemistry, Vol. 47, No. 18, 2008