Reactions of group V metal atoms with water molecules. Matrix isolation FTIR and quantum chemical studies

Article abstract of DOI:10.1021/ja003072z

Laser-ablated group V metal atoms (V, Nb, Ta) were co-deposited with water molecules in excess argon. The V atoms reacted with water to form the inserted HVOH molecule spontaneously. The Nb atoms reacted with water to form the NbOH₂ complex and

Full text of DOI:10.1021/ja003072z

J. Am. Chem. Soc. 2001, 123, 135-141
135
Reactions of Group V Metal Atoms with Water Molecules. Matrix
Isolation FTIR and Quantum Chemical Studies
Mingfei Zhou,* Jian Dong, Luning Zhang, and Qizong Qin
Contribution from the Department of Chemistry, Laser Chemistry Institute, Fudan UniVersity,
Shanghai, P. R. China
ReceiVed August 17, 2000
Abstract: Laser-ablated group V metal atoms (V, Nb, Ta) were co-deposited with water molecules in excess
argon. The V atoms reacted with water to form the inserted HVOH molecule spontaneously. The Nb atoms
reacted with water to form the NbOH2 complex and the inserted HNbOH molecule. Broad-band photolysis
produced the H2VO and H2NbO molecules as well as the VO and NbO monoxides. For Ta + H2O reactions,
neither TaOH2 nor HTaOH was observed, while the H2TaO molecule was produced on annealing, and the H2
elimination process was not observed on photolysis. The aforementioned species were identified via isotopic
substitutions as well as density functional calculations. Qualitative analysis of the possible reaction paths leading
to the observed products is proposed. The results have been compared with our earlier works concerning the
Sc and group IV metal atoms with water reactions in order to observe existent trends for the early transition
metal atoms.
Introduction
Ti, and V atoms could react with water to form the insertion
products spontaneously, while the late transition metal atoms
reacted with water to form metal-water adducts. These adducts
rearranged to the insertion molecules on photolysis.16,17
Recently, we performed matrix isolation FTIR and theoretical
study of reactions of laser-ablated Sc and group IV metal atoms
with water molecules in solid argon.18,19 For Sc, the difference
between laser ablated and thermal evaporated Sc atom reactions
is the observation of HScO and ScOH molecules with laser
ablation. Of more importance, a new reaction path leading to
the formation of H2MO (M ) Ti, Zr, Hf) was observed for
group IV metal atoms. Here we report the reactions of group V
metal atoms with water molecules, completing our study on the
early transition metal atoms and water molecule reactions.
The interaction of transition metal atoms and cations with
water molecules has attracted considerable attentions. The M+
+ H2O f MO+ + H2 and its reverse reactions in the gas phase
have been studied both experimentally and theoretically.1-14 It
was found that early transition metal cations (Sc+, Ti+, V+)
are more reactive than their oxides, and the formation of the
low-lying states MO+ + H2 is the only exothermic process.1-3,12,13
But for middle transition metals, the oxides are more reactive
than the metal cations. However, the reactions of transition metal
atoms and water molecules have received far less attention. Lin
and Parson reported that atomic Sc reacted with water to give
ScO in the gas phase.15 Matrix isolation infrared absorption
studies reported by Kauffman et al. showed that thermal Sc,
Experimental and Theoretical Methods
* Corresponding author: (e-mail) mfzhou@srcap.stc.sh.cn; (fax) 0086-
21-65102777.
The experimental setup for pulsed laser ablation and matrix infrared
spectroscopic investigation has been described previously20 and is
similar to the technique employed earlier by the Andrews group.21 The
1064-nm Nd:YAG laser fundamental (Spectra Physics, DCR 150, 20-
Hz repetition rate and 8-ns pulse width) was focused onto the rotating
metal target through a hole in a CsI window, and the ablated metal
atoms were co-deposited with H2O in excess argon onto an 11 K CsI
window, which was mounted on a cold tip of a closed-cycle helium
refrigerator (Air Products, model CSW202) for 1 h at a rate of 2-4
mmol/h. Typically, 5-10 mJ/pulse laser power was used. H2O, H218O
(96%18O) and D2O were subjected to several freeze-pump-thaw cycles
before use. Infrared spectra were recorded on a Bruker IFS113V
(1) Clemmer, D. E.; Aristov, N.; Armentrout, P. B. J. Phys. Chem. 1993,
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122, 114.
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Phys. 1999, 242, 81.
(21) Burkholder, T. R.; Andrews, L. J. Chem. Phys. 1991, 95, 8697.
10.1021/ja003072z CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/14/2000

136 J. Am. Chem. Soc., Vol. 123, No. 1, 2001
Zhou et al.
spectrometer at 0.5-cm-1 resolution using a DTGS detector. Matrix
samples were annealed at different temperatures, and selected samples
were subjected to broad-band photolysis using a high-pressure mercury
lamp.
Quantum chemical calculations were performed using the Gaussian
98 program.22 The three-parameter hybrid functional according to Becke
with additional correlation corrections due to Lee, Yang, and Parr were
utilized (B3LYP).23,24 Recent calculations have shown that this hybrid
functional can provide accurate results for the geometries and vibrational
frequencies for transition metal-containing compounds.12-14,25-29 The
6-311++G(d,p) basis sets were used for H and O atoms, the all electron
basis sets of Wachters-Hay as modified by Gaussian were used for V
atom, and the Los Alamos ECP plus DZ were used for Nb and Ta
atoms.30-32 These ECPs incorporate the mass velocity and Darwin
relativistic effects into the potential. Reactants, various possible
transition states, intermediates, and products were optimized. The
vibrational frequencies were calculated with analytic second derivatives,
and zero point vibrational energies (ZPVE) were derived.
Results and Discussion
Figure 1. Infrared spectra in the 1740-1540- and 1040-960-cm-1
regions from co-deposition of laser-ablated V with 0.2% water in
argon: (a) 1-h sample deposition at 11 K, (b) 25 K annealing, (c) 20-
min broad-band photolysis, and (d) annealing to 30 K.
Infrared Spectra. Experiments were done with water
concentrations ranging from 0.2 to 0.5% in argon, and typical
infrared spectra for the reactions of laser-ablated V, Nb, and
Ta atoms with water molecules in excess argon in the selected
regions are shown in Figures 1-3, respectively, and the product
absorptions are listed in Table 1. The stepwise annealing and
photolysis behavior of the product absorptions is also shown in
the figures and will be discussed below. Experiments were also
done with D2O and H218O samples, and the representative spec-
tra in selected regions are shown in Figures 4-6, respectively.
Calculation Results. Calculations were done on three isomers
of MH2O, namely, the inserted HMOH molecules, the H2MO
molecules, and the MOH2 complexes. The geometric parameters
and relative stabilities are shown in Figure 7, and the vibrational
frequencies and intensities are listed in Tables 2-4. For the
inserted HMOH molecules, stable minimums have been found
on both the quartet and doublet potential energy surfaces, but
no stable structure was found on the sextet potential energy
surface. All three inserted HMOH molecules were calculated
4
to have A′′ ground states. For MOH2, only the states that
correlated to the ground-state metal atoms were calculated.33
4
The VOH2 has a B1 ground state with planar C2V symmetry.
(22) Gaussian 98, Revision A.7. Frisch, M. J.; Trucks, G. W.; Schlegel,
H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.;
Montgomery, J. A., Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam,
J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.;
Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian, Inc.: Pittsburgh, PA, 1998.
Figure 2. Infrared spectra in the 1720-1550- and 990-950-cm-1
regions from co-deposition of laser-ablated Nb with 0.2% water in
argon: (a) 1-h sample deposition at 11 K, (b) 25 K annealing, (c) 20-
min broad-band photolysis, and (d) annealing to 30 K.
6
4
The NbOH2 and TaOH2 were predicted to have A′ and A′′
ground states with nonplanar geometry. All three H2MO
molecules were predicted to have 2A′ ground states with
4
nonplanar geometry. At the B3LYP level of theory, the A′′
HVOH was predicted to be the most stable structure followed
(23) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
2
2
by the A′ H2VO molecule. For Nb and Ta, the A′ H2MO
molecules are more stable than the inserted HMOH molecules
and the MOH2 complexes.
(24) Lee, C.; Yang, E.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(25) Bauschlicher, C. W., Jr.; Ricca, A.; Partridge, H.; Langhoff, S. R.
In Recent AdVances in Density Functional Theory; Chong, D. P., Ed.; World
Scientific Publishing: Singapore, 1997; Part II.
(26) Bytheway, I.; Wong, M. W. Chem. Phys. Lett. 1998, 282, 219.
(27) Siegbahn, P. E. M. Electronic Structure Calculations for Molecules
Containing Transition Metals. AdV. Chem. Phys. 1996, XCIII.
(28) Bauschlicher, C.W., Jr.; Maitre, P. J. Chem. Phys. 1995, 99, 3444.
(29) Hartmann, M.; Clark, T.; Van Eldik, R. J. Am. Chem. Soc. 1997,
119, 7843.
(30) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639.
Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980,
72, 650.
(31) Wachter, J. H. J. Chem. Phys. 1970, 52, 1033. Hay, P. J. J. Chem.
Phys. 1977, 66, 4377.
B3LYP calculations were also done on monoxides, and the
results are listed in Table 5. Both VO and NbO were predicted
to have 4Σ- ground states, while TaO was calculated to have a
2∆ ground state, in agreement with previous reports.34-38
(33) Moore, C. E. Atomic Energy LeVels; National Bureau of Stan-
dards: Washington, DC, 1959.
(34) Weltner, W., Jr.; McLeod, D., Jr. J. Chem. Phys. 1965, 42, 882.
(35) Brom, J. M.; Durham, C. H.; Weltner, W., Jr. J. Chem. Phys. 1974,
61, 970.
(36) Dyke, J. M.; Ellis, A. M.; Feher, M.; Morris, A.; Paul, A. J.; Stevens,
J. C. H. J. Chem. Soc. Faraday Trans. 1987, 83, 1555.
(32) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.

Group V Metal Atom Reaction with Water Molecules
J. Am. Chem. Soc., Vol. 123, No. 1, 2001 137
Figure 4. Infrared spectra in the 1260-1120- and 1050-960-cm-1
regions from co-deposition of laser-ablated V with 0.4% (H2O + HDO
+ D2O) in argon: (a) 1-h sample deposition at 11 K, (b) 25 K annealing,
(c) 20-min broad-band photolysis, and (d) annealing to 30 K.
Figure 3. Infrared spectra in the 1800-1730- and 1030-950-cm-1
regions from co-deposition of laser-ablated Ta with 0.2% water in
argon: (a) 1-h sample deposition at 11 K, (b) 25 K annealing, (c) 20-
min broad-band photolysis, and (d) annealing to 30 K.
Table 1. Infrared Absorptions (cm-1) from Co-Deposition of
Laser-Ablated V, Nb, and Ta Atoms with Water Molecules in
Excess Argon
H2O
D2O
H218O
assignment
(a) V + H2O/Ar
1710.6
1680.4
1567.0
992.0
1710.6
1680.4
1567.0
1035.9
1032.3
1029.4
987.3
1235.1
1215.3
1128.4
1035.5
1031.9
1029.1
987.3
H2VO sym-VH2
H2VO asy-VH2
HVOH V-H
H2VO site
H2VO site
H2VO V-O
VO
988.2
986.4
944.9
(b) Nb + H2O/Ar
1704.5
1704.5
1665.2
1587.5
1569.1
979.2
976.9
970.7
1224.0
1197.7
1141.2
1153.2
978.4
976.1
970.7
H2NbO sym-NbH2
H2NbO asy-NbH2
HNbOH Nb-H
NbOH2 H2O bending
H2NbO site
H2NbO Nb-O
NbO
1665.2
1567.0
932.6
930.4
923.7
920.4
966.5
966.5
NbO site
Figure 5. Infrared spectra in the 1720-1540- and 1250-1120-cm-1
regions from co-deposition of laser-ablated Nb with 0.4% (H2O + HDO
+ D2O) in argon: (a) 1-h sample deposition at 11 K, (b) 25 K annealing,
(c) 20-min broad-band photolysis, and (d) annealing to 30 K.
(c) Ta + H2O/Ar
1780.8
1780.4
1762.3
1014.4
986.9
H2TaO sym-TaH2
H2TaO asy-TaH2
TaO
1264.7
1014.4
984.9
1762.7
961.4
936.7
H2TaO Ta-O
The 1014.4-cm-1 band in the Ta + H2O experiments is
assigned to the TaO molecule based on isotopic substitution
experiments and previous work.34,38 This molecule was pre-
MO. The 987.3-cm-1 band was produced only on broad-
band photolysis; it exhibited no deuterium isotopic shift but was
shifted to 944.9 cm-1 with H218O, and gave an isotopic 16/18
ratio of 1.0449. This band is assigned to the VO molecule, which
is in good agreement with recent matrix isolation study of V +
O2 reaction.37 The vibrational fundamental of VO was predicted
at 1040 cm-1 at the B3LYP/6-311+G(d) level.
2
dicted to have a ∆ ground state with vibrational fundamental
at 1028 cm-1
.
No MO2 (M ) V, Nb, Ta) absorptions was observed in these
experiments.37,38
MOH2. The 1569.1-cm-1 band in the Nb + H2O experiments
markedly increased on annealing but decreased on broad-band
photolysis. It shifted to 1153.2 cm-1 with D2O and to 1567.0
cm-1 with H218O. The isotopic H/D ratio of 1.3606 and 16O/
18O ratio of 1.0013 indicate a H2O bending vibration. The
isotopic doublet structure observed in the mixed H216O + H218O
experiment confirms that only one H2O unit is involved. The
1569.1-cm-1 band is assigned to the H2O bending vibration of
the NbOH2 complex. DFT calculation predicted that NbOH2
In the Nb + H2O experiments, a broad band centered at 966.5
cm-1 was also produced on broad-band photolysis. It showed
the diatomic Nb-O stretching vibrational frequency ratio, and
only one oxygen atom is involved. This band was also observed
on (Nb + O2)/Ar experiments38 and is assigned to the NbO
molecule. The NbO was predicted to have 4Σ- ground state with
vibrational fundamental at 976 cm-1
.
(37) Chertihin, G. V.; Bare, W. D.; Andrews, L. J. Phys. Chem. A 1997,
101, 5090.
(38) Zhou, M. F.; Andrews, L. J. Phys. Chem. A 1998, 102, 8251.
6
has a A′ ground state, with a H2O bending vibration at 1603
cm-1, and isotopic frequency ratios in good agreement with

138 J. Am. Chem. Soc., Vol. 123, No. 1, 2001
Zhou et al.
Table 3. Calculated Vibrational Frequencies (cm-1) and Intensities
(km/mol) for HNbOH, H2NbO, NbOH2 and the Transition States
(TS1, TS2) on the Nb + H2O Reaction Paths
HNbOH(4A′′) HNbOH(2A′′) H2NbO(2A′) NbOH2(6A′) TS1 TS2
3864(153)
1671(342)
691(139)
577(77)
494(208)
345(176)
3858(161)
1686(324)
696(134)
579(74)
441(210)
354(162)
1785(142) 3839(72) 1785 1859
1758(385) 3737(29) 1664 1738
1000(179) 1603(104) 910 978
625(113)
571(16)
432(3)
304(249) 438 809
274(8) 1542i 1368i
521 924
535(141)
with the H2VO absorptions greatly enhanced, suggesting that
the 1567.0-cm-1 band may due to a vibrational mode of a
structural isomer of the H2VO molecule. This band is assigned
to the V-H stretching vibration of the HVOH molecule
following the HScOH and HTiOH examples.18,19 Present DFT
4
calculations predicted the HVOH to have a A′′ ground state
with bent geometry and is the most stable structural isomer of
V-H2O. The V-H and V-OH stretching vibrational modes
were calculated at 1635 and 714 cm-1 with 334:177 relative
intensities. Our spectrum below the 700-cm-1 region is noisy,
and the V-OH mode was not observed. In previous thermal V
atom and water reaction study, absorptions at 1583.0 and 703.3
cm-1 were assigned to the V-H and V-OH stretching modes
of the HVOH molecule.17 No absorption around 1583 cm-1 was
observed in our experiments. We note that previous thermal
experiments were performed at 15 K and employed higher metal
and water concentrations than our laser ablation experiments.
We suggest that the 1583.0- and 703.3-cm-1 absorptions in
previous experiments were most probably due to cluster species.
Figure 6. Infrared spectra in the 990-900-cm-1 region from co-
deposition of laser-ablated Nb with 0.4% (H216O + H218O) in argon:
(a) 1-h sample deposition at 11 K, (b) 25 K annealing, (c) 20-min broad-
band photolysis, and (d) annealing to 30 K.
The weak band at 1587.5 cm-1 in the Nb + H2O experiments
is assigned to the Nb-H stretching vibration of the HNbOH
molecule. The deuterium counterpart is observed at 1141.2
cm-1, which gave an isotopic H/D ratio of 1.3911. DFT
4
calculations predicted that the HNbOH molecule has a A′′
ground state, which is ∼16.3 kcal/mol higher in energy than
the 2A′ H2NbO molecule. The strongest absorption of the
HNbOH molecule is the Nb-H stretching vibration calculated
Figure 7. B3LYP calculated geometric parameters (bond length in
Å, bond angle in degree) and relative stability (kcal/mol) of the MH2O
(M ) V, Nb, Ta) isomers.
at 1671 cm-1
.
H2MO. In the V + H2O reaction, absorptions at 1029.4,
1680.4, and 1710.6 cm-1 can be grouped together by their
consistent behavior upon annealing and photolysis. These bands
were weaker on sample deposition, but were greatly enhanced
on broad-band photolysis, and sharpened on 30 K annealing.
The 1029.4-cm-1 band shifted to 986.4 cm-1 with H218O sample
and gave a 16O/18O isotopic ratio of 1.0436, suggesting that this
band is mainly due to a terminal V-O stretching vibration. This
band has been assigned to the VO molecule in previous thermal
V atom reactions with water in solid argon.17 However, this
band was not observed in the V + O2 reactions in solid argon.33
Of more importance, it shifted to 1029.1 cm-1 with D2O sample;
the 0.3-cm-1 deuterium isotopic shift indicates that this band is
not due to a pure V-O stretching vibration and is slightly
perturbed by hydrogen atoms. In concert, the 1680.4- and
1710.6-cm-1 bands showed no oxygen-18 shift with H218O
sample but were shifted to 1215.3 and 1235.1 cm-1 with D2O
sample and gave isotopic H/D ratios of 1.3827 and 1.3850,
respectively. The isotopic H/D ratios indicate that these two
bands are due to V-H stretching vibrations. In the mixed H2O
+ HDO + D2O experiment, two additional bands at 1695.3
and 1225.5 cm-1 were produced, suggesting that two equivalent
H atoms are involved in these two modes. Accordingly, these
three bands are assigned to the H2VO molecule. The 1695.3-
and 1225.5-cm-1 bands in the mixed H2O + HDO + D2O
Table 2. Calculated Vibrational Frequencies (cm-1) and Intensities
(km/mol) for HVOH, H2VO, VOH2, and the Transition States (TS1,
TS2) on the V + H2O Reaction Paths
HVOH(4A′′) HVOH (2A′′) H2VO(2A′) VOH2(4B1) TS1 TS2
3901(136)
1635(334)
714(181)
518(135)
447(289)
287(189)
3888(140)
1663(332)
732(182)
542(108)
453(264)
317(167)
1815(138) 3737(12) 1769 1878
1778(337) 3624(517) 1707 1736
1113(217) 1564(133) 987 1093
628(79)
534(10)
506(171)
390(4)
318(5)
132(89) 1766i 1295i
539
471
895
838
experimental values (calculated isotopic ratios: H/D 1.3641,
16O/18O 1.0043).
No evidence was found for the VOH2 and TaOH2 complexes.
4
DFT calculations predicted that VOH2 has a B1 ground state
with a H2O bending vibration at 1564 cm-1. The TaOH2 has a
4A′′ ground state with a H2O bending vibration at 1595 cm-1
.
HMOH. The 1567.0-cm-1 band in the V + H2O experiments
increased on 25 K annealing but was destroyed on broad-band
photolysis, while annealing to 30 K allowed regeneration of
this band. This band showed a negligible oxygen-18 shift, but
was shifted to 1128.0 cm-1 with D2O and gave an isotopic H/D
ratio of 1.3892. The isotopic shifts suggest assignment to a V-H
stretching mode. Photolysis destroyed the 1567.0-cm-1 band

Group V Metal Atom Reaction with Water Molecules
J. Am. Chem. Soc., Vol. 123, No. 1, 2001 139
Table 4. Calculated Vibrational Frequencies (cm-1) and Intensities (km/mol) for HTaOH, H2TaO, TaOH2, and the Transition States (TS1,
TS2, TS3) on the Ta + H2O Reaction Paths
HTaOH(4A′′)
HTaOH(2A′′)
H2TaO(2A′)
TaOH2(4A′′)
TS1
TS2
TS3
3914(183)
1738(281)
713(118)
556(89)
517(151)
308(123)
3894(226)
1827(213)
748(71)
608(89)
585(115)
395(93)
1854(109)
1833(311)
1006(144)
732(30)
594(6)
520(73)
3789(63)
3683(59)
1595(96)
458(6)
352(230)
244(2)
1829
1673
942
649
435
1853
1704
959
923
817
1989
1610
1017
998
881
1638i
1484i
1492i
mentally and theoretically.2-4,12 It is generally accepted that the
initial interaction between transition metal cation and water
molecule is to form a metal cation-water complex. Then, one
hydrogen atom is transferred from oxygen to the metal, leading
to the HMOH+ intermediate. The reactions of transition metal
atoms with water molecules are similar to the metal cation
reactions. The initial step is the formation of neutral metal-
water complexes, reactions 1-3.
Table 5. Calculated Bond Length (Å), Relative Energies (kcal/
4
2
mol), and Vibrational Frequencies (cm-1) of Σ- and ∆ State VO,
NbO, and TaO
relative energy bond length frequency(intensity)
VO (4Σ-)
VO (2∆)
0
+31.2
0
1.580
1.569
1.711
1.699
1.712
1.694
1040(256)
1052(270)
976(170)
1012(180)
976(116)
1028(103)
NbO (4Σ-)
NbO (2∆)
TaO (4Σ-)
TaO (2∆)
+21.6
0
-9.8
V(4F) + H2O(1A1) f VOH2(4B1)
∆E ) -11.5 kcal/mol (1)
experiment are due to V-H and V-D stretching vibrations of
the HDVO molecule.
Nb(6D) + H2O(1A1) f NbOH2(6A′)
∆E ) -12.6 kcal/mol (2)
The H2VO assignment was strongly supported by DFT
calculations. As shown in Figure 7, the H2VO molecule was
2
predicted to have a A′ ground state with nonplanar geometry
and is only slightly higher in energy than the inserted HVOH
Ta(4F) + H2O(1A1) f TaOH2(4A′′)
∆E ) -8.3 kcal/mol (3)
molecule. The V-O, antisymmetric and symmetric VH2 stretch-
ing vibrations were calculated at 1113, 1778, and 1815 cm-1
,
which require scaling factors of 0.925, 0.945, and 0.942 to fit
the observed values, respectively.
From the metal-water complex MOH2, one hydrogen atom
is passed from oxygen to the metal to form the insertion product,
reactions 4-6.
The 976.9-, 1665.2-, and 1704.5-cm-1 absorptions in the Nb
+ H2O experiments were generated on broad-band photolysis
and are assigned to the H2NbO molecule following the H2VO
example. The 976.9-cm-1 band underwent only an 0.8 cm-1
deuterium isotopic shift, but was shifted to 930.4 cm-1 with
H218O sample; the isotopic 16O/18O ratio 1.0500 is characteristic
of a Nb-O stretching vibration. The doublet feature in the mixed
H2O + H218O experiment indicates the presence of only one
oxygen atom. The 1665.2- and 1704.5-cm-1 bands showed no
oxygen-18 shift with H218O sample, but gave deuterium
counterparts at 1197.7 and 1224.0 cm-1 and defined H/D ratios
of 1.3903 and 1.3926, respectively, indicating that these two
bands are due to Nb-H stretching vibrations. As shown in
Figure 5, two intermediate bands were observed at 1685.3 and
1210.9 cm-1; these two bands are due to Nb-H and Nb-D
stretching vibrations of the HDNbO molecule. The H2NbO
assignment was further supported by DFT calculations, which
predicted a 2A′ ground state with Nb-O, and NbH2 stretching
vibrations at 1000, 1758, and 1785 cm-1, with 179:385:142
relative intensities.
VOH2 (4B1) f HVOH (4A′′)
NbOH2 (6A′) f HNbOH (4A′′)
TaOH2 (4A′′) f HTaOH (4A′′)
∆E ) -43.4 kcal/mol
(4)
∆E ) -42.6 kcal/mol
(5)
∆E ) -53.0 kcal/mol
(6)
Although reactions 1-3 are exothermic, and all conserve spin,
only the NbOH2 was observed in the experiments. Our DFT
calculations showed that all three HMOH (M ) V, Nb, Ta)
insertion molecules have quartet ground states, and reactions
4-6 are highly exothermic. The NbOH2 has sextet ground state;
there is spin crossing for reaction 5. Both VOH2 and TaOH2
molecules have quartet ground states- there is no spin crossing
for reactions 4 and 6. These suggest that the VOH2 and TaOH2
are very short-lived, rapidly rearranging to the HVOH and
HTaOH molecules. As will be discussed, the insertion molecules
HMOH can further be isomerized to the H2MO molecules. There
is spin crossing from 4A′′ HMOH to 2A′ H2MO. For V and Nb,
the isomerization reactions can only proceed on photolysis, while
for Ta, the isomerization reaction proceeded spontaneously on
annealing; this suggests that the HTaOH is also a short-lived
species and it rapidly rearranges to the H2TaO molecule.
In the V and Nb experiments, the H2VO, H2NbO and VO,
and NbO absorptions increased markedly on broad-band pho-
tolysis at the expense of the HVOH, NbOH2, and HNbOH. The
H2VO and H2NbO molecules are most likely produced by
photoinduced isomerization from the HVOH and HNbOH
molecules via reactions 7 and 8, while the VO and NbO are
Similar bands at 986.9, 1762.3, and 1780.4 cm-1 in the Ta
+ H2O experiments are assigned to the H2TaO molecule. These
three bands increased together on annealing. Present DFT
2
calculations predicted that the H2TaO molecule also has a A′
ground state with nonplanar geometry. The Ta-O, antisym-
metric and symmetric TaH2 stretching vibrations were calculated
at 1006, 1833, and 1854 cm-1, respectively.
There is no evidence of the metal hydride and hydroxide
molecules.39,40
Reaction Mechanism. The reactions of transition metal
cations with water molecules have been studied both experi-
(39) Xiao, Z. L.; Hauge, R. H.; Margrave, J. L. J. Phys. Chem. 1991,
95, 2696.
(40) Dai, D. G.; Cheng, W.; Balasubramanian, K. J. Chem. Phys. 1991,
95, 9094.

140 J. Am. Chem. Soc., Vol. 123, No. 1, 2001
Zhou et al.
HVOH(4A′′) f H2VO(2A′)
HNbOH(4A′′) f H2NbO(2A′)
∆E ) +9.3 kcal/mol (7)
∆E ) -16.3 kcal/mol
(8)
HVOH(4A′′) f VO(4Σ-)+H2(1Σg )
+
∆E ) +17.3 kcal/mol (9)
HNbOH(4A′′) f NbO(4Σ-)+H2(1Σg )
+
∆E ) +5.0 kcal/mol (10)
HTaOH(4A′′) f H2TaO(2A′)
∆E ) -32.4 kcal/mol
(11)
+
HTaOH(4A′′) f TaO(2∆)+H2(1Σg )
∆E ) -0.9 kcal/mol (12)
Figure 8. Potential energy surface following the reaction paths from
HVOH leading to the H2VO and VO + H2 products. Energies given
produced by H2 elimination of the HVOH and HNbOH
molecules via reactions 9 and 10. In the Ta experiments, the
H2TaO absorptions increased on annealing but the TaO absorp-
tion was not enhanced on broad-band photolysis, which indicates
that reaction 11 can proceed spontaneously in the matrix, and
the H2 elimination process (reaction 12) was not observed on
photolysis.
4
are in kcal/mol and are relative to the A′′ HVOH.
Figures 8-10 show doublet and quartet potential energy
surfaces following the HMOH f MO + H2 or H2MO reaction
paths. From doublet HMOH, the hydrogen transfers from
oxygen to the metal center to form the H2MO through transition
state 1 (TS1). This process involves the breaking of the O-H
bond and the formation of a M-H σ bond and a M-O Π bond.
On the quartet surface, the hydrogen transfers from oxygen to
hydrogen through transition state 2. This transition state leads
to the H2 elimination to form the monoxides. The H2 elimination
process involves the breaking of the H-O bond and one
covalent M-H bond, with the formation of the H-H bond and
a M-O π bond. The calculated structural parameters of the
aforementioned transition states are shown in Figure 11.
In the V system, both the HVOH and VO molecules have
quartet ground states, the reaction from HVOH to VO conserves
spin, but this reaction is endothermic by ∼17.3 kcal/mol, and
the transition state (TS2) lies 35.8 kcal/mol higher in energy
Figure 9. Potential energy surface following the reaction paths from
HNbOH leading to the H2NbO and NbO+H2 products. Energies given
4
are in kcal/mol and are relative to the A′′ HNbOH.
4
4
than the A′′ HVOH. There is spin crossing from A′′ HVOH
to 2A′ H2VO, and this reaction is also predicted to be
endothermic by ∼9.3 kcal/mol. Apparently, both reactions that
lead to the formation of H2VO and VO require external energy.
The Nb system is quite similar to the V system, both the
HNbOH and NbO molecules were predicted to have quartet
ground states, the formation of NbO is endothermic by ∼5.0
kcal/mol, and there is ∼37.4 kcal/mol energy barrier from the
has higher efficiency in matrix. Different for V and Nb, the
energy barrier for the formation of H2TaO (reaction 11) is
predicted to be only 21.7 kcal/mol, lower than the reaction
energy of 32.4 kcal/mol. Reaction 11 is spontaneous as
evidenced by the increase of H2TaO absorptions on annealing.
As was discussed in our previous report,18 the only reaction
path of the HScOH molecule is the H2 elimination process to
form ScO; as Sc has only three valence electrons, there are not
enough electrons to satisfy chemical bonding in H2ScO, so the
H2ScO species is unstable. For groups IV and V metal atoms,
there are enough valence electrons to satisfy chemical bonding
in H2MO, so the formation of H2MO is the major reaction path.
The reactions of water with the early first-row transition metal
atoms are slightly different from the early first-row transition
metal cations. Both experimental and theoretical studies have
shown that, for the reaction of water with metal cations, the
only exothermic product is the low-lying state MO + H2.2,12
The H2MO+ (M ) Sc, Ti, V) corresponds to the final
intermediate on the reaction path, from this intermediate, the
loss of H2 proceeds without transition state to the final products
MO++H2. The bonding of H2MO+ is also quite different from
the H2MO molecules observed in our experiments. The H2MO+
4A′′ HNbOH to the Σ- NbO. From the A′′ HNbOH, there is
also spin crossing leading to the 2A′ H2NbO molecule. Although
this reaction is predicted to be exothermic by ∼16.3 kcal/mol,
there is a ∼35.1 kcal/mol energy barrier. The H2NbO absorp-
tions greatly enhanced only on photolysis, suggesting that
reaction 8 requires activation energy. In the case of Ta, the
HTaOH has 4A′′ ground state, but the ground state of TaO is a
2∆ state, the formation of both H2TaO(2A′) and TaO (2∆)
requires spin crossing. However, the formation of TaO is
predicted to be exothermic by only ∼0.9 kcal/mol, while the
formation of H2TaO is exothermic by 32.4 kcal/mol, and the
energy barrier leading to the TaO is much higher than the barrier
leading to the H2TaO. The formation of H2TaO is energetically
4
4
4
2
favored over the formation of TaO + H2. The A′′ and A′′
states of HTaOH lie very close in energy, and spin crossing

Group V Metal Atom Reaction with Water Molecules
J. Am. Chem. Soc., Vol. 123, No. 1, 2001 141
Table 6. Scaling Factors and Observed and Calculated Isotopic
Vibrational Frequency Ratios of the Observed Reaction Products
H/D
obs calcd
16O/18O
obs calcd
scaling
factor
molecule
H2VO
mode
sym-VH2
asy-VH2
V-O
0.942 1.3850 1.4026 1.0000 1.0000
0.945 1.3827 1.3938 1.0000 1.0000
0.925 1.0003 1.0013 1.0436 1.0442
0.955 1.3926 1.4077 1.0000 1.0000
0.947 1.3903 1.4025 1.0000 1.0000
0.977 1.0008 1.0019 1.0500 1.0503
H2NbO sym-NbH2
asy-NbH2
Nb-O
H2TaO
sym-TaH2
asy-TaH2
Ta-O
0.960
1.4108 1.0000 1.0000
0.961 1.3935 1.4073 1.0000 1.0000
0.981 1.0020 1.0032 1.0536 1.0538
0.958 1.3887 1.3995 1.0000 1.0000
0.950 1.3911 1.4060 1.0000 1.0000
HVOH
HNbOH Nb-H
V-H
NbOH2 H2O bending 0.979 1.3606 1.3641 1.0013 1.0043
VO
NbO
TaO
V-O
Nb-O
Ta-O
0.949
0.994
0.986
1.0449 1.0452
1.0509 1.0511
1.0551 1.0553
Figure 10. Potential energy surface following the reaction paths from
HTaOH leading to the H2TaO and TaO + H2 products. Energies given
Scheme 1
4
are in kcal/mol and are relative to the A′′ HTaOH.
the inserted HNbOH molecule. Broad-band photolysis produced
the H2VO and H2NbO molecules as well as the VO and NbO
monoxides. For Ta + H2O reactions, neither TaOH2 nor HTaOH
was observed, while the H2TaO molecule was produced on
annealing, and the H2 elimination process was not observed on
photolysis. The aforementioned species were identified via
isotopic substitutions as well as density functional calculations.
Table 6 lists the scaling factors and the observed and calculated
isotopic vibrational frequency ratios of the reaction products.
The results indicated that density functional theory using B3LYP
and effective core potentials predicted the vibrational frequencies
and normal modes of the transition metal compounds quite well.
From these results together with our earlier work covering
the Sc, Ti, Zr, and Hf + H2O reactions, the following con-
clusions are drawn:
(1) For the reactions of early transition metal atoms with water
molecules, the reaction paths shown in Scheme 1 are followed.
Both reaction paths leading to the H2MO and the MO + H2 are
exothermic. As the valence electrons of Sc cannot satisfy
chemical bonding in H2ScO, only path 2 was observed. For Ti,
V, and Nb, both reaction paths were observed, while for Zr,
Hf, and Ta, only path 1 was observed.
(2) The MOH2 and HMOH species are important intermedi-
ates in the reaction paths. The stability of these intermediates
depends mainly on their reactivity. For MOH2, only the NbOH2
was experimentally observed, probably due to the low efficiency
of the spin crossing reaction from NbOH2 to HNbOH. The other
MOH2 are short-lived species, rapidly rearranging to the HMOH
molecules. For HMOH, the HTiOH, HZrOH, HVOH, and
HNbOH were observed, while the HHfOH and HTaOH mole-
cules are short-lived species and were not observed in experi-
ments.
Figure 11. B3LYP calculated geometric parameters (bond length in
Å, bond angle in degree) of the transition states.
species can only be viewed as ion-molecule complexes, as no
M-H covalent bond exists in these H2MO+ complexes.
From groups IV and V metal atom and water reactions, some
clear trends can be observed. For Ti, V, and Nb, the formations
of both H2MO and MO were observed. Although the reactions
from HMOH to MO + H2 (M ) Ti, V, Nb) conserve spin,
these reactions were predicted to be endothermic. The reactions
from HMOH to H2MO (M ) Ti, V, Nb) were predicted to be
slightly endothermic or exothermic, but these reactions require
spin crossing. So the H2MO and MO can only be produced on
photolysis. For Zr, Hf, and Ta, the H2MO absorptions increased
on annealing, and no MO was produced on photolysis. In these
three systems, the reactions from HMOH to H2MO were
predicted to be exothermic. There is no spin crossing from
HHfOH to H2HfO. For Zr and Ta, although there is spin crossing
from HMOH to H2MO, the low-spin and high-spin states
HMOH are very close in energy, and the spin crossing has high
efficiency.
Conclusions
The reactions of V, Nb, and Ta atoms with water molecules
have been investigated using matrix isolation FTIR and density
functional theoretical calculations. The V atoms reacted with
water to form the inserted HVOH molecule spontaneously. The
Nb atoms reacted with water to form the NbOH2 complex and
Acknowledgment. This work is supported by NSFC (Grant
20003003) and the Chinese NKBRSF.
JA003072Z