Infrared spectra of M(OH)1,2,4 (M = Pb, Sn) in solid argon

Article abstract of DOI:10.1021/jp053420p

Infrared absorptions for the matrix-isolated lead and tin hydroxides M(OH), M(OH)₂ and M(OH)₄ (M = Pb, Sn) were observed in laser-ablated metal atom reactions with H₂O₂ during condensation in excess argon. The major M(OH)₂ product was also observed with H₂ and O₂ mixtures, which allowed the substitution of ¹⁸O₂. The band assignments were confirmed by appropriate D₂O₂, D₂, ¹⁶O ¹⁸O, and ¹⁸O₂ isotopic shifts. MP2 and B3LYP calculations were performed to obtain molecular structures and to reproduce the infrared spectra. The minimum energy structure found for M(OH)₂ has C_s symmetry and a weak intramolecular hydrogen bond. In experiments with Sn, HD, and O₂, the internal D bond is favored over the H bond for Sn(OH)(OD). The Pb(OH)₄ and Sn(OH)₄ molecules are calculated to have S4 symmetry and substantial covalent character.

Full text of DOI:10.1021/jp053420p

J. Phys. Chem. A 2005, 109, 9013-9020
9013
Infrared Spectra of M(OH)1,2,4 (M ) Pb, Sn) in Solid Argon
Xuefeng Wang and Lester Andrews*
Chemistry Department, UniVersity of Virginia, CharlottesVille, Virginia 22904-4319
ReceiVed: June 23, 2005; In Final Form: August 10, 2005
Infrared absorptions for the matrix-isolated lead and tin hydroxides M(OH), M(OH)2 and M(OH)4 (M ) Pb,
Sn) were observed in laser-ablated metal atom reactions with H2O2 during condensation in excess argon. The
major M(OH)2 product was also observed with H2 and O2 mixtures, which allowed the substitution of 18O2.
The band assignments were confirmed by appropriate D2O2, D2, 16O18O, and 18O2 isotopic shifts. MP2 and
B3LYP calculations were performed to obtain molecular structures and to reproduce the infrared spectra.
The minimum energy structure found for M(OH)2 has Cs symmetry and a weak intramolecular hydrogen
bond. In experiments with Sn, HD, and O2, the internal D bond is favored over the H bond for Sn(OH)(OD).
The Pb(OH)4 and Sn(OH)4 molecules are calculated to have S4 symmetry and substantial covalent character.
Introduction
the rotating high purity metal targets (Johnson Matthey), which
gave bright plumes spreading uniformly to the cold CsI window.
Lead is one of the most common dispersed heavy metals in
the atmosphere in the modern industrial era.1-3 The toxicity on
living organisms has been confirmed as displacement of vital
metals in the organism leading to anemia and damage to the
nervous system.4,5 The PbOH radical might be produced in the
atmosphere, but no definitive experimental observation has been
made based on our knowledge.6 However, two weak, broad
near-infrared emission bands in a study of lead monohalides
have been tentatively assigned to HPbO (or PbOH).7
The reactions of lead and tin with H2 and O2 in solid matrices
have been studied separately, and the MO, MO2, MH2, and MH4
molecules have been identified through infrared spectra.8,9 The
analogous SnX2, SnX4, and PbX2 (X ) Cl, Br, I) molecules
have been observed by electron diffraction.10 However, tetrava-
lent lead is not stable since relativistic effects reduce the M-X
bond strength, so only PbCl4 has been observed experimen-
tally.10,11 It is very interesting to consider the lead and tin
hydroxide molecules and their bonding and structure since very
little is known about group 14 metal hydroxides.12a Solubility
product constant data indicate that Sn(OH)2 and Pb(OH)2 are
very weak bases, much weaker than Mg(OH)2.12b
Recently we developed a new method to investigate metal
hydroxide molecules using laser-ablated metal atom reactions
with H2O2 or H2 + O2 mixtures in low-temperature matrices.13
With this approach we have the advantage to identify most
infrared active modes without overlapping excess water absorp-
tions. For example, ionic M(OH)2 (M ) group 2 metals), ionic
M(OH)2 and M(OH)4 (M ) group 4 metals), and covalent
M(OH)2 molecules (M ) group 12 metals) have been investi-
gated. We present here a matrix infrared spectroscopic study
of laser-ablated tin and lead atom reactions with H2O2 and H2
+ O2 in solid argon and identify the new metal hydroxide
molecules M(OH), M(OH)2 and M(OH)4 (M ) Sn, Pb).
The tin and lead targets were polished to remove the oxide
coating and immediately placed in the vacuum chamber. The
laser energy was varied about 10-20 mJ/pulse. Since the tin
and lead targets eroded rapidly during the ablation because of
metal softness, the targets were adjusted every 5 min to get a
fresh surface. FTIR spectra were recorded at 0.5 cm-1 resolution
on Nicolet 750 with 0.1 cm-1 accuracy using an MCTB detector.
Matrix samples were annealed at different temperatures, and
selected samples were irradiated by a medium-pressure mercury
arc lamp (Philips, 175 W) with the globe removed.14
Urea hydrogen peroxide (UHP) (Aldrich, 98%) was used as
the H2O2 source.13,15 At room-temperature UHP was put into a
Chemglass high vacuum valve with Teflon stem and argon gas
was passed over the sample to provide H2O2. Deuterated urea-
D2O2 was prepared following previous workers.16 Samples of
H2, D2, HD, O2, 18O2, and 16,18O2 were diluted in argon as
received.
Complementary MP2 calculations were performed using the
Gaussian 98 program system,14 the 6-311++G(3df,3pd) basis
set for hydrogen and oxygen atoms, and Los Alamos ECP plus
DZ (LANL2DZ) for tin and lead.17 All geometrical parameters
were fully optimized and the harmonic vibrational frequencies
were obtained analytically at the optimized structures. Additional
B3LYP density functional calculations were done for compari-
son.
Results
Infrared spectra of products formed in the reactions of laser-
ablated lead and tin atoms with H2O2 or H2 and O2 mixtures in
excess argon during condensation at 10 K will be presented in
turn. Theoretical calculations were performed to support the
identifications of new tin and lead hydroxide molecules. The
metal oxides and hydrides produced in these experiments have
been assigned in previous studies.8,9 Common species generated
by the laser-ablation process and trapped in solid argon, such
as O3, O4-, HO2, and ArnH+ have been discussed in previous
papers.18-23
Experimental and Computational Methods
Laser-ablated Sn and Pb atom reactions with oxygen and with
hydrogen in excess argon at 10 K have been described in our
previous papers.9 The Nd:YAG laser fundamental (1064 nm,
10 Hz repetition rate with 10 ns pulse width) was focused onto
Pb + H2O2. Infrared spectra of laser-ablated lead atoms with
H2O2 in excess argon at 10 K, with annealing and irradiation
afterward, (Figure 1) show the following spectral features: (i)
* Corresponding author. E-mail: lsa@virginia.edu.
10.1021/jp053420p CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/21/2005

9014 J. Phys. Chem. A, Vol. 109, No. 40, 2005
Wang and Andrews
Figure 1. Infrared spectra in selected regions for laser-ablated lead
atom reaction products with hydrogen peroxide in excess argon at 10
K: (a) spectrum of Pb and H2O2 codeposited for 60 min; (b) spectrum
after annealing to 24 K; (c) spectrum after >220 nm irradiation, (d)
spectrum after annealing to 34 K, (e) spectrum of Pb + H2 +O2
codeposited for 60 min, after ultraviolet irradiation and annealing to
22 K, (f) spectrum of Pb and D2O2 codeposited for 60 min, (g) spectrum
after annealing to 24 K, (h) spectrum after >220 nm irradiation, (i)
spectrum after annealing to 34 K, and (j) spectrum of Pb + D2 +O2
codeposited for 60 min, after ultraviolet irradiation and annealing to
22 K. The label C denotes the HOH‚‚‚O complex (see text) and HPC
indicates an aggregate species common to laser-ablation experiments
with hydrogen peroxide.
Figure 2. Infrared spectra in the O-H and Pb-O stretching regions
for Pb and H2 + O2 reaction products in excess argon at 10 K: (a)
spectrum of Pb + H2(6%) + O2(0.4%) codeposited for 60 min, (b)
spectrum after 240-380 nm irradiation, (c) spectrum after >220 nm
irradiation, (d) spectrum after annealing to 20 K, (e) spectrum of Pb +
H2(6%) + 16,18O2[20% 16O2 + 50% 16O18O + 30% 18O2](0.4%), (f)
after 240-380 nm irradiation, (g) spectrum after >220 nm irradiation,
(h) spectrum after annealing to 20 K, (i) spectrum of Pb + H2(6%) +
18O2(0.4%) codeposited for 60 min, (j) spectrum after 240-380 nm
irradiation, (k) spectrum after >220 nm irradiation, and (l) spectrum
after annealing to 20 K.
TABLE 1: New Infrared Absorptions (cm-1) Produced on
Reactions of Pb + H2O2 and Pb + H2 + O2 in Excess Argon
H2O2
D2O2
16O2, H2
16,18O2, H2
18O2, H2 16O2, D2 identification
3640.2 3640.2, 3629.0
3628.9 2685.4
3598.0 2661.9
2660.4
Pb(OH)2
Pb(OH)2
Pb(OH)4
Pb(OH)4
Pb(OH)2
Pb(OH)4
Pb(OH)2
Pb(OH)2
Pb(OH)
Pb(OH)2
3609.3 3609.3, 3598.1
3607.5
899.3
706.8
556.6
552.5
671.8
545.9
555.4
533.5 533.7, 530.8, 517.2, 507.0 507.0
506.1
502.7 502.9, 492.5, 480.0, 477.6 477.6
509.0
487.3
On deposition absorptions at 502.7 and 533.5 cm-1 (stronger)
and 552.5 and 706.8 cm-1 (weaker) track with two equal
intensity bands at 3609.3 and 3640.2 cm-1 (group d) are
observed. With D2O2, these bands shift to 487.3, 509.0, 545.9,
596.2, 2685.3, and 2693.8 cm-1, respectively (Table 1). On
annealing to 20 and 24 K the intensities of group d bands
doubled, and they increased 10% on full arc >220 nm
irradiation. (ii) Weak group t bands at 556.6, 899.3, and 3607.5
cm-1 on deposition increased markedly on ultraviolet irradia-
tion. With D2O2 the bands shifted to 555.4, 671.8, and 2684.6
cm-1, respectively. (iii) A weak group m shoulder absorption
observed at 506.1 cm-1 beside the 502.7 cm-1 band on
deposition decreased on annealing but increased on broadband
irradiation (note the absence of a shoulder on the 533.5 cm-1
band). In addition weak lead oxide absorptions were observed
at 711.2 cm-1 (PbO), 764.8 cm-1 (PbO2), and 555.6, 466.4 cm-1
(Pb2O2) in agreement with previous work.8,9 These bands
appeared on deposition and decreased on annealing. Finally,
absorptions common to hydrogen peroxide experiments with
laser-ablated metals (labeled C) appear at 3730 and 3633 cm-1
for the HOH‚‚‚O complex identified previously.13,16
Figure 3. Infrared spectra in selected regions for laser-ablated tin atom
reaction products with hydrogen peroxide in excess argon at 10 K: (a)
spectrum of Sn and H2O2 codeposited for 60 min, (b) spectrum after
>220 nm irradiation, (c) spectrum after annealing to 26 K, (d) spectrum
after second >220 nm irradiation, (e) spectrum of Sn + H2 +O2
codeposited for 60 min, after ultraviolet irradiation and annealing to
22 K, (f) spectrum of Sn and D2O2 codeposited for 60 min, (g) spectrum
after 240-380 nm irradiation, (h) spectrum after >220 nm irradiation,
(i) spectrum after annealing to 24 K, (j) spectrum after annealing to 28
K, and (k) spectrum of Sn + D2 +O2 codeposited for 60 min, after
ultraviolet irradiation and annealing to 22 K. The label C denotes the
HOH‚‚‚O complex (see text) and HPC indicates an aggregate species
common to laser-ablation experiments with hydrogen peroxide.
group d product bands appeared very weakly. On >380 nm
irradiation, the PbH2 band disappeared and group d product
bands increased slightly. Further ultraviolet irradiation increased
group d bands markedly as well as lead oxide bands. The group
d bands were observed within 0.3 cm-1of the positions using
H2O2, but the bands due to group t and m were not observed in
this experiment (shoulders are observed on both broader group
d bands). One spectrum after ultraviolet irradiation and anneal-
ing is compared in Figure 1e. With Pb + D2 + O2, the group
d product bands in Figure 1j show the same shifts as with D2O2.
In addition, we observed lead deuteride bands for PbD (1055.3
cm-1) and PbD2 (1099.3 cm-1) and the same lead oxide
Pb + H2 + O2. Complementary experiments were done with
Pb/O2/H2 in excess argon. On deposition stronger lead oxide
bands and weaker lead hydride bands for PbH (1472.3 cm-1
)
and PbH2 (1532.7 cm-1) were observed.9b In addition broader

Infrared Spectra of M(OH)1,2,4
J. Phys. Chem. A, Vol. 109, No. 40, 2005 9015
TABLE 2: New Infrared Absorptions (cm-1) Produced on Reactions of Sn + H2O2 and Sn + H2 + O2 in Excess Argon
H2O2
D2O2
16O2, H2
16,18O2, H2
18O2, H2
3648.5
16O2, HD
16O2, D2
18O2, D2
2683.3
identification
3659.8
3656.3
3625.1
843.3
727.4
646.5
640.0
631.9
598.8
3660.0, 3684.5
3660.3, 3625.1
2699.7
Sn(OH)2
Sn(OH)4
Sn(OH)2
Sn(OH)4
Sn(OH)2
Sn(OH)4
Sn(OH)2
Sn(OH)4
Sn(OH)2
2696.0
3625.1, 3613.7
3613.7
724.2
2699.6, 2673.1
2673.5
2657.2
656.9, 646.1
646.1
599.5, 596.7
580.7, 570.2
570.5
539.1
601
569
597.3
571.6
531.2
569.5
565.7
567.6
575.7
Sn(OH)
Sn(OH)2
566.2, 556.1
541.8, 539.3
TABLE 3: Calculated Frequencies for M(OH) and HMO (M ) Pb, Sn) at the MP2 Level of Theory and Comparison with
Observed of Frequencies
Pb(OH)
Pb(OD)
Pb(18OH)
calcda
HPbO
calcda
calcda
obsdb
506.1
calcda
obsdb
assignment
3899.8 (83)
641.6 (40)
512.3 (144)
2839.7 (56)
462.9 (5)
511.3 (161)
3886.9 (80)
639.9 (38)
485.5 (131)
[1608.6 (806)]
609.9 (44)
489.4 (115)
O-H [Pb-H] stretching
Pb-O-H bending
Pb-O stretching
Sn(OH)
Sn(OD)
Sn(18OH)
calcd
HSnO
calcd
calcda
obsdb
569.5
calcda
obsdb
577.8
assignment
3916.4 (92)
655.0 (31)
576.8 (169)
2852.0 (60)
475.3 (29)
574.4 (146)
3903.4 (89)
653.1 (34)
548.2 (151)
[1765.1 (456)]
564.7 (26)
515.9 (66)
O-H [Sn-H] stretching
Sn-O-H bending
Sn-O stretching
a Frequencies, cm-1 (intensities, km/mol). b Argon matrix, cm-1
.
bands.9a,b A sample of 18O2 + H2 gave 18O shifts as listed in
Table 1. With scrambled isotopic O2 (20% 16O2 + 50% 16O18O
+ 30% 18O2) the two lower bands for group d exhibited quartet
distributions while the upper two bands revealed a doublet band.
Sn + H2O2. As shown in Figure 3 laser-ablated Sn atom
reactions with H2O2 in excess argon gave new absorptions at
565.7, 598.8, 640.0, 727.4, 3625.1, and 3656.3 cm-1 (group
d), at 631.9, 646.5, 843.3, and 3618.7 cm-1 (group t), and at
569.5 cm-1 (group m). On annealing to 20 K, all product bands
increased slightly, and on broadband irradiation, group d bands
increased by 20% and group t bands by 150%, but group m
changed very little. Further annealing sharpened group d and t
bands but destroyed group m bands. Experiments with D2O2
gave large red shifts for all upper bands and small shifts for all
lower bands, and the results are listed in Table 2. Weak tin
oxide bands were observed (SnO, 811.7 cm-1; SnO2, 867.1
cm-1; Sn2O2, 610.7, 521.5 cm-1 in solid argon).
Figure 4. Infrared spectra in the O-H, O-D, and Sn-O stretching
regions for Sn and H2 + O2 reaction products in excess argon at 10 K:
(a) spectrum of Sn + H2(6%) + O2(0.4%) codeposited for 60 min, (b)
spectrum after 240-380 nm irradiation, (c) spectrum after >220 nm
irradiation, (d) spectrum after annealing to 20 K, (e) spectrum of Sn +
HD(6%) + O2(0.4% O2), (f) spectrum after >220 nm irradiation, (g)
spectrum after annealing to 16 K, (h) spectrum of Sn + D2(6%) +
O2(0.4%) codeposited for 60 min, (i) spectrum after >220 nm
irradiation, and (j) spectrum after second >220 nm irradiation.
Additional Sn + H2O2 experiments were done under different
conditions. Higher laser energy and laser plume irradiation
markedly increased the t bands relative to the d bands. Next,
the H2O2 sample tube was surrounded with ice and the H2O2
precursor absorption intensities were reduced 10-fold:
A
comparable Sn experiment resulted in an 8-fold reduction of
the strong t absorption at 3656.3 cm-1 relative to d at 3659.8
cm-1. The six d absorptions were observed with reduced
intensity, but the 646.5 cm-1 t band was not detected.
Sn + H2 + O2. Experiments with Sn and H2 + O2 reproduced
the new bands as observed with Sn + H2O2, but the bands were
broadened and shifted slightly. The tin oxide absorptions were
stronger with weaker tin hydrides (SnH, 1641.7 cm-1; SnH2,
1657.0, 1654.8 cm-1).9,24 These bands appeared on deposition
and increased markedly on broadband photolysis. The deuterium
counterparts were observed accordingly using Sn + D2 + O2
sample. Tin reactions were done with HD + O2, and the results
are shown in Figure 4. Additional experiments with 18O2 and
16,18O2 (scrambled) gave shifted bands, and the absorptions are
listed in Table 2.
Calculations. Lead and tin mono-, di-, and tetrahydroxides
were calculated at MP2 and B3LYP levels of theory to assist
in new product identification. Computations for Pb(OH) gave
PbOH and HPbO conformers; however, PbOH is 72 kcal/mol
lower in energy than HPbO at the MP2 level. The analogous
SnOH molecule is computed to be 55 kcal/mol lower than

9016 J. Phys. Chem. A, Vol. 109, No. 40, 2005
Wang and Andrews
TABLE 4: Calculated Frequencies for Pb(OH)2 (Cs), Pb(OH)2 (C2W), and HPbO(OH) at the MP2 Level of Theory and
Comparison with Observed Frequencies
Pb(OH)2 (Cs)
Pb(OD)2 (Cs)
Pb(18OH)2 (Cs)
Pb(OH)2 (C2V)
HPbO(OH)
calcda
calcda
obsdb
calcda
obsdb
calcda
obsdb
calcda
approximately mode
3905.3 (58)
3861.1 (60)
736.1 (40)
646.0 (52)
531.5 (111)
501.7 (144)
460.7 (74)
343.4 (136)
166.1 (13)
3640.2
3609.3
706.8
552.5
533.5
502.7
2843.3 (43)
2810.2 (42)
557.6 (81)
524.4 (113)
497.7 (113)
466.5 (7)
340.8 (48)
254.1 (76)
154.3 (11)
2693.8
2685.3
596.2
545.9
509.0
487.3
3892.5 (56)
3848.5 (57)
732.0 (37)
634.2 (48)
503.9 (102)
475.7 (131)
458.3 (71)
341.6 (131)
158.6 (11)
3628.9
3598.0
3900.3 (a1, 75)
3899.0 (b2, 11)
691.6 (a1, 1)
3868.3 (79)
[1933.7 (106)]
843.9 (65)
808.5 (121)
555.6 (23)
503.4 (116)
467.5 (19)
360.9 (109)
162.7 (55)
O-H stretching
O-H stretching [Pb-H]
Pb-O-H bending
Pb-O-H bending
Pb-O stretching
560.9 (b2, 81)
517.9 (a1,98)
496.1 (b2, 174)
385.8 (b1, 241)
293.3 (a2, 0)
507.0
477.6
Pb-O stretching
176.6 (a1, 21)
a Frequencies, cm-1 (intensities, km/mol). b Argon matrix, cm-1
.
TABLE 5: Calculated Frequencies for Sn(OH)2 (Cs), Sn(OH)2 (C2W), and HSnO(OH) at the MP2 Level of Theory and
Comparison with Observed Frequencies
Sn(OH)2 (Cs)
Sn(OD)2 (Cs)
Sn(18OH)2 (Cs)
Sn(OH)2 (C2V)
HSnO(OH)
calcda
calcda
obsdb
calcda
obsdb
calcda
obsdb
calcd a
approx mode
3902.9 (66)
3857.4 (57)
782.3 (43)
697.5 (69)
573.9 (115)
541.6 (146)
470.6 (70)
359.4 (132)
182.0 (15)
3660.0
3625.1
727.4
640.0
598.8
565.7
2841.6 (46)
2807.4 (40)
573.3 (93)
567.5 (118)
535.9 (114)
504.9 (6)
348.3 (45)
265.9 (72)
169.1 (13)
2696.0
2673.0
646.1
597.3
575.7
3890.1 (63)
3844.8 (55)
778.0 (40)
694.5 (64)
545.7 (107)
515.1 (135)
468.2 (68)
357.5 (130)
174.0 (14)
3648.5
3613.7
724.2
3894.6 (a1, 5)
3894.3 (b2, 138)
762.7 (a1, 80)
709.6 (b2, 58)
569.2 (a1, 102)
551.0 (b2, 167)
423.1 (b1, 172)
355.4 (a2, 0)
3898.4 (93)
[2013.5 (104)]
839.9 (32)
823.8 (130)
624.2 (112)
601.1 (112)
461.5 (14)
O-H stretching
O-H stretching [Sn-H]
Sn-O-H bending
Sn-O-H bending
Sn-O stretching
570.5
539.1
Sn-O stretching
348.5 (140)
189.8 (58)
200.3 (a1, 1)
a Frequencies, cm-1 (intensities, km/mol). b Argon matrix, cm-1
.
HSnO. The calculated frequencies are given in Table 3. Our
B3LYP calculations gave similar results. A previous combined
B3LYP/CCSD investigation found PbOH to be 54 kcal/mol
lower energy than HPbO.6
For [Pb(OH)2] three different conformers, Pb(OH)2 (Cs), Pb-
(OH)2 (C2V), and HPbO(OH) were calculated, and the Cs and
C2V structures are very close in energy while HPbO(OH) is 79
kcal/mol higher. Note that the Cs structure is stabilized on the
potential energy surface by a weak internal hydrogen bond. At
the MP2 level, we use 6-311++(d,p) for H and O and find a
Ha-Ob distance of 2.777 Å, which is reduced to 2.714 Å with
the large 6-311++G(3df,3pd) basis set. Apparently polarization
and diffuse functions for H and O atoms are critical to describe
the hydrogen bond. As we will discuss later, the calculated
frequencies match experimental values much better using large
basis sets. Similar calculations for Sn(OH)2 and at the MP2 level
find that Sn(OH)2 lies lowest in energy while Sn(OH)2 (C2V) is
2.8 kcal/mol higher and HSnO(OH) is 40.0 kcal/mol higher in
energy. The weak Ha-Ob hydrogen bond is shorter, 2.664 Å,
for the tin dihydroxide. The calculated frequencies are listed in
Tables 4 and 5.
Figure 5. Structures computed for lead and tin hydroxides at the MP2/
6-311++G(3df,3pd)/LANL2DZ level of theory. Bond lengths are given
in angstroms and bond angles in degrees.
The B3LYP density functional gave comparable structures
for the dihydroxides of Sn and Pb. For Sn(OH)2, the B3LYP
functional found 3% shorter Sn-O bond lengths and other
parameters almost the same. For Pb(OH)2, the computed
structures were almost identical, and the B3LYP frequencies
were slightly lower as expected.26
covalent bonding character.25 The B3LYP functional gave
almost identical computed structures for both M(OH)4 mol-
ecules.
Discussion
Calculations were also done for Pb(OH)4 and Sn(OH)4, and
stable S4 symmetry structures were converged instead of Td
symmetry found for the Hf(OH)4 and Zr(OH)4 molecules.13d
The structures and parameters are given in Figure 5, and
frequencies are listed in Table 6 for the MP2 level calculations.
The bent M-O-H bond angles obtained for all lead and tin
hydroxides suggest that the molecules exhibit substantial
The new lead and tin mono-, di-, and tetrahydroxides will
be identified through the use of different reagents, photochemical
properties, isotopic substitution, and comparison with theoretical
frequency calculations.
Pb(OH)2. Two strong new infrared absorptions at 533.5 and
502.7 cm-1 in the Pb-O stretching region and two new bands

Infrared Spectra of M(OH)1,2,4
J. Phys. Chem. A, Vol. 109, No. 40, 2005 9017
TABLE 6: Calculated Frequencies for Pb(OH)4 and Sn(OH)4 at the MP2 Level of Theory in S4 Symmetry and Comparison
with Observed Frequencies
Pb(OH)4
calcda
Pb(OD)4
calcda
Sn(OH)4
calcda
Sn(OD)4
calcda
obsdb
obsdb
obsdb
obsdb
approx mode
3881.5 (0)
2826.5 (0)
3928.5 (0)
2861.2 (0)
O-H stretching
O-H stretching
O-H stretching
M-O-H bending
M-O-H bending
M-O-H bending
M-O stretching
M-O stretching
M-O stretching
3879.5 (44)
3879.2 (150 × 2)
878.6 (89 × 2)
876.8 (60)
2823.8 (28)
2823.7 (99 × 2)
653.5 (77 × 2)
652.6 (63)
3927.2 (56)
3926.6 (144 × 2)
822.8 (115 × 2)
815.7 (55)
2858.8 (37)
2858.6 (96 × 2)
610.4 (35 × 2)
602.7 (6)
3607.5
899.3
2684.6
671.8
3656.3
843.3
2696.0
861.3 (0)
625.7 (0)
802.0 (0)
606.7 (0)
565.6 (99 × 2)
556.6
555.9 (75 × 2)
555.4
638.7 (136 × 2)
626.9 (127)
610.5 (0)
646.5
631.9
636.3 (165 × 2)
624.4 (139)
580.8 (0)
654.4
650.9
556.7 (99)
545.8 (65)
542.8 (0)
536.9 (0)
261.0 (176)
227.0 (48 × 2)
178.7 (24)
210.5 (117)
175.9 (51 × 2)
168.7 (6)
275.2 (169)
236.6 (66 × 2)
215.5 (29)
233.8 (119)
199.3 (57 × 2)
199.4 (1)
163.9 (0)
129.6 (0)
173.5 (0)
57.7 (0)
162.7 (23 × 2)
146.6 (3 × 2)
193.1 (12 × 2)
159.3 (2 × 2)
129.7 (0)
116.4 (0)
151.4 (0)
118.0 (0)
92.5 (57)
81.5 (48)
101.6 (104)
86.3 (80)
a Frequencies, cm-1 (intensities, km/mol). The a mode has 0 intensity and the b mode has the given intensity, and the e mode has ×2 intensity.
b Argon matrix, cm-1
.
at 3640.2 and 3609.3 cm-1 in the O-H stretching region labeled
d track together in the Pb + H2O2 experiments. In the reaction
with D2O2, the Pb-O bands shift to 509.0 and 487.3 cm-1 and
the O-H bands to 2685.4 and 2661.9 cm-1, respectively. The
red-shift of Pb-O stretching modes with deuterium substitution
indicates that these two modes are coupled to the H atom
motion. The Pb-O stretching frequencies of PbO and PbO2 in
solid argon at 711.2 and 764.8 cm-1 show considerable
differences in PbO bonding for the new product molecule.
Complementary experiments with Pb + H2 + O2 gave slightly
broader bands centered at 533.5 and 502.7 cm-1 and at 3640.2
and 3609.3 cm-1, which shift to 507.0 and 477.6 cm-1 and to
3628.9 and 3598.0 cm-1 with Pb + H2 + 18O2. The isotopic
frequency ratios for the upper bands (H/D, 1.3556, 1.3559 and
16/18, 1.00311, 1.00314) are characteristic of O-H stretching
modes, and the 16/18 ratios for the lower bands (1.0523, 1.0526)
describe an antisymmetric O-Pb-O stretching mode (the ratios
for PbO2 (1.0513) and PbO (1.0561) are distinctly different).9a
The isotopic frequency patterns with 16O2 + 16,18O2 +18O2 (1:
2:1) show quartet distributions for the two lower modes (Figure
2), demonstrating that two inequivalent oxygen atoms are
involved. However, for the two upper modes two doublets were
observed at 3640.4, 3629.0 cm-1 and at 3609.3 and 3598.1
cm-1, which indicate very little or no coupling between two
inequivalent O-H groups. Therefore, the Pb(OH)2 molecule
with two inequivalent O-H subunits is identified, and the group
d bands are assigned accordingly. This is distinctively different
from group 2, 4, and 12 dihydroxides, which exhibited one
strong antisymmetric stretching mode in the O-H and M-O
stretching regions for these M(OH)2 molecules with two
equivalent O-H subunits.13
predicted 18O2 shifts are slightly more than experimental, but
the calculated quartet isotopic patterns for each mode match
experiment very well. With MP2 two O-H stretching modes
are predicted at 3905.3 and 3861.1 cm-1 with almost the same
intensities, which are overestimated by 8.2% and 6.1%, respec-
tively, and are in line with expectations.26 Meanwhile the
calculation reveals identical O-H stretching modes for O atoms
substituted by 18O2 or 16,18O2, showing no coupling between
the two O-H stretching modes.
The two sharp weaker group d bands at 706.8 and 552.5 cm-1
are 4 and 14% below the calculated O-H bending frequencies.
Clearly, the free O-H bending mode is described better by the
MP2 calculation that the O-H group involved in the weak
intramolecular hydrogen bond. The 706.8 cm-1 band shifts to
545.9 cm-1 with D2O2 (H/D ratio 1.2947) and gains considerable
intensity from mixing with Pb-O stretching modes. The
deuterium counterpart for the weaker 552.5 cm-1 band is not
detected.
Calculations for Pb(OH)2 with the Cs structure using B3LYP
give slightly lower Pb-O stretching modes at 523.4 and 494.5
cm-1 and O-H stretching modes at 3862.6 and 3825.3 cm-1
.
However predicted deuterium shifts are only 2-3 cm-1 for both
Pb-O stretching modes, meaning that the B3LYP calculation
does not describe these modes as well as MP2. Our B3LYP
calculation found for the optimized structure a Hb-Oa distance
0.043 Å longer than the MP2 value, and as a result the H atom
coupling is underestimated.
On the other hand, frequencies calculated for the C2V structure
(Table 4) have several shortcomings. The computed O-H
stretching mode separation of 1.3 cm-1 for two equivalent bonds
is far from the observed 30.9 cm-1 and Cs computed 44.2 cm-1
values, and the 21.8 cm-1computed Pb-O stretching mode
separation is in poor agreement with the observed 30.8 cm-1
and Cs computed 29.8 cm-1 values. Finally, the C2V structure
has only one bending mode with observable intensity and the
Cs structure has two in good agreement with the observed
absorptions.
The insertion reaction of Pb into H2O2 is exothermic by 148
kcal/mol (MP2) and 131 kcal/mol (B3LYP), as shown in
reaction 1. Spontaneous insertion reaction is observed on
annealing of Pb + H2O2 suggesting that no activation energy
is required. Similar insertion reactions were observed for group
2, 4,and 12 metals.13 For the reaction of Pb + O2 + H2, we
The identification of Pb(OH)2 is confirmed by MP2 frequency
calculations (Table 4). The planar Cs structure at the MP2 level
gives two strong Pb-O stretching modes calculated at 531.5
and 501.7 cm-1, which are in excellent agreement with the 533.5
and 502.7 cm-1 observed values. The two modes are predicted
to red-shift by 33.8 and 35.2 cm-1 for Pb(OD)2, which are larger
than the experimental shifts of 24.5 and 15.4 cm-1. Obviously
the theoretical calculation predicts more H atom coupling than
is observed for the two modes. It is interesting to note that the
533.5 cm-1 band has a greater deuterium shift than the 502.7
cm-1 band, which tells us that the two modes couple with H
(and D) atoms differently for this asymmetric structure. The

9018 J. Phys. Chem. A, Vol. 109, No. 40, 2005
Wang and Andrews
propose that OPbO is formed first on photolysis, and then reacts
further with H2 in the solid matrix cage to give Pb(OH)2.
Reaction 2b is 105 kcal/mol exothermic (MP2 level).
mode for Pb(OH)2. Our MP2 calculation for Pb(OH) predicts
the Pb-O stretching mode at 512.3 cm-1, which is in good
agreement with the 506.1 cm-1 band. Our B3LYP calculation
gives a very similar result. The insertion product HPbO is not
observed here because of its very high energy relative to PbOH.
Unfortunately, the Pb(OD) counterpart is not observed due to
lower product yield.
Pb + H2O2 f Pb(OH)2 (∆E ) -148 kcal/mol) (1)
Pb + O2 f OPbO (∆E ) -74 kcal/mol)
(2a)
Energetic laser-ablated lead atoms react with H2O2 to give
excited Pb(OH)2 that can either be trapped in the solid matrix
or decomposed to Pb(OH) + OH. On photolysis and further
annealing the Pb(OH) absorptions decrease, possibly reacting
with OH to give Pb(OH)2. Reaction 4 is exothermic but not
nearly as much so as reaction 1.
OPbO + H2 f Pb(OH)2 (∆E ) -105 kcal/mol) (2b)
Pb(OH)4. Three new infrared absorptions at 556.6, 899.3,
and 3607.5 cm-1 labeled t in Pb + H2O2 experiments appeared
very weakly on deposition and increased upon sample irradiation
and annealing, but these bands were not observed with the
hydrogen/oxygen reagent. With Pb + D2O2 these bands shifted
to 555.4, 671.8, and 2660.4 cm-1, giving H/D isotopic ratios
of 1.0022, 1.3386, and 1.3560, respectively. Apparently the
556.6 cm-1 band has a very small deuterium shift, and it can
be assigned to the Pb-O stretching mode. The 899.3 and 3607.5
cm-1 bands have large deuterium shifts, which are due to Pb-
O-H bending and O-H stretching modes, respectively. These
group t bands are appropriate for Pb(OH)4. Comparison with
frequencies calculated by MP2 and B3LYP show very good
agreement with experimental values. Absorptions of Pb(OH)4
are predicted by B3LYP calculation to give a stronger degener-
ate Pb-O stretching mode at 553.1 cm-1, Pb-O-H bending
Pb + H2O2 f [Pb(OH)2]* f Pb(OH) + OH
(∆E ) -43 kcal/mol) (4)
Sn(OH)2. The group d bands at 565.7, 598.8, 640.0, 727.4,
3625.1, and 3660.0 cm-1 track together in experiments with
Sn + H2O2 upon annealing, irradiation, and changes in hydrogen
peroxide concentration, and they can be assigned and to Sn-
(OH)2. The same absorptions were found in Sn + H2 + O2
reactions but with slightly lower intensities. The 565.7 and 598.8
cm-1 bands shift to 539.1 and 570.5 cm-1 with 18O2 substitution,
suggesting two Sn-O stretching modes, while the 640.0 and
727.4 cm-1 bands show very small shifts, which are appropriate
for the Sn-O-H bending modes. The 3660.0 and 3625.1 cm-1
bands exhibited 11.5 and 11.4 cm-1 red-shifts in the Sn + H2
mode at 880.6 cm-1, and O-H stretching mode at 3837.3 cm-1
,
and counterparts of Pb(OD)4 are found at 543.2 (Pb-O
stretching), 655.5 (Pb-O-H bending), and 2793.3 cm-1 (O-H
stretching). Our MP2 calculation gives slightly higher frequen-
cies (Table 6). Unfortunately in Pb + H2 + O2 experiments we
did not observe these Pb(OH)4 absorptions because of the
different reaction mechanism, and no 18O and 16,18O isotopic
frequencies were observed to confirm the assignment.
Formation of Pb(OH)4 must come from the reaction of Pb-
(OH)2 and H2O2 (reaction 3), which is exothermic by 65 kcal/
mol (MP2) and 49 kcal/mol (B3LYP). Notice that reaction 3 is
less than half as exothermic as reaction 1. Lead in the tetravalent
state is destabilized in part because of the relativistic effect,
which increases s orbital ionization energy.10,11,27 As a result
the bond strength is reduced for Pb(IV) species.28,29 The Pb-
(IV) halides are much less favorable than Pb(II) halides.10 The
yield of Pb(OH)4 increases significantly on photolysis but barely
on annealing, implying much less exothermic reaction. Although
no absorption of Pb(OH)4 is detected in the Pb + O2 + H2
experiment, this is significantly different from Zr and Hf, where
the straightforward reactions produce major products, Zr(OH)4
and Hf(OH)4 based on very large computed exothermic reaction
energies.13d
+
18O2 experiment, which are typical for O-H stretching modes
in a metal hydroxide. The oxygen isotopic quartet pattern for
both 565.7 and 598.8 cm-1 bands and doublets for the 3660.0
and 3625.1 cm-1 bands were observed with 16O2 + 16O18O +
18O2 + H2, showing two inequivalent oxygen atoms, which are
very similar that found for Pb(OH)2. With D2O2 the 598.8 cm-1
band shifts red only 1.5 cm-1 to 597.3 cm-1, while the 565.7
cm-1 band shifts blue by 10.0 cm-1, indicating different
couplings of the O-D bending vibrations with these modes.
This is not the case for Pb(OH)2, for which both Pb-O modes
shift red with deuterium substitution. The O-D stretching modes
appeared at 2699.7 and 2673.5 cm-1, giving 1.3556 and 1.3559
H/D ratios, which again are typical for metal dihydroxides.13
The O-D stretching modes red shifted 16.4 and 16.3 cm-1 with
Sn + D2 + 18O2, which is in line with previous observations.13
The Sn-18OD stretching modes were observed at 571.6 and
531.2 cm-1. The upper band exhibits a reasonable 18O shift,
but the lower band appears to have a considerably different
amount of mixing with the Sn-O-D bending mode for the
blue shift described above.
The vibrational assignment of Sn(OH)2 is supported by
theoretical calculations. Our MP2 calculation shows that two
structures, namely Cs and C2V, are very close in energy but very
different in frequencies (Table 5). The calculated frequencies
of the Cs structure predict the experimental frequencies satis-
factorily, but the C2V frequencies suffer from the mode separation
deficiencies described above for lead dihydroxide. These are
Sn-O stretching modes at 573.9 and 541.6 cm-1, O-H
stretching modes at 3902.9 and 3857.4 cm-1, which must be
scaled down by 6.2 and 6.0%, respectively, and Sn-O-H
bending modes at 782.3 and 697.5 cm-1. It is not surprising
that the two predicted quartets for two Sn-O stretching modes
Pb(OH)2 + H2O2 f Pb(OH)4 (∆E ) -65 kcal/mol) (3)
The relative stability of Pb(OH)4 and Pb(OH)2 is expected to
be comparable to that observed for the chlorides and fluorides,
which is better than for the recently described case for PbH4
and PbH2.9c Although the PbH2 + H2 f PbH4 reaction is slightly
endothermic,30,31 PbH4 has been formed from PbH2 in solid
hydrogen.9c The corresponding reaction 3 is exothermic, which
suggests more stability for Pb(OH)4 than for PbH4.
Pb(OH). A weak absorption at 506.1 cm-1 in Pb + H2O2
experiments can be tentatively assigned to the Pb-O stretching
mode of Pb(OH) based on annealing and photochemical
behavior. This species is reduced quickly on annealing but is
regenerated on ultraviolet irradiation, and is decreased on further
annealing like the behavior of an active radical. The weaker
O-H stretching fundamental is probably obscured by the nearby
and two doublets for O-H stretching modes with 16O and 18
O
substitution match experimental bands very well. The predicted
O-D stretching frequencies at 2841.6 and 2807.4 cm-1 are in
reasonable agreement (scale down by 5.0 and 4.7%), but the
Sn-O stretching modes are predicted to shift down 6.4 and

Infrared Spectra of M(OH)1,2,4
J. Phys. Chem. A, Vol. 109, No. 40, 2005 9019
5.7 cm-1. Apparently the O-H coupling effect for these modes
is underestimated. The upper O-H(D) stretching mode is due
to the free O-H(D) bond and the lower mode to O-H(D) in
the intramolecular hydrogen bond.
The Sn(OH)2 molecule is formed spontaneously from com-
bination of Sn and H2O2 (reaction 5), which is exothermic by
154 kcal/mol (MP2) and 145 kcal/mol (B3LYP) and is slightly
more exothermic than that found in the lead reaction. Formation
of Sn(OH)2 is also through reaction of Sn with H2 and O2
(reaction 6), and ultraviolet irradiation promoted this reaction
significantly.
for the reaction to form Pb(OH)4. Notice that the yield of Sn-
(OH)4 is slightly higher and weak bands due to Sn(OH)4 were
observed in Sn + H2 + O2 experiments, indicating Sb(OH)4 is
more stable than Pb(OH)4. In fact only PbCl4 is observed
experimentally while several SnX4 (X ) Cl, Br, I) molecules
have been identified. Tetrahydroxide molecules have also been
observed for group 4 metals in even more exothermic reactions
with hydrogen peroxide in excess argon.13d
Sn(OH)2 + H2O2 f Sn(OH)4 (∆E ) -123 kcal/mol) (7)
Sn(OH). A weak band at 569.5 cm-1 (Sn-O stretching) in
Sn + H2O2 experiments is tentatively assigned to Sn(OH). With
D2O2 the band shifts to 567.6 cm-1. These bands appear on
sample irradiation along with Sn(OH)2 and Sn(OD)2 and then
decrease on further annealing as expected for a reactive species.
Our MP2 calculation predicts this Sn-O stretching mode at
576.8 cm-1 with a 2.4 cm-1 shift for Sn(OD) (Table 3), which
are in good agreement. The weaker O-H stretching mode is
probably masked by the nearby mode for Sn(OH)2. The
formation of Sn(OH) is through reaction 8, and the product is
then trapped in the low-temperature matrix.
Sn + H2O2 f Sn(OH)2 (∆E ) -154 kcal/mol) (5)
Sn +O2 f OSnO (∆E ) -106 kcal/mol)
(6a)
OSnO + H2 f Sn(OH)2 (∆E ) -79 kcal/mol) (6b)
[We note that the difference in the energies of reactions 1 and
2 compared to reactions 5 and 6, namely -31 kcal/mol, is in
fact the energy of formation of hydrogen peroxide computed at
the MP2 level, -31 kcal/mol.]
The Sn, HD, O2 reaction was done to examine the distribu-
tion of isomers involving H or D in the intramolecular hydro-
gen bonding position, and the spectra are compared in Figure 4
with those from similar H2 and D2 experiments. This is
analogous to HD and F2 reactions, which formed primarily the
H-F‚‚‚D-F dimer.32 Our calculations show no coupling
between the O-H(D) bonds so the frequencies are the same
for both Sn(OH)(OD) isomers as in the Sn(OH)2 and Sn(OD)2
molecules. Note for the HD + O2 spectrum that the 3660 and
2673 cm-1 bands are 60 ( 10% stronger relative to the 3625
and 2700 cm-1 counterparts for Sn(OH)2 and Sn(OD)2. This
means that the (HO)Sn(OD) isomer [D‚‚‚O] is favored over the
(DO)Sn(OH) isomer [H‚‚‚O]. Computed zero point vibrational
energies find the former 44 cal/mol more stable. Recall that
these molecules are formed in reaction 6b with approximately
79 kcal/mol of excess internal energy.
Sn(OH)4. The group t bands at 631.9, 646.5, 843.3, and
3656.3 cm-1 are assigned to Sn(OH)4 in the Sn + H2O2
experiment. Apparently the 631.9 and 646.5 cm-1 bands are
due to Sn-O stretching modes and the 3656.3 cm-1 band is
due to the O-H stretching mode based on similar bond
properties with Sn(OH)2. The deuterium counterparts were found
at 650.9, 654.4, and 2696.0 cm-1 with Sn + D2O2. Here both
Sn-O modes show blue shifts suggesting strong O-D coupling,
since the 843.3 cm -1 Sn-O-H bending mode shifts into this
region on deuterium substitution as found for the same mode
in Sn(OD)2. The Sn(OH)4 molecule is calculated to have S4
symmetry at MP2 level, and the Sn-O stretching mode splits
into an active b component at 626.9 cm-1 and a degenerate e
mode at 638.7 cm-1, which underestimate the observed values
by 5.0 and 7.8 cm-1. The Sn-O stretching modes in Sn(OD)4
are predicted at 624.4 and 636.3 cm-1, respectively, which
unfortunately deviate from experimental values. Again the
density functional theoretical calculation does not describe the
O-H coupling correctly. The predicted b and e O-H stretching
modes are too close to resolve. The stronger e mode for Sn-
(OH)4 at 3926.6 cm-1 and O-D stretching mode for Sn(OD)4
at 2858.6 cm-1 must scale 6.9 and 5.7% to fit the observed
3656.3 and 2696.0 cm-1 bands. Our B3LYP calculation gave
very similar results.
Sn + H2O2 f [Sn(OH)2]* f Sn(OH) + OH
(∆E ) -51 kcal/mol) (8)
Bonding in Group 14 Metal Hydroxides. The Cs symmetry
structures calculated and observed for Pb(OH)2 and Sn(OH)2
are unique: (i) the O-M-O bond is close to a right angle,
which is very different from group 2 and transition metal
hydroxides, (ii) a weak intramolecular hydrogen bond is formed
that is not found in other metal hydroxides, and (iii) Pb(OH)4
and Sn(OH)4 are minor reaction products although Pb(IV) and
Sn(IV) halides have been observed experimentally.10 First, MH2
and MX2 (M ) Pb, Sn, X ) halogen) triatomic molecules favor
bent structure with near 90° bond angles, which has been
explained by pure p orbital bonding because of high s orbital
ionization energy.10,11 However OPbO and OSnO molecules are
linear based on matrix infrared spectra and theoretical calcula-
tions, which suggests that both s and p orbitals participate in
this bonding interaction. Recall that group 2 metal hydroxides
and oxides have very similar O-M-O bond angles since only
two s electrons are involved in the bonding.13 Second, the Pb-O
and Sn-O bonds in Pb(OH)2 and Sn(OH)2 have substantial
covalent character. The O-H stretching frequencies are very
near this mode in the most covalent metal hydroxides such as
Cd(OH)2 and Hg(OH)2, (3659.3 and 3629.4 cm-1), but some-
what lower than O-H stretching frequencies in group 2 and
group 4 metal hydroxides.13 Third, the smaller O-Pb-O bond
angle provides a shorter distance between Ob and Ha, which
attract each other giving extra stabilization energy from a weak
intramolecular hydrogen bond. Only the Cs geometry is observed
although the calculated energies of the Cs and C2V structures
are very close. Finally, the intramolecular hydrogen bond
computed here for Sn(OH)2 and Pb(OH)2 is weaker and
substantially longer (2.7 Å) than that computed for the strong
phenol-ammonia hydrogen bonded complexes (1.9 Å).33
The formation of tetrahydroxides of lead and tin is analogous
to their tetrahalides. Theoretical calculations show that Sn(OH)4
is more stable than Pb(OH)4, which can be confirmed from
experiments in that the yield of Sn(OH)4 is more than that of
Pb(OH)4. Obviously relativistic effects play an important role
here and cause the lead tetravalent state to be less favorable.10,11
The Sn(OH)4 and Pb(OH)4 molecules with S4 structures and
bent M-O-H bonds are clearly more covalent25 than the Zr-
The stable Sn(OH)4 molecule is formed by further reaction
of Sn(OH)2 with H2O2 (reaction 7). This reaction is exothermic
by 123 kcal/mol, which is almost twice as high as calculated

9020 J. Phys. Chem. A, Vol. 109, No. 40, 2005
Wang and Andrews
(OH)4 and Hf(OH)4 molecules with Td structures.13d The O-H
stretching frequencies have the same relationship described for
the dihydroxides, namely the more covalent Sn and Pb tetrahy-
droxides have lower (3656.3 and 3607.5 cm-1) O-H modes
than the more ionic Zr and Hf tetrahydroxides (3782.6 and
3796.4 cm-1).
Phys. Chem. A 2002, 106, 7696, (Pb, Sn + H2). (c) Wang, X.; Andrews, L.
J. Am. Chem. Soc. 2003, 125, 6581, (Pb + H2).
(10) Haigittai, M. Chem. ReV. 2000, 100, 2233 and references therein.
(11) Pyykko, P. Chem. ReV. 1988, 88, 563.
(12) (a) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.: Bochmann, M.
AdVanced Inorganic Chemistry, 6th ed.; Wiley: New York, 1999. (b) CRC
Handbook, 66th ed.; CRC Press: Boca Raton, FL, 1985.
(13) (a) Wang, X.; Andrews, L. J. Phys. Chem. A 2005, 109, 2782 (group
2 metal hydroxides). (b) Wang, X.; Andrews, L. J. Phys. Chem. A 2005,
109, 3849 (Zn, Cd hydroxides). (c) Wang, X.; Andrews, L. Inorg. Chem.
2005, 44, 108 (Hg(OH)2). (d) Wang, X.; Andrews, L. Inorg. Chem. 2005,
44, in press (hafnium metal hydroxides). Wang, X.; Andrews, L. J. Phys.
Chem. A 2005, 109, in press (group 4 metal hydroxides).
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(15) Pettersson, M.; Tuominen, S.; Rasanen, M. J. Phys. Chem. A 1997,
101, 1166.
Conclusions
Laser-ablated lead and tin atoms react with H2O2 to form
the hydroxides M(OH), M(OH)2, and M(OH)4 (M ) Pb, Sn),
which were observed in infrared spectra after sample condensa-
tion in solid argon. The major M(OH)2 product was also
produced from H2 and O2 mixtures, which allowed 18O2
substitution. The band assignments were confirmed by appropri-
ate D2O2, D2, 16O18O, and 18O2 isotopic shifts. Complementary
MP2 and B3LYP calculations provided molecular structures and
vibrational frequencies to aid in assignment of the infrared
spectra. The minimum energy structure found for M(OH)2 has
Cs symmetry and a weak intramolecular hydrogen bond. In
experiments with Sn, HD, and O2, the internal D bond is favored
over the internal H bond for Sn(OH)(OD). Calculations for the
Pb(OH)4 and Sn(OH)4 molecules find S4 symmetry and sub-
stantial covalent character, and relativistic effects limit the yield
of the less stable lead tetrahydroxide molecule.
(16) Pehkonen, S.; Pettersson, M.; Lundell, J.; Khriachtchev, L.;
Rasanen, M. J. Phys. Chem. A 1998, 102, 7643 and references therein.
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(24) See ref 8(a) for Kr matrix observations. In solid argon, Sn16O peaked
at 810.2 and Sn18O at 769.9 cm-1. The SnO2 bands gave resolved 116Sn,
118Sn, and 120Sn isotopic triplets at 870.2, 868.5, and 867.1 cm-1 for Sn16O2,
at 854.2, 852.7, and 851.2 cm-1 for Sn16O18O, and at 831.7, 830.1, and
828.5 cm-1 for Sn18O2.
Acknowledgment. We appreciate financial support from
NSF Grant CHE 03-53487.
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