Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride

Article abstract of DOI:10.1016/j.saa.2013.11.017

An infrared spectroscopic and MP2/6-311++G(2d,2p) study of hydrogen bonded complexes of formaldoxime with ammonia and hydrogen chloride trapped in solid argon matrices is reported. Both 1:1 and 1:2 complexes between formaldoxime and ammonia, hydrogen chloride have been identified in the CH₂NOH/NH₃/Ar, CH₂NOH/HCl/Ar matrices, respectively, their structures were determined by comparison of the spectra with the results of calculations. In the 1:1 complexes present in the argon matrices the OH group of formaldoxime acts as a proton donor for ammonia and the nitrogen atom acts as a proton acceptor for hydrogen chloride. In the 1:2 complexes ammonia or hydrogen chloride dimers interact both with the OH group and the nitrogen atom of CH₂NOH to form seven membered cyclic structures stabilized by three hydrogen bonds. The theoretical spectra generally agree well with the experimental ones, but they seriously underestimate the shift of the OH stretch for the 1:1 CH₂NOH?NH₃ complex.

Full text of DOI:10.1016/j.saa.2013.11.017

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Formaldoxime hydrogen bonded complexes with ammonia
and hydrogen chloride
Barbara Golec , Małgorzata Mucha , Magdalena Sałdyka , Austin Barnes , Zofia Mielke a,
a
a
a
b,
⇑
⇑
a
Faculty of Chemistry, University of Wrocław, Joliot Curie 14, 50-383 Wrocław, Poland
Materials & Physics Research Centre, University of Salford, Salford M5 4WT, United Kingdom
b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
ꢀ
1:1 and 1:2 CH
2
NOH complexes with
NH and HCl are trapped in the argon
3
matrices.
Formaldoxime complexes with
ammonia are stabilized by strong
OAHꢁ ꢁ ꢁN bond.
Formaldoxime complexes with HCl
are stabilized by strong Nꢁ ꢁ ꢁHACl
bond.
Hydrogen bonds in the cyclic 1:2
complexes show strong cooperativity.
a r t i c l e i n f o
a b s t r a c t
Article history:
An infrared spectroscopic and MP2/6–311++G(2d,2p) study of hydrogen bonded complexes of formal-
doxime with ammonia and hydrogen chloride trapped in solid argon matrices is reported. Both 1:1
and 1:2 complexes between formaldoxime and ammonia, hydrogen chloride have been identified in
Received 6 September 2013
Received in revised form 30 October 2013
Accepted 5 November 2013
Available online xxxx
2 3 2
the CH NOH/NH /Ar, CH NOH/HCl/Ar matrices, respectively, their structures were determined by com-
parison of the spectra with the results of calculations. In the 1:1 complexes present in the argon matrices
the OH group of formaldoxime acts as a proton donor for ammonia and the nitrogen atom acts as a proton
acceptor for hydrogen chloride. In the 1:2 complexes ammonia or hydrogen chloride dimers interact both
Keywords:
Formaldoxime
Ammonia
Hydrogen bond
Matrix isolation
ab initio calculations
Molecular complexes
with the OH group and the nitrogen atom of CH
lized by three hydrogen bonds. The theoretical spectra generally agree well with the experimental ones,
but they seriously underestimate the shift of the OH stretch for the 1:1 CH complex.
2
NOH to form seven membered cyclic structures stabi-
2
NOHꢁ ꢁ ꢁNH
3
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
hydrogen bond motifs involving oximes play an important role in
molecular design [1,2]. The probability of formation of the cyclic
heterodimer between carboxylic acid and oxime is as high as 90%
when both molecules are present in a crystal.
Oximes exhibit significant molecular association even in the di-
lute gas phase which is a relatively rare phenomenon [3]. The self-
association of the simplest ketoxime, namely acetone oxime, have
been extensively studied in solution [3–5], in the solid state [6–8]
and, more recently, in the gas phase [9]. The dimerisation of the
simplest aldoxime, namely formaldoxime has been studied with
the help of the matrix isolation technique and quantum chemistry
Oximes with the characteristic >C@NOH group are important
biological and chemical systems. The >C@NOH group involves
the OH hydrogen bond donor and two hydrogen bond acceptor
sites, namely the C@N nitrogen and the OAH oxygen, thus oximes
may form a variety of hydrogen bonds. The intermolecular
⇑
Corresponding authors. Tel.: +48 71 3757475; fax: +48 71 3282348 (Z. Mielke).
E-mail addresses: a.j.barnes@salford.ac.uk (A. Barnes), zofia.mielke@chem.uni.
wroc.pl (Z. Mielke).
1
386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.11.017
Please cite this article in press as: B. Golec et al., Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride, Spectrochimica Acta
Part A: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.org/10.1016/j.saa.2013.11.017

2
B. Golec et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx
methods [10]. The ability of oximes to form hetero-aggregates with
various proton donors and acceptors was much less studied than
oximes homo-aggregation in spite of the fact that the proton-donor
and proton-acceptor properties of the >C@NOH group play an
important role in structural motifs involving oximes. As a part of
a more general study on the ability of oximes to engage in hydro-
gen bond formation we reported recently the results of studies on
formaldoxime complexes with nitrogen [11], nitrous acid [12] and
water [13]. In this paper we present an infrared matrix isolation
and theoretical study of the complexes formed by formaldoxime
with hydrogen chloride and ammonia. Ammonia and hydrogen
chloride serve as an archetypal strong proton acceptor and strong
proton donor, respectively, in studies of hydrogen bonding [14,15].
The study of the formaldoxime complexes with these two mole-
cules should provide information on the proton acceptor and pro-
ton donor abilities of the >C@NOH group.
monomer absorptions which facilitated their assignment to the
perturbed vibrations of the CH NOH and NH or HCl molecules.
2
3
Formaldoxime–ammonia complexes
The new bands that appeared in the spectra of the CH
2
NOH/
NH /Ar matrices can be classified into two groups. The bands
3
belonging to group I (2936.2, 1494.3, 1370.4, 1173.8, 1049.2,
ꢂ1
936.5 and 926.5 cm ) strongly decreased whereas those belong-
ing to group II (2834.1, 1501.2, 1381.2, 1176.1, 1098.5, 1082.4,
ꢂ1
933.9 and 929.3 cm ) increased after matrix annealing. Moreover
the relative intensities of bands II grew with respect to bands I
when the NH
above experimental data indicate that bands I can be assigned with
confidence to the 1:1 CH complex whereas bands II
NOHꢁ ꢁ ꢁNH
can be attributed to a CH complex. All the wave-
NOHꢁ ꢁ ꢁ(NH
3
concentration in the matrix was increased. The
2
3
2
3 2
)
numbers identified for the bands belonging to the groups I and II
are collected in Table 1. In Fig. 1 the most representative regions
Experimental and computational details
2 3
of the spectra of the CH NOH/NH /Ar matrix recorded directly after
matrix deposition and after annealing are presented.
Infrared matrix isolation studies
ꢂ1
The bands identified at 1049.2 cm
082.4 cm (II) are attributed to the perturbed ammonia bending
(I) and at 1098.5,
ꢂ1
1
Formaldoxime was generated from formaldoxime trimer hydro-
chloride (Aldrich, >98%) in the following way. A small amount of
the salt was placed in a glass flask connected to the vacuum vessel
of the cryostat. Upon heating to 323–338 K the salt decomposed,
vibrations, dNH
formaldoxime modes. The
3
; all other absorptions are assigned to perturbed
m
OH stretching vibration of the CH2-
ꢂ1
NOHꢁ ꢁ ꢁNH
3
complex appears at 2936.2 cm and shows a very
ꢂ1
large, ca. 685 cm , red shift with respect to the corresponding
3
releasing gaseous formaldoxime. Formaldoxime and NH /Ar or
2
vibration of CH NOH. The perturbation of the formaldoxime mOH
HCl/Ar mixtures with concentration varying from 1/100 to 1/800
were simultaneously deposited onto a gold-plated copper mirror
held at 11 K by a closed cycle helium refrigerator (Air Products,
Displex 202A). The concentration of formaldoxime in the CH2-
vibration in the complex with ammonia is much larger than in
ꢂ1
the complex with the water molecule (ꢂ138.9 cm ) [13]. The
large red shift of the OH stretch in the CH
2
NOHꢁ ꢁ ꢁNH
3
complex is
accompanied by relatively strong blue shifts of the dNOH and
3
NOH/NH (HCl)/Ar mixtures was varied by changing the flow rate
ꢂ1
ꢂ1
m
NO vibrations (+58.4 cm , +43.2 cm , respectively). The vibra-
of argon gas as well as the temperature of the hydrochloride salt.
Infrared spectra with resolution 0.5 cm were recorded in a reflec-
tion mode with a Bruker 113v spectrometer using a liquid N
cooled MCT detector.
tions of ammonia are also strongly perturbed as evidenced by
ꢂ1
ꢂ1
the relatively large blue shift of dNH
3
(+74.9 cm ). Such a pattern
2
of bands indicates that formaldoxime forms with ammonia a
strong complex stabilized by an OAHꢁ ꢁ ꢁN hydrogen bond. The
3
comparison of the perturbations of dNH vibrations in the ammo-
Computational details
nia complexes with hydroxylamine [27], water [28] and formal-
ꢂ1
doxime (+56, +62, +74.9 cm
, respectively) indicates that
The Gaussian 09 program [16] was used for the geometry opti-
mization and harmonic and anharmonic vibrational calculations.
CH NOHꢁ ꢁ ꢁNH is the strongest among the three complexes.
2
3
The ab initio calculations at the MP2/6–311++G(2d,2p) level
indicated three stationary points for the CH NOHꢁ ꢁ ꢁNH system
2 3
The structures of the monomers (CH NOH, NH , HCl) and the struc-
2
3
tures of the CH NOH–NH and CH NOH–HCl complexes were fully
2
3
2
that are shown in Fig. 2. The selected bond distances (in Å) and
ꢂ1
optimized at the MP2 level of theory with the 6–311++G(2d,2p) ba-
sis set. Vibrational wavenumbers were computed for both the
monomers and the complexes. Interaction energies were corrected
by the Boys–Bernardi full counterpoise procedure [17], and zero-
point vibrational energy corrections were also calculated.
Nonadditivity is one of the most important characteristic of tri-
mers [18–22]. This effect was quantitatively measured by the en-
ergy defined as:
interaction energies (in kJ mol ) are also presented. In Table 1S,
Supporting material, the geometrical parameters for the three
structures are collected and in Table 2S the calculated harmonic
and anharmonic wavenumbers are presented. Structure IA
CP
ꢂ1
(
D
E
¼ ꢂ26:22 kJ mol ) stabilized by the OAHꢁ ꢁ ꢁN bond is much
ZPE
CP
ZPE
ꢂ1
more stable than structures I
B
(DE
¼ ꢂ7:46 kJ mol ) and I
C
CP
ꢂ1
(D
E
¼ ꢂ7:30 kJ mol ) in which ammonia acts as a proton donor
ZPE
forming an NAHꢁ ꢁ ꢁO or NAHꢁ ꢁ ꢁN hydrogen bond. There is probably
an additional weak interaction between the CH group of CH NOH
and a nitrogen atom in the I and I structures. The formation of
the OAHꢁ ꢁ ꢁN hydrogen bond in structure I is reflected in a strong
decrease of the calculated OH stretching wavenumber and an in-
NO wavenumbers (
calc = ꢂ407, +82,
2
E
NA
¼
D
E
int;ABC
ꢂ
D
E
int;AB
ꢂ
D
E
int;BC
ꢂ
DE
int;AC
B
C
A
where
DEint,ABC is the interaction energy of the ABC trimer,
int,AB
DE ,
m
DE , DEint,AC are energies of respective dimers, A, B, C denotes
int,BC
crease of the dNH
3
and
m
Dm
the monomers.
ꢂ1
+28 cm respectively). The comparison of the calculated wave-
numbers for the three structures with those identified for the 1:1
complex trapped in the matrix clearly shows that the complex
Results
has the I
A
structure. However, one should notice the relatively
ꢂ1
Before the studies of the complexes were undertaken the infra-
red spectra of formaldoxime, ammonia and hydrogen chloride iso-
lated in argon matrices were recorded; they were in accord with
the literature spectra [23–26]. In the infrared spectra of matrices
containing both formaldoxime and ammonia or hydrogen chloride
new band sets were observed. They appeared in the vicinity of the
large difference between the observed (
calculated (
D
m
exp = ꢂ684.5 cm ) and
ꢂ1
D
m
calc = ꢂ407 cm ) wavenumber shifts for the
mOH
stretching vibration. The formation of the NAHꢁ ꢁ ꢁO bond in the I
B
complex is reflected in the noticeable red shift of the calculated
ꢂ1
NAO stretching wavenumber (
turbations of the OH stretch and NOH bend are very small. In turn,
D
m
calc = ꢂ19 cm ) whereas the per-
Please cite this article in press as: B. Golec et al., Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride, Spectrochimica Acta
Part A: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.org/10.1016/j.saa.2013.11.017

B. Golec et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx
3
Table 1
The identified wavenumbers for the CH
2
NOHꢁ ꢁ ꢁNH
3
and CH
2
NOHꢁ ꢁ ꢁ(NH
NOHꢁ ꢁ ꢁNH
exp. group I
3 2
) complexes and comparison of the observed and calculated anharmonic wavenumber shifts, Dm
a.
Assignment
Monomers
CH
2
3
2
CH NOHꢁ ꢁ ꢁ(NH
3 2
)
m
exp.
m
D
m
exp.
D
m
calc.
I
A
mexp. group II
D
m
exp.
Dmcalc. II
A
CH
OH
dCH
dHON
CH
CH
NO
2
NOH
m
3620.7
1408.3
1314.2
1153.7
953.1
2936.2
1494.3
1370.4
1173.8
936.5
ꢂ684.5
+86.0
+58.4
+20.1
ꢂ16.6
+43.2
ꢂ407
+79
+62
+13
ꢂ18
+28
2834.1
1501.2
1381.2
1176.1
933.9
ꢂ786.6
+92.9
+67.0
+22.4
ꢂ19.2
+46.0
ꢂ732
+154
+68
2
q
x
m
2
+18
2
ꢂ26
886.4
926.5
929.3
+45
8
80.2
NH
dHNH
3
974.3
1049.2
+74.9
+82
1098.5
+124.2
+108.1
+132
+77
1082.4
a
D
m
=
m
comp
mon
ꢂ m .
the formation of the I
vibrations (see Table 2S). Neither of these two complexes was
identified in the studied matrices.
C
complex only slightly affects the NOH group
of the bands belonging to groups I or II are constant within
experimental error in all performed experiments. The above
experimental data allowed us to assign the bands I and II to the
All bands II assigned to the 1:2 formaldoxime–ammonia com-
plex are shifted in the same direction as bands I (toward lower
or higher wavenumbers) with respect to the corresponding bands
of ammonia or formaldoxime monomers, however they show lar-
CH
2
NOHꢁ ꢁ ꢁHCl and CH
2
NOHꢁ ꢁ ꢁ(HCl)
2
complexes, respectively.
Moreover, in the spectra of matrices recorded after annealing weak
bands at 3485.5, 1354.0 and 969.2 cm appeared which also grew
after annealing but their relative intensities with respect to the
bands II varied in the performed experiments. The bands are also
tentatively assigned to CH
structure than that producing the bands II. All wavenumbers iden-
tified for the bands belonging to groups I and II are collected in Ta-
ble 2. In Fig. 3 the most representative regions of the spectra of the
2
CH NOH/HCl/Ar matrix recorded directly after matrix deposition
and after annealing are presented; the region of HCl stretching
vibrations is presented in Fig. 1S, Supporting material.
All bands belonging to group I appear in the vicinity of the
formaldoxime monomer absorptions and can be assigned with
2
confidence to the perturbed CH NOH vibrations. The largest per-
turbations are observed for the NOH group vibrations;
and
tively, (see Table 2) with respect to the CH
tions. However, the shifts are much smaller than those observed
for the corresponding CH NOH vibrations in the CH
3
complex, particularly for the OH stretch. Unfortunately, no absorp-
tion due to the hydrogen bonded HCl molecule was identified
which may due to the band being broad and diffuse.
ꢂ1
ger shifts than the bands I (see Table 1). The band II attributed to
ꢂ1
the OH stretch is 786.6 cm red shifted with respect to
mOH of
2
NOHꢁ ꢁ ꢁ(HCl)
2
complexes of different
CH
2
NOH monomer and the bands II due to the NH
3
bending vibra-
ꢂ1
tions are 124.2, 108.1 cm blue shifted as compared to the band of
NH
The MP2/6–311++G(2d,2p) calculations performed for the CH2-
system identified four stationary points that are pre-
3
monomer.
NOHꢁ ꢁ ꢁ(NH
3
)
2
sented in Fig. 2. The selected bond distances (in Å) and interaction
ꢂ1
energies (in kJ mol ) are also presented. In Table 1S, Supporting
material, the selected geometrical parameters for the four struc-
tures are collected and in Table 3S the calculated harmonic and
anharmonic wavenumbers are shown. The most stable is the se-
m
OH, dNOH
CP
ꢂ1
ꢂ1
ꢂ1
ven-membered cyclic structure II
A
(
D
E
¼ ꢂ45:75 kJ mol ) in
m
NO are shifted by ꢂ56.1 cm and +37.8, +27.4 cm , respec-
ZPE
which ammonia dimer is interacting with the OH group and with
the nitrogen atom of formaldoxime. The complex is stabilized by
two hydrogen bonds between formaldoxime and ammonia:
OAHꢁ ꢁ ꢁN, NAHꢁ ꢁ ꢁN and one NAHꢁ ꢁ ꢁN bond between the two
2
NOH monomer absorp-
2
2
NOHꢁ ꢁ ꢁNH
CP
ZPE
ꢂ1
ammonia molecules. The structures II
B
(D
E
¼ ꢂ34:52 kJ mol
)
CP
ZPE
ꢂ1
and II
C
(DE
¼ ꢂ32:60 kJ mol ) have comparable stabilities. In
both structures one ammonia molecule is attached to the OH group
of CH
NOH forming an OAHꢁ ꢁ ꢁN bond whereas the second ammo-
nia molecule serves as a proton donor toward the oxygen atom in
The calculations performed at the MP2/6–311++G(2d,2p) level
2
A B C
predict the stability of three structures, I , I and I for the CH2-
NOHꢁ ꢁ ꢁHCl complex. All optimized structures are shown in Fig. 4;
their interaction energies and selected geometrical parameters
are also presented. In Table 4S, Supplementary data, all calculated
parameters for the optimized structures are listed and in Table 5S
the calculated harmonic and anharmonic wavenumbers are
collected.
B C D
II and toward the nitrogen atom in II . In the weakest II complex
CP
ꢂ1
(DE
¼ ꢂ13:13 kJ mol ) the ammonia dimer is attached to the
ZPE
oxygen atom of formaldoxime.
The comparison of the calculated wavenumbers and wavenum-
bers shifts for the II
for the bands II shows that the CH
in the matrix has the II structure (see Tables 1 and 3S).
A
, II , II
B C
and II
D
structures with those observed
CP
ZPE
ꢂ1
2
NOHꢁ ꢁ ꢁ(NH complex trapped
3
)
2
In the most stable I
A
structure (
DE
¼ ꢂ15:85 kJ mol ) hydro-
A
gen chloride serves as a proton donor toward the nitrogen atom of
CH
2
NOH forming Nꢁ ꢁ ꢁHACl bond. The Nꢁ ꢁ ꢁH distance is equal to
Formaldoxime–hydrogen chloride complexes
1.82 Å and the h(NHCl) angle is 159°. The non-linearity of the
h(NHCl) angle suggests an additional very weak interaction be-
tween the chlorine atom of HCl and the OH group of formaldoxime.
2
The new bands appearing in the spectra of the CH NOH/HCl/Ar
matrices can also be separated into two groups. The group I in-
CP
ZPE
ꢂ1
In the I
B
structure (
DE
¼ ꢂ11:01 kJ mol ) hydrogen chloride is
volves the bands at 3564.6, 1422.0, 1342.0, 1171.7, 963.7, 966.0,
bonded to the oxygen atom of formaldoxime forming an Oꢁ ꢁ ꢁHACl
ꢂ1
9
10.7 cm which are relatively intense in the spectra of dilute
hydrogen bond. In turn, in the less stable
I
C
complex
CP
ZPE
ꢂ1
matrices and strongly diminish after matrix annealing to 33 K.
(DE
¼ ꢂ3:07 kJ mol ), the OH group of formaldoxime serves
The bands belonging to group II appear at 3497.6, 1357.9, 1184.7,
as a proton donor toward the chlorine atom of HCl and an
OAHꢁ ꢁ ꢁCl bond is formed.
ꢂ1
9
59.3, 911.5 cm . They are very weak or are not observed in the
spectra of dilute matrices but their intensities increase with HCl
concentration and after matrix annealing. The relative intensities
The comparison of the observed wavenumbers and wavenum-
bers shifts with the calculated ones for the three structures (see
Please cite this article in press as: B. Golec et al., Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride, Spectrochimica Acta
Part A: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.org/10.1016/j.saa.2013.11.017

4
B. Golec et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx
complex is stabilized by a very weak OAHꢁ ꢁ ꢁCl bond forming a cyc-
lic structure. A similar structure was observed for the NH2-
OHꢁ ꢁ ꢁHAF complex that was stabilized by a strong Nꢁ ꢁ ꢁHAF and
much weaker OAHꢁ ꢁ ꢁF bonds [29].
The bands II exhibit larger shifts with respect to the formal-
doxime monomer bands than the absorptions I but the correspond-
ing bands within the two groups are shifted in the same direction
(
toward higher or lower wavenumbers with respect to formal-
doxime vibrations). This fact suggests that in the CH
2
NOHꢁ ꢁ ꢁ(HCl)
2
complex, like in CH
bonds are formed.
2
NOHꢁ ꢁ ꢁHCl, Nꢁ ꢁ ꢁHACl and OAHꢁ ꢁ ꢁCl hydrogen
The ab initio calculations at the MP2/6–311++G(2d,2p) level
indicated four stationary points for the CH system
NOHꢁ ꢁ ꢁ(HCl)
2
2
that are shown in Fig. 4. In the most stable seven-membered cyclic
CP
ꢂ1
structure II
A
(DE
¼ ꢂ30:05 kJ mol ) the nitrogen atom of form-
ZPE
aldoxime serves as a proton acceptor for one hydrogen chloride
subunit of the HCl dimer and the OH group acts as a proton donor
toward a chlorine atom of the second HCl molecule. The Nꢁ ꢁ ꢁHACl
and OAHꢁ ꢁ ꢁCl bonds in the 1:2 complex are stronger than in the
1
:1 one as indicated by the shortening of the Nꢁ ꢁ ꢁH and Hꢁ ꢁ ꢁCl dis-
tances in II
A
as compared to I
A
(1.68 Å versus 1.82 Å for Nꢁ ꢁ ꢁH and
2
.32 Å versus 2.84 Å for Hꢁ ꢁ ꢁCl). The angles h(NHCl) and h(OHCl)
are close to linear (178.2°, 170.9°, respectively). In the II
B
structure
CP
ZPE
ꢂ1
(DE
¼ ꢂ24:95 kJ mol ) one HCl molecule acts as a proton donor
for the nitrogen atom and as a weak proton acceptor for the OH
group of formaldoxime. The second HCl molecule serves as a pro-
ton donor for the oxygen atom of formaldoxime. So, the complex
is stabilized by two strong hydrogen bonds Nꢁ ꢁ ꢁHACl, Oꢁ ꢁ ꢁHACl
and a very weak OAHꢁ ꢁ ꢁCl bond. In turn, in the II
C
structure
CP
ZPE
ꢂ1
(DE
¼ ꢂ20:30 kJ mol ) one HCl molecule is attached to the
nitrogen atom and a second one to the OH group which serves as
D
a proton donor for the chlorine atom. In the least stable II complex
CP
ꢂ1
(DE
¼ ꢂ19:13 kJ mol ) two HCl molecules are bonded to an
ZPE
oxygen atom which serves as a double acceptor.
The comparison of the bands II wavenumbers and wavenumber
shifts with those calculated for the four structures leads to the con-
clusion that the bands II correspond to the II
A
structure. The struc-
tures II and II could be immediately rejected as their formation
B
D
should lead to a red shift of the NO vibration whereas a blue shift
is observed for the complex present in the matrix (see Table 6S).
The patterns of wavenumber shifts for the II
A C
and II complexes
are very similar to each other except for the HCl vibrations which
are much more perturbed in II
A
than in II
C
. The more intense of the
ꢂ1
two perturbed HCl vibrations is calculated to exhibit a 927 cm
ꢂ1
red shift in II
A
and a 547 cm red shift in II
C
. Only one perturbed
HCl vibration was tentatively identified for the 1:2 complex as a
ꢂ1
broad diffuse band at ca. 2080 cm ; the absorption exhibits a ca.
ꢂ1
8
08 cm red shift with respect to the HCl monomer absorption.
The position of this band and its shift with respect to the HCl
monomer absorption do not give a definitive answer as to whether
3 2
Fig. 1. Selected regions of the spectra of the NH /Ar = 1/300 (a); CH NOH/Ar (b) and
CH
3 K for 10 min (c and d). The arrows indicate the bands due to the 1:1 (I) and 1:2
II) complexes.
2 3
NOH/NH /Ar matrices recorded directly after deposition and after annealing to
it corresponds to a complex of the II
A
or II
C
structure. However, the
and is
A
. Taking this into account as well
3
(
ꢂ1
8
08 cm red shift is much larger than that calculated for II
C
close to the shift calculated for II
A
as the fact that II is the most stable structure we assigned bands II
Tables 2 and 5S) indicates that the most stable I
trapped in the matrix. The identified OH wavenumber shows a
distinct (but not large) red shift whereas the dNOH and NO wave-
A
complex is
to a complex of IIA structure. The additional bands that were ob-
served in the spectra of the studied matrices at 3485.5, 1354.0,
1190.7 and 969.2 cm most probably belong to the IIB complex.
m
ꢂ1
m
numbers show blue shifts with respect to the corresponding CH2-
NOH vibrations, in accordance with the calculated shifts for the
I
A
structure. In the I
B
complex the calculated dNOH and
mNO wave-
Discussion
numbers exhibit red shifts whereas the perturbations of the I
C
complex vibrations are smaller than those observed for the com-
plex trapped in the matrix. The calculations show, in accord with
the experimental spectra, the distinct red shift of the OH stretch
and blue shifts of the NOH bend and NO stretch. Such a spectral
pattern suggests that in addition to a strong Nꢁ ꢁ ꢁHACl bond the
The CH NOHꢁ ꢁ ꢁNH complex present in the matrix is stabilized
2
3
by a strong OAHꢁ ꢁ ꢁN(H ) hydrogen bond as evidenced by the large
3
ꢂ1
red shift,
D
m
exp
= ꢂ684.5 cm , of the OH stretch of the bonded
formaldoxime molecule. The calculations indicate that the
OAHꢁ ꢁ ꢁN bond is almost linear (h(OHN) ffi 165°), the calculated
Please cite this article in press as: B. Golec et al., Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride, Spectrochimica Acta
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B. Golec et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx
5
CP
ZPE
ꢂ1
Fig. 2. The MP2/6–311++G(2d,2p) optimized structures of the CH
2
NOHꢁ ꢁ ꢁNH
3
and CH
2
NOHꢁ ꢁ ꢁ(NH
)
3 2
complexes. The energy values,
D
E
[kJ mol ], are also presented.
Table 2
The identified wavenumbers for the CH
2
NOHꢁ ꢁ ꢁHCl and CH
CH
NOHꢁ ꢁ ꢁHCl
exp. group I
2
NOHꢁ ꢁ ꢁ(HCl)
2
complexes and comparison of the observed and calculated anharmonic wavenumber shifts,
CH
NOHꢁ ꢁ ꢁ(HCl)
exp. group II
D
m
a.
Assignment Monomers
2
2
2
m
exp.
m
D
m
exp.
D
m
calc.
I
A
m
D
m
exp.
D
mcalc. II
A
CH
OH
dCH
dHON
CH
CH
2
NOH
m
3620.7
1408.3
1314.2
1153.7
953.1
3564.6
1422.0
1342.0
1171.7
963.7
ꢂ56.1
+11.7
+37.8
+18.0
+11.8
ꢂ64
+11
+53
+13
ꢂ2
3497.6
–
1357.9
1184.7
959.3
–123.1
–
+43.7
+31.0
+6.2
ꢂ162
+21
+52
+29
ꢂ4
2
q
x
2
2
9
66.0
mNO
886.4
910.7
+27.4
+23
911.5
+28.2
+49
880.2
HCl
HCl
c
b
c
m
2888.0
ꢂ500 (1318)
ꢃ2080
ꢂ808
ꢂ250 (626)
c
ꢂ927 (2241)
a
b
c
D
m
=
m
comp
mon
ꢂ m .
Tentative assignment.
The intensities (km mol ) are given in parentheses.
ꢂ1
Hꢁ ꢁ ꢁN bond length equals 1.83 Å and the interaction energy,
tion studies performed for the ammonia complex with hydrogen
halides showed extreme sensitivity of the proton stretching wave-
CP
ZPE
ꢂ1
DE
¼ ꢂ26:22 kJ mol . The theoretical spectra generally agree
well with the experimental ones, however they underestimate
number of the H
environment [14,30–36].
The CH
NOHꢁ ꢁ ꢁ(NH
ven-membered cyclic structure; the OH group serves as a proton
donor and the nitrogen atom of CH NOH as an acceptor for the
3
Nꢁ ꢁ ꢁHX (X = Cl, Br, I) complexes to the matrix
ꢂ1
the shift of the OH stretch which is predicted as
(
D
m
calc = ꢂ407 cm
for anharmonic wavenumbers). The discrepancy between the ob-
2
3 2
)
complex present in the matrix has a se-
served and calculated wavenumber shifts for the OH stretch may
be due to limited accuracy of calculated anharmonic wavenum-
bers, however the effect of argon environment on the structural
properties of the complex cannot be excluded. Earlier matrix isola-
2
ammonia dimer. So, in addition to the NAHꢁ ꢁ ꢁN bond between
the two ammonia molecules, the complex is stabilized by the
Please cite this article in press as: B. Golec et al., Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride, Spectrochimica Acta
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6
B. Golec et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx
CP
ꢂ1
equals
DE
¼ ꢂ45:75 kJ mol . In the II
B
, II
C
complexes one NH
and the second one
) or
3
ZPE
molecule is attached to the OH group as in I
A
to the acceptor site of CH
2
NOH, namely to the oxygen (II
B
nitrogen atoms (II ) like in the I
C
B
or I
are equal
C
, respectively. The interac-
CP
tion energies of II
B
and II
C
DE
¼ ꢂ34:52;
ZPE
ꢂ1
ꢂ32:60 kJ mol , respectively. In the least stable complex, II
D
CP
ꢂ1
(DE
¼ ꢂ13:13 kJ mol ), the ammonia dimer is attached to an
ZPE
oxygen atom of formaldoxime. The calculated three-body coopera-
ꢂ1
tive effect equals ENA = ꢂ8.23, ꢂ0.21, ꢂ0.50 and ꢂ0.38 kJ mol for
A B C D
II , II , II and II , respectively. The cooperativity leads to relatively
strong stabilization of the trimer energy in II
II , II and II the effect is small.
In the CH
A
structure while for
B
C
D
2
NOHꢁ ꢁ ꢁHCl complex present in the matrix the hydro-
gen chloride molecule acts as a proton donor toward the nitrogen
atom and, simultaneously, as a weak proton acceptor for the OH
group of formaldoxime, forming a strong Nꢁ ꢁ ꢁHACl and a weak
OAHꢁ ꢁ ꢁCl bonds. Unfortunately, the
m
HCl vibration of the 1:1 com-
ꢂ1
plex was not identified; the calculations predict a ꢂ500 cm
wavenumber shift of the HCl stretch. A weak OAHꢁ ꢁ ꢁCl interaction
is reflected in a distinct perturbation of the NOH group vibrations
of formaldoxime. The calculated interaction energy equals
ꢂ1
ꢂ15.85 kJ mol
.
In the CH
2
NOHꢁ ꢁ ꢁ(HCl)
2
complex the formaldoxime molecule
interacts with the hydrogen chloride dimer forming a seven-mem-
bered cyclic ring. The complex is stabilised by Nꢁ ꢁ ꢁHACl, OAHꢁ ꢁ ꢁCl
bonds between formaldoxime and hydrogen chloride, similar to
those formed in the I
A
, I
C
1:1 complexes, and by the Clꢁ ꢁ ꢁHACl bond
of the HCl dimer. Due to the cooperative effect the Nꢁ ꢁ ꢁHACl and
OAHꢁ ꢁ ꢁCl bonds become stronger in the 1:2 complex than in the
1
:1 ones as indicated by larger perturbations of the formaldoxime
vibrations. The calculations show a shortening of the Nꢁ ꢁ ꢁH dis-
tance from 1.82 Å in the 1:1 complex to 1.68 Å in the 1:2 complex
and a shortening of the Hꢁ ꢁ ꢁCl distance from 2.47 Å to 2.32 Å. The
ꢂ1
calculated interaction energy equals ꢂ30.05 kJ mol . The calcu-
lated shift for
m
HCl of the hydrogen chloride molecule bonded to
ꢂ1
a nitrogen atom (ꢂ927 cm
for anharmonic wavenumbers) is
slightly larger than the experimental shift for the tentatively iden-
tified perturbed hydrogen chloride stretching wavenumber
ꢂ1
(
ꢂ808 cm ). In the II
B
, II
C
complexes one of the two HCl molecules
, II
(where it
is bonded to the oxygen atom) and the role of proton acceptor in
II (in which the chlorine atom acts as a proton acceptor for the
OH group). In II structure an oxygen atom of formaldoxime serves
acts as a proton donor being attached to a nitrogen atom (II
and the second HCl plays the role of proton donor in II
B
C
)
B
C
D
as a proton acceptor for two HCl molecules, for this complex
CP
ꢂ1
D
E
¼ ꢂ19:13 kJ mol . The ENA values for the hydrogen chloride
ZPE
ꢂ1
complexes equal to ꢂ10.98, +1.63, ꢂ1.50 and +6.64 kJ mol for II
A
,
Fig. 3. Selected regions of the spectra of the HCl/Ar = 1/300 (a); CH
2
NOH/Ar (b) and
II
B C D
, II and II , respectively. They confirm a large percentage contri-
2
CH NOH/HCl/Ar matrices recorded directly after deposition and after annealing to
bution of an attractive three body interaction energy to the cyclic
2
1
1
8 K and 33 K for 10 min (c–e). The arrows indicate the bands due to the 1:1 (I) and
:2 (II) complexes. The dots indicate bands that are also tentatively assigned to the
:2 complexes and the star denotes the band due to the HCl complex with water.
II
II
A
structure and small contribution to the II
and II structures anti-cooperative effect occurs which is partic-
. Two hydrogen bonds donated to the same dou-
C
one. In contrast, in
B
D
ularly strong in II
D
ble acceptor, as is the case of II
anticooperative [19].
D
structure, are known to be
OAHꢁ ꢁ ꢁN(H
3
) and H
2
NAHꢁ ꢁ ꢁN hydrogen bonds. The OAHꢁ ꢁ ꢁN(H
3
)
In Table 3 the observed and calculated wavenumbers shifts
for the OH stretching vibration in the
complex are compared with the corresponding
bond is stronger in the 1:2 complex than in the 1:1 as would be ex-
pected from the cooperative effect; the infrared spectra demon-
(DmOHexp, DmOHcalc)
2
CH NOHꢁ ꢁ ꢁNH
3
ꢂ1
strate a ꢂ786.6 cm shift for the OH stretching vibration in this
shifts for the ammonia complexes with various OH proton donors.
With the exception of two complexes for which anharmonic wave-
numbers were calculated (see Table 3) all other values correspond
complex. The calculations indicate that the OAHꢁ ꢁ ꢁN(H
3
) bond is
practically linear (h(OHN) ffi 176°), the calculated Hꢁ ꢁ ꢁN bond
length, 1.77 Å, is 0.06 Å shorter than in the 1:1 complex. The
to harmonic calculations. The H
2
Oꢁ ꢁ ꢁNH
3
and CH
3
OHꢁ ꢁ ꢁNH
3
com-
2
H NAHꢁ ꢁ ꢁN bond, in which CH
2
NOH acts as a proton acceptor,
plexes involve OAHꢁ ꢁ ꢁN bonds of medium strength as indicated
deviates more from linearity (h(NHN) ffi 162°). The calculated
Hꢁ ꢁ ꢁN distance, 2.16 Å, can be compared with that in the ammonia
dimer, 2.14 Å, indicating comparable strength of the two NAHꢁ ꢁ ꢁN
by the experimental and calculated
D
mOH values lying within the
ꢂ1
range 200–300 cm [37–40]. As illustrated in Table 3, the calcu-
lated
D
mOHcalc values are very close to the experimental ones for
hydrogen bonds in the complex. The interaction energy of II
A
these two complexes. In turn, for CH
2
NOHꢁ ꢁ ꢁNH , OOHꢁ ꢁ ꢁNH and
3
3
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B. Golec et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx
7
CP
ZPE
ꢂ1
Fig. 4. The MP2/6–311++G(2d,2p) optimized structures of the CH
2
NOHꢁ ꢁ ꢁHCl and CH
2
NOHꢁ ꢁ ꢁ(HCl)
2
complexes. The energy values,
D
E
[kJ mol ], are also presented.
ꢂ1
Table 3
2100 cm [47] whereas the calculations predicted only ca. 1170,
1
Comparison of the observed wavenumbers and the observed and calculated
wavenumber shifts for the OH stretching vibration in ammonia complexes with
various OH group proton donors.
ꢂ1
398.8 or 1447 cm shifts [46–48]. This comparison raises the
question whether the discrepancies between the experimental
and calculated wavenumbers are due to inaccurate calculations
of anharmonic effects, to the effect of matrix environment on the
structural and vibrational properties of the complex or to both fac-
tors. Further studies are needed to explain this phenomenon.
In the context of the above discussion it is worth to note that, in
Experimental
Calculated
m
ꢂ
D
m
Ref.
ꢂ
D
m
Ref.
H
2
O
3434.9
203.1
[37]
190.6
[38]
[39]
[40]
[41]
This work
[44]
a
2
38
CH
NOH
CH NOH
3
OH
3400.7
3290
266.1
345
[40]
[27]
This work
[42]
273.4
279
contrast with the CH
NH one the calculated
NOHꢁ ꢁ ꢁNH
complex, for the CH
NOHꢁ ꢁ ꢁ
2
3
2
H
2
ꢂ1
(
3
)
2
D
m
OHcalc value (ꢂ732 cm ) is quite
a
2
2936.2
2654.4
684.5
758.6
407
ꢂ1
close to the experimental one (ꢂ786.6 cm ). The wavenumbers
HOO
559.1
613.5
925.3
7
05.3
of the OH stretching and NOH bending frequencies (2834.1,
b
ꢂ1
HONO
2765.2
818.7
[43]
[43]
1381.2 cm , respectively) of CH
2 3 2
NOHꢁ ꢁ ꢁ(NH ) indicate that in
2737.5
this case a Fermi resonance interaction may occur between OH
stretching fundamental (2834.1 cm ) and a first overtone of the
NOH bending vibration whose wavenumber is close to the OH
stretching fundamental (2ꢁ1381.2-
Fermi resonance will affect the position of the band due to the
NOHꢁ ꢁ ꢁNH
OH stretching vibration. In the case of the CH complex
the Fermi resonance interaction is very weak or does not exists as
the (OH) fundamental and 2d(NOH) overtone lie quite apart from
HNO
SO
3
1870
1400
1650
2100
[45]
[47]
[46]
[47]
[46]
[48]
ꢂ1
a
H
2
4
1170
1
1
398.8
447
j, j – anharmonic correction).
a
Calculated anharmonic wavenumbers.
Calculated with respect to the centre of the m(OH) doublet.
b
2
3
m
each other (2936.2, 2ꢁ1370.4-
j).
ONOHꢁ ꢁ ꢁNH
3
, the observed wavenumbers shifts are in the range
50–850 cm indicating the presence of strong OAHꢁ ꢁ ꢁN bonds
ꢂ1
6
in these complexes [42,43]. For all of the three complexes the cal-
culated value, OHcalc, is much lower than the experimental one,
OHexp (407, 559.1, 613.5 cm versus 684.5, 705.3, 818.7 cm
for the CH NOH, HOO and HONO complexes, respectively) [42–
4]. The difference between OHexp and OHcalc becomes even
Conclusions
D
m
ꢂ1
ꢂ1
D
m
1:1 and 1:2 complexes between formaldoxime and ammonia or
hydrogen chloride have been identified in CH NOH/NH /Ar,
2
2
3
4
D
m
D
m
CH NOH/HCl/Ar matrices, respectively; their structures were
2
larger for the strongest ammonia complexes with nitric and sulfu-
ric acids. The experiments demonstrated a ca. 1650 cm red shift
for the ammonia complex with nitric acid [45] whereas the calcu-
lations result in a 925.3 cm shift [46]. In turn, the experimental
determined on the basis of MP2/6–311++G(2d,2p) calculations. In
ꢂ1
the 1:1 complexes ammonia is attached to the OH group and
hydrogen chloride to the nitrogen atom of formaldoxime. In the
1:2 complexes the ammonia or hydrogen chloride dimers interact
both with the OH group as a proton donor and the nitrogen atom as
ꢂ1
DmOHexp value for the complex with sulfuric acid is as large as
Please cite this article in press as: B. Golec et al., Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride, Spectrochimica Acta
Part A: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.org/10.1016/j.saa.2013.11.017

8
B. Golec et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2013) xxx–xxx
a proton acceptor to form seven-membered rings. The three hydro-
gen bonds within the ring exhibit a substantial amount of cooper-
ativity. The theoretical spectra generally agree well with the
experimental ones, however they seriously underestimate the shift
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Please cite this article in press as: B. Golec et al., Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride, Spectrochimica Acta
Part A: Molecular and Biomolecular Spectroscopy (2013), http://dx.doi.org/10.1016/j.saa.2013.11.017