Molecular structures of triethylamine complexes with benzoic and pivalic acids

Article abstract of DOI:10.1134/S0036023610080127

Dissolution of benzoic or pivalic acid in excess triethylamine followed by crystallization was found to yield single crystals of 1 : 1 and 1 : 2 complexes, respectively. X-ray crystallography have shown that the complex with benzoic acid is an (Et₃

Full text of DOI:10.1134/S0036023610080127

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 8, pp. 1228–1233. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © M.A. Yakovleva, E.V. Perova, I.S. Kislina, N.B. Librovich, S.E. Nefedov, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 8,
pp. 1303–1308.
COORDINATION
COMPOUNDS
Molecular Structures of Triethylamine Complexes
with Benzoic and Pivalic Acids
M. A. Yakovlevaa, E. V. Perovaa, I. S. Kislinab, N. B. Librovichb, and S. E. Nefedova
a Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
b Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia
Received November 1, 2009
Abstract—Dissolution of benzoic or pivalic acid in excess triethylamine followed by crystallization was found
to yield single crystals of 1 : 1 and 1 : 2 complexes, respectively. Xꢀray crystallography have shown that the
complex with benzoic acid is an (Et3NH)+(OOCPh)– ion pair, in which the proton is transfered from the acid
to the base (N···O 2.629(2) Å), and the complex with pivalic acid contains, in addition to the ion pair (N···O
2.649 Å), the homoconjugate anion (ButCOO)(H)(OOCBut)– (O···O 2.521 Å).
DOI: 10.1134/S0036023610080127
Nonaqueous solutions of acids are widely used as
The identification of acid–base complexes and
media for homogeneous reactions in metal complex ions formed due to strong quasiꢀsymmetric hydrogen
[1] and acid–base [2] catalyses. High solubilities of
reagents and the possibility to smoothly adjust the catꢀ
alytic properties of a medium give rise to research
interest in compositions and structures of the acid–
base complexes present in acid–solvent systems.
Acid–base interactions in the solutions are characterꢀ
ized by the following equilibria: B (base, solvent) +
bonds is usually performed on the basis of their IR
spectra [10]. However, it is difficult to determine the
geometric parameters of the hydrogen bridge (the disꢀ
tance between the central proton and the side “heavy”
atoms) from the spectral data. Studies of acid–base
complexes formed by strong symmetric (or quasiꢀ
symmetric) hydrogen bonds by Xꢀray crystallography
allows one to obtain some valuable information on the
geometry of these particles that cannot be provided by
vibrational spectroscopy. When Xꢀray crystallographic
studies give no possibility to locate the proton position
HA (acid)
⋅⋅⋅ ⋅⋅⋅ (quasiꢀion pair, i.e., the ion pair with incomꢀ
plete proton transfer)
ВН+ А– (ion pair) ВН+ +
А– (ions) [2]. In addition, ВН+ particles can interact
В
⋅
HA (molecular complex)
В
Н А
⋅
with solvent molecules to form ions with strong symꢀ in the bridge, the location can be performed using
metric hydrogen bonds (В⋅⋅⋅
Н
⋅⋅⋅В)+ and (В⋅⋅⋅
Н .
⋅⋅⋅АН)+
quantumꢀchemical calculations, according to which
the shortened distance between “heavy” atoms
(smaller than 2.6 Å) indicates that the potential funcꢀ
tion of proton in the Hꢀbridge has one minimum; i.e., a
strong quasiꢀsymmetric hydrogen bond is formed [9].
Anions А– also can produce (А⋅⋅⋅
Н
⋅⋅⋅А)– ions under
certain conditions. Each of the above mentioned
acid–base complexes and ions has its own catalytic
activity (the possibility to protonate or ionize an
organic substrate) [3] and characteristic vibrational
At the same time, reactions of binuclear transition
spectra [4]. Ions (А⋅⋅⋅Н
⋅⋅⋅А)–, termed as homoconjuꢀ
metal carboxylates M2( ꢀOOCR)4(NEt3)2 (M = Zn,
μ
gate anions [5], play an essential role in acid–base
catalysis [2, 3] and in proton transfer in transition
metal hydrides [6–8]. However, their structures have
been poorly studied, and the available data deal mainly
only with the stoichiometric compositions. These ions
can have different structures. In many cases, (А–
Cu, Ni, Co; R = Ph, Me, But), which contain coordiꢀ
nated triethylamine with organic molecules that can
be protonated (for example, 3,5ꢀdimethylpyrazole),
imply that protons are bound to the bridging carboxyꢀ
late anion with formation of complexes
Et3NH+(OOCR)–. The composition and structure of
these products are determined by both the nature of
the transition metal and the donor ability of the R subꢀ
stituent in the carboxylate anion [12–20].
Н
⋅⋅⋅А)– species are formed, in which the AH acid molꢀ
ecule is bound to the А– anion by a common hydrogen
bond [5]. In distinction from these particles, the
anions formed by strong quasiꢀsymmetric hydrogen
bonds are more stable and capable of taking part in
chemical reactions as individual particles [9]. In addiꢀ
tion, the position of proton in the hydrogen bridge
In this work, we discuss the structure of complexes
of carboxylic acids obtained by dissolution in excess
triethylamine depending on the nature of the R subꢀ
determines the catalytic activity (the ability to ionize) stituent in the carboxylate anion, which results in the
of ions or complexes [2].
strength of the acids studied HOOCPh > HOOCBut
1228

MOLECULAR STRUCTURES OF TRIETHYLAMINE COMPLEXES
1229
10–5
Table 1. Crystal data and refinement details for structures 1
and 2
(dissociation constants in water at 25
and 0.93
°С
are 6.27
×
×
10–5 , respectively [21]).
1
2
EXPERIMENTAL
Triethylamine and benzoic and pivalic acids Chemical formula
(Acros) were used for the synthesis of the complexes.
Triethylamine and pivalic acid were preliminary disꢀ
C13H21NO2
223.31
C16 H35NO4
305.45
FW
tilled in an argon flow.
Xꢀray diffraction studies were performed by the
standard procedure using an automated Bruker
Color
Colorless
Orthorhombic
Pbca
Colorless
Monoclinic
Crystal system
SMART Apex II diffractometer with a CCD detector
(
λMo, graphite monochromator,
ω
scan). The strucꢀ
Space group
P2(1)/n
tures were solved with the use of the SHELXTL PLUS
(PC version) and refined with the SHELXTLꢀ97 proꢀ
gram package [23, 24]. The positions of hydrogen
Unit cell parameꢀ
ters, Å, deg
a
b
c
=11.3589(6)
= 10.8041(6)
= 20.9045(11)
a
b
c
= 6.268(6)
atoms in the ion pairs in (Et3NH)+(OOCPh)– (
1
) and
), as well as in
, were determined from
= 14.097(11)
= 21.821(15)
(
Et3NH)+[(OC(But)O]–(HOOCBut) (
the homoconjugate anion in
2
2
difference maps and refined in the isotropic approxiꢀ
mation.
α
β
γ
= 90
= 90
= 90
2565.5(2)
8
α
β
= 90
Crystal data and refinement parameters are shown
in Table 1. Atomic coordinates and selected geometric
parameters of the complexes studied are compiled in
Tables 2–5.
= 91.575(17)
γ
= 90
1927(3)
V
, Å3
Synthesis of complex (Et3NH)+(OOCPh)– (1)
.
Benzoic acid (0.5 g, 4.1 mmol) was dissolved in 4 mL
(28.8 mmol) of triethylamine and heated to 100°C.
Very hygroscopic white crystals were formed on slow
cooling with the oil bath. The crystals were used for the
Xꢀray crystallographic experiments.
Z
4
ρcalcd, mg/cm3
1.156
0.077
976
1.053
0.074
680
–1
μ, mm
Synthesis of complex (Et3NH)+[(OC(But)O]–
(HOOCBut) (2). Pivalic acid (0.5 g, 4.9 mmol) was
dissolved in 4 mL (28.8 mmol), and 3 mL of hexane
F(000)
Crystaldimensions, 0.20
mm
×
0.18
×
0.16 0.14
×
0.12 × 0.10
was added. The resulting solution was kept at +5 С for
°
a day. The white crystals formed (melt at room temꢀ
perature) were used for Xꢀray crystallography.
θ
scan range, deg
2.65–29.00
2.36–25.00
Reflection index
range
–15
–14
–26
≤
≤
≤
h
k
≤
≤
14,
14,
–7
–16
–25
≤
≤
≤
h
k
≤
≤
6,
RESULTS AND DISCUSSION
16,
It was found that dissolution of benzoic or pivalic
acid in excess triethylamine yields colorless single
l
≤
28
l ≤ 25
crystals
Et3NH)+(OOCPh)– (
(HOOCBut) (
, which melts at room temperature.
of,
respectively,
1
hygroscopic
(
) and (Et3NH)+[(OC(But)O]–
Reflections meaꢀ
sured
19898
9577
2)
According to the Xꢀray diffraction data, in adduct
of strong benzoic acid with Et3N (Fig. 1, Tables 2, 3),
the proton is transfered from the acid to the amine
with formation of the О(2)···Н(1)–N(1) bond. The
oxygen–nitrogen distance in the bond (2.629(2) Å) is
characteristic of ion pairs with a low ability to ionize [3].
Independent reflecꢀ
tions
3364
(int) = 0.0313]
3282
(int) = 0.1119]
1
[
R
[
R
GOOF
1.013
0.912
R
for
I
> 2
σ
(
I
)
R1 = 0.0384,
R1 = 0.0685,
Another picture is observed for complex
2 (Fig. 2,
wR2 = 0.0936
wR2 = 0.1099
Tables 4, 5), which is formed by weaker pivalic acid
and triethylamine and has the 2 : 1 composition. The
triethylamine molecule is protonated with a proton of
one of the acid molecules, and the distance
О(2)···N(1), 2.649(6) Å, virtually coincides with that
R
tions
(
for all reflecꢀ
)
R
1 = 0.0493
R
1 = 0.1882,
wR2 = 0.1016
wR2 = 0.1385
Residual electron
density (max/min),
e Å–3
0.282 and –0.164 0.180 and –0.278
found for complex
1
. However, in distinction from the
pair benzoic acid–NEt3, complex
2
is an ion pair forꢀ
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 8 2010

1230
YAKOVLEVA et al.
104) and equivalent isotropic factors (Å2
Table 2. Atomic coordinates (
×
×
103) for complex 1
Atom
x
y
z
Ueq
O(1)
N(1)
O(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
5845(1)
6539(1)
6466(1)
5705(1)
4542(1)
4311(1)
3252(1)
2423(1)
2642(1)
3698(1)
6696(1)
7359(1)
6259(1)
5126(1)
5668(1)
5653(1)
2063(1)
8139(1)
3655(1)
2851(1)
2890(1)
3842(1)
3884(1)
2962(1)
2012(1)
1972(1)
8194(1)
9341(1)
6843(1)
6323(1)
9074(1)
9177(1)
6739(1)
6725(1)
6146(1)
6313(1)
5956(1)
5526(1)
5192(1)
5286(1)
5714(1)
6054(1)
7436(1)
7654(1)
6512(1)
6785(1)
6492(1)
5769(1)
32(1)
23(1)
27(1)
22(1)
23(1)
28(1)
39(1)
45(1)
43(1)
31(1)
27(1)
32(1)
26(1)
32(1)
28(1)
36(1)
Table 3. Bond lengths (d) and bond angles (ω) for complex 1
Bond , Å
d
Bond
d, Å
O(1)–C(1)
N(1)–C(8)
O(2)–C(1)
C(2)–C(3)
C(3)–C(4)
C(5)–C(6)
C(8)–C(9)
1.242 (1)
1.498(1)
1.274(1)
1.391(1)
1.391 (1)
1.384(2)
1.520(1)
1.514 (1)
N(1)–C(12)
1.496(1)
1.504(1)
1.517(1)
1.394(1)
1.384(2)
1.395(2)
1.516(1)
0.97 (1)
N(1)–C(10)
C(1)–C(2)
C(2)–C(7)
C(4)–C(5)
C(6)–C(7)
C(10)–C(11)
N(1)–H(1)
C(12)–C(13)
Angle
ω
,
deg
Angle
ω, deg
C(12)N(1)C(8)
C(8)N(1)C(10)
O(1)C(1)C(2)
C(3)C(2)C(7)
C(7)C(2)C(1)
C(5)C(4)C(3)
C(5)C(6)C(7)
N(1)C(8)C(9)
N(1)C(12)C(13)
112.10(7)
110.86(7)
118.84(8)
119.34(9)
120.51(9)
119.57(11)
120.42(11)
112.83(8)
112.48(8)
C(12)N(1)C(10)
O(1)C(1)O(2)
O(2)C(1)C(2)
C(3)C(2)C(1)
C(2)C(3)C(4)
C(4)C(5)C(6)
C(2)C(7)C(6)
N(1)C(10)C(11)
113.13(8)
125.15(9)
116.01(8)
120.15(9)
120.79(10)
120.17(10)
119.70(11)
114.38(8)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 8 2010

MOLECULAR STRUCTURES OF TRIETHYLAMINE COMPLEXES
1231
C(11)
С(7)
С(6)
O(1)
C(10)
C(1)
C(2)
N(1)
C(8)
H(1)
С(5)
C(9)
O(2)
C(3)
C(12)
C(4)
C(13)
Fig. 1. Structure of complex 1.
mally consisting of the Et3NН+ cation and the pivalic of neutron diffraction studies of the homoconjugate
anion (О2NO⋅⋅⋅H
⋅⋅⋅ONO2)– in the composition of the
acid dimer anion, in which the distance О(1)···О(3)
(2.520(6) Å) allows us to assume that a homoconjugate
anion appears due to formation of a strong quasiꢀsymꢀ
metric hydrogen bond. Note that the presence of the
ion pair with Cs+ cation with nearly symmetric proton
transfer and the О···О distance in the bridge (2.468 Å)
[24]) close to that in 2.
strong symmetric hydrogen bond in 2 is confirmed by
Thus, the studies have shown that, in the presence
of a base taken in excess, strong carboxylic acids form
the quantum chemical calculations performed for
complexes of similar structures [9], as well as by the data
4
Table 4. Atomic coordinates (
×
10 ) and equivalent isotropic
Table 5. Bond lengths (d) and bond angles (ω) for complex 2
2
3
factors (
Å
×
10 ) for complex 2
Bond
d, Å
Bond
d, Å
Atom
x
y
z
U
eq
O(1)–C(1)
O(3)–C(6)
N(1)–C(11)
N(1)–C(13)
C(2)–C(3)
C(2)–C(5)
C(7)–C(9)
C(7)–C(10)
C(13)–C(14)
Angle
1.293(5)
1.256(4)
1.484(5)
1.509(4)
1.516(6)
1.538(5)
1.511(5)
1.535(5)
1.512(4)
O(2)–C(1)
O(4)–C(6)
N(1)–C(15)
C(1)–C(2)
C(2)–C(4)
C(6)–C(7)
C(7)–C(8)
C(11)–C(12)
C(15)–C(16)
Angle
1.212(4)
1.249(4)
1.490(4)
1.524(6)
1.528(5)
1.530(5)
1.514(5)
1.510(6)
1.509(5)
O(1)
O(2)
O(3)
O(4)
N(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
10228(4)
9581(4)
8993(4)
10168(4)
10845(4)
10018(5)
10455(5)
9594(7)
12877(5)
9454(6)
9557(5)
9487(5)
10928(6)
7215(5)
7054(2) 1890(2)
5730(2) 1385(1)
7266(2) 3365(1)
6041(2) 2842(1)
8903(2) 3112(2)
6567(3) 1390(2)
42(1)
53(1)
41(1)
40(1)
30(1)
36(1)
36(1)
64(1)
53(1)
56(1)
32(1)
29(1)
52(1)
50(1)
47(1)
45(1)
56(1)
36(1)
47(1)
41(1)
53(1)
7134(2)
6606(3)
7225(3)
8128(3)
812(2)
252(2)
777(2)
844(2)
ω,
deg
ω, deg
C(11)N(1)C(13)
O(2)C(1)O(1)
O(1)C(1)C(2)
C(3)C(2)C(1)
C(3)C(2)C(5)
C(1)C(2)C(5)
O(4)C(6)C(7)
C(9)C(7)C(8)
C(8)C(7)C(6)
C(8)C(7)C(10)
N(1)C(11)C(12)
N(1)C(15)C(16)
113.9(3) C(15)N(1)C(13) 111.0(3)
6414(3) 3326(2)
5813(2) 3909(2)
6272(3) 4392(2)
5799(3) 4124(2)
4803(2) 3782(2)
9172(3) 3752(2)
9268(3) 4166(2)
9543(2) 2811(2)
122.8(4) O(2)C(1)C(2)
113.9(4) C(3)C(2)C(4)
109.9(3) C(4)C(2)C(1)
110.3(3) C(4)C(2)C(5)
110.9(3) O(4)C(6)O(3)
119.2(3) O(3)C(6)C(7)
109.9(3) C(9)C(7)C(6)
108.2(3) C(9)C(7)C(10)
109.6(3) C(6)C(7)C(10)
123.3(4)
109.5(4)
106.7(3)
109.4(3)
123.5(4)
117.3(4)
108.2(3)
110.7(3)
110.2(3)
C(10) 10273(6)
C(11)
C(12)
C(13)
C(14)
11429(6)
9549(7)
9192(5)
9912(5) 10563(2) 2755(2)
C(15) 12746(5)
C(16) 14199(5)
8804(2) 2722(2)
8003(2) 2924(2)
114.1(3) C(14)C(13)N(1) 113.6(3)
112.9(3)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 8 2010

1232
YAKOVLEVA et al.
C(14)
C(13)
C(5)
C(15)
N(1)
C(4)
C(11)
C(2)
H(2)
C(12)
C(16)
O(1)
C(3)
C(1)
H(1)
O(3)
C(8)
C(6)
O(2)
O(4)
C(7)
C(9)
C(10)
Fig. 2. Structure of complex 2.
ion pairs of the 1 : 1 composition, and weaker acids
may form ion pairs and homoconjugate anions with
quasiꢀsymmetric hydrogen bond of the composition
1 : 2.
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