L-Alanine halogenides with L-alanine L-alaninium dimeric cation

Article abstract of DOI:10.1016/j.molstruc.2018.03.016

Crystalline salts l-alanine l-alaninium chloride (I) l-alanine l-alaninium bromide (II) and l-alanine l-alaninium iodide (III) were obtained, which have dimeric cations in the structure. The salts crystallize in the monoclinic crystal system with the space group P2₁ (Z = 4). l-Alanine··· l-alaninium dimers are realized via rather short O–H?O hydrogen bonds between carboxyl and carboxylate groups with the O?O distances equal to 2.421(2), 2.423(2) ? in (I), 2.437(10), 2.413(8) ? in (II) and 2.421(5), 2.442(5) ? in (III) at 200 K. The salts (I) and (II) are isotypic, while the salt (III) has different packing so the structure is distinct. The infrared and Raman spectra and the crystal structures of these compounds are discussed. Besides, we obtained for the first time a new simple salt l-alaninium iodide.

Full text of DOI:10.1016/j.molstruc.2018.03.016

Accepted Manuscript
L-Alanine halogenides with L-alanine L-alaninium dimeric cation
V.V. Ghazaryan, G. Giester, M. Fleck, A.M. Petrosyan
PII:
S0022-2860(18)30299-0
10.1016/j.molstruc.2018.03.016
MOLSTR 24955
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 5 December 2017
Revised Date: 3 March 2018
Accepted Date: 6 March 2018
Please cite this article as: V.V. Ghazaryan, G. Giester, M. Fleck, A.M. Petrosyan, L-Alanine halogenides
with L-alanine L-alaninium dimeric cation, Journal of Molecular Structure (2018), doi: 10.1016/
j.molstruc.2018.03.016.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
L-Alanine halogenides with L-alanine L-alaninium dimeric cation
V.V. Ghazaryana1, G. Giester b, M. Fleckb, A.M. Petrosyana
a Institute of Applied Problems of Physics, NAS of Armenia,
25 Nersisyan Str., 0014 Yerevan, Armenia
b Institute of Mineralogy and Crystallography, University of Vienna,
Althanstr. 14, A-1090 Vienna, Austria
Abstract
Crystalline salts L-alanine L-alaninium chloride (I), L-alanine L-alaninium bromide (II) and
L-alanine L-alaninium iodide (III) were obtained, which have dimeric cations in the structure.
The salts crystallize in the monoclinic crystal system with the space group P21 (Z=4). L-
alanine···L-alaninium dimers are realized via rather short O–H···O hydrogen bonds between
carboxyl and carboxylate groups with the O···O distances equal to 2.421(2), 2.423(2) Å in
(I), 2.437(10), 2.413(8) Å in (II) and 2.421(5), 2.442(5) Å in (III) at 200K. The salts (I) and
(II) are isotypic, while the salt (III) has different packing so the structure is distinct. The
infrared and Raman spectra and the crystal structures of these compounds are discussed.
Besides, we obtained for the first time a new simple salt L-alaninium iodide.
Keywords: L-alanine L-alaninium dimeric cation, hydrogen bond, structure, vibrational
spectra
1. Introduction
Formation of salts has been extensively investigated for a range of amino acids [1]. A
particular type of salt includes dimeric (A···A+) cations composed of one A zwitterion and
one A+ cation tightly connected by a strong O–H···O hydrogen bond. With a singly charged
anion X–, such cations form a unique series of (A···A+)X– salts. Their preparation is,
however, not straightforward; considerable efforts must often be spent determining the
optimal, often non-stoichiometric composition of the initial solution, as stoichiometric ratios
do not ensure synthesis of the desired salt (or indeed of any salt at all) [2-4]. Among the
known salts of the amino acid alanine, simple salts prevail over the salts with dimeric cations.
The first known salt of alanine with (alanine···alaninium) dimeric cation was 2L-
Ala·HNO3 obtained in 2001 by Silva et al. [5], although the system L-alanine–HNO3–water
had been studied previously and only (L-AlaH)NO3 was obtained [6]. Alanine moieties have
1
Corresponding author: Tel.: +374 10 241106; fax: +374 10 281861;
vahram.ghazar@gmail.com, vghazaryan@iapp.sci.am (V.V. Ghazaryan)

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the only conformation, where N1, C2, C1 atoms and O atoms of the carboxyl(ate) group are
ca. in the same plane, and the O-C1-C2-C3 torsion angles close to –60° and 120°. However,
the mutual arrangement of zwitterionic and cationic alanine moieties in the dimeric cation
can be distinct, and is characterized by the several angles presented in Scheme 1 and Table 1
(one can also use angles <CCOHO and <OHOCC instead of <OCOHO and <OHOCO). In this
case, carboxyl and carboxylate groups are ca. in the same plane. We designate this type of
dimeric cation as type-A (Fig. 1).
Later 2L-Ala·HNO3 was investigated as NLO crystal [7,8]. Inelastic neutron scattering
and Raman spectra of 2L-Ala·HNO3 were investigated at different temperatures and the
distinctions were discussed in view of the structure [9].
The second salt 2L-Ala·H3PO3·H2O was obtained and characterized (crystal structure,
piezoelectric and pyroelectric behavior) by Pankova and coauthors [10-12]. Here, alanine and
alaninium moieties are arranged otherwise. Carboxyl and carboxylate groups are trans
oriented and <COHOC equals to –154°. Oxygen atoms, those forming the dimeric cation via
O–H···O hydrogen bond of 2.530(2) Å, are trans positioned to the N atoms of NH3 groups
and the corresponding OCCN torsion angles equal to 168° and 164°. Chronologically, we
denote this conformation of the cation as type-B. Types A and B differ in the angles
<OHOCO and <OHOCC (see Table 1).
The salt L-alanine L-alaninium triiodide was synthesized while trying to obtain L-
alaninium iodide from a solution containing excess of HI [13, 14]. It also forms dimeric
cations of type-B.
The next halogenide D-alanine D-alaninium bromide was obtained by Fischer [15] not
directly, but as an unplanned product of a reaction of D-alanine with 2,3-dibromosuccinic
acid. The main distinction of D-alanine D-alaninium dimer from the dimers of type-A and
type-B is the gauche-orientation of carboxyl and carboxylate groups when the angle
<COHOC equals to –87°. It represents a further type of dimers – type-C.
With picric acid at least two salts of 2:1 ratio were obtained, one of which is an anhydrous
sample based on vibrational spectra [16], and the second one is a monohydrate 2L-Ala·picric
acid·H2O structurally confirmed in [17]. In the structure of L-alanine L-alaninium picrate
monohydrate alanine moieties form the fourth type of alanine dimers called type-D by us.
The type-D is closer to the type-B. The only distinction is that in this type of dimeric cation
the alanine moiety forms a dimer via oxygen atom, which is in the cis-position to the NH3
group, unlike to previously mentioned types of dimeric cations, where it is trans-positioned.
Alanine dimers of type-D also exist in the structure of L-AlaH·(L-Ala···L-AlaH)SiF6·H2O
[18].
We published preliminary data on obtaining of L-alanine L-alaninium chloride and L-
alanine L-alaninium bromide in [16].
In the present work, we have focused on detailed results of investigation of the
halogenide systems L-Ala–HCl–H2O, L-Ala–HBr–H2O and L-Ala–HI–H2O. We obtained

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salts with dimeric cation in all three systems. Preparation of the 2L-Ala·HI was possible
using stabilized hydriodic acid, bearing in mind previous experience in [13,14], where the
hydriodic acid without stabilizer undergoes a partial oxidation resulting in the formation of an
–
–
I3 anion and the corresponding salt (L-Ala···L-Ala+)I3 . Besides, we have managed to obtain
the L-alaninium iodide.
2. Experimental
2.1. Synthesis and crystal growth
As initial reagents we used L-alanine (≥98%, TLC) and hydriodic acid (57% w/w,
distilled, stabilized with <1.5% hypophosphorous acid, 99.95%) from “Sigma-Aldrich”
Chem. Co., and hydrochloric (32% w/w, chemically pure grade) and hydrobromic (40.5%
w/w, ultrapure grade) acids from “Reakhim” Co. All compounds have been obtained at room
temperature by evaporation of aqueous solutions containing non-stoichiometric ratios of
solved components: L-alanine and hydrochloric, hydrobromic or hydriodic acid. From 2:1 M-
ratio first L-alanine bulk crystals are formed, and then the needles of 2L-Ala·HCl (or 2L-
Ala·HBr, or 2L-Ala·HI). By collecting and weighting L-alanine crystals, we calculated that
the 2L-Ala·HCl (or 2L-Ala·HBr, or 2L-Ala·HI) starts to form from ca. 1.4:1 M-ratio, which
we tried and confirmed experimentally. From 1:1 M-ratio using HCl or HBr, a mixture of
salts 2L-Ala·HCl and L-Ala·HCl (2L-Ala·HBr and L-Ala·HBr) is formed. Thus, to obtain
pure L-Ala·HCl and L-Ala·HBr crystals we used solutions with 1:1.5 M-ratio of components,
i.e. with excess of hydrochloric or hydrobromic acid. To obtain L-Ala·HI the 1:1 M-ratio was
used. Alanine used for preparation in experiments taken from 1 to 2g.
2.2. Crystal structure determination
Suitable single crystals of the title compounds were manually selected and checked for
irregularities under the microscope. Well-developed crystals were mounted on glass needles
with laboratory grease. Single-crystal X-ray intensity data were obtained at 200K (Oxford
Cryosystems Cryostream 600 resp. 800 Plus) by a measurement on a Enraf Nonius Kappa
CCD diffractometer, sealed tube, equipped with a graphite monochromator and
monocapillary optics using Mo-Kα (λ = 0.71073 Å) radiation for 2L-Ala·HCl or on a Bruker
APEXII diffractometer equipped with a CCD area detector and an Incoatec Microfocus
Source IµS (30 W, multilayer mirror, Mo-Kα) for 2L-Ala·HBr and 2L-Ala·HI. The structures
were solved using direct methods; subsequent difference Fourier syntheses and least-squares
refinements yielded the positions of the remaining atoms. Non-hydrogen atoms were refined
with independent anisotropic displacement parameters, hydrogen atoms with isotropic
displacement parameters. The hydrogen atoms were treated as riding on their parent atoms,
except for the hydrogen atoms of the oxygen and nitrogen atoms. All calculations were
performed using Enraf Nonius or Bruker instrument software (APEX3 software suite) and the
SHELX97 program package [19-21].

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The crystallographic data as well as details of the measurements are listed in Table 2. Further
crystallographic data have been deposited with the Cambridge Crystallographic Data Centre
and can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
+44 1223 336033), citing the title of this paper and the CCDC nos. 1556749-1556751.
2.3. Vibrational spectra
Attenuated total reflection Fourier-transform infrared spectra (FTIR ATR) were
registered by a Nicolet 5700 spectrometer using Smart Performer single-reflection ATR
accessory (ZnSe prizm, Happ-Genzel apodization, corrected for ATR distortion, number of
scans 32, resolution 4 cm-1). Nujol mull technique used to register part of the IR spectrum in
the region 600–400 cm-1 (number of scans 32, resolution 2 cm-1).
Fourier-transform Raman spectra were registered by a NXR FT-Raman Module of a
Nicolet 5700 spectrometer at room temperature with resolution 4 cm-1. Number of scans and
laser power at the sample were 256 and 0.44W for (I), 384 and 0.44W for (II), 512 and
0.37W for (III), 256 and 0.35W for (IV), 256 and 0.36W for (V) and 256 and 0.32W for
(VI).
3. Results and discussion
3.1. Molecular and crystal structures
The salts 2L-Ala·HCl, 2L-Ala·HBr and 2L-Ala·HI crystallize in the monoclinic crystal
system with the space group P21, Z=4 (see Table 2). The structures of 2L-Ala·HCl and 2L-
Ala·HBr are isotypic but differ from 2L-Ala·HI as already recognizable from the unit cell
parameters (Table 2). Let us start from the structure of 2L-Ala·HCl. The unit cell contains
two (L-Ala···L-Ala+) dimeric cations and two chloride anions in the asymmetric unit (Fig. 2).
Bond lengths and valence angles are normal (see Table S1 in supporting material). The C–O
lengths are changed, which is expected and the reason of which is the rather short O–H···O
hydrogen bond between the carboxyl group of alaninium moiety and the carboxylate group of
zwitterionic alanine moiety. Thus, in the L-Ala(A)···L-Ala(B)+ and L-Ala(C)···L-Ala(D)+
two dimeric cation’s distances of O–H···O hydrogen bonds equal to 2.421(2) Å and 2.423(2)
Å, respectively (for 2L-Ala·HBr they have lengths of 2.437(10) Å and 2.413(8) Å). The
dimeric cations in the structure are of type-C (Fig. 1). Carboxyl and carboxylate groups are at
an angle to each other, so the COHOC angles, passing O–H···O hydrogen bond, are equal to
78° and 75° (in 2L-Ala·HBr 91° and 87°). One can name it as a gauche-conformation.
Characteristic torsion angles of dimeric cations are listed in Table 1. In contrast to the type-C,
in the types-A and B, carboxyl and carboxylate groups are almost coplanar having trans-
conformation and <COHOC tends to 180°. Somewhat other situation is in the type-D, where
+
<COHOC = –126°. In the L-alaninium cations of L-alanine compounds, NH3 and OH groups
are in some cases located side by side [23,24], but are commonly located in the opposite sides
as in the known types of dimeric cations of L-alanine. As concerns to zwitterionic L-alanine,

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the oxygen atom forming dimeric cation and the amino group mainly are oppositely directed.
The only exception is type-D, where they are neighboring. The difference between type-A
and type-B may be characterized with <OHOCO angle.
The crystal 2L-Ala·HCl has a layered structure. Layers are arranged perpendicular to the
b-axis (Fig. 3). Since methyl groups are located at the outer sides of the layers, no hydrogen
bond i.e. no strong interaction exists between layers, so the crystal has cleavage. In the layers,
one can distinguish the chains built with L-Ala(A)···L-Ala(B)+ dimeric cations and Cl1
anions serially connected with N1A–H12A···Cl1···H12B–N1B hydrogen bonds (see details
of all H-bonds in Table 3). The angle between the chain orientation and the c-axis is 43°.
Such chains are located parallel to each other in the same plane parallel (010) and are
interconnected with N1A–H13A···Cl1 and N1B–H13B···Cl1 hydrogen bonds, thus forming
“semilayers” (Fig. 4). Fully identical chains and network exist between L-Ala(C)···L-Ala(D)+
dimeric cations and Cl2 anions, thus forming a second “semilayer”. In this case chain-
forming hydrogen bonds are N1C–H12C···Cl2 and N1D–H12D···Cl2, and the
interconnections are N1C–H13C···Cl2 and N1D–H13D···Cl2. The directions of the previous
and the later chains are ca. perpendicular in projection onto (010) and are at an angle equal to
86°. The structural layers of the crystal are formed from these two “semilayers” linked from
one hand with N–H···O type hydrogen bonds N1A–H11A···O2C and N1C–H11C···O2A
between zwitterionic L-Ala(A) and L-Ala(C) moieties, and from the other hand with N–
H···Cl type hydrogen bonds N1B–H11B···Cl2 and N1D–H11D···Cl1 attracting L-Ala(B)+
and L-Ala(D)+ cationic moieties. This type of semilayers was called as S1 type hydrogen
bonded sheets in [25] and also found in some salts of other amino acids. Comparison of the
crystal structures of 2L-Ala·HBr obtained by us (or 2L-Ala·HCl, which is isotypic) and 2D-
Ala·HBr obtained by A. Fischer [15] showed, that the structural layers are similar, but they
are different in arrangement in between (see Fig.5). In the structure of 2L-Ala·HBr the layers
alternately are arranged oppositely, while in the structure of 2D-Ala·HBr they are
unidirectional. Although symmetries are the same, there are one dimeric cation and a bromide
anion in the asymmetric unit of 2D-Ala·HBr and Z=2. Possibly, the difference in preparation
method leads to the formation of different structures. It is interesting to note, that the crystal
structure of 2L-Ala·HBr is less compact (Dcalc=1.553 gcm-3 at 296K), than that of 2D-
Ala·HBr (Dcalc=1.561 gcm-3 at 299K). Examining L-Ala(A) and L-Ala(B) couple in the
structure of 2L-Ala·HI, on the assumption of C-O bonds lengths one can conclude that the H-
atom of the carboxyl group should be attached to the (B) moiety, however it is close to (A)
and we have L-Ala(B)···L-Ala(A)+ dimeric cation instead of L-Ala(A)···L-Ala(B)+ in 2L-
Ala·HCl and 2L-Ala·HBr. Ignoring this, one can say that 2L-Ala·HI also consists of similar
layers, which is a result of identical hydrogen bonds (see Tables 3-5). So, three different
crystal structures are observed which crystallize in the same symmetry group and are built by
corresponding structural blocks (layers).
3.2. Infrared and Raman spectra
The vibrational spectra of 2L-Ala·HCl (I), 2L-Ala·HBr (II) and 2L-Ala·HI (III) are shown in
the Figs. 6-8, and the spectra of L-Ala·HCl (IV), L-Ala·HBr (V) and L-Ala·HI (VI) are

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presented in the Figs. 9-11 for comparison. The wavenumbers of peaks and their assignments
are listed in Tables 6 and 7.
A detailed investigation of the spectra of (I, II, III) in comparison with those of (IV, V, VI)
shows several differences. In the high frequency region one can expect the observation of N–
+
H, C–H and O–H stretching vibrations of NH3 , CH3, CH and COOH groups. It is true for the
1:1 compounds (IV, V, VI) but not in the case of 2:1 compounds with dimeric cation (I, II,
III). As is noted above, in the structure of (I), (II) and (III) the OH of the carboxylic group
are engaged in the rather strong O–H···O hydrogen bond, thus the stretching mode of O–H
occurs not in the region of N–H stretching vibrations, but in the low frequency region
centered at ca. 800 cm-1. This value is in good agreement with the correlation between ν(OH)
and R(O···O) [26]. Therefore, the baseline of the IR spectra of (I), (II) and (III) is curved
around that region (1700-400 cm-1). It is easy to see, that in the same region of the IR spectra
of (IV), (V) and (VI) the baseline is straight. So, one can find the ν(CH) vibrational modes as
strong Raman lines in the regions 3019-2885 cm-1 for (I), 3013-2884 cm-1 for (II) and 3010-
2883 cm-1 for (III). Nearby medium-intensity lines are caused by ν(NH) vibrations, which
have their counterparts in the IR spectra in the form of strong bands (3062, 3030, 2926 in Fig.
6 and 3071, 3025, 2913 cm-1 in Fig. 7 and 3072, 2902 cm-1 in Fig. 8) overlapping ν(CH)
weak bands. One more feature of the spectra arises because of strong hydrogen bond in a
dimeric cation. Such strong hydrogen bond leads to change of covalent bond lengths in
carboxyl and carboxylate groups (see Table S1 in supporting material) which in turn leads to
decreasing of stretching vibration frequency of carboxylic C=O in comparison with “free”
carboxyl groups of 1:1 samples. The ν(C=O) vibration, which appears as a strong band with
peaks 1718 cm-1 in L-Ala·HCl (Fig.9), and 1719 cm-1 in L-Ala·HBr (Fig.10) and 1728, 1716
cm-1 in L-Ala·HI (Fig.11), is shifted to the lower frequency region and observed as a broad
band at 1673 cm-1 in 2L-Ala·HCl (Fig.5), 1667 cm-1 in 2L-Ala·HBr (Fig.7) and 1666 cm-1 in
2L-Ala·HI (Fig.8), overlapped with νas(COO–) vibrations. Characterization of some further
peaks can be seen in Tables 6 and 7.
4. Conclusions
L-alanine L-alaninium chloride, L-alanine L-alaninium bromide and L-alanine L-alaninium
iodide are salts with a (L-Ala···L-Ala+) dimeric cation and crystallize in the monoclinic space
group P21. The O···O distances of O–H···O hydrogen bonds in dimeric cations are among
shortest found in likewise salts and equal to 2.421(2), 2.423(2) Å in 2L-Ala·HCl, 2.437(10),
2.413(8) Å in 2L-Ala·HBr, and 2.421(5), 2.442(5) Å in 2L-Ala·HI. A bit shorter distances of
–
dimers’ hydrogen bond have only two salts of amino acids, namely (L-Trp···L-Trp+)·HgCl3
with 2.41(2) Å O···O distance [27] and (L-Pro···L-Pro+)·NO3 with 2.414(3) Å O···O
distance [28]. However, for (L-Trp···L-Trp+)·HgCl3 the measurement accuracy is low. 2L-
–
–
Ala·HCl and 2L-Ala·HBr are isotypic, while 2L-Ala·HI has different structure. In spite of
this, the crystal structures consist of similar structure moieties.

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Table 1. Types of conformations of L-alanine L-alaninium dimeric cations in the structures of
known salts and torsion angles (in °) for specification.
<O*CCN
<O*CCN
ψ1(L-
<OCOHO
<COHOC
<OHOCO
Ref.
[5]
ψ1(L-Ala)
AlaH)
type-A
(L-Ala···L-AlaH)NO3
156
168
–171
–166
–12
173
168
159
type-B
(L-Ala···L-AlaH)H2PO3·H2O
(L-Ala···L-AlaH)I3
–3
4
0
–154
162
170
–11
0
1
164 [11]
–179
166
[14]
type-C
(L-Ala···L-AlaH)Cl
(L-Ala···L-AlaH)Br
(L-Ala···L-AlaH)I
–179
–176
–178
–177
177
–2
4
–3
0
–6
–3
–2
78
75
91
–6
–9
–9
–10
–11
–10
–9
178
173
175
174
175
172
this
work
this
work
this
87
106
100
87
work
–179
–179
(D-Ala···D-AlaH)Br **
176 [15]
type-D
(L-Ala···L-AlaH)picrate·H2O
L-AlaH·(L-Ala···L-AlaH)SiF6·H2O
178
–177
–4
12.8
–126
–160
–28
31
–16 [17]
–20 [18]
* taken oxygen atom which forms dimeric O–H···O hydrogen bond.
** there are given inverted values of D-alanine to be easy comparable with L-alanine
samples.

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Table 2. Crystal data and details of the refinement for L-alanine L-alaninium chloride (I), L-
alanine L-alaninium bromide (II), D-alanine D-alaninium bromide [15] and L-alanine L-
alaninium iodide (III).
(I)
(II)
[15]
(III)
Formula
Mr
C3H7NO2·C3H8NO2·Cl C3H7NO2·C3H8NO2·Br C3H7NO2·C3H8NO2·Br C3H7NO2·C3H8NO2·I
214.65
259.11
259.11
306.10
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
P21
5.0763(10)
19.268(4)
10.909(2)
90.00
90.43(3)
90.00
1067.0(4), 4
1.336
Monoclinic
P21
5.1817(10)
18.821(4)
11.173(2)
90.00
90.235(1)
90.00
1089.6(4), 4
1.579
Monoclinic
P21
9.485(4)
5.1678(6)
11.258(2)
90.00
92.97(3)
90.00
551.087, 2
1.561
Monoclinic
P21
11.6812(4)
5.2997(2)
19.4133(6)
90.00
103.369(2)
90.00
1169.25(7), 4
1.739
α
β
(°)
(°)
γ(°)
V(Å3), Z
Dcalc(gcm-3)
µ(Mo Kα) (cm-1)
F(000)
0.347
456
3.762
528
2.729
600
T(K)
200(2)
200(2)
299
200(2)
hkl range
Reflections measured 14543
-7/7, -29/28, -16/16
-7/7, -26/26, -14/15
14672
-17/17, -8/8, -29/29
42047
Reflections unique
Data with (Fo > 4σ
(Fo))
7676
6420
5284
3329
8835
7544
Rint
0.0272
249
-0.004(16)
0.0338
0.0709
251
0.038(11)
0.0524
0.0322
250
0.001(10)
0.0327
Parameters refined
Flack parameter [21]
R(F)* (for Fo >
4σ(Fo))
wR(F2)* (all
reflections)
0.0481
0.0996
0.0412
Weighting
0.035 / 0.104
0.025 / 0.000
1.058 / -1.047
0.013 / 1.237
1.077 / -1.675
parameters a / b
ꢀρfin (max/min) [e Å– 0.235 / -0.198
3
]
CCDC no.
1556749
1556750
629449
1556751
2
4 1/2
2
* R1 = Σ Fo  - Fc  / Σ Fo, wR2 = [Σ w(Fo - Fc2)2 / Σ wFo ] ,w = 1/[σ2(Fo )+(a × P)2+ b ×
2
P], P = (Fo +2Fc2)/3
Table 3. Hydrogen bonds parameters for L-alanine L-alaninium chloride (in Å and °).
D–H···A
D–H
1.03(3)
1.07(3)
0.91
0.91
0.91
0.91
0.91
0.91
0.91
H···A
1.40(3)
1.37(3)
1.90
2.38
2.48
2.36
2.39
2.34
1.91
D···A
2.421(2)
2.423(2)
2.779(2)
3.2793(19)
3.3678(18)
3.2662(18)
3.2776(19)
3.248(2)
2.778(2)
3.254(2)
3.378(2)
3.2500(18)
3.2664(19)
<DHA
170(3)
165(3)
162
170
167
174
165
177
160
O1B–H1B···O1Ai
O1D–H1D···O1C
N1A–H11A···O2C
N1A–H12A···Cl1ii
N1A–H13A···Cl1iii
N1B–H11B···Cl2
N1B–H12B···Cl1iv
N1B–H13B···Cl1
N1C–H11C···O2Ai
N1C–H12C···Cl2i
N1C–H13C···Cl2
N1D–H11D···Cl1iii
N1D–H12D···Cl2iii
0.91
0.91
0.91
0.91
2.35
2.48
2.34
2.38
172
168
177
164

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N1D–H13DC···Cl2ii
Symmetry codes: (i) x–1, y, z; (ii) x, y, z+1; (iii) x+1, y, z+1; (iv) x+1, y, z.
0.91
2.33
3.240(2)
173
Table 4. Hydrogen bonds parameters for L-alanine L-alaninium bromide (in Å and °).
D–H···A
D–H
0.89(3)
0.90(3)
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
H···A
1.63(6)
1.66(7)
1.89
2.48
2.61
2.52
2.54
2.49
1.91
D···A
<DHA
149(9)
139(9)
161
175
162
168
160
176
154
O1B–H1B···O1Ai
O1D–H1D···O1C
N1A–H11A···O2C
N1A–H12A···Br1ii
N1A–H13A···Br1iii
N1B–H11B···Br2
N1B–H12B···Br1iv
N1B–H13B···Br1
N1C–H11C···O2Ai
N1C–H12C···Br2i
N1C–H13C···Br2
N1D–H11D···Br1iii
N1D–H12D···Br2iii
N1D–H13DC···Br2ii
2.437(10)
2.413(8)
2.765(9)
3.388(9)
3.491(8)
3.419(7)
3.314(8)
3.397(6)
2.786(9)
3.396(6)
3.484(8)
3.388(7)
3.411(6)
3.390(8)
2.50
2.58
2.48
2.53
167
170
173
165
2.48
174
Symmetry codes: (i) x–1, y, z; (ii) x, y, z+1; (iii) x+1, y, z+1; (iv) x+1, y, z.
Table 5. Hydrogen bonds parameters for L-alanine L-alaninium iodide (in Å and °).
D–H···A
D–H
1.11(6)
1.05(10)
0.91
0.91
0.91
0.91
0.91
0.91
0.91
H···A
1.54(6)
1.49(9)
1.89
2.71
2.76
2.74
2.80
2.70
1.96
D···A
<DHA
131(4)
148(6)
157
169
168
162
152
172
147
O1A–H1A···O1Bi
O1D–H1D···O1C
N1A–H11A···O2C
N1A–H12A···I1ii
N1A–H13A···I1
N1B–H11B···I2
N1B–H12B···I1iii
N1B–H13B···I1iv
N1C–H11C···O2Aii
N1C–H12C···I1ii
N1C–H13C···I1
N1D–H11D···I1
N1D–H12D···I2v
N1D–H13D···I2vi
2.421(5)
2.442(5)
2.753(4)
3.611(6)
3.658(6)
3.620(3)
3.628(6)
3.605(6)
2.764(5)
3.623(5)
3.664(6)
3.641(3)
3.630(5)
3.609(6)
0.91
0.91
0.91
0.91
2.77
2.75
2.76
2.78
157
177
163
155
0.91
2.70
175
Symmetry codes: (i) x, y–1, z; (ii) x, y+1, z; (iii) x+1, y, z; (iv) x+1, y+1, z; (v) x–1, y–1, z;
(vi) x–1, y, z
Table 6. Wavenumbers (in cm-1) and assignment of peaks in IR and Raman spectra of L-
alanine L-alaninium chloride (I), L-alanine L-alaninium bromide (II), L-alanine L-alaninium
iodide (III)
I
II
III
Assignment
IR
Raman
3094;3019;3 3071;3025
IR
Raman
3097;3013;3 3072
IR
Raman
3096
+
3062;3030
ν(NH) NH3

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009;2999
2984;2971;2 2969;
944;2885
2913
002
2969
2926
2985;2971;2 2970;2938
943;2884
2902
3010;2988;2
971;2939
2917;2883
2730
ν(CH) CH, CH3
+
ν(NH) NH3
2732
2729
ν(OH) COOH
2695;2605;2
474
2686;2589;2
460
2683;2573;2
469
Combi
1980
1673
1978
1681
1940
1667
1947
1676
1866
1666
1885
1670
Combi
ν(C=O) and
νas(COO–)
+
1593;1581
1504
1483
1464;1409
1371
1341
1597
1596;1575
1494
1474
1409
1369
1606;1577
1595;1569
1570
δas(NH3 )
+
1486sh
1460;1416
1375
1347
1307
1489
1466;1414
1366
δs(NH3 )
δas(CH3)
δs(CH3)
1458;1418
1374
1343
1456
1372
1343
1302
1339
1303
1338
1307
1306
δ(CH)
1256
1208
1121;1111
995
1252
1201
1108
990
ρ(CH3)
δ(COH )
ρ(NH3 )
1211
1214
1204
1127;1113
993
1202
1110
988
+
1129;1113
1001
1136;1116
997
948
942
947
919
918
916
855
852
851
828
768;758
612;600
834
762
616
826
768;757
612;593
834
761
619
819
768;754
615;583
834
759
620;589sh
569
ν(CN)
δ(COO)
508
429
506
425
502;483
419
423
416
411
406
404
377;336;195
361;327;198
356sh;322
combi-combination, overtone, sh-shoulder, s-symmetric, as-asymmetric, ν-stretching, δ-
deformation, ρ-rocking.
Table 7. Wavenumbers (in cm-1) and assignment of peaks in IR and Raman spectra of L-
alaninium chloride (IV), L-alaninium bromide (V) and L-alaninium iodide (VI).
IV
V
VI
Assignment
IR
Raman
IR
Raman
IR
Raman
+
3213sh;3199;3 3202;3163
166
3202;3156;297
1;2912
3143;3109;303 3117;3050;303
ν(NH) NH3
9;2994
1;3024;3011;3
000
2963;2915;288 3016;2991;296
3017;2993;296
3;2948;2897
2950;2945;293
2;2896
ν(CH) CH, CH3
8
4;2951;2928;2
917sh;2898
2840
+
2838
2801
2927;2917
2793
2918
ν(NH) NH3
ν(OH) COOH
2717;2792;264 2746;2720;269 2701;2609;256 2746;2612;257 2688;2597;256 2758
Combi
8;2627;2580;2 7;2658;2626;2 7;2523;2483;2
538;2496;2465 581;2542;2504 452
;2467
1
1;1546;2471;2
456;2398
1968
1973
1933
1734sh
1719
1933
1738sh
1725
1903
Combi
Combi
ν(C=O)
1718
1606;1582
1724
1584
1728;1716
1584;1572
1740;1719
+
1600;1574
1600;1576
1589;1574;155 δas(NH3 )
5
1530
1493
1519
1485
+
1495
1485
1484
1481
δs(NH3 )

ACCEPTED MANUSCRIPT
1469;1418
1471;1458;143 1466;1413
1457;1419
1461sh;1455;1 1455;1412
406
δas(CH3)
δs(CH3)
2;1424
1385
1352
1316
1382
1349
1316
1381
1344
1309
1385
1347
1311
1383
1335
1298;1289
1254
1388
1335
1316
δ(CH)
ρ(CH3)
δ(COH )
1234
1197
1139;1114
1240
1222
1229
1196
1132;1116
1210
1185
1215
1194
1199
1193
ρ(CH3)
+
1143;1118
1128;1112
1108
1121;1111;109 ρ(NH3 )
1
1008
976
1010
981
955
921
1001
971
1004
976
993
976
996
977
919
916
919
913
806
915;894;872;8
61;849
846
813
848
816
817
792
818
798
810
789
ν(CN)
770
738
613
520
765
698
609
774
712;695
614
740
615
522
731
609
515
734
611
518
δ(COO)
516
402
338;277;179
396;361
331;274;206
308;379
321;280
combi-combination, overtone, sh-shoulder, s-symmetric, as-asymmetric, ν-stretching, δ-
deformation, ρ-rocking.
Scheme 1. Illustration of selected torsion angles in L-alanine L-alaninium dimer.

ACCEPTED MANUSCRIPT
Fig. 1. L-alanine L-alaninium dimer types in the structures of known salts.
(a)
(b)
Fig. 2. Asymmetric unit of L-alanine L-alaninium chloride (a) (note, that L-alanine L-
alaninium bromide is isotypic) and L-alanine L-alaninium iodide (b).

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Fig. 3. Packing diagram of L-alanine L-alaninium chloride, viewed along [100].
Fig. 4. H-bond network in semilayer of L-alanine L-alaninium chloride, viewed along [010].

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L-alanine L-alaninium bromide
D-alanine D-alaninium bromide

ACCEPTED MANUSCRIPT
L-alanine L-alaninium iodide
Fig. 5. Packing diagrams of L-alanine L-alaninium bromide, D-alanine D-alaninium bromide
and L-alanine L-alaninium iodide. It is easy to see, that colored layers are similar.

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Fig. 6. Infrared and Raman spectra of L-alanine L-alaninium chloride.

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Fig. 7. Infrared and Raman spectra of L-alanine L-alaninium bromide.

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Fig. 8. Infrared and Raman spectra of L-alanine L-alaninium iodide.

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Fig. 9. Infrared and Raman spectra of L-alaninium chloride.

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Fig. 10. Infrared and Raman spectra of L-alaninium bromide.

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Fig. 11. Infrared and Raman spectra of L-alaninium iodide.

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Highlights
# Dimeric L-alanine L-alaninium cations are formed via short O-H···O hydrogen bonds
# There are four known types of L-alanine L-alaninium dimeric cations
# Three halogenides of L-alanine with dimeric cation are presented