Synthesis, crystal structures and thermal behaviour of organic-inorganic hybrids incorporating a chiral diamine

Article abstract of DOI:10.1016/j.jorganchem.2011.11.023

A series of noncentrosymmetric metal sulfates [R-C₅H ₁₄N₂][M^II(H₂O)₆](SO ₄)₂ and [S-C₅H₁₄N ₂][M^II(H₂O)₆](SO₄) ₂ (M^II = Mn (1, 2), Fe (3, 4), Co (5, 6) and Ni (7, 8)) have been synthesized by slow evaporation conditions through the use of enantiomorphically pure sources of either R-2-methylpiperazine (R)-C ₅H₁₂N₂ or S-2-methylpiperazine (S)-C ₅H₁₂N₂. These materials crystallize in the polar, noncentrosymmetric space group P2₁ (No. 4), crystal class 2 (C₂). Isolated [M^II(H₂O)₆] ²⁺, [(R)-C₅H₁₄N₂]²⁺ or [(S)-C₅H₁₄N₂]²⁺ cations and (SO ₄)^2- anions linked together via two types of hydrogen bonds, O_w-H_w?O and N-H?O, from which supramolecular structures are formed. The use of single enantiomer of either R-2-methylpiperazine or S-2-methylpiperazine precludes inversion symmetry within the crystal lattices and forces crystallization in noncentrosymmetric structures. Compounds 1-8 were characterized using single crystal X-ray diffraction, infrared spectroscopy and thermal analyses. The structural arrangements and the intermolecular interactions such as hydrogen-bonding are discussed.

Full text of DOI:10.1016/j.jorganchem.2011.11.023

Journal of Organometallic Chemistry 700 (2012) 110e116
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, crystal structures and thermal behaviour of organiceinorganic hybrids
incorporating a chiral diamine
a
a
,
a
b
*
Fadhel Hajlaoui , Houcine Naïli , Samia Yahyaoui , Alexander J. Norquist ,
a
c
Tahar Mhiri , Thierry Bataille
Laboratoire de l’Etat Solide, Département de Chimie, Université de Sfax, BP 1171, 3000 Sfax, Tunisie, Tunisia
Department of Chemistry, Haverford College, Haverford PA 19041, USA
a
b
c
Sciences Chimiques de Rennes (UMR CNRS 6226), Groupe Matériaux Inorganiques, Chimie Douce et Réactivité, Université de Rennes I, Avenue du Général Leclerc,
3
5042 Rennes CEDEX, France
a r t i c l e i n f o
a b s t r a c t
II
II
Article history:
Received 25 August 2011
Received in revised form
5 14 2 2 6 4 2 5 14 2
A series of noncentrosymmetric metal sulfates [R-C H N ][M (H O) ](SO ) and [S-C H N ][M
II
(
H
2
O)
conditions through the use of enantiomorphically pure sources of either R-2-methylpiperazine
R)-C or S-2-methylpiperazine (S)-C These materials crystallize in the polar, non-
centrosymmetric space group P2 (No. 4), crystal class 2 (C
6
](SO
4
)
2
(M ¼ Mn (1, 2), Fe (3, 4), Co (5, 6) and Ni (7, 8)) have been synthesized by slow evaporation
16 November 2011
(
5
H
12
N
2
5 12 2
H N .
Accepted 17 November 2011
II
2þ
2þ
2
N ]
1
2
). Isolated [M (H
2ꢀ
4
cations and (SO ) anions linked together via two types of hydrogen bonds, O
2
O)
6
]
, [(R)-C
5
H
14
or
/O
2
þ
[
(S)-C
5
H
14
N
2
]
w
eH
w
Keywords:
and NeH/O, from which supramolecular structures are formed. The use of single enantiomer of either
R-2-methylpiperazine or S-2-methylpiperazine precludes inversion symmetry within the crystal lattices
and forces crystallization in noncentrosymmetric structures. Compounds 1e8 were characterized using
single crystal X-ray diffraction, infrared spectroscopy and thermal analyses. The structural arrangements
and the intermolecular interactions such as hydrogen-bonding are discussed.
Noncentrosymmetric
Single enantiomer
Hydrogen bonds
Supramolecular structures
Ó 2011 Elsevier B.V. All rights reserved.
II
II
1
. Introduction
noncentrosymmetric hexaaqua-metal sulfates using Mn , Fe ,
II
II
Co or Ni and enantiomerically pure sources of either R-2-
methylpiperazine or S-2-methylpiperazine. The synthesis, crystal
structures and the thermal behaviour of these new compounds are
The chemistry of noncentrosymmetric sulfate materials has
been the focus of significant interest for several years, owing to the
great structural diversity such compounds exhibit [1e9] and the
desirable physical properties that such compounds can exhibit,
including magnetic, catalysis, fluorescent materials, optical activity
and ferroelectric materials [10e13]. As all these properties require
crystallographic noncentrosymmetry, several strategies [14e16]
are currently employed to deter inversion symmetry in new
compounds, including the use of chiral organic amines [17e19].
During the last two decades, specific interest in non-
centrosymmetric organiceinorganic materials has been focused on
the possibility of combining excellent features from both types
of constituents within a single material [20e22]. In addition,
a fundamental understanding of how specific connectivities and
compositions affect these symmetry dependent properties is crit-
ical for the development of new technologies. As such, the strategy
employed in this study involves the synthesis of four pairs of polar,
II
discussed in the context of amine symmetry and M size.
2. Experimental section
2.1. Materials
MnSO
CoSO $7H
methylpiperazine (99%, Aldrich), (S)-(þ)-2-methylpiperazine
99%, Aldrich) and H SO (96%, Carlo Erba) were used as received.
Deionized water was used in these syntheses.
4
$H
2
O
(99%, Merck), FeSO
4
$7H
2
O
(99%, Merck),
4
2
O (99%, Merck), NiSO
4
$ 6H O (99%, Merck), (R)-(-)-2-
2
(
2
4
2.2. Chemical preparation
Single crystals of [R-C
Mn(H O) ](SO (2), [R-C
Fe(H O) ](SO (4), [R-C
Co(H O) ](SO (6), [R-C
O) ](SO
5
H
14
14
14
14
N
N
N
N
2
][Mn(H
][Fe(H
][Co(H
][Ni(H
2
O)
O)
6
](SO
](SO
4
)
)
4 2
2
(1), [S-C
(3), [S-C
(5), [S-C
(7), [S-C
5
H
5
H
5
H
5
H
14
N
14
N
14
N
14
N
2
]
2
]
2
]
2
]
[
[
[
2
6
4
)
)
2
5
H
2
2
6
2
6
4
2
5
H
2
2
O)
O)
6
](SO
](SO
4
)
)
2
2
6
4
)
2
5
H
2
2
6
4
2
*
Corresponding author. Tel.: þ216 98 66 00 26; fax: þ216 74 274 437.
E-mail address: houcine_naili@yahoo.com (H. Naïli).
[Ni(H
2
6
4
)
2
(8) were grown from solutions containing 1 mmol
0
022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.11.023

F. Hajlaoui et al. / Journal of Organometallic Chemistry 700 (2012) 110e116
111
II
of the appropriate metal sulfate hydrate M SO
4 2
$nH O, 3 mmol of
2.5. Infrared spectroscopy
either R-2-methylpiperazine or S-2-methylpiperazine and 1 mmol
of H SO , in 10 mL of distilled water. Initial solution pHs were
2
4
Infrared measurements were obtained using a PerkineElmer
FT-IR Spectrum. Samples were diluted with spectroscopic grade
KBr and pressed into a pellet. Scans were run over the range of
between 1.5 and 3 for all reactions. Prismatic crystals were observed
after a few days for each reaction. The experimental powder X-ray
diffraction patterns for these compounds match well with those
simulated from single crystal structure data, indicating that the
eight compounds were isolated as single phases.
ꢀ
1
400e4000 cm
.
3. Results
2
.3. Single-crystal X-ray diffraction and structure determination
Compounds 1e8 are all constructed from octahedrally coordi-
nated transition metal cations coordinated by six water molecules
II
2þ
2ꢀ
A suitable single crystal of each compound was carefully
[M (H O) ] , isolated sulfate anions (SO ) , and either [(R)-
2
6
4
2
þ
2þ
selected under a polarizing microscope and glued to a glass fibre
C H N ]
or [(S)-C H N ]
cations, all of which are held
5
14
2
5
14
2
mounted on a four-circle Nonius Kappa CCD area-detector diffrac-
tometer. Intensity data sets were collected using MoKa radiation
together through extensive hydrogen-bonding networks. MneOw
bond lengths range by the transition metal with averages of
2.182(2), 2.128(3), 2.096(2) and 2.062(2) Å observed for Mn, Fe, Co
and Ni, respectively. Variations in the bond lengths between
enantiomeric pairs are small, with deviations of between 0.0153
and 0.125%.
through the program COLLECT [23]. Corrections for Lorentz-
polarisation effect, peak integration and background determina-
tion were carried out with the program DENZO [24]. Frame scaling
and unit cell parameters refinement were performed with the
program SCALEPACK [23]. Analytical absorption corrections were
performed by modeling the crystals faces [25]. The structures
analyses were carried out with the monoclinic symmetry, space
Strong similarities in both structure and composition are
observed in compound 1e8. The asymmetric units in each
2
þ
2þ
compound consists of one [R-C H N ] or [S-C H N ] cation,
5
14
2
5
14
2
2
ꢀ
II
2þ
2þ
2þ
group P2
1
(No. 4), according to the automated search for space
two distinct (SO ) anions and one M (M ¼ Mn , Fe , Co and
4
II
2þ
group available in WinGX [26]. Transition metal atoms (M : Mn, Fe,
Co and Ni) and sulfur atoms were located using the direct methods
with program SHELXS-97 [27]. The oxygen atoms and the organic
moieties were found from successive Fourier calculations using
SHELXL-97 [28]. The drawings were made with Diamond [29].
The aqua H atoms were located in a difference map and refined
with OeH distance restraints of 0.85(1) Å and HeH restraints of
Ni ) cation octahedrally coordinated by six water molecules,
2
2
6
4 2
which is similar to the well known Tutton’s salt, A M(H O) (XO )
(A ¼ monovalent cation, M ¼ bivalent cation, X ¼ hexavalent
cation) [30e33]. Extensive hydrogen-bonding networks are
2
þ
2þ
observed between the [C H N ] and [M(H O) ] cations and
5
14
2
2
6
2
ꢀ
2þ
2
and
(SO4)
anions in each compound, with the [C H N ]
[M(H O) ] cations acting as donor with sulfate acceptors. Similar
5
14
2
þ
2
6
1
.39(1) Å. Hydrogen atoms on the organic amines were positioned
structures have been observed in other organically templated metal
sulfates [1e5,32,34,35]. In addition, all eight compounds crystallize
in the noncentrosymmetric space group P21 (No. 4), in which
geometrically and allowed to ride on their parent atom, with CeH
and NeH bonds were fixed at 0.97 and 0.90 Å, respectively. Crys-
tallographic data and structural refinements are summarized in
Table 1. Selected bond distances are provided in Table 2. Full tables
of bond lengths, bond angles and hydrogen bonds are available in
CIF format from the CambridgeCrystallographic Data Center (see
Supplementary Data).
only 2 screw axes are present. However, despite the similarities
1
in compositions in compounds 1e8, distinct differences in three-
II
dimensional packing are observed between the Mn compounds
II
II
II
(1 and 2) and Fe (3 and 4), Ni (5 and 6) and Co (7 and 8)
analogues. The three-dimensional packing of compounds 1 and 2
are shown in Fig. 1, while packing images of compounds 3e8 are
shown in Fig. 2.
2.4. Thermal analyses
þ
The local coordination environment around the [Mn(H O)
2 6
]2
DTA-TG investigations were performed using a “multi-module
2 SETARAM” analyser operating from room temperature up to
cations in compounds 1 and 2 is shown in Fig. 3. The octahedra
environment of Mn cations are not regular, see Table 2, as seen in
II
9
ꢁ
ꢁ
ꢀ1
1000 C at a constant rate of 5 C min under flowing air.
other isostructural metal sulfates [1,36]. The MeO
w
bond distances
Table 1
II
Crystal data and structure refinement for [C
5
H N
14 2
][M (H
2
O)
6
](SO
4
)
2
(M ¼ Mn, Fe, Co, Ni) (1e8).
Compound
1
2
3
4
5
6
7
8
Empirical formula
Formula weight
Temperature (K)
Space group
a (Å)
C
5
H
26MnN
2
O
14
S
2
C
5
H
26MnN
2
O
14
S
2
C
5
H
26FeN
2
O
14
S
2
C
5
H
26FeN
2
O
14
S
2
C
5
H
26CoN
2
O
14
S
2
C
5
H
26CoN
2
O
14
S
2
C
5
H
26NiN
2
O
14
S
2
5 2 14 2
C H26NiN O S
461.11
293(2)
457.34
293(2)
P2
6.62720(10)
11.0877(2)
12.6073(2)
101.9720(10)
906.24(3)
2
457.34
293(2)
P2
458.25
293(2)
P2
10.9270(10)
7.8540(10)
11.7870(10)
116.235(10)
907.36(16)
2
458.25
293(2)
P2
10.9444(4)
7.8602(3)
11.8020(4)
116.170(2)
911.19(6)
2
461.33
293(2)
P2
10.8770(3)
7.8576(2)
11.7446(2)
116.2890(10)
899.96(4)
2
461.33
293(2)
P2
10.8707(5)
7.8521(3)
11.7389(5)
116.3950(10)
897.55(7)
2
461.11
293(2)
P2
10.8343(2)
7.8405(2)
11.6769(3)
116.3890(10)
888.55(4)
2
1
(No. 4)
1
(No. 4)
1
(No. 4)
1
(No. 4)
1
(No. 4)
1
(No. 4)
1
(No. 4)
1
P2 (No. 4)
6.6276(2)
10.8320(10)
7.84220(10)
11.6735(2)
116.3880(10)
888.30(2)
2
b (Å)
c (Å)
11.0852(3)
12.6084(2)
101.974(2)
906.16(4)
2
b
(deg)
3
V (Å )
Z
r
calc, (g cm 3
ꢀ
)
1.676
1.676
1.677
1.670
1.702
1.725
1.723
1.724
L (Å)
m
0.71073
1.027
0.71073
1.027
0.71073
1.129
0.71073
0.0345
0.71073
1.254
0.71073
1.272
0.71073
1.396
0.71073
1.396
(mm 1
ꢀ
)
Flack parameter
ꢀ0.016(15)
ꢀ0.016(17)
ꢀ0.04(2)
0.020(9)
0.0345
0.0775
ꢀ0.015(10)
ꢀ0.013(13)
ꢀ0.036(15)
ꢀ0.001(9)
0.0218
0.0551
a
R
1
0.0294
0.0353
0.0388
0.0353
0.0309
0.0313
b
WR
2
0.0695
0.0955
0.0932
0.0864
0.0818
0.0727
a
R
wR
1
¼ SkF
o
rꢀF
c
k/SrF
o
r.
b
2
2
2
2
)2]1/2.
2
¼ [Sw(F
o
ꢀF
) /[Sw(F
c o

112
F. Hajlaoui et al. / Journal of Organometallic Chemistry 700 (2012) 110e116
Table 2
Selected bond lengths (Å) in compounds 1e8.
Compound
1
2
3
4
5
6
7
8
M(1)ꢀO
M(1)ꢀO
M(1)eO
M(1)eO
M(1)eO
M(1)eO
w
(1)
w
(2)
w
(3)
w
(4)
w
(5)
w
(6)
2.1639(2)
2.1880(2)
2.214(2)
2.1521(2)
2.1790(2)
2.1930(2)
2.150(2)
2.214(2)
2.188(2)
2.163(2)
2.195(2)
2.182(2)
2.110(3)
2.144(3)
2.128(2)
2.131(3)
2.101(3)
2.145(3)
2.1443(1)
2.1494(1)
2.1314(1)
2.1358(2)
2.1121(1)
2.1019(2)
2.1179(2)
2.0693(2)
2.0922(1)
2.1218(2)
2.0778(2)
2.0969(2)
2.119(2)
2.069(2)
2.0972(2)
2.118(2)
2.075(2)
2.0923(2)
2.054(2)
2.071(2)
2.047(3)
2.072(2)
2.065(2)
2.059(3)
2.0518(2)
2.0663(1)
2.0732(1)
2.0552(2)
2.0684(1)
2.0596(1)
range between 2.152(2) and 2.214(2) Å and between 2.150(2) and
.214(2) Å for 1 and 2, respectively. These values are in agreement
with the values calculated from the bond valence program
VALENCE [37] for a six-fold oxygen coordinated manganese atom,
Both 1 and 2 contain [Mn(H
[100] and [010] directions and are separated by SO
]2 cations stacked along the
þ
2 6
O)
2
ꢀ
2
4
anions and
cations, in 1 and 2, respec-
cation donates hydrogen bonds to six
ꢀ
groups, each of which accepts hydrogen bonds
2þ
2þ
2
N ]
either [R-C
tively. Each [Mn(H
adjacent (SO )
4
5
H
14
N
2
]
or [S-C
O) ]
6
5
H
14
2
þ
2
2
2
.211 Å in compounds 1 and 2, respectively. The cis-OeMneO
ꢁ
ꢁ
angles range from 86.21(8) to 95.77(8) in 1 and between
from at least two H
2
O ligands on the same Mn center. The [R-
ꢁ
ꢁ
2þ
2þ
8
6.31(9) to 95.89(9) in 2. While the trans-OeMneO angles
C
5
H
14
N
2
]
and [S-C
5
14
H N
2
]
cations also donate hydrogen bonds
ꢁ
2ꢀ
deviate from the ideal value by approximately 3 for the two
compounds.
to nearby (SO
4
)
groups, creating an extended, supramolecular
structure. The cation-anion distances range between 2.680(3) and
2
2
.800(3) Å for NeH/O interactions and between 2.666(3) and
.982(3) Å for O eH/O interactions in 1 and 2, respectively.
The [Mn(H O)
w
2
þ
cations are separated from one another
2
6
]
through two short, four intermediate and four long distances, with
approximate values of 6.627 ꢂ 2, 8.486 ꢂ 2, 8.577 ꢂ 2, 9.493 Å ꢂ 4.
These Mn/Mn distances are both shorter and longer than those
find in others analogous phases containing other diammonium
2þ
cations, 7.303 Å for diazabicyclo[2.2.2]octaneH
2
]
[36], and
þ
[1]. The trend in these distances
2
2
6.544 Å for [piperazineH ]
mirrors the sizes of the included organic cations. The Flack
parameters for these compounds refined to ꢀ0.016(15) and
ꢀ
0.016(17), indicating absolute configurations. The enantiomeric
structures are inverses of one another and are isostructural with
a related copper phase [5].
þ
]2 and [S-C
2þ
cations in
The presences of the [R-C
5
H
14
N
2
5
14
H N
2
]
compounds 1 and 2 were confirmed using infrared spectroscopy.
ꢀ1
CeH bands were observed at 1405 and 2955 cm , while NeH
ꢀ
1
bands were present 1612 and 3110 cm . A SeO band was centered
ꢀ
1
at 1105 cm
2
for compound 1. Analogous CeH (1409 and
ꢀ
1
ꢀ1
ꢀ1
953 cm ), NeH (1627 and 3213 cm ), SeO (1109 cm ) bands
were observed in 2.
Compounds 3e8 are all isostructural, with 3 and 4, 5 and 6 and 7
and 8 existing as enantiomeric pairs. Each contains a single unique
II
transition metal (M ¼ Fe, Co and Ni), a single organic cation and
II
two sulfate tetrahedra, all of which lie on general positions. The M
cations exhibit irregular, largely octahedral coordination environ-
w
ments, as shown in Fig. 4. The average MeO bond lengths
decrease from 2.128(3) to 2.062(2) Å, as one moves from iron to
nickel. This reflects a decrease in the ionic radius of nickel versus
w
iron. These MeO distances are provided in Table 2. These values
agree with calculated distances, based upon bond valence sums, in
2
þ
2þ
2þ
which the values of the Fe eOw, Co eOw and Ni eOw
distances are equal to 2.135 Å, 2.075 Å and 2.047 Å for 3, 4, 5, 6, 7
and 8, respectively.
II
2þ
cations stack along the [010] and [001]
The [M (H
2
O)
6
]
directions in 3e8, and form inorganic pseudo-layers with the
2
ꢀ
2þ
6
(SO
4
)
in the bc plane. See Fig. 2. The [M(H
2
O)
]
cations in 3e8
tetrahedra, as
2
ꢀ
donate hydrogen bonds to six adjacent (SO
4
)
shown in Fig. 4. The geometries of these interactions differ from
2
þ
compounds 1 and 2, as each [M(H
2
O)
6
]
cation is surrounded by
2
ꢀ
one monodentate two bidentate and two tridentate (SO
4
)
anions.
Fig. 1. Three-dimensional packing in (a) 1 and (b) 2. Selected hydrogen-bonding
interactions are shown as dashed lines. Purple, yellow, red, blue, black and white
represent manganese, sulphur, oxygen, nitrogen, carbon and hydrogen atoms,
respectively. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
2þ
2þ
As in compounds 1 and 2, the [R-C
5
H
14
N
2
]
and [S-C
5
H
)
14
N
2
]
2ꢀ
cations also donate hydrogen bonds to neighboring (SO
hedra. The NeH/O distances range between 2.733(3) and 2.925(4)
Å, while the O eH/O distances range between 2.664(3) and
4
tetra-
w

F. Hajlaoui et al. / Journal of Organometallic Chemistry 700 (2012) 110e116
113
Fig. 2. Three-dimensional packing in (a) for 3, 5 and 7 and (b) 4, 6 and 8. Selected hydrogen-bonding interactions are shown as dashed lines. Green, yellow, red, blue, black and
II
white represent metal (M ¼ Fe, Co and Ni), sulphur, oxygen, nitrogen, carbon and hydrogen atoms, respectively. (For interpretation of the references to colour in this figure legend,
the reader is referred to the web version of this article.)
2
.834(2) Å. These values agree with those currently observed in
inorganic salts containing the organic groups used in this work
5,7,38]. One again, extended, supramolecular structures are con-
structed from these molecular units by hydrogen-bonding.
[
II
Fig. 3. Neighbouring sulfates in the environment of [Mn(H
2
O)
6
] in 1 and 2. Purple,
2 6
Fig. 4. Neighbouring sulfates in the environment of [M (H O) ] in 3, 4, 5, 6, 7 and 8.
yellow, red and white represent manganese, sulphur, oxygen and hydrogen atoms,
respectively. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
Green, yellow, red and white represent manganese, sulphur, oxygen and hydrogen
atoms, respectively. (For interpretation of the references to colour in this figure legend,
the reader is referred to the web version of this article.)

114
F. Hajlaoui et al. / Journal of Organometallic Chemistry 700 (2012) 110e116
II
2þ
Each [M (H
2
O)
cations through two short, two intermediate and
two long distances. The average values of these distances are
.035(3), 7.091(3) and 7.851(3) Å. The Flack parameters are
6
]
octahedron is separated from six other
This transformation is accompanied by three peaks on the DTA
II
2þ
ꢁ
[
M (H
2
O)
6
]
curve, i. e. two exothermic peaks observed at 416 and 525 C and
ꢁ
one endothermic peak at 871 C.
7
[S-C
5
H
14
N
2
][Fe(H
2
O)
6
](SO
4
)
2
(4). The results of TG-DTA
][Fe(H O) ](SO are illustrated in
refined to ꢀ0.04(2), 0.020(9), ꢀ0.015(10), ꢀ0.013(13), ꢀ0.036(15)
measurements for [S-C
5
H
14
N
2
2
6
4 2
)
and ꢀ0.001(9) for 3e8, respectively.
Fig. 5b. The TG curve shows that the compound is stable to
2
þ
2þ
ꢁ
The presence of [R-C
5
H
14
N
2
]
and [S-C
5
H
14
N
2
]
cations was
approximately 105 C. The first transformation occurs in the
ꢁ
confirmed using infrared spectroscopy with average positions of
453 and 2849 cm for CeH bands, 3155 cm for NeH and OeH
bands and 1113 cm for SeO bands.
The thermal properties of compounds 1e8 were probed using
thermogravimetric (TG) and differential thermal analyses (DTA).
Data were collected on one compound in each enantiomeric pair
was studied, as little or no variability is expected between analo-
gous compounds. See Fig. 5.
temperature range 105e145 C. The weight loss of 5.834% is in
ꢀ
ꢀ
1
ꢀ1
1
2
agreement with the departure of 1.5$H O molecules (calculated
1
weight loss, 5.892%). This phenomenon is accompanied with an
ꢁ
endothermic peak on the DTA curve, at 125 C. The second weight
ꢁ
loss of 17.532%, observed between 145 and 215 C, (endothermic
ꢁ
peak at 171 C on the DTA curve) corresponds to the departure of
the last water molecules (calculated weight loss, 17.676%), leading
5 14 2 4 2
to the anhydrous phase [S-C H N ]Fe(SO ) . The decomposition of
ꢁ
[S-C
5
H
14
N
2
][Mn(H
2
O)
6
](SO
4
)
2
(2). Fig. 5a shows the TG-DTA
the anhydrous phase starts at about 280 C and leads to crystalline
ꢁ
curves obtained during the decomposition of compound 2 in the
temperature range 25e1000 C. The TG curve shows that the first
weight loss of 6.734% starts at about 90 C and corresponds to the
departure of 1.75$H
Fe
2
(SO
4
)
3
(PDF N 01-073e0148). This result is evidenced by
ꢁ
a weight loss of 48.033% (calculated weight loss, 47.771%). The
ꢁ
decomposition of Fe
and 670 C, in agreement with the global formula Fe
2
(SO
4
)
3
leads to stage observed between 500
(SO ). These
ꢁ
2
O molecules (calculated weight loss, 6.8887%).
2
O
2
4
The second weight loss, observed on the TG curve between 128
and 203 C, is attributed to departure of the remaining water
phenomena are accompanied by several endothermic peaks on the
ꢁ
ꢁ
DTA curve between 300 and 690 C). The last transformation starts
ꢁ
molecules to form the anhydrous compound [S-C
5
H
14
N
2
]Mn(SO
4
)
2
.
at about 700 C and corresponds to the formation of iron oxide
These phenomena are accompanied by two endothermic peaks on
the DTA curve, with a maximum at 211 C. The amine decompo-
2 3
Fe O .
ꢁ
[S-C
5
H
14
N
2
][Co(H ](SO
2
O)
6
4 2
) (6). The TG-DTA curves of [S-
sition together with loss of one sulfate group ([S-C
gives rise to the manganese sulfate at w401 C (observed weight
loss, 42.932%; theoretical, 43.308%). This phenomenon is accom-
5
H
14
N
2
]$SO
4
)
C
5
H
14
N
2
][Co(H O) ](SO ) , between room temperature and
2
6
4 2
ꢁ
ꢁ
1000 C, are shown in Fig. 5c. According to the TG curve the
dehydration of the precursor occurs in two stages. First, an
immediate weight loss of 3.866% observed at 139 C corresponds to
the departure of only one water molecule (calculated weight loss,
3.901%). The second stage of the dehydration takes place between
ꢁ
ꢁ
panied by two endothermic peaks on the DTA curve, at 334 C and
ꢁ
ꢁ
3
9
70 C, respectively. The last step takes place between 410 and
10 C and corresponds to the decomposition of MnSO to Mn O .
4 2 3
II
, MII ¼ Mn (2), Fe (4), Co (6) and Ni (8).
Fig. 5. DTA-TG curves of thermal decomposition of [S-C
5
14
H N
2
][M (H
2
O)
6
](SO
4
)
2

F. Hajlaoui et al. / Journal of Organometallic Chemistry 700 (2012) 110e116
115
ꢁ
1
54 and 219 C, and corresponds to the loss of the remaining water
Second, they act as hydrogen bond donors and participate in the
molecules (observed weight loss, 19.735%; calculated weight loss,
supramolecular extended structures of compounds 1e8. Third, the
2
þ
2þ
2
19.508%) giving rise to the anhydrous compound [S-C
5
14
H N
2
]
chirality of [R-C H
5 14
N
2
]
and [S-C
5
H
14
N
]
cations is reflected in
Co(SO . These phenomena are accompanied by two endothermic
4
)
2
the extended symmetry of the resulting compound. The presence
of such cations precludes the cancellation of the local distortions
via formation of inversion centers because inversion symmetry
ꢁ
peaks on the DTA curve, maximum at 180 C. The next trans-
ꢁ
formation starts at w295 C and corresponds to the decomposition
2
þ
of the amine entity and partial decomposition of the sulfate groups
would require the presence of both [R-C
C H N ]
5 14 2
each enantiomer can be chemically controlled; if [R-C H N ]
5 14 2
5
H
14
N
2
]
and [S-
þ
cations in the structures. The presence or absence of
2
leading to the CoSO
4
phase (observed weight loss, 41.988%; calcu-
2
þ
lated weight loss, 42.933%). This transformation is accompanied, on
the DTA curve, by two endothermic peaks and one exothermic peak
cations alone are present in a structures, they can never be related
to one another through centers of inversion because the required
ꢁ
ꢁ
ꢁ
observed at 326 C, 365 C and 387 C, respectively. The last stage
2
þ
corresponds to the decomposition of the cobalt sulfate, starting at
[S-C
5
H
14
N
2
]
cations are absent. In addition, the mild conditions
ꢁ
about 780 C, and gives rise to the cobalt oxide Co
3
O
4
.
used in the experiments described above preclude inversion of the
amine chiralities. Therefore the formation of any inversion centers
is prohibited and the space group of these materials is constrained
to be noncentrosymmetric, as shown in Fig. 6. The chirality of the
5 14 2 2 6 4 2
[S-C H N ][Ni(H O) ](SO ) (8). Coupled TG-DTA curves for
compound 8 are shown in Fig. 5d. The first two weight losses of
ꢁ
9
.723 and 13.594, observed at 155 and 223 C, are accompanied by
2
þ
2þ
to endothermic peaks. They are ascribed to the release of 2.5$H
calculated weight loss, 9.759%) and 3.5H O (calculated weight loss,
3.663%) molecules found in the structure. The degradation of the
2
O
[R-C
H
5 14
N
2
]
and [S-C
5
H
14
N
2
]
cations is reflected in the enan-
).
(
2
tiomorphic and polar crystal class of these compounds, 2 (C
2
1
The possibility of pseudosymmetry in compounds 1e8 was
investigated. The organic cations were removed from the crystal-
lographic models, and PLATON [39] was used to probe for missing
symmetry. The ADDSYM command suggests the possibility of
ꢁ
organic part with one sulfate group occurs between 277 and 485 C
observed weight loss, 42.654%, calculated weight loss, 42.955%).
(
This transformation is evidenced by high exothermic peak
ꢁ
observed on DTA, in the range 284e400 C. Above this temperature
1
a missing additional symmetry leading to the P2 /c space
NiSO
4
is formed. The last stage corresponds to the decomposition of
group (No. 14), with inversion symmetry directly between the
metal centers. The position of the methyl groups on the 2-
methylpiperazinediium cations rings violates the pseudosymme-
try found by PLATON, does not recognize the contribution of
ꢁ
nickel sulfate to NiO, starting at about 548 C.
4
. Discussion
a single eCH
systematic absences are not correct for P2
3
group over the rest of the structure. In addition, the
/c. Specifically, the ex-
Compounds 1e8 were obtained by slow evaporation of solutions
1
containing either R-2-methylpiperazine or S-2-methylpiperazine,
in an effort to force crystallization in a noncentrosymmetric space
group. This technique has been used with success in a variety of
systems [5,17,38]. The role of 2-methylpiperazinediium cations in
these reactions is three-fold. First, they assume the well-
established role of protonated amines in which they help achieve
charge neutrality with the other charged inorganic moieties.
pected l ¼ 2nþ1 absences in h0l reflections are not present. These
results confirm the crystallographic noncentrosymmetry in
compounds 1e8.
Despite the clear similarities between compounds 1e8, distinct
differences exist. Notably, the local hydrogen-bonding around the
2
þ
centers differs between structure types. In compounds
[M(H
2
O)
6
]
2ꢀ
2þ
6
1 and 2, six (SO
4
)
anions coordinate to each [Mn(H
2
O)
]
cation
Fig. 6. Cation structures in 1e8. The symmetry element is shown. Blue and black represent nitrogen and carbon atoms, respectively. Transition metal, oxygen, sulphur and hydrogen
atoms have been removed for clarity. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

116
F. Hajlaoui et al. / Journal of Organometallic Chemistry 700 (2012) 110e116
)2 anions that
ꢀ
Acknowledgment
in a bidentate fashion. In contrast, the six (SO
4
2þ
coordinate to each [M(H
compounds 3e8 include two (SO
2 6
O) ]
(M ¼ Fe, Ni, Co) cation in
2
ꢀ
4
)
anions that accept just
Grateful thanks are expressed to Dr. T. Roisnel (Centre de Dif-
fractométrie X, Université de Rennes I) for the assistance in single-
crystal X-ray diffraction data collection. A.J.N. acknowledges the
Henry Dreyfus Teacher-Scholar Awards program.
a single hydrogen bond from the cation. See Figs. 3 and 4. This
change in the hydrogen-bonding structure affects the three-
dimensional packings of the compounds. Indeed, Compounds 1 and
2
adopt a distinctly different packing arrangement with respect to
compounds 3e8. See Figs. 1 and 2. Both differences can be attrib-
uted to a gradual decrease in the ionic radius of the metal as one
Appendix A. Supplementary material
move from Mn to Ni. Compounds 1 and 2 contain the largest
CCDC 823970e823977; contain the supplementary crystallo-
graphic data for tables of hydrogen bond details for all compounds.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
II
transition metal cations, Mn , from which the longest MeO
are observed, see Table 2. In these compounds, six (SO )
4
w
bonds
ꢀ
anions
2
are able to fit around each cation. As the ionic radius of the metal
centers decrease in Fe, Co and Ni, a corresponding decrease in
2
þ
MeO
become smaller, the six (SO
the same hydrogen-bonding structure and a shift in connectivity is
w
bond lengths is observed. As the [M(H
2
O)
ꢀ
anions are no longer able to adopt
6
]
cations
2
4
)
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