W. Rekik et al. / Inorganica Chimica Acta 359 (2006) 3954–3962
3961
IV may also be explained by the elongated Cu–Ow3 dis-
tance while the octahedron around Fe is quite regular, as
shown in transition metal selenates [40]. The structure of
IV (Cu) differs from that of I (Mn), but the onsets of
dehydration are similar for the two compounds. Indeed,
the hydrogen bonds formed with the sulfate groups are
comparable in the two structures. In addition, the amor-
phous anhydrous phases obtained from compounds III
and IV, which have similar structures, crystallise at high
temperature. Since no crystal structure is available for
0
20
40
60
80
4 12 2 2 6 4 2
(C H N )[Cu(H O) ](SO )
-
-
-
-
4 12 2 4 2
(C H N )Cu(SO )
CuSO
4
(
C H N )Cu(SO ) , no explanation can be given for that
4 12 2 4 2
1
/2Cu
2
O(SO
4 2
)
phenomenon.
CuO
The second feature is that the Mn, Co [19], Ni and Zn
25] phases belong to one structure type, while Fe and Cu
[
compounds belong to a second one, with a unit-cell volume
about half of the first-cited compounds. It is surprising
since there is no relation between the increase of ionic
0
200
400
600
800
1000
T (˚C)
2
+
2+
Fig. 8. TG curve for the decomposition of (C
IV) in air (15 ꢁC h ).
4
12 2 2 6 4 2
H N )[Cu(H O) ](SO )
radius of the cation from Mn to Zn and the structural
arrangement observed for these supramolecular sulfates.
ꢀ1
(
þ
On the contrary, the use of NH4 instead of piperazinedi-
and least-squares refinements of the 28 diffraction lines
available led to the unit cell dimensions a = 6.201(1) A,
ium with all transition metal sulfates gives rise to the iso-
structural Tutton’s salts structures [41–46]. Further
studies to understand the templating role of diamines in
the presence of transition metal sulfates are under way.
˚
˚
˚
b = 11.476(2) A, c = 12.352(3) A, a = 66.46(2)ꢁ, b =
3
˚
8
0.70(2)ꢁ, c = 84.60(2)ꢁ and V = 794.81 A [M20 = 57.5,
F28 = 121(0.0050, 46), refined zero-shift 0.047ꢁ (2h)].
Unfortunately, high background contribution and instabil-
ity of diffracted intensities did not allow further structural
investigations of the compound.
4. Conclusion
Four metal sulfate compounds templated by piperazine
have been synthesised and characterised by single crystal
X-ray diffraction, powder thermodiffractometry and ther-
mogravimetric analyses. The four structures consist of iso-
(
C H N )Cu(SO ) is not stable and decomposes into
4 12 2 4 2
CuSO (weight loss 64.7%). As shown in Fig. 7, some dif-
4
fraction lines appear to coexist with CuSO in the temper-
4
II
ature range 530–590 ꢁC. These are attributed to Cu OSO ,
lated M octahedrally coordinated by six water molecules,
2
4
as also evidenced by the weight loss of 72.8% (calc. 73.5%)
observed on the TG curve at the inflection. The final trans-
formation corresponds to the formation of copper oxide,
CuO, which crystallises immediately after Cu OSO starts
diprotonated piperazinium cations and sulfate anions
linked by hydrogen bonds only. Two structure types were
distinguished and described. The thermal behaviour of
the precursors is shown to be dependent not only on the
structure type but also on the transition metal atom
involved in the structure.
2
4
to decompose.
.3. Discussion
These studies show that there are similar changes in the
3
Acknowledgement
decomposition of precursors with somewhat small differ-
ences, which could be associated with the structural varia-
tions. The first noticeable point is related to the difference
of the dehydration temperatures that could be explained
by the nature of the metal as well as the hydrogen bonds
involved in the structures. For compound II (Ni), dehydra-
tion takes place at higher temperature than the three other
compounds, while its crystal structure is similar to that of I
The authors are indebted to G. Marsolier for his techni-
cal assistance in powder X-ray data collection.
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(
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[
2
+
is certainly due to the fact that [Fe(H O) ] forms hydro-
2
6
(
2ꢀ
gen bonds with eight sulfate anions, instead of six SO4
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