Crystal synthesis of hybrid organometallic-inorganic hydrogen bonded salts of acid oxoanions

Article abstract of DOI:10.1039/b400667d

Partially deprotonated inorganic oxoanions derived from sulfuric and phosphoric acids have been used to assemble organometallic cations in inorganic-organometallic hybrid systems. The organometallic sandwich cations [(η⁵-C₅H₅

Full text of DOI:10.1039/b400667d

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F U L L P A P E R
Crystal synthesis of hybrid organometallic–inorganic hydrogen
bonded salts of acid oxoanions
Dario Braga,*a Marco Curzi,a Lucia Maini,a Marco Politoa and Fabrizia Grepioni*b
a
Dipartimento di Chimica G. Ciamician, Università di Bologna, Via Selmi 2, 40126, Bologna,
Italy. E-mail: dario.braga@unibo.it
Dipartimento di Chimica, Universita’di Sassari, Via Vienna 2, 07100, Sassari, Italy.
b
E-mail: grepioni@ssmain.uniss.it
Received 15th January 2004, Accepted 18th June 2004
First published as an Advance Article on the web 8th July 2004
Partially deprotonated inorganic oxoanions derived from sulfuric and phosphoric acids have been used to assemble
organometallic cations in inorganic–organometallic hybrid systems. The organometallic sandwich cations [(5-C5H5)2Co]+,
[(5-C5Me5)2Co]+ and [(5-C5Me5)2Fe]+ have been used because they do not interfere with hydrogen bonding formation
forcing self-assembling of the inorganic acids anions HSO4− and H2PO4− into hydrogen bonded mono- and bi-dimensional
networks.
Hydrogen bonding interactions between ions have been a subject of
continuing investigations in solution1 and in the solid state2 as well
as of theoretical studies by both empirical and ab initio methods.3
More recently hydrogen bonds (HB) between ions have begun to be
systematically utilised in the crystal engineering of new materials,
with remarkable achievements.4,5 The reason for this interest stems
from the fact that HB between ions combine the strength of the
Coulombic field generated by the ions with the directionality and
reproducible topology of hydrogen bonding interactions.6
two crystalline materials composed of pyridine and formic acid of
different composition and different location of the H-atom in the
OHN bond. In a recent study, we have investigated proton
location in O–HN bonds by a combination of X-ray and solid-
state NMR spectroscopy.14
Because of this combination of practical and academic interests,
we have undertaken a systematic study of the preparation, charac-
terization and, possibly, evaluation of hybrid systems formed by
inorganic acid oxoanions and organometallic cations.
Considerable efforts have been made to correlate concepts such
as acidity and basicity to HB formation and stability.7 Correlations
between pK of the acids and HB distances are available.8 It has
been recently argued, however, that hydrogen bonding ability can
be better appreciated by examining the charge distribution in the HB
system rather than its acid–base chemistry.9
In this first paper we report the investigation of hydrogen
sulfate and dihydrogen phosphate salts of the organometallic
sandwich cations [(5-C5H5)2Co]+, [(5-C5Me5)2Co]+ and [(5-
C5Me5)2Fe]+. In particular, we will discuss the structures and
hydrogen bonding interactions in the hydrogen sulfate systems
[(5-C5Me5)2Co][H3O]2[SO4HSO4]·2H2O, 1Co, [(5-C5Me5)2Fe]-
[H3O]2[SO4HSO4]·2H2O, 1Fe and [(5-C5Me5)2Fe]2[H3O][HSO4]3
2Fe, as well as in the dihydrogen phosphate systems [(5-
A field of potential practical applications of HB between ions is
that of protonics and superprotonic conductivity exploited in fuel
cell technology. The existence of different configurations of the
hydrogen atom location within O–HO systems is at the basis
of the possibility of constructing proton conducting materials.
These materials, in particular those based on solid-acid salts such
as CsHSO4, Rb3H(SeO4)2, etc.10a have applications in a number
of devices such as H2 and H2O sensors, fuel and steam cells and
high energy density batteries. The solid-acid salts derived from
polyprotic acids such as H3PO4 and H2SO4 by partial deprotonation
all show the presence of strong inter-anionic hydrogen bonding
association. At high temperature, these systems often undergo
an order–disorder phase transition, denoted a superprotonic
transition, which is associated with a dramatic increase of the
conductivity.10b,c For this reason, and because they are thermally
stable (up to 500–550 K), they have been recently begun to be
exploited as solid fuel cell electrolytes. Hybrid anionic systems,
such as Cs2(HSeO4)(H2PO4), have also begun to be investigated.11
The phenomenon of superprotonic conductivity is explained with
the possibility of proton jumps from one anion to the nearby one
associated with the onset of the reorientational motion of the oxo-
acid anions.
Another aspect of interest of HB between ions arises from the
consideration that proton transfer processes in hydrogen bonding
interactions, whether associated with a phase transition or not, may
imply the transformation of a molecular crystal into a molecular
salt. Wilson12 has discussed, on the basis of an elegant neutron dif-
fraction study, the migration of the proton along an O–HO bond
in a co-crystal, urea–phosphoric acid (1:1), whereby the proton
migrates towards the mid-point of the hydrogen bonding interac-
tion as the temperature is increased, becoming essentially centred at
T = 335 K. Mootz and Wiechert,13 on the other hand, have isolated
C5Me5)2Co][H3PO4][H2PO4],
3Co,
[(5-C5Me5)2Fe][H3PO4]-
[H2PO4], 3Fe and [(5-C5H5)2Co]H3PO4][H2PO4], 4Co. The choice
of using sandwich cations derived from cobaltocene, decamethyl-
cobaltocene and ferrocene is dictated by the well known stability
of these cations and by the structural non-rigidity of these systems
and of their parent neutral molecules in the solid state.15 Further-
more, these sandwich cations do not carry functional groups able to
compete in the formation of strong hydrogen bonding interactions
because the periphery is covered by C–H groups that can only take
part in C–HO hydrogen bonding interactions with the oxoan-
ions. This characteristic is required in order to force inter-anionic
hydrogen bonding formation between the inorganic anions, which
is a prerequisite for the desired proton mobility. The inter-anionic
hydrogen bonding motifs will be compared with those observed in
other organometallic salts of the same anions.
Results and discussion
In view of their structural similarity the compounds listed below
will be discussed in two separate subsets, those derived from sulfu-
ric acid and those derived from phosphoric acid. Relevant hydrogen
bonding parameters are listed in Table 1.
Hydrogen bonding patterns and crystal structures of [(5-
C5Me5)2Co][H3O]2 [SO4HSO4]·2H2O, 1Co, [(5-C5Me5)2Fe]-
[H3O]2[SO4HSO4]·2H2O, 1Fe and [(5-C5Me5)2Fe]2[H3O]-
[HSO4]3, 2Fe
Compounds 1Co and 1Fe possess the same stoichiometry and
show the same hydrogen bonding patterns in their solids. The two
crystals can be described as constituted of layers containing the
2 4 3 2
D a l t o n T r a n s . , 2 0 0 4 , 2 4 3 2 – 2 4 3 7
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Table 1 Relevant hydrogen bonding parameters
Compound
Interaction
O–H/Å
HO/Å
OO/Å
O–HO/°
Operators for generating equivalent atoms
1Co
O1–H100O1(I)
O5–H500O2
O5–H501O3(II)
O5–H502O6
O6(III)–H600O4
O6–H601O4(IV)
1.26
1.26
2.519(4)
2.546(4)
2.572(4)
2.438(4)
2.702(3)
2.718(3)
180
−x + 1, −y + 1, −z + 1
−x + 1, y, −z + 1
1.16(13)
0.72(5)
1.12(10)
0.86(5)
0.73(5)
1.40(13)
1.96(5)
1.33(10)
1.87(5)
2.00(5)
168(10)
143(5)
172(9)
161(5)
169(4)
−x + 1, y + 1/2, −z + 3/2
−x + 1, y − 1/2, −z + 3/2
1Fe
O1–H100O1(I)
O5–H500O2
O5–H501O3(II)
O5–H502O6
O6(III)–H600O4
O6–H601O4(IV)
1.26
1.26
2.515(5)
2.555(5)
2.433(6)
2.554(6)
2.705(5)
2.718(5)
180
−x + 1/2, −y + 3/2, −z
0.80(8)
0.88(7)
1.12(8)
0.83(5)
0.74(5)
1.78(8)
1.72(8)
1.31(8)
1.93(5)
2.00(5)
160(9)
157(8)
173(8)
157(5)
165(5)
−x + 1/2, −y + 1/2, −z
−x + 1/2, y + 1/2, −z + 1/2
−x + 1/2, y − 1/2, −z + 1/2
2Fe
O1O8
O3O13
O4O5
O7O13′
2.52(1)
2.51(1)
2.63(1)
2.77(2)
−x + 1/2, y + 1/2, −z + 1/2
3Co
O1′–H100O5
O2–H200O6
O3′–H300O6
O7–H700O5
O8–H800O4
0.71(10)
0.84(7)
0.75(9)
0.96(14)
0.75(10)
1.82(9)
1.76(7)
1.80(8)
1.64(14)
1.80(9)
2.531(9)
2.559(8)
2.553(8)
2.606(8)
2.550(9)
176(9)
159(8)
173(8)
176(9)
177(10)
x − 1/2, y + 3/2, z − 1/2
x − 1/2, y + 3/2, z − 1/2
3Fe
O1′–H100O5
O2–H200O6
O3′–H300O6
O7–H700O5
O8–H800O4
0.94(6)
0.92(6)
0.92(7)
0.80(7)
0.97(7)
1.59(5)
1.64(6)
1.66(7)
1.80(7)
1.59(6)
2.527(4)
2.549(4)
2.565(4)
2.590(4)
2.548(5)
174(6)
165(5)
166(6)
171(8)
172(5)
x − 1/2, y + 3/2, z − 1/2
x − 1/2, y + 3/2, z − 1/2
4Co
O1–H100O3″
O2–H200O8
O4–H400O5′
O6–H600O5′
O7–H700O3″
1.00
0.82
0.94
1.16
0.98
1.57
1.62
1.65
1.46
1.62
2.565(4)
2.431(3)
2.562(4)
2.591(4)
2.587(4)
171
171
163
163
169
−x + 2, y + 1/2, −z + 1
−x + 1, y + 1/2, −z + 1
−x + 1, y + 1/2, −z + 1
−x + 2, y + 1/2, −z + 1
COVYUH10a
EDUQUP
O3O3′
O1–H21O4′
O2–H22O3″
—
0.62(3)
0.63(3)
—
1.94(3)
2.01(3)
2.679
2.559(2)
2.640(2)
—
175(3)
179(2)
−x + 1, −y, −z + 1
x, −y + 1/2, z − 1/2
x, −y + 1/2, z + 1/2
LELXIJ
O2–H11O1″
O4O5′
1.03
—
1.58
—
2.576(4)
2.792
162
—
x, −y + 1, z + 1/2
−x + 1, −y, −z
YIGYUIa
a No H atom coordinates for the anions are present in the database files.
organometallic cations alternated with inorganic layers (see Fig. 1).
The two crystalline salts, though similar, are not isomorphous, the
difference arising from the relative disposition of the inorganic
layers. As shown in Fig. 1, while in compound 1Co the layers are
“anti parallel”, in 1Fe the layers are “parallel” and slightly shifted
with respect to those in 1Co.
The sulfate and hydrogen sulfate anions are not distinguishable,
since the proton lies on a crystallographic inversion centre; they
form a dimer with a short interanionic hydrogen bonding interaction
[OO 2.519(4) and 2.515(5) Å for 1Co and 1Fe, respectively] so
that the anionic moiety can be better described as the superanion
[SO4HSO4]3−.
The two solvate moieties, containing the remaining two inde-
pendent oxygen atoms, are constituted by a water molecule and
an oxonium ion. Although the OO distances of 2.438(4) and
2.433(6) Å in 1Co and 1Fe, respectively, would be consistent with
the presence of an [H5O2]+ unit,16 the overall network of intermo-
lecular connections and the distribution of the hydrogen atoms sug-
gest the presence of an [H3O]+ cation and of a water molecule. The
oxonium ion interacts via hydrogen bonding with the anions [OO
distances in the range 2.546(4)–2.572(4) and 2.554(6)–2.555(5) Å
for 1Co and 1Fe, respectively], while the water molecule, in the
addition to the short hydrogen bonding interaction with the oxo-
nium ion mentioned above, forms significantly longer hydrogen
bonding interactions with the superanions [SO4HSO4]3− [OO
distances in the range 2.702(3)–2.718(3) and 2.705(5)–2.718(5) Å
for 1Co and 1Fe, respectively].
hydrogen bonding rings (see Fig. 2). In the following, we have
adopted the graph-set notation system17 as a tool to describe the
differences in the hydrogen bonding pattern.
The three ring motifs are indicated by different colours in
Fig. 2. The ring evidenced in yellow and marked with “1” is,
in graph set notation, of the R44(12) type, and is formed by the
[SO4HSO4]3− and [H3O]+ ions and a water molecule. There are
four different hydrogen bonds within the ring: three short ones in
the [SO4HSO4]3− unit [OO distances 2.519(4) and 2.515(5) Å
for 1Co and 1Fe, respectively], between [H3O]+ and [H2O] [OO
distances 2.438(4) and 2.433(6) Å for 1Co and 1Fe, respectively],
and between [H3O]+ and the anion [OO distances 2.572(4) and
2.555(5) Å for 1Co and 1Fe, respectively], and a long one between
the water molecule and the [SO4HSO4]3− unit [OO distances
2.702(3) and 2.705(5) Å for 1Co and 1Fe, respectively]; the ring
evidenced in green and marked with “2” is again of the R44(12)
type, and is formed by two halves of [SO4HSO4]3− (with two oxy-
gen atoms for the sulfate moiety involved in the hydrogen bonds)
and two [H3O]+; two independent OO distances are present
[OO 2.546(4) and 2.572(4) for 1Co, 2.555(5) and 2.554(6) Å
for 1Fe]. The third ring, evidenced in light blue and indicated by
“3” is, in graph set notation, of the R45(12) type. It is constituted
of one [H3O]+ ion, two water molecules and two independent
sulfate anions, for a total of four different hydrogen bonds. The
[H3O]+ forms short hydrogen bonds with the sulfate anions and
the water molecule [OO distances 2.438(4) and 2.546(4) Å for
1Co, 2.433(6) and 2.555(5) for 1Fe]; one water molecule acts as
a bridge between the two sulfate anions [OO distances 2.702(3)
and 2.718(3) for 1Co, 2.705(5) and 2.718(5) for 1Fe]. The last
water molecule closes the ring linking the [H3O]+ ion and one
sulfate ion.
The inorganic ions and solvent molecules are interconnected by
means of a large number of hydrogen bonds. One of the possible
ways of describing the hydrogen bonding network is by focusing the
attention on the oxonium ion, which is involved in three different
D a l t o n T r a n s . , 2 0 0 4 , 2 4 3 2 – 2 4 3 7
2 4 3 3

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Fig. 3 Parallel “wavy” chains of inorganic moieties in crystalline [(5-
C5Me5)2Fe]2[H3O][HSO4]3 2Fe (top; H atoms not shown for clarity); the
hydrogen bonding pattern within a single chain (bottom). Only one of the
two images of the disordered anion is shown for clarity. Blue spheres repre-
sent the oxonium cations.
Fig. 1 Comparison between the layered hydrogen bonded structures
(view along the b-axis in both cases) in compounds [(5-C5Me5)2Co][H3O]2-
[SO4HSO4]·2H2O, 1Co (top) and [(5-C5Me5)2Fe][H3O]2[SO4HSO4]·2H2O,
1Fe (bottom). Note how the hydrogen oxoanion chains possess different rel-
ative orientations in the two crystals (H atoms not shown for clarity).
(see Experimental section), takes part in the formation of an R33(10)
ring, interacting both with the R22(8) ring system and the [H3O]+ cat-
ion. The oxonium cation is involved in three hydrogen bonds with
the three independent hydrogen sulfate anions. Unfortunately the
quality of the crystal did not allow location of the hydrogen atoms
belonging to the inorganic moieties.
Hydrogen bonding and crystal structures of [(5-C5Me5)2Co]-
[H3PO4][H2PO4], 3Co, [(5-C5Me5)2Fe][H3PO4][H2PO4], 3Fe
and [(5-C5H5)2Co]H3PO4][H2PO4], 4Co
Compounds [(5-C5Me5)2Co][H3PO4][H2PO4], 3Co and [(5-
C5Me5)2Fe][H3PO4] [H2PO4], 3Fe are isomorphous and their
crystal structures will be described together. As in the case of the
compounds discussed previously, the crystals can be described as
constituted of alternating layers of organometallic and inorganic
units. Fig. 4 shows the elegant network of hydrogen bonding:
phosphoric acids and [H2PO4]− anions are linked into rings of the
R22(8) type, and the rings are organized in a honeycomb structure,
completed by the presence of hydrogen bonded rings involving two
H3PO4 units. The large hexagonal rings can be described as R610(32)
in graph-set notation. OO distances are in the range 2.527(4)–
2.606(8) Å (see Table 1), with the longest values [2.606(8) and
2.590(4) Å for 3Co and 3Fe, respectively] observed for O–HO
interactions between the [H2PO4]− anions.
Compound 4Co possesses the same stoichiometry as 3Co and
3Fe, and again the crystal can be seen as formed by alternating
layers of organometallic cations and inorganic molecules/anions;
due to the smaller size of the cations, however, the hydrogen
bonding network within the inorganic layer is markedly different.
Fig. 5 shows how the layer is formed by alternated chains of H3PO4
molecules and [H2PO4]− anions. The lateral oxygen atoms are in-
volved in hydrogen bonds with adjacent chains.
In order to put the above analysis in the perspective of the
hydrogen bonding motifs observed in other organometallic salts
containing partially protonated oxoanions, the Cambridge Crystal-
lographic Data Base (ConQuest version 1.6, October 200318) has
been searched for organometallic systems containing dihydrogen
Fig. 2 The complex hydrogen bonding pattern forming the anionic layers
in crystalline 1Co and 1Fe.
The salt [(5-C5Me5)2Fe]2[H3O][HSO4]3 2Fe adopts a different
structure. The layered structure is lost in this salt; the hydrogen
sulfate anions and the oxonium cation form parallel “wavy”
chains in the crystal (see Fig. 3, top), with the organometallic
cations accommodated among the chains. Fig. 3 (bottom) shows
the hydrogen bonding pattern within a single chain. Two hydrogen
sulfate anions (S1 and S2) form rings of the R22(8) type, in graph set
notation [OO 2.52(1) and 2.63(1) Å], while the third anion (S3),
which is affected by rotational disorder around the S3–O9 bond
2 4 3 4
D a l t o n T r a n s . , 2 0 0 4 , 2 4 3 2 – 2 4 3 7

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Fig. 4 The honeycomb type hydrogen bonding network in compounds
[(5-C5Me5)2Co][H3PO4][H2PO4], 3Co and [(5-C5Me5)2Fe][H3PO4]-
[H2PO4], 3Fe. The elegant network of hydrogen bonding: phosphoric acids
and [H2PO4]− anions are linked into rings of the R22(8) type.
Fig. 6 Hydrogen bonding patterns involving the dihydrogen phosphate
and hydrogen sulfate anions in compounds (from top to bottom) CO-
VYUH10, EDUQUP, LELXIJ and YIGYUI (see Table 1 for relevant dis-
tances and angles). H atoms for COVYUH10 and YIGYUI are not present
in the database files.
Conclusions
In this paper we have reported the utilization of partially deprot-
onated inorganic oxoanions derived from sulfuric and phosphoric
−
−
acids, e.g. HSO4 and H2PO4 in the preparation of hybrid inor-
ganic–organometallic systems. The organometallic cations [(5-
C5H5)2Co]+, [(5-C5Me5)2Co]+ and [(5-C5Me5)2Fe]+ have been used
because they do not interfere in the formation of strong hydrogen
bonding interactions. This results in preferential association of the
inorganic acids anions HSO4− and H2PO4− into chains or honeycomb
type structures with or without the participation of water molecules.
The formation of hydrates in the case of HSO4− salts and of anhy-
drous crystals in the case of H2PO4− salts can be explained precisely
on the basis of the need to increase the number of hydrogen bond-
ing donors in the former case. The HSO4− anion possesses a total of
four acceptor sites and only one hydrogen bonding donor group. On
the other hand the presence of two donor groups in H2PO4− anions
brings about the possibility of hydrogen bonding ring formation
within extended structures. Although the species discussed herein
do not undergo a superprotonic phase transition, hence they are
not suitable for proton conductivity applications, it is clear from
this study that proton transfer via the mechanism associated with
reorientational motion of the tetrahedral inorganic cations would
be favoured by chain formation rather than by ring formation, since
this latter arrangement is much more stiff. On the other hand, an-
hydrous species would be preferable because water may interfere
with the proton transport. Work is in progress to explore the pos-
sibility of preparing mixed-cation and mixed-anion systems as well
as to prepare anhydrous crystalline systems by de-hydration of the
hydrated ones.
Fig. 5 Achain of H3PO4 molecules and [H2PO4]− anions in 4Co (top). The
lateral oxygen atoms are involved in hydrogen bonds with adjacent chains,
with formation of layers (bottom).
phosphate or hydrogen sulfate anions. Four compounds (identified
here by the relative CSD REFCODES: COVYUH10, EDUQUP,
LELXIJ and YIGYUI) have been found that respond to the criterion
that no hydrogen bonding interactions between the organometallic
cationic moieties and the anionic/neutral fragments are present.
Fig. 6 shows that basic packing motifs and the topology of the
hydrogen bonding interactions in these four crystal structures. It
can be seen that the dihydrogen phosphate anions salts EDUQUP
and LELXIJ form chains of eight-membered rings (Fig. 6(b) and
(c)), and that the eight-membered ring is also present in the hydro-
gen sulfate salt YIGYUI (Fig. 6(d)) while the dihydrogen phosphate
phosphoric acid salt COVYUH10 presents a more complex system
of interactions whereby a dimeric [H3PO4–H2PO4]− unit is hosted in
a channelled structure. The OO distances for these compounds
(see Table 1) are in the range observed for the compounds described
in the present work.
Experimental
Crystal synthesis
All products were purchased from Aldrich and used without further
purification.
Synthesis of 1Co. [(5-C5Me5)2Co] [0.235 g, 0.7 mmol] was
suspended in a solution of 14 ml of 0.1 M H2SO4 (1.4 mmol) and
80 ml of absolute ethanol and oxidized by stirring the suspension
in the presence of air for 24 h. The solution was filtered and the
volume reduced to 40 ml under low pressure. The solution was
D a l t o n T r a n s . , 2 0 0 4 , 2 4 3 2 – 2 4 3 7
2 4 3 5

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Table 2 Crystal data and details of measurements for all compounds
1Co
1Fe
2Fe
3Co
3Fe
4Co
Formula
M
System
Space group
Z
C20H41CoO12S2
596.58
Orthorhombic
Pccn
C20H41FeO12S2
593.50
Monoclinic
C2/c
C40H66Fe2O13S3
962.81
Monoclinic
P21/n
C20H35CoO8P2
524.35
Monoclinic
P21/n
C20H35FeO8P2
521.27
Monoclinic
P21/c
C10H15CoO8P2
384.09
Monoclinic
P21
4
4
4
4
4
2
a/Å
b/Å
c/Å
21.213(4)
7.680(2)
16.748(3)
90
2729(1)
1264
23.872(4)
7.755(7)
16.671(4)
117.03(1)
2749(3)
1260
9.923(1)
18.754(1)
24.377(2)
91.48(1)
4534.9(6)
20040
12.241(2)
17.457(4)
12.376(2)
115.72(2)
2382.6(8)
1104
12.27(8)
17.51(4)
12.33(2)
116.06(4)
2380(17)
1100
8.450(4)
9.431(2)
9.038 (2)
105.45(3)
694.2(4)
392
/°
V/Å3
F(000)
(Mo-K)/mm−1
 Range/°
Measured reflections
Unique reflections
Refined parameters
Gof on F2
R1 [on F, I > 2(I)]
wR2 (on F2, all data)
0.838
3–25
2751
2389
158
1.040
0.0413
0.1205
0.757
3–25
2490
2395
159
1.015
0.0401
0.1178
0.838
3–25
8029
7841
464
1.020
0.0782
0.2606
0.897
3–25
4385
4183
254
0.816
0.0598
0.2322
0.810
3–25
4394
4192
264
0.992
0.0526
0.1639
1.502
3–30
2244
2126
174
1.075
0.0285
0.0791
allowed to slowly evaporate to obtain yellow crystals suitable for
single crystal X-ray diffraction.
for structure solution and refinement based on F2. Non-hydrogen
atoms were refined anisotropically. HCH atoms in the organometallic
cations were added in calculated positions.
Synthesis of 1Fe and 2Fe. All attempts to obtain pure phases
of 1Fe and 2Fe were unsuccessful since the two phases crystal-
lize together. Fast crystallization favours formation of 1Fe. [(5-
C5Me5)2Fe] [0.295 g, 0.9 mmol] was dissolved in 50 ml of absolute
ethanol; 1 M H2SO4 [1.8 ml, 1.8 mmol] was added and the solution
was stirred in air overnight. The green solution obtained was re-
duced in volume to 30 ml, slow evaporation of the solvent at room
temperature yielded crystals of 1Fe and crystalline powder of 2Fe,
while slow evaporation at 4 °C (15 days) resulted in crystals of 1Fe
and crystalline powder of 2Fe. Unreacted [(5-C5Me5)2Fe] was re-
moved by washing the solid compounds with cyclohexane.
HOH atoms in 1Co, 1Fe, 3Co and 3Fe were located in the final
difference Fourier map and refined without constraints.
The Co atom in 1Co lies on a two-fold axis, while in 1Fe the
metal atom lies on an inversion centre. The asymmetric unit in 2Fe
contains one organometallic cation in a general position and two
half independent organometallic cations on independent inversion
centres. All C5Me5 groups were refined as rigid groups with fixed
geometry. In 2Fe one of the three hydrogen sulfate anions (S3) is
disordered over two positions (occupancy ratio 50:50) around the
unique S3–O9 bond. Due to the disorder, OO distances between
the hydrogen sulfate anion and the oxonium cation are poorly char-
acterized, and they are not discussed here. HOH atoms attached to O1
and O5 were added in calculated positions, while no attempt was
made to model the H atom belonging to the disordered hydrogen
sulfate anion and to the oxonium cation.
HOH atoms in 4Co were located in the final difference Fourier
map but not refined. The H3PO4 unit in 4Co presents a short distance
(1.506(2) Å) for one of the P–O single bonds; however, the shortest
P–O distance in the fragment (1.490(2) Å) is, as expected, the one
corresponding to the double bond. SCHAKAL9919b was used for the
graphical representation of the results. The program PLATON19c,d
was used to calculate the hydrogen bonding interactions reported
in Table 1.
Synthesis of 3Co. [(5-C5Me5)2Co] [0.230 g, 0.7 mmol] was
suspended in a solution of 1 M H3PO4 [1.4 ml, 1.4 mmol] and
80 ml of absolute ethanol and oxidized by stirring the suspension
in the presence of air for 24 h. The solution was filtered and the
volume reduced to 40 ml under low pressure. Slow evaporation of
the solution yielded yellow crystals suitable for single crystal X-ray
diffraction.
Synthesis of 3Fe. [(5-C5Me5)2Fe] [0.300 g, 0.9 mmol] was
dissolved in 80 ml of absolute ethanol; 1 M H3PO4 [1.8 ml, 0.18
mmol] was added, and the solution was stirred in air overnight.
The green solution obtained was reduced in volume to 30 ml. Slow
evaporation of the solution yielded dark green crystals suitable for
single crystal X-ray diffraction. Unreacted [(5-C5Me5)2Fe] was
removed by washing the crystals with cyclohexane.
CCDC reference numbers 228908–228913.
See http://www.rsc.org/suppdata/dt/b4/b400667d/ for crystallo-
graphic data in CIF or other electronic format.
For all species discussed in this paper powder diffractograms
were measured and compared with those calculated on the basis of
the single-crystal structure.
Powder diffraction data were collected on a Philips PW-1710
automated diffractometer and on an X’Pert Philips diffractometer;
both with Cu–K radiation and graphite monochromator. The
program PowderCell 2.220 was used for calculation of X-ray pow-
der patterns.
Synthesis of 4Co. [(5-C5H5)2Co] [0.265 g, 1.4 mmol] was
suspended in a solution of 1 M H3PO4 [2.8 ml, 2.8 mmol] and 80 ml
of absolute ethanol and oxidized by stirring the suspension in the
presence of air for 24 h. The solution was filtered and the volume
reduced to 40 ml. Slow evaporation of the solution yielded yellow
crystals suitable for single crystal X-ray diffraction.
DSC measurements. The thermal behaviour of compounds
1Co, 3Co, 3Fe and 4Co was characterized by DSC measurements.
No solid–solid phase transition was observed, up till melting was
reached. The melting points of the compounds are: 63 °C (1Co),
260 °C (3Co), 220 °C (3Fe), 146 °C (3Fe).
Acknowledgements
We thank MIUR, FIRB and the Universities of Bologna and Sassari
for financial support. We thank Prof. S. M. Haile for many useful
discussions and for the DSC measurements.
Crystal structure determinations. Crystal data of all com-
pounds were collected at room temperature on a Nonius CAD4
diffractometer. Crystal data and details of measurements are sum-
marised in Table 2. Common to all compounds: Mo-K radiation,
 = 0.71073 Å, monochromator graphite. SHELX9719a was used
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D a l t o n T r a n s . , 2 0 0 4 , 2 4 3 2 – 2 4 3 7
2 4 3 7