Synthesis, X-ray structures, electrochemistry, magnetic properties, and theoretical studies of the novel monomeric [CoI2(dppfO2)] and polymeric chain [CoI2(μ-dppfO2)n]

Article abstract of DOI:10.1039/B205942H

The new compound [Co(η⁵-C₅H₅)(dppf-P,P′)I]I, 1, was synthesised by the stoichiometric reaction of the Co(III) complex [Co(η⁵-C₅H₅)(CO)I₂], 2, with 1,1′-bis(diphenylphosphino)ferrocene (dppf) in CH₂Cl₂, and was characterised by multinuclear NMR spectroscopy. Exposure to air of THF or CH₂Cl₂ solutions of compound 1 gave, in an unexpected way, a polymeric chain comprising bridging 1,1′-bis(oxodiphenylphosphoranyl)ferrocene (dppfO₂) joining tetrahedral Co(II) units [CoI₂(μ-dppfO₂)]_n, 3. Attempts to obtain the polymeric chain 3 by the direct reaction of dppfO₂ with CoI₂, in CH₂Cl₂, gave instead the monomeric compound [CoI₂(dppfO₂)], 4, in which dppfO₂ is coordinated in a chelating mode. The structural characterisation of compounds 2, 3, and 4 was carried out by single crystal X-ray diffraction studies. The magnetic behaviour of [CoI₂(dppfO₂)] and [CoI₂(μ-dppfO₂)]_n was studied, and the results are consistent with tetrahedral S = 3/2 Co^II, possessing a ⁴A₂ ground state, and S = 0 Fe^II. In these compounds, Co^II negative zero field splittings were determined from an analysis of the magnetic susceptibility temperature dependence, with D/k = -13 and -14 K for CoI₂(dppfO₂) and [CoI₂(μ-dppfO₂)]_n, respectively. DFT calculations were performed in order to understand the electronic structure of [Co(η⁵-C₅H₅)(dppf-P,P′)I]I, 1, as well as that of the paramagnetic specie [CoI₂(dppfO₂)], 4. The [CoI₂(μ-dppfO₂)]_n chain was also analysed and found to behave very similarly to the monomeric iodine derivative 4. The calculations showed the unpaired electrons to be localized on the Co(II) centre in all these species. The rather complicated electrochemical behaviour exhibited by the dppf complex [Co^III(η⁵-C₅H₅)(dppf-P,P′) I]I and by [Co(dppfO₂)I₂] is discussed.

Full text of DOI:10.1039/B205942H

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Synthesis, X-ray structures, electrochemistry, magnetic properties,
and theoretical studies of the novel monomeric [CoI2(dppfO2)] and
polymeric chain [CoI2(ꢀ-dppfO2)n]
Teresa Avilés,a António Dinis,a José Orlando Gonçalves,a Vitor Félix,b Maria José Calhorda,c,d
Ângela Prazeres,c Michael G. B. Drew,e Helena Alves,f Rui T. Henriques,g Vasco da Gama,f
Piero Zanelloh and Marco Fontanih
a Departamento de Química, Centro de Química Fina e Biotecnologia,
Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica,
Portugal. E-mail: tap@dq.fct.unl.pt
b Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
E-mail: vfelix@dq.ua.pt
c ITQB, UNL, Apartado 127, 2781-901Oeiras, Portugal. E-mail: mjc@itqb.unl.pt.
d Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa,
1749-016 Lisboa, Portugal
e Department of Chemistry, University of Reading, Whiteknights, Reading, UK RG6 2AD
f Departamento de Química, Instituto Tecnológico e Nuclear, Est. Nacional 10,
P-2686-953 Sacavém, Portugal
g Departamento de Engenharia Química, Instituto Superior Técnico, Av. Rovisco Pais,
P-1049-001 Lisboa, Portugal
h Dipartimento di Chimica dell’Università di Siena, Via Aldo Moro, 53100 Siena, Italy
Received 19th June 2002, Accepted 2nd October 2002
First published as an Advance Article on the web 14th November 2002
The new compound [Co(η5-C5H5)(dppf-P,PЈ)I]I, 1, was synthesised by the stoichiometric reaction of the
Co() complex [Co(η5-C5H5)(CO)I2], 2, with 1,1Ј-bis(diphenylphosphino)ferrocene (dppf ) in CH2Cl2, and was
characterised by multinuclear NMR spectroscopy. Exposure to air of THF or CH2Cl2 solutions of compound 1
gave, in an unexpected way, a polymeric chain comprising bridging 1,1Ј-bis(oxodiphenylphosphoranyl)ferrocene
(dppfO2) joining tetrahedral Co() units [CoI2(µ-dppfO2)]n, 3. Attempts to obtain the polymeric chain 3 by the
direct reaction of dppfO2 with CoI2, in CH2Cl2, gave instead the monomeric compound [CoI2(dppfO2)], 4, in which
dppfO2 is coordinated in a chelating mode. The structural characterisation of compounds 2, 3, and 4 was carried
out by single crystal X-ray diffraction studies. The magnetic behaviour of [CoI2(dppfO2)] and [CoI2(µ-dppfO2)]n was
studied, and the results are consistent with tetrahedral S = 3/2 CoII, possessing a 4A2 ground state, and S = 0 FeII. In
these compounds, CoII negative zero field splittings were determined from an analysis of the magnetic susceptibility
temperature dependence, with D/k = Ϫ13 and Ϫ14 K for CoI2(dppfO2) and [CoI2(µ-dppfO2)]n, respectively. DFT
calculations were performed in order to understand the electronic structure of [Co(η5-C5H5)(dppf-P,PЈ)I]I, 1, as
well as that of the paramagnetic specie [CoI2(dppfO2)], 4. The [CoI2(µ-dppfO2)]n chain was also analysed and found
to behave very similarly to the monomeric iodine derivative 4. The calculations showed the unpaired electrons to be
localized on the Co() centre in all these species. The rather complicated electrochemical behaviour exhibited by the
dppf complex [CoIII(η5-C5H5)(dppf-P,PЈ)I]I and by [Co(dppfO2)I2] is discussed.
or THF solutions gave rise unexpectedly to a new poly-
meric coordination compound of Co() of formulation
Introduction
Ferrocenylphosphine ligands are currently attracting much
attention, mainly because their complexes have applications in
homogeneous catalysis and for their potential as redox active
ligands. Their usefulness is related to the variety of bonding
modes they can exhibit, ranging from chelating one single metal
centre, to bridging two or more metals. All these modes are
well documented. For instance, 1,1Ј-bis(diphenylphosphino)-
ferrocene (dppf ) has been shown to coordinate metal fragments
with different geometries and electron counts.1
In this work, the coordinating ability of the bulky dppf
ligand towards Co() precursor complexes was investigated.
Some Co() complexes containing dppf have already been
reported.2 In the reaction of the Co() complex [Co(η5-C5H5)-
(CO)I2] with dppf in CH2Cl2, the new compound [Co(η5-C5H5)-
(dppf-P,PЈ)I]I, 1, was formed. Upon exposure to air, CH2Cl2
[CoI2(µ-dppfO2)]n, 3. There are few transition metal complexes
containing dppfO2 as a ligand; only some Cu() and Cu()
complexes have been described.3 Attempts were made to obtain
the polymeric chain [CoI2(µ-dppfO2)]n by the direct reaction of
CoI2 and dppfO2, but, instead, the monomeric compound
[CoI2(dppfO2)], 4, in which dppfO2 is coordinated to Co() in a
chelating mode, was formed. Two different coordination modes
of the ligand dppfO2, bridging and chelating, are illustrated in
this work. The two compounds were structurally characterised
by single crystal X-ray diffraction techniques, and their mag-
netic properties were studied. DFT4 calculations (ADF pro-
gram)5 were performed on several mononuclear species and on
a model of the [CoI2(µ-dppfO2)]n chain, in order to understand
the nature of the frontier orbitals and the properties of these
compounds, also in connection with their redox propensity. The
DOI: 10.1039/b205942h
J. Chem. Soc., Dalton Trans., 2002, 4595–4602
This journal is © The Royal Society of Chemistry 2002
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tight-binding approach6 within the extended Hückel method
Table 1 Selected bond lengths (Å) and angles (Њ) for complexes 2, 3,
and 4
was used to study the one-dimensional chain.7
[CoCp(CO)I2], 2
Results and discussion
Co–I
2.565(3)
94.0(1)
Co–C(1)
1.764(9)
Chemical studies
I–Co–IЈ
I–Co–C(1)
Co–C(1)–O(1)
89.1(2)
179.8(9)
The reaction of equimolar quantities of [Co(η5-C5H5)(CO)I2],
2, and dppf in CH2Cl2 at room temperature yields brown–red
crystals of the new compound [Co(η5-C5H5)(dppf-P,PЈ)I]I, 1,
(see Scheme 1) in ca. 80% yield (η5-C5H5 = Cp).
[CoI2(µ-dppfO2)]n, 3
Co–I(1)
Co–I(2)
P(1)–O(1)
2.585(3)
2.517(3)
1.497(9)
Co–O(1)
Co–O(2)
P(2)–O(2)
1.956(9)
1.940(8)
1.519(8)
I(1)–Co–I(2)
I(1)–Co–O(1)
I(2)–Co–O(1)
P(1)–O(1)–Co
114.7(12)
107.3(3)
108.7(3)
150.2(6)
O(1)–Co–O(2)
I(1)–Co–O(2)
I(2)–Co–O(2)
P(2)–O(2)–Co
106.9(4)
111.3(3)
107.7(3)
154.5(5)
[CoI2(dppfO2)], 4
Co–I(1)
Co–I(2)
P(1)–O(1)
2.601(3)
2.582(3)
1.497(5)
Co–O(1)
Co–O(2)
P(2)–O(2)
1.950(5)
1.967(5)
1.504(4)
Scheme 1
I(1)–Co–I(2)
I(1)–Co–O(1)
I(2)–Co–O(2)
P(1)–O(1)–Co
117.8(1)
106.3(2)
108.0(1)
167.6(3)
I(1)–Co–O(2)
I(2)–Co–O(1)
O(1)–Co–O(2)
P(2)–O(2)–Co
106.1(1)
109.8(2)
108.4(2)
150.7(3)
The 1H NMR spectrum in CDCl3 shows four singlets at
δ 4.27, 4.48, 4.52 and 5.3 for the ferrocenyl ring protons as
has been observed in the similar complex {[Rh(η5-C5H5)-
(dppf-P,PЈ)Cl](PF6)2}8 having a chelated structure. The 31P
NMR spectrum shows a singlet at δ 47.29. The liquid secondary
ion mass spectra (LSIMSϩ) shows the parent peak at m/z 805
[Co(η5-C5H5)(dppf-P,PЈ)I]ϩ (7%), the base peak [Co(η5-C5H5)-
(dppf-P,PЈ)]2ϩ at m/z 678 (100%) and dppf at m/z 554 (30%). So
far and after several attempts, we have been unable to grow
crystals suitable for X-ray structural determination. This reac-
tion is similar to the one described for Co(η5-C5H5)(CO)I2 with
bis(tertiary phosphines).9 Exposure of THF or CH2Cl2 solu-
tions of 1 to air results in a colour change from red–brown to
green in one or two days; from the green solutions green crystals
can be obtained. The reaction was repeated several times and
although a colour change was always observed, it was difficult
to obtain crystals in all cases, and the yields were erratic. The
green crystals obtained from a THF solution were of good
quality for an X-ray structure determination, which led to the
formulation [CoI2(µ-dppfO2)]n, 3. The Cp ring is lost and the
oxidised dppf coordinates through the oxygen atom, in a bridg-
ing manner, joining tetrahedral Co() units and giving rise to a
polymeric chain (see Scheme 2).
ligands by O donor ligands in the coordination sphere of
Co(), the complex is more easily reduced, yielding the Co()
derivative.
Metal mediated oxidation of phosphines is well known and
several mechanisms have been invoked.10 However, in the reac-
tion described above the ligand dppf itself already contains a
metal, and therefore the mechanism of oxidation of dppf could
be quite different from that of bis(tertiary phosphines). For
instance, dppfO2 can be formed from the electrochemical oxid-
ation of dppf in the presence of solvents with traces of water.11
Attempts to obtain compound 3 by the direct reaction of
dppfO2 with CoI2 in CH2Cl2 gave instead the monomeric com-
pound [CoI2(dppfO2)], 4, as green crystals, in almost quanti-
tative yield, the ligand dppfO2 being coordinated in a chelating
form. The liquid secondary ion mass spectra (LSIMSϩ) of both
compounds 3 and 4 show the base peak at m/z 772 [CoI-
(dppfO2)] (100%). Other fragments, like [Co(dppfO2)] (m/z 645)
and dppfO2 (m/z 587), are also found in both complexes. The IR
spectra of compounds 3, and 4, display strong absorption
bands in the region ν 1169–1148 cmϪ1 in Nujol mulls; this is the
absorption region for ν(P᎐O). Uncoordinated dppfO displays a
᎐
2
strong ν(P᎐O) absorption at 1168 cmϪ1 in Nujol mull.3
᎐
Polymeric [CoI2(µ-dppfO2)]n, 3, and monomeric [CoI2-
(dppfO2)], 4, were structurally characterised by single crystal
X-ray diffraction studies, as well as the starting material 2.
Crystallographic studies of [CoCp(CO)I2], 2, [CoI2(ꢀ-dppfO2)]n,
3, and [CoI2(dppfO2)], 4
The crystal structures of neutral cobalt derivatives of dppfO2,
namely, [CoI2(µ-dppfO2)]nؒ0.5THF, 3ؒ0.5THF, and [CoI2-
(dppfO2)]ؒCH2Cl2, 4ؒCH2Cl2, and of the starting material
[CoCp(CO)I2], 2, were determined by X-ray diffraction.
Selected bond distances and angles in the cobalt coordination
sphere are given in Table 1 for complexes 2, 3, and 4,
respectively.
The crystal structure of 3 is formed by one-dimensional
chains of CoI2O2 distorted tetrahedral units, covalently linked
by dppfO2 bridges and THF solvate molecules. The asymmetric
unit consists of one [CoI2(dppfO2)] moiety and one independ-
ent THF solvent molecule with the occupation factor set to
0.50, which was assigned in order to give reasonable temper-
ature factors for the atoms. Fig. 1 presents the overall geometry
of one 1-D polymeric chain with the labelling scheme adopted.
Scheme 2
This result is quite unexpected, since in the similar complexes
[Co(η5-C5H5)(P–P)I]I, [P–P = bis(tertiary phosphine)] described
in ref. 9 the reaction proceeds in a different way. When solutions
of the complexes were exposed to air, the product consisted of
the neutral complex [Co(η5-C5H5){(O)P–P}I2], with a mono-
dentate (O)P–P ligand bonded to the metal through the
phosphorus atom. Some free (O)P–P(O) was also detected.
Although the mechanism of formation of the Co() complex
3 from the Co() complex 1 is not known, it is certain that the
metal complex is required for the oxidation of dppf, since with-
out it, dppf is stable under the same conditions. Although in
most known examples the metal keeps its formal oxidation
state, it may be thought that upon replacement of P donor
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Fig. 1 An ORTEP view of the one-dimensional chain of [CoI2(µ-dppfO2)]n, 3, showing its overall geometry and the labelling scheme adopted
(40% thermal ellipsoids; Ј denotes the symmetry operation: x, Ϫy ϩ 0.5, z ϩ 0.5).
{CoI2O2} tetrahedral units are connected by dppfO2 bridges,
with P–O distances of 1.497(9) and 1.519(8) Å, and Co–O–P
angles of 150.2(6) and 154.5(5)Њ, respectively. The chain has a
crystallographically imposed centrosymmetric structure.
The crystal structure of complex 4 consists of discrete
[CoI2(dppfO2)] complex units and CH2Cl2 solvent molecules.
The molecular structure of this binuclear complex, including
the labelling scheme adopted, is shown in Fig. 2. As found for
Fig. 3 An ORTEP view of the molecular structure of [CoCp(CO)I2],
2, with labelling scheme adopted (40% thermal ellipsoids; Ј denotes the
symmetry operation: x, Ϫy ϩ 0.5, z).
Fig. 3 depicts the molecular structure of the starting material
[CoCp(CO)I2], 2, showing the cobalt centre bound to the η5-Cp
ring, one carbonyl and two iodine atoms, in a pseudo tetra-
hedral coordination environment. The molecule contains a
crystallographic symmetry plane running through the carbonyl
ligand and the cobalt() centre leading to equal Co–I dis-
tances of 2.565(3) Å, which are similar to those found for
complex 3.
Fig. 2 An ORTEP view of the molecular structure of [CoI2(dppfO2)],
4, with labelling scheme adopted (40% thermal ellipsoids).
Magnetic properties of [CoI2(ꢀ-dppfO2)]n, 3, and [CoI2(dppfO2)],
4
complex 3, two oxygen atoms from a dppfO2 ligand and
two iodine atoms define a distorted tetrahedral arrangement
around the cobalt centre. However, in the latter complex, the
dppfO2 acts as a chelating ligand, adopting a cis-configuration.
In 3 dppfO2 coordinates in a bridging mode with a trans-
configuration. Furthermore, the chelating behaviour of dppfO2
results in an almost eclipsed arrangement for the FeCp2 unit,
with an α torsion angle between the centroids of two Cp rings
and the carbon atoms bound to the phosphorus of 73.2Њ.
Another related complex with a comparable distorted tetra-
hedral geometric arrangement is [PdCl2(dppfO2)],12 which has
an α torsion angle of 79.3Њ and Pd–O distances of 1.968 and
1.974 Å, respectively. In complex 3, on the other hand, the
FeCp2 units display an almost staggered conformation with a
torsion angle of 178.4Њ. The angles subtended at the cobalt
centre(s) and the distances have comparable values in 3 and 4.
In the case of the polymeric [CoI2(µ-dppfO2)]n and monomeric
[CoI2(dppfO2)] compounds, the magnetic susceptibility, χ, tem-
perature dependence and the magnetisation field dependence at
low temperatures were studied. The temperature dependence of
the χT product is shown in Fig. 4, for polycrystalline samples
with an applied field of 5 T and both compounds present a
similar χT temperature dependence. The obtained effective
magnetic moments, 4.50 and 4.53 µB for [CoI2(dppfO2)] and
[CoI2(µ-dppfO2)]n, respectively, are in good agreement with the
values reported for tetrahedral high spin compounds.13 The
paramagnetic susceptibility deviates considerably from a simple
Curie behaviour, χ = C/T , as can be observed in Fig. 4 through
the presence of a maximum in χT at ca. 30 K and a minimum at
ca. 120 K.
J. Chem. Soc., Dalton Trans., 2002, 4595–4602
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Table 2 Summary of the results from the fits for [CoI2(dppfO2)], 4, [CoI2(µ-dppfO2)]n, 3, [CoCl2(PPh3)2], and [CoBr2(PPh3)2] using eqns. (1)–(3)
Compound
ꢀ/Њ
gz
g⊥
DkϪ1/K
TIP/emu molϪ1
θ/K
[CoI2(dppfO2)], 4
[{CoI2(µ-dppfO2}n], 3
[CoCl2(PPh3)2]
43.5
38.4
2.25
2.26
2.21
2.32
2.24
2.27
2.20
2.20
Ϫ13.0
Ϫ14.0
Ϫ17.9
Ϫ24.1
4.97 × 10Ϫ4
4.69 × 10Ϫ4
5.36 × 10Ϫ4
6.10 × 10Ϫ4
Ϫ2.02
Ϫ1.86
[CoBr2(PPh3)2]
other CoII S = 3/2 tetrahedral compounds, such as [Co(PPh3)2-
Cl2] and [Co(PPh3)2Br2],15 where negative zero field splitting
was also observed.16 In the case of these last compounds the
existence of antiferromagnetic interactions were considered
since they show AFM ordering at low temperatures,16 while in
the case of [CoI2(dppfO2)]n and [CoI2(dppfO2)], the low tem-
perature magnetic field dependence, closely following the
Brillouin function calculated values, indicates that the magnetic
interactions can be neglected.
Electrochemical studies
Fig. 5 shows the rather complex redox pattern exhibited in
cyclic voltammetry by the Co() derivative [Co(η5-C5H5)-
(dppf-P,PЈ)I]I, 1, in dichloromethane solution.
Fig. 4 χT temperature dependence of [CoI2(µ-dppfO2)]n, 3, (᭹) and
[CoI2(dppfO2)], 4, (᭿). Fits to the experimental results are represented
by the solid and dashed lines, for 3 and 4, respectively (see text).
The non-Curie behaviour is consistent with the existence of a
strong paramagnetic anisotropy due to zero field splittings
(ZFS), which are common on Co S = 3/2 tetrahedral com-
pounds,14 together with orientation effects due to the strong
external applied magnetic field, and with a temperature inde-
pendent paramagnetic (TIP) contribution. At high temper-
atures (120 < T < 300 K), the behaviour of χT is dominated by
the TIP contribution. The increase of χT, below 120 K, is
attributed to a partial alignment of the crystals with the applied
field that originates a dominance of the parallel susceptibility in
4
relation to the perpendicular component, which for the A2,
S = 3/2, electronic state are given by ref. 14:
(1)
(2)
Fig. 5 Cyclic voltammetric responses recorded, under opposite scan
directions, at a platinum electrode on a CH2Cl2 solution containing
[Co(η5-C5H5)(dppf-P,PЈ)I]I (1.2 × 10Ϫ3 mol dmϪ3) and [NBu4][PF6]
where N is Avogadro’s number, µB is the Bohr magneton, k is
the Boltzmann constant, gz and g⊥ are the parallel and
perpendicular components of the g factor, x = D/k and D is
the ZFS parameter. At lower temperatures (T < 30 K), the
fast decrease in χT is attributed to the non-linear field depend-
ence of the magnetization for large values of H/T . This is con-
sistent with the position of the maximum, which was observed
to shift to lower temperatures with smaller applied fields.
At 1.7 K, the magnetization nearly saturates for H ≥ 2 T, at
MS ≈ 3NµB.
(0.2 mol dmϪ3). Scan rate 0.2 V sϪ1
.
As seen, the overall redox profile is independent from the
scan direction. In this light, let us first discuss the anodic
path. The two processes occurring in the range from 0 to
0.7 V are typical of free iodide ions17 and are hence assigned
to the oxidation of the iodide counteranion. The further
reversible oxidation at about 1 V is conceivably due to the
oxidation of dppf ligand. As a matter of fact, analysis18
of such response with scan rate varying from 0.02 to 0.5 V
The solid and dashed lines in Fig. 4 represent the fits for
compounds 3 and 4, respectively, taking into account the orien-
tation effect on the susceptibility, through eqns. (1) and (2), plus
a TIP contribution:
s
Ϫ1, shows that the current ratio ipc/ipa is constantly equal
to 1, the current function ipavϪ1/2 remains substantially
constant, the peak-to-peak separation increases from 65
to 72 mV. It is useful to note that under the same experi-
mental conditions the (first) oxidation of free dppf occurs
at ϩ0.57 V. In this connection, anodic shifts of about 0.4 V
have been also observed for the Co()-dppf complexes
[Co(acac)2(dppf )]ϩ 19 and [Co(NO)2(dppf )]ϩ,20 which point
χ = cos2(φ)χ|| ϩ sin2(φ)χ⊥ ϩ TIP
(3)
the obtained parameters are shown in Table 2 and compared
with the ones from single crystal measurements obtained with
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Table 3 Formal electrode potentials (in V, vs. SCE) for the redox changes exhibited by the present cobalt–dppf and cobalt–dppfO2 complexes in
dichloromethane solution
Oxidation processes
Reduction processes
Species
EЊЈa
EЊЈa
EЊЈb
EЊЈc
EЊЈd
EЊЈe
EЊЈf
[CpCoI(dppf )]I
ϩ0.30g
—
—
—
—
ϩ0.57
—
—
—
—
—
—
—
ϩ0.94
—
—
Ϫ0.20g
Ϫ0.06
—
—
—
Ϫ0.72
Ϫ0.85g
—
—
—
[CpCoI2(CO)]
[CoI2(dppfO2)]
dppf
dppfO2
[NBu4]I
ϩ1.25g
ϩ1.08
—
ϩ0.44g
ϩ0.57
ϩ0.82h
—
—
—
ϩ0.57
—
—
ϩ0.18
—
—
a Oxidation of free IϪ ions. b Co()/Co() oxidation. c Oxidation of the ferrocene-based ligand. d Oxidation of coordinated halogen. e Co()/Co()
reduction. f Co()/Co() reduction. g Peak potential values for processes coupled to fast chemical complications; measured at 0.2 V sϪ1 h From ref. 11.
.
out the high affinity of cobalt fragments towards the dppf
ligand.
Less straightforward appears the attribution of the cathodic
path. From a qualitative viewpoint the two consecutive reduc-
tion processes are preliminarily assigned to the sequence
Co()/Co()/Co(), also in view of the behaviour exhibited by
the parent Co() derivative [Co(η5-C5H5)(CO)I2], which dis-
plays a first, partially reversible reduction at about Ϫ0.1 V and
a further irreversible reduction at about Ϫ0.8 V. As the actual
first reduction step does not display any associated reoxidation
peak even at 20 V sϪ1, it must be taken into account that the
corresponding exhaustive reduction of the original red solution
of [Co(η5-C5H5)(dppf-P,PЈ)I]I (Ew = Ϫ0.4 V) consumes one-
electron/molecule, and the resulting yellow–orange solution
exhibits in cyclic voltammetry a redox profile substantially simi-
lar to that illustrated in Fig. 5, but for the disappearance of
the first irreversible reduction and the increase of free iodide
oxidation. A possible mechanism for the reduction sequence
could therefore be formulated as:
The formal electrode potentials of the above discussed redox
changes are compiled in Table 3.
Let us now pass to the dppfO2–Co() derivative [CoI2-
(dppfO2)], 4. As illustrated in Fig. 6, it exhibits a rather complex
voltammetric pattern.
Fig. 6 Cyclic (a) and OSWV (b) voltammograms recorded at a
platinum electrode on a CH2Cl2 solution containing [Co(dppfO2)I2]
(1.1 × 10Ϫ3 mol dmϪ3) and [NBu4][PF6] (0.2 mol dmϪ3). Scan rates
(a) 0.02 V sϪ1; (b) 0.1 V sϪ1
.
Molecular orbital study of [Co(ꢁ5-C5H5)(dppf-P,PЈ)I]I, 1, the
polymeric chain [CoI2(ꢀ-dppfO2)]n, 3, [CoI2(dppfO2)], 4, and
some related complexes
A first oxidation at about ϩ0.4 V, which is accompanied by
almost overlapping minor processes, precedes a further better
defined anodic process at about ϩ 1 V, which possesses features
of chemical reversibility. The picture is best defined by the
Osteryoung Square Wave Voltammogram (OSWV). Since
controlled potential coulometry in correspondence to the first
anodic step indicated the consumption of about 1.2 electrons
per molecule, we assume that [CoI2(dppfO2)] undergoes at first
the CoII/CoIII oxidation followed in turn by the dppfO2–FeII/
FeIII oxidation. The minor complications accompanying the
CoII/CoIII step are likely due to free iodide ions, which can be
present in traces as complications either preceding (slight dis-
sociation of the original complex) or following the electron
transfer. From a speculative viewpoint, we point out that the
shift induced in the oxidation potential of the dppfO2 ligand
with respect to free dppfO2 is significantly smaller than that
observed for dppf in [CoIII(C5H5)(dppf )I]ϩ (0.26 vs. 0.37 V),
likely precluding a slightly lower affinity of dppfO2 with respect
to dppf towards cobalt coordination.
DFT calculations4 (ADF program)5 were performed on some
of the complexes studied. The simplest is the diamagnetic
Co() cationic complex, [Co(η5-C5H5)(dppf-P,PЈ)I]ϩ, 1, for
which a full geometry optimization was carried out, using a
model based on the structures of the other complexes described
above. The optimized structure is shown in Fig. 7. The distances
and angles are similar to those found in this type of complex.
The P–Co–P and P–Co–I angles are very close to 90Њ, showing
how this part of the molecule approaches a half octahedron.
The Co ؒ ؒ ؒ Fe distance is 4.159 Å, the only communication
between metals being through the bridging ligands.
The HOMO and the HOMO Ϫ 1 of this complex are 82.0
and 78.3% localized on Fe, or 94.8 and 93.2% on the (C5H4)Fe
fragment, respectively. The LUMO, on the other hand, is con-
centrated 40.5% on Co, 24.6% on I, and 5.5% on the two P
atoms, the LUMO ϩ 1 being comparable. These compositions
J. Chem. Soc., Dalton Trans., 2002, 4595–4602
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polymer, when conveniently ended, provides a good molecular
model that can be used to study accurately the electronic struc-
ture of this compound. DFT calculations were thus performed
for a model [CoI2(µ-dppfO2)2], extracted from the chain and
with the phenyl groups replaced by hydrogen atoms. This new
species resembles [CoI2(dppfO2)] in that Co() has the same
coordination environment, but differs because dppfO2 binds
as a monodentate rather than a chelate ligand. The energy
levels are shifted to lower energies compared to those of
[CoI2(dppfO2)], but the spin density is strongly localized in Co
(2.507), with a strong contribution of iodine (0.208, 0.191).
Iron, as low spin d6 Fe(), contributes significantly to the
LUMO, the t2g type orbitals being stabilized relative to the Co d
levels. This qualitative bonding model agrees with the experi-
mental findings concerning the magnetic behaviour of the
polymeric chain, which assigns the magnetic properties to a
cobalt() centre.
Fig. 7 The fully optimized geometry of [Co(η5-C5H5)(dppf-P,PЈ)I]ϩ,
1, with some relevant distances (Å).
Conclusions
A new Co() complex, [Co(η5-C5H5)(dppf-P,PЈ)I], 1, was pre-
pared and characterised by multinuclear NMR spectroscopy.
Upon exposure to air of solutions of compound 1, a polymeric
chain containing bridging dppfO2 units joining tetrahedral
Co() centres, [CoI2(µ-dppfO2)]n, 3, was formed. In an attempt
to obtain 3 via a different route, direct reaction of dppfO2 with
CoI2, was checked and found instead to lead to the monomeric
[CoI2(dppfO2)], 4, with dppfO2 as a chelate. The structures of
these Co() derivatives were confirmed by single crystal X-ray
diffraction. The electrochemical study showed that the Co()
species was reduced to Co(), followed by loss of iodine and
further reduction to Co(). DFT calculations led to a calculated
structure and an electronic structure which was consistent with
the electrochemical data. The derivatives 3 and 4 behaved as
agree extremely well with the proposed redox processes for oxi-
dation and reduction (see above).
The other complex studied by cyclic voltammetry was the
paramagnetic Co() derivative [CoI2(dppfO2)] and spin
unrestricted DFT calculations were performed. The optimized
structure can be compared with the experimental crystal struc-
ture so that the reliability of the calculational method can be
evaluated, as seen in Fig. 8.
tetrahedral S = 3/2 CoII, possessing a A2 ground state, and
4
S = 0 FeII complexes with three unpaired electrons, when their
magnetic behaviour was investigated and temperature depend-
ence of the magnetic susceptibility analysed {D/k = Ϫ13 and
Ϫ14 K for [CoI2(dppfO2)] and [CoI2(µ-dppfO2)]n, respectively}.
Comparison of the electrochemical behaviour of [CoIII-
(η5-C5H5)(dppf )I]ϩ and [CoIII2(dppfO2)] with that of the
respective free diphenylphosphinoferrocene ligands (namely,
dppf and dppfO2) suggests that the oxygenated diphosphine
has a lower affinity towards cobalt coordination.
Fig. 8 The fully optimized geometry of [CoI2(dppfO2)], 4, DFT (left)
and the X-ray structure (right), with some relevant distances (Å) and
angles (Њ, italics).
The agreement between the calculated and the experimental
structures is very good, both for distances and angles. The only
parameter which deviates significantly is the I–Co–I angle (126Њ
calc.; 117Њ exp.). The calculated spin density for this complex
resides mostly on the Co atom (2.527), the second largest con-
tributions being those of the two iodines (0.207, 0.192). All the
other atoms contribute almost nothing to the spin density. This
indicates that the three highest singly occupied molecular
orbitals (SOMOs) have a strong contribution from cobalt,
which behaves as a typical tetrahedral Co() centre. In order to
get a simpler picture of the molecular orbitals, a single point
restricted calculation was also performed. The five highest
occupied molecular orbitals are essentially Co d orbitals (71.4
to 84.7%). The contribution of Fe to these orbitals goes up to
1.4, 2.1, and 2.8% in the SOMOs of this iodine derivative. The
contribution of iodine to the mainly Co d orbitals is relatively
large (11.3, 26.8, 24.2, 18.4, 21.7%). It is difficult to predict
exactly, from these results, what happens during the oxidation
processes, though in principle Fe should not be involved. On the
other hand, the LUMOs are strongly localized on Fe and reduc-
tion should involve the ferrocenyl moiety. Also, the character-
ization of the magnetic properties of the iodine complexes as
being identical to those of tetrahedral d7 Co complexes is con-
sistent with the previous description of the molecular levels.
The polymeric chain [CoI2(µ-dppfO2)]n, 3, was initially
studied as a one-dimensional polymer, using the extended
Hückel method6 with the tight-binding approach.7 It was found
that the bands were extremely flat, so that the unit cell of the
Experimental
General procedures and materials
All reactions and manipulations of solutions, except for the
exposure to air experiments, were performed under an argon
atmosphere using Shlenck techniques. Solvents were of reagent
grade and were dried according to literature methods. CoI2 was
purchased from Aldrich and Co2(CO)8 was purchased from
Fluka and were used as supplied.
Physical methods
Infrared spectra were recorded as mulls on NaCl plates using an
ATI Mattson Genesis FTIR spectrometer. Elemental analyses
were performed at the microanalytical laboratory of the
Universidade Técnica de Lisboa, Portugal. Mass spectra
were recorded on a VG Autospec instrument (LSIMS) using
3-nitrobenzylalcohol as matrix and a caesium gun, at the
Instituto de Ciencias de Materiales de Aragon, Zaragoza,
Spain. NMR samples were recorded on a Bruker ARX 400
using TMS as internal reference. Magnetic susceptibility data
of polycrystalline CoI2(dppfO2) samples, using a Teflon sample
holder, were obtained, in the range 4–300 K, with a longitudinal
Faraday system (Oxford Instruments), with a 7 T superconduct-
ing magnet, under a magnetic field of 5 T and forward and
4600
J. Chem. Soc., Dalton Trans., 2002, 4595–4602

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reverse gradients fields of 1 T mϪ1. The force was measured with
a microbalance (Sartorius S3D-V). The data were corrected for
contributions due to sample holder and core diamagnetism,
estimated from tabulated Pascal constants.
direct and difference Fourier syntheses followed by least-
squares refinement. After all positions of non-hydrogen atoms
of complexes 3 and 4 had been located, it was clear from the
Fourier difference maps that the solvent molecules were present
in the asymmetric unit of these complexes. Thus, one molecule
of THF with an occupancy of 0.50 and one CH2Cl2 molecule
were found for complexes 3 and 4, respectively. The occupancy
factors of the THF molecule was set to 0.50 in order to give
reasonable isotropic thermal parameters and low R values. The
hydrogen atoms on the carbon atoms were included in calcu-
lated positions and given thermal parameters equivalent to
1.2 times those of the atom to which they were attached. All
non-hydrogen atoms of the three complexes were refined
anisotropically, except the carbon and oxygen atoms of
THF molecules, which were refined with individual isotropic
temperature factors.
Synthesis of complexes
The ligands 1,1Ј-bis(diphenylphosphino)ferrocene (dppf )21 and
1,1Ј-bis(diphenylphosphoranyl)ferrocene (dppfO2)22 and the
complexes [Co(η5-C5H5)(CO)2]23 and [Co(η5-C5H5)(CO)I2], 2,24
were prepared as previously reported.
[Co(ꢁ5-C5H5)(dppf-P,PЈ)I]I, 1. A solution of dppf (0.68 g,
1.2 mmol) in CH2Cl2 (25 cm3) was added to a solution of
[Co(η5-C5H5)(CO)I2], 2, (0.47 g, 1.2 mmol) in CH2Cl2 (50 cm3),
magnetically stirred at room temperature; a colour change was
observed from the very dark violet of the initial solution to a
red–brown. Gas evolution was immediately observed (presum-
ably CO). The mixture was left stirring for about 30 minutes, the
solution was concentrated by removal of the solvent in vacuo,
petroleum ether (bp 40–60 ЊC) was added until becoming turbid
and the solution was then filtered and left in the refrigerator.
After a few days (two or three) brown–reddish crystals formed
which were recovered by filtration, washed with petroleum ether
(bp 40–60 ЊC), and dried in vacuo to give pure 1. Yield 0.9 g
(80%) (Found: C, 49.97; H, 3.60. Calc. for C39H33CoFeP2I2: C,
50.23; H, 3.54%). Mass spectrum: m/z 805 (7%, Mϩ Ϫ I), 678
(100, Mϩ Ϫ 2I), 554 (30, dppf ). NMR (CDCl3): 1H, δ 7.77–7.47
(m, 10H, Ph), 5.3 (s, 2H, C5H4), 5.22 (s, 5H, C5H5), 4.52 (s, 2H,
C5H4), 4.48 (s, 2H, C5H4), 4.27 (s, 2H, C5H4); 31P, δ 47.29 (s).
The structures were refined on F 2 until convergence. All
calculations required to solve and refine the structures were
carried out with SHELXS and SHELXL within the SHELX-97
package.27 Molecular and crystal packing diagrams were drawn
with PLATON.28
CCDC reference numbers 164967–164969.
See http://www.rsc.org/suppdata/dt/b2/b205942h/ for crystal-
lographic data in CIF or other electronic format.
Electrochemistry
Materials and apparatus for electrochemistry have been
described elsewhere.29 All the potential values are referred to the
Saturated Calomel Electrode (SCE). Under the present experi-
mental conditions the one-electron oxidation of ferrocene
occurs at EЊЈ = ϩ0.39 V. N,N-Dimethyl-1-[1Ј,2-bis(diphenyl-
phosphino)ferrocenyl]ethylamine was an Aldrich product.
[CoI2(ꢀ-dppfO2)]n, 3. Exposure of a CH2Cl2 or THF solution
of 1 to air resulted in a colour change from red–brown to green
in a few days. Green crystal of 3 can be obtained from the green
solution; the reaction was repeated several times and although a
colour change is always observed it is difficult to obtain crystals
and the yields are erratic. A sample obtained when CH2Cl2 was
used as solvent was used for elemental analyses. (Found: C,
43,26; H, 3.09. Calc. for C35H30CoFeCl2P2O2I2: C, 42.70; H,
3.05%). Mass spectrum: m/z 772 {100%, [CoI(dppfO2)]}, 645
Computational studies
Density functional calculations4 were carried out with the
Amsterdam Density Functional (ADF) program developed by
Baerends and co-workers (release 2.3 and ADF-1999).5 Vosko,
Wilk and Nusair’s local exchange correlation potential was
used,30 with Becke’s nonlocal exchange31 and Perdew’s corre-
lation corrections.32 The geometry optimization procedure
was based on the method developed by Versluis and Ziegler,33
using the non-local correction terms in the calculation of the
gradients, together with non-local exchange and correlation
corrections. Unrestricted calculations were performed for para-
magnetic species unless otherwise stated. The structures of the
complexes described in this work were used to prepare input
files for the optimization of the geometry of the model com-
plexes. The model for the chain was obtained by replacing
phenyl groups by hydrogen atoms and ending the unit cells with
hydrogen atoms. Full optimizations without symmetry con-
straints were always performed. In all the calculations, a triple-ζ
Slater-type orbital (STO) basis set was used for Co and Fe 3s,
3p, 4s, 4p, 3d, as well as for I 5s, 5p; triple-ζ STO augmented
with a single-ζ polarization function were used for P 3s and 3p,
C, O, 2s and 2p, and H 1s. A frozen core approximation was
used to treat the core electrons of C and O (1s), P ([1–2]s, 2p),
Co and Fe ([1–2]s, 2p), and I ([1–4]s, [1–4]p, [3,4]d).
{45, [Co(dppfO2)]}, 587 (32, dppfO2). IR (Nujol, ν/cmϪ1): P᎐O
᎐
1169–1148cmϪ1
.
[CoI2(dppfO2)], 4. A solution of dppfO2 (0.36 g, 0.6 mmol) in
CH2Cl2 (15 cm3) was added to a suspension of CoI2 (0.19 g,
0.6 mmol) in CH2Cl2 (30 cm3), magnetically stirred at room
temperature, a bright green solution formed which was left stir-
ring for 1 hour, at which point the solution was filtered and
concentrated by vacuum removal of the solvent until becoming
turbid. The solution was then filtered and left in the refrigerator
whereupon green crystals formed; they were separated by filtra-
tion and recrystallized from CH2Cl2–petroleum ether (bp 40–60
ЊC) to give well formed crystals of 4. The yield was essentially
quantitative (Found: C, 43.15; H, 2.90. Calc. for C35H30CoFe-
Cl2P2O2I2: C, 42.70; H, 3.05%). Mass spectrum: m/z 772 {100%,
[CoI(dppfO2)]}, 645 {32, [Co(dppfO2)]}, 587 (20, dppfO2). IR
(Nujol, ν/cmϪ1): P᎐O 1169–1148cmϪ1
.
᎐
Crystallography
Extended Hückel7 calculations were carried out with modi-
fied Hij values,34 and using the tight-binding approach on poly-
meric chain 3.6 The basis set for the metal atoms consisted of ns,
np and (n Ϫ 1)d orbitals. The s and p orbitals were described by
single Slater-type wave functions, and the d-orbitals were taken
as contracted linear combinations of two Slater-type wave func-
tions. The parameters used were [Hii (eV), ζ]: Co 4s Ϫ9.21,
2.000; 4p Ϫ5.29, 2.000; 3d Ϫ13.18, 5.55, 2.100 (ζ2), 0.5679 (C1),
0.6059 (C2); Fe 4s Ϫ9.100, 1.900; 4p Ϫ5.32, 1.900; 3d Ϫ12.60,
5.35, 2.000 (ζ2), 0.5505 (C1), 0.6260 (C2); I 5s Ϫ18.00, 2.679; 5p
Ϫ12.700, 2.322. Standard parameters were used for other
atoms. The program YAeHMOP was used in calculations.35
Crystal data together with refinement details for complexes 2, 3
and 4 are given in Table 4.
The X-ray data were collected on a MAR research plate
system using graphite Mo-Kα radiation at Reading University.
The crystals were positioned 70 mm from the image plate. 95
frames were taken at 2Њ intervals using a counting time between
2 and 10 min adequate to the crystal under study. Data analysis
was performed with XDS program.25 Intensities of 2 and 3 were
corrected empirically for absorption effects using a version of
DIFABS modified for image plate geometry.26 The structures of
complexes 2, 3, and 4 were solved by a combination of the
J. Chem. Soc., Dalton Trans., 2002, 4595–4602
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Table 4 X-Ray room temperature data and structure refinement details for complexes [CoCp(CO)I2], 2, [CoI2(µ-dppfO2)]n, 3, and [CoI2(dppfO2)], 4
Compound
2
3ؒ0.5THF
4ؒCH2Cl2
Empirical formula
C6H5CoI2O
C36H32CoFeI2O2.5P2
C34H28CoFeI2O2P2ؒ
CH2Cl2
984.01
Monoclinic
P21/n
M
405.83
Monoclinic
P21/m
935.14
Monoclinic
P21/c
Crystal system
Space group
a/Å
b/Å
c/Å
6.730(12)
11.167(17)
7.033(12)
117.49(1)
468.9
12.922(17)
20.001(29)
17.820(25)
110.66(1)
4309.4
4
11.371(15)
17.971(25)
18.211(25)
91.04(1)
3720.8
β/Њ
V/Å3
Z
2
4
Dc/g cmϪ3
2.875
8.350
1.441
2.255
1.757
2.755
µ/mmϪ1
Reflections collected
Independent reflections
Rint
1358
832
0.0323
12554
7540
0.0615
10861
6211
0.0256
Final R indices
R1, wR2 [I > 2σ(I )]
R1, wR2 (all data)
0.0378, 0.1050
0.0389, 0.1063
0.0974, 0.2782
0.1904, 0.3254
0.0454, 0.1066
0.0804, 0.1212
8 J.-F. Ma and Y. Yamamoto, J. Organomet. Chem., 1999, 574, 148.
9 Q.-B. Bao, S. J. Landon, A. L. Rheingold, T. M. Haller and
T. B. Brill, Inorg. Chem., 1985, 24, 900.
10 (a) A. Sen and J. Halpern, J. Am. Chem. Soc., 1977, 99, 8337;
(b) V. M. Miskowski, J. L. Robbins, G. S. Hammond and H. B. Gray,
J. Am. Chem. Soc., 1976, 98, 2477; (c) J. B. Birk, J. Halpern and
A. L. Pickard, J. Am. Chem. Soc., 1968, 90, 4491; (d ) D. D. Schmidt
and J. T. Yoke, J. Am. Chem. Soc, 1971, 93, 637.
11 G. Pilloni, B. Longato and B. Corain, J. Organomet. Chem, 1991,
420, 57.
12 J. S. L. Yeo, J. J. Vittal and T. S. A. Hor, Chem. Commun., 1999, 1477.
13 R. L. Carlin, Magnetochemistry, Springer-Verlag, Berlin, 1986.
14 R. L. Carlin, Science, 1985, 227, 4692.
Acknowledgements
This work was partially supported by PRAXIS XXI (2/2.1/
QUI/419/94 and PRAXIS/PCNA/C/QUI/103/96). P. Zanello
gratefully acknowledges the financial support from the
University of Siena (PAR 2001). T. A., M. J. C. and P. Z. thank
the bilateral program CNR/ICCTI for funding. Thanks are
given to Prof. Mariano Laguna from the Instituto de Ciencias
de Materiales de Aragon for the mass spectra. We thank the
EPSRC and the University of Reading for funds for the Image
Plate system.
15 J. E. Davies, M. Gerloch and D. J. Phillips, J. Chem. Soc., Dalton
Trans., 1979, 1836.
16 R. L. Carlin, R. D. Chirico, E. Sinn, G. Mennenga and L. J. de
Jongh, Inorg. Chem., 1982, 21, 2218.
17 G. Dryhurst and P. J. Elving, Anal. Chem., 1967, 39, 606–615 and
references therein.
References
1 (a) A. Togni and T. Hayashi, Ferrocenes, VCH, Weinheim, 1995;
(b) F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8,
31.
2 M. Adachi, M. Kita, K. Kashiwabara, J. Fujita, N. Iitaka,
S. Kurachi, S. Ohba and D.-M. Jin, Bull. Chem. Soc. Jpn., 1992, 65,
2037.
3 (a) G. Pilloni, G. Valle, C. Corvaja, B. Longato and B. Corain,
Inorg. Chem., 1995, 34, 5910; (b) P. Pinto, M. J. Calhorda, V. Felix,
T. Avilés and M. G. B. Drew, Monatsh. Chem., 2000, 131, 1253.
4 R. G. Parr and W. Yang, Density Functional Theory of Atoms and
Molecules, Oxford University Press, New York, 1989.
18 E. R. Brown and J. R. Sandifer, in Physical Methods of Chemistry,
Electrochemical Methods, B. W. Rossiter and J. F. Hamilton, eds.,
Wiley, New York, 1986, vol. 2, ch. 4.
19 M. Adachi, M. Kita, K. Kashiwabara, J. Fujita, N. Iitaka,
S. Kurachi, S. Ohba and D. Jin, Bull. Chem. Soc. Jpn., 1992, 65,
2037–2044.
20 A. E. Gerbase, E. J. S. Vichi, E. Stein, L. Amaral, A. Vasquez,
M. Horner and C. Maichle-Mössmer, Inorg. Chim. Acta, 1997, 266,
19–27.
5 (a) ADF(1999), E. J. Baerends, A. Bérces, C. Bo, P. M. Boerrigter,
L. Cavallo, L. Deng, R. M. Dickson, D. E. Ellis, L. Fan, T. H.
Fischer, C. Fonseca Guerra, S. J. A. van Gisbergen, J. A.
Groeneveld, O. V. Gritsenko, F. E. Harris, P. van den Hoek,
H. Jacobsen, G. van Kessel, F. Kootstra, E. van Lenthe, V. P. Osinga,
P. H. T. Philipsen, D. Post, C. C. Pye, W. Ravenek, P. Ros, P. R. T.
Schipper, G. Schreckenbach, J. G. Snijders, M. Sola, D. Swerhone,
G. te Velde, P. Vernooijs, L. Versluis, O. Visser, E. van Wezenbeek,
G. Wiesenekker, S. K. Wolff, T. K. Woo and T. Ziegler, Vrije
Universiteit, Amsterdam, The Netherlands, 1999; (b) C. Fonseca
Guerra, O. Visser, J. G. Snijders, G. te Velde and E. J. Baerends,
Parallelisation of the Amsterdam Density Functional Programme in
Methods and Techniques for Computational Chemistry, E. Clementi
and C. Corongiu, eds., STEF, Cagliari, 1995, pp. 303–395;
(c) C. Fonseca Guerra, J. G. Snijders, G. te Velde and E. J. Baerends,
Theor. Chem. Acc., 1998, 99, 391; (d ) E. J. Baerends, D. Ellis and
P. Ros, Chem. Phys., 1973, 2, 41; (e) E. J. Baerends and P. Ros,
Int. J.Quantum Chem., 1978, S12, 169; ( f ) P. M. Boerrigter,
G. te Velde and E. J. Baerends, Int. J. Quantum Chem., 1988, 33, 87;
(g) G. te Velde and E. J. Baerends, J. Comp. Phys., 1992, 99, 84.
6 (a) M. H. Whangbo and R. Hoffmann, J. Am. Chem. Soc., 1978,
100, 6093; (b) M. H. Whangbo, W. M. Walsh, jun., R. C. Haddon
and E. Wudl, Solid State Commun., 1982, 43, 637; (c) M. H.
Whangbo, J. M. Williams, M. A. Beno and J. R. Dorfman,
J. Am. Chem. Soc., 1983, 105, 645.
21 J. J. Bishop, A. Davison, M. L. Katcher, D. W. Lichtenberg,
R. E. Merrill and J. C. Smart, J. Organomet. Chem., 1971, 27, 241.
22 W. E. Slinkard and D. W. Meek, J. Chem. Soc., Dalton Trans., 1973,
1024.
23 M. D. Rausch and R. A. Genetti, J. Org. Chem., 1970, 35, 3888.
24 R. B. King, Inorg. Chem., 1966, 5, 82.
25 W. Kabsch, J. Appl. Crystallogr., 1988, 21, 916.
26 DIFABS, N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983,
39, 158.
27 G. M. Sheldrick, SHELX-97, University of Göttingen, Germany,
1997.
28 A. L. Spek, PLATON, A Multipurpose Crystallographic tool,
Utrecht University, Utrecht, The Netherlands, 1999.
29 P. Zanello, F. Laschi, M. Fontani, C. Mealli, A. Ienco K. Tang,
X. Jin and L. Li, J. Chem. Soc., Dalton Trans., 1999, 965.
30 S. H. Vosko, L. Wilk and M. Nusair, Can. J. Phys., 1980, 58, 1200.
31 A. D. Becke, J. Chem. Phys., 1987, 88, 1053.
32 (a) J. P. Perdew, Phys. Rev., 1986, B33, 8822; (b) J. P. Perdew,
Phys. Rev., 1986, B34, 7406.
33 (a) L. Versluis and T. Ziegler, J. Chem. Phys., 1988, 88, 322;
(b) L. Fan and T. Ziegler, J. Chem. Phys., 1991, 95, 7401.
34 J. H. Ammeter, H.-J. Bürgi, J. C. Thibeault and R. Hoffmann,
J. Am. Chem. Soc., 1978, 100, 3686.
35 G. A. Landrum, YAeHMOP: Yet Another extended Hückel
Molecular Orbital Package, YAeHMOP is available on the WWW
at: http://yaehmop.sourceforge.net.
7 (a) R. Hoffmann, Chem. Phys., 1963, 39, 1397; (b) R. Hoffmann and
W. N. Lipscomb, J. Chem. Phys., 1962, 36, 2179.
4602
J. Chem. Soc., Dalton Trans., 2002, 4595–4602