Synthesis and characterisation of iron and cobalt complexes with phosphinothiolate ligands

Article abstract of DOI:10.1016/S0020-1693(03)00398-0

Neutral iron complexes of a series of arenephosphinothiol proligands, Ph_xP(ArSH)_3-x, (x=0-2, Ar=C₆H₄, C₆H₃SiMe₃) have been synthesised. Compounds [Fe{2-(Ph₂PO)C₆H₄S}₃] (1), [Fe{2-(Ph₂P)-6(Me₃Si)C₆H₃S} ₃] (2), [Fe{2-(Ph₂PO)-6(Me₃Si)C ₆H₃S}₃] (3) and [Fe₂{PhP(C ₆H₄S-2)₂}₃] (4) were obtained most conveniently by the electrochemical oxidation of an iron anode in a cell containing an acetonitrile solution of the corresponding proligand. [Fe{2-(Ph₂P)C₆H₄S}₂(CO) ₂] (5) was obtained by the addition of the appropriate proligand to an acetonitrile solution of FeCl₂ saturated with CO. The reaction of FeCl₂ with PhP(C₆H₄SH-2)₂ in methanol in the presence of CO and bis-diphenylphosphinoethane (dppe) gave [Fe{PhP(C₆H₄S-2)₂}(dppe)(CO)] (6) in good yield. The reaction of FeCl₂ with the potentially tetradentate P(C₆H₄SH-2)₃ proligand in presence of PMe ₂Ph or dppe allows the synthesis of [Fe{P(C₆H ₄S-2)₃}(PMe₂Ph)₂] (7) and [Fe{P(C₆H₄S-2)₃}(dppe)] (8). Corresponding reactions of the phosphinothiolates with CoCl₂ in the presence of CO and/or phosphine ligands gave [CoCl{PhP(C₆H₄S-2) ₂}(dppe)] (9), [Co{PhP(C₆H₄S-2) ₂}(dppe)(CO)]BPh₄ (10), [Co{PhP(C₆H ₄S-2)₂}(dppe) ] (11), [Co(P(C₆H ₄S-2)₃L] (L=dppe, 12, L=PMe₂Ph, 13. The X-ray crystal structures of complexes 2, 4, 7 and 8, are discussed.

Full text of DOI:10.1016/S0020-1693(03)00398-0

Inorganica Chimica Acta 356 (2003) 193Á202
/
www.elsevier.com/locate/ica
Synthesis and characterisation of iron and cobalt complexes with
phosphinothiolate ligands
Paulo Pe´rez-Lourido a, Jaime Romero b,*, Jose´ A. Garc´ıa-Va´zquez b, Jesu´s Castro a,
Antonio Sousa b,*, Lyndsey Cooper c, Jonathan R. Dilworth c,*,
Raymond L. Richards d,*, Yifan Zheng c, Jon A. Zubieta e
a Inorganic Chemistry Department, University of Vigo, 36200 Pontevedra, Spain
b Inorganic Chemistry Department, University of Santiago, 15706 Santiago, Spain
c Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, UK
d School of Chemistry, Physics and Environmental Sciences, University of Sussex, Brighton BN1 9QJ, UK
e Chemistry Department, University of Syracuse, Syracuse, NY 13244, USA
Received 14 March 2003; accepted 17 April 2003
In honour of Prof. J.J.R. Frau´sto da Silva
Abstract
Neutral iron complexes of a series of arenephosphinothiol proligands, PhxP(ArSH)3ꢀx, (xꢁ
/
0Á
/
2, ArꢁC6H4, C6H3SiMe3) have
/
been synthesised. Compounds [Fe{2-(Ph2PO)C6H4S}3] (1), [Fe{2-(Ph2P)-6(Me3Si)C6H3S}3] (2), [Fe{2-(Ph2PO)-6(Me3Si)C6H3S}3]
(3) and [Fe2{PhP(C6H4S-2)2}3] (4) were obtained most conveniently by the electrochemical oxidation of an iron anode in a cell
containing an acetonitrile solution of the corresponding proligand. [Fe{2-(Ph2P)C6H4S}2(CO)2] (5) was obtained by the addition of
the appropriate proligand to an acetonitrile solution of FeCl2 saturated with CO. The reaction of FeCl2 with PhP(C6H4SH-2)2 in
methanol in the presence of CO and bis-diphenylphosphinoethane (dppe) gave [Fe{PhP(C6H4S-2)2}(dppe)(CO)] (6) in good yield.
The reaction of FeCl2 with the potentially tetradentate P(C6H4SH-2)3 proligand in presence of PMe2Ph or dppe allows the synthesis
of [Fe{P(C6H4S-2)3}(PMe2Ph)2] (7) and [Fe{P(C6H4S-2)3}(dppe)] (8). Corresponding reactions of the phosphinothiolates with
CoCl2 in the presence of CO and/or phosphine ligands gave [CoCl{PhP(C6H4S-2)2}(dppe)] (9), [Co{PhP(C6H4S-
2)2}(dppe)(CO)]BPh4 (10), [Co{PhP(C6H4S-2)2}(dppe) ] (11), [Co(P(C6H4S-2)3L] (Lꢁ
/
dppe, 12, LꢁPMe2Ph, 13. The X-ray
/
crystal structures of complexes 2, 4, 7 and 8, are discussed.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Cobalt complexes; Iron complexes; Phosphinothiolate ligands
1. Introduction
transition metals [1]. Although there are many examples
of thiolate ligands in combination with tertiary phos-
phines [2], their chemistry with iron and cobalt has
received relatively little attention. The reported com-
plexes with iron are restricted to a recent report of the
There is considerable current interest in heterodonor
polydentate ligands involving tertiary phosphine groups
in combinations with nitrogen, oxygen or sulphur
donors. Of these, phosphinothiolates derived from
thiophenol have been shown to be very versatile ligands
that form stable complexes with a wide range of
elements including lanthanides, transition and post
monomeric species [FeX{P(C6H3-3-SiMe3-2-S)3}], Xꢁ
/
Cl, Br, I, and the dinuclear complex [Fe2{P(C6H3-3-
SiMe3-2-S)3}2] [3]. There are no reported complexes of
iron with the tridentate ligand PhP(C6H4S-2)2 and the
only example with tetradentate P(C6H4S-2)3 is
[Fe2{P(C6H4S-2)3}2S2] in which two trigonal bipyrami-
dal iron centres are linked by a bridging S2 ligand [4].
Complexes with cobalt are also rare and limited to
* Corresponding authors. Tel.: ꢂ
677 196.
E-mail address: r.richards@susx.ac.uk (R.L. Richards).
/
44-1273-606 755; fax: ꢂ44-1273-
/
complexes of the type [CoL3] where Lꢁ 2-(Ph2P)-
/
0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00398-0

194
P. Pe´rez-Lourido et al. / Inorganica Chimica Acta 356 (2003) 193Á202
/
6(Me3Si) C6H4S or 2-(Ph2PO)-6(Me3Si)C6H3 [5]. We
here describe the synthesis and structures of new
homoleptic iron and cobalt complexes with bi-, tri-
and tetradentate phosphinothiolate ligands, with and
without sterically hindering substituents, together with
complexes also containing coordinated phosphines or
carbon monoxide. The structures of the ligands used are
summarised in Fig. 1. The synthesis of the complexes
with the bidentate ligands is shown to proceed more
cleanly using electrochemical oxidation of the metal
than by direct reaction with metal salts.
nothiolate proligands. This type of mechanism has
previously been observed in the synthesis of other metal
complexes in which low oxidation state species are the
initial electrochemical products [6,10]. In the case of 1,
the analytical data show that all the phosphorous atoms
have been oxidised, and the compound has to be
formulated as [Fe{2-(Ph2PO)C6H4S}3]. The IR data of
1 confirm the presence of the Pꢀ
The IR spectra of these complexes show no bands
attributable to n(SÁH), which in the free proligands
appear at 2500Á
2400 cmꢀ1. This is indicative that the
/O group, vide infra.
/
/
ligands are in the anionic thiolate form in the complex.
The spectra also show bands in the aromatic region
characteristic of the co-ordinated phosphinothiolate
ligand. The IR spectrum of compound 2, containing
trimethylsilyl groups, shows a strong band at 854 cmꢀ1
2. Results and discussion
2.1. Iron complexes with bidentate and tridentate
phosphinothiolates
characteristic of the n(SiÁ
also exhibit a strong band around 1130 cmꢀ1 due to
n(PÁO).
The FAB mass spectra of 1Á
/C). The IR spectra of 1 and 3
/
2.1.1. Electrochemical syntheses
/
4 show peaks at m/z 674
Iron (III) phosphinothiolato complexes 1Á4 were
/
[Mꢀ
/
L]ꢂ, 786 [Mꢀ
/
L]ꢂ, 818 [Mꢀ
/
L]ꢂ and 1085
prepared in good yield by oxidation of an iron anode
in a cell containing a solution of the proligand and a
small amount of tetramethylammonium perchlorate as
support electrolyte. The compounds obtained are air
stable crystalline solids soluble in chloroform, dichlor-
omethane and other common organic solvents.
[M]ꢂ, respectively. Peaks associated with further loss
of ligands are also observed. The peak clusters have
appropriate isotope distributions.
Crystals suitable for X-ray studies of 2 were obtained
by recrystallisation from dichloromethaneꢂethanol and
/
those of 4 by slow concentration of an acetonitrile
solution. Attempts to obtain crystals of 1 and 3 suitable
for X-ray studies were unsuccessful, but analytical and
spectroscopic data confirm the presence of Fe(III)
compounds with three bidentate monoanionic ligands.
Presumably these complexes have octahedral structures
similar to that of 2, vide infra; in these cases with
[FeO3S3] environments. The presence of the bulky Me3Si
group in the six position of the thiophenolate arene
group does not influence the stoichiometry or structures
of the [FeL3] type complexes.
The electrochemical efficiency for the process, Ef,
defined as the number of moles of metal dissolved per
faraday of charge, was always close to 0.5 mol Fꢀ1
.
These values suggest that the anodic oxidation of the
metal leads initially to an Fe(II) species, which is further
oxidised to Fe(III) in solution. This and the evolution of
the hydrogen at the cathode is compatible with a
mechanism such as:
cathode: 2 PSHꢂ2eꢀ0 2PSꢀ ꢂH2
anode: Feꢂ2PSꢀ0[Fe(PS)2]ꢂ2eꢀ
[Fe(PS)2]ꢂPSH 0[Fe(PS)3]ꢂ1=2H2
2.1.2. Reactions of 2-(Ph2P)C6H4SH with iron
dichloride
where PSH represents one of the bidentate phosphi-
Anhydrous FeCl2 reacts with an excess of 2-
(Ph2P)C6H4SH in acetonitrile at room temperature for
1 h to give a brick red solid. Elemental analysis was not
consistent with the formation of [Fe{2-(Ph2P)C6H4S}3]
and the observation of 1% nitrogen suggested some
incorporation of acetonitrile in the product. However
the FAB mass spectrum shows a major peak at m/z 642
corresponding to [Fe{2-(Ph2P)C6H4S}2]ꢂ. It proved
impossible to purify the complex by recrystallisation
and it appears probably that [Fe{2-(Ph2P)C6H4S}3] is
produced, albeit in an impure form.
When this reaction was carried out in MeCN satu-
rated with CO an orange solid was produced, which
analysed closely as [Fe{2-(Ph2P)C6H4S}2(CO)2] (5). The
IR spectrum showed an intense sharp band at 1979
Fig. 1. Structures and formulae of phosphinothiolate ligands used.
cmꢀ1 due to n(Cꢀ
/
O). The observation of a single CO

P. Pe´rez-Lourido et al. / Inorganica Chimica Acta 356 (2003) 193Á
/202
195
stretching vibration suggests a trans-CO, trans(P,P),
trans(S,S) symmetrical structure The complex loses CO
on standing in the solid state to give a brown solid. This
is very insoluble in all solvents and presumably is
doublet in the Mossbauer spectrum, (isomer shift 0.1
¨
mm sꢀ1 and quadruple splitting 2.90 mm sꢀ1) char-
acteristic of low spin Fe(III). Crystals of this compound
suitable for X-ray studies were obtained from
polymeric with thiolateÁ/S bridges.
dichloromethaneÁhexane. The directly analogous com-
/
Attempts to prepare mixed Fe complexes with the
PSH ligand and mono- or di-tertiary phosphines or
isocyanide produced complexes, which although con-
taining the additional ligand, were clearly mixtures, and
could not be purified.
plex [Fe{P(C6H4S-2)3}(dppe)] 8 was prepared similarly
and fully characterised by X-ray studies.
2.2. X-ray crystal structures of complexes 2, 4, 7 and 8
2.2.1. Molecular structure of [Fe{2-(Ph2P)-
6(Me3Si)C6H3S}3]] (2)
2.1.3. Reactions of PhP(C6H4SH-2)2 with iron
dichloride
The molecular structure of [Fe{2-(Ph2P)-6(Me3-
Si)C6H3S}3] (2), together with the atom labelling
scheme, is showed in Fig. 2. Selected bond distances
and angles are given in Table 2. A summary of the X-ray
data for complexes 2, 4, 7 and 8 appears in Table 1. The
compound 2 consists of discrete molecules with the
metal co-ordinated to three monoanionic (P, S) biden-
tate ligands. The geometry around the metal can be
described as [FeP3S3] slightly distorted octahedral; all
the dihedral angles between the coordination planes
defined by four donor atoms being close to 908. Angles
defined by two trans donor atoms and the metal, are in
Reaction of FeCl2 with PhP(C6H4SH-2)2 in acetoni-
trile gave a dark red solid, which was soluble in
dichloromethane to give a red solution, which turned
blue in air after a few hours. HPLC measurements
suggested that this was essentially a single species in
CH2Cl2 solution. However no satisfactory formulation
could be derived from the elemental analysis. The
observation of one doublet in the Mossbauer spectrum
¨
with isomer shifts and quadruple splitting indicative of
single Fe(III) site, suggests that the asymmetric dimer 4
formed by electrolysis as described above is not formed.
This is supported by the lack of any peak at m/z 1085
due to the [Fe2{PhP(C6H4S-2)2}3] species. No suitable
crystals could be obtained for an X-ray structure
determination and the exact formulation remains un-
clear. However it is certainly not the complex 4.
In view of the problems encountered with the FeCl2/
PhP(C6H4SH-2)2 system, we attempted to simplify the
chemistry by introduction of the chelating ditertiary
phosphine Ph2PCH2CH2PPh2 (dppe). Reaction of FeCl2
with dppe and PhP(C6H4SH-2) in methanol in the
presence of CO gave orange neutral [Fe{PhP(C6H4S-
2)2}(dppe)(CO)] (6) in reasonable yield. This complex
was diamagnetic and showed a single strong IR band
the range 168.05(3)Á
iron and two mutually cis donor atoms, lie in the range
of 82.55(3)Á101.76(3)8, and are also close to the
/
175.16(3)8, and those involving the
/
expected values. Even those corresponding to five
membered chelate rings are close to optimal with values
of 83.09(3), 86.58(2) and 85.20(2)8.
The three sulfur and phosphorous atoms are mer-
idional. This is the arrangement found in other com-
plexes containing similar ligands, such as [Tc{2-
(Ph2P)C6H4S}3] and [Re{2-( Ph2P)C6H4S}3] [8], [Ir{2-
(Ph2P)C6H4S}3] [9], [In{2-(Ph2P)C6H4S}3] [10] and
[Co{2-(Ph2P)-6-(Me3Si)C6H3S}3] [5]. The FeÁ
FeÁP distances are unremarkable and close to the
values found in complexes such as
/S and
/
assigned to n(Cꢀ
/
O) at 1930 cmꢀ1. The Mossbauer
¨
spectrum is consistent with the presence of Fe(II) with a
narrow doublet with isomer shift 0.11 mm sꢀ1 and
[FeCl{P(C6H4S)3}]2ꢀ. It appears that the bulky tri-
methylsilyl substituents have little impact on the overall
structure adopted.
quadruple splitting of 0.23 mm sꢀ1
.
2.1.4. Reactions of P(C6H4SH-2)3 with iron dichloride
Anhydrous FeCl2 was stirred at room temperature
with 2 equiv. of PMe2Ph in acetonitrile and 1 equiv. of
P(C6H4SH-2)3 was added to give a dark red solution.
On heating under reflux for 1 h and cooling a dark red
precipitate was formed. The elemental analysis of the
initial product gave values intermediate between
2.2.2. Molecular structure of [Fe2{PhP(C6H4S-2)2}3]
(4)
The molecular structure of [Fe2{PhP(C6H4S-2)2}3] (4)
is shown in Fig. 3, together with the atomic numbering
scheme adopted. Selected bond distances and angles are
in Table 3. The compound is a dimer with each iron
having distorted octahedral geometry and sharing a
common face comprising three bridging thiolate sulphur
atoms. The environment around each metal atom is
different due to the variation in the bonding mode of the
phosphinothiolate ligands. One of them uses both
sulfurs as terminal donors and on the other, one of the
sulfurs is terminal and the other acts as a bridge between
the metals. Both sulfurs of the third ligand bridge the
[Fe{P(C6H4S-2)3}(PMe2Ph)]
and
[Fe{P(C6H4S-
2)3}(PMe2Ph2)2] and the FAB MS showed peaks
assignable to both species. As has been reported for
the [Tc{P(C6H4S-2)3}(PrNC)n] species (nꢁ1, 2) there is
/
a facile equilibrium between the five and six co-ordinate
species [7]. Recrystallisation gave the bis(phosphine)
product 7 essentially pure, and this showed a single

196
P. Pe´rez-Lourido et al. / Inorganica Chimica Acta 356 (2003) 193Á202
/
Fig. 2. Representation of the structure of [Fe{2Á(Ph2P)-6(Me3Si)C6H3S}3], complex 2, showing the atom labelling scheme.
/
Table 1
Summary of crystallographic data for [Fe{2-(Ph2P)-6-(Me3Si)C6H3S}3] (2), [Fe2{PhP(C6H4S-2)2}3] (4), [Fe{PC6H4S-2)}3(PMe2Ph)] (7) and
[Fe{P(C6H4S-2)3}(dppe)] (8)
2
4
7
8
Chemical formula
Formula weight
T (K)
C63H66FeNP3S3Si3
1152.37
293(2)
C54H39Fe2P3S6
1083.83
293(2)
C34H34FeP3S3
687.55
293(2)
C22H18Fe0.5P1.5S1.5
404.83
293(2)
Crystal size (mm3)
Crystal system
Space group
0.12ꢃ
triclinic
¯
P1
/
0.12ꢃ
/
0.15
0.20ꢃ
monoclinic
P21/n
/
0.20ꢃ
/0.30
0.2ꢃ
triclinic
¯
P1
/
0.1ꢃ
/0.1
0.5ꢃ
monoclinic
P21/c
/
0.7ꢃ1.1
/
Unit cell dimensions
˚
a (A)
˚
12.6337(4)
14.0774(4)
19.2919(6)
73.2977(9)
82.9835(6)
76.5493(9)
3190.53(17)
2
10.8055(2)
39.7963(3)
13.0715(2)
90
9.9489(19)
9.9539(19)
16.757(4)
89.642(17)
88.230(17)
73.828(17)
1593.0(6)
2
11.2538(13)
20.424(2)
16.628(2)
90
b (A)
˚
c (A)
a (8)
b (8)
103.4240(10)
90
98.110(9)
90
g (8)
3
V (A )
˚
5467.42(14)
4
0.881
3783.6(7)
8
0.724
Z
m (mmꢀ1
Reflections collected
)
0.502
23283
0.845
6768
33828
12956
6563
3337
Independent reflections
a
15070
0.0494
4417
0.0399
R
0.0928
0.1707
0.0268
0.06560
b
Rw
0.1122
0.1017
a
Rꢁ
wR2ꢁ
/
S(jFojꢀ
/
jFcj)/SjFoj.
b
2 1/2
/
[(S w(jFojꢀ
/
jFcj)2/S wjFoj ]
.
metal atoms. Fe(1), therefore, has a [FePS5] array of
donors produced by two terminal sulfurs, the phospho-
rus atoms of one ligand and three bridging sulfurs
belonging to two other ligands. The donor set around
Fe(2) is [FeS4P2], with the metal coordinated to one
phosphorus and two bridging sulfur atoms of one
ligand, and to one phosphorus, a terminal sulfur and a
bridging sulfur of the other ligand. The metalÁmetal
/
˚
˚
distance, 2.8212(11) A, is similar to the 2.715(A) found
in the [Fe2{P(C6H3-3-SiMe3-2-S)3}2] complex with two
iron(III) atoms in a pentacoordinate environment and a
˚
3.0 A suggested
bond distance that is in the range of 2.5Á
for metalÁ
plexes [2].
/
/
metal interaction in polynuclear iron com-

P. Pe´rez-Lourido et al. / Inorganica Chimica Acta 356 (2003) 193Á
/202
197
Table 2
with phosphinothiolate ligands such as [Fe2(m-
S2){P(C6H4S)3}2]2ꢀ, for which the average value for
˚
Bond lengths (A) and bond angles (8) for [Fe{2-(Ph2P)-6(Me3-
Si)C6H3S}3] (2)
FeÁ
/
S(thiolate) and FeÁP bond distances are 2.20 and
/
˚
2.212(2) A, respectively [3].
Bond lengths
FeÁ
FeÁ
FeÁ
S(1)Á
S(3)Á
P(1)Á
P(2)Á
P(2)Á
P(3)Á
/
S(2)
P(2)
P(3)
2.2449(7)
2.2926(7)
2.3264(7)
1.767(3)
1.753(2)
1.831(3)
1.817(3)
1.849(3)
1.848(3)
FeÁ
FeÁ
FeÁ
S(2)Á
P(1)Á
P(1)Á
P(2)Á
P(3)Á
P(3)Á
/
S(1)
S(3)
P(1)
2.2821(7)
2.3068(7)
2.3289(7)
1.771(2)
1.827(3)
1.846(3)
1.848(2)
1.813(3)
1.849(3)
/
/
2.2.3. Molecular structures of 7 and 8
/
/
Representations of the molecular structures of com-
plexes 7 and 8 are shown in Figs. 4 and 5 and selected
bond lengths and angles in Tables 4 and 5. Both
complexes are essentially octahedral with comparable
distortions arising from the presence of the tetradentate
/C(11)
/
C(41)
/C(76)
/
C(16)
C(21)
C(51)
C(71)
C(91)
/
C(31)
C(46)
C(61)
C(81)
/
/
/
/
/
/
/
PS3 ligands. The FeÁ
/
P and FeÁS distances are compar-
/
Bond angles
able with other Fe(III) complexes with phosphinothio-
late ligands [3]. It appears that the relatively small and
basic dimethylphenylphosphine and the chelating dipho-
sphine are able to impose an octahedral geometry on
these systems whereas co-ligands such as halide give
trigonal bipyramidal species.
S(2)Á
S(1)Á
S(1)Á
S(2)Á
P(2)Á
S(2)Á
P(2)Á
P(3)Á
/
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
/
S(1)
P(2)
S(3)
P(3)
101.76(3)
85.59(2)
82.55(3)
90.52(3)
95.80(3)
91.98(3)
168.05(3)
96.08(3)
S(2)Á
S(2)Á
P(2)Á
S(1)Á
S(3)Á
S(1)Á
S(3)Á
/
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
/
P(2)
86.58(2)
175.16(3)
91.58(2)
167.70(3)
85.20(2)
83.09(3)
90.74(3)
/
/
/
/S(3)
/
/
/
/
S(3)
P(3)
P(3)
P(1)
P(1)
/
/
/
/
/
/
P(3)
/
/
/
/P(1)
/
/
/
/
P(1)
/
/
/
/
P(1)
2.3. Synthesis of cobalt complexes
2.3.1. With potentially tridentate phosphinothiolate
ligands
The three FeÁ
different, 2.3984(17) and 2.2999(17) A
˚
2.3932(17) and 2.2621(16) A for S(3), and 2.3006(15)
/
S bridge bond distances are slightly
˚
Reaction of CoCl2 with PhP(C6H4SH-2)2 (PS2H2) in
acetonitrile in the presence of Et3N gave a purple solid
which was evidently a mixture and could not be purified.
However in the presence of dppe a dark green solid
analysing as [CoCl(PS2)(dppe)] 9 was obtained. The
FAB mass spectrum showed a peak at m/z 851
for S(2),
˚
and 2.2832(15) A for S(4). The FeÁ
/S terminal bond
distances are similar, 2.2299(17), 2.2144(17) and
˚
2.2809(18) A. The FeÁ
/
S terminal and FeÁP bond
/
1]ꢂ ion, together with a
˚
distances, 2.2083(15) , 2.2111(17) and 2.2195(17) A are
close to those found in other dinuclear iron complexes
corresponding to the [Mꢂ
/
peak due to [Mꢀ
/
Cl]ꢂ, both having appropriate isotope
Fig. 3. Representation of the structure of [Fe2{PhP(C6H4S-2)2}3], complex 4, showing the atom labelling scheme.

198
P. Pe´rez-Lourido et al. / Inorganica Chimica Acta 356 (2003) 193Á202
/
Table 3
˚
Selected bond lengths (A) and bond angles (8) for [Fe2{PhP(C6H4S-
2)2}3] (4)
Bond lengths
Fe(1)Á
Fe(1)Á
Fe(1)Á
Fe(1)Á
Fe(2)Á
Fe(2)Á
Fe(2)Á
/
P(1)
S(1)
S(3)
Fe(2)
P(7)
S(22)
S(2)
2.2083(15) Fe(1)Á
2.2299(17) Fe(1)Á
2.3932(17) Fe(1)Á
2.8212(11) Fe(2)Á
2.2195(17) Fe(2)Á
2.2809(18) Fe(2)Á
/
S(12)
S(4)
S(2)
P(3)
S(3)
S(4)
2.2144(17)
2.3006(15)
2.3984(17)
2.2111(17)
2.2621(16)
2.2832(15)
/
/
/
/
/
/
/
/
/
/
/
2.2999(17)
Bond angles
P(1)ÁFe(1)Á
S(12)ÁFe(1)Á
S(12)ÁFe(1)Á
P(1)ÁFe(1)Á
S(1)ÁFe(1)Á
P(1)ÁFe(1)Á
S(1)ÁFe(1)Á
S(3)ÁFe(1)Á
P(3)ÁFe(2)Á
P(3)ÁFe(2)Á
S(3)ÁFe(2)Á
P(7)ÁFe(2)Á
S(22)ÁFe(2)Á
P(7)ÁFe(2)ÁS(2)
S(22)ÁFe(2)ÁS(2)
/
/
S(12)
88.32(6)
98.12(7)
96.18(6)
88.36(6)
168.96(7)
95.15(6)
94.42(6)
75.56(6)
87.73(6)
88.85(7)
89.55(7)
87.88(6)
169.05(7)
84.23(6)
103.62(7)
P(1)Á
P(1)Á
S(1)Á
S(12)Á
S(4)ÁFe(1)Á
S(12)Á
S(4)ÁFe(1)Á
P(3)ÁFe(2)Á
P(7)ÁFe(2)Á
P(7)ÁFe(2)Á
P(3)ÁFe(2)Á
S(3)ÁFe(2)Á
P(3)ÁFe(2)Á
S(3)ÁFe(2)Á
S(4)ÁFe(2)Á
/
Fe(1)Á
Fe(1)Á
Fe(1)Á
/
S(1)
S(4)
S(4)
87.94(6)
173.95(7)
87.43(6)
92.17(7)
95.48(6)
167.10(7)
81.34(5)
109.56(6)
161.70(7)
85.00(7)
85.71(6)
99.71(6)
162.39(7)
80.10(6)
83.88(6)
/
/
S(1)
S(4)
/
/
/
/
/
/
/
/
S(3)
/
Fe(1)Á
/S(3)
/
/S(3)
/
/
S(3)
/
/
S(2)
S(2)
S(2)
/
Fe(1)Á
/S(2)
/
/
/
/
S(2)
/
/
/
/
P(7)
S(3)
S(22)
S(4)
S(4)
/
/
S(3)
/
/
/
/
S(22)
/
/
Fig. 5. Representation of the structure of [Fe{P(C6H4S-2)3}(dppe)],
complex 8, showing the atom labelling scheme.
/
/S(22)
/
/
/
/
S(4)
S(4)
/
/
/
/
/
/
S(2)
S(2)
S(2)
Reaction of 9 with CO at atmospheric pressure in
methanol for few minutes gave a vivid purple solution
from which [Co(PS2)(CO)(dppe)]ꢂ 10 was isolated in
high yield as a tetraphenylborate salt. The IR spectrum
showed a strong band at 2052 cmꢀ1 due to the CO
ligand as well as bands characteristic of the PS2 and
dppe ligands. The complex was not sufficiently stable
for complete characterisation as it decomposed rapidly
in solution with loss of CO to give poorly-defined
polymeric materials. The complex is a rare example of
a Co(III) carbonyl complex and the high CO stretching
frequency reflects the relatively high formal metal
oxidation state and the overall positive charge. Attempts
/
/
/
/
/
/
/
/
distributions. Despite the formal Co(III) oxidation state
and the presence of ligands likely to induce spin-pairing,
it proved impossible to obtain satisfactory H or 31P
1
NMR spectra. This may be due to the presence of
paramagnetic impurities. However, crystals suitable for
an X-ray structure determination were grown from
dichloromethaneÁ
formulation above, but is not discussed here.
/hexane and the structure verifies the
Fig. 4. Representation of the structure of [Fe{P(C6H4S-2)3}(PMe2Ph)2], complex 7, showing the atom labelling scheme.

P. Pe´rez-Lourido et al. / Inorganica Chimica Acta 356 (2003) 193Á
/202
199
Table 4
complex 8 discussed above. In view of the similarity of
the structures the data for the cobalt complex is not
included here. As was observed for iron, with PMe2Ph
the product appeared to be a mixture of the mono- and
bis(phosphine) adducts with mass ions corresponding to
both species being exhibited in the FAB mass spectrum.
The facile loss of phosphine in solution precluded
meaningful NMR measurements being made.
˚
Selected bond lengths (A) and bond angles (8) for [Fe{PC6H4S-
2)}3(PMe2Ph)] (7)
Bond lengths
FeÁ
FeÁ
FeÁ
/
P(1)
S(3)
P(3)
2.1604(10)
2.2924(11)
2.3095(11)
1.771(3)
1.772(4)
1.807(3)
1.823(4)
1.838(4)
1.821(4)
FeÁ
FeÁ
FeÁ
S(2)Á
P(1)Á
P(1)Á
P(2)Á
P(3)Á
P(3)Á
/
S(1)
S(2)
P(2)
2.2549(10)
2.2929(11)
2.3694(11)
1.758(3)
1.799(4)
1.817(3)
1.828(3)
1.819(4)
1.826(3)
/
/
/
/
S(1)Á
S(3)Á
P(1)Á
P(2)Á
P(2)Á
P(3)Á
/
C(12)
/C(22)
/C(32)
/
C(31)
C(21)
C(51)
C(91)
C(71)
/
C(11)
C(61)
C(41)
C(81)
/
/
/
/
/
/
/
3. Experimental
Bond angles
P(1)ÁFeÁS(1)
S(1)ÁFeÁ
S(1)ÁFeÁ
P(1)ÁFeÁ
S(3)ÁFeÁ
P(1)ÁFeÁ
S(3)ÁFeÁ
P(3)ÁFeÁ
/
/
87.68(4)
165.62(4)
95.49(4)
167.91(4)
96.92(4)
96.07(4)
85.56(4)
95.84(4)
P(1)Á
P(1)Á
S(3)Á
S(1)Á
S(2)Á
S(1)Á
S(2)Á
/
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
/
S(3)
S(2)
81.96(4)
85.70(4)
93.66(4)
95.27(4)
82.36(4)
85.65(4)
177.94(4)
All manipulations were carried under an inert atmo-
sphere of dry nitrogen. Iron (Aldrich Chemie) was used
/
/S(3)
/
/
/
/S(2)
/
/
S(2)
P(3)
P(3)
P(2)
P(2)
as plates (ca. 2ꢃ2 cm). Synthesis of ligands were carried
/
/
/P(3)
/
/
out using slight modifications of the standard literature
procedure involving lithiation of benzenethiol [11], using
Schlenk techniques and dry solvents. Elemental analyses
were performed with a Carlo-Erba EA 1108 microana-
lyser. IR spectra were recorded in KBr discs using a
Bruker IFS 66v spectrophotometer. The FAB mass
spectra were recorded on a Kratos MS-50TC instru-
ment, using 3-nitrobenzyl alcohol (3-NOBA) as a matrix
material.
/
/P(3)
/
/
/
/P(2)
/
/
/
/P(2)
/
/
/
/P(2)
Table 5
˚
Bond lengths (A) and bond angles (8) for [Fe{P(C6H4S-2)3}(dppe)] (8)
Bond lengths
FeÁ
FeÁ
FeÁ
P(1)Á
P(1)Á
P(2)Á
P(3)Á
P(3)Á
/
P(1)
S(1)
S(2)
2.1725(8)
2.2875(8)
2.3208(8)
1.785(5)
1.820(3)
1.848(3)
1.833(5)
1.845(3)
FeÁ
FeÁ
FeÁ
P(1)Á
P(2)Á
P(2)Á
P(3)Á
/
S(3)
P(3)
P(2)
2.2747(14)
2.2985(7)
2.3275(14)
1.798(4)
/
/
/
/
3.1. Preparation of the complexes
/
C(31)
C(11)
C(2)
/
C(21)
C(51)
C(41)
C(71)
/
/
1.830(3)
Complexes 1Á4 were obtained using an electrochemi-
/
/
/
1.849(5)
cal procedure. An acetonitrile solution of the ligand
containing about 15 mg of tetramethylammonium
perchlorate as a support electrolyte was electrolysed
using a platinum wire as the cathode and an iron plate
/C(1)
/
1.833(4)
/C(61)
Bond angles
P(1)ÁFeÁS(3)
S(3)ÁFeÁ
S(3)ÁFeÁ
P(1)ÁFeÁ
S(1)ÁFeÁ
P(1)ÁFeÁ
S(1)ÁFeÁ
S(2)ÁFeÁ
/
/
86.47(4)
95.40(4)
88.47(4)
79.48(3)
161.34(3)
103.36(4)
81.30(4)
91.09(4)
P(1)Á
P(1)Á
S(1)Á
S(3)Á
P(3)Á
S(3)Á
P(3)Á
/
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
FeÁ
/
S(1)
85.70(3)
174.45(5)
97.07(3)
94.95(4)
98.69(3)
169.29(3)
81.87(4)
/
/S(1)
/
/P(3)
as the sacrificial anode. Applied voltages of 10Á15 V
/
/
/P(3)
/
/
P(3)
S(2)
allowed sufficient current flow for smooth dissolution of
the metal. During electrolysis, nitrogen gas was bubbled
through the solution to provide an inert atmosphere and
also to stir the reaction mixture. The cells can be
/
/S(2)
/
/
/
/S(2)
/
/S(2)
/
/
P(2)
P(2)
P(2)
/
/
P(2)
P(2)
/
/
/
/
/
/
summarised as: Fe(ꢂ)/CH3CNꢂP(SH)x/Pt(ꢀ).
/
to introduce hydrazide type ligands by reaction of 9 with
Me2NHNH2 gave a virtually insoluble amber solid,
which based on analysis has the empirical formula
[Co(PS2)(dppe)] (11). No MS or solution spectroscopic
data could be obtained, but the lack of solubility
suggests the product 11 is a thiolate bridged oligomer.
3.1.1. [Fe{2-(Ph2PO)C6H4S}3] (1)
Electrolysis of an acetonitrile solution (50 cm3)
containing 2-(diphenylphosphino)benzenethiol (0.220
g, 0.75 mmol) at 14 V and 10 mA for 2 h, dissolved 22
mg of metal (Efꢁ
0.52 mol Fꢀ1). As the reaction
/
proceeded a solid was formed immediately at the anode
and hydrogen evolved at the cathode. At the end of the
experiment the solid obtained was filtered, washed with
cool acetonitrile and ethyl ether and dried under vacuum
(0.20 g, 0.214 mmol, 84%). Anal. Calc. for
C54H42FeO3P3S3: C, 65.9; H, 4.3; S, 9.8. Found: C,
66.0; H, 4.50; S, 9.3%. IR (KBr, cmꢀ1): 1575(m), 1438
(s), 1417 (m), 1122 (s), 1093 (m), 1037 (m), 997 (w), 744
(s), 729 (w), 694 (s), 543 (s).
2.3.2. With potentially tetradentate phosphinothiolate
ligands
The reaction of CoCl2 with P(C6H4SH-2)3 (PS3H3) in
the presence of phosphine ligands was analogous to that
with FeCl2. With dppe, red crystalline [Co(PS3)(dppe)]
(12) was obtained and this was shown by X-ray crystal-
lography to be essentially isostructural with the iron

200
P. Pe´rez-Lourido et al. / Inorganica Chimica Acta 356 (2003) 193Á202
/
3.1.2. [Fe{2-(Ph2P)-6(Me3Si)C6H3S}3] (2)
rapidly decomposes to leave a CO-free, pale brown
polymeric solid.
A solution of acetonitrile (50 cm3) containing 2-
diphenylphosphino-6-trimethylsilylbenzenethiol (0.273
g, 0.75 mmol) was electrolysed at 17 V and 10 mA
during 2 h and 20 mg of iron metal were dissolved from
3.1.6. [Fe{PhP(C6H4S-2)2} (dppe)(CO)] (6)
An MeCN (20ml) solution of FeC12 (0.06g, 048
mmol) and dppe (0.18g, 0.45 mmol) was saturated
with CO and PhP(C6H4SH-2)2 (0.15g, 0.46 mmol) was
added and the slow stream of CO through the solution
was maintained for 30 min during which time the
complex precipitated as an orange solid (0.27 g, 72%).
Anal. Calc. for C43H37FeOP3S2 C, 67.0; H, 4.0. Found:
C, 66.4; H, 4.7% IR 1930[n(CO)], 1572, 1096, 737, 694
the anode, Efꢁ
0.48 mol Fꢀ1. The resulting microcrys-
/
talline product was washed with acetonitrile and ethyl
ether and dried, (0.193 g, 0.168 mmol, 67%). Suitable
crystals for X-ray studies were obtained by crystal-
lisation from dichloromethaneꢂmethanol. Anal. Calc.
/
for C63H66FeP3S3Si3: C, 65.7; H, 5.8; S, 8.3. Found: C,
65.1; H, 5.6; S, 8.1%. IR(KBr, cmꢀ1): 3055(m), 2949(m),
2893(m), 1556(m), 1437(m), 1246(m), 1074(w), 1039(w),
997(w), 854(s), 752(s), 692(m), 557(s).
cmꢀ1. Mossbauer: narrow doublet, isomer shift 0.11
¨
mm sꢀ1, quadrupole splitting 0.23 mm sꢀ1. The
instability of the complex with respect to CO loss
precluded MS measurements.
3.1.3. [Fe{2-(Ph2PO)-6(Me3Si)C6H3S}3] (3)
Electrochemical oxidation of an iron anode in a
solution of 2-(diphenylphosphinyl)-6-(trimethylsilyl)
benzenethiol (0.214 g, 0.56 mmol) in acetonitrile (50
cm3), at 10 V and 10 mA for 2 h caused 16 mg of iron to
3.1.7. [Fe{P(C6H4S-2)3}(PMe2Ph)2] (7)
To a pink solution of FeCl2 (0.06 g, 0.48 mmol) and
PMe2Ph (0.13 ml, 0.95 mmol) was added P(C6H4SH-2)3
(0.16 g, 0.47 mmol). The resulting dark red solution was
heated under reflux for 1 h. On cooling the complex
precipitated as a dark red solid (0.26 g, 80%).The
elemented analysis obtained was intermediate between
be dissolved (Efꢁ
0.51 mol.Fꢀ1). During the electrolysis
/
hydrogen was evolved at the cathode and after 1.5 h,
black crystalline needles appeared on the electrodes and
at the bottom of the vessel. The solid was filtered,
washed with acetonitrile and ether and dried under
vacuum, (0.14 g, 0.117 mmol, 62%). Anal. Calc. for
C63H66FeP3O3S3Si3: C, 63.1; H, 5.5; S, 8.0. Found: C,
62.1; H, 5.6; S, 7.5%. IR (KBr, cmꢀ1): 3057(m),
2951(m), 2891(m), 1554(m), 1439(m), 1354(s), 1244(m),
1130(s), 1074(m), 997(w), 854(s), 750(m), 694(m), 559(s).
[Fe{P(C6H4S-2)3}(PMe2Ph)]
and
[Fe{P(C6H4S-
2)3}(PMe2Ph)2]. The FAB MS showed an intense peak
at m/z 566 due to the monophosphine adduct, and a
much weaker peak due to the bis(phosphine) complex.
3.1.8. [Fe{P(C6H4S-2)3}(dppe)] (8)
FeCl2 (0.068 g, 0.54 mmol), dppe (0.4 g, 0.1 mmol)
and P(C6H4SH-2)3 (0.19 g, 0.53 mmol) in MeCN (30ml)
were heated under reflux for 1 h. On cooling the
complex precipitated as a dark red solid (yield 0.32 g,
74%). Even after attempted recrystallisation no satisfac-
tory analyses could be obtained, but the MS showed an
3.1.4. [Fe2{PhP(C6H4S-2)2}3] (4)
A similar experiment (10 V, 10 mA, 2.5 h) with 0.152
g (0.466 mmol) of the ligand PhP(C6H4SH-2)2 in 50 cm3
of acetonitrile, dissolved 25 mg of iron, Efꢁ0.48 mol
/
Fꢀ1. A black crystalline solid formed at the anode
during the electrolysis. Hydrogen was evolved at the
cathode. The solid was collected, washed with cool
acetonitrile, diethyl ether and dried under vacuum
(0.131 g, 0.120 mmol, 78%). Crystals suitable for X-
ray studies were obtained by concentration of the
acetonitrile solution. Anal. Calc. for C54H39Fe2P3S6:
C, 59.8; H, 3.6; S, 17.7. Found: C, 58.3; H, 3.5; S, 17.3%.
IR (KBr, cmꢀ1): 1572(m), 1442 (s), 1423(m), 1246(m)
1124(s), 1097(m), 999(w), 742(s), 729(w), 692(s), 538(s).
intense peak due to [Mꢂ1] at m/z 807.
/
3.1.9. [CoCl{PhP(C6H4S-2)2}(dppe)] (9)
CoCl2 (0.30 g, 2.33 mmol) and dppe (0.6 g, 1.5 mmol)
were stirred in MeCN (30 ml) for 15 min to give a green
solution. PhP(C6H4SH-2)2 (0.5 g, 1.53 mmol) was then
added to give a deep red solution which was then heated
under reflux for 1 h. Cooling to r.t. gave complex 9 as a
dark brown solid (yield 0.76 g, 60%). Anal. Calc. for
C42H37C1CoP3S2: C, 64.7, H, 4.6. Found: C, 64.0, H,
4.6%. IR: 1571, 741, 727, 692 cmꢀ1 FAB MS: m/z 815
3.1.5. [Fe{2-(Ph2P)C6H4S-2}2(CO)2] (5)
A solution of FeCl2 (0.02g, 0.15 mmol) in MeCN
(30ml) was saturated with CO gas for 15 min at room
temperature (r.t.). 2-(Ph2P)C6H4SH (0.1 g, 0.34 mmol)
was added and bubbling of CO through the solution was
continued for 30 min. An orange precipitate of 5 was
produced (0.09 g, 85%). Anal. Calc. for C38H28Fe-
P2O2S2: C, 65.3; H, 4.0; S, 9.2. Found C, 65.3; H,
(weak) [M]ꢂ m/z 780 (strong), [Mꢀ
/
C1]ꢂ m/z 383
strong, [MꢀC1Á
/
/
dppe]ꢂ. All peaks have appropriate
isotope distribution.
3.1.10. [Co{PhP(C6H4S-2)2}(CO)(dppe)]BF4 (10)
Complex 9 (0.06 g) was suspended in MeOH (30 ml)
and CO bubbled through the solution at r.t. for 10 min.
Na[BPh4] (0.5 g) was added to the purple solution to
precipitate 10 as a purple solid (yield 0.07 g, 84%). The
4.6%; S, 9.8%. IR 1979[y(CO)], 1573, 736, 695 cmꢀ1
The complex 5 can be stored under CO but otherwise
.

P. Pe´rez-Lourido et al. / Inorganica Chimica Acta 356 (2003) 193Á
/202
201
instability of the complex with respect to loss of CO
prevented satisfactory elemental analyses, or solution
NMR spectra or mass spectra being obtained. IR:
[14]. For the compound 4 the SQUEEZE program was
used to correct the reflection data for the diffuse
scattering due to disorder solvent [15]. All non-hydrogen
atoms were anisotropic. The hydrogen atoms were
included in idealised positions with Uiso free to refine.
The crystal parameters and other experimental details of
the data collection are summarised in Table 1. A
complete description of the details of the crystallo-
graphic methods is given in Section 5 [12,16].
n(CO) 2052 cmꢀ1
.
3.1.11. [Co{PhP(C6H4S-2)2}(dppe)] (11)
Prepared in a directly analogous manner to 8 using
CoC12 as a dark red solid in 70% yield. Analysis of
sample recrystallised from CH2Cl2Á/hexane: Calc. for
C
44.H37 Cl P3 S3 Co: C, 62.5; H, 4.7. Found C, 63.5; H,
4.4% IR: bands characteristic of phenyl groups 1568,
740, 639 cmꢀ1 FAB MS: m/z 812 [Mꢂ]. An X-ray
crystal structure revealed the complex was essentially
isostructural with complex 8.
4. Conclusions
A number of new phosphinothiolate complexes of
Fe(II), Fe(III), Co(II) and Co(III) have been prepared
and fully characterised. The preferred synthetic route to
complexes with PSH and PS2H2 ligands involves elec-
trochemical oxidation of the metal in the presence of the
ligand and direct reaction with metal halides gives
impure products unless an additional phosphine ligand
is present. Alternatively CO can act as the additional
ligand to give Fe(II) carbonyl complexes, and for Co a
Co(III) carbonyl was obtained. The dominant structural
motif found is pseudo-octahedral geometry with various
combinations of P and thiolate S donors making up the
coordination sphere. Those ligands with bulky tri-
methylsilyl groups in the six-position form complexes
directly analogous to those which are sterically unen-
cumbered. In the case of tetradentate PS3 ligands on Fe
and Co in combination with dimethylphenylphosphine a
facile equilibrium between five and six coordinate forms
is observed although the bis(phosphine) adduct appears
to be favoured in the solid state.
3.1.12. [Co{P(C6H4S-2)3}(PMe2Ph)2] (13)
This was prepared directly analogously to complex 7
using CoCl2 as a dark red solid in 72% yield. Anal. Calc.
for C34H36P3S3Co: C, 59.1; H, 5.0. Found: C, 59.0; H,
4.9%. IR 1567, 943, 907, 726, 701 cmꢀ1 FAB MS.
Strong peak at m/z 551 [Mꢀ
/
PMe2Ph]ꢂ; weak peak at
m/z 691 due to [M]ꢂ.
3.2. X-ray crystal structure determinations
Compounds 2 and 4 were studied on a Siemens
(Bruker) Smart system with a CCD detector. Data
collection was carried out under ambient conditions,
˚
0.71073 A).
using graphite monochromated Mo Ka (lꢁ
/
The crystal parameters and other experimental details of
the data collection are summarised in Table 1. A
complete description of the details of the crystallo-
graphic methods is given in Section 5.
Intensity data of 8 were collected on an EnrafÁ
/
Nonius CAD4 diffractometer with monochromated
Mo Ka radiation. Cell constants were obtained from
least squares refinement of the setting angles of 25
5. Supplementary material
centred reflections in the range 15B
/
u B178. The data
/
Supporting information available: tables in CIF
format providing atomic positional parameters, bond
distances and angles, anisotropic thermal parameters
and calculated hydrogen atoms positions for 2 and 4.
were collected in the v/2u scan mode and three
standard reflection were measured every 2 h of expo-
sure. No loss of intensity was observed which was
linearly corrected during processing. Three standard
reflections were measured every 200 reflections to check
the crystal orientation. The data were corrected Lorentz
and polarisation factors and an absorption correction
was applied using psi-scans of nine reflections.
Acknowledgements
Intensity data for compound 7 were collected on an
Delft-Instruments FAST-TV area detector diffract-
ometer with graphite-monochromated Mo Ka radia-
tion. Cell constants were obtained from least-squares
refinement of the setting angles of 250 reflections having
We thank the Xunta de Galicia (Spain) (Xuga
20910B93 and Xuga PGIDT99PXI20306B) for financial
support.
uꢁ2.34-25.09.
/
References
The structures were solved by direct methods and
refined by a full-matrix least-squares procedure [12].
Neutral atom scattering factors were taken from Cromer
and Waber [13] and anomalous dispersion from Cromer
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