Facile synthesis of a rare example of an iron(III) iodide complex, [FeI3(AsMe3)2], from the reaction of Me 3AsI2 with unactivated iron powder

Article abstract of DOI:10.1016/j.poly.2013.02.066

The reaction of Me₃AsI₂ with unactivated iron powder provides a synthetic entry into the coordination chemistry of iron(III) iodide, which is inaccessible by traditional routes due to the low stability of the parent halide FeI₃. The reaction of iron powder with Me ₃AsI₂ results in the formation of a trigonal bipyramidal complex, [FeI₃(AsMe₃)₂], which features the iodide ligands in the equatorial positions, and the Me₃As groups occupying the axial positions. This complex is a rare example of an iron(III) iodide complex, and is the first iron(III) complex of a monodentate tertiary arsine ligand. The preparation of [FeI₃(AsMe₃) ₂] via the direct oxidation of iron powder further demonstrates that complexes of soft donor ligands can be prepared with hard transition metal centres, such as iron(III), in direct contravention of the HSAB principle. The structure of [FeI₃(AsMe ₃)₂] is isomorphous with all previously reported [MX ₃(EMe₃)₂] (M = main group or transition metal, X = halide, E = N, P, As) trigonal bipyramidal structures.

Full text of DOI:10.1016/j.poly.2013.02.066

Polyhedron 55 (2013) 67–72
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Facile synthesis of a rare example of an iron(III) iodide complex,
[FeI3(AsMe3)2], from the reaction of Me3AsI2 with unactivated iron powder
⇑
Nicholas A. Barnes , Stephen M. Godfrey, Nicholas Ho, Charles A. McAuliffe, Robin G. Pritchard
School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of Me3AsI2 with unactivated iron powder provides a synthetic entry into the coordination
chemistry of iron(III) iodide, which is inaccessible by traditional routes due to the low stability of the par-
ent halide FeI3. The reaction of iron powder with Me3AsI2 results in the formation of a trigonal bipyrami-
dal complex, [FeI3(AsMe3)2], which features the iodide ligands in the equatorial positions, and the Me3As
groups occupying the axial positions. This complex is a rare example of an iron(III) iodide complex, and is
the first iron(III) complex of a monodentate tertiary arsine ligand. The preparation of [FeI3(AsMe3)2] via
the direct oxidation of iron powder further demonstrates that complexes of ‘‘soft’’ donor ligands can be
prepared with ‘‘hard’’ transition metal centres, such as iron(III), in direct contravention of the HSAB prin-
ciple. The structure of [FeI3(AsMe3)2] is isomorphous with all previously reported [MX3(EMe3)2]
(M = main group or transition metal, X = halide, E = N, P, As) trigonal bipyramidal structures.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 22 January 2013
Accepted 15 February 2013
Available online 5 March 2013
Dedicated to the memory of the late Dr.
Steve Godfrey (1966–2011), and Prof. Noel
McAuliffe (1941–2002).
Keywords:
Activation of metal powders
Transition metal complexes
Tertiary arsine complexes
HSAB theory
1. Introduction
complexes [FeI3{S@C(NMe2)2}] and [FeI3{O@C(NMe2)2}], [15,16]
both of which have been crystallographically characterised and
Iron(III) iodide stands out amongst the binary halides of iron
due to its low stability. Indeed, for many years FeI3 was believed
to be non-existant, since iron(III) is reduced by [I]ꢀ to iron(II), with
formation of I2 (especially in aqeuous media) [1]. Only as recently
as 1988 Yoon and Kochi reported the first preparation of FeI3,
which was obtained as a black solid via the photochemical reaction
of [Fe(CO)4I2] with I2 in hexane [2,3]. In the solid-state, FeI3 shows
moderate stability, but can only be synthesised in small quantities,
and is highly unstable in solution. It is clear that the paucity of
reports on neutral complexes of FeI3 is a consequence of the insta-
bility of the parent halide.
There are only a few reports of iron(III) iodide coordination
complexes, usually obtained via oxidation of an iron(II) complex,
or utilising a combination of FeI2 and I2. Salts containing the tetra-
hedral [FeI4]ꢀ anion may be prepared, either from the reaction of
[FeCl4]ꢀ with anhydrous HI [4], or via oxidation of FeI2 with I2 in
the presence of an iodide salt [5–7]. The structures of a number
of salts featuring the [FeI4]ꢀ anion have been reported [6–14], with
Fe–I bonds typically varying between 2.51 and 2.57 Å. The related
[FeI3(THF)]ꢀ anion has also been crystallographically characterised
in the mixed iron(II)/(III) salt [Fe(THF)6][FeI3(THF)]2 [7]. The only
neutral iron(III) iodide complexes to have been reported are the
feature the iron atom in a tetrahedral geometry. A small number
of ionic iron(III) iodide complexes of chelating phosphines and
arsines have been reported via the oxidation of iron(II) iodide com-
plexes with concentrated HNO3. The reactions of [FeI2(L–L)2], L–
L = o-C6H4(PMe2)2, o-C6H4(AsMe2)2, o-C6F4(AsMe2)2, with HNO3 in
the presence of HBF4 results in the formation of [FeI2(L–L)2][BF4]
[17]. Subsequently, the [FeI2{o-C6H4(AsMe2)2}2]+ cation has been
crystallographically characterised as the [I3]ꢀ salt, and contains
octahedral iron(III) with mutually trans iodide ligands [18].
We have previously shown that metal complexes can be synths-
ised from the reaction of R3EX2 compounds (E = P, As, Sb; X = Br, I)
directly with unactivated metal powders [19]. A number of com-
plexes prepared by this synthetic route cannot be synthesised via
conventional routes, and some, such as [CoI3(SbPh3)2] [20], defy
Pearsons HSAB principle [21].
The reaction of unactivated iron powder has been employed in a
number of these reactions. For example, Me2PhPBr2 reacts with
iron powder to produce a white solid, which when exposed to trace
amounts of O2 forms a deep–purple iron(III) complex [FeBr3{-
PPhMe2}2] [22]. The structure of this complex has been determined
and shown to be trigonal bipyramidal at iron, with the phosphine
ligands occupying the axial positions. Alternatively, the iron(0) car-
bonyl [Fe2(CO)9] could be oxidised by R3EX2 (E = P, As; X = Br, I) [8],
to yield either either iron(II) species, [R3EX][FeX3(ER3)], or iron(III)
species, [R3EX][FeX4]. The latter were only observed when X = Br.
⇑
Corresponding author. Tel.: +44 (0)161 306 4516; fax: +44 (0)161 306 4559.
E-mail address: nick_barnes28@hotmail.com (N.A. Barnes).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.02.066

68
N.A. Barnes et al. / Polyhedron 55 (2013) 67–72
We have noticed the tendency of Me3EX2 adducts to behave dif-
sine ligands to have been crystallographically characterised are the
iron(II) complex [FeI2{o-C6H4(AsMe2)2}2] and the cationic iron(III)
species in [FeI2{o-C6H4(AsMe2)2}2][I3]ꢂ2CH2Cl2 [18].
ferently towards metal powders than other R3EX2 systems [19].
The reaction generally does not produce ionic complexes (which
are often formed with larger R groups). Instead, trigonal bipyrami-
dal complexes of formula [MX3(EMe3)2] are formed, even when the
+3 oxidation state is uncommon for phosphine/arsine complexes,
as in the case of [CoI3(EMe3)2] [23,24], or [NiI3(EMe3)2] [22,24],
(E = P, As), or when the CFSE strongly favours a different geometry,
as in the case of [AuI3(PMe3)2], where a square–planar geometry
would have been expected [25]. We now report the reaction of
Me3AsI2 with elemental iron powder to see if this synthetic route
provides an entry into neutral FeI3 complexes.
In view of the limited structural data for iron–halide complexes
with arsenic donors we sought to obtain crystals of [FeI3(AsMe3)2].
2.2. Structural features of [FeI3(AsMe3)2]
Crystals were obtained by dissolving the complex in warm
dichloromethane:ether (50:50), followed by cooling to ca. 2 °C.
Dark black–green crystals formed after several days. An ORTEP rep-
resentation of the crystal structure of [FeI3(AsMe3)2] is shown in
Fig. 1, along with selected bond lengths and angles.
Strikingly, [FeI3(AsMe3)2] is isomorphous with all 14 previously
reported trigonal bipyramidal [MX3(EMe3)2] (E = N, P, As) struc-
tures, all of which crystallise in the orthorhombic space group
Pnma, with similar cell dimensions, [23–25,28b,28h,33–41], see
Table 1.
The iodide ligands in [FeI3(AsMe3)2] occupy the equatorial
positions of the trigonal bipyramid, whilst the Me3As ligands are
located in the axial positions. The structure has a crystallographi-
cally imposed mirror plane running through atoms Fe(1), As(1),
As(2), I(2), C(2) and C(4). This type of symmtery is identical to that
observed throughout the isomorphous [MX3(EMe3)2] (E = N, P, As)
series of structures. The distortion from an idealised D3h trigonal
bipyramidal symmetry is low, with both Fe–As bonds being similar
in magnitude to each other, 2.414(3) and 2.419(3) Å, as are the Fe–I
bonds which vary between 2.571(3) to 2.5828(14) Å. The angles
around the iron atom are also close to the expected for a trigonal
bipyramidal geometry, with the As–Fe–As angle close to linear at
178.46(11)°, whilst the As–Fe–I angles are close to 90°, as they vary
between 88.48(8) and 90.79(6)°.
2. Results and discussion
2.1. Synthesis of [FeI3(AsMe3)2]
The reaction of Me3AsI2 and iron powder was performed in a
2:1 ratio in anhydrous diethyl ether. After stirring at ambient tem-
perature for ca. four days all the iron powder had been consumed,
and a dark green precipitate was formed which was slightly solu-
ble in diethyl ether. The solid was isolated and analysed as [FeI3(-
AsMe3)2], although the overall reaction also produces half an
equivalent of iodine, see Eq. (1). The iodine can be removed from
the product by washing with anhydrous hexane.
O
2Me3AsI2 þ Fe E!t2 ½FeI3ðAsMe3Þ2ꢁ þ 1=2I2
ð1Þ
The presence of iodine was confirmed from the electronic spec-
trum of the filtrate, which, in addition to peaks due to the iron
complex, exhibited a band at 525 nm, typical for diiodine in diethyl
ether [26]. The electronic spectrum of the black–green iron
complex displayed two ꢀp1rominent bands, one at 461 nm
The Fe–As bonds in [FeI3(AsMe3)2] are considerably longer than
those observed in low oxidation state complexes with the AsMe3
ligand, such as [Fe(CO)4(AsMe3)], d(Fe–As): 2.30(3) Å [31], and
(
(
e
e
max = 9100 dm3 molꢀ1 cm ), and the other at 671 nm
max = 6900 dm3 molꢀ1 cmꢀ1). The former band is attributed to
an iodine ligand-to-metal charge-transfer transition, I(
p) ? Fe,
[Fe2(CO)6(l–CF2)(AsMe3)2], d(Fe–As): 2.3713(5) to 2.3782(6) Å
whilst the latter is assigned as As( ) ? Fe, by comparison with re-
r
[32]. These bonds are also longer than those observed for the
iron(II)/iron(III) redox pair, [FeI2{o-C6H4(AsMe2)2}2]/[FeI2{o-C6H4
(AsMe2)2}2]+ [18]. In the neutral iron(II) complex the Fe–As bonds
are 2.3372(5) and 2.3388(5) Å, whilst in the iron(III) cation the Fe–
ported data for other iron(III) arsine complexes [17,27]. Addition-
ally, the spectrum also displays two shoulder peaks at 542 and
600 nm, which may arise due to d–d transitions.
The formation of an iron arsine complex in a high oxidation
state (+3) is unexpected, (on the basis of the HSAB principle)
[21], as is formation of a five-coordinate complex for a d5 iron(III)
configuration. A search of the CSD database (Dec. 2012) shows that
the vast majority of reported iron(III) complexes exhibit a six-coor-
dinate octahedral geometry. There are far fewer reports of neutral
five-coordinate [FeX3(L)2] structures, (ten in total, eight of which
are FeCl3 complexes, [28] and two are FeBr3 complexes). [29]1
The structure of [FeI3(AsMe3)2] thus represents the first example of
this geometry when X = I. All of the five-coordinate structures have
a trigonal bipyramidal geometry, with the halide atoms in the equa-
torial positions, and the neutral ligands occupying the axial posi-
tions, as is the case in [FeI3(AsMe3)2]. Additionally, there are two
crystallographically characterised examples of [FeCl3(L–L)] com-
plexes with chelating ligands, where the five-coordinate geometry
is distorted between trigonal bipyramidal and square pyramidal by
the chelating ligand [30].
There is also very little structural data known for complexes
with Fe–As bonds. A number of structures of organometallic com-
plexes with iron in a low oxidation state are known. These include
the iron(0) complex [Fe(CO)4(AsMe3)], which is trigonal bipyrami-
dal with the Me3As ligand occupying one of the axial positions [31],
and a number of cluster complexes with difluorocarbene, CO and
AsMe3 ligands. [32] The only iron–halide complexes containing ar-
Fig. 1. ORTEP representation of the molecular structure of [FeI3(AsMe3)2]. Thermal
ellipsoids are shown at the 30% probability level. Selected bond lengths [Å] and
angles [°]: Fe(1)–I(1): 2.5828(14), Fe(1)–I(2): 2.571(3), Fe(1)–As(1): 2.414(3), Fe(1)–
As(2): 2.419(3), As(1)–C(1): 1.912(13), As(1)–C(2): 1.94(2), As(2)–C(3): 1.911(14),
As(2)–C(4): 1.928(16), As(1)–Fe(1)–As(2): 178.46(11), I(1)–Fe(1)–I(2): 120.93(4),
I(1)–Fe(1)–I(1i): 118.11(8), I(1)–Fe(1)–As(1): 90.79(6), I(1)–Fe(1)–As(2): 90.00(6),
I(2)–Fe(1)–As(1): 89.98(8), I(2)–Fe(1)–As(2): 88.48(8). Symmetry operations to
generate equivalent atoms: (i): x, ½ ꢀ y, z.
1
JODFOX: See Ref. [22].

N.A. Barnes et al. / Polyhedron 55 (2013) 67–72
69
Table 1
Comparison of crystal data for the isomorphous series of [MX3(EMe3)2] trigonal bipyramidal structures which crystallise in the orthorhombic Pnma spacegroup: CSD database
search (Dec. 2012).
Complex
CCDC code
Cell parameters, a, b, c (Å)
Cell volume (Å3)
Refs.
[TiBr3(NMe3)2]
[VCl3(NMe3)2]
[CrCl3(NMe3)2]
[FeCl3(NMe3)2]
[AlCl3(NMe3)2]
[InCl3(NMe3)2]
[MnI3(PMe3)2]
[FeCl3(PMe3)2]
[CoI3(PMe3)2]
[NiI3(PMe3)2]
[AuI3(PMe3)2]
[InCl3(PMe3)2]
[FeI3(AsMe2)2]
[CoI3(AsMe3)2]
[NiI3(AsMe3)2]
TMATBI
CLTAMV
TMAMCR
FINJIV
10.23(2), 10.28(2), 13.46(3)
9.817(20), 10.127(14), 13.152(14)
9.69(1), 10.12(1), 13.05(2)
9.753(9), 10.150(11), 13.156(12)
9.645(8), 9.994(2), 12.918(6)
9.99(1), 10.09(1), 13.08(1)
10.509(1), 11.167(8), 14.398(2)
9.846(2), 10.680(3), 13.439(7)
10.217(4), 11.184(2), 14.252(4)
10.197(3), 11.155(8), 14.213(3)
10.488(4), 11.122(3), 14.279(3)
10.418(8), 10.769(9), 13.808(9)
10.412(2), 11.3617(10), 14.543(3)
10.142(3), 11.210(3), 14.291(4)
10.298(5), 11.363(3), 14.440(5)
1415(1)
1307.5
1268(1)
1302.4(9)
1245.2(12)
1318.7
[33]
[34]
[33]
[28b]
[35], [36]
[37]
[38], [39]
[28g]
[23]
[40]
[25]
[41]
this work
[24]
QQQCMP
DOHBAD
CEVTEC
SAVHOM
VUHZIH
GAPYAX
TURBOH
VOXBUF
this work
ZOJMEQ
ZOJMIV
1689.7
1413(1)
1629(1)
1616.7(5)
1148(1)
1549(2)
1720.4(5)
1625(1)
1690(2)
[24]
As bonds are longer, at 2.3792(4) and 2.3822(5) Å. The Me3As li-
gands in [FeI3(AsMe3)2] are therefore more weakly bound than in
these previously reported examples, which is consistent with the
expected weaker nature of the Fe–As bond due to the increased
mismatch of the soft arsenic donor and the harder iron(III) metal
In almost all of the complexes the M–X bonds to the two halide
ligands related by the mirror plane are longer than the M–X bond
to the third halide ligand. Only [FeCl3(PMe3)2] is an exception to
this, where the Fe–Cl bonds are equal within experimental error
[28g]. In a number of cases, as in [FeI3(AsMe3)2], the difference
centre, and the reduction in the contribution of
p
-backbonding
(D) between the two M–X distances is very small, but is much
for the higher oxidation state, as recognised by Levason and co-
workers for the redox pair above [18].
more marked in other complexes, such as [TiBr3(NMe3)2]. Distor-
tion in the M–X bond lengths and X–M–X angles in a number of
these complexes has been attributed to Jahn–Teller effects.
[40,42–43] In a trigonal bipyramidal field the d1, d3, d5(LS),
d6(HS), d7(LS) and d8(HS) configurations may be Jahn–Teller active.
A relationship between distortions in the magnitude of the equato-
rial X–M–X angles and expected Jahn–Teller activity can be seen in
A comparison of the Fe–I bonds in [FeI3(AsMe3)2] with the small
number of crystallographically characterised iron(III) iodide com-
plexes is shown in Table 2. The Fe–I bonds of 2.571(3) to
2.5828(14) Å are significantly longer than those observed for the
tetrahedral neutral iron(III) iodide complexes, [FeI3{S@C(NMe2)2}]
and [FeI3{O@C(NMe2)2}], [15,16] but are not as elongated as the
Fe–I bonds of 2.6009(3) Å in the cationic [FeI2{o-C6H4(AsMe2)2}2]+
species [18].
A comparison of bond lengths and angles within the isomor-
phous series of [MX3(EMe3)2] structures shows that some of the
complexes display some distortion from an ideal trigonal bipyra-
midal geometry. This distortion is mainly observed in the M–X
bonds to the equatorial halide ligands, and in the X–M–X angles
between the equatorial ligands, see Table 3. In contrast, the angles
between the axial EMe3 ligands are close to the expected linear
geometry, (in all the structures the angles are between 176° and
180°).
Table 3, where
D
(X–M–X) varies considerably between different
complexes in the series. For example,
D
(X–M–X) is only 2.4° for
[CoI3(AsMe3)2], but is 12.9° for [CrCl3(NMe3)2]. The chromium
complex has a d3 configuration and is expected to be Jahn–Teller
active, [33,42] whereas the cobalt complex has been assigned a
low-spin d6 configuration [43], and hence is Jahn–Teller inactive.
The distortion in [TiBr3(NMe3)2] (d1) manifests itself in the varia-
tion observed between the equatorial M–X bond lengths [44], as
the differences between the X–M–X angles is rather small. Distor-
tions in the nickel complex [NiI3(PMe3)2] have also previously been
discussed in terms of Jahn–Teller effects [40]. The only complex to
show unexpected marked distortions is [AuI3(PMe3)2] [25], where
Jahn–Teller activity would only be expected for a high-spin com-
plex, however the strong field expected for a 5d8 system, coupled
with the advantagous CFSE in pairing all the d electrons would
strongly favour a low-spin configuration for this complex.
Table 2
Comparison of Fe–I bond lengths in iron(III) iodide complexes.
In the structure of [FeI3(AsMe3)2] the
D(X–M–X) is small, with
Complex
Fe–I (Å)
Refs.
I–Fe–I angles of 118.11(8)° and 120.93(4) °. The smaller of these
two angles is the angle between the symmetry related I(1) atoms,
which is the smallest angle in all of the [MX3(EMe3)2] structures.
The amine complex [FeCl3(NMe3)2] also shows similar features
[28b], whilst there is more distortion in [FeCl3(PMe3)2], where
[FeI3(AsMe3)2]
2.571(3)–
2.5828(14)
this
work
[15]
[16]
[18]
[6]
[7]
[8]
[9]
[10]
[FeI3{S@C(NMe2)2}]
[FeI3{O@C(NMe2)2}]
[FeI2{o-C6H4(AsMe2)2}2][I3]
[Et4N][FeI4]
[Fe(OCH2)6][FeI4]
[Ph4Sb][FeI4].Ph3SbI2
2.530(1)–2.553(1)
2.526(1)–2.532(1)
2.6009(3)
2.531(3)–2.540(3)
2.517(4)–2.567(4)
2.525(7)–2.553(7)
2.518(2)–2.548(2)
2.5369(11)–
2.5511(11)
2.5451(7)–
2.5468(8)
2.519(2)–2.548(2)
D
(X–M–X) is 7.4(2)°, compared to 2.9(5)° for [FeCl3(NMe3)2] and
2.82(8)° for [FeI3(AsMe3)2]. The complex [FeCl3(PMe3)2] is known
to be low-spin d5 [28g], which would be Jahn–Teller active in a tri-
gonal bipyramidal field. The much lower distortion for the NMe3
and AsMe3 complexes may indicate that these are high-spin d5,
and hence Jahn–Teller inactive.
Molecules of [FeI3(AsMe3)2] pack in a regular fashion at dis-
tances beyond van der Waals contacts, as shown in Fig. 2, viewed
down the a-cell dimension. One of the methyl groups on the AsMe3
ligand As(2) is oriented towards the two symmetry related I(1)
atoms on a neighbouring molecule, although the H4(B)ꢂ ꢂ ꢂI(1) inter-
[{Cp2Cr2(
l-SCMe3)–(
l3-S)2}2Fe][FeI4]
[Cp2Co][FeI4]
[{(C2H5)4C4P}2Fe][FeI4]
[11]
[12]
[{(o-C6H4SMe)S(CH2)2S(o-
C6H4SMe)}Fe(CO)I][FeI4]
[(Cp⁄)2Mo2(
l
-I)4][FeI4]
2.510(3)–2.546(3)
2.526(5)–2.569(4)
2.611(2)
[13]
[14]
[7]
[(Me2N)2C@S–S@C(NMe2)2][FeI4]
[Fe(THF)6][FeI3(THF)]2

70
N.A. Barnes et al. / Polyhedron 55 (2013) 67–72
Table 3
Comparison of equatorial M–X bonds [Å] and X–M–X angles [°] around the metal centre for the isomorphous series of [MX3(EMe3)2] (E = N, P, As) trigonal bipyramidal structures.
The X–M–X angle of lowest magnitude is that between the two symmetry related halide ligands.
Complex
M–Xeq (Å)
M–X (Å)
X–M–X (°)
(X–M–X) (°)
Refs.
[TiBr3(NMe3)2]
[VCl3(NMe3)2]
[CrCl3(NMe3)2]
[FeCl3(NMe3)2]
[AlCl3(NMe3)2]
[InCl3(NMe3)2]
[MnI3(PMe3)2]
[FeCl3(PMe3)2]
[CoI3(PMe3)2]
[NiI3(PMe3)2]
[AuI3(PMe3)2]
[InCl3(PMe3)2]
[FeI3(AsMe2)2]
[CoI3(AsMe3)2]
[NiI3(AsMe3)2]
2.400(8), 2.445(5) ꢃ 2
2.236(5), 2.241(5) ꢃ 2
2.222(3), 2.253(5) ꢃ 2
2.207(2), 2.228(1) ꢃ 2
2.1676(10), 2.1725(5) ꢃ 2
2.343(8), 2.376(4) ꢃ 2
2.605(6), 2.635(3) ꢃ 2
2.232(5), 2.231(13) ꢃ 2
2.543(2), 2.551(1) ꢃ 2
2.530(1), 2.551(1) ꢃ 2
2.709(3), 2.761(2) ꢃ 2
2.453(4), 2.503(3) ꢃ 2
2.571(3), 2.5828(14) ꢃ 2
2.510(5), 2.530(3) ꢃ 2
2.531(9), 2.550(5) ꢃ 2
0.045(8)
0.005(5)
0.031(5)
0.021(2)
0.0049(10)
0.033(8)
0.030(6)
0.001(13)
0.008(2)
0.021(1)
0.052(3)
0.050(4)
0.0118(14)
0.020(5)
0.019(9)
117.5(3), 121.3(2) ꢃ 2
118.1(2), 121.0(1) ꢃ 2
111.4(2), 124.3(1) ꢃ 2
118.0(5), 120.99(4) ꢃ 2
117.85(3), 121.07(2) ꢃ 2
117.45(19), 121.27(14) ꢃ 2
117.5(1), 121.3(1) ꢃ 2
115.1(2), 122.46(9) ꢃ 2
118.17(8), 120.91(4) ꢃ 2
114.70(4), 122.65(2) ꢃ 2
115.01(9), 122.49(4) ꢃ 2
116.1(1), 122.0(1) ꢃ 2
118.11(8), 120.93(4) ꢃ 2
118.4(2), 120.8(1) ꢃ 2
114.7(3), 122.6(1) ꢃ 2
3.8(3)
2.9(3)
[33]
[34]
[33]
[28b]
[35,36]
[37]
[38,39]
[28g]
[23]
[40]
[25]
[41]
this work
[24]
12.9(1)
2.9(5)
3.22(3)
3.82(19)
3.8(1)
7.4(2)
2.74(8)
7.95(4)
7.48(9)
5.9(1)
2.82(8)
2.4(2)
7.9(3)
[24]
Fig. 2. Packing of molecules of [FeI3(AsMe3)2] viewed down the crystallographic a-axis.
actions of 3.43 to 3.53 Å are notably longer than the sum of the van
der Waals radii of hydrogen and iodine (3.18 Å).
bipyramidal geometry is consistent with the isomorphous set of
[MX3(EMe3)2] (M = TM or main group metal, X = any halogen,
E = N, P, As) complexes, all of which crystallise in the orthorhombic
Pnma space group, irrespective of the nature of M, X or E. A study of
this series of complexes shows that some complexes exhibit devi-
ations from an ideal trigonal bipyramidal geometry, and these
deviations appear to be due to Jahn–Teller effects.
The crystallographic cone angles for the Me3As ligands in [FeI3(-
AsMe3)2] have been calculated directly from the structure, and are
116.7° for the As(1) ligand, and 116.3° for the As(2) ligand. These
values are close to that of 121° calculated for Me3As by Imyanitov
[45]. An examination of other metal complexes with Me3As ligands
show that similar cone angles are observed. For example, the cone
angles lie between 114.0° and 116.3° for the Me3As ligands in the
iron clusters [Fe2(CO)6(l-CF2)(AsMe3)2] and [Fe2(CO)5(l–CF2)(-
4. Experimental
AsMe3)3] [32], and between 115.9° and 118.0° in the series of tet-
rahedral [GaX3(AsMe3)] (X = Cl, Br, I) complexes [46].
4.1. Reagents and physical measurements
The iron(III) complex [FeI3(AsMe3)2] is highly sensitive to air
and moisture, therefore standard Schlenk techniques were em-
ployed throughout, with all additions being performed under a
stream of dry argon. Diethyl ether and hexane were purchased
commercially (BDH) and freshly distilled from sodium/benzophe-
none ketyl before use. Dichloromethane was purchased (Aldrich)
as anhydrous grade and stored over 4 Å molecular sieves. Me3AsI2
was prepared as previously described [47]. Iron powder (10–
40 mesh) was purchased commercially (Aldrich) and used as re-
3. Conclusion
The oxidation of unactivated iron powder with Me3AsI2 pro-
vides an entry route into the coordination chemistry of iron(III) io-
dide, which is inaccessible via traditional synthetic routes, due to
the low stability of the parent halide. [FeI3(AsMe3)2] is an example
of a complex which defies the HSAB principle, as the hard iron(III)
centre has a very soft As2I3 donor set. The adoption of a trigonal

N.A. Barnes et al. / Polyhedron 55 (2013) 67–72
71
ceived. Elemental analyses were performed by the Chemistry
Acknowledgements
Departmental Microanalytical service. Electronic spectra were pre-
pared in anhydrous diethyl ether in 1 cm path quartz cells fitted
The authors would like to thank EPSRC for a research student-
ship (NH), and for providing funding for the X–ray facility (Re-
search Initiative Grant). We would like to thank Dr S. A. Cotton,
University of Birmingham for productive discussions.
with PTFE seals, and recorded on
spectrophotometer.
a Shimadzu UV-2101PC
4.2. Crystallographic details
Appendix A. Supplementary material
Details of the structural analysis for [FeI3(AsMe3)2] are summa-
rised in Table 4. Diffraction data were recorded on a Rigaku AFC 6S
CCDC 177337 contains the supplementary crystallographic data
for [FeI3(AsMe3)2]. This data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
four-circle diffractometer using graphite-monochromated Mo K
a
radiation (k = 0.71073 Å), at 293(2) K. Structural data were solved
by direct methods, with full-matrix least squares refinement on
F2 using the SHELX-97 program [48] Absorption corrections were ap-
plied by the psi-scan method [49]. Non-hydrogen atoms were re-
fined with anisotropic thermal parameters. The hydrogen atom
treatment was mixed, with all modeled in ideal positions, except
for atoms H(2A)/(2B) and H(4A)/(4B). All thermal ellipsoid plots
were generated using ORTEP-3 for Windows [50], and other pictures
generated using the MERCURY program [51]. The crystallographic
cone angles were calculated directly from the crystal structure,
using the method of Immirzi and Musco [52].
References
[1] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic
Chemistry, sixth Ed., Wiley and Sons, New York, 1999 (Chapter 17, p. 788).
[2] K.B. Yoon, J.K. Kochi, Z. Anorg, Allg. Chem. 561 (1988) 174.
[3] K.B. Yoon, J.K. Kochi, Inorg. Chem. 29 (1990) 869.
[4] J.L. Ryan, Inorg. Chem. 8 (1969) 2058.
[5] S. Pohl, W. Saak, Z. Naturforsch. Teil B. 39 (1984) 1236.
[6] S. Pohl, W. Saak, Z. Anorg, Allg. Chem. 523 (1985) 25.
[7] W. Saak, S. Pohl, Z. Anorg, Allg. Chem. 552 (1987) 186.
[8] H.P. Lane, S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard, J. Chem. Soc., Dalton
Trans. (1994) 3249.
[9] A.A. Pasynskii, I.L. Eremenko, E.E. Stomakhina, S.E. Nefedov, O.G. Ellert, A.I.
Yanovsky, Y.T. Struchkov, J. Organomet. Chem. 406 (1991) 383.
[10] J.M. Migliori, W.M. Reiff, A.M. Arif, Inorg. Chem. 43 (2004) 6875.
[11] X. Sava, L. Ricard, F. Mathey, P. Le Floch, J. Organomet. Chem. 671 (2003) 120.
[12] D. Sellmann, G. Mahr, F. Knoch, M. Moll, Inorg. Chim. Acta 224 (1994) 45.
[13] J.C. Gordon, P.E. Fanwick, R. Poli, Acta Crystallogr., Sect. C: Struct. Commun. 52
(1996) 1098.
[14] U. Bierbach, W. Saak, D. Haase, S. Pohl, Z. Naturforsch., Teil B. 45 (1990) 45.
[15] S. Pohl, U. Bierbach, W. Saak, Angew. Chem., Int. Ed. 28 (1989) 776.
[16] S. Pohl, U. Opitz, W. Saak, D. Haase, Z. Anorg, Allg. Chem. 619 (1993) 608.
[17] N.R. Champness, W. Levason, R.D. Oldroyd, S.R. Preece, Inorg. Chem. 33 (1994)
2060.
[18] W. Levason, M.L. Matthews, B. Patel, G. Reid, M. Webster, Polyhedron 23
(2004) 605.
[19] S.M. Godfrey, C.A. McAuliffe, Modern Coordination Chemistry. The Legacy of
Joseph Chatt, RSC, Cambridge, 2002. pp. 79–88, and references therein.
[20] S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard, J. Chem. Soc. Chem. Commun.
(1994) 45.
4.3. Synthetic details
4.3.1. Reaction of Me3AsI2 with Fe powder
0.645 g (1.73 ꢃ 10ꢀ3 mol) of Me3AsI2 was suspended in 30 mL
of anhydrous Et2O. Under a stream of argon 0.048 g (8.63 ꢃ 10ꢀ4
-
mol) of iron powder was added. The solution was left to stir for ca.
7 days, after which time the dark black–green solid was isolated by
standard Schlenk techniques, washed with 5 mL of anhydrous hex-
ane to remove any remaining iodine, and dried in vacuo. The solid
was then transferred in the glove box to pre-dried argon-filled am-
poules. Yield = 0.376 g (64.4%). Anal. Calc. for C6H18As2FeI3: C, 10.6;
H, 2.7; I, 56.3%; Found: C, 10.4; H, 2.6; I, 56.5%. UV–Vis, Et2O, k/nm
(e
max/dm3 molꢀ1 cmꢀ1): 461(9100), 542(sh), 600(sh), 671(6900).
[21] R.G. Pearson, J. Am. Chem. Soc. 85 (1963) 3533.
[22] S.M. Godfrey, D.G. Kelly, A.G. Mackie, P.P. MacRory, C.A. McAuliffe, S.M.
Watson, J. Chem. Soc., Chem. Commun. (1991) 1447.
Table 4
Crystallographic parameters for [FeI3(AsMe3)2].
[23] C.A. McAuliffe, S.M. Godfrey, A.G. Mackie, R.G. Pritchard, Angew. Chem., Int. Ed.
31 (1992) 919.
[24] N. Bricklebank, S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard, J. Chem. Soc.,
Dalton Trans. (1996) 157.
[25] S.M. Godfrey, N. Ho, C.A. McAuliffe, R.G. Pritchard, Angew. Chem., Int. Ed. 35
(1996) 2344.
[26] F.T. Lang, R.L. Strong, J. Am. Chem. Soc. 87 (1965) 2345.
[27] J.I. Zink, P.-H. Liu, B. Anfield, Inorg. Chem. 18 (1979) 1013.
[28] (a) NPRFE: J-.C. Daran, Y. Jeannin, L.M. Martin, Inorg. Chem. 19 (1980) 2935;
(b) . FINJIV:K.R. Millington, S.R. Wade, G.R. Willey, M.G.B. Drew, Inorg. Chim.
Acta 89 (1984) 185;
[FeI3(AsMe3)2]
Empirical formula
Fw
C6H18As2FeI3
676.59
Green–black, needle
Orthorhombic
Pnma (No. 62)
0.25 ꢃ 0.15 ꢃ 0.15
Colour, habit
Crystal system
Space group
Crystal size (mm)
Unit cell dimensions
a (Å)
10.412(2)
11.3617(10)
(c) . IJIYIJ:X-L. Li, D-Z. Niu, Z-S. Lu, D-Q. Shi, K-B. Yu, Chin. J. Struct. Chem. 22
(2003) 47;
b (Å)
(d) . KAJTOE:L.V. Ivakina, N.R. Streltsova, V.K. Belskii, P.A. Storozhenko, B.M.
Bulychev, A.B. Tarasov, Russ. J. Gen. Chem. 57 (1987) 1600;
(e) . UJIMUV:J. Spandl, M. Kusserow, I. Brüdgam, Z. Anorg. Allg. Chem. 629
(2003) 968;
(f) . ZOCYUL:U. Russo, B. Zarli, G. Favero, G. Valle, G.J. Long, Inorg. Chim. Acta
239 (1995) 67;
c (Å)
14.543(3)
90
90
90
1720.4(5)
293(2)
4
2.612
0.71073
a
(°)
b (°)
(°)
c
Volume (Å3)
T (K)
(g) . SAVHIG/SAVHOM:J.D. Walker, R. Poli, Inorg. Chem. 28 (1989) 1793.
[29] (a) D. Lundberg, A.-S. Ullström, P. D’Angelo, D. Warminska, I. Persson, Inorg.
Chim. Acta 360 (2007) 2744.
[30] K. Marjani, M. Mousavi, D.L. Hughes, Transition Met. Chem. 34 (2009) 85;
L.E.N. Allan, M.P. Shaver, A.J.P. White, V.C. Gibson, Inorg. Chem. 46 (2007)
8963.
[31] J.-J. Legendre, C. Girard, M. Huber, Bull. Soc. Chim. Fr. (1971) 1988.
[32] M. DelaVarga, W. Petz, B. Neumüller, R. Costa, Inorg. Chem. 45 (2006) 9053.
[33] P.T. Green, B.J. Russ, J.S. Wood, J. Chem. Soc. (A) (1971) 3636.
[34] P.T. Green, P.L. Orioli, J. Chem. Soc. (A) (1969) 1621.
[35] I.R. Beattie, G.A. Ozin, H.E. Blayden, J. Chem. Soc. (A) (1969) 2535.
[36] T. Gelbrich, U. Dümichen, J. Sieler, Acta Crystallogr., Sect. C: Struct. Commun.
55 (1999) 1797.
Z
Dcalc(mg/m3)
k (Å)
l
(Mo-K) (mmꢀ1
)
10.044
1220
F(000)
h (°)
No. of reflections
Final R indices (all data)
range 3.00–24.98
1581 (1581 unique)
R1 = 0.0376, 0.0871
wR2 = 0.1132, 0.1134
0.919 and ꢀ1.158
1.002
Largest diff. peak and hole (e Åꢀ3
Goodness-of-fit (GOF)
)

72
N.A. Barnes et al. / Polyhedron 55 (2013) 67–72
[37] R. Karia, G.R. Willey, M.G.B. Drew, Acta Crystallogr., Sect. C: Struct. Commun.
42 (1986) 558.
[38] B. Beagley, C.A. McAuliffe, K. Minten, R.G. Pritchard, J. Chem. Soc., Chem.
Commun. (1984) 658.
[39] B. Beagley, C.A. McAuliffe, K. Minten, R.G. Pritchard, J. Chem. Soc., Dalton Trans.
(1987) 1999.
[40] D.J. Chandler, R.A. Jones, B.R. Whittlesey, J. Coord. Chem. 16 (1987) 19.
[41] I.A. Degnan, N.W. Alcock, S.M. Roe, M.G.H. Wallbridge, Acta Crystallogr., Sect.
C: Struct. Commun. 48 (1992) 995.
[45] N.S. Imyanitov, Koord. Khim. 11 (1985) 1171.
[46] F. Cheng, A.L. Hector, W. Levason, G. Reid, M. Webster, W. Zhang, Inorg. Chem.
46 (2007) 7215.
[47] N. Bricklebank, S.M. Godfrey, H.P. Lane, C.A. McAuliffe, R.G. Pritchard, J.-M.
Moreno, J. Chem. Soc., Dalton Trans. (1995) 3873.
[48] G.M. Sheldrick, SHELX-97, University of Göttingen, Göttingen, Germany, 1998.
[49] A.C.T. North, D.C. Phillips, F.S. Matthews, Acta Crystallogr., Sect. A: Foundt.
Crystallogr. 24 (1968) 351.
[50] ORTEP 3 for Windows L.J. Farugia, J. Appl. Crystallogr. 30 (1997) 565.
[51] MERCURY: C.F. Macrae, P.R. Edgington, P. McCabe, G.P. Shields, R. Taylor, M.
Towler, J. van de Streek, J. Appl. Crystallogr. 39 (2006) 453.
[52] A. Immirzi, A. Musco, Inorg. Chim. Acta 25 (1977) L41.
[42] G.W.A. Fowles, P.T. Green, J.S. Wood, Chem. Commun. (1967) 971.
[43] R.J. Deeth, J. Chem. Soc., Dalton Trans. (1997) 4203.
[44] B.J. Russ, J.S. Wood, Chem. Commun. (1966) 745.