Synthesis and structural characterization of [NEt4][Fe3(μ3-O)(μ3-AuPPh 3)(μ-CO)3(CO)6], the new [Au6(μ3-S)2(PPh3) 6][Fe3(μ3-S)(μ-AuPPh 3)(CO)9]2.

Article abstract of DOI:10.1016/s0020-1693(99)00134-6

The new [Fe₃(μ₃-O)(μ₃-AuPPh ₃)(μ-CO)₃(CO)₆]^- and [Fe₃(μ₃-S)(μ-AuPPh₃)(CO) ₉]^- monoanionic congeners have been obtained by reacting the [Fe₃(μ₃-E)(CO)₉]^2- (E=O, S) dianions with one equivalent of Au(PPh₃)Cl. The gold adduct of the oxygen derivative has been crystallized as tetraethylammonium and trimethylbenzylammonium salt either from THF and n-hexane or acetone and isopropyl alcohol, and structurally characterized in its tetraethylammonium salt (monoclinic, C2/c (No. 15), a=15.859(2), b=12.859(2), c=40.217(8) A?, β=96.41(1)° Z=8). The [Fe₃(μ₃-S)(μ-AuPPh₃)(CO) ₉]^- gold adduct, in contrast, partially reverts to the parent dianion upon crystallization under the above experimental conditions, and could be precipitated only as the [Au₆(μ₃-S)₂(PPh₃) ₆][Fe₃(μ₃-S)(μ-AuPPh ₃)(CO)₉]₂ salt (triclinic, P1? (No. 2), a=18.998(8), b=19.933(8), c=22.94(1) A?, α=99.91(4), β=98.91(4), γ=107.42(3)°, Z=2), by addition of an equivalent of the [Au₃(μ₃-S)(PPh₃)₃]⁺ sulfonium cation to the reaction mixture. The [Fe₅(μ₃-S)₂(CO)₁₄]^2- dianion does not form a gold adduct even in the presence of the sulfonium cation and only the corresponding [Au₆(μ₃-S)₂(PPh₃) ₆][Fe₅(μ₃-S)₂(CO)₁₄] salt could be obtained. The [Fe₃(μ₃-O)(μ₃-AuPPh ₃)(μ-CO)₃(CO)₆]^- and [Fe₃(μ₃-S)(μ-AuPPh₃)(CO) ₉]^- gold adducts are not isostructural and the possible factors leading to their structural diversities are discussed. The [Au₆(μ₃-S)₂(PPh₃) ₆][Fe₃(μ₃-S)(μ-AuPPh ₃)(CO)₉]₂ and [Au₆(μ₃-S)₂(PPh₃) ₆][Fe₅(μ₃-S)₂(CO)₁₄] salts represent further examples of ionic solids assembled from cluster-cations and cluster-anions.

Full text of DOI:10.1016/s0020-1693(99)00134-6

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 291 (1999) 372–379
Synthesis and structural characterization of
[NEt4][Fe3(m3-O)(m3-AuPPh3)(m-CO)3(CO)6], the new
[Au6(m3-S)2(PPh3)6][Fe3(m3-S)(m-AuPPh3)(CO)9]2 and
[Au6(m3-S)2(PPh3)6][Fe5(m3-S)2(CO)14] ionic solids containing
assemblages of cluster-cations and cluster-anions
Vincenzo G. Albano a, Carlo Castellari a, Cristina Femoni b, Maria Carmela Iapalucci b,
Giuliano Longoni b,*, Magda Monari a, Maddalena Rauccio b, Stefano Zacchini b
a Dipartimento di Chimica ‘G. Ciamician’, 6ia F. Selmi 2, 40126 Bologna, Italy
b Dipartimento di Chimica Fisica ed Inorganica, 6iale Risorgimento 4, 40136 Bologna, Italy
Received 8 January 1999; accepted 2 March 1999
Abstract
The new [Fe3(m3-O)(m3-AuPPh3)(m-CO)3(CO)6]− and [Fe3(m3-S)(m-AuPPh3)(CO)9]− monoanionic congeners have been obtained
by reacting the [Fe3(m3-E)(CO)9]2− (E=O, S) dianions with one equivalent of Au(PPh3)Cl. The gold adduct of the oxygen
derivative has been crystallized as tetraethylammonium and trimethylbenzylammonium salt either from THF and n-hexane or
acetone and isopropyl alcohol, and structurally characterized in its tetraethylammonium salt (monoclinic, C2/c (No. 15),
−
,
a=15.859(2), b=12.859(2), c=40.217(8) A, i=96.41(1)° Z=8). The [Fe3(m3-S)(m-AuPPh3)(CO)9] gold adduct, in contrast,
partially reverts to the parent dianion upon crystallization under the above experimental conditions, and could be precipitated
(
,
only as the [Au6(m3-S)2(PPh3)6][Fe3(m3-S)(m-AuPPh3)(CO)9]2 salt (triclinic, P1 (No. 2), a=18.998(8), b=19.933(8), c=22.94(1) A,
h=99.91(4), i=98.91(4), k=107.42(3)°, Z=2), by addition of an equivalent of the [Au3(m3-S)(PPh3)3]+ sulfonium cation to the
reaction mixture. The [Fe5(m3-S)2(CO)14]2− dianion does not form a gold adduct even in the presence of the sulfonium cation and
only the corresponding [Au6(m3-S)2(PPh3)6][Fe5(m3-S)2(CO)14] salt could be obtained. The [Fe3(m3-O)(m3-AuPPh3)(m-CO)3(CO)6]−
and [Fe3(m3-S)(m-AuPPh3)(CO)9]− gold adducts are not isostructural and the possible factors leading to their structural diversities
are discussed. The [Au6(m3-S)2(PPh3)6][Fe3(m3-S)(m-AuPPh3)(CO)9]2 and [Au6(m3-S)2(PPh3)6][Fe5(m3-S)2(CO)14] salts represent fur-
ther examples of ionic solids assembled from cluster-cations and cluster-anions. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Iron complexes; Gold complexes; Cluster complexes
1. Introduction
unexpected stability has been interpreted in terms of
auriophilicity, that is formation of intramolecular sub-
van der Waals Au–Au contacts [5]. These studies were
originally inspired by the LAu+ –H+ isolobal analogy
[6].
In view of the existence of the above oxonium and
sulfonium cations and the different reactivity of
[Fe3(m3-E)(CO)9]2− (E=O [7], S [8], Se [8h,9,10], Te
[8h,11,12]) with the isolobal H+ and CH3+ fragments,
we became interested in examining the reaction of
[Fe3(m3-O)(CO)9]2− and [Fe3(m3-S)(CO)9]2− with
Gold exhibits pronounced oxo- and thio-philicity as
shown by the existence of [(PR3Au)3E]+ (R=alkyl or
aryl substituent; E=O [1], S [2]) cations and hyperco-
ordinated tetrahedral [(P(o-Tol)3Au)4O]2+[3] and
square-pyramidal [(PPh3Au)4S]2+ [4] dications. Their
* Corresponding author. Tel.: +39-51-644 3691; fax: +39-51-644
3690.
E-mail address: longoni@ms.fci.unibo.it (G. Longoni)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00134-6

V.G. Albano et al. / Inorganica Chimica Acta 291 (1999) 372–379
373
[Au(PPh3)]+. Indeed, the proton attacks the m3-O cap-
ping heteroatom in [Fe3(m3-O)(CO)9]2− to give [Fe3(m3-
OH)(CO)9]− [7], at difference of the [Fe3(m3-E)(CO)9]2−
(E=S [8], Se [9,10], Te [11,12]) congeners, where it has
been shown to span an Fe–Fe edge. On the other side,
carbocations such as CH3+ bind to EꢀO and S [7,8g,h],
but give rise to iron s-alkyls when E is a Se or a Te
heteroatom [8h]. Such differential reactivity is in keeping
with the expected relative strength of the E–R and Fe–R
(R=H, CH3) bonds, as well as the nucleophilicity of the
m3-E capping heteroatom. Indeed, the lone pair increas-
ingly becomes more diffuse and the fractional negative
charge delocalized onto the heteroatom decreases on
descending the group. That is inferable from the progres-
sive shortening of the Fe–C and lengthening of the C–O
bond distances, which point out a progressively increas-
ing back-donation onto the CO ligands on going from
[Fe3(m3-O)(CO)9]2− to its heavier congeners [7,8d,e,10].
In keeping with an increased negative charge delocal-
ized on the Fe3 triangle, the corresponding attack of
[Au(PPh3)]+ also occurs at an Fe–Fe edge for E=Te
[11]. On the contrary, the coordination site of gold for
the lighter [Fe3(m3-E)(CO)9]2− (E=O, S and Se) con-
geners is yet unknown. Only the reaction of [Fe3(m3-
S)(CO)9]2− with Au(PPh3)Cl has previously been
investigated; the neutral Fe3(m3-S)(m3-AuPPh3)(m4-Au-
PPh3)(CO)9 bis-adduct was isolated with no evidence of
the intermediate formation of the mono-gold adduct [8c].
It was, therefore, of interest to verify whether the
greatest nucleophilicity of the oxygen heteroatom and the
oxophilicity of gold could lead to the formation of a
[Fe3(m3-O“AuPPh3)(CO)9]− adduct with a dangling
AuPPh3 moiety, or a butterfly [Fe3Au(m4-O)(CO)9-
(PPh3)]− and, eventually, a capped square-pyramidal
Fe3Au2(m4-O)(CO)9(PPh3)2, related to [Fe3Mn(m4-
O)(CO)12]− [13] and [Fe2Ru3(m4-O)(CO)14]2−, respec-
tively, [14]. These studies resulted in the synthesis and
structural characterization of the new [Fe3(m3-O)(m3-
AuPPh3)(m-CO)3(CO)6]− and [Fe3(m3-S)(m-AuPPh3)-
(CO)9]− monoanionic congeners. The latter is isostruc-
tural with the previously reported [Fe3(m3-Te)(m-
AuPPh3)(CO)9]− derivative [11]. As a corollary, we have
isolated and characterized the [Au6(m3-S)2(PPh3)6]-
[Fe3(m3-S)(m-AuPPh3)(CO)9]2 and [Au6(m3-S)2(PPh3)6]-
[Fe5(m3-S)2(CO)14] salts, which represent new examples of
ionic solids assembled from cluster-cations and cluster-
anions [15–17].
solvents such as THF, acetone and acetonitrile. The
formation of the [Fe3(E)(AuPPh3)(CO)9]− adducts is
signaled by a darkening of the solution, which turns dark
red from orange–red, and a shift of ca. 40 cm−1 to higher
wavenumbers of the infrared carbonyl absorptions. The
conversion of [Fe3(m3-O)(CO)9]2− into the [Fe3(O)-
(AuPPh3)(CO)9]− adduct is quantitative, as inferable
from the infrared spectrum at the end of the reaction,
which shows complete disappearance of absorptions
attributable to the starting material. The reaction solu-
tion of the [Fe3(O)(AuPPh3)(CO)9]− (w(CO) in THF at
2017 mw, 1970 s, 1960 sh, 1939 sh, 1912 mw cm−1
)
adduct displays an IR pattern and absorption wavenum-
bers very similar to those featured by the butterfly
[Fe3(m3-Te)(m-AuPPh3)(CO)9]− (w(CO) in THF at 2016
mw, 1975 s, 1962 sh, 1931 sh cm−1) [11] congener. The
[NEt4]+ and [NMe3CH2Ph]+ salts of the [Fe3(O)-
(AuPPh3)(CO)9]− anion have been isolated in a pure
crystalline state in 70–80% yields by evaporation in
vacuum of the reaction solution, extraction in THF and
precipitation with n-hexane.
The [NEt4][Fe3(S)(AuPPh3)(CO)9] adduct shows in-
frared carbonyl absorptions (w(CO) in THF at 2019 mw,
1971 s, 1962 sh, 1933 m, 1915 mw cm−1) almost identical
to those of [Fe3(O)(AuPPh3)(CO)9], but different from
the latter as it undergoes a dissociation equilibrium in
solution, as a function of the polarity of the solvent. As
a result, its crystallization in analogous conditions, as
well as in other solvents, gives rise to mixtures of orange
and red crystals of the starting [NEt4]2[Fe3(S)(CO)9]
material and [NEt4][Fe3(S)(AuPPh3)(CO)9], respectively.
The above equilibrium shifts almost completely toward
dissociation upon crystallization of the corresponding
[NMe4]+ and [NMe3CH2Ph]+ salts, as a result of the
lower solubility of these salts of [Fe3(S)(CO)9]2− with
respect to [Fe3(S)(AuPPh3)(CO)9]−; this may explain
previous failures in observing the formation of this
mono-gold adduct [8c]. It has been, therefore, necessary
to modify the reaction conditions in order to isolate the
butterfly [Fe3(m3-S)(m-AuPPh3)(CO)9]− monoanion as a
pure salt (see later). The mechanically separated crystals
of [NEt4][Fe3(S)(AuPPh3)(CO)9] show an infrared spec-
trum in nujol mull very similar to that of the mother
liquor solution (w(CO) at 2018 mw, 1960 s, 1953 sh, 1930
sh, 1910 sh cm−1).
In contrast, it was immediately apparent that an
isomer different from the one present in solution was
obtained upon crystallization of both the [NEt4]+ and
[NMe3CH2Ph]+ salts of the [Fe3(O)(AuPPh3)(CO)9]−
adduct. Indeed, their crystals in nujol mull show infrared
carbonyl absorptions both in the terminal (2010 mw,
2. Results and discussion
2.1. Synthesis of [Fe3(v3-O)(v3-AuPPh3)(CO)6
(v-CO)3]− and [Fe3(v3-S)(v-AuPPh3)(CO)9]−
1954 s and 1910 s cm−1) and bridging (1790 ms cm−1
)
region. The bridging carbonyl absorptions were un-
equivocally absent in the mother liquor solution
before crystallization. Accordingly, the determination
The [Fe3(m3-E)(CO)9]2− (E=O, S) salts readily react
with Au(PPh3)Cl in a 1:1 molar ratio in most organic

374
V.G. Albano et al. / Inorganica Chimica Acta 291 (1999) 372–379
[Au3(m3-O)(PPh3)3]+ oxonium cation is a good alterna-
tive to Au(PPh3)Cl or Au(PPh3)Cl-TlPF6 mixtures for
the addition of [Au(PPh3)]+ fragments to cluster com-
pounds [23,24]. In doing that, we have isolated pure
crystals of a salt-like compound in which both cations
and anions are molecular clusters, that is [Au6(m3-S)2-
(PPh3)6][Fe3(m3-S)(m-AuPPh3)(CO)9]2 salt. Several exam-
ples of such ionic solids are already known [15–17].
These have been obtained serendipitously [15–17] or by
charge-transfer reaction between the parent neutral spe-
cies [16]. Most of them are constituted by M4Cp4X4
(M=Cr, Mo, Fe; X=S, Se) cubane mono-cations and
Fe4(NO)4S4 cubane mono-anions. Cluster salts involving
a carbonyl cluster anion, e.g. the [Os6(CO)18]2− dianion
[16], or both a carbonyl cluster cation and a carbonyl
cluster anion [15] are also documented. To the best of our
knowledge, however, the [Au6(m3-S)2(PPh3)6][Fe3(m3-
S)(m-AuPPh3)(CO)9]2 and the related [Au6(m3-S)2(PPh3)6]
[Fe5(m3-S)2(CO)14] salt described below are the first
examples of ionic compounds assembled from preformed
cluster-cations and cluster-anions. Reactions of cluster
cations (e.g. [Au3(m3-O)(PPh3)3]+) with cluster anions
have previously been investigated. However, they were
aimed at increasing the cluster nuclearity either by
condensation or addition of single [Au(PPh3)]+ moieties,
and the observed results were in keeping with the
objectives [23,24]. Evidently, the [Au3(m3-S)(PPh3)3]+ is
much less effective than [Au3(m3-O)(PPh3)3]+ in releasing
by X-ray diffraction studies (see later) of the structure of
the [NEt4]+ salt has disclosed a trigonal bipyramidal
[Fe3(m3-O)(m3-AuPPh3)(m-CO)3(CO)6]− geometry, the
apices of which are the oxygen atom and the [Au(PPh3)]+
moiety.
The [Fe3(m3-O)(m3-AuPPh3)(m-CO)3(CO)6]− mono-
anion re-isomerizes to the butterfly [Fe3(m3-O)(m-
AuPPh3)(CO)9]− upon dissolving its salts in most or-
ganic solvents (e.g. CH3CN, THF, acetone and CH2Cl2),
as shown by the almost complete disappearance of
absorptions around 1790 cm−1. Besides, evaporation of
the solvent under vacuum gives a dark red solid material
which in nujol mull does not exhibit bridging carbonyl
absorptions, the IR pattern being very similar to that of
[Fe3(m3-E)(m-AuPPh3)(CO)9]− (E=S, Te [11]). More-
over, it has been observed that further isomerization can
occur by dissolving and drying the same sample under
vacuum. After a few cycles a yet different IR spectrum
is observed, which could be interpreted as arising from
the presence of the [Fe3(m3-O“AuPPh3)(CO)9]− (n(CO)
in THF at 2039 mw, 1970 s, 1944 ms, 1916 m cm−1
)
isomer and trace amounts of the starting [Fe3(m3-
O)(CO)9]2− dianion. A related dangling adduct of
[Fe3(m3-S)(CO)9]2− with the isolobal Re(CO)5+ fragment
has already been reported [18]. The above suggestion
stems from the close similarity, both in pattern and
wavenumbers, between the above IR spectrum and that
of the [Fe3(m3-OR)(CO)9]− (R=H, Me, SiMe3) [7]
derivative. In conclusion, there are unequivocal IR
[Au(PPh3)]+
fragments
and
[Fe3(m3-S)(m-
AuPPh3)(CO)9]− is little prone to give the di-gold
derivatives under the above experimental conditions.
To better exploit the possibility of isolating ionic solids
made by a cluster cation and a cluster anion, we
investigated the reaction of the [Au3(m3-S)(PPh3)3]+
sulfonium cation with the [Fe5(m3-S)2(CO)14]2− dianion
[8d,f], in the presence or not of an equimolar amount of
Au(PPh3)Cl. In all cases we succeeded in isolating only
[Au6(m3-S)2(PPh3)6][Fe5(m3-S)2(CO)14].1 No evidence was
obtained for the possible formation of a mono-gold
spectroscopic
evidences
that
the
mono-gold
[Fe3(O)(AuPPh3)(CO)9]− adduct can exist in three differ-
ent isomers, that is [Fe3(m3-O“AuPPh3)(CO)9]−,
[Fe3(m3-O)(m-AuPPh3)(CO)9]−
and
[Fe3(m3-O)(m3-
AuPPh3)(m-CO)3(CO)6]−; the former two are stable in
solution and the latter in the solid state. The stabilization
of the most compact and symmetrical isomer in the solid
state is not fortuitous. Very likely a higher steric regular-
ity allows a more efficient packing and consequent lower
solubility of this isomer that can selectively crystallize
even if it is present in minor amounts in solution.
It was of interest to confirm the above isomerization
equilibria in solution by variable temperature 13C NMR
adduct of [Fe5(m3-S)2(CO)14]2−
,
corresponding to
[HFe5(m3-S)2(CO)14]− [8f]. Likewise, we do not have
any evidence of a charge transfer from the anion to the
cation, which could lead to the oxidized [Fe5(m3-
S)2(CO)14]n− (n=0, 1) congener [8f]. This stems from
the low redox propensity of the [Au6(m3-S)2(PPh3)6]2+
dication.
studies.
Unfortunately,
isotopic
exchange
of
[Fe3(O)(AuPPh3)(CO)9]− with 13CO was hindered by its
rapid degradation under a carbon monoxide atmosphere,
which leads to
a
mixture of the well-known
In any case, the isolation of [Au6(m3-S)2(PPh3)6]-
[Fe3(m3-S)(m-AuPPh3)(CO)9]2 and [Au6(m3-S)2(PPh3)6]-
Au2Fe(CO)4(PPh3)2 [19,20] and [HFe3(CO)11]− [21] com-
pounds.
Returning to the [Fe3(m3-S)(m-AuPPh3)(CO)9]− ad-
duct, in the attempt to isolate its pure salts, we decided
to carry out the crystallization in the presence of the
[Au3(m3-S)(PPh3)3]+ sulfonium cation, [2,22] hopping
that this could behave as an effective source of
[Au(PPh3)]+ fragments and depress dissociation of the
former. Indeed, it is well known that its corresponding
1 The dimeric nature of the gold cation in [Au6(m3-S)2-
(PPh3)6][Fe5(m3-S)2(CO)14] has been determined by an X-ray diffrac-
(
tion study (triclinic, space group P1, a=13.234(4), b=20.56(1),
o,
,
c=22.267(9) A, h=90.53(4), i=96.59(3), k=98.54(3) Z=2). Be-
cause of the poor quality of the crystal, only the positions of the
heavier atoms were determined with reasonable accuracy and there-
fore details of the structural study are not reported.

V.G. Albano et al. / Inorganica Chimica Acta 291 (1999) 372–379
375
Table 1
[Fe5(m3-S)2(CO)14] shows that preparation of ionic
,
Selected bond lengths (A) and angles (°) for [Fe3(m3-O)(m3-
AuPPh3)(m-CO)3(CO)6] · 0.5C4H8O
solids assembled from cluster-cations and cluster-anions
is more general than expected, and its exploitation
could lead to interesting new materials.
Au–Fe(1)
Au–Fe(2)
Au–Fe(3)
Au–P
Fe(1)–Fe(2)
Fe(1)–Fe(3)
Fe(1)–O(10)
Au···C(9)
2.736(2)
2.708(2)
2.720(2)
2.293(2)
2.528(3)
2.489(3)
1.89(1)
Fe(2)–O(10)
Fe(3)–O(10)
Fe–C(bridging)(avg.)
Fe–C(avg.)
C–O(bridging)(avg.)
C–O(avg.)
1.89(1)
1.90(1)
2.05
1.76
1.14
1.14
2.78(2)
2.78(2)
2.2. The X ray molecular structures of
[NEt4][Fe3(v3-O)(v3-AuPPh3)(v-CO)3(CO)6]
and [Au6(v3-S)2(PPh3)6][Fe3(v3-S)(v-AuPPh3)(CO)9]2
Au···C(1)
Au···C(5)
2.2.1. Molecular structure of [Fe3(v3-O)(v3-AuPPh3)-
(v-CO)3(CO)6]− as its [NEt4]+ salt
2.77(2)
Fe(1)–C(1)–O(1) 178(2)
Fe(3)–C(9)–O(9) 174(2)
Fe(2)–C(5)–O(5) 174(2)
Fe(1)–C(3)–O(3) 140(2)
Fe(1)–C(7)–O(7) 145(2)
Fe(2)–C(6)–O(6) 143(2)
Fe(1)–C(2)–O(2)
Fe(2)–C(4)–O(4)
Fe(3)–C(8)–O(8)
Fe(2)–C(3)–O(3)
Fe(3)–C(7)–O(7)
Fe(3)–C(6)–O(6)
178(2)
175(2)
177(2)
144(2)
141(2)
140(2)
The solid state structure of the anion of [Fe3(m3-
O)(m3-AuPPh3)(m-CO)3(CO)6]− is shown in Fig. 1 and
relevant bond lengths and angles are reported in Table
1. The anion contains a Fe3 triangle whose edges are
spanned by three bridging CO ligands; the remaining
six CO groups are terminally bonded in a C36 array of
the fragment. A m3-O2− anion and a m3-Au(PPh3)+
cation cap the faces of the Fe3 triangle. The idealized
symmetry of the anion is C36 if only the ipso atoms of
the phenyl rings are considered; a C3 symmetry is a
good approximation of the anion as a whole. The
Fe–Fe interactions are very close each other (2.528,
removed from the Fe3 triangle in establishing the inter-
action with the acidic [Au(PPh3)]+ fragment. The Fe–
O distances are equivalent (1.89, 1.89, 1.90(1) A) and
identical to those reported for the aforementioned dian-
ion. Noteworthy the [Au(PPh3)]+ fragment, different
from what was observed in other chalcogen-containing
clusters of the type [Fe3(m3-E)(m-AuPPh3)(CO)9]− (E=
S, Te [11]), is triply bridging the Fe3 unit (Au–Fe
,
,
2.528, 2.488(4) A) and slightly longer than those ob-
served in the parent [Fe3(m3-O)(CO)9]2− dianion (2.480,
,
2.480, 2.492(1) A) [7]. The slight lengthening of the
,
distances 2.736, 2.708 and 2.720(3), average 2.72 A)
Fe–Fe distances upon decreasing the overall molecular
charge probably means that bonding electron density is
instead of doubly bridging one Fe–Fe bond (see also
Section 2.2.2). This bonding mode of the Au(PPh3)
group has been reported only in [Fe6C(m3-
AuPPh3)(CO)16]− [25] (Au–Fe 2.733, 2.732, 2.785(2),
,
avg. 2.75 A). It should be noted that gold, as usual
when favorable stereochemical conditions occur, ex-
hibits secondary bonding interactions with the facing
,
CO ligands (average Au···CO contact 2.77 A). The
attractive nature of this interaction is demonstrated by
the fact that the V shaped terminal carbonyl groups are
not symmetrically placed above and below the Fe3
plane. Those involved in the Au···CO attraction are
,
farther from this plane (avg. 1.35 A) than those on the
,
opposite side (avg. 1.17 A). The latter have normal
,
contacts with the m3-O atom (avg. m3-O···CO 2.66 A).
2.2.2. Molecular structure of [Au3(v3-S)(PPh3)3]2-
[Fe3(v3-S)(v-AuPPh3)(CO)9]2
The crystals of the title compound are made up of
2+
dimeric [Au3(m3-S)(PPh3)3]2
cluster cations and
[Fe3(m3-S)(m-AuPPh3)(CO)9]− cluster anions; the inde-
pendent part is one formula unit.
2.2.2.1. [Au3(v3-S)(PPh3)3]22+. The cluster dication is
shown in Fig. 2 and relevant bond lengths and angles
are reported in Table 2. The solid state structure of the
2+
[Au3(m3-S)(PPh3)3]2
cation is an assemblage of two
Au3(m3-S) triangles facing each other edge-to-edge, thus
realizing two additional Au···Au contacts. Was not for
the asymmetry of these two additional contacts (see
Fig. 1. ORTEP drawing of the anion [Fe3(m3-O)(m3-AuPPh3)(m-
CO3(CO)6]− (thermal ellipsoids are drawn at 30% probability level).

376
V.G. Albano et al. / Inorganica Chimica Acta 291 (1999) 372–379
2.2.2.2. [Fe3(v3-S)(v-AuPPh3)(CO)9]−. The overall
molecular geometries of the two independent anions are
substantially equivalent and therefore only one is
shown in Fig. 3. Relevant bond lengths and angles are
reported in Table 2. The anions consist of a triangle of
iron atoms with a face-capping sulfur atom and an
Au(PPh3) group bridging one Fe–Fe edge and lying
below the Fe3S tetrahedron. Each iron carries three
terminal carbonyls at variance with what has been
observed in [Fe3(m3-O)(m3-AuPPh3)(m-CO)3(CO)6]−,
where there are three edge bridging COs (previous
section). The anions conform to an idealized Cs symme-
try with a mirror plane passing through S, Au, P and
one Fe atom, if the orientations of the phenyl rings are
ignored. The Fe–Fe interactions define isosceles trian-
Fig. 2), the two units would have been related by
inversion. These auriophilic interactions are non-equiv-
alent (Au(2)···Au(4) 2.985 and Au(1)···Au(6) 4.194(2)
,
A) and generate a weakly bonded supramolecule. The
Au–Au and Au–S distances in the sulfur-capped trian-
gles fall in the expected ranges: Au–Au 3.055–3.238(2),
,
average 3.162 A, Au–S 2.310–2.362(3), average 2.331
,
A. Each Au atom bears one PPh3 ligand realizing an
almost linear S–Au–P coordination (average S–Au–P
angle 177°). This dimeric motif is not unusual and has
already been reported in its [PF6]− salt [26]. In the
latter cluster the gold aggregation between the two
monomers is more symmetric than in the case under
,
study (Au···Au contacts 3.236 and 3.361(3) A). How-
ever, upon changing the counterion the monomeric
cation [Au3(m3-S)(PPh3)3]+ has been found in
its [BF4]− salt [27]. The above described structural
variations in the solid state on one hand give an idea of
the weakness of the auriophilic interactions and on the
other hand confirm the relevance of the secondary
valence forces in influencing the stereochemistry of
gold(I) compounds.
,
gles (2.592, 2.586, 2.704(2) and 2.758, 2.597, 2.596(3) A)
in which the longer edges are those spanned by the
Au(PPh3) groups, as it has been found in the related
[Fe3(m3-Te)(m-AuPPh3)(CO)9]− (2.836, 2.620 and
,
2.622(4) A, respectively) [11] and in the neutral [Fe3(m3-
i
,
SPr )(m-AuPPh3)(CO)9] (2.800, 2.644 and 2.631(8) A,
respectively) [28]. The Fe–S bonds (2.188, 2.185,
,
,
2.177(3), average 2.18 A, and 2.188, 2.184, 2.176(3) A,
Fig. 2. ORTEP drawing of the dication [Au6(m3-S)2(PPh3)6]2+ (thermal ellipsoids are drawn at 30% probability level). Hydrogen atoms have been
omitted for clarity.

V.G. Albano et al. / Inorganica Chimica Acta 291 (1999) 372–379
377
Table 2
,
radii (3.2 A) [29]. It is therefore evident that a C36
structure is destabilized in the anions of the heavier
chalcogenides. In fact in the all terminal CO arrangement
adopted by the S and Te derivatives, the CO ligands
remain far from the m3-E ligand. More subtle electronic
factors are probably involved in the stabilization of the
m2 bonding mode of the AuPPh3 fragment when the edges
of the Fe3 triangle are free from CO ligands.
,
Selected bond lengths (A) and angles (°) for [Au6(m3-S)(PPh3)6]-
[Fe3(m3-S)(m-AuPPh3)(CO)9]2
[Au6(m3-S)2(PPh3)6]2+
Au(1)–Au(2)
Au(2)–Au(3)
Au(1)–Au(3)
Au(1)–P(1)
Au(2)–P(2)
Au(3)–P(3)
Au(1)–S(2)
Au(3)–S(2)
Au(5)–S(1)
Au(2)–Au(4)
3.238(2)
3.064(2)
3.193(2)
2.261(3)
2.277(3)
2.263(3)
2.310(3)
2.326(3)
2.316(3)
2.985(2)
Au(4)–Au(5)
Au(5)–Au(6)
Au(4)–Au(6)
Au(4)–P(4)
Au(5)–P(5)
Au(6)–P(6)
Au(2)–S(2)
Au(4)–S(1)
Au(6)–S(1)
Au(1)...Au(6)
3.055(2)
3.162(2)
3.259(2)
2.281(3)
2.257(3)
2.260(3)
2.358(3)
2.362(3)
2.315(3)
4.194(2)
3. Experimental
All reactions including sample manipulations were
carried out using standard Schlenk techniques under
nitrogen and in carefully dried solvents. The
[Fe3O(CO)9]2− [7]; [Fe3S(CO)9]2− [8a,f]; [Fe5S2-
(CO)14]2− [8f] and [Au3S(PPh3)3]Cl [22] salts have been
prepared according to the literature. Analyses of Fe
and Au were performed by atomic absorption on a
Pye-Unicam instrument. Infrared spectra were recorded
on a Perkin Elmer 1605 interferometer using CaF2 cells.
S(2)–Au(2)–P(2)
S(2)–Au(3)–P(3)
S(2)–Au(1)–P(1)
174.3(1)
177.3(1)
176.8(1)
S(1)–Au(4)–P(4)
S(1)–Au(5)–P(5)
S(1)–Au(6)–P(6)
175.5(1)
177.3(1)
178.4(1)
[Fe3(m3-S)(m-AuPPh3)(CO)9]−
Anion 1
Anion 2
Fe(1)–Fe(2)
Fe(2)–Fe(3)
Fe(1)–Fe(3)
Fe(1)–S(3)
Fe(2)–S(3)
Fe(3)–S(3)
Fe(1)–Au(7)
Fe(3)–Au(7)
Au(7)–P(7)
Fe–C(avg.)
C–O(avg.)
2.592(2)
2.586(2)
2.704(2)
2.188(3)
2.177(3)
2.185(3)
2.648(2)
2.710(2)
2.275(3)
1.76
Fe(4)–Fe(5)
Fe(5)–Fe(6)
Fe(4)–Fe(6)
Fe(4)–S(4)
Fe(5)–S(4)
Fe(6)–S(4)
Fe(4)–Au(8)
Fe(5)–Au(8)
Au(8)–P(8)
Fe–C(avg.)
C–O(avg.)
2.758(3)
2.596(3)
2.597(3)
2.188(4)
2.184(3)
2.176(4)
2.659(2)
2.657(2)
2.295(3)
1.15
3.1. Synthesis of [NEt4][Fe3(v3-O)(v3-AuPPh3)(CO)9]
Solid [NEt4]2[Fe3(m3-O)(CO)9] (1.51 g, 2.17 mmol) and
1.15
1.15
Au(7)···C(7)
Au(7)···C(1)
Au(7)···C(2)
Au(7)···C(9)
2.72(1)
2.70(1)
2.63(1)
2.77(1)
Au(8)···C(15)
Au(8)···C(11)
Au(8)–C(10)
2.62(2)
2.60(1)
2.99(1)
,
average 2.18 A) are slightly asymmetric and in both
anions the shorter Fe–S distance is that to the iron atoms
not involved in the bonding to the Au(PPh3) unit. The
Au(PPh3) groups make an asymmetric and a symmetric
,
bridge in the two independent anions (2.648, 2.710(2) A
,
and 2.659, 2.657(2) A, respectively), the Fe–Au distances
being comparable to those reported for the afore-
mentioned [Fe3(m3–Te)(m-AuPPh3)(CO)9]− (2.681 and
,
2.652(3) A) [11]. A major difference between the two
anions lies in the Fe3Au butterfly (dihedral angles be-
tween the planes Fe–Fe–Fe and Fe–Fe–Au 147.30 and
118.04°, respectively). This effect and the already men-
tioned asymmetry in the Fe–Au distances are conse-
quences of asymmetry in the packing forces. As described
above the oxygen derivative in the family of anions
[Fe3(E)(AuPPh3)(CO) 9]− (E=O, S, Te) exhibits a more
regular C36 structure than the heavier congeners whose
stereogeometries conform to a Cs symmetry. The steric
factors involved in the structural differences can be
appreciated if a structural model is built in which a m3-S
,
ligand replaces the oxygen (Fe–S distances 2.18 A)
keeping the CO ligands where found in the oxygen
Fig. 3. ORTEP drawing of one of the anions [Fe3(m3-S)(m-
AuPPh3)(CO)9]− (thermal ellipsoids are drawn at 30% probability
level).
,
derivative. S···CO contacts as short as 2.7 A are calcu-
lated, much shorter than the sum of the van der Waals

378
V.G. Albano et al. / Inorganica Chimica Acta 291 (1999) 372–379
Table 3
Crystal data and experimental details for [NEt4][Fe3(m3-O)(m3-AuPPh3)(m-CO)3(CO)6] · 0.5C4H8O and [Au6(m3-S)2(PPh3)6][Fe3(m3-S)(m-
AuPPh3)(CO)9]2
Empirical formula
Formula weight
Temperature (K)
C35H35AuFe3NO10P · 0.5C4H8O
1061.18
293(2)
C162H120Au8Fe6O18P8S4
4641.41
293(2)
,
Wavelength (A)
0.71069
monoclinic
C2/c (No. 15)
15.859(2)
12.859(2)
40.217(8)
90
96.46(1)
90
8149(3)
8
1.730
4.731
4192
0.71069
triclinic
Crystal symmetry
Space group
(
P1 (No. 2)
,
a (A)
18.998(8)
19.933(8)
22.94(1)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
99.91(4)
98.41(4)
107.42(3)
7982(6)
2
1.931
8.040
4416
3
,
Cell volume (A )
Z
Dc (Mg m−3
)
v(Mo Ka) (mm−1
F(000)
)
Crystal size (mm)
q Range (°)
0.40×0.40×0.50
2.5–30
0.12×0.20×0.23
2.5–25
Scan mode
ꢀ
ꢀ
Reflections collected
12 240 (+h, +k, 9l)
11 499
1.229
0.0922, 0.2390
a=0.0620, b =401.0833b
1.916 and −2.560
28 703 (9h, 9k, +l)
27 907
0.908
0.0347, 0.0822
a=0.0589, b=0.2926b
0.958 and −1.897
Unique observed reflections [Fo\4|(Fo)]
Goodness-of-fit on F2
R1 (F)a, wR2 (F2)b
Weighting scheme
Largest difference peak and hole (e A
−3
,
)
a R1=S ꢀꢀ Fo ꢀ−ꢀ Fc ꢀ/S ꢀ Fo ꢀ.
b wR2=[Sw(Fo2−Fc2)2/S w(Fo2)2]1/2 where w=1/[|2(Fo2)+(aP)2+bP] where P=(Fo2+2Fc2)/3.
Au(PPh3)Cl (1.17 g, 2.37 mmol) were mixed in a 100 ml
flask under a nitrogen atmosphere. Anhydrous THF
(30 ml) was added and the suspension was rapidly
stirred for 6 h. After this period of time IR monitoring
only showed the presence of the infrared absorptions of
[Fe3(m3-O)(m3-AuPPh3)(CO)9]2−. The suspension was
filtered and the resulting red solution was evaporated to
dryness under vacuum. The residue was washed with
water (20 ml) and toluene (20 ml). Extraction of the
residue with THF (30 ml) and precipitation by diffusion
of n-hexane (50 ml) gave 1.38 g of [NEt4][Fe3(m3-O)(m3-
AuPPh3)(CO)9] as dark red crystals. Anal. Found: Au,
19.01; Fe, 16.15; C, 41.27; H, 3.66. Calc. for
[NEt4][Fe3(m3-O)(m3-AuPPh3)(CO)9]: Au, 19.22; Fe,
16.35; C, 40.99; H 3.42%.
Extraction of the residue with acetone (40 ml) and
precipitationbydiffusionofisopropylalcohol(70ml)gave
1.76gof[Au6(m3-S)2(PPh3)6][Fe3(m3-S)(m-AuPPh3)(CO)9]2
as dark red crystals. Anal. Found: Au, 33.6; Fe, 7.05; C,
41.8; H, 2.63. Calc. for [Au6(m3-S)(PPh3)6][Fe3(m3-S)(m-
AuPPh3)(CO)9]2: Au, 33.97; Fe, 7.22; C, 41.91; H, 2.59%.
3.3. Synthesis of [Au6(v3-S)2(PPh3)6][Fe5(v3-S)2(CO)14]
Solid [NEt4]2[Fe5S2(CO)14] (0.52 g, 0.52 mmol) and
[Au3S(PPh3)3]Cl (1.56 g, 1.08 mmol) were mixed in a 100
ml flask under a nitrogen atmosphere. Anhydrous THF
(30 ml) was added and the suspension was rapidly stirred
for 2 h. The resulting red suspension was evaporated to
dryness under vacuum and the residue was washed with
water (50 ml in portions) and toluene (20 ml). Extraction
of the residue with acetone (40 ml) and precipitation by
diffusion of isopropyl alcohol (70 ml) gave 0.76 g of
[Au6(m3-S)2(PPh3)6][Fe5(m3-S)2(CO)14]asdarkredcrystals.
Anal. Found: Au, 33.1; Fe, 7.62; C, 41.34; H, 2.61. Calc.
for [Au6(m3-S)2(PPh3)6][Fe5(m3-S)2(CO)14]: Au, 33.26; Fe,
7.86; C, 41.20; H, 2.53%.
3.2. Synthesis of [Au6(v3-S)(PPh3)6][Fe3(v3-S)(v-
AuPPh3)(CO)9]2
Solid [NEt4]2[Fe3S(CO)9] (0.86 g, 1.21 mmol) and
Au(PPh3)Cl (0.62 g, 1.25 mmol) were mixed in a 100 ml
flask under a nitrogen atmosphere. Anhydrous THF (30
ml) was added and the suspension was rapidly stirred for
2 h. Solid [Au3S(PPh3)3]Cl (1.73 g, 1.2 mmol) was added
under stirring. The resulting red suspension was evapo-
ratedtodrynessundervacuumandtheresiduewaswashed
with water (50 ml in portions) and toluene (20 ml).
3.4. Crystallography
Crystal data and details of the data collection for
[NEt4][Fe3(m3 -O)(m3-AuPPh3)(m-CO)3(CO)6] · 0.5C4H8O

V.G. Albano et al. / Inorganica Chimica Acta 291 (1999) 372–379
379
References
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Acknowledgements
We wish to acknowledge financial support from the
MURST and the University of Bologna (projects ‘Sintesi,
modelli e caratterizzazione per materiali funzionali’ and
‘Funds for Selected Research Topics’).