Mixed Fe/Mo mixed-chalcogenide 'hour-glass' clusters, [FE4Mo(CO)14(μ3-E)2(μ 3-E′)2] and [Fe3Mo(CO)11(μ3-E)(μ 3-E′)-(μ-E′-E′)] (E, E′ = S, Se or Te)

Article abstract of DOI:10.1039/a702408h

The room-temperature reactions of [Fe₂(CO)₆(μ-EE′)] (EE′ = SeTe, STe, SSe, S₂ or Se₂) with [Mo(CO)₅(thf)] (thf = tetrahydrofuran) yielded two types of mixed-metal, mixed-chalcogenide 'hour-glass' clusters: [Fe₄Mo-(CO)₁₄(μ₃-E)₂(μ ₃-E′)₂] (E, E′ = Se, Te 1; S, Te 2; S, Se 4; S, S 7; Se, Se 9) and [Fe₃Mo(CO)₁₁(μ₃-E)(μ ₃-E′)(μ-E′-E′)] ( E, E′ = S, Te, E′-E′ = Te-Te 3; E, E′ = S, Se, E′-E′ = Se-Se 5; E, E′ = S, S, E′-E′ = S-Se 6; E, E′ = S, S, E′-E′ = S-S 8; E, E′ = Se, Se, E′-E′ = Se-Se 10). The crystal structures of 2, 5, 6 and 8 were elucidated by X-ray methods. The structure of 2 consists of two distorted square-pyramidal cores in each of which the alternate corners of the base are occupied by Fe and chalcogen atoms and a Mo atom occupies the common apical site. In 5, 6 and 8 a Mo atom occupies the common apical site of a square-pyramidal core and a tetrahedral core. The base of the square-pyramidal unit consists of alternate Fe and chalcogen atoms and the tetrahedral base consists of a Fe atom and two chalcogen atoms.

Full text of DOI:10.1039/a702408h

View Article Online / Journal Homepage / Table of Contents for this issue
Mixed Fe/Mo mixed-chalcogenide ‘hour-glass’ clusters,
[Fe4Mo(CO)14(ì3-E)2(ì3-EЈ)2] and [Fe3Mo(CO)11(ì3-E)(ì3-EЈ)-
(ì-EЈ᎐EЈ)] (E, EЈ = S, Se or Te)
Pradeep Mathur,*,a Perumal Sekar,a Arnold L. Rheingoldb and Louise M. Liable-Sandsb
a
Department of Chemistry, Indian Institute of Technology, Bombay 400 076, India
b Department of Chemistry, University of Delaware, Newark, Delaware 19716, USA
The room-temperature reactions of [Fe2(CO)6(µ-EEЈ)] (EEЈ = SeTe, STe, SSe, S2 or Se2) with [Mo(CO)5(thf)]
(thf = tetrahydrofuran) yielded two types of mixed-metal, mixed-chalcogenide ‘hour-glass’ clusters: [Fe4Mo-
(CO)14(µ3-E)2(µ3-EЈ)2] (E, EЈ = Se, Te 1; S, Te 2; S, Se 4; S, S 7; Se, Se 9) and [Fe3Mo(CO)11(µ3-E)(µ3-EЈ)(µ-EЈ᎐EЈ)]
(E, EЈ = S, Te, EЈ᎐EЈ = Te᎐Te 3; E, EЈ = S, Se, EЈ᎐EЈ = Se᎐Se 5; E, EЈ = S, S, EЈ᎐EЈ = S᎐Se 6; E, EЈ = S, S, EЈ᎐EЈ =
S᎐S 8; E, EЈ = Se, Se, EЈ᎐EЈ = Se᎐Se 10). The crystal structures of 2, 5, 6 and 8 were elucidated by X-ray methods.
The structure of 2 consists of two distorted square-pyramidal cores in each of which the alternate corners of the
base are occupied by Fe and chalcogen atoms and a Mo atom occupies the common apical site. In 5, 6 and 8 a
Mo atom occupies the common apical site of a square-pyramidal core and a tetrahedral core. The base of the
square-pyramidal unit consists of alternate Fe and chalcogen atoms and the tetrahedral base consists of a Fe
atom and two chalcogen atoms.
Facile addition of co-ordinatively unsaturated transition-metal
species to the reactive E᎐E bonds of [Fe2(CO)6(µ-E2)] (E = S, Se
or Te) provides a convenient method to obtain numerous
chalcogen-bridged mixed-metal carbonyl clusters.1 The add-
ition of mononuclear carbonyl fragments to form square-
pyramidal cluster cores can occur in one of two possible ways:
one is accompanied by formation of one new metal–metal bond
and the heterometal atom occupies a basal site (A), and the
other in which two new metal–metal bonds are formed and the
heterometal occupies the apical site (B).2–4 Reactions of
[Mo(CO)5(thf)] and [W(CO)5(thf)] (thf = tetrahydrofuran) with
Fig. 1 The structure of [Fe4Mo(CO)14(µ3-Se)2(µ3-Te)2]
[Fe2(CO)6(µ-E2)] to form type B mixed-metal clusters have been
found to be dependent on the nature of E in [Fe2(CO)6(µ-E2)].
When E = Te, [W(CO)5(thf)] reacts to form [Fe2W(CO)10(µ3-
Te)2], but there is no reaction of [Mo(CO)5(thf)]. When E = Se
both molybdenum and tungsten moieties add to form [Fe2-
M(CO)10(µ3-Se)2] (M = Mo or W) clusters. In order to further
investigate the influence of the different chalcogen ligands in
mixed-metal cluster syntheses, we have looked at the reactivity
of the mixed-chalcogenide compounds [Fe2(CO)6(µ-EEЈ)] with
[Mo(CO)5(thf)]. In a preliminary communication we reported
the formation of an unusual ‘hour-glass’ cluster [{Fe2(CO)6(µ3-
Se)(µ3-Te)}2Mo(CO)2] (Fig. 1) from the reaction of [Fe2(CO)6-
(µ-SeTe)] with [Mo(CO)5(thf)].5 Formation of 1 was thought
to proceed via initial formation of the square-pyramidal
[Fe2Mo(CO)10(µ3-Se)(µ3-Te)], though the latter could not be
isolated.
In continuation of our investigation on the influence of dif-
ferent chalcogen ligands in mixed-metal cluster growth reac-
tions and to understand the mechanism of formation of the
hour-glass cluster, we report here the reactions of the mixed
chalcogenide [Fe2(CO)6(µ-STe)] and [Fe2(CO)6(µ-SSe)] with
[Mo(CO)5(thf)]. In order to complete the study on the homo-
chalcogenide series, we have also examined closely the reac-
tion of [Fe2(CO)6(µ-S2)] and of [Fe2(CO)6(µ-Se2)] with [Mo-
(CO)5(thf)] and have isolated two new clusters with hitherto
unknown core geometries.
S2 or Se2) and a freshly prepared solution of [Mo(CO)5(thf)]
were stirred in hexane–thf solvent at room temperature (r.t.) for
3 h the reaction mixture changed from orange to green and the
infrared spectrum indicated some new bands in the CO region.
Chromatographic work-up separated two types of clusters from
these reaction mixtures: green clusters of the general form
[Fe4Mo(CO)14(µ3-E)2(µ3-EЈ)2] (EEЈ = SeTe 1, STe 2, SSe 4, S2 7 or
Se2 9) and the orange clusters [Fe3Mo(CO)11(µ3-E)(µ3-EЈ)-
(µ-EЈ2)] (EEЈ, EЈ2: STe, Te2 3; SSe, Se2 5; SS, SSe 6; SS, S2 8; or
SeSe, Se2 10) (Scheme 1). The relative yields of these two types
of clusters obtained in each reaction depended on the nature of
E and EЈ in the reactant, [Fe2(CO)6(µ-EEЈ)]. When the E, EЈ
combinations in [Fe2(CO)6(µ-EEЈ)] are Se, Te or S, Te, the green
Fe4Mo cluster is the sole or the major product, respectively,
isolated from the reaction mixture. For the other chalcogen
combinations the green clusters are minor products and the
orange Fe3Mo clusters are the major products. From the
reaction of [Fe2(CO)6(µ-SSe)] with [Mo(CO)5(thf)] two orange
clusters with different chalcogen combinations were isolated,
[Fe3Mo(CO)11(µ3-S)(µ3-Se)(µ-Se2)] 5 and [Fe3Mo(CO)11(µ3-S)2-
(µ-SSe)] 6. Close monitoring of the reactions by TLC and infra-
Results and Discussion
Synthesis
When 2 equivalents of [Fe2(CO)6(µ-EEЈ)] (EEЈ = SeTe, STe, SSe,
J. Chem. Soc., Dalton Trans., 1997, Pages 2949–2954
2949

View Article Online
Scheme 1 Preparation of ‘hour-glass’ clusters
Scheme 2 Conversion of the square-pyramidal [Fe2Mo(CO)10(µ3-S)-
(µ3-Te)] into the ‘hour-glass’ [Fe4Mo(CO)14(µ3-S)2(µ3-Te)2]
red spectroscopy indicated that initially a maroon band is
formed the infrared spectrum of which shows a carbonyl
stretching frequency pattern similar to that observed for
the square-pyramidal [Fe2Mo(CO)10(µ3-E)(µ3-EЈ)] clusters,
reported previously.4 During the course of the reaction the
maroon bands gradually faded as the amounts of the green and
orange clusters grew. Attempts to isolate pure maroon bands
for complete identification proved to be unsuccessful. In most
cases, during the chromatography, they converted into the green
bands of the Fe4Mo clusters. In case of the reaction of
[Fe2(CO)6(µ-STe)] with [Mo(CO)5(thf)] the maroon band was
sufficiently stable to enable investigation of its reaction with
[Fe2(CO)6(µ-STe)]; on stirring for 3 h at room temperature,
almost quantitative formation of the green [Fe4Mo(CO)14-
(µ3-S)2(µ3-Te)2] 2 was observed (Scheme 2). The green bands 4, 7
and 9 gradually converted into orange compounds 5, 8 and 10
during the chromatographic work-up.
Compounds 2, 5, 6 and 8 were characterised by IR spec-
troscopy and their structures established by single-crystal X-ray
diffraction analysis; 3, 4, 7, 9 and 10 were identified by com-
parison of their infrared spectra with those of the structurally
characterised analogous compounds 2, 5 and 8. The infrared
spectra of 2, 4, 7 and 8 show the presence of only terminally
bonded carbonyl groups with a complex CO stretching pattern
similar to that observed for [Fe4Mo(CO)14(µ3-Se)2(µ3-Te)2].5 The
infrared spectra of 3, 6, 8 and 10 were similar with an identical
CO stretching pattern. There is a regular shift of the corres-
ponding bands to lower ν(CO) values in [Fe4Mo(CO)14(µ3-E)2-
(µ3-EЈ)2] for the following combination of EEЈ ligands: S2 >
SSe > Se2 > STe > SeTe. Attempts to prepare the tellurium
analogue of [Fe4Mo(CO)14(µ3-E)2(µ3-EЈ)2] were unsuccessful.
The infrared spectral data for compounds 1–10 are given in
Table 1.
Fig. 2 Molecular structure of compound 2
Molecular structure of compound 2
Dark red crystals of compound 2 suitable for X-ray diffraction
analysis were grown from a hexane–dichloromethane mixture
by slow evaporation of the solvents at Ϫ5 ЊC and an X-ray
diffraction study was undertaken. An ORTEP 6 diagram of the
molecular structure of 2 is shown in Fig. 2. The Mo atom occu-
pies the common apical site of two distorted square-pyramidal
cores, in each of which the two Fe atoms, one S atom and one
Te atom occupy the basal sites. Two terminally bonded car-
bonyl ligands on the Mo atom give it an overall co-ordination
number of ten. Each Fe atom has three terminal carbonyl
groups. Three of the four Mo᎐Fe bond distances [2.815(2)–
2.848(2) Å] (Table 2) are comparable with the Mo᎐Fe bond
lengths reported for other Mo/Fe mixed-metal clusters stabil-
ised by chalcogen ligands, [{(C5H4Me)MoS2Fe(CO)3}2],
2.853(3)
Å,7
[MoFeCo(η-C5H5)(CO)7(PMePrPh)(µ3-S)],
2.793(2) Å,8 [{(OC)2MoFeCo(CO)6(µ3-S)}2{η5-C5H4C(O)CH2-
CH2C(O)C5H4-η5}], 2.801(1) Å,9 and [Mo2Fe2(η-C5H5)2(CO)6-
(µ3-CO)2(µ3-S)2], 2.816(5) Å,10 whereas the fourth bond is some-
what long [Mo᎐Fe(1) 3.052(2) Å], making one of the square
pyramids more distorted than the other. While the two Mo᎐S
2950
J. Chem. Soc., Dalton Trans., 1997, Pages 2949–2954

View Article Online
Table 1 Preparation of [Fe4Mo(CO)14(µ3-E)2(µ3-EЈ)2] (E = S or Se; EЈ = S, Se or Te) and [Fe3Mo(CO)11(µ3-E)(µ3-EЈ)(µ-EЈ2)] (E = S; EЈ = Se or Te;
E = EЈ = S or Se)
Amount used/g (mmol)
[Fe2(CO)6(µ-EEЈ)]
Carbon
analysisa
(%)
M.p.
[Mo(CO)6]
Product
Yield/g (%)
0.053 (31)
IR (ν CO/cmϪ1, hexane)
(ЊC)b
[Fe2(CO)6(µ-SeTe)]
0.068 (0.26)
[Fe4Mo(CO)14(µ3-Se)2(µ3-Te)2] 1
2083w, 2057vs, 2050vs,
2043vs, 2019w, 2009s,
1996w, 1989w, 1982w
2087w, 2061vs, 2053vs,
2046vs, 2026w, 2022w,
2013s, 1999w, 1993w, 1984w
2087w, 2064s, 2054vs,
2045vs, 2023w, 2015s,
2003m, 1994w
15.3
(15.0)
174–176
156–158
147–149
0.25 (0.51)
[Fe2(CO)6(µ-STe)]
0.15 (0.57)
[Fe4Mo(CO)14(µ3-S)2(µ3-Te)2] 2
0.31 (40)
16.5
(16.3)
0.5 (1.14)
[Fe3Mo(CO)11(µ3-S)(µ3-Te)(µ-Te2)] 3 0.11 (14)
13.1
(12.7)
[Fe2(CO)6(µ-SSe)]
0.4 (1.02)
0.135 (0.51)
[Fe4Mo(CO)14(µ3-S)2(µ3-Se)2] 4
0.07 (12)
2091w, 2062vs, 2052vs,
2025w, 2015s, 1997w (br)
2090w, 2066vs, 2056vs,
2051vs, 2028w, 2016s,
2002w, 1997w
18.2
(18.0)
15.0
146–148
141–143
[Fe3Mo(CO)11(µ3-S)(µ3-Se)(µ-Se2)] 5 0.2 (35)
(14.7)
[Fe3Mo(CO)11(µ3-S)2(µ-SSe)] 6
[Fe4Mo(CO)14(µ3-S)4] 7
0.13 (27)
0.035 (5)
0.2 (30)
0.04 (7)
0.05 (10)
2093w, 2067vs, 2053vs,
2029w, 2017s, 2005w,
1999w
2095w, 2069vs, 2057vs,
2053vs, 2033w, 2025w,
2016s, 1998w
2088w, 2063vs, 2054vs,
2028s, 2017w, 2012w,
2005m
2089w, 2065vs, 2052vs,
2045vs, 2031w, 2013s,
1989w
17.6
(17.7)
134–138
[Fe2(CO)6(µ-S2)]
0.5 (1.45)
0.19 (0.72)
0.15 (0.57)
c
c
[Fe3Mo(CO)11(µ3-S)2(µ-S2)] 8
[Fe4Mo(CO)14(µ3-Se)4] 9
17.7
(17.5)
127–129
c
[Fe2(CO)6(µ-Se2)]
0.5 (1.14)
c
[Fe3Mo(CO)11(µ3-Se)2(µ-Se2)] 10
2090w, 2064vs, 2053vs,
2048vs, 2027s, 2011w,
2005w, 1996w
15.3
(14.9)
145–147
a
Calculated values in parentheses. b With decomposition. c Values are not available because of instability of the product.
Table 2 Selected bond lengths (Å) and angles (Њ) for [Fe4Mo(CO)14-
(µ3-S)2(µ3-Te)2] 2
Mo᎐Fe(1)
Mo᎐Fe(2)
Mo᎐Fe(3)
Mo᎐Fe(4)
Mo᎐S(1)
Mo᎐S(2)
Mo᎐Te(1)
Mo᎐Te(2)
3.052(2)
2.815(2)
2.830(2)
2.848(2)
2.431(3)
2.433(3)
2.741(11)
2.798(14)
Fe(1)᎐S(1)
Fe(2)᎐S(1)
Fe(3)᎐S(2)
Fe(4)᎐S(2)
Fe(1)᎐Te(1)
Fe(2)᎐Te(1)
Fe(3)᎐Te(2)
Fe(4)᎐Te(2)
2.286(3)
2.256(3)
2.256(4)
2.244(3)
2.572(2)
2.558(2)
2.546(2)
2.537(2)
Fe(2)᎐Mo᎐Fe(1)
S(1)᎐Mo᎐Fe(1)
S(1)᎐Mo᎐Fe(2)
Te(1)᎐Mo᎐Fe(1)
Te(1)᎐Mo᎐Fe(2)
Fe(3)᎐Mo᎐Fe(4)
S(2)᎐Mo᎐Fe(3)
S(2)᎐Mo᎐Fe(4)
Te(2)᎐Mo᎐Fe(3)
Te(2)᎐Mo᎐Fe(4)
Fe(3)᎐Mo᎐Fe(1)
Fe(4)᎐Mo᎐Fe(1)
S(2)᎐Mo᎐Fe(1)
S(2)᎐Mo᎐Fe(2)
74.7(5)
47.7(7)
50.3(8)
52.4(4)
54.8(4)
77.6(5)
50.1(8)
49.5(8)
53.8(4)
53.4(4)
97.5(6)
96.9(5)
133.3(9)
151.9(10)
Te(2)᎐Mo᎐Fe(1)
Te(2)᎐Mo᎐Fe(2)
Fe(2)᎐Mo᎐Fe(3)
Fe(2)᎐Mo᎐Fe(4)
S(1)᎐Mo᎐Fe(3)
S(1)᎐Mo᎐Fe(4)
Te(1)᎐Mo᎐Fe(3)
Te(1)᎐Mo᎐Fe(4)
S(1)᎐Mo᎐S(2)
S(1)᎐Mo᎐Te(1)
S(1)᎐Mo᎐Te(2)
S(2)᎐Mo᎐Te(1)
S(2)᎐Mo᎐Te(2)
Te(1)᎐Mo᎐Te(2)
58.9(4)
133.5(5)
138.4(6)
143.3(5)
94.0(8)
142.6(9)
146.9(9)
91.4(4)
142.9(10)
75.9(7)
92.1(8)
138.4(8)
74.5(9)
94.6(4)
Fig. 3 Molecular structure of compound 5
distances are similar [2.431(3), 2.433(3) Å], there is a consider-
able difference in the two Mo᎐Te bond lengths [2.741(11),
2.798(14) Å].
The sulfur and tellurium ligands adopt the µ3 bridging mode
and thereby function as four-electron donors to the cluster. In
terms of electron-counting rules, 2 is a 82-electron cluster, and
the formal application of the 18-electron rule would predict
four metal–metal bonds, as observed.
their hexane–dichloromethane solvent mixtures at Ϫ5 ЊC and
X-ray structural analyses were carried out. The ORTEP dia-
grams of their molecular structures are shown in Figs. 3–5,
selected bong lengths and angles in Tables 3–5. Clusters 5, 6 and
8 are isomorphous and isostructural, and consist of a Mo atom
which occupies the common apical site of square-pyramidal
and tetrahedral cores. The square base in 5, 6 and 8 consists of
an alternate arrangement of Fe and chalcogen atoms, whereas
the triangular base consists of one Fe and two chalcogen atoms.
Two terminally bonded carbonyl ligands on the Mo atom give it
Molecular structures of compounds 5, 6 and 8
Red plate crystals of compounds 5, 6 and 8 were grown from
J. Chem. Soc., Dalton Trans., 1997, Pages 2949–2954
2951

View Article Online
Table 3 Selected bond lengths (Å) and angles (Њ) for [Fe3Mo-
(CO)11(µ3-S)(µ3-Se)(µ-Se2) 5
Mo᎐Fe(1)
Mo᎐Fe(2)
Mo᎐Fe(3)
Mo᎐Se(1)
Mo᎐Se(2)
Mo᎐SSe(3)
Mo᎐SSe(4)
2.844(11)
Se(1)᎐Se(2)
Se(1)᎐Fe(1)
Se(2)᎐Fe(1)
SSe(3)᎐Fe(2)
SSe(3)᎐Fe(3)
SSe(4)᎐Fe(2)
SSe(4)᎐Fe(3)
2.313(12)
2.357(13)
2.379(13)
2.276(2)
2.284(2)
2.274(2)
2.277(2)
2.768(11)
2.752(11)
2.581(10)
2.581(9)
2.437(2)
2.492(2)
Se(1)᎐Mo᎐Fe(1)
Se(2)᎐Mo᎐Fe(1)
Fe(3)᎐Mo᎐Fe(2)
SSe(3)᎐Mo᎐Fe(2)
SSe(3)᎐Mo᎐Fe(3)
SSe(4)᎐Mo᎐Fe(2)
SSe(4)᎐Mo᎐Fe(3)
Se(1)᎐Mo᎐Fe(2)
Se(1)᎐Mo᎐Fe(3)
Se(2)᎐Mo᎐Fe(2)
Se(2)᎐Mo᎐Fe(3)
51.2(3)
51.7(3)
76.5(3)
51.4(5)
51.8(4)
50.9(4)
51.2(4)
133.4(4)
95.7(4)
100.0(3)
133.9(4)
Fe(2)᎐Mo᎐Fe(1)
Fe(3)᎐Mo᎐Fe(1)
SSe(3)᎐Mo᎐Fe(1)
SSe(4)᎐Mo᎐Fe(1)
Se(1)᎐Mo᎐Se(2)
SSe(3)᎐Mo᎐SSe(4)
SSe(3)᎐Mo᎐Se(1)
SSe(3)᎐Mo᎐Se(2)
SSe(4)᎐Mo᎐Se(1)
SSe(4)᎐Mo᎐Se(2)
144.6(4)
137.4(4)
134.2(5)
151.0(5)
53.2(2)
74.5(5)
87.5(5)
89.7(5)
146.7(5)
150.7(4)
Table 4 Selected bond lengths (Å) and angles (Њ) for [Fe3Mo(CO)11-
(µ3-S)2(µ-SSe)] 6
Mo᎐Fe(1)
Mo᎐Fe(2)
Mo᎐Fe(3)
Mo᎐SSe(1)
Mo᎐SSe(2)
Mo᎐S(1)
2.819(2)
2.735(2)
2.750(2)
2.556(2)
2.560(2)
2.450(3)
2.411(3)
SSe(1)᎐SSe(2)
SSe(1)᎐Fe(1)
SSe(2)᎐Fe(1)
Fe(2)᎐S(1)
Fe(2)᎐S(2)
Fe(3)᎐S(1)
2.275(2)
2.318(2)
2.355(2)
2.235(3)
2.265(3)
2.238(3)
2.261(3)
Fig. 4 Molecular structure of compound 6
Mo᎐S(2)
Fe(3)᎐S(2)
SSe(1)᎐Mo᎐Fe(1)
SSe(2)᎐Mo᎐Fe(1)
Fe(2)᎐Mo᎐Fe(3)
S(1)᎐Mo᎐Fe(2)
S(1)᎐Mo᎐Fe(3)
S(2)᎐Mo᎐Fe(2)
S(2)᎐Mo᎐Fe(3)
SSe(1)᎐Mo᎐Fe(2)
SSe(1)᎐Mo᎐Fe(3)
SSe(2)᎐Mo᎐Fe(2)
SSe(2)᎐Mo᎐Fe(3)
50.81(5)
51.67(5)
76.32(5)
50.71(7)
50.59(7)
51.76(7)
51.45(8)
95.94(6)
133.57(6)
133.68(6)
100.30(5)
Fe(2)᎐Mo᎐Fe(1)
Fe(3)᎐Mo᎐Fe(1)
S(1)᎐Mo᎐Fe(1)
S(2)᎐Mo᎐Fe(1)
SSe(1)᎐Mo᎐SSe(2)
S(2)᎐Mo᎐S(1)
S(1)᎐Mo᎐SSe(1)
S(1)᎐Mo᎐SSe(2)
S(2)᎐Mo᎐SSe(1)
S(2)᎐Mo᎐SSe(2)
137.29(6)
144.92(6)
151.66(8)
133.93(8)
52.82(5)
74.08(9)
146.51(8)
150.79(8)
87.54(8)
89.54(8)
Table 5 Selected bond lengths (Å) and angles (Њ) for [Fe3Mo(CO)11-
(µ3-S)2(µ-S2)] 8
Mo᎐Fe(1)
Mo᎐Fe(2)
Mo᎐Fe(3)
Mo᎐S(1)
Mo᎐S(2)
Mo᎐S(3)
Mo᎐S(4)
2.735(8)
2.757(8)
2.802(9)
2.453(13)
2.408(13)
2.448(14)
2.449(13)
S(3)᎐S(4)
2.041(2)
2.241(14)
2.266(14)
2.239(14)
2.258(14)
2.233(2)
2.247(2)
Fe(1)᎐S(1)
Fe(1)᎐S(2)
Fe(2)᎐S(1)
Fe(2)᎐S(2)
Fe(3)᎐S(3)
Fe(3)᎐S(4)
Fig. 5 Molecular structure of compound 8
Fe(1)᎐Mo᎐Fe(2)
S(1)᎐Mo᎐Fe(1)
S(1)᎐Mo᎐Fe(2)
S(2)᎐Mo᎐Fe(1)
S(2)᎐Mo᎐Fe(2)
S(3)᎐Mo᎐Fe(3)
S(4)᎐Mo᎐Fe(3)
Fe(1)᎐Mo᎐Fe(3)
Fe(2)᎐Mo᎐Fe(3)
S(1)᎐Mo᎐Fe(3)
S(2)᎐Mo᎐Fe(3)
76.4(2)
50.8(3)
50.5(3)
51.8(3)
51.3(3)
49.8(4)
50.1(3)
137.3(3)
144.6(3)
152.5(4)
133.3(4)
S(3)᎐Mo᎐Fe(1)
S(3)᎐Mo᎐Fe(2)
S(4)᎐Mo᎐Fe(1)
S(4)᎐Mo᎐Fe(2)
S(2)᎐Mo᎐S(1)
S(3)᎐Mo᎐S(4)
S(3)᎐Mo᎐S(1)
S(2)᎐Mo᎐S(3)
S(4)᎐Mo᎐S(1)
S(2)᎐Mo᎐S(4)
97.1(4)
132.8(4)
132.7(4)
101.7(4)
73.9(4)
49.3(5)
147.9(5)
87.6(5)
an overall co-ordination number of nine in each compound.
Three terminal carbonyl groups are bonded to each iron atom
in all three molecules. The bond distance between the Mo atom
and the Fe atom in the triangular base is longer (2.802–2.844 Å)
than the bonds between Mo and the square-base Fe atoms
(2.735–2.768 Å), the former being comparable to the Mo᎐Fe
bond distances observed in 1 and 2 (2.815–2.889 Å). The
S᎐S bond distance in 8 [2.041(2) Å] is similar to that in
[Fe2(CO)6(µ-S2)]11 (2.011 Å). Likewise, the Se᎐Se bond distance
in 5 [2.313(12) Å] is similar to that of [Fe2(CO)6(µ-Se2)]12
[2.293(2) Å].
Although the exact mechanism of formation of compounds
5, 6 and 8 is not established as yet, it involves the formal loss of
one Fe(CO)3 group from [Fe2(CO)6(µ-S2)] or [Fe2(CO)6(µ-Se2)]
which is formed from [Fe2(CO)6(µ-SSe)] while stirring with
[Mo(CO)5(thf)] at room temperature, and the addition of one
152.2(5)
89.6(4)
Fe(CO)3E2 group (E = S or Se) and [Fe2(CO)6(µ-S2)] or
[Fe2(CO)6(µ-SSe)] respectively thus formed to one Mo(CO)4
group. Formally, one[Fe2(CO)6(µ-E2)]moleculeundergoescleav-
age of a Fe᎐Fe and two Fe᎐E bonds and the other [Fe2(CO)6(µ-
S2)] or [Fe2(CO)6(µ-SSe)] molecule undergoes one Fe᎐Fe and one
S᎐S or S᎐Se bond scissions, and there is an overall formation of
2952
J. Chem. Soc., Dalton Trans., 1997, Pages 2949–2954

View Article Online
Table 6 Crystal data for [Fe4Mo(CO)14(µ3-S)2(µ3-Te)2] 2 and [Fe3Mo(CO)11(µ3-E)(µ3-EЈ)(µ-EЈ2)] (E = S, EЈ = Se or S; EЈ2 = Se2 5, SSe 6 or S2 8)
2
5
6
8
Formula
M
C14Fe4MoO14S2Te2
1030.8
C11Fe3MoO11SSe3
840.54
C11Fe3MoO11S3Se
746.74
C11Fe3MoO11S4
699.84
Crystal size/mm
Crystal system
Space group
a/Å
b/Å
c/Å
0.40 × 0.40 × 0.40
Orthorhomic
Pna21
14.469(3)
11.627(1)
0.40 × 0.40 × 0.20
Monoclinic
P21/n
10.896(2)
17.538(1)
11.667(1)
108.93(1)
2108.9(4)
4
0.40 × 0.20 × 0.10
Monoclinic
P21/n
10.801(2)
17.456(3)
11.594(3)
108.85(3)
2068.6(10)
4
0.40 × 0.30 × 0.20
Monoclinic
P21/n
10.7703(9)
17.630(1)
11.609(2)
108.49(1)
2090.5(3)
4
15.473(3)
β/Њ
U/Å3
2603.1(4)
4
2.630
50.65
1912
Z
Dc/g cmϪ3
µ(Mo-Kα)/cmϪ1
F(000)
2.647
79.30
1568
2.398
47.68
1424
2.224
30.77
1352
T/K
298(2)
298(2)
247(2)
298(2)
θ Range/Њ
hkl Ranges
2.25–24.98
Ϫ1 to 17, Ϫ1 to 13,
Ϫ18 to ϩ1
3060
2561
0.0435
2.18–22.50
Ϫ1 to 11, Ϫ1 to 18,
Ϫ12 to ϩ12
1496
2760
0.0327
2.19–22.50
Ϫ1 to 11, Ϫ1 to 18,
Ϫ12 to ϩ12
3464
2705
0.0397
2.18–22.50
Ϫ1 to 11, Ϫ1 to 18,
Ϫ12 to ϩ12
3496
2732
0.0247
Reflections collected
Independent reflections
Rint
Data, restraints, parameters
Goodness of fit on F 2
Final R indices [I > 2σ(I)]*
(all data)
2558, 1, 335
1.515
0.0353
0.0858
0.934, Ϫ0.707
2760, 0, 274
1.085
0.0328, 0.0713
0.0466, 0.0731
0.622, Ϫ0.726
2702, 0, 273
1.231
0.0428, 0.1031
0.0704, 0.1191
1.117, Ϫ0.816
2732, 0, 271
1.127
0.0301, 0.0702
0.0399, 0.0748
0.482, Ϫ0.467
Largest difference peak and hole/e ÅϪ3
¹
* R = Σ|(Fo Ϫ Fc)|/ΣFo; wR2 = Σw(Fo2 Ϫ Fc )2/Σ[w(Fo2)2]².
2
seven new bonds, three Fe᎐Mo, one S᎐Mo and three E᎐Mo.
Both the sulfur and selenium ligands adopt the µ3 bridging mode
in 5, 6 and 8 and thereby function as four-electron donors to the
clusters.
of [Fe2Mo(CO)10(µ3-E)(µ3-EЈ)] {EEЈ = SeTe, 0.045 g, 9%, based
on [Fe2(CO)6(µ-SeTe)] consumed; STe, 0.02 g, 8%, based on
[Fe2(CO)6(µ-STe)] consumed; Se2, 0.1 g, 20%, based on
[Fe2(CO)6(µ-Se2)] consumed}, unchanged [Fe2(CO)6(µ-EEЈ)]
(EEЈ = SeTe, 40; STe, 34; SSe, 37; S2, 40; Se2, 50%), a green band
of [Fe4Mo(CO)14(µ3-E)2(µ3-EЈ)2] and an orange band of
[Fe3Mo(CO)11(µ3-E)(µ3-EЈ)(µ-EЈ2)].
Experimental
General procedures
X-Ray crystallography
All reactions and manipulations were performed using stand-
ard Schlenk techniques under an atmosphere of prepurified dry
argon. Solvents were purified, dried and distilled under an
argon or nitrogen atmosphere prior to use. Infrared spectra
were recorded on a Nicolet Impact 400 FT spectrometer as
hexane solutions in 0.1 mm path length NaCl cells. Elemental
analyses were performed on a Carlo-Erba automatic analyser.
The compounds [Fe2(CO)6(µ-EEЈ)]13 (E = S or Se; EЈ = S, Se or
Te) and [Mo(CO)5(thf)]14 were prepared by established pro-
cedures; [Mo(CO)6] was obtained from Aldrich Chemical Co.
and used as such. Photochemical reactions were carried out in a
water-cooled double-walled quartz vessel having a 125 W
immersion-type mercury lamp manufactured by Applied
Photophysics Ltd.
Dark red crystals of compounds 2, 5, 6 and 8 were grown by
layering hexane on their dichloromethane solutions and slow
evaporation of the solvents at Ϫ5 ЊC. Suitable crystals were
selected and mounted on thin glass fibres with epoxy cement.
Crystal data and structure refinement details are given in Table
6. The data were measured on a Siemens P4 diffractometer
using graphite-monochromated Mo-Kα radiation (λ = 0.710 73
Å). The unit-cell parameters were obtained by least-squares
refinement of the angular settings of 24 reflections (20 р
2θ р 25Њ). Preliminary photographic data indicated an ortho-
rhombic crystal system for 2 and a monoclinic crystal system
for 5, 6 and 8. The systematic absences in the diffraction data
are consistent with either Pna21 or Pnma for 2, and uniquely
P21/n for 5, 6 and 8. The E statistics suggested the non-
centrosymmetric option for 2. Solution and refinement in Pna21
produced a plane defined by Fe(1), Fe(2), S(2) and Te(2) that is
nearly perpendicular to the crystallographic z axis. If the atoms
S(1) and Te(1) were disordered, this plane would constitute a
molecular mirror plane. However, the results of refinement
strongly support the non-centrosymmetric alternative for these
reasons: bond distances and angles fall into narrow and expected
ranges, no positional element in the correlation matrix exceeds
0.5, and the isotropic equivalent thermal parameters for S(1)
(0.035) and Te(1) (0.038) are nearly equal when refined as pure
elements. Similarly, no compositional disorder is seen at the
S(2) and Te(2) sites. The structures were solved by direct
methods, completed by subsequent Fourier-difference syntheses
and refined by full-matrix least-squares procedures. Semiem-
pirical absorption corrections were applied. All non-hydrogen
atoms were refined with anisotropic displacement coefficients.
Hydrogen atoms were treated as idealised contributions. Two of
Typical preparation of [Fe4Mo(CO)14(ì3-E)2(ì3-EЈ)2] (E = S or
Se; EЈ = S, Se or Te) and [Fe3Mo(CO)11(ì3-E)(ì3-EЈ)(ì-EЈ2)]
(E = S; EЈ = Se or Te; E = EЈ = S, Se)
Conditions used for the preparation of compounds 1–10 and
yields of products are summarised in Table 1. In a typical prep-
aration, a thf solution (120 cm3) of [Mo(CO)6] (0.26–0.72
mmol) was irradiated with 366 nm UV light in an immersion-
type photolysis instrument for 10 min under a constant argon
purge. The yellow-green thf solution of [Mo(CO)5(thf)] was
added to a hexane solution (50 cm3) containing [Fe2(CO)6-
(µ-EEЈ)], (E = S or Se; EЈ = S, Se or Te) (0.51–1.45 mmol). The
reaction mixture was stirred at room temperature for 3 h. The
solvent was removed in vacuo, and the residue subjected to
chromatographic work-up on a silica gel column. Using hexane
as eluent, the following bands were obtained, in order of
elution: [Mo(CO)6] (trace), previously reported maroon band
J. Chem. Soc., Dalton Trans., 1997, Pages 2949–2954
2953

View Article Online
5 P. Mathur and P. Sekar, Chem. Commun., 1996, 727.
6 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National
Laboratory, Oak Ridge, TN, 1976.
7 B. Cowans, J. Noordik and M. R. DuBois, Organometallics, 1983, 2,
931.
8 F. Richter and H. Vahrenkamp, Chem. Ber., 1982, 115, 3243.
9 L.-C. Song, J.-Y. Shen, Q.-M. Hu and X.-Y. Huang, Organometal-
lics, 1995, 14, 98.
10 P. D. Williams, M. D. Curtis, D. N. Duffy and W. M. Butler,
Organometallics, 1983, 2, 165.
11 C. H. Wei and L. F. Dahl, Inorg. Chem., 1965, 4, 1.
12 C. F. Campana, F. Y.-K. Lo and L. F. Dahl, Inorg. Chem., 1979, 18,
3060.
the chalcogen atoms in 5 and 6 were found to be statistically
disordered over two positions with an occupancy distribution
of 70:30 and 75:25 respectively. This disorder was modelled by
refining the occupancies of the chalcogen atoms which were
arbitrarily identified as selenium atoms [labelled as SSe(3) and
SSe(4) in 5; SSe(1) and SSe(2) in 6]. All software and sources of
the scattering factors are contained in the SHELXTL (5.3) pro-
gram library.15 Final cycles of refinement converged at R and
RЈ values listed in Table 2.
CCDC reference number 186/601.
13 P. Mathur, D. Chakrabarty and Md. M. Hossain, J. Organomet.
Chem., 1991, 401, 167; P. Mathur, P. Sekar, C. V. V. Satyanarayana
and M. F. Mahon, Organometallics, 1995, 14, 2115.
14 W. J. Schlientz and J. K. Ruff, Inorg. Chem., 1972, 11, 2265.
15 G. M. Sheldrick, Siemens XRD, Madison, WI, 1996.
References
1 P. Mathur, D. Chakrabarty and I. J. Mavunkal, J. Cluster Sci., 1993,
4, 351; P. Mathur, I. J. Mavunkal and A. L. Rheingold, J. Chem.
Soc., Chem. Commun., 1989, 382.
2 D. A. Lesch and T. B. Rauchfuss, Inorg. Chem., 1983, 22, 1854.
3 P. Mathur, D. Chakrabarty, Md. M. Hossain, R. S. Rashid,
V. Rugmini and A. L. Rheingold, Inorg. Chem., 1992, 31, 1106.
4 P. Mathur, P. Sekar, C. V. V. Satyanarayana and M. F. Mahon,
J. Chem. Soc., Dalton Trans., 1996, 2173.
Received 8th April 1997; Paper 7/02408H
2954
J. Chem. Soc., Dalton Trans., 1997, Pages 2949–2954