Chromium-manganese selenide carbonyl complexes: Paramagnetic clusters and relevance to C = O activation of acetone

Article abstract of DOI:10.1021/ic101118y

The paramagnetic even-electron cluster, [Et₄N] ₂[Se₂Cr₃(CO)₁₀], was found to react readily with Mn(CO)₅Br in acetone to produce two unprecedented mixed chromium-manganese selenide carbonyl complexes, [Et₄N][Me ₂CSe₂{Mn(CO)₄}{Cr(CO)₅} ₂] ([Et₄N][1]) and [Et₄N]₂[Se ₂Mn₃(CO)₁₀{Cr(CO)₅}₂] ([Et₄N]₂[2]). X-ray crystallographic analysis showed that anion 1 consisted of two Se-Cr(CO)₅ moieties, which were further bridged by one isopropylene group and one Mn(CO)₄ moiety. The dianionic cluster 2 was shown to display a Se₂Mn₃ square-pyramidal core with each Se atom externally coordinated by one Cr(CO)₅ group. The formation of complex 1, presumably via C=O activation of acetone, was further facilitated by acidification of the reaction of [Et₄N]₂[Se₂Cr₃(CO)₁₀] with Mn(CO)₅Br in acetone. Complex 1 readily transformed into 2 upon treatment with Mn₂(CO)₁₀ in a KOH/MeOH/MeCN solution. Cluster 2 was a 51-electron species, which readily converted to the known 49-electron cluster [Se₂Mn₃(CO)₉]^2- upon heating and bubbling with CO. Magnetic studies of the even-electron cluster, [Et₄N]₂[Se₂Cr₃(CO) ₁₀], and the odd-electron species, [Et₄N]₂[2] and [PPN]₂[Se₂Mn₃(CO)₉], were determined by the SQUID measurement to have 2, 3, and 1 unpaired electrons, respectively. In addition, the nature and formation of complexes 1 and 2 are discussed, and the magnetic properties and electrochemistry of [Se ₂Cr₃(CO)₁₀]^2-, 2, and [Se ₂Mn₃(CO)₉]^2- were further studied and elucidated by molecular orbital calculations at the PW91 level of density functional theory.

Full text of DOI:10.1021/ic101118y

8056 Inorg. Chem. 2010, 49, 8056–8066
DOI: 10.1021/ic101118y
Chromium-Manganese Selenide Carbonyl Complexes: Paramagnetic Clusters
and Relevance to CdO Activation of Acetone
Minghuey Shieh,* Chien-Nan Lin, Chia-Yeh Miu, Miao-Hsing Hsu, Yi-Wen Pan, and Li-Fang Ho
Department of Chemistry, National Taiwan Normal University, Taipei 116, Taiwan, Republic of China
Received June 3, 2010
The paramagnetic even-electron cluster, [Et4N]2[Se2Cr3(CO)10], was found to react readily with Mn(CO)5Br in
acetone to produce two unprecedented mixed chromium-manganese selenide carbonyl complexes, [Et4N][Me2-
CSe2{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1]) and [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2]). X-ray crystallographic
analysis showed that anion 1 consisted of two Se-Cr(CO)5 moieties, which were further bridged by one isopropylene
group and one Mn(CO)4 moiety. The dianionic cluster 2 was shown to display a Se2Mn3 square-pyramidal core with
each Se atom externally coordinated by one Cr(CO)5 group. The formation of complex 1, presumably via CdO
activation of acetone, was further facilitated by acidification of the reaction of [Et4N]2[Se2Cr3(CO)10] with Mn(CO)5Br
in acetone. Complex 1 readily transformed into 2 upon treatment with Mn2(CO)10 in a KOH/MeOH/MeCN solution.
Cluster 2 was a 51-electron species, which readily converted to the known 49-electron cluster [Se2Mn3(CO)9]2- upon
heating and bubbling with CO. Magnetic studies of the even-electron cluster, [Et4N]2[Se2Cr3(CO)10], and the odd-
electron species, [Et4N]2[2] and [PPN]2[Se2Mn3(CO)9], were determined by the SQUID measurement to have 2, 3,
and 1 unpaired electrons, respectively. In addition, the nature and formation of complexes 1 and 2 are discussed, and
the magnetic properties and electrochemistry of [Se2Cr3(CO)10]2-, 2, and [Se2Mn3(CO)9]2- were further studied and
elucidated by molecular orbital calculations at the PW91 level of density functional theory.
Introduction
Although transition metal clusters bridged by main group
elements have been well studied, there has been little explora-
tion of group 6 carbonyl chalcogenide complexes.8-10 Com-
pared to the larger number of main group-containing
homonuclear metal clusters, there are few heteronuclear
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*To whom all correspondence should be addressed. E-mail: mshieh@
ntnu.edu.tw.
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r
pubs.acs.org/IC
Published on Web 08/03/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 17, 2010 8057
metal carbonyl clusters.1a,b We previously explored the
chemistry of chromium carbonyl chalcogenide clusters and
found it full of interest and challenge.11 Previous studies have
shown that paramagnetic metal carbonyl complexes were
rare.10c,11f,12,13 In the present study, we demonstrate the
unusual reactivity exhibited by the previously reported sele-
Mn(CO)5Br in acetone to form novel mixed Cr-Mn selenide
complexes. According to a search of the Cambridge Crystallo-
graphic Data Centre, mixed Cr-Mn selenide complexes are
rare,13e,14 and there were only five examples of Se-Cr-
Mn complexes reported in the literature.
The present study provides details of the synthesis of two
Cr-Mn selenide carbonyl complexes, [Et4N][Me2CSe2{Mn-
(CO)4}{Cr(CO)5}2] ([Et4N][1]) and [Et4N]2[Se2Mn3(CO)10-
{Cr(CO)5}2] ([Et4N]2[2]), from the reaction of [Et4N]2[Se2-
Cr3(CO)10] with Mn(CO)5Br in acetone, in which the former
complex was formed via the CdO activation of acetone and
the latter was a result of the cluster-expansion reaction.
Cluster 2 was found to exhibit unusual paramagnetic proper-
ties with S = 3/2 at room temperature, and was further
transformed to its structurally related paramagnetic cluster,
[Se2Mn3(CO)9]2-, with S = 1/2, by bubbling with CO. In
addition, the electronic, magnetic, and electrochemical pro-
perties of the even-electron complex, [Se2Cr3(CO)10]2-, and
the odd-electron species, 2 and [Se2Mn3(CO)9]2-, were in-
vestigated and are systematically discussed with the aid of
density functional theory (DFT) calculations.
nium-capped trichromium cluster closo-[Se2Cr3(CO)10]2- 11a
,
which is found to be paramagnetic and can readily react with
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Results and Discussion
Synthesis and Structures of [Et4N][Me2CSe2{Mn(CO)4}-
{Cr(CO)5}2] ([Et4N][1]) and [Et4N]2[Se2Mn3(CO)10{Cr-
(CO)5}2] ([Et4N]2[2]). Two mixed manganese-chromium
selenide carbonyl complexes, [Et4N][Me2CSe2{Mn(CO)4}-
{Cr(CO)5}2] ([Et4N][1]) and [Et4N]2[Se2Mn3(CO)10{Cr-
(CO)5}2] ([Et4N]2[2]), were produced from the reaction of
[Et4N]2[Se2Cr3(CO)10] with Mn(CO)5Br in a molar ratio
1:1.8 in an acetone solution at 35 °C with yields of 40 and
29%, respectively (Scheme 1). Compounds 1 and 2 were
both characterized on the basis of IR, NMR, ICP-AES,
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8058 Inorganic Chemistry, Vol. 49, No. 17, 2010
Shieh et al.
Scheme 1
knowledge, a related example has been observed only in
the sulfur complex W(CO)5(SdCMe2), which was obtained
from the reaction of W(CO)5(SH)- with ketones upon the
addition of acids.17
Cluster 2 was a cluster-expansion product. As shown in
Figure 2, the Se2Mn4-linked di-Cr(CO)5 cluster 2, which
has a crystallographic center of symmetry at the center of
the disordered Se2Mn4 octahedral core and a mirror plane
through the Se2Mn(2)Mn(2a) base. The core geometry of
2 could be viewed as two Cr(CO)5 units sandwiching a
disordered Se2Mn4 unit in which the Mn(2) and Mn(2a)
atoms are disordered and present in a 50:50 ratio. Besides,
Mn(2) atom is coordinated with two terminal COs, where
C(6), C(7), O(6), and O(7) atoms are also disordered
with 50% occupancy. The selenium-selenium distance
Figure 1. ORTEP diagram of anion 1, showing 30% probability thermal
ellipsoids.
˚
of 3.037(1) A is regarded formally as nonbonding. Thus,
reported values for M(CO)5(SdCMe2) (M = Cr, Mo, W).15
The upfield 13C absorption (δ 47.1) for the quaternary
carbon of the Me2CSe2 moiety was close to the value (δ
49.4) reported to the analogous sulfur fragment,16 attribu-
table to its negative natural charges (see DFT Calculations,
Table 2). An Oak Ridge thermal ellipsoid plot (ORTEP)
diagram of the structure of 1is shown in Figure 1. Complex 1
was shown to have two Se atoms bridged by an isopropylene
group and one Mn(CO)4 fragment, to give a four-membered
SeCSeMn ring in which each Se atom is externally coordi-
nated by one Cr(CO)5 fragment.
cluster 2 can be considered to have a distorted Se2Mn3
square-pyramidal core with each basal Se atom bonded to
one Cr(CO)5 fragment. In this point of view, two basal
Mn(1) and Mn(1a) atoms of the Se2Mn3 square-pyrami-
dal core each had two terminal carbonyl ligands and one
bridging CO, while the apical Mn(2) atom possessed two
terminal carbonyl groups with two bridging COs shared
with the other Mn(1) and Mn(1a) atoms, where the Se(1)-
Mn(1), Se(1)-Mn(2), Se(1)-Mn(1a), Se(1a)-Mn(2) dis-
˚
tances are 2.448(1), 2.389(2), 2.448(1), and 2.408(2) A, while
the Mn(1)-Se(1)-Mn(1a), Se(1)-Mn(1)-Se(1a), Se(1)-
Mn(2)-Mn(1), Se(1a)-Mn(2)-Mn(1) anglesare103.33(4),
76.67(4), 57.54(4), and 57.35(4)°. The Se2Mn2 base was
precisely planar and also coplanar with the pendant chro-
mium atoms, Cr(1) and Cr(1a), which were in perfect exter-
nally bisecting positions since Mn(1)-Se(1)-Cr(1) =
Mn(1a)-Se(1)-Cr(1) = 128.31(2)°.
A search of the Cambridge Crystallographic Data
Centre failed to identify any structurally characterized
compound with a SeCSeMn ring. Complex 1 represents
the first example of a SeCSeMn ring compound. Further,
the Se(1)-C(15)-Se(2) and Se(1)-Mn-Se(2) bond an-
gles were 101.2(2)° and 75.91(3)°, reflecting a strained
four-membered SeCSeMn ring, with a mean deviation of
For further comparison, the distances of the Se-Cr,
Se-Mn, and Mn-Mn bonds of 1 and 2 and other related
complexes are listed in Table 1. The average Se-Cr bond
˚
0.091 A from the ideal plane. Surprisingly, the two Cr-
(CO)5 moieties occupied the syn orientation because
of the steric hindrance of the Mn(CO)4 fragment. The
formation of 1 is believed to have resulted from the
CdO bond cleavage of acetone under our reaction con-
ditions, which is rare in the literature. To the best of our
˚
distance of 1 was 2.586(3) A, which was longer than that
˚
(2.541(1) A) of complex 2 and significantly longer than
those in related complexes11a,d,f,13e,14 (Table 1), reflecting
the reactive nature of complex 1. In complex 1, the
˚
average Se-Mn bond was 2.5044(8) A, comparatively
longer than that in 2 (2.43(3) A), [Se2Mn3(CO)9]
2-
˚
(15) Gingerich, R. G. W.; Angelici, R. J. J. Organomet. Chem. 1977, 132,
377–386.
€
(16) Windhager, J.; Gorls, H.; Petzold, H.; Mloston, G.; Linti, G.;
(17) Gingerich, R. G. W.; Angelici, R. J. J. Am. Chem. Soc. 1979, 101,
5604–5608.
Weigand, W. Eur. J. Inorg. Chem. 2007, 4462–4471.

Article
Inorganic Chemistry, Vol. 49, No. 17, 2010 8059
Figure 2. ORTEP diagram of anion 2, showing 30% probability thermal ellipsoids.
˚
Table 1. Average Bond Distances (A) of [Et4N][Me2CSe2{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1]), [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2]), and Related Complexes
complex
Se-Cr
Se-Mn
Mn-Mn
ref
[Et4N][1]
[Et4N]2[2]
[Et4N]2[Se2Cr3(CO)10
[PPN]2[Se2Cr2Fe(CO)10
[Et4N]2[Se2Cr2Mo(CO)10
[Et4N]2[Se2Cr2W(CO)10
Cp02Cr2(μ-SPh)2(μ3-Se)Mn2(CO)9
Cp02Cr2(μ-SPh)2(μ4-Se)Mn2(CO)8
CpMnSe2Cr(CO)7
CpMnSe2Cr2(CO)12
[PPh4]2[Se2Mn3(CO)9]
2.586(3)
2.541(1)
2.5(1)
2.5044(8)
2.43(3)
a
a
2.671(2)
]
11a
11f
11d
11d
13e
13e
14
]
2.50(1)
]
2.416(4)
2.418(2)
2.453(9)
2.4635(7)
2.503(2)
2.50(1)
]
2.5506(5)
2.419(8)
2.50(1)
2.53(2)
2.43(2)
2.486(9)
2.475(2)
2.51(2)
2.9502(7)
2.835(3)
14
2.76(6)
13d
10a
10a
18
[PPN]2[C2Se8Mn2(CO)6]
[PPN]2[Se2Mn4(CO)12]
[PPh4]2[Mn2(Se4)2(CO)6]
[Et4N]2[Mn(SePh)4]
2.705(8)
2.567(5)
19
a This work.
Table 2. Results of Natural Bond Order and Natural Population Analyses of [Se2Cr3(CO)10
]
2-, 1, 10, 2, and [Se2Mn3(CO)9]2- at the Level of PW91/LanL2DZ
Wiberg bond index
natural charge
complex
Se-Mn Mn-Mn Se-Cr Se-Ca
Se
Mn
Cr
Ca
Se2Mn3(CO)x (sum) Cr2(CO)10 (sum)
2-b
[Se2Cr3(CO)10
]
0.426
-0.134
0.218
0.213
-0.028 -0.569 -1.332
-0.127 -0.577
-0.711
1
0.358
0.360
0.305
0.423
0.320
0.316
0.284
0.892
0.891
-0.862 -1.332 -0.272
-0.953
-0.953
-1.045
10
2
-0.850 -1.343
-0.266
0.099
0.116
-0.955 (x = 10)
-2 (x = 9)
[Se2Mn3(CO)9]2-
a The quaternary carbon. b Single-point calculations.
(2.43(2) A),13d [C2Se8Mn2(CO)6]2- (2.486(9) A), [Se2-
10a
average Mn-Mn bond (2.671(2) A) of complex 2 was the
shortest among the Mn-Mn bonds of the related complexes
(See Table 1). Overall, the average Se-Mn and Se-Cr bond
distances of 2 were shorter than the corresponding distances
in 1, suggesting stronger skeletal bonds in complex 2versus 1,
probably because of the additional Mn-Mn bonds.
˚
˚
˚
Mn4(CO)12]2- (2.475(2) A), and Cp02Cr2(μ-SPh)2(μ4-
10a
˚
13e
˚
Se)Mn2(CO)8 (2.419(8) A)
but shorter than that in
[Mn2(Se4)2(CO)6]2- (2.51(2) A),18 [Mn(SePh)4]2- (2.567(5)
˚
19
13e
A), Cp02Cr2(μ-SPh)2(μ3-Se)Mn2(CO)9 (2.5506(5) A),
˚
˚
14
and CpMnSe2Cr2(CO)12 (2.53(2) A). Additionally, the
˚
Formation of the CdO Activated Complex 1. The
formation of complex 1, via CdO activation of acetone,
was further facilitated by the acidification of the reaction
of [Et4N]2[Se2Cr3(CO)10] with Mn(CO)5Br in acetone.
(18) O’Neal, S. C.; Pennington, W. T.; Kolis, J. W. Inorg. Chem. 1990, 29,
3134–3138.
(19) Tremel, W.; Krebs, B.; Greiwe, K.; Simon, W.; Stephan, H.-O.;
Henkel, G. Z. Naturforsch. 1992, 47B, 1580–1592.

8060 Inorganic Chemistry, Vol. 49, No. 17, 2010
Shieh et al.
Scheme 2
Scheme 3
The yield of 1 increased from 40 to 61%, and the minor
product 2 decreased to 12%. The formation of 1 may have
occurred via the nucleophilic attack of the reactive “Se”
sites of [Se2Cr3(CO)10]2- on the carbon center of the
acetone and the Mn atom of the incoming [Mn(CO)5]þ
group, accompanied by complicated bond breakage and
formation processes, to give rise to the CdO activated
product 1. The acidification of the reaction may have
increased the electrophilicity of the carbon center of the
acetone, and thereby enhanced the yields of complex 1.
However, the trace amount of aqueous HCl may have
broken the metal skeleton of 2 to result in a decreased
yield. On the other hand, we wondered whether CdO
activation of the acetone analogue could be observed in
the reaction of [Se2Cr3(CO)10]2- with Mn(CO)5Br. It
turned out that when the reaction was treated with
butanone under similar conditions, only complex 2 was
isolated, with no observation of the CdO activation
product [Me(Et)CSe2Cr2Mn(CO)14]- (10) (discussed later
with DFT Calculations). Even when the reaction with
butanone was acidified, the degradation product [Se2-
Mn3(CO)9]-10a was formed instead.
to give complex 2under the controlled conditions, but instead
led to the formation of the known complexes [Se2Mn3-
(CO)9]- and [Cr(CO)5Br]-.10a,20 However, complex 2 was
obtained from the reaction of complex 1with Mn2(CO)10 in a
KOH/MeOH/MeCN solution. Complex 2 also underwent
cluster degradation via Se-Cr bond breakage to form
[Se2Mn3(CO)9]- upon its reaction with Mn(CO)5Br in acet-
one. These results indicate that the pathways of the formation
of compounds 1 and 2 in the reaction of [Se2Cr3(CO)10]2-
with Mn(CO)5Br in acetone are different, and the Se-Mn
bonds are stronger than the Se-Cr bonds in complexes 1 and
2 (See Table 1). This phenomenon is also supported by DFT
calculations (Wiberg bond index in Table 2).
Transformation of 2 to the Paramagnetic [Se2Mn3-
(CO)9]2-. Complex 2 was thermally stable in refluxing
MeCN solution. However, when CO was bubbled through
a solution of complex 2 in MeCN at 50 °C, the known
49-electron complex, [Se2Mn3(CO)9]2- 13d
resulted along
,
with the formation of Cr(CO)6 which was identified by IR
(Scheme 3). On the basis of the result, it was believed that
cluster 2 underwent two Se-Cr(CO)5 bond breakage with
the elimination of Cr(CO)6 to give the structurally related
square-pyramidalSe2Mn3 complex[Se2Mn3(CO)9]2-. This
reaction also implied that a CO molecule was removed
from the Mn3 core to give one of the Cr(CO)6 molecules.
Decarbonylation reactions in anionic metal carbonyl
complexes are generally quite difficult.21
Transformation of 1 and 2. To better understand the
reactivity of complexes 1 and 2, their structural transfor-
mations were carefully examined (Scheme 2). We investi-
gated whether complex 1 could be transformed to 2 under
our reaction conditions for the reaction of [Se2Cr3(CO)10]2-
with Mn(CO)5Br. As shown in Scheme 2, compound 1 failed
(20) (a) Abel, E. W.; Butler, I. S.; Reid, J. G. J. Chem. Soc. 1963, 2068–
(21) (a) Bernhardt, W.; Vahrenkamp, H. Organometallics 1986, 5, 2388–
2389. (b) Huang, T.-K.; Chi, Y.; Peng, S.-M.; Lee, G.-H.; Wang, S.-L.; Liao, F.-L.
Organometallics 1995, 14, 2164–2166.
€
2070. (b) Fischer, E. O.; Ofele, K. Z. Naturforsch. 1959, 14B, 736–737.
€
(c) Fischer, E. O.; Ofele, K. Chem. Ber. 1960, 93, 1156–1161.

Article
Inorganic Chemistry, Vol. 49, No. 17, 2010 8061
diffraction data,11a and the geometries of 1, 2, and [Se2-
Mn3(CO)9]2- were optimizedwiththe samelevel oftheory.
On the basis of the single-crystal diffraction data of com-
plex 1, the isopropylene group of complex 1 was replaced
by the sec-butylene group, forming the proposed structure
[Me(Et)CSe2Cr2Mn(CO)14]- (10), which was also fully
optimized with the same level of theory. In addition, the
Wiberg bond indices24 and natural population analyses
(NPA)25 for [Se2Cr3(CO)10]2-, 1, 10, 2, and [Se2Mn3-
(CO)9]2- were calculated, and the results are further
analyzed and listed in Table 2.
The calculated results reveal that the active sites of the
paramagnetic [Se2Cr3(CO)10]2- for the formation of com-
plexes 1 and 2 could be related to the higher singly occupied
molecular orbital (SOMO) of [Se2Cr3(CO)10]2-. As shown
in Figure 4, the higher-energy SOMO of [Se2Cr3(CO)10]2-
had a significant contribution from the d orbitals of the Cr
atoms, each attached to three COs, and the p orbitals of the
Se atoms. Thus, it is proposed that the less hindered “Se”
sites of [Se2Cr3(CO)10]2- could undergo nucleophilic attack
onto the carbon center of the acetone or/and the incoming
[Mn(CO)5]þ fragment, accompanied by complicated Se-Cr
and Cr-Cr bond breakage and Se-C and Se-Mn or
Mn-Mn formation, to give rise to the formation of complex
1or 2. In addition, natural population analyses show that the
Se atoms in complex 1 or 2 became more positively charged
(0.218 or -0.028) than those in [Se2Cr3(CO)10]2- (-0.134),
which accounts for the dispersed electron density of Se atoms
onto additional Mn and Cr atoms. It is noted that the Se-Cr
bonds are weaker than the Se-Mn bonds in 1and 2, whichis
consistent with the calculated Wiberg bond indices (0.320 vs
0.358 and 0.284 vs 0.305) (Table 2). Moreover, the Wiberg
bond indices for the Se-C bonds (0.892) in the SeCSeMn
ring of 1 were significantly greater than Se-Mn (0.358)
and Se-Cr (0.320) bonds, indicative of stronger Se-C
bonds, which should contribute to the stability of the
SeCSeMn ring in the CdO activated complex 1. Therefore,
the Se-C fragments played an important role in stabilizing
complex 1.
Figure 3. Temperature-dependent magnetic susceptibility data for
[Et4N]2[Se2Cr3(CO)10] (red symbol), [Et4N]2[2] (blue symbol), and
[PPN]2[Se2Mn3(CO)9] (black symbol): χM vs T (O) and μeff vs T (9)
plots.
Magnetic Properties of [Et4N]2[Se2Cr3(CO)10], [Et4N]2-
[2], and [PPN]2[Se2Mn3(CO)9]. Although the synthesis
and structure of [Et4N]2[Se2Cr3(CO)10] have been repor-
ted,11a its magnetic properties were unknown. Surpris-
ingly, according to SQUID analysis, [Et4N]2[Se2Cr3-
(CO)10] obeyed electron-counting rules, but nonetheless
exhibited paramagnetic properties. The magnetic data
(see Supporting Information), in the form of χM versus
T and μeff versus T plots for [Et4N]2[Se2Cr3(CO)10], are
shown in Figure 3. At 300 K, [Et4N]2[Se2Cr3(CO)10] had
the effective magnetic moment μeff = 3.05 μB. This value
is close to the spin-only value (μeff = 2.83 μB) predicted
for a simple S =1 species. [Et4N]2[Se2Cr3(CO)10] is an
electron-precise species and coordinated only with carbo-
nyl ligands, but it is highly paramagnetic, which is
an unusual phenomenon.13g In addition, cluster 2 is a
51-electron species, which possesses one more than the 50
electrons expected for a square-pyramidal cluster having
three metals with two metal-metal bonds. Since cluster 2
is an electron-rich species, its magnetic properties were
also investigated (Figure 3). The measurements showed
that [Et4N]2[2] had an effective magnetic moment μeff
=
The optimized structure of the proposed complex
[Me(Et)CSe2{Mn(CO)4}{Cr(CO)5}2]- (10) was calculated
to understand why this complex was not found in the
reaction of [Se2Cr3(CO)10]2- with Mn(CO)5Br in buta-
none. The Wiberg bond indices and natural population
analyses (NPA) for complexes 1 and 10 were also com-
pared (see Table 2). The calculations showed that the
corresponding Wiberg bond indices for 1 and 10 were
similar. In addition, each Se atom in 1 and 10 carried slight
positive charges (0.218, 0.213), while the bridging C atom
carried -0.272 and -0.266, respectively, indicative of
the comparative Coulomb force of the Se-C bonds in 1
and 10. These results indicate that the thermal stability of 1
and 10 is similar, which contrasted with the experimental
results that the analogous CdO activated product in
butanone was not observed under our reaction condi-
tions. Therefore, the failure to produce complex 10 was
probably due to the large steric repulsion between the sec-
butylene group and carbonyls of the Cr(CO)5 fragment
(See Supporting Information, Figure S1).
3.56 μB at 300 K. This value is close to the spin-only value
(μeff = 3.87 μB) predicted for a simple S = 3/2 species. At
low temperature, [Et4N]2[2] gave the μeff = 1.59 μB at 2 K,
which corresponds to an S = 1/2 species. SQUID analysis
of the 49-electron [PPN]2[Se2Mn3(CO)9] was also carried
out for comparison, which gave μeff = 2.11 μB at 300 K,
corresponding to an S=1/2 species (Figure 3). As
observed in the case of [PPh4]2[Se2Mn3(CO)9],13d the 1H
NMR signals of the [Et4N]þ salt of [Et4N]2[Se2Cr3-
(CO)10], [Et4N]2[2], and [Et4N]2[Se2Mn3(CO)9] were sig-
nificantly broad, reflecting the paramagnetic properties
of these complexes.
DFT Calculations. The DFT method was employed to
develop an understanding of the nature of [Se2Cr3-
(CO)10]2-, 1, 2, and [Se2Mn3(CO)9]2- to rationalize their
transformation behaviors. All thecalculations werecarried
out at the PW9122,23/LanL2DZ level of theory. The geo-
metry of [Se2Cr3(CO)10]2- was taken from single-crystal
(22) Burke, K.; Perdew, J. P.; Wang, Y. In Electronic Density Functional
Theory: Recent Progress and New Directions; Dobson, J. F., Vignale, G., Das,
M. P., Eds.; Plenum: New York, 1998.
(24) Wiberg, K. B. Tetrahedron 1968, 24, 1083–1096.
(23) (a) Perdew, J. P. Phys. Rev. B. 1986, 33, 8822–8824. (b) Perdew, J. P.;
Wang, Y. Phys. Rev. B. 1992, 45, 13244–13249.
(25) (a) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983, 78, 4066–4073.
(b) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985, 83, 735–746.

8062 Inorganic Chemistry, Vol. 49, No. 17, 2010
Shieh et al.
Figure 4. Spatial graphs (isovalue = 0.03-0.04) of selected frontier molecular orbitals of [Se2Cr3(CO)10] .
2-, 2, and [Se2Mn3(CO)9]2-
The active sites for the reaction of compound 1 with
Mn2(CO)10/KOH to give complex 2 may, furthermore, be
related to the lowest unoccupied molecular orbital (LUMO)
of complex 1. As shown in Figure 4, the LUMO of 1
received a significant contribution from the d orbitals of
the Mn atom and the s and p orbitals of the Se atoms. It is
reasonable to suggest that the incoming Mn-anions could
interact with the Mn and Se atoms of complex 1, accom-
panied by Se-CMe2 bond breakage and Se-Mn and
Mn-Mn bond formation, to produce complex 2. Finally,
ΔG = -16.36 and ΔE = -1.33 kcal/mol were calculated
for the reaction of 2 with CO to give [Se2Mn3(CO)9]2-. In
this case, the LUMO of complex 2 received major contribu-
tions from the s and p orbitals of the Se atoms and p and d
orbitals of the Cr atoms (Figure 4), indicating that CO
can nucleophilically attack the “Se-Cr” bonds of complex
2 to induce Se-Cr bond breakage to give Cr(CO)6 and
Spin Density Distribution of [Se2Cr3(CO)10]2-, 2, and [Se2-
Mn3(CO)9]2-. To better understand the magnetic properties
of paramagnetic [Se2Cr3(CO)10]2-, 2, and[Se2Mn3(CO)9]2-
,
the spin population of each complex was calculated, and the
results are summarized in Table 3. As shown in Figure 5, the
spin density of [Se2Cr3(CO)10]2- was highly concentrated
around the central Cr3 ring (1.370), but with uneven
delocalization26 around three Cr atoms (0.118, Cr2; 0.626,
Cr3; 0.626, Cr13), where Cr3 and Cr13 are coordinated with
three COs and Cr2 is bonded to four COs. This is parallel to
the probability density distribution predicated from the
SOMOs of [Se2Cr3(CO)10]2-. It is of interest that the spin
densities of cluster 2 and [Se2Mn3(CO)9]2- were mostly con-
centrated on the Mn atoms (2.581 and 0.873, respectively),
and an increasing population of Mn atoms in cluster 2versus
(26) Koukaras, E. N.; Zdetsis, A. D. Organometallics 2009, 28, 4308–
4315.
[Se2Mn3(CO)9]2-
.

Article
Inorganic Chemistry, Vol. 49, No. 17, 2010 8063
2-
Table 3. Calculated Mulliken Spin Density for [Se2Cr3(CO)10
]
(S = 1),
The small energy gap and the increasing contribution of
Mn atoms for the two near SOMO-184 and SOMO-185
orbitals might suggest spin-pairing for complex 2 at low
temperature. Moreover, the energy gap between LUMO
and the highest SOMO (SOMO-185) of complex 2 was
about 0.84 eV, while the energy difference between LUMO
and SOMO for complex [Se2Mn3(CO)9]2- was calculated
to be 1.40 eV. Complex 2 can be regarded as being
composed of the core complex [Se2Mn3(CO)9]2- with an
additional CO on the Mn atoms and the two Se atoms
externally bonded with two Cr(CO)5 units, and therefore
the energy gaps for 2 would diminish with the increase
in effective magnetic moment, compared with [Se2Mn3-
(CO)9]2-. These results suggest that a progressive tighten-
ing of the frontier energy levels as a function of the size of
the metal clusters could trigger magnetism in complexes
with an increasing number of metals.12a
2 (S = 3/2), and [Se2Mn3(CO)9]2- (S = 1/2) at the Level of PW91/LanL2DZ
total spin
density
spin
densitya
complex
atom
atom
2-b
[Se2Cr3(CO)10
]
Se
0.500
1.370
Se1
Se12
Cr2
Cr3
Cr13
C
0.250
0.250
0.118
0.626
0.626
-0.007
0.136
0.075
0.075
0.596
1.389
0.596
0.059
0.059
-0.034
0.105
0.037
0.042
0.052
0.040
0.393
0.096
0.384
0.019
0.016
Cr
CO for Cr
Se
0.129
0.150
2.581
O
2
Se1
Se19
Mn2
Mn3
Mn22
Cr4
Cr27
C
O
C
O
Se3
Se4
Mn1
Mn2
Mn9
C
Mn
Cr
0.118
0.071
0.079
0.092
0.873
CO for Mn
CO for Cr
Se
Electrochemistry of [Et4N]2[Se2Cr3(CO)10], [Et4N]2[2],
and [PPN]2[Se2Mn3(CO)9]. In view of the interesting
paramagnetism and the structural relationship among
[Et4N]2[Se2Cr3(CO)10], [Et4N]2[2], and [PPN]2[Se2Mn3-
(CO)9], the electrochemical behavior of these three com-
plexes was further investigated using cyclic voltammetry
(CV) and differential pulse voltammetry (DPV) in MeCN
(Figure 6, Supporting Information, Figure S3, Table 4,
and Supporting Information, Table S5). Because of the
interference of [Et4N]þ and [PPN]þ, the scan range was
set between ∼1.00 to ∼ -1.00 V for these studies.
[Se2Mn3(CO)9]2-
Mn
CO for Mn
0.035
O
a The negative values represent the β spin density. b Single-point
calculations.
[Se2Mn3(CO)9]2- was noted as the additional two Cr(CO)5
units and one CO were introduced. Further, the net spin
densities of COs in 2 revealed that significant overlaps
between the 3d orbitals of Mn atoms and 3σ orbitals of
COs occurred and gave rise to spin pairing. The uneven spin
densities around the central Mn3 core were also found for
complexes 2 and [Se2Mn3(CO)9]2- (complex 2: 1.389, Mn3;
0.596, Mn2; 0.596, Mn22; [Se2Mn3(CO)9]2-: 0.096, Mn2;
0.393, Mn1; 0.384, Mn9), suggesting that the Mn3 atoms
may play an important role in further reactivity.
The calculations show that complex 2 with one unpaired
electron was more stable than 2 with three unpaired
electrons, by -41.05 kcal/mol at 0 K in the gas phase
(single-point energy calculated by PW91/LanL2DZ). In
addition, the optimized 2 with one unpaired electron was
also more stable than the configuration with three unpaired
electrons by ΔG = -26.26 and ΔE = -28.35 kcal/mol at
the same level of calculation. These results are consistent
with the experimentally determined magnetic data for 2 at 2
K (μeff = 1.59 μB). However, the experimental studies
indicate that complex 2 converted into its high-spin state
(S = 3/2) at 300 K (μeff = 3.56 μB). Thus, the higher
paramagnetism of complex 2 at 300 K might be explained
by the thermal excitation3a of the paired electrons into the
unpaired ones. As shown in Supporting Information,
Figure S2, it is interesting to note that a substantial alter-
nation in the orbital coefficients of the Mn atoms of the
three SOMOs was observed. The calculations showed that
the contribution from the d and p orbitals of the Mn atoms
of the SOMOs was in increasing order of SOMO-183 <
SOMO-184 < SOMO-185 for complex 2 with three un-
paired electrons (see Figure 4 and Supporting Information,
Table S4). In addition, the energy gap between SOMO-185
and SOMO-184 was smaller than that between SOMO-184
and SOMO-183 (see Supporting Information, Figure S2).
As shown in Figure 6, the CV of [Et4N]2[Se2Cr3(CO)10]
exhibited two broad anodic peaks around ∼0.458 and ∼
-0.147 V, which were further resolved by the DPV study
to have four quasi-reversible redox couples (Epred = 0.371
red
V, W1/2 = 140 mV; Ep = 0.067 V, W1/2 = 103 mV;
red
red
Ep = -0.037 V, W1/2 = 102 mV; Ep = -0.189 V,
W1/2 = 133 mV). The SOMOs of [Se2Cr3(CO)10]2- re-
ceived a significant contribution from the d orbitals of
Cr3 atoms (Figure 4), indicating that the rich redox reac-
tions mainly occurred in the central Cr3 ring. On the other
hand, the CV of 2 exhibited broad anodic peaks around
∼0.439 and ∼0.182 V, which were further confirmed by
DPV to have three redox couples (Epred = 0.464 V, W1/2
=
86 mV; Epred = 0.368 V, W1/2 = 106 mV; Epred = 0.160 V,
W1/2 = 138 mV). In addition, [PPN]2[Se2Mn3(CO)9] dis-
played three broad oxidation peak around ∼0.591 V, ∼
-0.051 and ∼ -0.210 V, which were further confirmed by
DPV (Epred = 0.572 V, W1/2 = 106 mV; Epred = -0.105 V,
red
W1/2 = 99 mV; Ep = -0.273 V, W1/2 = 109 mV),
indicating three one-electron quasi-reversible redox cou-
ples. These results indicated that a similar type, with three
redox couples, was observed for complex 2 and the re-
lated [Se2Mn3(CO)9]2-. The explanation may be that the
SOMOs of 2 and the LUMO and SOMO of [Se2Mn3-
(CO)9]2- each received a significant contribution from the d
orbitals of Mn3 atoms (Figure 4), indicating the redox
reactions mainly occurred in the Mn3 atoms. DPV
further showed that the three quasi-reversible redox
couples of 2 were, in general, shifted to more positive
potentials than those of [Se2Mn3(CO)9]2-, which indi-
cated that 2 was easier to be reduced, but more difficult
to be oxidized because of the two attached electron-
withdrawing Cr(CO)5 fragments. Furthermore, as shown
in Table 2, the natural charges for each Se2Mn3(CO)x
core in [Se2Mn3(CO)9]2- and 2 were decreasing in negative

8064 Inorganic Chemistry, Vol. 49, No. 17, 2010
Shieh et al.
Figure 5. Spatial graphs (isovalue = 0.004) of the electron spin density of [Se2Cr3(CO)10] .
2-, 2, and [Se2Mn3(CO)9]2-
Table 4. Differential Pulse Voltammetry of [Et4N]2[Se2Cr3(CO)10], [Et4N]2[2],
and [PPN]2[Se2Mn3(CO)9]
oxidation process
reduction process
compound
Epox/Va
Epred/Vb
Epox/Va
Epred/Vb
[Et4N]2[Se2Cr3(CO)10
]
0.367
0.067
0.428
0.340
0.132
0.520
0.371
0.067
0.464
0.368
0.160
0.572
-0.029
-0.201
-0.037
-0.189
[Et4N]2[2]
[PPN]2[Se2Mn3(CO)9]
-0.105
-0.257
-0.105
-0.273
a Epox = oxidative peak potential. b Epred = reductive peak potential.
the paramagnetic cluster [Et4N]2[Se2Cr3(CO)10] with Mn-
(CO)5Br in acetone, in which a novel CdO activation com-
plex 1 and an unusual paramagnetic cluster 2 were obtained.
Cluster 2 can react with CO to produce a structurally related
cluster [Se2Mn3(CO)9]2-. Surprisingly, SQUID analysis
showed that the even-electron complex, [Se2Cr3(CO)10]2-
,
and the odd-electron species, 2 and [Se2Mn3(CO)9]2-, possess
2, 3, and 1 unpaired electrons, respectively. Furthermore, the
electrochemical studies showed an anodic shift for the redox
couples of complex 2 compared with those of its related
cluster [Se2Mn3(CO)9]2- that can be attributed to the electron-
withdrawing effect of the externally bonded Cr(CO)5 frag-
ments, which was supported by theoretical calculations.
Experimental Section
All reactions were performed under an atmosphere of pure
nitrogen using standard Schlenk techniques.27 Solvents were
purified, dried, and distilled under nitrogen prior to use. Mn-
(CO)5Br (Strem), Mn2(CO)10 (Strem), and KOH (Showa)
were used as received. Compound [Et4N]2[Se2Cr3(CO)10] was
prepared according to the published method.11a Infrared
spectra were recorded on a Perkin-Elmer Paragon 500 IR
spectrometer as solutions in CaF2 cells. The NMR spectra
were obtained on a Bruker AV 400 at 400.13 MHz for 1H and
100.61MHzfor13CoronaBrukerAV500at500.13MHzfor
1H and 125.76 MHz for 13C. HMQC (heteronuclear multiple
quantum coherence) was performed by using standard Bru-
ker pulse sequences. 1H and 13C chemical shifts are reported
in parts per million and were calibrated relative to DMSO-d6
(1H: 2.49 ppm, 13C: 39.5 ppm) or acetone-d6 (1H: 2.05 ppm,
13C: 29.92, 206.68 ppm) as the internal standard. FAB mass
spectra were produced using a JEOL SX-102A mass spectro-
meter. Elemental analyses for C, H, and N were performed
on a Perkin-Elmer 2400 analyzer at the NSC Regional
Instrumental Center at National Taiwan University, Taipei,
Taiwan. The manganese and chromium contents of com-
plexes 1 and 2 were determined with an inductively coupled
Figure 6. DPVs in MeCN for [Et4N]2[Se2Cr3(CO)10] (red), [Et4N]2[2]
(blue), and [PPN]2[Se2Mn3(CO)9] (black). Conditions: electrolyte, 0.1 M
Bu4NClO4; working electrode, platinum disk; scan rate, 100 mV s-1
Potentials are versus SCE.
.
values, indicating the electron-withdrawing effect of
the Cr(CO)5 fragments.
Summary
We have discovered a new series of mixed chromium-
manganese selenide carbonyl complexes from the reaction of
(27) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air-Sensitive
Compounds; Wiley-VCH Publishers: New York, 1986.

Article
Inorganic Chemistry, Vol. 49, No. 17, 2010 8065
plasma-atomic emission (ICP-AES) spectrometer (Perkin-
Elmer Optima 3000DV) at the NSC Regional Instru-
mental Center at National Tsing Hua University, Hsinchu,
Taiwan.
to give [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2]) (yield
0.45 g, 0.36 mmol, 28% based on [Et4N]2[Se2Cr3(CO)10]).
Acidification of [Et4N]2[Se2Cr3(CO)10] with Mn(CO)5Br in
Butanone. A butanone solution (20 mL) of [Et4N]2[Se2Cr3-
(CO)10] (0.48 g, 0.56 mmol), Mn(CO)5Br (0.28 g, 1.02 mmol),
and 4 M HCl (1.33 mL) was stirred at 35 °C for 10 h. The
solution was filtered, and the solvent was evaporated under
vacuum. The residue was washed with hexanes several times,
and extracted with Et2O to give a reddish-brown solution which
was recrystallized with hexanes/Et2O to give [Et4N][Se2Mn3-
(CO)9]10a (yield 0.15 g, 0.21 mmol, 38% based on [Et4N]2[Se2-
Cr3(CO)10]).
The magnetic susceptibility of the compounds was mea-
suredin gelatin capsules from 2 to 300 K in a magnetic field of
10,000 G using a Quantum Design MPMS5 SQUID magneto-
meter. Electrochemical measurements were performed at
room temperature undera nitrogen atmosphere andrecorded
using a BAS-100W and CHI 621D electrochemical potentio-
stat. A platinum disk working electrode, a platinum wire
auxiliary electrode, and a non-aqueous Ag/Agþ electrode
were used in a three-electrode configuration. Tetra-n-butyl-
ammonium perchlorate (TBAP) was used as the support-
ing electrolyte, and the solute concentration was ∼10-3 M.
The redox potentials were calibrated with a ferrocenium/
ferrocene (Fcþ/Fc) couple in the working solution.
Reaction of [Et4N][Me2CSe2{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1])
with Mn2(CO)10/KOH. To a MeCN solution (20 mL) of [Et4N]-
[Me2CSe2{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1]) (0.15 g, 0.17 mmol)
was added Mn2(CO)10 (0.07 g, 0.18 mmol) and KOH (0.56 g, 9.98
mmol) in MeOH (5 mL). The mixed solution was stirred for 48 h.
The solution was filtered, and the solvent was evaporated under
vacuum. The residue was washed with hexanes and Et2O several
times and extracted with CH2Cl2 to give a solution which was recry-
stallized with CH2Cl2 and with Et2O/CH2Cl2 to give [Et4N]2[Se2-
Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2]) (yield 0.07 g, 0.06 mmol, 35%
based on [Et4N][1]).
Synthesis of [Et4N][Me2CSe2{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1])
and [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2]). Method 1.
An acetone solution (30 mL) of [Et4N]2[Se2Cr3(CO)10] (0.64 g,
0.75 mmol) and Mn(CO)5Br (0.38 g, 1.38 mmol) was stirred at 35 °C
for 10 h. The solution was filtered, and the solvent was evaporated
under vacuum. The residue was washed several times with hexanes
and extracted with Et2O to give a reddish-orange solution, which
was recrystallized with hexanes/Et2O to give [Et4N][Me2CSe2-
{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1]) (yield 0.26 g, 0.30 mmol, 40%
based on [Et4N]2[Se2Cr3(CO)10]). IR (νCO, CH2Cl2): 2072 (w), 2050
(m), 1989 (s, br), 1930 (vs), 1889 (m, br) cm-1. Anal. Calcd for
[Et4N]2[1]: C, 34.07; H, 2.97; N, 1.59. Found: C, 33.74; H, 2.98; N,
1.55. ICP-AES: Mn: Cr = 1: 1.93. Negative ion FAB MS: m/z
752.96 (calcd: 753). 1H NMR (500 MHz, acetone-d6, 300 K): δ 1.41
(t,-CH2CH3),1.82(s,-CH3),3.51(q,-CH2CH3).13CNMR(125
MHz, acetone-d6, 300 K): δ 7.76 (-CH2CH3), 41.4 (-CH3), 47.1
(-CMe2), 53.1(-CH2CH3), 212.9, 218.2, 218.7, 219.6, 220.1, 223.9,
225.0 (-CO). Crystals of [Et4N][1] suitable for X-ray diffraction
were grown from Et2O. The residue was extracted with CH2Cl2 to
give a yellowish-brown solution, which and then with Et2O/CH2Cl2
to give [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2]) (yield 0.27
Reaction of [Et4N][Me2CSe2{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1])
with Mn(CO)5Br. An acetone solution (15 mL) of [Et4N][Me2-
CSe2{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1]) (0.11 g, 0.12 mmol) and
Mn(CO)5Br (0.06 g, 0.22 mmol) was stirred at 35 °C for 9 h. The
solution was filtered, and the solvent was evaporated under va-
cuum. The residue was washed with hexanes several times and
extracted with Et2O to give a reddish-brown solution which was
recrystallized with hexanes/Et2O to give [Et4N][Se2Mn3(CO)9]10a
(yield 0.05 g, 0.07 mmol, 58% based on [Et4N][1]). The residue was
then extracted with CH2Cl2 to give [Cr(CO)5Br]-20 confirmed by
IR spectroscopy.
Reaction of [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2])
with Mn(CO)5Br. An acetone solution (20 mL) of [Et4N]2-
[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2]) (0.16 g, 0.13 mmol)
and Mn(CO)5Br (0.06 g, 0.22 mmol) was stirred at 35 °C for
18 h. The solution was filtered, and the solvent was evaporated
under vacuum. The residue was washed with hexanes several
times and extracted with Et2O to give a reddish-brown solution
which was recrystallized with hexanes/Et2O to give [Et4N][Se2-
Mn3(CO)9]10a (yield 0.05 g, 0.07 mmol, 54% based on [Et4N]2[2]).
The residue was then extracted with CH2Cl2 to give [Cr(CO)5Br]-20
confirmed by IR spectroscopy.
g, 0.22 mmol, 29% based on [Et4N]2[Se2Cr3(CO)10]). IR (νCO
,
CH2Cl2): 2048 (m), 1986 (vs), 1977 (s, sh), 1925 (s, br), 1876 (m,
br) cm-1. Anal. Calcd for [Et4N]2[2]: C, 34.66; H, 3.23; N, 2.25.
Found: C, 34.43; H, 3.28; N, 2.20. ICP-AES: Mn: Cr = 1.49: 1. 1H
NMR (400 MHz, DMSO-d6, 300 K): δ 1.15 (br, -CH2CH3), 3.20
(br, -CH2CH3). 13C NMR (100 MHz, DMSO-d6, 300 K): δ 7.55
(-CH2CH3), 51.9 (-CH2CH3), 213.7, 216.9, 217.3, 221.0, 225.2
(-CO). Crystals of [Et4N]2[2] suitable for X-ray diffraction were
grown from Et2O/CH2Cl2. 1H NMR (400 MHz, DMSO-d6, 300 K)
for [Et4N]2[Se2Cr3(CO)10]: δ 1.15 (br, -CH2CH3), 3.20 (br,
-CH2CH3).
Method 2. An acetone solution (20 mL) of [Et4N]2[Se2Cr3-
(CO)10] (0.56 g, 0.66 mmol), Mn(CO)5Br (0.33 g, 1.20 mmol),
and 4 M HCl (1.33 mL) was stirred at 35 °C for 10 h. The
solution was filtered, and the solvent was evaporated under
vacuum. The residue was washed with hexanes several times and
extracted with Et2O to give a reddish-orange solution that was
recrystallized with hexanes/Et2O to give [Et4N][Me2CSe2{Mn-
(CO)4}{Cr(CO)5}2] ([Et4N][1]) (yield 0.35 g, 0.40 mmol, 61%
based on [Et4N]2[Se2Cr3(CO)10]). The residue was extracted
with CH2Cl2 to give a yellowish-brown solution and then with
Et2O/CH2Cl2 to give [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4-
N]2[2]) (yield 0.10 g, 0.08 mmol, 12% based on [Et4N]2[Se2-
Cr3(CO)10]).
Reaction of [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2])
with CO. Carbon oxide was bubbled through a solution of
[Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2]) (0.16 g, 0.13
mmol) in MeCN (20 mL) at 50 °C for 15 min. After stirring
for another 12 h at 50 °C, the color of the solution changed from
yellowish-brown to reddish-brown. The solution was filtered,
and the solvent was evaporated under vacuum. The residue was
washed with hexanes that were shown by IR spectroscopy to
contain Cr(CO)6. The residue was further extracted with
CH2Cl2 to give [Et4N]2[Se2Mn3(CO)9]13d (yield 0.07 g, 0.08
mmol, 62% based on [Et4N]2[2]). 1H NMR (400 MHz,
DMSO-d6, 300 K, ppm) for [Et4N]2[Se2Mn3(CO)9]: δ 1.11 (br,
-CH2CH3), 3.32 (br, -CH2CH3).
X-ray Structural Characterization of [Et4N][1] and [Et4N]2[2].
Selected crystallographic data for [Et4N][1] and [Et4N]2[2] are
given in Table 5. All crystals were mounted on glass fibers with
epoxy cement. Data collection for [Et4N][1] was carried out
using a Nonius (CAD-4) diffractometer with graphite-mono-
chromated Mo KR radiation at 298 K in the 2θ range of 2.0-50°
employing θ-2θ scans, and an empirical absorption correction
by azimuthal (ψ) scans was applied.28 Data collection for
Reaction of [Et4N]2[Se2Cr3(CO)10] with Mn(CO)5Br in Buta-
none. A butanone solution (40 mL) of [Et4N]2[Se2Cr3(CO)10]
(1.11 g, 1.30 mmol) and Mn(CO)5Br (0.64 g, 2.33 mmol) was
stirred at 35 °C for 10 h. The solution was filtered, and the
solvent was evaporated under vacuum. The residue was washed
with hexanes and Et2O several times, and extracted with CH2Cl2
to give a yellowish-brown solution and then with Et2O/CH2Cl2
(28) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351–358.

8066 Inorganic Chemistry, Vol. 49, No. 17, 2010
Shieh et al.
Table 5. Crystallographic Data for [Et4N][Me2CSe2{Mn(CO)4}{Cr(CO)5}2] ([Et4N][1]) and [Et4N]2[Se2Mn3(CO)10{Cr(CO)5}2] ([Et4N]2[2])
[Et4N][1]
[Et4N]2[2]
a
empirical formula
Fw
cryst syst
C25H26Cr2MnNO14Se2
881.33
triclinic
C20Cr2Mn3O20Se2
986.94
monoclinic
C2/m
space group
crystal dimens, mm
P1
0.40 ꢀ 0.30 ꢀ 0.15
0.30 ꢀ 0.10 ꢀ 0.05
˚
a, A
9.757(2)
13.4239(5)
20.1031(8)
9.2313(3)
˚
b, A
11.2691(8)
16.900(6)
81.77(2)
˚
c, A
R, deg
β, deg
γ, deg
76.05(3)
98.817(3)
71.590(9)
1706.5(7)
2
1.715
3.185
Nonius (CAD4)
0.71073
298(2)
3
˚
V, A
Z
2461.7(2)
2
1.332
2.707
D (calcd), g cm-3
μ, mm-1
diffractometer
Nonius (Kappa CCD)
0.71073
298(2)
˚
radiation (λ), A
temp, K
θ range for data collecn, deg
Tmin/Tmax
1.91-24.92
0.37/0.62
2.03-25.00
0.67/0.72
no. of indep reflns (I > 2 σ(I))
no. of parameters
R1b/wR2b
4010 (Rint = 0.0188)
385
0.033/0.085 (I > 2 σ(I))
0.072/0.103
1701 (Rint = 0.0679)
130
0.050/0.141 (I > 2 σ(I))
0.067/0.152
R1b/wR2b (all data)
a Two cationic molecules, Et4Nþ, are excluded in the formula, formula weight, calculated density, μ, and F(000) according to the Platon Squeeze
P
P
P
P
procedure. b The functions minimized during least-squares cycles were R1 = ||Fo| - |Fc||/ |Fo| and wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2
.
[Et4N]2[2] was carried out using a Bruker-Nonius Kappa CCD
diffractometer with graphite-monochromated Mo KR radiation
at 298 K employing the θ-2θ scan mode, and an empirical
absorption correction by multiscans was applied. The structures
of [Et4N][1] and [Et4N]2[2] were refined by the SHELXL
package.29
SQUEEZE option of PLATON. Except for the C atoms on
the cations of [Et4N][1], all of the non-hydrogen atoms for
[Et4N][1] and 2 were refined with anisotropic temperature
factors. Additional crystallographic data in the form of CIF
files are available as Supporting Information.
Computational Details. All calculations reported in the pre-
sent study were performed via the DFT with the exchange and
correlation functionals of the gradient correction proposed in
1991 by Perdew and Wang (PW91)22,23 and with a LanL2DZ
basis set using the Gaussian 03 series of packages.30 The
geometry of [Se2Cr3(CO)10]2- was taken from single-crystal
X-ray diffraction data, and the isopropylene group of complex
1 was replaced by the sec-butylene group, forming the proposed
structure 10. The geometries of 1, the proposed complex 10, 2,
and [Se2Mn3(CO)9]2- were fully optimized with the same level of
theory. Wiberg bond indices24 and natural charges25 were
evaluated using the Weinhold NBO method.31 Graphical repre-
sentations of the molecular orbitals and spin densities were
obtained using CS Chem3D 5.0.
For [Et4N][1] and [Et4N]2[2], there are several close inter
N
C and C C contacts because of the disorder which
3 3 3
3 3 3
implies disorder of the [Et4N]þ cations. For [Et4N][1], the N1
and N2 atoms on the [Et4N]þ each reside on a crystallographic
inversion center with a site-occupation factor of 0.5. The C18,
C20 (on N1 atom), C22, and C24 (on N2 atom) were disordered
50% in the first moiety and 50% for C180, C200 (on N1 atom),
C220, and C240 (on N2 atom). Thus, the C atoms on the
disordered cations of [Et4N][1] were refined with isotropic
temperature factors. For [Et4N]2[2], the final structure of 2
was refined without the two cations, [Et4N]þ, by using the
€
(29) Sheldrick, G. M. SHELXL97, version 97-2; University of Gottingen:
€
Gottingen, Germany, 1997.
(30) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji,
H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox,
J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.;
Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.;
Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision
B.04; Gaussian, Inc.: Wallingford, CT, 2004.
Acknowledgment. This work was supported by the National
Science Council of Taiwan (NSC Grant 98-2113-M-003-006-
MY3 to M.S.). We are also grateful to the National Center for
High-Performance Computing, where the Gaussian package
and computer time were provided.
Supporting Information Available: X-ray crystallographic files
in CIF format for [Et4N][1] and [Et4N]2[2] and magnetic measure-
ments (PDF) for [Et4N]2[Se2Cr3(CO)10], [Et4N]2[2], and [PPN]2-
[Se2Mn3(CO)9]. Computational details for [Se2Cr3(CO)10]2-, 1, 10,
2, and [Se2Mn3(CO)9]2-. This material is available free of charge via
the Internet at http://pubs.acs.org.
(31) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88,
899–926.