Mixed-metal assemblies based on cyanide-bridged cubane-type Mo 3CuS4/Mo3S4 clusters and molybdenum carbonyls

Article abstract of DOI:10.1021/ic9002302

The substitutional lability of Mo - Cl and Cu - Cl bonds in cubane-type Mo₃CuS₄ and incomplete cubane-type Mo₃S ₄ clusters is exploited in an attempt to prepare cyanide-terminated complexes, namely [Mo₃

Full text of DOI:10.1021/ic9002302

Inorg. Chem. 2009, 48,
DOI:10.1021/ic9002302
4837
Mixed-Metal Assemblies Based on Cyanide-Bridged Cubane-Type Mo3CuS4/Mo3S4
Clusters and Molybdenum Carbonyls
Rosa Llusar,*,† Ivan Sorribes,† and Cristian Vicent*,‡
†
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Departament de Quimica Fisica i Analitica, Universitat Jaume I, Avenida Sos Baynat s/n, 12071 Castello, Spain,
‡
ꢀ
ꢀ
and Serveis Centrals d’Instrumentacio Cientifica, Universitat Jaume I, Avenida Sos Baynat s/n, 12071 Castello,
Spain
Received February 4, 2009
The substitutional lability of Mo-Cl and Cu-Cl bonds in cubane-type Mo3CuS4 and incomplete cubane-type
Mo3S4 clusters is exploited in an attempt to prepare cyanide-terminated complexes, namely [Mo3S4(CuCN)
(dmpe)3Cl3]PF6 ([2]PF6) and [Mo3S4(dmpe)3(CN)3]PF6 ([5]PF6), and to subsequently use them as precursors in
low-dimensional linking reactions. Mixed-metal assemblies formulated as [Mo3S4(Cu-μCN
Mo(CO)5)
3 3 3
Mo(CO)5)3]+ ([6]+) are obtained by reaction of tetrahydrofuran
(dmpe)3Cl3]+ ([3]+) and [Mo3S4(dmpe)3( μCN
3 3 3
solutions of [2]BPh4 and [5]BPh4 with the complex (THF)Mo(CO)5. The intrinsic stability of the (M0-μCN
Mo
3 3 3
(CO)5) linkages (M0 = Cu in 3+ and Mo in 6+) in solution and in the gas phase is investigated through a combination
of variable-temperature 31P NMR, IR, UV-vis spectroscopies, and electrospray ionization tandem mass
spectrometry. The spectroscopic and electrochemical consequences of CN coordination as well as Mo(CO)5
ligation either at the Cu or the Mo site in Mo3CuS4 and Mo3S4 clusters are reported. Replacement of Cl by CN or
CN
exerts a profound anodic shift of 220 and 500 mV upon Cl to CN and Cl to CN
respectively.
Mo(CO)5 at the Cu site does not affect the redox potentials, whereas analogous substitution at Mo sites
Mo(CO)5 replacement,
3 3 3
3 3 3
Introduction
attached to the Mo6Cl8 and Ta6Cl12 clusters acting as
central metal ions.5 Other examples include the linkage of
mononuclear Mn or Cr metallocyanides to metal-carbonyl
clusters,6 Mo2,7 Re2,8 Ru2, Co3, Ni5,9 or Fe4S4 entities.10
Inspired by the success of using mononuclear metallocya-
nides as building units to construct functional solids,
several groups are currently exploring the use of their
expanded CN-coordinated cluster analogues on the basis
of the rationale that their large size combined with struc-
tural and electronic diversity of these multinuclear species
may lead to novel structural and physicochemical proper-
ties. This is illustrated with the use of octahedralface-capped
Cyanide-coordinated metal complexes have been exten-
sively used as building blocks of mixed-metal assemblies,1,2
because of the ability of the CN ligand to act as an efficient
charge transfer mediator,3 or to allow magnetic exchange
interactions.4 The simplest way of constructing such ag-
gregates is the attachment of metallocyanides to metal
centers of mono- or polynuclear entities in an attempt to
combine the physicochemical properties of both compo-
nents. This idea of using high nuclearity compounds as
central units was pioneered by Shriver, who demonstrated
that several mononuclear cyanomanganese units can be
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*To whom correspondence should be addressed. E-mail: barrera@
sg.uji.es (C.V.); Rosa.llusar@qfa.uji.es (R.L.).
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©
2009 American Chemical Society
Published on Web 4/20/2009
pubs.acs.org/IC

4838 Inorg. Chem., Vol. 48, No. 11, 2009
Llusar et al.
Figure 1. Schematic representation with designations of Mo3CuS4 and Mo3S4 clusters.
[Re6Q8(CN)6]4- (Q = S, Se, Te)11,12 and [W6S8(CN)6]6-13 or
edge-bridged [Nb6Cl12(CN)6]4- 14 cluster units in linking
reactions with transition metals. CN-coordinated cubane-
replace iodide by solvent or bidentate ligands.17 This might
not only offer us a variety of extended structures but also help
to circumvent the insolubility problem mentioned above.
Recently, our group have been involved in the preparation
of cubane-type Mo3CuS4 and Mo3S4 complexes bearing
diphosphane ligands and the study of their non linear opti-
cal,18 electrochemical, and catalytic properties.19 The two
Mo3CuS4 and Mo3S4 moieties are topologically related. The
trinuclear cluster core in Mo3S4 is formed by three molybde-
num atoms defining an equilateral triangle, one capping sulfur
and three bridging sulfur ligands, which can be regarded as an
incomplete-cuboidal structure (see Figure 1). The vacant
corner of the cube can be occupied by a copper atom leading
to the cubane-type Mo3CuS4 arrangement in which the four
chalcogen atoms are capping each face of the tetrahedra
defined by the Mo3Cu core (see Figure 1). The coordination
environment around the Mo sites is filled by halide and
diphosphane ligands, the latter being substitutionally inert so
that they can lock the desired ligand configurations onto the
clusters, retain the overall C3 symmetry of the complex, and in
our experience, promote the stability and crystallinity of the
new Mo3CuS4 and Mo3S4 formed products.18,20
type clusters, namely [M4Te4(CN)12]n- (M = W,15 Re12,16
)
have also proved to be versatile building blocks in the
preparation of larger discrete or extended solids.
A challenge remaining in this direction is that insoluble
products are typically formed whose intimate structure is
difficult to anticipate, mainly because of the large number of
potential CN-bridged species. One way to direct and/or
control the formation of low-dimensional extended networks
consists of making clusters with mixed ligands that have
different binding energies or labilities, so that one can
selectively coordinate bidentate ligands by replacing the
thermodynamically less favorable or labile ligands while
leaving the thermodynamically more favorable or inert
ligands unaffected. As illustrated for the series of site-differ-
entiated hexanuclear [Re6(μ-Se)8(PEt)6I6-n]
(n-4)+ (n = 4-6)
clusters, the remarkable stability of phosphane ligands is very
suited for this purpose because it allows one to selectively
(11) (a) Mironov, Y., V.; Cody, J. A.; Albrecht-Schmitt, T. E.; Ibers, J. A.
J. Am. Chem. Soc. 1997, 119, 493. (b) Beauvais, L. G.; Shores, M. P.; Long, J.
R. Chem. Mater. 1998, 10, 3783. (c) Naumov, N. G.; Virovets, A. V.;
Sokolov, M. N.; Artemkina, S. B.; Fedorov, V. E. Angew. Chem., Int. Ed.
1998, 37, 1943. (d) Naumov, N. G.; Artemkina, S. B.; Virovets, A. V.;
Fedorov, V. E. Solid State Sci. 1999, 1, 473. (e) Beauvais, L. G.; Long, J. R. J.
Am. Chem. Soc. 1999, 121, 775. (f ) Shores, M. P.; Beauvais, L. G.; Long, J. R.
J. Am. Chem. Soc. 1999, 121, 775. (g) Magliocchi, C.; Xie, X.; Hughbanks, T.
Inorg. Chem. 2000, 39, 5000. (h) Beauvais, L. G.; Shores, M. P.; Long, J. R. J.
Am. Chem. Soc. 2000, 122, 2763. (i) Bennet, M. V.; Shores, M. P.; Beauvais, L.
G.; Long, J. R. J. Am. Chem. Soc. 2000, 122, 6664. ( j) Naumov, N. G.;
Artemkina, S. B.; Virovets, A. V.; Fedorov, V. E. J. Solid State Chem. 2000,
153, 195. (k) Naumov, N. G.; Virovets, A. V.; Fedorov, V. E. Inorg. Chem.
Commun. 2000, 3, 71. (l) Naumov, N. G.; Soldatov, D. V.; Ripmeester, J. A.;
Artemkina, S. B.; Fedorov, V. E. Chem. Commun. 2001, 571. (m) Bennet, M.
V.; Beauvais, L. G.; Shores, M. P.; Long, J. R. J. Am. Chem. Soc. 2001, 123,
8022. (n) Jin, S.; DiSalvo, F. Chem. Commun. 2001, 1586. (o) Kim, Y.; Park,
S. M.; Nam, W.; Kim, S. J. Chem. Commun. 2001, 1470. (p) Kim, Y.; Park, S.
M.; Kim, S. J. Inorg. Chem. Commun. 2002, 5, 592. (q) Artemkina, S. B.;
Naumov, N. G.; Virovets, A. V.; Oeckler, O.; Simon, A.; Erenburg, S. B.;
Bausk, N. V.; Fedorov, V. E. Eur. J. Inorg. Chem. 2002, 1198.
The use of these Mo3CuS4 and Mo3S4 clusters as building
blocks of larger mixed-metal assemblies remains largely
unexplored. In this sense, for cubane-type Mo3CuS4 and
Mo3S4 cluster complexes to serve as molecular building
blocks, it must be possible to connect things together with
them. This implies complete control of substitution reactions
in the labile Cu-Cl and Mo-Cl positions by bidentate
ligands to subsequently explore their assembly. Herein, we
describe such a study in which we have used cyanide ligands
that have the capability of bridging to other metal centers and
thereby enable, in principle, the assembly of mixed-metal
complexes retaining the Mo3CuS4 and Mo3S4 clusters. The
pentacarbonyl molybdenum Mo(CO)5 fragment is chosen
because of its great spectroscopic utility because of the fact
that the carbonyl infrared stretching frequencies are extre-
mely sensitive probes of the electronic structure of the
complex. A combination of experimental techniques are used
(12) Mironov, Y., V.; Fedorov, V. E.; Ijjaali, I.; Ibers, J. A. Inorg. Chem.
2001, 40, 6320.
to investigate the intrinsic stability of the M0-μCN
3 3 3
(13) (a) Jin, S.; DiSalvo, F. Chem. Mater. 2002, 14, 3448. (b) Jin, S.;
Venkataraman, D.; DiSalvo, F. Inorg. Chem. 2000, 37, 2747.
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Zhou, H.; Lachgar, A. Eur. J. Inorg. Chem. 2007, 1053. (c) Zhang, J.;
Lachgar, A. J. Am. Chem. Soc. 2007, 129, 250.
Mo(CO)5 (M0= Cu, Mo) linkages as well as the spectro-
scopic and electrochemical consequences of CN coordination
as well as Mo(CO)5 ligation either on the Mo or the Cu site in
Mo3CuS4 and Mo3S4 clusters.
(15) (a) Fedin, V. P.; Virovets, A. V.; Kalinina, I. V.; Ikorskii, V. N.;
Elsegood, M. R. J.; Clegg, W. Eur. J. Inorg. Chem. 2000, 2341. (b) Fedin, V.
P.; Kalinina, I. V.; Gerasimenko, A.; Virovets, A. V. Inorg. Chim. Acta 2002,
331, 48. (c) Fedin, V. P.; Kalinina, I. V.; Virovets, A. V.; Fenske, D. Russ.
Chem. Bull. 2003, 52, 123. (d) Kalinina, I. V.; Virovets, A. V.; Dolgushin, V.
M.; Antipin, M. Y.; Llusar, R.; Fedin, V. P. Inorg. Chim. Acta 2004, 357,
3390.
(16) (a) Mironov, Y., V.; Efremova, O. A.; Naumov, D. Y.; Scheldrick, W.
S.; Fedorov, V. E. Eur. J. Inorg. Chem. 2003, 2591. (b) Brylev, K. A.;
Mironov, Y. V.; Naumov, N. G.; Fedorov, V. E.; Ibers, J. A. Inorg. Chem.
2004, 43, 4833. (c) Efremova, O. A.; Mironov, Y., V.; Fedorov, V. E. Eur. J.
Inorg. Chem. 2006, 2533.
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2163. (b) Gray, T. G.; Holm, R. H. Inorg. Chem. 2002, 41, 4211. (b) Selby, H.
D.; Roland, B. K.; Zheng, Z. Acc. Chem. Res. 2003, 36, 933.
(18) Feliz, M.; Garriga, J. M.; Llusar, R.; Uriel, S.; Humphrey, M. G.;
Lucas, N. T.; Samoc, M.; Luther-Davies, B. Inorg. Chem. 2001, 40, 6132.
(19) (a) Feliz, M.; Guillamon, E.; Llusar, R.; Vicent, C.; Stiriba, S. E.;
Perez-Prieto, J.; Barberis, M. Chem.;Eur. J. 2006, 12, 1486. (b) Guillamon,
E.; Llusar, R.; Perez-Prieto, J.; Stiriba, S. E. J. Organomet. Chem. 2008, 693,
1723.
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2813.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
4839
Experimental Section
products with the time-of-flight analyzer (TOF). The isolation
was ca. 1 Da and argon was used as a collision gas to produce
a pressure of 9 ꢀ 10-4 mbar in the T-wave collision cell. EDESI-
MS/MS representations were carried out with the aid of the EDit
computer program.24
General Procedures. In the sections that follow, clusters are
designated as 1+-6+ according to Figure 1. All reactions were
carried out under a nitrogen atmosphere using standard Schlenck
techniques. Compound Na[NCMo(CO)5] and tetra- and trinuclear
[Mo3(CuCl)S4(dmpe)3Cl3]PF6 ([1]PF6) and [Mo3S4(dmpe)3Cl3]
PF6 ([4]PF6) clusters were prepared according to literature meth-
ods.21 The general procedure for metathesis of PF6- by BPh-4 was
carried out by addition of an excess of NaBPh4 to methanol
solutions of a given [M]PF6 complex precipitating the desired
[M]BPh4 compound.22 (THF)Mo(CO)5 was generated in situ by
UV light irradiating a suspension of Mo(CO)6 in THF for 1 h. The
remaining reactants were obtained from commercial sources and
used as received. Solvents for synthesis were dried and degassed by
standard methods before use.
Syntheses. [Mo3(CuCN)S4(dmpe)3Cl3]PF6 ([2]PF6). To a
green solution of [4](PF6) (0.095 g, 0.085 mmol) in CH3CN
(25 mL) was added an excess of CuCN (0.114 g, 1.270 mmol)
under nitrogen. The solution color turned brown within 5 min.
After the mixture was stirred for 1 h, it was filtered to eliminate
the excess of CuCN. Thefiltratewas concentratedandthe desired
product precipitated with diethyl ether (20 mL). The precipitate
was washed with water, isopropanol, and diethyl ether. Finally,
the precipitate was redissolved in CH3CN and an air stable
microcrystalline brown solid was obtained by slow diffusion of
diethyl ether (0.066 g, 64%). (Found: C, 18.78; H, 4.06; N, 1.05.
Mo3S4C19H48Cl3NP7F6 requires: C, 18.90; H, 4.01; N, 1.16%).
IR (CH2Cl2) νmax (cm-1): 2140m (CN). 31P NMR (T = 30 °C): δ
Physical Measurements. Elemental analyses were
performed on an EA 1108 CHN microanalyzer. 31P{1H} and
1H NMR spectra were recorded on Varian MERCURY 300
MHz spectrometer, using CD2Cl2 as solvent and are referenced
1
31.40 (d, JP-P = 11 Hz), 26.35 (d, JP-P = 11 Hz). H NMR
(T = 30 °C): δ 1.04 (d, 9H, CH3, 2JHP = 12.8 Hz), 1.62 (d, 9H,
=
to external 85% H3PO4 and to the residual solvent signal for 31
P
CH3, 2JHP = 12.5 Hz), 1.88 (m, 3H), 1.91 (d, 9H, CH3, 2JHP
1
and H, respectively. IR spectra were recorded on a JASCO
FTIR 6200 in the 300-3000 cm-1 range using CH2Cl2 as
solvent. Electronic spectra (250-800 nm) were recorded
with a VARIAN UV/vis spectrophotometer (model CARY
500 SCAN) using different solvents. Cyclic voltammetry
13.6 Hz), 2.09 (d, 9H, CH3, 2JHP = 12.1 Hz), 2.08 (m, 3H), 2.32
(m, 3H), 2.71 (m, 3H). ESI-MS(+) m/z: 1061.7 [M]+.
Mo3(Cu-μCN Mo(CO)5)S4(dmpe)3Cl3]BPh4 ([3]BPh4).
3 3 3
To a brown solution of [2](BPh4) (0.05 g, 0.036 mmol) at T =
0 °C in THF (8 mL) was added a 10-fold excess of (THF)Mo
(CO)5 under nitrogen. The solution color turned red immedi-
ately. After the mixture was stirred for 1 h, the red solution was
taken to dryness, redissolved in CH2Cl2 and absorbed onto a
silica gel column. A very concentrated brown solution was eluted
with CH2Cl2. This solution was taken to dryness to yield an air-
stable brown solid characterized as [3](BPh4) (0.021 g, 36%).
(Found: C, 34.92; H, 4.36; N, 0.91. Mo4S4C43H68NP6O5Cu
requires: C, 35.64; H, 4.24; N, 0.87). IR (CH2Cl2) νmax (cm-1):
2151w (CN); 2064m, 1984m 1939s, 1901m (CO). 31P NMR (T =
30 °C): δ 29.85 (d, JP-P = 10 Hz), 25.67 (d, JP-P = 10 Hz). 1H
experiments were performed with
a Echochemie Pgstat
20 electrochemical analyzer. All measurements were carried
out with a conventional three-electrode configuration consisting
of platinum working and auxiliary electrodes and a Ag/AgCl
reference electrode containing aqueous 3 M KCl The solvent
used in all experiments was CH2Cl2 (Merck HPLC grade).
The supporting electrolite was 0.1 M tetrabutylammonium
hexafluorophosphate. E1/2 values were determined as 1/2
(Ea + Ec), where Ea and Ec are the anodic and cathodic peak
potentials, respectively.
Electrospray Ionization (ESI) Mass Spectrometry and
Energy-Dependent ESI Tandem Mass Spectrometry. Elec-
trospray ionization (ESI) mass spectra were recorded on a Q-
TOF Premier (quadrupole-T-wave-time-of-flight) instrument
using CH2Cl2:CH3OH mixtures as solvent. A capillary voltage
of 3.5 KV was used in the positive scan mode and the cone
voltage (Uc) wasset to 20V tocontrol theextent offragmentation
of the identified ions. For ESI-MS reaction monitoring, after
mixing cluster [2]BPh4 or [5]BPh4 and tetrahydrofuran solutions
of (THF)Mo(CO)5, a drop of the solution was extracted and
diluted in THF and a positive-ion mass spectrum collected. The
reaction solution was reexamined at 15 min intervals until no
change in solution speciation was observed. The chemical com-
position of each peak was assigned by comparison of the isotope
experimental pattern with that calculated using the MassLynx
4.1 program. ESI-MS/MS spectra were recorded in a convenient
way to obtain energy dependent ESI-MS/MS (EDESI-MS/MS)
representations as previously reported.23 Typically, the cations
of interest were mass-selected using the first quadrupole (Q1) and
interacted with argon in the T-wave collision cell at variable
collision energies (stepped by increments of 2 eV after 40 scans in
the Elaboratory = 0-70 eV range) while mass analyzing the
2
NMR (T = 30 °C): δ 1.03 (d, 9H, CH3, JHP = 9.3 Hz), 1.69
(d, 9H, CH3, 2JHP = 11.2 Hz), 1.97 (d, 9H, CH3, 2JHP = 9.8 Hz),
2.02 (m, 3H), 2.08 (d, 9H, CH3, 2JHP = 10.3 Hz), 2.12 (m, 3H),
2.32 (m, 3H), 2.72 (m, 3H). ESI-MS(+) m/z: 1299.5 [M]+.
[Mo3S4(dmpe)3(CN)3]PF6 ([5]PF6). To a green solution of [4]
(PF6) (0.090 g, 0.081mmol) in MeOH (15 mL) was added an
excess of KCN (0.026 g, 0.400 mmol) under nitrogen and the
reaction mixture was refluxed for 2 h, without any apparent
color change. After the mixture was cooled to room tempera-
ture, the resulting solution was taken to dryness, redissolved in
CH2Cl2, and filtered in order to eliminate the insoluble KCN
inorganic salt. The resulting green solution was adsorbed onto a
silica gel column. After washing the column with CH2Cl2/
acetone mixtures (4:1), elution with a KPF6 solution in acetone
(10 mg mL-1) afforded a very concentrated green solution. This
solution was taken to dryness, redissolved in CH2Cl2, and
filtered in order to eliminate the insoluble KPF6 inorganic salt.
Finally, an air-stable microcrystalline green solid was obtained
by slow diffusion of diethyl ether into the filtrate (0.044 g, 50%).
(Found: C, 23.62; H, 4.96; N, 3.91. Mo3S4C21H48N3P7F6
requires: C, 23.15; H, 4.44; N, 3.86). IR (CH2Cl2) νmax (cm-1):
2118m, 2098m (CN). 31P NMR (T = 30 °C): δ 31.15 (d, JP-P
11 Hz), 16.50 (d, JP-P = 11 Hz). 1H NMR (T = 30 °C): δ 0.78
(d, 9H, CH3, JHP = 14.5 Hz), 1.53 (d, 9H, CH3, JHP =
=
2
2
(21) Estevan, F.; Feliz, M.; Llusar, R.; Mata, J. A.; Uriel, S. Polyhedron
2001, 20, 527–535.
(22) (a) Feliz, M.; Llusar, R.; Uriel, S.; Vicent, C.; Coronado, E.; Gomez-
12.1 Hz), 1.95 (m, 3H), 2.06 (d, 9H, CH3, 2JHP = 12.6 Hz), 2.17
ꢀ
2
(d, 9H, CH3, JHP = 13.5 Hz), 2.31 (m, 3H), 2.41 (m, 3H),
Garcia, C. Chem.;Eur. J. 2004, 10, 4308. (b) Algarra, A. G.; Basallote, M.
G.; Feliz, M.; Fernandez-Trujillo, M. J.; Guillamon, E.; Llusar, R.; Vicent,
C. Inorg. Chem. 2006, 45, 5576.
(23) (a) Dyson, P. J.; Johnson, B. F. G.; McIndoe, J. S.; Langridge-Smith,
R. R. Rapid Commun. Mass Spectrom. 2000, 14, 311. (b) Dyson, P. J.;
Hearley, A.; Johnson, B. F. G.; McIndoe, J. S.; Langridge-Smith, R. R.;
Whyte, C. Rapid Commun. Mass Spectrom. 2001, 15, 895. (c) Butcher, C. P.
G.; Dyson, P. J.; Johnson, B. F. G.; Langridge-Smith, P. R. R.; McIndoe, J.
S.; Whyte, C. Rapid Commun. Mass Spectrom. 2002, 16, 1595.
2.85 (m, 3H). ESI-MS(+) m/z: 943.8 [M]+.
[Mo3S4(dmpe)3(μCN Mo(CO)5)3]BPh4 ([6]BPh4). To a
3 3 3
green solution of [5](BPh4) (0.02 g, 0.015 mmol) at T = 0 °C
in THF (10 mL) was added a solution of (THF)Mo(CO)5
(24) Husheer, S. L. G.; Forest, O.; Henderson, M.; McIndoe, J. S. Rapid
Commun. Mass Spectrom. 2005, 19, 1352–1354.

4840 Inorg. Chem., Vol. 48, No. 11, 2009
Llusar et al.
Scheme 1.
(i) KCN in CH3OH; (ii) CuCN in CH3CN; (iii) (THF)Mo(CO)5 in THF.
(0.025 mg, 0.091mmol) in THF (7 mL) under nitrogen, produ-
cing a color change to dark red within 5 min. After the mixture
was stirred for 30 min, it was taken to dryness to afford an air-
stable dark red solid characterized as [6](BPh4) (0.03 g, 99%).
(Found: C, 36.62; H, 3.26; N, 1.91. Mo6S4C60H68N3P6O15
requires: C, 36.45; H, 3.48, N, 2.13). IR (cm-1): νmax (cm-1):
2124w, 2104w (CN); 2070m, 1984m 1941s, 1908m (CO). 31P
final R indices [I > 2σ (I)] R1 = 0.0539, wR2 = 0.1327; R indices
(all data) R1 = 0.1003, wR2 = 0.1586. Compound [5]PF6: The
structure was successfully solved in the I23 space group consider-
ing a merohedral twinning. All cluster atoms were refined
anisotropically, whereas the positions of the hydrogen atoms
were generated geometrically, assigned isotropic thermal para-
meters, and allowed to ride on their respective parent carbon
atoms. One of the PF-6 anion lies on a special position (intersec-
tion of three 2-fold axis), and its atoms were also refined
anisotropically. This accounts for six out of the eight negative
charges within the unit cell. The other set of independent PF6-
ions, revealed in the Fourier map as highly disordered, were
refined as a rigid group with perfect octahedral geometry, placing
the phosphorus atom on the highest electron density peak. The
site occupancies of the highly disordered PF-6 anions were
assigned to ensure a cluster:PF6 ratio of 1, compatible with the
observed cluster charge. This kind of disorder is often observed in
isostructural tungsten [W3Q4(dmpe)3X3]PF6 (Q = S, Se; X =
OH, Br) complexes that crystallize in the cubic space group
I23.20,27 Empirical formula C21H48F6Mo3N3P7S4; FW=
1089.47; crystal system, cubic; unit-cell dimensions a = 21.039
(7) A; V = 9304.6(5) A3; T = 293(2) K; space group I23; Z = 8;
no. of reflns collected = 20 215; no. of independent reflns = 2729
[R(int) = 0.1089]; final R indices [I > 2σ(I)] R1 = 0.0599, wR2 =
0.1659; R indices (all data) R1 = 0.1015, wR2 = 0.1923.
NMR (T = 0 °C): δ 35.79 (d, JP-P = 10 Hz), 20.85 (d, JP-P
=
10 Hz). 1H NMR (T = 0 °C): δ 0.81 (d, 9H, CH3, 2JHP = 10.5 Hz),
1.73 (d, 9H, CH3, 2JHP = 10.1 Hz), 1.95 (m, 3H), 2.04 (d, 9H,
2
2
CH3, JHP = 11.6 Hz), 2.20 (d, 9H, CH3, JHP = 11.3 Hz),
2.25 (m, 3H), 2.40 (m, 3H), 3.06 (m, 3H). ESI-MS(+) m/z:
1653.5 [M]+.
X-ray Crystallographic Study. Suitable crystals for X-ray
studies for compounds [2]PF6 1/2CH2Cl2 and [5]PF6 were grown
3
by slow diffusion of diethylether into dichloromethane sample
solutions. X-ray diffraction experiments were carried out on a
Bruker SMART CCD diffractometer using Mo KR radiation
(λ = 0.71073 A) at room temperature. Data were collected with a
frame width of 0.3 ° in ω and a counting time of 30 s per frame for
both compounds at a crystal to detector distance of 4 cm. The
diffraction frames were integrated using the SAINT package and
corrected for absorption with SADABS.25 The structures were
solved by direct methods and refined by the full-matrix method
based on F2 using the SHELXTL software package.26 Com-
pound [2]PF6 1/2CH2Cl2: despite all angles being close to 90°,
3
the structure was successfully refined in the monoclinic space
group P2(1)/n considering a merohedral twinning. All cluster
atoms were refined anisotropically and the positions of all
hydrogen atoms were generated geometrically, assigned isotropic
thermal parameters, and allowed to ride on their respective
parent carbon atoms. One PF-6 anion was found in a general
position compatible with the 1+ charge of the cluster. Half a
molecule of dichloromethane was found in the last Fourier map
and was refined isotropically as rigid group. Hydrogen atoms in
this molecule were not included in the refinement. Empirical
formula C19.50H49Cl4CuF6Mo3NP7S4; FW= 1249.79; crystal
system, monoclinic; unit-cell dimensions a = 12.729(7) A; b =
23.199(12) A, c = 16.397(8) A, β = 90.150(14), V = 4842(4) A3;
T = 293(2) K; space group P2(1)/n; Z = 4; no. of reflns collec-
ted = 27 808; no. of independent reflns = 8536 [R(int) = 0.0860];
Results and Discussion
Cyanide-Terminated Clusters. The present study
focused primarily on two aspects of the reactivity of Mo3-
CuS4 and Mo3S4 complexes. First, the substitutional lability
of the chloride ligands attached to the Cu or Mo sites toward
cyanide ligands is investigated. Second, we explore the use of
the resulting cyanide-terminated complexes to generate
mixed-metal assemblies that retain the cubane-type Mo3-
CuS4 and Mo3S4 cores. The previously reported clusters
[Mo3(CuCl)S4(dmpe)3Cl3]PF6 ([1]PF6) and [Mo3S4(dm-
pe)3Cl3]PF6 ([4]PF6) are tested as convenient starting mate-
rials.18 Cyano-terminated [Mo3(CuCN)S4(dmpe)3Cl3]PF6
([2]PF6)and[Mo3S4(dmpe)3(CN)3]PF6 ([5]PF6) compounds
are accessible by reactions summarized in scheme 1 and were
isolated as air-stable PF-6 salts.
(25) (a) SAINT 5.0; Bruker Analytical X-ray Systems: Madison, WI, 1996.
(b) Sheldrick, G. M. SADABS Empirical Absorption Program; University of
Gttingen Gttingen, Germany, 1996.
(26) Sheldrick, G. M. SHELXTL 5.1; Bruker Analytical X-ray Systems:
Madison, WI, 1997.
(27) Algarra, A. G.; Basallote, M. G.; Fernandez-Trujillo, M. J.; Llusar,
R.; Safont, V. S.; Vicent, C. Inorg. Chem. 2006, 45, 5774.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
4841
Figure 2. ORTEP representation (50% probability level ellipsoids) of the cationic cluster (a) 2+ and (b) 5+
.
Reaction of methanol solutions of [1]PF6 with 1 equiv.
of KCN was investigated aimed at obtaining cluster 2+.
This reaction invariably leads to cluster degradation to
afford Mo3S4 clusters, the trinuclear [Mo3S4(dmpe)3Cl3]
PF6 ([4]PF6) complex being the only characterizable
product as judged by ESI-MS. These results suggest that
the presence of free CN- in the reaction media is not
compatible with compounds featuring a Mo3CuS4 cluster
core. Thus, an alternative strategy was necessary to
selectively obtain the desired Mo3CuS4 complex with
Mo-Cl and Cu-CN groups. For this purpose, we use
the trinuclear [4]PF6 complex and CuCN as a source of
copper. This approach is so-called [3 +1] building block
strategy and has proven to be the most efficient route to
construct cuboidal complexes with a Mo3M0S4 (M0 =
transition metal) core both in aqueous and organic
media.28 In these reactions, the preassembled Mo3 tri-
nuclear complex is typically reacted with a second
M0-containing reagent to afford the desired compound.
The reaction of complex [4]PF6 with a 3-fold excess of
CuCN cleanly affords [Mo3(CuCN)S4(dmpe)3Cl3]PF6
([2]PF6) in 64% yield. We believe that the low solubility
of CuCN in the reaction media and the short reaction
time avoid possible Mo3CuS4 cluster degradation be-
cause of the presence of free CN-. Regarding the
Mo3S4 clusters, reaction of methanol solutions of [4]PF6
and a 5-fold excess of KCN affords [5]PF6 in 50% yield.
Clusters [2]PF6 and [5]PF6 exhibit characteristic ν(CN)
stretching frequencies in their IR spectra. An IR spectrum
of dichloromethane solutions of [2]PF6 shows a ν(CN)
stretching frequency at 2140 cm-1. Compound [5]PF6
displays two stretching frequencies at 2111 and 2094 cm-1
which are comparable to those found for other sulfur-rich
molybdenum complexes featuring terminal CN ligands,
namely the trinuclear K5[Mo3S4(CN)9] (ν(CN) = 2122
and 2118 cm-1),29 and the hexanuclear K7[Mo6S8(CN)6]
(ν(CN) = 2095 cm-1) complex.30 Suitable single crystals
for X-ray analysis were obtained for compounds [2]PF6
and [5]PF6. ORTEP representations for both 2+ and 5+
cations are shown in structures a and b in Figure 2 .
The metal cluster core in the 2+ cation consists of a
slightly distorted tetrahedral arrangement of one copper
and three molybdenum atoms from which the essential
cubane-type motif is readily inferred. The coordination
sphere on the copper atom appears in a tetrahedral
environment defined by three bridging sulfur atoms and
one cyanide ligand whereas the coordination sphere
around each molybdenum atom is octahedral with three
sulfurs, one chlorine and two phosphorus atoms of the
diphosphane ligand. For the trinuclear 5+ cation, ligand
distribution around the molybdenum sites is essentially
the same as that found in 2+ except that the chlorine
atoms are replaced by cyanide ligands. In general, cation
5
+ shares the main geometric features with other incom-
plete cubane-type Mo3S4 complexes bearing diphosphane
ligands.31 Cations 2+ and 5+ preserve the stereochemis-
try of their 1+ and 4+ precursors, possess an idealized C3
symmetry and are conveniently identified in solution by
1
31P{1H} and H NMR spectroscopy. Two phosphorus
2
resonances (typical JP-P values of 11 Hz) are observed
for the 2+ and 5+ cations, as expected for three equiva-
lent diphosphane ligands, whereas 1H NMR spectra
comprise four doublets (corresponding to the four none-
quivalent methyl groups of the diphosphane coupled with
the neigbouring P atoms) together with four strongly
coupled diastereotopic H atoms from the ethylene
bridged backbone. Further support on the integrity of
compounds [2]PF6 and [5]PF6 in solution is provided by
ESI mass spectrometry where the 2+ (m/z = 1061.7) and
5
in their respective spectra.
+ (m/z = 943.7) cations are observed as the base peaks
Cyanide-Bridged Mixed-Metal Clusters. Once selective
cyanide coordination is achieved at the Cu site in [2]PF6 or
Mo sites in [5]PF6, it is now possible to use them as secondary
building units to clusters of higher nuclearities. Hence, the
reaction of complexes 2+ and 5+ with (THF)Mo(CO)5 in
tetrahydrofuran (THF) was investigated. Because of the
limited solubility of the PF-6 salts in THF, we use as
precursors the corresponding tetraphenylborate salts,
namely [2]BPh4 and [5]BPh4 (see Experimental Section).
(28) (a) Hidai, M.; Kuwata, S.; Mizobe, Y. Acc. Chem. Res. 2000, 33, 46.
(b) Hernandez-Molina, R.; Sokolov, M. N.; Sykes, A. G. Acc. Chem. Res.
2001, 34, 223. (c) Llusar, R.; Uriel, S. Eur. J. Inorg. Chem. 2003, 1271.
::
(29) Muller, A.; Jostes, R.; Eltzner, W.; Nie, C. S.; Diemann, E.; Bogge,
H.; Zimmermann, M.; Dartmann, M.; Reinsch-Vogell, U.; Che, S.; Cyvin, S.
(31) (a) Cotton, F. A.; Llusar, R. Polyhedron 1987, 6, 1741. (b) Algarra, A.
G.; Basallote, M. G.; Fernandez-Trujillo, M. J.; Guillamon, E.; Llusar, R.;
Segarra, M. D.; Vicent, C. Inorg. Chem. 2007, 46, 7668.
J.; Cyvin, B. N. Inorg. Chem. 1985, 24, 2872.
(30) Brylev, K. A.; Virovets, A. V.; Naumov, N. G.; Mironov, Y. V.;
Fenske, D.; Fedorov, V. E. Russ. Chem. Bull., Int. Ed. 2001, 50, 1140.

4842 Inorg. Chem., Vol. 48, No. 11, 2009
Llusar et al.
Figure 3. ESI mass spectra of the reaction of compound [5]BPh4 with a 6-fold excess of (THF)Mo(CO)5 in tetrahydrofuran at different reaction times.
Reaction of complexes [2]BPh4 and [5]BPh4 with (THF)Mo
(CO)5 was monitored by electrospray ionization mass
spectrometry (ESI-MS). ESI mass spectra of the reac-
tion of complex [2]BPh4 with (THF)Mo(CO)5 reveal a
progressive decrease of the signal of the 2+ cation (m/z =
1061.7) concomitant with the formation of cation 3+
(m/z = 1299.5). Completion of the reaction was achieved
within 1 h. Both the mass-to-charge ratio and the isotopic
pattern of 3+ confirm that incorporation of a Mo(CO)5
fragment has occurred. Even though ESI mass spectra
suggest a clean incorporation of Mo(CO)5 fragments into
2+, chromatographic workup was necessary to obtain [3]
BPh4 in analytically pure form. Treatment of THF solutions
of [5]BPh4 with a 6-fold excess of (THF)Mo(CO)5 at 0 °C
produces a gradual color change from green to dark violet.
The temporal evolution of this reaction was also monitored
using ESI-MS and representative spectra are shown in
Figure 3.
At the early stages of the reaction, the solution mostly
consists of the starting 5+ cation at m/z = 943.7 together
with a small amount of [5 + Mo(CO)5]+ cation centered
at m/z = 1180.7. After 15 min, the 5+ cation signal has
considerably diminished and new signals due to higher
nuclearity species are observed; these include the [5 +
2Mo(CO)5]+ cation centered at m/z = 1417.6 and the 6+
species at m/z = 1653.5 (formally corresponding to the
[5 + 3Mo(CO)5]+ cation). After half an hour, changes
are essentially in intensity rather than speciation and
complete coordination of Mo(CO)5 fragments to the
three Mo3S4-cyanide groups can be inferred (see Figure 3
bottom). All attempts to grow diffraction-quality crystals
of complexes [3]BPh4 and [6]BPh4 were unsuccessful;
however, the presence of Mo(CO)5 fragments in [3]BPh4
and [6]BPh4 was further supported by elemental analysis,
IR, UV-vis, and 31P{1H} NMR spectroscopies.
(two A1 and one E vibration mode) in the ν(CO) region
of the infrared spectra, consistent with the presence of a
monosubstituted molybdenum hexacarbonyl moiety.32
These ν(CO) stretching frequencies are sensitive probes
of the electronic nature of metalloligands Mo3S4Cu and
Mo3S4 in complexes 3+ and 6+. Specifically, the lower A1
frequency band (which derives most of its character from
the CO vibration trans to the CN group) can be used as a
probe of the electronic nature of the substituted ligand in
hexacarbonyl derivatives. Hence, an inherently richer
electron donor (or poorer electron acceptor) metalloli-
gand coordinated to the Mo(CO)5 fragment should cause
a greater amount of the charge to be displaced into the
vacant antibonding π-orbital of the trans-carbonyl, thus
decreasing the stretching frequency. In the present case,
the lower A1 band frequency remains almost unchanged
for 3+ and 6+ (1901 and 1908 cm-1, respectively), there-
fore suggesting similar electron donor (acceptor) abilities
for the metalloligands Mo3S4Cu and Mo3S4. This experi-
mental evidence indicate that a similar intrinsic stability
of the Cu-μCN Mo(CO)5 and Mo-μCN Mo(CO)5
3 3 3
3 3 3
linkages is expected on the basis of electronic considera-
tions, although the distinctive steric hindrance for the
Cu-CN and Mo-CN groups in 2+ and 4+ also play an
important role as we will discuss below.
UV-visible spectra of compounds 1+-6+ are domi-
nated by intense bands at high energy (below 360 nm),
less intense bands in the 380-490 nm range, and weak
bands at lower energy in the 530-640 nm range.
Absorption bands in the visible are ubiquitous in
Mo3S4 and Mo3S4Cu clusters and are typically asso-
ciated to transitions involving predominantly metal-
based molecular orbitals (1e f 2a1 for Mo3S4 clusters
and 3e f 4e for Mo3S4Cu clusters) whereas higher
energy bands are associated with metal to ligand charge
transfer or intraligand transitions.33 Table 1 collects
absorption maxima positions and intensities in the
UV-vis spectra for the series 1+-6+.
IR and UV-Vis Spectroscopies. The characteristic
ν(CN) stretching vibration shifts from 2140 cm-1 (for
2+) to 2151 cm-1 (in cluster 3+) upon coordination of
one Mo(CO)5 fragment. On going from compound 5+ to
6+, ν(CN) stretching frequencies also shift from 2111/
2094 cm-1 to 2124/2104 cm-1 as expected on going
from terminal to bridged CN ligands.2 Both compounds
3+ and 6+ exhibit the expected three-band pattern
(32) Stolz, I. W.; Dobson, G. R.; Sheline, R. K. Inorg. Chem. 1963, 2, 323.
::
(33) (a) Muller, A.; Fedin, V. P.; Diemann, E.; Boegge, H.; Krickemeyer,
E.; Soelter, D.; Giuliani, A. M.; Barbieri, R.; Adler, P. Inorg. Chem. 1994, 33,
2243. (b) Bahn, C. S.; Tan, A.; Harris, S. Inorg. Chem. 1998, 37, 2770.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
4843
Table 1. Spectroscopic Data in CH3CN (ca. 1 ꢀ 10-5 M) and Redox Potentials of Mo3CuS4 and Mo3S4 Clusters 1+-6+ in Dichloromethanea
compd
λ
abs (nm) (ε (ꢀ 103 dm3 mol-1 cm-1))
oxidation Ecb (V)
reduction E1/2 (ΔE c) (V)
[1]PF6
[2]PF6
[3]BPh4
[4]PF6
[5]PF6
[6]BPh4
364(5.4), 493 (2.4), 649 (0.42)
360(5.9), 470 (3.1), 621 (0.49)
355(5.8), 485 (2.0), 612 (0.49)
341(6.0), 398 (4.6), 634 (0.42)
328(5.8), 400 (4.1), 590 (0.62)
290(6.2), 380 (2.85), 529 (0.55)
-0.36 (57)
-0.34 (70)
-0.32 (137)
-0.75 (89)
-0.52 (68)
-0.24 (131)
d
0.95
0.91
d
a Referenced to Fc/Fc+ at E1/2 = 0.44 V (vs Ag/AgCl). b Potentials measured at 100 mV/s. c ΔE = |Ea - Ec|. d An irreversible oxidation
wave corresponding to the BPh-4 anion was observed at Ea = 1.05 V.
Mo-CN functional groups. Understanding of interac-
tions between both cyanide-terminated Mo3CuS4 or
Mo3S4 clusters and the Mo(CO)5 fragment is of funda-
mental importance in developing further discrete or
extended materials based on these clusters. In particular,
the strength of the interaction of both entities as well as
the tendency toward cyanide/isocyanide isomerization
can be easily addressed by solution or gas-phase techni-
ques such as NMR or ESI tandem mass spectrometry.
In this context, cyanide/isocyanide conversion involv-
ing group 6 pentacarbonyls is not common,34 the
only example reported to date being the isomerization
of [(PPh3)3Cu-μ-CN W(CO)5] to [(PPh3)3Cu NCμ-
3 3 3
3 3 3
W(CO)5].35 In the present study, we observe that com-
pound 3+ was stable in common organic solvents at room
temperature for days. Solutions of 6+ were also stable for
days at low temperature (typically below T = 0 °C);
however, after allowing to stand THF solutions of 6+ at
room temperature for hours, gradual rearrangement
of the CN bridge was observed as evidenced by the
presence of the free anion [(NC)Mo(CO)5]- in solu-
tion (a prominent species centered at m/z = 262 is
observed in the ESI(-) mass spectrum) accompanied
by the appearance of a black precipitate, characteristic
of cluster decomposition. For compound 6+, we did
not observe direct evidence (neither IR spectrum nor
color change) of the presence of the linkage isomer of
Figure 4. UV-vis spectra of solutions of compound [6]BPh4 in CH2Cl2,
THF, CH3OH, CH3CN, and DMF.
Selective substitution of halide by cyanide ligands at the
Cu or Mo sites has allowed us to investigate the spectro-
scopic consequences of sequential replacing at both the
Cu and Mo sites in Mo3CuS4 and Mo3S4 complexes. For
cubane-type Mo3CuS4 clusters, replacement of Cl by CN
at the Cu site in proceeding from 1+ to 2+ results in a blue
shift of 28 cm-1. An analogous blue shift (44 cm-1) is
observed upon Cl by CN replacement at the Mo sites in
proceeding from 4+ to 5+. Introduction of Mo(CO)5
fragments in proceeding from 2+ to 3+ results in a blue-
shift in the absorption maximum of 9 cm-1, whereas a
more significant blue-shift (61 cm-1) is observed on going
from 5+ to 6+. Within the whole 1+-6+ series, only the
lowest energy absorption band in the absorption spec-
trum of 6+ is strongly dependent on the solvent used. The
absorption spectra in five different solvents shifts from
λ = 510 nm in dimethylformamide to 585 nm in CH2Cl2.
This is also evidenced by a color change of the solution
from dark red to dark violet on going from DMF to
dichloromethane solutions (see Figure 4). This lowest
energy band displays significant negative solvatochro-
mism (ca. 75 nm) with increasing solvent polarity, which
means that a change in the solvent polarity leads to
differential stabilization of the ground and excited states
involved in this electronic transition. Because of the
absence of solvatochromism for the whole series 1+-
5+, we hypothesize a prominent involvement of the
Mo3S4 to Mo(CO)5 moieties in the HOMO-LUMO
orbitals of the ground and excited states.
compound 6+, that is, the putative [Mo3S4(dmpe)3
3 3 3
(NCμ-Mo(CO)5)3]+ species, which is believed to irrever-
sibly undergo rapid [(NC)Mo(CO)5]- liberation once
formed, according to reactions 1 and 2. In agreement
with this hypothesis, all attempts to coordinate the anion
[(NC)Mo(CO)5]- to Mo3S4 clusters by reacting Na[(NC)
Mo(CO)5] and [3]PF6 were unsuccessful.
½Mo3S4ðdmpeÞ ðμ ꢁ CN MoðCOÞ5Þ3ꢂþ
3
3 3 3
f ½Mo3S4ðdmpeÞ3
ðNCμ ꢁ MoðCOÞ5Þ3ꢂþ ð1Þ
3 3 3
½Mo3S4ðdmpeÞ3 3 3 3 ðNC ꢁ MoðCOÞ5Þ3ꢂþ
-
f ½NCMoðCOÞ5ꢂ þ black precipitate ð2Þ
The higher ability of C-bound cyanide to accept electron
density from the electron richer Mo(CO)5 fragments rather
than from the Mo3S4 cluster is likely the driving force of
Solution vs Gas-Phase Stability of the M0-μCN Mo
(34) (a) Zhu, N.; Vahrenkamp, H. Angew. Chem., Int. Ed. 1994, 33, 2090.
(b) Calhorda, M. J.; Costa, P. J.; Drew, M. G. D.; Felix, V.; Gamelas, C. A.;
Goncalves, I. S.; Pereira, C. C. L.; Romao, C. C. Inorg. Chim. Acta 2003, 356,
297. (c) Palazzi, A.; Sabatino, P.; Stagni, S.; Bordoni, S.; Albano, V. G.;
Castellari, C. J. Organomet. Chem. 2004, 689, 2324.
3 3 3
(CO)5 Linkage (M0 = Cu, Mo) in Mo3CuS4 and Mo3S4
Clusters. Unlike extended solids based on cyanide-
bridged complexes, discrete mixed-metal assemblies 3+
and 6+ offer the opportunity to study in detail the
fundamental properties of both terminal Cu-CN and
(35) Darensbourg, D. J.; Yoder, J. C.; Holtcamp, M. W.; Klausmeyer, K.
K.; Reibenspies, J. H. Inorg. Chem. 1996, 35, 4764.

4844 Inorg. Chem., Vol. 48, No. 11, 2009
Llusar et al.
decomposition is accelerated), in agreement with a
thermally driven dynamic process. On the basis of this
experimental evidence, we tentatively propose that 31P
NMR line broadening is caused by thermally induced
lability of the Mo(CO)5 fragments attached to the
Mo-CN groups.
To obtain further details on the fundamental features
of the M0-μCN Mo(CO)5 linkages (M0 = Cu, Mo) in
3 3 3
clusters 3+ and 6+, we investigate their intrinsic stability
in the gas phase. As shown above on the basis of IR
spectra, electron donor abilities of metalloligands Mo3-
CuS4 (in 3+) and Mo3S4 6+ (in 6+) are similar ,whereas
the distinctive steric hindrance at the Cu-CN or
Mo-CN sites in complexes 3+ and 6+ seem to play
an important role on the intrinsic stability of the
Figure 5. VT-31P{1H} NMR spectra in the T = -10 to T = 20 °C range
of compound [6]BPh4 in CD2Cl2. The insets show the expanded regions in
the δ = 35-36 and 20-21 range.
M0-μ-CN Mo(CO)5 linkages (M0 = Cu, Mo) in solu-
3 3 3
tion. In this regard, gas phase studies provide valuable
complementary information in the absence of solvent or
counterion effects, which can be easily obtained from
tandem mass spectrometric techniques such as collision-
induced dissociation (CID) experiments. In the particular
case of carbonyl cluster compounds, CID typically causes
progressive stripping of all CO ligands down to the metal
core.36 Because of their rich dissociation patterns, such
compounds can be studied in detail using energy-depen-
dent ESI tandem mass spectrometry (EDESI-MS/MS)
methodologies, to afford the complete fragmentation
pattern as a two-dimensional map.23 EDESI-MS/MS is
essentially a two-dimensional projection (collision energy
vs m/z) of a three-dimensional surface (ion intensity).
Each crosspeak on the map represents different pro-
duct ions generated as the collision energy is increased.
EDESI-MS/MS representations of cations 3+ and 6+ are
shown in Figure 6.
such isomerization process in compound 6+. This would
also apply for compound 3+ featuring a Cu-μCN Mo
3 3 3
(CO)5 linkage; however, no isomerization was observed in
this latter case, therefore suggesting that besides electronic
considerations, steric factors may also play an important
role at triggering cyanide/isocyanide conversion. In parti-
cular, the environment provided by diphosphane ligands
around each Mo-CN group (in compound 6+) is more
congested than that in Cu-CN groups (in compound 3+)
and may preclude an effective approximation of the
Mo(CO)5 fragment, thus yielding labile Mo-μCN Mo
3 3 3
(CO)5 linkages that would permit facile rearrangement of
the cyanide bridge. This is also manifested in the 31P {1H}
NMR spectra of compounds [3]BPh4 and [6]BPh4. CD2Cl2
solutions of compound [3]BPh4 display a 31P {1H} NMR
pattern identical to that registered for the [2]PF6 precursor
with two doublets at 29.85 and 25.67 ppm, in agreement
with preservation of the C3 symmetry upon Mo(CO)5
coordination. Conversely, 31P {1H} NMR spectra of
CD2Cl2 solutions of [6]BPh4 were broad with unresolved
2JP-P coupling at room temperature in contrast to the sharp
signals observed for the starting [5]BPh4. On cooling from
30 to -40 °C, the 31P{1H} NMR spectra of [6]BPh4
progressively narrow and 2JP-P coupling is evident at near
0 °C. This dynamic behavior confirms that the C3 symmetry
of [6]BPh4 is frozen on the NMR time scale. Representa-
tive VT-31P{1H} NMR spectra are shown in figure 5 in the
20 to -10 °C range.
Each series of peaks (namely X, Y, or Z) correspond to
singly charged species, and each peak in their respective
series is 28 mass units apart, corresponding to the sequen-
tial loss of carbonyl ligands. For cation 3+, upon increas-
ing the collision energy (thus moving up the y axis, see
Figure 6 a), up to five carbonyl ligands are stripped from
the metal core denoted as Xi (i = 1-5) species. At higher
collision energies (typically above collision energy =
30 eV), EDESI-MS/MS of 3+ is dominated by the
liberation of neutral diphosphane,37 and further increas-
ing the energy (near Elaboratory = 40 eV) results in the
formal expulsion of Mo fragments. These results indicate
Solvent-mediated fluxionality has been invoked to
account for the line broadening in cyanide mixed-metal
assemblies involving group 6 pentacarbonyl groups. For
a remarkable stability of the Cu-μCN Mo(CO)5 link-
age in the gas phase, which is comparable to that of the
3 3 3
Mo-diphosphane dissociation energy.
EDESI-MS/MS map of cation 6+ is shown in
Figure 6b, revealing the presence of the precursor 6+
ion (m/z = 1653, appears in the bottom right-hand corner
of the map) at low collision energy. At a collision energy
of 5 eV, the first CO ligand is lost, and as the Elaboratory is
further increased (moving up the y axis), CO stripping
continues, producing the series of ions marked with Xi in
example, compound [(PPh3)3Cu NCμ-W(CO)5] un-
3 3 3
dergoes a rapid exchange reaction that involves the
insertion of a solvent molecule into the cyanide-bridging
unit to yield the putative [(PPh3)3Cu CH2Cl2 NCμ-
3 3 3
3 3 3
W(CO)5] species, which causes the 13C resonances to
broaden; however, no solvent insertion was observed,
and consequently, narrow 13C resonances were registered
for its linkage isomer [(PPh3)3Cu-μ-CN W(CO)5].35
3 3 3
For compound [6]BPh4, VT-31P {1H} NMR spectra were
identical regardless of the solvent used, thus suggesting
that solvent insertion on the CN bridging unit is unlikely.
Moreover, this temperature-dependent behavior is repro-
ducible over different temperature cycles from -40 to
20 °C with the same sample (above T = 40 °C, cluster
(36) (a) Butcher, C. P. G.; Dyson, P. J.; Johnson, B. F. G.; Khimyak, T.;
McIndoe, J. S. Chem.;Eur. J. 2003, 9, 944. (b) Butcher, C. P. G.; Dinca, A.;
Dyson, P. J.; Johnson, B. F. G.; Langridge-Smith, P. R. R.; McIndoe, J. S.
Angew. Chem., Int. Ed. 2003, 42, 5752.
(37) (a) Guillamon, E.; Llusar, R.; Pozo, O.; Vicent, C. Int. J. Mass
Spectrom. 2006, 254, 28. (b) Vicent, C.; Feliz, M.; Llusar, R. J. Phys. Chem. A
2008, 112, 12550.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
4845
Figure 6. EDESI-MSMS representations of cations 3+ (left) and 6+ (right) in the Elaboratory = 0-70 eV range. Product ions labeled as Xi denote
sequential iCO losses; Product ions labeled as Yi and Zi refer to species of general formula [6-Mo(CO)5-iCO]+ and [6-2Mo(CO)5-iCO]+, respectively.
Figure 6 (i = 1-15; formally corresponding to [6 -
iCO]+). However, it is immediately evident that unlike
to 3+, the loss of CO ligands does not occur in a regular
fashion. These discontinuities are caused by a second type
of dissociation that consist in the formal liberation of
neutral Mo(CO)5 fragments. Once a Mo(CO)5 fragment
is liberated, a similarly steady CO loss pattern is seen to
produce the series of the metal cluster [6-(CO)5Mo-
iCO]+ (i = 0-10) and [6-2(CO)5Mo-iCO]+ (i = 0-5)
cations denoted as the series of Yi and Zi species, respec-
tively. As can be inferred in Figure 6, the series of species
Y and Z are significantly broader than that of X as a
consequence of the polyisotopic nature of Mo.
first reduction process corresponds to a quasireversible
two electron reduction attributed to MoI3V T MoIV Mo2III,
although under certain experimental conditions (solvent,
counterion, etc.), this process is seen as two one electron
reduction waves.38 Previous studies in our group have
shown that insertion of Cu(I) into the Mo3S4 units
produces a significant anodic shift in the first reduc-
tion potential, which was tentatively assigned to the
Mo3IVCuI T Mo2IVMoIIICuI process. Table 1 lists relevant
electrochemical data for the Mo3CuS4 and Mo3S4 cluster
cations 1+-6+ (for sake of comparison, all measure-
ments were done in dichloromethane).
A comparison of the first reduction potential of Mo3-
CuS4 cluster cations 1+-2+ reveals minor differences
regardless of the X (X = Cl or CN) ligand attached at the
Cu site. Coordination of the neutral Mo(CO)5 unit does
not have any significant effect on the redox potential of
the Mo3CuS4 clusters, the most remarkable feature being
This characteristic dissociation in turn provides infor-
mation about the molecular organization of cation 6+,
confirming the presence of up to 15 CO groups as
expected for the coordination of three Mo(CO)5 frag-
ments. From the distinctive dissociation patterns of
cations 3+ and 6+, it is possible to qualitatively compare
the presence of an irreversible oxidation wave at E1/2
=
the strong of Mo-μCN Mo(CO)5 linkage in 6+ versus
0.95 V that is characteristic of the Mo(CO)5 fragment.
Incorporation of CuCl and CuCN fragments to com-
pound 4+ shows comparable anodic shift already
reported when inserting CuCl to 4+.18 Cyclic voltammo-
grams of trinuclear complexes [Mo3S4(dmpe)3(X)3]+
3 3 3
that found in 3+. The absence of breaking for the
Cu-μCN Mo(CO)5 linkage in 3+ at low collision
energies contrasts with the easiness of Mo(CO)5 libera-
3 3 3
tion in 6+, thus clearly proving that the Mo-CN Mo
3 3 3
3 3 3
(CO)5 linkage is inherently less stable that Cu-μCN Mo
(CO)5 in the gas phase. This experimental results closely
where (X = Cl, CN, CN Mo(CO)5), numbered as 4+,
3 3
5+, and 6+, are shown in Figure 7.
parallel those found in solution on the basis of VT- 31P
The trinuclear Mo3S4 clusters 4+, 5+, and 6+ reveal a
unique reduction wave displaying features of chemical
reversibility in the cyclic voltammetric time scale at E1/2 =
NMR and once again suggest a less roboust Mo-μCN Mo
3 3 3
(CO)5 linkage in 6+ than that of Cu-μCN Mo(CO)5 in
3 3
compound 3+.
-0.74, -0.52, and -0.24 V, respectively. Replacement of
Cl by CN produces a strong anodic shift (ca. 220 mV)
which is further pronounced upon coordination of
Mo(CO)5 fragments (ca. 500 mV). These experimental
Electrochemistry. Electrochemical properties of the
series of cubane-type 1+-3+ and incomplete cubane-
type 4+-6+ complexes have been investigated by cyclic
voltammetry (CV). The trinuclear molybdenum (IV)
Mo3S44+ clusters are electron precise with six electron
available for the formation of three single metal-metal
bonds. CopperinsertionintotheMo3S44+ affordscubane-
type Mo3CuS54+ compounds with 16 metal electrons and
a formal oxidation of +1 for the copper atoms where the
molybdenum oxidation state remains unchanged. In the
case of the trinuclear [M3S4X3(dmpe)3]+ (M = Mo, W;
X = halide) clusters, the most common behavior for the
evidence essentially means that CN and CN Mo(CO)5
3 3 3
fragment exert a dramatic electron-withdrawing effect on
the Mo3S4 cluster core as compared to Cl, whereas minor
differences are found upon ligand substitution at the Cu
site. Like compound 3+, cyclic voltammograms of com-
plexes [6]BPh4 display an irreversible oxidation wave at
(38) Cotton, F. A.; Llusar, R.; Eagle, C. T. J. Am. Chem. Soc. 1989, 111,
4332.

4846 Inorg. Chem., Vol. 48, No. 11, 2009
Llusar et al.
CO, ease disruption of the Mo-μCN-Mo(CO)5 linkages.
These results suggest a stronger interaction for the Cu-CN-
Mo(CO)5 than the Mo-CN-Mo(CO)5 linkage. The electro-
chemical measurements reported herein further complete
the knowledge gathered on the effect of ancillary ligands
on the redox characteristics of Mo3M0S4 (M0 = Cu, Ni,
Co) and Mo3S4 clusters. For example, we have previously
reported that the S/Se exchange in their [Mo3M0Q4]+ (M0
= Cu, Co; Q = S, Se) and [Mo3Q4]+ starting materials
does not significantly affect the redox behavior.39 In the
present work, we demonstrate that for the cubane-type
Mo3CuS4 and Mo3S4 complexes, redox variations are
strongly affected upon CN ligation at the Mo site, where-
as CN coordination to the Cu site produces only a mod-
erate effect on the redox potentials as compared with
their Cl counterparts. An identical effect has been pre-
viously reported for other cubane-type clusters. For ex-
ample, redox potentials of cubane-type Fe4S4 clusters can
be increased by means of cyanide ligation, facilitating
the isolation of the first synthetic cluster in the all-ferrous
[Fe4S4]0 oxidation state.40 Likewsie, cyanide coordina-
tion at the iron sites in cubane-type clusters MFe3S4
(M = Mo, V) produce a profound influence on the redox
potentials.41
Figure 7. Cyclic voltammogram of compounds 4+, 5+, and 6+ re-
corded in CH2Cl2 at 250 mV/s scan rate.
E1/2 = 0.91 V, which is attributed to the presence of the
three Mo(CO)5 fragments. The observation of a single
reduction step is indicative of negligible electronic com-
munication between Mo(CO)5 fragments through the
Mo3S4 cluster core.
Conclusions
Synthetic procedures have been explored to facilitate the
replacement of terminal chlorine ligands in cubane-type
Mo3CuS4 and Mo3S4 cluster complexes to afford the
cyanide-terminated complexes at the Cu or Mo site,
namely [2]PF6 and [5]PF6, respectively, for ultimate use
in the preparation of mixed-metal assemblies. Clean re-
placement of terminal CuCl by CuCN groups in compound
[1]PF6 is not generally possible in a direct ligand substitu-
tion reaction, but can be done by [3 + 1] building block
synthesis starting from the trinuclear [4]PF6 and CuCN.
The present study represents the first in which cubane-type
Mo3CuS4 and Mo3S4 complexes have been incorporated
into mixed-metal assemblies in which Mo(CO)5 fragments
are bound to the Mo3CuS4 and Mo3S4 cores through CN-
containing linkages. Electronic features of Cu-CN and
Mo-CN groups in 3+ and 6+ are similar while Mo-CN
groups in 6+ are more sterically crowded than Cu-CN sites
in 3+. Consequently one may expect differences in the
strength of the interaction between the molybdenum car-
bonyl fragments at both the Cu or the Mo sites. This is
clearly demonstrated in solution where thermal cyanide/
isocyanide isomerization is observed for 6+. Fundamental
information about the intrinsic stability of cations 3+
and 6+ in the gas phase is provided by energy-depen-
dent electrospray ionization tandem mass spectrometry
(EDESI-MS/MS). EDESI-MS/MS representations pre-
sent, besides the progressive loss of carbonyl ligands as
Acknowledgment. This work was supported by the
ꢀ
Spanish Ministerio de Educacion y Ciencia (MEC) (Pro-
ject CTQ2005-09270-C02-01), Ministerio de Ciencia e
ꢀ
Innovacion (Projects CTQ2008-02670/BQU), and
ꢀ
Fundacio Bancaixa-Universitat Jaume
P1.1B2007-12). The authors are also grateful to the
I (Projects
ꢀ
ꢀ
Serveis Centrals d’Instrumentacio Cientifica (SCIC) of
the Universitat Jaume I for providing us with mass
spectrometry, NMR, and X-ray facilities.
Supporting Information Available: Crystallographic data
(excluding structure factors) for the structures reported in this
paper.This material is available free of charge via the Internet at
http://pubs.acs.org.
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ꢀ
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