Nickel(II)-molybdenum(III)-cyanide clusters: Synthesis and magnetic behavior of species incorporating [(Me3tacn)Mo(CN)3]

Article abstract of DOI:10.1021/ja011645h

The substitution of Mo^III for Cr^III in metal-cyanide clusters is demonstrated as an effective means of increasing the strength of the magnetic exchange coupling and introducing magnetic anisotropy. Synthesis of the octahedral complex [(Me₃tacn)Mo(CN)₃] (Me₃tacn = N,N′,N″-trimethyl-1,4,7-triazacyclononane) is accomplished with the addition of precisely 3 equiv of LiCN to a solution of [(Me₃tacn)Mo(CF₃SO₃)₃] in DMF. An excess of LiCN prompts formation of a seven-coordinate complex, [(Me₃tacn)Mo(CN)₄]^1-, whereas less LiCN produces multinuclear species such as [(Me₃tacn)₂Mo₂(CN)₅] ₁₊. In close parallel to reactions previously performed with [(Me₃tacn)Cr(CN)₃], assembly reactions between [(Me₃tacn)Mo(CN)₃] and [Ni(H₂O)₆]²⁺ or [(cyclam)Ni(H₂O)₂]₂₊ (cyclam = 1,4,8,11-tetraazacyclotetradecane) afford face-centered cubic [(Me₃tacn)₈Mo₈Ni₆(CN) ₂₄]¹²⁺ and linear [(Me₃tacn)₂(cyclam)NiMo₂(CN)₆] ²⁺ clusters, respectively. Generation of the former involves a thermally induced cyanide linkage isomerization, which rapidly leads to a low-spin form of the cluster containing diamagnetic Ni^II centers. The cyclic voltammagram of this species in DMF reveals a sequence of six successive reduction waves spaced approximately 130 mV apart, suggesting class II mixed-valence behavior upon reduction. The magnetic properties of the aforementioned linear cluster are consistent with the expected ferromagnetic coupling and an S = 4 ground state, but otherwise vary slightly with the specific conformation adopted (as influenced by the packing of associated counteranions and solvate molecules in the crystal). Magnetization data indicate an axial zero-field splitting parameter with a magnitude falling in the range |D| = 0.44-0.72 cm^-1 and fits to the magnetic susceptibility data yield exchange coupling constants in the range J = 17.0-17.6 cm^-1. These values represent significant increases over those displayed by the analogous Cr^III-containing cluster. When perchlorate is used as a counteranion, [(Me₃tacn)₂(cyclam)NiMo₂(CN)₆] ₂₊ crystallizes from water in a dimeric form with pairs of the linear clusters directly linked via hydrogen bonding. In this case, fitting the magnetic susceptibility data requires use of two coupling constants: one intramolecular with J = 14.9 cm^-1 and another intermolecular with J′ = -1.9 cm^-1. Reacting [(Me₃tacn)Mo(CN)₃] with a large excess of [(cyclam)Ni(H₂O)₂]₂₊ produces a [(Me₃tacn)₂(cyclam)₃(H₂O) ₂Ni₃Mo₂(CN)₆]⁶⁺ cluster possessing a zigzag structure that is a simple extension of the linear cluster geometry. Its magnetic behavior is consistent with weaker ferromagnetic coupling and an S = 6 ground state. Similar reactions employing an equimolar ratio of reactants afford related one-dimensional chains of formula [(Me₃tacn)(cyclam)NiMo(CN)₃]₂₊. Once again, the ensuing structure depends on the associated counteranions, and the magnetic behavior indicates ferromagnetic coupling. It is hoped that substitutions of the type exemplified here will be of utility in the design of new single-molecule magnets.

Full text of DOI:10.1021/ja011645h

Published on Web 02/14/2002
Nickel(II)-Molybdenum(III)-Cyanide Clusters: Synthesis and
Magnetic Behavior of Species Incorporating
[(Me3tacn)Mo(CN)3]
Matthew P. Shores, Jennifer J. Sokol, and Jeffrey R. Long*
Contribution from the Department of Chemistry, UniVersity of California,
Berkeley, California 94720-1460
Received July 6, 2001
Abstract: The substitution of MoIII for CrIII in metal-cyanide clusters is demonstrated as an effective means
of increasing the strength of the magnetic exchange coupling and introducing magnetic anisotropy. Synthesis
of the octahedral complex [(Me3tacn)Mo(CN)3] (Me3tacn ) N,N′,N′′-trimethyl-1,4,7-triazacyclononane) is
accomplished with the addition of precisely 3 equiv of LiCN to a solution of [(Me3tacn)Mo(CF3SO3)3] in
DMF. An excess of LiCN prompts formation of a seven-coordinate complex, [(Me3tacn)Mo(CN)4]1-, whereas
less LiCN produces multinuclear species such as [(Me3tacn)2Mo2(CN)5]1+. In close parallel to reactions
previously performed with [(Me3tacn)Cr(CN)3], assembly reactions between [(Me3tacn)Mo(CN)3] and [Ni-
(H2O)6]2+ or [(cyclam)Ni(H2O)2]2+ (cyclam ) 1,4,8,11-tetraazacyclotetradecane) afford face-centered cubic
[(Me3tacn)8Mo8Ni6(CN)24]12+ and linear [(Me3tacn)2(cyclam)NiMo2(CN)6]2+ clusters, respectively. Generation
of the former involves a thermally induced cyanide linkage isomerization, which rapidly leads to a low-spin
form of the cluster containing diamagnetic NiII centers. The cyclic voltammagram of this species in DMF
reveals a sequence of six successive reduction waves spaced approximately 130 mV apart, suggesting
class II mixed-valence behavior upon reduction. The magnetic properties of the aforementioned linear cluster
are consistent with the expected ferromagnetic coupling and an S ) 4 ground state, but otherwise vary
slightly with the specific conformation adopted (as influenced by the packing of associated counteranions
and solvate molecules in the crystal). Magnetization data indicate an axial zero-field splitting parameter
with a magnitude falling in the range |D| ) 0.44-0.72 cm-1, and fits to the magnetic susceptibility data
yield exchange coupling constants in the range J ) 17.0-17.6 cm-1. These values represent significant
increases over those displayed by the analogous CrIII-containing cluster. When perchlorate is used as a
counteranion, [(Me3tacn)2(cyclam)NiMo2(CN)6]2+ crystallizes from water in a dimeric form with pairs of the
linear clusters directly linked via hydrogen bonding. In this case, fitting the magnetic susceptibility data
requires use of two coupling constants: one intramolecular with J ) 14.9 cm-1 and another intermolecular
with J′ ) -1.9 cm-1. Reacting [(Me3tacn)Mo(CN)3] with a large excess of [(cyclam)Ni(H2O)2]2+ produces a
[(Me3tacn)2(cyclam)3(H2O)2Ni3Mo2(CN)6]6+ cluster possessing a zigzag structure that is a simple extension
of the linear cluster geometry. Its magnetic behavior is consistent with weaker ferromagnetic coupling and
an S ) 6 ground state. Similar reactions employing an equimolar ratio of reactants afford related one-
dimensional chains of formula [(Me3tacn)(cyclam)NiMo(CN)3]2+. Once again, the ensuing structure depends
on the associated counteranions, and the magnetic behavior indicates ferromagnetic coupling. It is hoped
that substitutions of the type exemplified here will be of utility in the design of new single-molecule magnets.
Introduction
of one day utilizing such “single-molecule magnets” for data
storage applications has fueled a search for clusters with higher
A decade ago, the molecular cluster [Mn12O12(CH3CO2)16-
(H2O)4] was discovered to exhibit slow magnetic relaxation at
low temperatures.1 This unusual behavior is attributed to the
presence of a high-spin ground state of S ) 10, which, combined
with an axial magnetic anisotropy of D ) -0.5 cm-1, leads to
blocking temperatures.3 However, of the dozen or so clusters
now demonstrated to display a slow relaxation effect, none
possess a spin reversal barrier greater than that of the Mn12
(3) Much additional interest in these clusters has been generated by the
observation of quantum tunneling of the magnetization: (a) Friedman, J.
R.; Sarachik, M. P.; Tejada, J.; Maciejewski, J.; Ziolo, R. J. Appl. Phys.
1996, 79, 6031. (b) Friedman, J. R.; Sarachik, M. P.; Tejada, J.; Ziolo, R.
Phys ReV. Lett. 1996, 76, 3830. (c) Thomas, L.; Lionti, F.; Ballou, R.;
Gatteschi, D.; Sessoli, R.; Barbara, B. Nature 1996, 383, 145. (d) Hernandez,
J. M.; Zhang, X. X.; Luis, F.; Tejada, J.; Friedman, J. R.; Sarachik, M. P.;
Ziolo, R. Phys ReV. B 1997, 55, 5858. (e) Sangregorio, C.; Ohm, T.;
Paulsen, C.; Sessoli, R.; Gatteschi, D. Phys. ReV. Lett. 1997, 78, 4645. (f)
Aubin, S. M. J.; Dilley, N. R.; Pardi, L.; Krzystek, J.; Wemple, M. W.;
Brunel, L.-C.; Maple, M. B.; Christou, G.; Hendrickson, D. N. J. Am. Chem.
Soc. 1998, 120, 4991 and references therein.
a spin reversal barrier of S2|D| ) 50 cm-1 1,2
.
The possibility
(1) (a) Caneschi, A.; Gatteschi, D.; Sessoli, R.; Barra, A. L.; Brunel, L. C.;
Guillot, M. J. Am. Chem. Soc. 1991, 113, 5873. (b) Sessoli, R.; Tsai, H.-
L.; Schake, A. R.; Wang, S.; Vincent, J. B.; Folting, K.; Gatteschi, D.;
Christou, G.; Hendrickson, D. N. J. Am. Chem. Soc. 1993, 115, 1804. (c)
Sessoli, R.; Gatteschi, D.; Caneschi, A.; Novak, M. A. Nature 1993, 365,
141.
(2) Villain, F.; Hartmann-Boutron, F.; Sessoli, R.; Rettori, A. Europhys. Lett.
1994, 27, 159.
9
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J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002 2279

A R T I C L E S
Shores et al.
prototype.1,4 These species are all homometallic clusters in which
the magnetic anisotropy stems from zero-field splitting associ-
ated with VIII, MnIII, or FeIII centers, and magnetic superex-
change occurs through bridging oxygen atoms. In view of the
difficulties in assembling predetermined structures and predict-
ing magnetic properties, the design of metal-oxo clusters with
larger barriers presents a formidable challenge. Consequently,
we5 and others6 have begun to develop alternative cluster
systems, wherein some measure of control over structures and
the critical parameters S and D might be attained.
In particular, metal-cyanide cluster systems offer several
advantages for achieving such control.7 Simple ligand substitu-
tion chemistry, wherein a terminal M-CN unit reacts with an
H2O-M′ moiety to generate a linear M-CN-M′ bridge, can
be employed in assembling clusters. The design of specific
bimetallic constructs is then aided by the expected regularity
of the cyanide bridges and metal coordination geometries.
Moreover, the nature of the magnetic exchange coupling
between M and M′ in the resulting cluster is readily predicted.8
Assuming an octahedral coordination environment for both
metal centers, unpaired electrons in adjacent metal orbitals of
compatible symmetry (t2g + t2g or eg + eg) will couple
antiferromagnetically across the cyanide bridge, whereas those
in orthogonal orbitals (t2g + eg) will couple ferromagnetically.
The antiferromagnetic interaction is typically stronger than the
ferromagnetic interaction and will dominate the superexchange
in a competitive situation. Finally, when confronted with cyanide
and other ligands having similar steric demands, a wide selection
of transition-metal ions prefer to adopt an octahedral coordina-
tion geometry. Thus, once a new cluster geometry containing
octahedral metal sites is discovered, it should generally prove
possible to adjust the ground-state spin and magnetic anisotropy
via substitution of appropriate metal ions.
(4) (a) Barra, A.-L.; Debrunner, P.; Gatteschim, D.; Schulz, C. E.; Sessoli, R.
Europhys. Lett. 1996, 35, 133. (b) Aubin, S. M. J.; Wemple, M. W.; Adams,
D. M.; Tsai, H.-L.; Christou, G.; Hendrickson, D. N. J. Am. Chem. Soc.
1996, 118, 7746. (c) Castro, S. L.; Sun, Z.; Grant, C. M.; Bollinger, J. C.;
Hendrickson, D. N.; Christou, G. J. Am. Chem. Soc. 1998, 120, 2365. (d)
Barra, A. L.; Caneschi, A.; Cornia, A.; Fabrizi de Biani, F.; Gatteschi, D.;
Sangregorio, C.; Sessoli, R.; Sorace, L. J. Am. Chem. Soc. 1999, 121, 5302.
(e) Barra, A. L.; Caneschi, A.; Gatteschi, D.; Goldberg, D. P.; Sessoli, R.
J. Solid State Chem. 1999, 145, 484. (f) Aubin, S. M. J.; Sun, Z.; Pardi,
L.; Krzystek, J.; Folting, K.; Brunel, L.-C.; Rheingold, A. L.; Christou,
G.; Hendrickson, D. N. Inorg. Chem. 1999, 38, 5329. (g) Yoo, J.; Brechin,
E. K.; Yamaguchi, A.; Nakano, M.; Huffman, J. C.; Maniero, A. L.; Brunel,
L.-C.; Awaga, K.; Ishimoto, H.; Christou, G.; Hendrickson, D. N. Inorg.
Chem. 2000, 39, 3615. (h) Goodwin, J. C.; Sessoli, R.; Gatteschi, D.;
Wernsdorfer, W.; Powell, A. K.; Heath, S. L. J. Chem. Soc., Dalton Trans.
2000, 1835. (i) Benelli, C.; Cano, J.; Journaux, Y.; Sessoli, R.; Solan, G.
A.; Winpenny, R. E. P. Inorg. Chem. 2001, 40, 188. (j) Boskovic, C.;
Brechin, E. K.; Streib, W. E.; Folting, K.; Hendrickson, D. N.; Christou,
G. Chem. Commun. 2001, 467.
Our approach to synthesizing high-nuclearity metal-cyanide
clusters employs multidentate capping ligands to inhibit growth
of an extended solid and direct the structure of the product.
For example, the reaction between [(tacn)Co(CN)3] (tacn )
1,4,7-triazacyclononane) and [(tacn)Co(H2O)3]3+ has been
(5) (a) Heinrich, J. L.; Berseth, P. A.; Long, J. R. Chem. Commun. 1998,
1231. (b) Berseth, P. A.; Sokol, J. J.; Shores, M. P.; Heinrich, J. L.; Long,
J. R. J. Am. Chem. Soc. 2000, 122, 9655. (c) Sokol, J. J.; Shores, M. P.;
Long, J. R. Angew. Chem., Int. Ed. Engl. 2001, 40, 236. (d) Heinrich, J.
L.; Sokol, J. J.; Hee, A. G.; Long, J. R. J. Solid State Chem. 2001, 159,
293.
(6) (a) Mallah, T.; Auberger, C.; Verdaguer, M.; Veillet, P. J. Chem. Soc.,
Chem. Commun. 1995, 61. (b) Scuiller, A.; Mallah, T.; Verdaguer, M.;
Nivorzkhin, A.; Tholence, J.-L.; Veillet, P. New J. Chem. 1996, 20, 1. (c)
Vahrenkamp, H.; Geiss, A.; Richardson, G. N. J. Chem. Soc., Dalton Trans.
1997, 3643 and references therein. (d) Rajendiran, T. M.; Mathonie`re, C.;
Golhen, S.; Ouahab, L.; Kahn, O. Inorg. Chem. 1998, 37, 2651. (e) Oshio,
H.; Tamada, O.; Onodera, H.; Ito, T.; Ikoma, T.; Tero-Kubota, S. Inorg.
Chem. 1999, 38, 5686. (f) Zhao, L.; Matthews, C. J.; Thompson, L. K.;
Heath, S. L. Chem. Commun. 2000, 265. (g) Zhong, Z. J.; Seino, H.;
Mizobe, Y.; Hidai, M.; Fujishima, A.; Ohkoshi, S.; Hashimoto, K. J. Am.
Chem. Soc. 2000, 122, 2952. (h) Larionova, J.; Gross, M.; Pilkington, M.;
Andres, H.; Stoeckli-Evans, H.; Gu¨del, H. U.; Decurtins, S. Angew. Chem.,
Int. Ed. Engl. 2000, 39, 1605. (i) Parker, R. J.; Spiccia, L.; Berry, K. J.;
Fallon, G. D.; Moubaraki, B.; Murray, K. S. Chem. Commun. 2001, 333.
(j) Depperman, E. C.; Bodnar, S. H.; Vostrikova, K. E.; Schultz, D. A.;
Kirk, M. L. J. Am. Chem. Soc. 2001, 123, 3133. (k) Smith, J. A.; Gala´n-
Mascaro´s, J.-R.; Cle´rac, R.; Sun, J.-S.; Ouyang, X.; Dunbar, K. R.
Polyhedron 2001, 20, 1727.
demonstrated to produce a cubic cluster, [(tacn)8Co8(CN)12]12+
,
consisting of a single cage unit excised from the Prussian blue
type framework.5a,9 Efforts to realize larger cluster geometries
capable of supporting higher spin ground states have since
utilized N,N′,N′′-trimethyl-1,4,7-triazacyclononane (Me3tacn) as
a capping ligand on just one of the two reaction components.5b-d
Accordingly, the following reaction carried out in boiling
aqueous solution was found to yield a face-centered cubic cluster
containing 14 metal centers.5b
8[(Me3tacn)Cr(CN)3] + 6[Ni(H2O)6]2+
f
(7) Many of these advantages have been exploited in manipulating the bulk
magnetic properties of Prussian blue type solids: (a) Mallah, T.; Thie´baut,
S.; Verdaguer, M.; Veillet, P. Science 1993, 262, 1554. (b) Entley, W. R.;
Girolami, G. S. Science 1995, 268, 397. (c) Ferlay, S.; Mallah, T.; Ouahe`s,
R.; Veillet, P.; Verdaguer, M. Nature 1995, 378, 701. (d) Sato, O.; Iyoda,
T.; Fujishama, A.; Hashimoto, K. Science 1996, 271, 49. (e) Sato, O.; Iyoda,
T.; Fujishama, A.; Hashimoto, K. Science 1996, 272, 704. (f) Larionova,
J.; Cle´rac, R.; Sanchiz, J.; Kahn, O.; Golhen, S.; Ouahab, L. J. Am. Chem.
Soc. 1998, 120, 13088. (g) Holmes, S. M.; Girolami, G. S. J. Am. Chem.
Soc. 1999, 121, 5593. (h) Hatlevik, Ø.; Buschmann, W. E.; Zhang, J.;
Manson, J. L.; Miller, J. S. AdV. Mater. 1999, 11, 914.
[(Me3tacn)8Cr8Ni6(CN)24]12+ (1)
Here, the heat employed during the synthesis promotes linkage
isomerization of the cyanide ligand to give a CrIII-NC-NiII
bridging arrangement, thereby rendering the NiII centers dia-
magnetic and disrupting the putative S ) 18 ground state of
the ferromagnetically coupled intermediate. Other two-compo-
nent reactions have combined Me3tacn ligated corner units with
complexes of the trans-directing ligand 1,4,8,11-tetraazacy-
clotetradecane (cyclam), in attempts to assemble a 20-metal
cluster adopting an edge-bridged cubic geometry. While forma-
tion of such a product has not yet been verified crystallographi-
cally, a cluster corresponding to a linear edge fragment with
an S ) 4 ground state was isolated from closely related
reactions:5b
(8) (a) Entley, W. R.; Treadway, C. R.; Girolami, G. S. Mol. Cryst. Liq. Cryst.
1995, 273, 153. (b) Weihe, H.; Gu¨del, H. U. Comments Inorg. Chem. 2000,
22, 75.
(9) Analogous cubic clusters featuring cyclopentadienyl and carbonyl ligands
have also been prepared: (a) Klausmeyer, K. K.; Rauchfuss, T. B.; Wilson,
S. R. Angew. Chem., Int. Ed. Engl. 1998, 37, 1694. (b) Klausmeyer, K.
K.; Wilson, S. R.; Rauchfuss, T. B. J. Am. Chem. Soc. 1999, 121, 2705.
(10) (a) Singer, L. S. J. Chem. Phys. 1955, 23, 379. (b) Elbers, G.; Remme, S.;
Lehmann, G. Inorg. Chem. 1986, 25, 896.
(11) (a) Gregson, A. K.; Anker, M. Aust. J. Chem. 1979, 32, 503. (b) Averill,
B. A.; Orme-Johnson, W. H. Inorg. Chem. 1980, 19, 1702.
(12) Backes-Dahman, G.; Herrman, W.; Wieghardt, K.; Weiss, J. Inorg. Chem.
1985, 24, 485.
(13) Markley, T. J.; Toby, B. H.; Pearlstein, R. M.; Ramprasad, D. Inorg. Chem.
1997, 36, 3376.
2[(Me3tacn)Cr(CN)3] + [(cyclam)Ni(H2O)2]2+
f
(14) (a) Bosnich, B.; Tobe, M. L.; Webb, G. A. Inorg. Chem. 1965, 4, 1109.
(b) Iwamoto, E.; Imai, K.; Yamamoto, K. Inorg. Chem. 1984, 23, 986.
(15) As discussed below, the results of elemental analysis, X-ray crystallography,
and mass spectrometry in combination suggest that this product is
contaminated with a slight amount of [(Me3tacn)2Mo2(CN)4Cl](BPh4).
Presumably, an impurity in the LiCN‚DMF serves as a source of chloride
ions.
[(Me3tacn)2(cyclam)NiCr2(CN)6]2+ (2)
Efforts to characterize additional high-nuclearity species are
ongoing.
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2280 J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002

Nickel(II)−Molybdenum(III)−Cyanide Clusters
A R T I C L E S
solid under a brown supernatant solution. The solid was collected by
filtration, washed with successive aliquots of DMF (5 mL), THF (3 ×
10 mL), and Et2O (15 mL), and dried in a dinitrogen atmosphere to
give 0.97 g (83%) of product. Absorption spectrum (H2O): λmax (ꢀM)
Although the metal complexes used in these exploratory
assembly reactions represent stable species that are easily
prepared and manipulated, they are not necessarily expected to
impart significant magnetic anisotropy to the resulting clusters.
To achieve the desired anisotropy, one viable strategy is to
incorporate analogous complexes of metal ions known to exhibit
a large single-ion anisotropy, such as those inherent to proven
single-molecule magnets: VIII, high-spin MnIII, and high-spin
FeIII. Another idea, however, is to move down the periodic table
and utilize complexes of second- and third-row transition-metal
ions, for which the greater spin-orbit coupling increases the
magnitude of the zero-field splitting. Thus, for example, whereas
[Cr(acac)3] has an axial zero-field splitting of magnitude |D| )
359 (93, sh), 392 (71, sh) nm. IR: νCN 2116, 2104, 2080, 2061 cm-1
.
µeff (295 K) 2.47 µB. Anal. Calcd. for C13H21MoLiN7: C, 41.28; H,
5.60; N, 25.92. Found: C, 40.97; H, 5.61; N, 25.53. Orange rod-shaped
crystals of 3‚2MeOH suitable for X-ray analysis were obtained by
diffusion of Et2O into a concentrated solution of the product in
methanol.
[(Me3tacn)Mo(O)(CN)2] (4). Compound 3 (0.20 g, 0.52 mmol) was
dissolved in 10 mL of water to form a brown solution. In the course of
heating at reflux for 1 day in air, the solution gradually changed color
from brown to green and, finally, to pale blue. After reducing the
volume of the solution to 1 mL, 5 mL of THF was added to precipitate
a white solid. The solution was collected by filtration and reduced to
dryness in vacuo. Addition of 5 mL of 95% EtOH gave a pale blue
solution over a white solid. Upon centrifugation, the solution was
decanted and then evaporated to dryness to afford a pale blue solid
(80 mg) containing the product. IR: νCN 2106, 2091, 2083 cm-1; νMoO
952 cm-1. Elemental analysis indicated this compound to be slightly
impure; however, further purification was not attempted. Pale blue
platelike crystals of 4‚H2O suitable for X-ray analysis were obtained
by allowing a concentrated aqueous solution of the solid to evaporate
slowly.
0.59 cm-1 10
-6.3 cm-1 11
,
[Mo(acac)3] exhibits a large negative D value of
.
Indeed, replacing CrIII centers with MoIII centers
would provide a means of increasing the magnetic anisotropy
of a cluster without altering its ground state spin. Furthermore,
the radially extended valence d orbitals of MoIII would be
expected to have greater overlap with the cyanide-based orbitals,
leading to stronger magnetic exchange coupling and a spin
ground state that is more isolated in energy. Herein we establish
the validity of this approach with the synthesis of [(Me3tacn)-
Mo(CN)3] and demonstration of its ability to replace [(Me3-
tacn)Cr(CN)3] in eqs 1 and 2 above.
[(Me3tacn)2Mo2(CN)5](BPh4) (5). A reaction between LiCN‚DMF
(0.23 g, 2.1 mmol) and 1 (0.60 g, 0.84 mmol) was carried out using a
procedure analogous to that described in the preparation of 2 above.
The ensuing gray-tan solid was dissolved in water, and a solution of
NaBPh4 (0.13 g, 0.38 mmol) in 1 mL of H2O was added to afford a
brown precipitate. The solid was collected by filtration, washed with
successive aliquots of water (3 × 10 mL), and dried in air to give
0.040 g (10%) of product.15 IR: νCN 2100, 2060 cm-1. Anal. Calcd.
for C47H62BMo2N11: C, 57.38; H, 6.35; N, 15.66. Found: C, 56.52;
H, 6.59; N, 14.54. Brown rod-shaped crystals suitable for X-ray analysis
were grown by diffusion of Et2O into a concentrated solution of the
product in acetonitrile.
Experimental Section
Preparation of Compounds. Preparations of compounds 1-3 were
carried out under a pure dinitrogen atmosphere; all other preparations
were conducted in air. Crude Me3tacn obtained from Unilever was
purified by vacuum distillation (36 °C, ca. 80 mTorr) prior to use. The
compounds [(Me3tacn)MoBr3],12 LiCN‚DMF,13 and [Ni(cyclam)X2] (X
-
14
) Br-, I-, ClO4
) were synthesized as described previously. Water
was distilled and deionized with a Milli-Q filtering system. Diethyl
ether and tetrahydrofuran were passed through alumina and degassed
prior to use. Acetonitrile was distilled over CaH2 and degassed prior
to use. All other reagents were obtained from commercial vendors and
used without further purification.
[(Me3tacn)Mo(CF3SO3)3] (1). A 150-mL Schlenck flask was fitted
with an oil bubbler and charged with a magnetic stir bar and solid
[(Me3tacn)MoBr3] (5.5 g, 11 mmol). Under a flow of dinitrogen,
trifluoromethanesulfonic acid (16 mL, 0.18 mol) was added to form a
deep red-purple solution. The solution was stirred and heated at 140
°C for 4 days, producing a dark brown solution. The solution was then
allowed to cool to room temperature, and 200 mL of Et2O was added
to precipitate a brown solid. The solid was filtered, washed with 50
mL of Et2O, and dried under dinitrogen to yield 7.7 g (99%) of light
tan product. IR: νSO 1189 cm-1. Anal. Calcd. for C12H21F9MoN3O9S3:
C, 20.17; H, 2.96; N, 5.88; S, 13.46. Found: C, 20.05; H, 2.91; N,
5.78; S, 13.26.
[(Me3tacn)Mo(CN)3] (2). Solid LiCN‚DMF (0.910 g, 8.43 mmol)
was added to a solution of 1 (2.00 g, 2.80 mmol) in 3.5 mL of DMF.
The resulting dark brown solution was stirred at room temperature for
2 days, whereupon a light tan precipitate formed. The solid was
collected by filtration, washed with THF (2 × 10 mL) and Et2O (2 ×
10 mL), and dried under dinitrogen to afford 0.388 g (40%) of product.
Absorption spectrum (H2O): λmax (ꢀM) 410 (48, sh), 490 (28, sh), 631
(18) nm. IR: νCN 2098, 2090 cm-1. µeff (295 K) 3.59 µB. Anal. Calcd.
for C12H21MoN6: C, 41.74; H, 6.13; N, 24.34. Found: C, 41.67; H,
6.30; N, 24.21. Brown block-shaped crystals of 2‚H2O suitable for X-ray
analysis were grown by slow evaporation of a concentrated aqueous
solution of the product.
[(Me3tacn)8Mo8Ni6(CN)24]Br12‚27H2O (6). A solution of NiBr2‚
6H2O (59 mg, 0.18 mmol) in 2 mL of water was added to a saturated
solution of 2 (75 mg, 0.22 mmol) in 3 mL of water. The resulting
yellow solution was stirred and heated until its volume was reduced to
2 mL. Upon cooling to room temperature, a yellow solid precipitated.
The solid was collected by filtration, washed with 10 mL of acetone
and 5 mL of Et2O, and dried in air to give 96 mg of product. Further
concentration of the mother liquor to ca. 0.5 mL produced a second
crop of product, for a total yield of 100 mg (80%). Absorption spectrum
(H2O): λmax (ꢀM) 254 (65200), 305 (27900, sh), 335 (16500, sh), 380
(7560, sh) nm. IR: νCN 2152 (sh), 2127, 2090 (sh) cm-1. ES+-MS:
m/z 1278 ([6 - 3Br - 27H2O]3+). Anal. Calcd. for C96H222Br12Mo8N48-
Ni6O27: C, 25.29; H, 4.91; N, 14.74. Found: C, 25.53; H, 4.78; N,
14.46. The water content of this compound was confirmed by
thermogravimetric analysis. Orange block-shaped crystals of 6‚3H2O
suitable for X-ray analysis were grown by slow evaporation of an
aqueous solution of the product.
[(Me3tacn)8Mo8Ni6(CN)24]I12‚18H2O (7). Solid NiI2 (0.23 g, 0.74
mmol) was added to a solution of 2 (0.33 g, 0.96 mmol) in 50 mL of
water. The mixture was stirred and heated at reflux for 1 h to obtain a
deep orange-red solution. A small amount of solid was separated from
the solution by filtration. The filtrate was concentrated to a volume of
25 mL by heating and then cooled to room temperature to precipitate
an orange microcrystalline powder. The solid was collected by filtration,
washed with acetone (2 mL) and Et2O (2 mL), and dried in air to afford
0.31 g of product. Further concentration of the mother liquor to a
volume of 5 mL produced a second crop of product, for a total yield
of 0.35 g (59%). ES+-MS: m/z 646 ([7-6I-18H2O]6+), 800 ([7-5I-
18H2O]5+), 1032 ([7-4I-18H2O]4+). IR: νCN 2147 (sh), 2123, 2085
Li[(Me3tacn)Mo(CN)4] (3). Solid LiCN‚DMF (3.0 g, 28 mmol) was
added to a stirring solution of 1 (2.2 g, 3.1 mmol) in 6 mL of DMF.
The resulting brown solution was stirred for 3 days to afford a tan
9
J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002 2281

A R T I C L E S
Shores et al.
(sh) cm-1. Anal. Calcd. for C96H204I12Mo8N48Ni6O18: C, 23.24; H, 4.14;
N, 13.55. Found: C, 23.34; H, 4.17; N, 13.32. The water content of
this compound was confirmed by thermogravimetric analysis. Crystals
of 7‚9H2O suitable for X-ray analysis were grown by slow evaporation
of an aqueous solution of the product.
[(Me3tacn)2(cyclam)3(H2O)2Ni3Mo2(CN)6]Br6‚9H2O (13). Com-
pound 2 (26.0 mg, 0.0753 mmol) and [Ni(cyclam)Br2] (0.160 g, 0.382
mmol) were dissolved in 10 mL of water and heated to reflux to produce
a brown solution. The solution was concentrated to a volume of 1 mL
and then allowed to evaporate to dryness by standing overnight at room
temperature. Brown crystals of 13‚5H2O suitable for X-ray analysis
were obtained, along with violet crystals of [Ni(cyclam)Br2]. This
compound only formed quantitatively from solutions containing a large
excess of [Ni(cyclam)Br2], and all attempts at cleanly separating the
product were unsuccessful. Consequently, all measurements were
performed on a finely ground mixture containing 13 and [Ni(cyclam)-
Br2] in a 1.00:7.13 molar ratio. IR: νCN 2121, 2107 cm-1. Anal. Calcd.
for C125.30H307.12Br20.26Mo2N52.52Ni10.13O11: C, 29.33; H, 6.03; N, 14.34.
Found: C, 29.45; H, 6.32; N, 13.95. The water content of this
compound was confirmed by thermogravimetric analysis.
[r-(Me3tacn)2(cyclam)NiMo2(CN)6]I2 (8). Solid [Ni(cyclam)I2] (82
mg, 0.16 mmol) was added to a saturated solution of 2 (100 mg, 0.30
mmol) in 5 mL of MeCN, whereupon the mixture darkened in color.
The mixture was stirred for 33 h and then filtered to give a light tan
powder and a brown filtrate. The solid was washed with successive
aliquots of MeCN (1 mL), Et2O (2 × 10 mL), THF (5 mL), and Et2O
(2 × 10 mL) and dried in air to afford 0.17 g (95%) of product. IR:
νCN 2245, 2220, 2118, 2091 cm-1. Anal. Calcd. for C34H66I2Mo2N16-
Ni: C, 33.94; H, 5.53; N, 18.62. Found: C, 34.05; H, 5.67; N, 18.26.
Crystals of 8‚2DMF suitable for X-ray analysis were grown by diffusion
of Et2O into a concentrated solution of the product in DMF.
[(Me3tacn)(cyclam)NiMo(CN)3]I2‚4H2O (14). Solid [Ni(cyclam)-
I2] (90 mg, 0.18 mmol) was added to a solution of 2 (60 mg, 0.17
mmol) in 5 mL of water. The brown solution was stirred and heated at
reflux until its volume was reduced to 2 mL. The solution was allowed
to stand at room-temperature overnight, whereupon yellow-brown rod-
shaped crystals suitable for X-ray analysis formed. The crystals were
collected by filtration, washed with 5 mL of Et2O, and dried in air to
afford 64 mg (40%) of product. IR: νCN 2121, 2117, 2102 cm-1. Anal.
Calcd. for C22H53I2MoN10NiO4: C, 28,41; H, 5.74; N, 15.06. Found:
C, 28.41; H, 5.81; N, 14.73.
[â-(Me3tacn)2(cyclam)NiMo2(CN)6]I2‚6H2O (9). Solid [Ni(cyclam)-
I2] (82 mg, 0.16 mmol) was added to a solution of 2 (110 mg, 0.32
mmol) in 25 mL of water. The brown solution was stirred and heated
at reflux until its volume was reduced to 2 mL. It was then cooled to
room temperature and further concentrated to a volume of 1 mL by
evaporation upon standing in air. After standing overnight at 5 °C, large
brown crystals had formed. These were collected by filtration, washed
with Et2O (10 mL), and dried in air to afford 0.14 g (69%) of brown
microcrystalline product. IR: νCN 2127, 2110, 2098 cm-1. Anal. Calcd.
for C34H78I2Mo2N16NiO6: C, 31.14; H, 5.99; N, 17.09. Found: C, 31.04;
H, 5.98; N, 16.83. The water content of this compound was confirmed
by thermogravimetric analysis. Crystals of 9‚H2O suitable for X-ray
analysis were grown by slow evaporation of an aqueous solution of
the product.
[(Me3tacn)(cyclam)NiMo(CN)3](ClO4)2‚1.5H2O (15). Solid [Ni-
(cyclam)](ClO4)2 (70 mg, 0.15 mmol) was added to a solution of 2 (52
mg, 0.15 mmol) in 5 mL of water. The resulting yellow solution was
concentrated to a volume of 3 mL by heating and was then allowed to
cool to room temperature. Upon standing overnight, brown rod-shaped
crystals suitable for X-ray analysis formed. The crystals were collected
by filtration, washed with 2 mL of Et2O, and dried in air to afford 71
mg (56%) of product. IR: νCN 2116, 2102 cm-1. Anal. Calcd. for
C22H48Cl2MoN10NiO9.5: C, 31.49; H, 5.89; N, 16.87. Found: C, 31.63;
H, 5.83; N, 16.48. Caution! This perchlorate-containing compound
poses an explosion hazard, and should only be handled with care and
in small quantities.
[r-(Me3tacn)2(cyclam)NiMo2(CN)6]Br2‚6H2O (10). This compound
was prepared from [Ni(cyclam)Br2] (0.15 g, 0.36 mmol) and 2 (0.24
g, 0.69 mmol) by a procedure analogous to that described for the
preparation of 9. The product was obtained as 0.24 g (57%) of brown,
X-ray-quality crystals and microcrystalline solid. IR: νCN 2127, 2114,
2096, 2089 cm-1. Anal. Calcd. for C34H78Br2Mo2N16NiO6: C, 33.54;
H, 6.46; N, 18.41. Found: C, 33.21; H, 6.39; N, 18.05. The water
content of this compound was confirmed by thermogravimetric analysis.
X-ray Structure Determinations. Structures were determined for
compounds 2-15 (see the Supporting Information). Single crystals were
coated with Paratone-N oil, attached to glass fibers, transferred to a
Siemens SMART diffractometer, and cooled in a dinitrogen stream.
Initial lattice parameters were obtained from a least-squares analysis
of more than 30 carefully centered reflections; these parameters were
later refined against all data. None of the crystals showed significant
decay during data collection. Data were integrated and corrected for
Lorentz and polarization effects using SAINT and were corrected for
absorption effects using SADABS.
[â-(Me3tacn)2(cyclam)NiMo2(CN)6](ClO4)2‚2H2O (11). A 5 mL
aqueous solution of [Ni(cyclam)](ClO4)2 (83 mg, 0.18 mmol) was added
to a stirring solution of 2 (0.12 g, 0.36 mmol) in 5 mL of water. The
resulting golden brown solution was stirred and heated in air until its
volume was reduced to 4 mL. Upon cooling to room temperature,
orange-brown crystals formed. These were collected by filtration,
washed with 5 mL of Et2O, and dried in air to afford 0.15 g (71%) of
brown microcrystalline product. IR: νCN 2112, 2089 cm-1. ES+-MS:
m/z 1049 ([11-ClO4]1+). Anal. Calcd. for C34H70Cl2Mo2N16NiO10: C,
34.48; H, 5.96; N, 18.92. Found: C, 34.33; H, 5.88; N, 18.54. The
water content of this compound was confirmed by thermogravimetric
analysis. Caution! When fully dehydrated by heating to temperatures
above 210 °C, this compound can decompose explosively. Crystals
suitable for X-ray analysis were obtained by slow evaporation of an
aqueous solution of the product.
Space group assignments were based on systematic absences, E
statistics, and successful refinement of the structures. Structures were
solved by direct methods with the aid of successive difference Fourier
maps and were refined against all data using the SHELXTL 5.0 software
package. Thermal parameters for all atoms with Z > 3 were refined
anisotropically, except for those disordered over multiple partially
occupied sites in the structures of 6‚3H2O, 7‚9H2O, 9‚H2O, 11, 13,
and 15. In the structure of compound 8‚2DMF, the positions of the
hydrogen atoms bound to the methyl carbons in the Me3tacn ligand
and DMF solvate molecule as well as the nitrogen atoms of the cyclam
ligand were located in the difference Fourier map and were refined
using isotropic thermal parameters. Hydrogen atoms associated with
solvate water molecules and disordered methylene carbon atoms (with
the exception of those in 15) were not included in the structural
refinements. All other hydrogen atoms were assigned to ideal positions
and refined using a riding model with an isotropic thermal parameter
1.2 times that of the attached carbon or nitrogen atom (1.5 times for
methyl hydrogens). In the structure of 3‚2MeOH, all carbon and
nitrogen atoms located within 1.7 Å of each other were restrained to
[(Me3tacn)2(cyclam)NiMo2(O)2(CN)4]I2‚6H2O (12). Solid [Ni-
(cyclam)I2] (45 mg, 0.088 mmol) was added to a solution of 2 (45 mg,
0.13 mmol) in 15 mL of water. The resulting brown solution was stirred
and heated at reflux until its volume was reduced to 5 mL. It was then
cooled to room temperature and further concentrated to 1 mL by
evaporation upon standing in air. After standing overnight at room
temperature, blue-green crystals suitable for X-ray analysis had formed.
The solid was collected by filtration, washed with successive aliquots
of cold water (1 mL) and Et2O (5 mL), and dried in air to afford 41
mg (49%) of product. IR: νCN 2109, 2098 cm-1. Anal. Calcd. for
C32H78I2Mo2N14NiO8: C, 29.76; H, 6.09; N, 15.18. Found: C, 30.02;
H, 6.12; N, 15.18.
9
2282 J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002

Nickel(II)−Molybdenum(III)−Cyanide Clusters
A R T I C L E S
have the same Uij parameters. In the structure of 5, the positions of the
C and N atoms in the bridging cyanide ligand are disordered. An
occupancy factor of 0.5C + 0.5N was assigned to each of the two
cyanide atom sites, and their thermal parameters were refined aniso-
tropically. Methylene carbon atoms in the structures of 6‚3H2O, 7‚
9H2O, and 15 were modeled as being disordered over two equally
occupied positions, corresponding to two distinct Me3tacn ligand
conformations. One methyl carbon atom and one nitrogen atom in the
structure of 15 were modeled similarly. Three of the bromide anions
and all of the solvate water molecules in the structure of 6‚3H2O were
modeled as being disordered over multiple positions. Two of the iodide
anions and all of the solvate water molecules in 7‚9H2O were treated
similarly, as were all of the solvate water molecules in 9‚H2O, three
oxygen atoms of the perchlorate anion and one solvate water molecule
in 11, three solvate water molecules in 13, and one chlorine and seven
oxygen atoms of perchlorate anions and all of the solvate water molec-
ules in 15. The final agreement factors for the structures of 6‚3H2O,
7‚9H2O, and 15 are high owing to the extensive disorder present in the
crystals and the accompanying poor quality of the data. The program
CHECKCIF revealed no crystallographic errors for these structures.
Magnetic Susceptibility Measurements. DC magnetic susceptibility
data were collected using a Quantum Design MPMS2 SQUID mag-
netometer at temperatures ranging from 5 to 295 K. Data were corrected
for diamagnetic contributions using Pascal’s constants. A temperature-
independent paramagnetism of 100 · 10-6 cgsu per Mo center and 200
· 10-6 cgsu per Ni center was assumed for each compound. Samples
for magnetization measurements were suspended in a petroleum jelly
mull to prevent torquing of the crystallites at high magnetic fields.
Susceptibility data were fit with theoretical models using a relative
error minimization routine (MAGFIT 3.1),16 except in the cases of 11
and 13-15, where data were simulated using MAGPACK.17 Reported
coupling constants are based on exchange Hamiltonians of the form Hˆ
) -2JSˆi‚Sˆj.
analyses were carried out in a dinitrogen atmosphere using a TA
Instruments TGA 2950. Electrochemical measurements were conducted
with a Bioanalytical Systems CV-50 potentiostat with platinum disk
working, platinum wire auxiliary, and silver wire reference electrodes.
Samples were measured with 0.1 M Bu4NBF4 as the supporting
electrolyte, and ferrocene was added as an internal reference after each
measurement.
Results and Discussion
Synthesis of [(Me3tacn)Mo(CN)3]. Overall, the route utilized
in the preparation of [(Me3tacn)Mo(CN)3] is similar to that
employed previously for the synthesis of [(Me3tacn)Cr-
(CN)3].5b,21 The complex [(Me3tacn)MoBr3]12 reacts with neat
triflic acid to give [(Me3tacn)Mo(CF3SO3)3] (1) in excellent
yield, although significantly more forcing conditions are required
to complete the substitution than those implemented in the
analogous preparation of [(Me3tacn)Cr(CF3SO3)3].5b,21,22 Com-
pound 1 then serves as a useful precursor for introducing cyanide
as a ligand. This process is complicated, however, by the larger
radius of MoIII and its propensity for adopting coordination
numbers greater than six. Indeed, the only homoleptic cyanide
complex of MoIII that has been structurally characterized to date
is the pentagonal bipyramidal species [Mo(CN)7]4- 23
Conse-
.
quently, the preparation of [(Me3tacn)Mo(CN)3] from the triflate
complex depends critically on the number of equivalents of
cyanide added in the reaction.
Use of an excess of LiCN leads to formation of Li[(Me3-
tacn)Mo(CN)4] (3). This compound contains the seven-
coordinate complex [(Me3tacn)Mo(CN)4]1-, as revealed in the
crystal structure of 3‚2MeOH (Figure 1b). The complex adopts
a monocapped octahedral geometry, in which a cyanide ligand
caps and distends the triangular face opposite to the Me3tacn
ligand in the molybdenum coordination sphere. A slight
distortion of the molecule away from its maximal point group
symmetry of C3V (ignoring tacn ring conformations) appears to
originate from interactions between two of the cyanide ligands
and Li+ ions, which link the complexes into one-dimensional
chains. Selected mean interatomic distances and angles from
the crystal structure are listed in Table 1. Notably, there is some
variation in the Mo-C distances, which fall within the range
2.075(12)-2.129(11) Å and are slightly shorter than those
observed for [Mo(CN)7]4- (2.157-2.164 Å).23 At room tem-
perature, 3 exhibits an effective magnetic moment of 2.47 µB.
Surprisingly, this is higher than the moment of 1.80 µB measured
for anhydrous K4[Mo(CN)7], which clearly indicates a low-spin
S ) 1/2 electron configuration.24 The effective moment of 3 is
too low to be consistent with a high-spin S ) 3/2 electron
configuration, and yet a variable temperature measurement
yielded no evidence for spin-equilibrium behavior. Thus, the
moment may indicate the presence of some unidentified
paramagnetic impurity in samples of 3.
A computer program (ANISOFIT) for fitting magnetization data was
developed for use in estimating the zero-field splitting parameters of
high-spin clusters. The program is implemented on the MATLAB
platform and assumes that only the spin ground state of the molecule
is populated, that g is isotropic, and that the principal axes of D and g
coincide. Accordingly, it utilizes a spin Hamiltonian with the following
form.
2
Hˆ ) DSˆz2 + E(Sˆx2 +Sˆy ) + gµBS‚B
(3)
The program REPULSION18 is employed in generating a set of points,
{θ, φ}, evenly distributed over the surface of a sphere, which is then
used to perform numerical integration over the Boltzmann distribution.19
The calculated values of D, E, and g are optimized relative to the data
through a least-squares minimization routine based on the Nelder-
Mead method. Data at all applied magnetic fields were utilized
simultaneously. The ideas presented by Day were closely followed
throughout the course of its development.20 This program will be made
available over the Internet at http://alchemy.cchem.berkeley.edu.
Other Physical Measurements. Absorption spectra were measured
with a Hewlett-Packard 8453 spectrophotometer. Infrared spectra were
recorded on a Nicolet Avatar 360 FTIR spectrometer equipped with
an attenuated total reflectance accessory. Mass spectrometric measure-
ments were performed in the positive ion mode on a VG Quattro
(Micromass) spectrometer or on a Bruker Apex II 7 T actively shielded
FTICR mass spectrometer, both of which were equipped with an
analytical electrospray ion source instrument. Thermogravimetric
Related reactions employing fewer than 3 equiv of LiCN
result in products contaminated by higher-nuclearity molybde-
num-cyanide species. With the use of just 2.5 equiv, a dinuclear
complex precipitates from the reaction mixture and can then
be crystallized as [(Me3tacn)2Mo2(CN)5](BPh4) (5). As depicted
(16) Schmitt, E. A., Ph.D. Thesis, University of Illinois at Urbana-Champaign,
1995.
(21) Shores, M. P.; Berseth, P. A.; Long, J. R. Inorg. Synth., submitted for
publication.
(17) Borra´s-Almenar, J. J.; Clemente-Juan, J. M.; Coronado, E.; Tsukerblat, B.
S. J. Comput. Chem. 2001, 22, 985.
(22) Ryu, C. K.; Lessard, R. B.; Lynch, D.; Endicott, J. F. J. Phys. Chem. 1989,
93, 1752.
(18) Bak, M.; Nielsen, N. C. J. Magn. Reson. 1997, 125, 132.
(19) (a) Vermaas, A.; Groeneveld, W. L. Chem. Phys. Lett. 1974, 27, 583. (b)
Marathe, V. R.; Mitra, S. Chem. Phys. Lett. 1974, 27, 103.
(20) Day, E. P. Methods Enzymol. 1993, 227, 437.
(23) Hursthouse, M. B.; Malik, K. M. A.; Soares, A. M.; Gibson, J. F.; Griffith,
W. P. Inorg. Chim. Acta 1980, 45, 81.
(24) Rossman, G. R.; Tsay, F.-D.; Gray, H. B. Inorg. Chem. 1973, 12, 824.
9
J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002 2283

A R T I C L E S
Shores et al.
Table 1. Selected Mean Interatomic Distances (Å) and Angles
(deg) for the Mo Complexes in the Structures of
[(Me3tacn)Mo(CN)3]‚H2O (2‚H2O), Li[(Me3tacn)Mo(CN)4]‚2MeOH
(3‚2MeOH), and [(Me3tacn)Mo(O)(CN)2]‚H2O (4‚H2O)a
[(Me3tacn)Mo(CN)3]
[(Me3tacn)Mo(CN)4]1-
[(Me3tacn)Mo(O)(CN)2]
Mo-C
Mo-N
2.15(1)
2.227(6)
2.11(1)
2.229(3)
2.14(2)
2.23(2)b
2.403(9)c
1.71(4)
1.14(2)
176(1)
Mo-O
C-NCN
Mo-C-N
C-Mo-C
1.16(1)
176.8(5)
91(2)
1.16(1)
177(2)
71(5)d
91(2)
109(12)e
84(5)e
C-Mo-N
94(2)
172(1)
89(4)
134(10)d
160.4(7)
99.3(9)
76(2)
99(2)
172(1)
C-Mo-O
N-Mo-N
N-Mo-O
79.3(1)
76.9(7)
a NCN indicates a N atom in a cyanide ligand. b N atoms located cis to
the O atom. c N atom located trans to the O atom. d Angles involving atom
C(1). e Angles not involving atom C(1).
Figure 2. Structure of the [(Me3tacn)2Mo2(CN)5]1+ cluster in 5, showing
40% probability ellipsoids. H atoms are omitted for clarity. The bridging
cyanide ligand is disordered between two orientations: the one depicted
and one in which the positions of atoms C(1) and N(1) are interchanged.
Selected interatomic distances (Å) and angles (°): Mo(1)-C(1) 2.020(5),
mean of other Mo-C 2.15(1), Mo(2)-N(1) 2.029(6), mean Mo-Ntacn
2.220(10), C(1)-N(1) 1.181(7), mean of other C-NCN 1.11(2), mean Mo-
C-N 177(1), mean C-Mo-C 91.3(9), C(4)-Mo(2)-N(1) 92.2(2), C(5)-
Mo(2)-N(1) 92.1(2), mean C-Mo-Ntacn 94(1), 172(1), N(1)-Mo(2)-
N(9) 95.8(2), N(1)-Mo(2)-N(10) 94.1(2), mean Ntacn-Mo-Ntacn 79.6(3).
listed in the figure legend. Significantly, the C-N distances
within the terminal cyanide ligands are anomalously short. We
attribute this phenomenon to the presence of a small amount of
compositional disorder in the crystal, in which a chloride
ligandspresumably originating from the LiCl used to prepare
LiCN‚DMFsis occasionally present in place of a cyanide
ligand. The effects of such disorder have been studied system-
atically for a series of crystals of composition [HB(3-Butpz)3]-
Zn(CN)1-xClx,25 and are in good agreement with our own results.
Furthermore, such a conclusion is supported by the slight
discrepancies in the elemental analysis of 5, as well as by the
observation of a minor peak corresponding to [(Me3tacn)2-
Mo2(CN)4Cl]1+ in the electrospray mass spectrum of the
compound. Irrespective of the disorder, certain aspects of the
crystal structure suggest the presence of strong π interactions
between the molybdenum centers and the bridging cyanide
ligand. The slightly elongated C-N and short Mo-C/N
distances associated with the cyanide bridge are consistent with
Figure 1. Structures of the mononuclear complexes [(Me3tacn)Mo(CN)3]
(a), [(Me3tacn)Mo(CN)4]1- (b), and [(Me3tacn)Mo(O)(CN)2] (c) in 2‚H2O,
3‚2MeOH, and 4‚H2O, respectively, showing 40% probability ellipsoids.
H atoms are omitted for clarity.
in Figure 2, its structure features two octahedral MoIII centers,
each coordinated by a Me3tacn group, two terminal cyanide
ligands, and either the carbon or nitrogen end of a bridging
cyanide ligand. The central cyanide bridge is almost perfectly
linear, and the two Me3tacn ligands are disposed in an anti
conformation. Selected interatomic distances and angles are
(25) Yoon, Y.; Parkin, G. Inorg. Chem. 1992, 31, 1656.
9
2284 J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002

Nickel(II)−Molybdenum(III)−Cyanide Clusters
A R T I C L E S
π-back-bonding. In addition, the perpendicular metal-ligand
axes are essentially coparallel for the two molybdenum centers,
as reflected in the C(2)-Mo(1)-Mo(2)-C(5) and C(3)-Mo-
(1)-Mo(2)-C(4) torsion angles of 172.8° and 174.6°, respec-
tively. A very strong antiferromagnetic exchange interaction
between the MoIII centers can therefore be expected; however,
characterization of the magnetic properties of the complex awaits
its further purification.
Addition of precisely 3 equiv of LiCN to a DMF solution of
[(Me3tacn)Mo(CF3SO3)3] yields the desired product [(Me3tacn)-
Mo(CN)3] (2). The crystal structure of 2‚H2O shows the
octahedral complex (Figure 1a) to be isostructural with [(Me3-
tacn)Cr(CN)3];5b selected mean interatomic distances and angles
are listed in Table 1. As expected, the larger radius of
molybdenum leads to longer M-C and M-N bonds and smaller
N-M-N angles. Surprisingly, the Mo-C distances, which
range between 2.138(5) Å and 2.159(4) Å, are actually longer
than those observed in the seven-coordinate complex [(Me3tacn)-
Mo(CN)4]1-. Compound 2 is soluble in highly polar solvents
such as methanol, acetonitrile, water, DMF, and DMSO. Its
cyclic voltammogram in DMF shows a reversible reduction
wave corresponding to the [(Me3tacn)Mo(CN)3]0/1- couple at
E1/2 ) -1.895 V (∆Ep ) 128 mV) versus Cp2Fe/Cp2Fe+. In
contrast to the behavior of the complexes [(Me3tacn)MoX3] (X
) Cl, Br, I) in acetonitrile,12 no reversible oxidation event is
apparent. The effective moment of 2 at room temperature was
measured as 3.59 µB, which is slightly below the spin-only value
for an S ) 3/2 species and indicates a g factor of 1.85. This
result differs somewhat from the magnetic properties observed
for MoIII in the presence of a more rigorously octahedral ligand
field, such as in [MoCl6]3- (g ) 1.93) and [Mo(H2O)6]3+ (g )
1.95).26 Further investigation of complex 2 using high-field EPR
spectroscopy is underway, in an effort to determine both the
sign and magnitude of its zero-field splitting parameter D.27
Upon exposure to air, 2 and 3 are stable for several months
as solids, but gradually decompose over the course of several
days in solution. In both cases, [(Me3tacn)MoO(CN)2] (4) is
prominent among the initial oxidation products. This six-
coordinate MoIV species is recognizable by its pale blue color
and crystallizes from aqueous solution as 4‚H2O. Two inde-
pendent complexes are present in the crystal structure, and one
of these is depicted in Figure 1c; relevant mean interatomic
distances and angles are listed in Table 1. The short Mo-O
distances of 1.741(5) and 1.687(4) Å are consistent with the
expected double-bond character and result in longer trans Mo-N
distances of 2.397(5) and 2.410(5) Å, respectively. In all, the
structure is quite comparable to that of [(Me3tacn)MoOI2].28
Face-Centered Cubic Mo8Ni6(CN)24. In an exact parallel
of eq 1, [(Me3tacn)Mo(CN)3] reacts with nickel(II) bromide in
boiling aqueous solution to give [(Me3tacn)8Mo8Ni6(CN)24]Br12‚
27H2O (6).
Figure 3. Structure of the face-centered cubic [(Me3tacn)8Mo8Ni6(CN)24]12+
cluster in 6‚3H2O. H atoms are omitted for clarity. Black, crosshatched,
shaded, small white, and large white spheres represent Mo, Ni, C, N, and
Br atoms, respectively. The cluster resides on a 3h symmetry site in the
crystal.
Table 2. Selected Mean Interatomic Distances (Å) and Angles
12+
(deg) for the Face-Centered Cubic [(Me3tacn)8M8Ni6(CN)24
]
(M
) Cr, Mo) Clusters in the Structures of
[(Me3tacn)8Cr8Ni6(CN)24]Br12‚45H2O,5b
[(Me3tacn)8Mo8Ni6(CN)24]Br12‚30H2O (6‚3H2O), and
[(Me3tacn)8Mo8Ni6(CN)24]I12‚27H2O (7‚9H2O)a
M ) Cr
6‚3H O
7‚9H O
2
2
M-NCN
2.031(7)
1.873(9)
1.145(6)
2.066(5)
5.019(2)
6.97(2)
8.844
2.126(6)
1.86(1)
1.15(2)
2.175(8)
5.114(2)
7.07(5)
9.177
2.10(2)
1.883(5)
1.14(2)
2.181(8)
5.10(1)
7.06(3)
9.186
Ni-C
C-NCN
M-Ntacn
M‚‚‚Ni
M‚‚‚M
trans-Ni‚‚‚Ni
Ni‚‚‚Xb
2.802
2.797
2.900
NCN-M-NCN
M-NCN-C
C-Ni-C
88.0(3)
169.1(5)
89.6(3)
170.0(5)
177(2)
94.4(2)
176.6(3)
83.0(1)
88.3(3)
170.6(8)
89.5(4)
168.6(1)
176.1(9)
95.3(2)
174.3(2)
80.4(2)
88.7(7)
171(1)
89.3(4)
167(1)
177(1)
95.5(5)
174.1(3)
80.0(3)
Ni-C-N
NCN-M-Ntacn
Ntacn-M-Ntacn
a NCN and Ntacn indicate N atoms in cyanide and Me3tacn ligands,
respectively. b X ) Br or I.
Single crystals of 6‚3H2O were obtained by allowing an aqueous
solution of the product to slowly evaporate, and X-ray analysis
revealed the compound to be isostructural with [(Me3tacn)8Cr8-
Ni6(CN)24]Br12‚45H2O.5b Figure 3 depicts the structure of the
[(Me3tacn)8Mo8Ni6(CN)24]12+ cluster, which features a tightly
connected metal-cyanide cage with eight MoIII ions positioned
at the corners of a cube and six NiII ions situated slightly above
each cube face. An outer bromide anion forms a weak axial
interaction with each square-planar nickel center, and ignoring
Me3tacn conformations, the cluster closely conforms to its
maximal point group symmetry of Oh. Table 2 provides a list
of mean interatomic distances and angles, along with those of
8[(Me3tacn)Mo(CN)3] + 6[Ni(H2O)6]2+
f
[(Me3tacn)8Mo8Ni6(CN)24]12+ (4)
(26) (a) Bowers, K. D.; Owen, J. Rep. Prog. Phys. 1955, 18, 304. (b) Jacobsen,
C. J. H.; Pedersen, E. Inorg. Chem. 1991, 30, 4477.
(27) Sokol, J. J.; Saylor, C.; Shores, M. P.; Brunel, L.-C.; Long, J. R. Work in
progress.
(28) Bu¨rger, K. S.; Haselhorst, G.; Sto¨tzel, S.; Weyhermu¨ller, T.; Wieghardt,
K.; Nuber, B. J. Chem. Soc., Dalton Trans. 1993, 1987.
9
J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002 2285

A R T I C L E S
Shores et al.
[(Me3tacn)8Cr8Ni6(CN)24]12+ for comparison. The chief geo-
metric differences between the two clusters are a consequence
of the larger size of MoIII, which leads to an overall expansion
of the face-centered cubic cage. The expansion is perhaps most
obvious in the increase of the trans-Ni‚‚‚Ni distances from 8.844
to 9.177 Å, which inflates the internal cavity to a minimum
diameter of 6.0 Å (based on the van der Waals radius of
nickel).29 As observed in the analogous chromium-containing
clusters,5b this cavity appears to be empty: no build-up of
electron density attributable to guest water molecules is evident
in the crystal structure, and no water molecules are associated
with peaks corresponding to the intact cluster in the electrospray
mass spectrum. Note that access in and out of the cavity is
severely hindered by the methyl groups of the Me3tacn ligands.30
Interestingly, the reaction between [(Me3tacn)Mo(CN)3] and NiI2
in aqueous solution produces the [(Me3tacn)8Mo8Ni6(CN)24]I12‚
18H2O (7), the iodide salt of the same cluster. In contrast, the
analogous reaction employing [(Me3tacn)Cr(CN)3] affords
[(Me3tacn)8Cr8Ni5(CN)24]I10‚27H2O, wherein a NiII center is
missing from the cluster cage and an iodide anion is trapped
inside the cavity.5c The crystal structure of 7‚9H2O reveals no
significant differences from the geometry observed in the
bromide salt of the cluster (see Table 2).
Figure 4. Cyclic voltammogram of [(Me3tacn)8Mo8Ni6(CN)24]Br12‚27H2O
(6) in DMF. Potentials are reported relative to Cp2Fe/Cp2Fe+. As the
potential becomes more reducing, peaks occur at -1.240, -1.434, -1.516,
-1.660, -1.783, and -1.910 V, whereas, in the return scan, peaks occur
at -1.843, -1.720, -1.587, -1.492, -1.318, and -1.158 V.
anticipated for the more diffuse valence d orbitals. This issue
is obscured somewhat, however, by the possible contributions
from zero-field splitting.
Carrying out the analogous reaction with [(Me3tacn)Cr(CN)3]
(eq 1) in methanol at -40 °C permits isolation of a green
metastable precursor to the [(Me3tacn)8Cr8Ni6(CN)24]12+ cluster,
which was found to display magnetic properties consistent with
an S ) 18 ground state.5b Although this high-spin species could
not be crystallized at low temperature, it is thought to possess
the same face-centered cubic cage topology, albeit with
paramagnetic nickel centers and CrIII-C-N-NiII bridges lead-
ing to ferromagnetic coupling. Upon warming to room temper-
ature, the cyanide ligands gradually isomerize (as monitored
by infrared spectroscopy), and the ferromagnetic coupling is
destroyed. Our initial expectation was that by replacing the CrIII
ions in the cluster with softer MoIII ions, the driving force for
linkage isomerization would be reduced substantially, possibly
enabling us to crystallize the high-spin form of the cluster. While
the reaction between [(Me3tacn)Mo(CN)3] and nickel(II) bro-
mide at -40 °C in methanol indeed produces a green metastable
precursor, its subsequent conversion to the low-spin cyanide-
isomerized product is actually much more rapid. At room
temperature, infrared spectra show the transformation of the
green solid into orange compound 6 to be essentially complete
after just five minutes. Thus, it appears that substituting MoIII
for CrIII may lower the activation barrier for the linkage
isomerization reaction. Presumably, this too occurs as a
consequence of the more diffuse valence d orbitals of MoIII,
which help stabilize the side-bound cyanide unit in the putative
MoIII-(η2:η2-CN)-NiII transition state.
Inherent to the formation of [(Me3tacn)8Mo8Ni6(CN)24]12+ is
a thermally induced linkage isomerization, in which the cyanide
ligands reorient to give a MoIII-N-C-NiII connectivity. This
type of isomerization also occurs during formation of the
analogous chromium-containing cluster5b and has long been
known to occur in certain Prussian blue analogues.31 The process
is driven by thermodynamics, with the softer carbon end of
cyanide preferring to bind the softer NiII ion. Ligation by the
stronger field end of cyanide then causes the nickel centers to
adopt a square-planar coordination geometry and a diamagnetic
electron configuration. Indeed, the core structure of [(Me3-
tacn)8Mo8Ni6(CN)24]12+ can be viewed as containing six slightly
bowed square-planar [Ni(CN)4]2- units capping the faces of an
Mo8 cube. Of course, the loss of unpaired electrons at the nickel
sites has a dramatic impact on the magnetic behavior of 6 (see
Figure S2 in the Supporting Information). At 295 K, the value
of øMT is 14.34 cm3 K/mol, slightly below the spin-only value
of 15.00 cm3 K/mol expected for eight uncoupled S ) 3/2 metal
ions. The low øMT value indicates a g factor of 1.956, which is
higher than that observed for [(Me3tacn)Mo(CN)3]. As the
temperature is lowered, øMT remains constant down to ap-
proximately 50 K, whereafter it begins to decrease, reaching a
value of 7.14 cm3 K/mol at 2.0 K. Analogous to the situation
in [(Me3tacn)8Cr8Ni6(CN)24]12+ 5b
the decrease in øMT is at-
,
tributed to weak antiferromagnetic interactions between MoIII
centers through the LUMO orbitals of the intervening [Ni(CN)4]2-
units. The fact that the decrease becomes apparent at a higher
temperature for the molybdenum-containing cluster is consistent
with a slightly stronger exchange interaction, as might be
With MoIII replacing CrIII, the new [(Me3tacn)8Mo8Ni6-
(CN)24]12+ cluster exhibits some unusual redox chemistry. The
reduction event observed at E1/2 ) -1.895 V for the [(Me3-
tacn)Mo(CN)3] complex (see Figure S1 in the Supporting
Information) is manifested as a sequence of six closely spaced
reduction waves in the cyclic voltammagram of cluster com-
pound 6 in DMF. As shown in Figure 4, the waves all occur at
less negative potentials, with E1/2 ) -1.199 V (∆Ep ) 82 mV),
-1.376 V (∆Ep ) 128 mV), -1.504 V (∆Ep ) 24 mV), -1.624
V (∆Ep ) 73 mV), -1.752 V (∆Ep ) 63 mV), and -1.877 V
(∆Ep ) 67 mV) versus Cp2Fe/Cp2Fe+. Thus, each electron
(29) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(30) Pertinently, water is also not observed inside the cavity of an analogous
[(tach)8Cr8Ni6(CN)24]12+ (tach ) 1,3,5-triaminocyclohexane) cluster featur-
ing less sterically demanding outer ligands: Yang, J. Y.; Shores, M. P.;
Sokol, J. S.; Long, J. R., manuscript in preparation.
(31) (a) Shriver, D. F.; Shriver, S. A.; Anderson, S. E. Inorg. Chem. 1965, 4,
725. (b) Brown, D. B.; Shriver, D. F.; Schwartz, L. H. Inorg. Chem. 1968,
7, 77. (c) Brown, D. B.; Shriver, D. F. Inorg. Chem. 1969, 8, 37. (d) House,
J. E., Jr.; Bailar, J. C., Jr. Inorg. Chem. 1969, 8, 672. (e) Reguera, E.;
Bertra´n, J. F.; Nun˜ez, L. Polyhedron 1994, 13, 1619.
9
2286 J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002

Nickel(II)−Molybdenum(III)−Cyanide Clusters
A R T I C L E S
added to the cluster is noticeably affected by the presence of
any previously added electrons. The separations between
successive reduction waves indicate comproportionation con-
stants falling in the range Kc ) 100-1000, consistent with class
II mixed-valence behavior.32 Similar to the situation in Prussian
blue,33 electron delocalization in a mixed-valence MoII/MoIII
redox state of the cluster may therefore be expected to give
rise to ferromagnetic coupling via a double-exchange mecha-
nism. Accordingly, the one-electron reduced cluster [(Me3-
tacn)8Mo8Ni6(CN)24]11+ is predicted to have an S ) 23/2 ground
state. Efforts to produce such reduced forms of the cluster via
titration of an appropriate reductant are underway.
Linear NiMo2(CN)6. Ultimately, we envision using trans-
directing cyclam complexes in combination with tacn-ligated
corner units to assemble edge-bridged cubic clusters of the type
[(tacn)8(cyclam)12M12M′8(CN)24]x+. As yet, reactions targeting
such a speciessincluding efforts employing [(Me3tacn)Mo-
(CN)3]shave either failed to give the desired product or have
not led to single crystals suitable for a complete X-ray analysis.
However, certain of these attempts have been found to follow
the course of eq 2 above, resulting in isolation and structural
characterization of [(Me3tacn)2(cyclam)NiCr2(CN)6]2+, a linear
cluster consisting of a single edge fragment of the larger 20-
metal species.5b In close parallel, reactions between [(Me3tacn)-
Mo(CN)3] and the bromide, iodide, and perchlorate salts of
[(cyclam)Ni(H2O)2]2+ afford linear [(Me3tacn)2(cyclam)NiMo2-
(CN)6]2+ clusters, as observed in 9-11.
Figure 5. Structure of the linear clusters [R-(Me3tacn)2(cyclam)NiMo2-
(CN)6]2+ in 8‚2DMF (upper), [â-(Me3tacn)2(cyclam)NiMo2(CN)6]2+ in 11
(middle), and [(Me3tacn)2(cyclam)Ni-Mo2(O)2(CN)4]2+ in 12 (lower),
showing 40% probability ellipsoids. H atoms are omitted for clarity. The
upper and lower clusters reside on crystallographic inversion centers.
Selected interatomic distances (Å) and angles (°) from the structure of 12:
Mo(1)-C(1) 2.163(7), Mo(1)-C(2) 2.152(7), Mo(1)-O(1) 1.754(5), Ni-
(1)-N(1) 2.127(5), C(1)-N(1) 1.145(8), C(2)-N(2) 1.156(9), Mo(1)-N(3)
2.238(5), Mo(1)-N(4) 2.255(5), Mo(1)-N(5) 2.387(7), Ni(1)-N(6) 2.087-
(5), Ni(1)-N(7) 2.091(5), C(1)-Mo(1)-C(2) 88.6(2), C(1)-Mo(1)-O(1)
95.2(3), C(2)-Mo(1)-O(1) 100.0(3), Mo(1)-C(1)-N(1) 171.4(6), Mo-
(1)-C(2)-N(2) 178.2(7), Ni(1)-N(1)-C(1) 161.8(5), N(3)-Mo(1)-C(1)
94.2(2), N(4)-Mo(1)-C(1) 165.1(2), N(5)-Mo(1)-C(1) 89.9(2), N(6)-
Ni(1)-N(1) 89.8(2), N(7)-Ni(1)-N(1) 89.8(2), N(6)-Ni(1)-N(7) 94.4-
(2).
2[(Me3tacn)Mo(CN)3] + [(cyclam)Ni(H2O)2]2+
f
[(Me3tacn)2(cyclam)NiMo2(CN)6]2+ (5)
The compounds are isolated cleanly by employing the 2:1 Mo:
Ni stoichiometry of eq 5, and are stable in air in the solid state.
Interestingly, the influence of the counteranions and solvate
molecules on the crystal structure of the product can play a
significant role in determining its magnetic properties.
Conducting eq 5 with [(cyclam)NiI2] in acetonitrile instead
of water produces [R-(Me3tacn)2(cyclam)NiMo2(CN)6]I2 (8) in
high yield. As crystallized from DMF, this compound features
the usual linear cluster connectivity, wherein two [(Me3tacn)-
Mo(CN)3] complexes coordinate a central [(cyclam)Ni]2+ unit
in a trans geometry (see Figure 5, upper). The cluster resides
on an inversion center, such that, with respect to its ap-
proximately linear [Mo-CN-Ni-NC-Mo]6+ core, the two
Me3tacn ligands are disposed in an anti conformation (here
denoted as the R isomer). The minimum C-Mo‚‚‚Mo-C torsion
angle of 90.6° provides a quantitative measure of the conforma-
tion, which, not surprisingly, can be influenced appreciably by
crystal packing forces. For example, the crystal structure of
[(Me3tacn)2(cyclam)NiCr2(CN)6](ClO4)2‚2H2O5b features an analo-
gous cluster, wherein the Me3tacn ligands are twisted toward
each other to give a minimum C-Cr‚‚‚Cr-C torsion angle of
34.1°. Selected mean interatomic distances and angles from the
two structures are compared in Table 3. Aside from the usual
differences arising from the larger size of MoIII, the most
noteworthy distinction between the two cluster geometries lies
in the Ni-NCN-C angles, which are more linear in the
conformation adopted by the chromium-containing species.
Substitution of MoIII for CrIII in the linear NiM2(CN)6 cluster
motif leads to stronger magnetic exchange coupling and
increased magnetic anisotropy. The magnetic properties of
[(Me3tacn)2(cyclam)NiCr2(CN)6](ClO4)2‚2H2O are consistent
with an S ) 4 ground state stemming from the predicted8
2
ferromagnetic coupling between the CrIII (t2g3) and NiII (t2g6eg )
centers.5b A fit to the susceptibility data gave g ) 2.00 and an
exchange coupling constant of J ) 10.9 cm-1, whereas the
magnetization behavior showed no appreciable zero-field
splitting.5b In contrast, zero-field splitting is evident in the
magnetization data obtained for [R-(Me3tacn)2(cyclam)NiMo2-
(CN)6]I2 (8), as recognizable in Figure 6 from the downturn of
the curves with increasing H/T. Assuming an S ) 4 ground
state and negligible population of excited states at the temper-
atures probed, the data were fit using ANISOFIT to give zero-
field splitting parameters of D ) 0.44 cm-1 and E ) 0.13 cm-1
with g ) 1.81. Note that the sign of D is not reliably established
(32) (a) Robin, M. B.; Day, P. AdV. Inorg. Chem. Radiochem. 1967, 10, 247.
(b) Richardson, D. E.; Taube, H. Inorg. Chem. 1981, 20, 1278. (c) Creutz,
C. Prog. Inorg. Chem. 1983, 30, 1. (d) Kaim, W.; Klein, A.; Glo¨ckle, M.
Acc. Chem. Res. 2000, 33, 755.
(33) Mayoh, B.; Day, P. J. Chem. Soc., Dalton Trans. 1976, 1483.
9
J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002 2287

A R T I C L E S
Shores et al.
Table 3. Selected Mean Interatomic Distances (Å) and Angles
(deg) for the Linear [(Me3tacn)2(cyclam)NiM2(CN)6]2+ (M ) Cr, Mo)
Clusters in the Structures of
of øMT with temperature observed for 8 is plotted in Figure 6.
At room temperature, it lies very near the spin-only value of
4.75 cm3 K/mol expected for one S ) 1 and two S ) 3/2 ions
in the absence of magnetic coupling. Consistent with ferromag-
netic coupling, øMT rises monotonically with decreasing tem-
perature before reaching a maximum of 7.74 cm3 K/mol at 16
K. The subsequent drop as the temperature continues to decrease
is attributed to zero-field splitting. Figure 6 shows the best fit
to the data above 16 K, which was obtained using MAGFIT
3.1 with a single pairwise exchange parameter and an exchange
Hamiltonian of the following form.
[(Me3tacn)2(cyclam)NiCr2(CN)6](ClO4)2‚2H2O,5b
[R-(Me3tacn)2(cyclam)NiMo2(CN)6]I2‚2DMF (8‚2DMF),
[â-(Me3tacn)2(cyclam)NiMo2(CN)6]I2‚7H2O (9‚H2O),
[R-(Me3tacn)2(cyclam)NiMo2(CN)6]Br2‚6H2O (10), and
[â-(Me3tacn)2(cyclam)NiMo2(CN)6](ClO4)2‚2H2O (11)a
M ) Cr
8‚2DMF
9‚H O
2
10
11
M-C
2.068(9) 2.16(2) 2.14(2) 2.13(2) 2.10(8)
2.108(8) 2.152(3) 2.107(7) 2.106(3) 2.113(7)
1.15(1) 1.12(3) 1.16(2) 1.17(3) 1.15(2)
2.107(3) 2.237(5) 2.233(3) 2.232(9) 2.22(2)
2.072(3) 2.068(7) 2.078(6) 2.077(6) 2.052(6)
89(2)
176(2) 174(4) 176(3) 176.0(5) 176(3)
177.4(1) 180 179.6(4) 180 177.5(2)
170(1) 163.6(3) 171.1(7) 164.8(3) 172(4)
94(2) 93(2) 95.4(9) 95(2) 94(2)
Ni-NCN
C-NCN
M-N
Ni-Ncyclam
C-M-C
M-C-NCN
93(4)
89(2)
91(1)
92(3)
Hˆ ) -2J[SˆNi‚(SˆMo(1) + SˆMo(2))]
(6)
N
CN-Ni-NCN
Ni-NCN-C
N-M-C
This fit gives g ) 1.80 and a coupling constant of J ) 17.6
cm-1. Thus, replacing CrIII with MoIII in the cluster appears to
increase the strength of the magnetic exchange coupling by as
much as 60%. Significantly, including a second exchange
parameter in eq 6 to account for long-range coupling between
the two molybdenum centers did not improve the fit and did
not reproduce the drop in øMT at lower temperatures.
175(1) 171(2) 173(1) 172(2) 170.9(8)
83.6(3) 79.6(2) 79.5(3) 79.3(2) 79.2(7)
N-M-N
N
cyclam-Ni-NCN
90(1)
90(1)
90(1)
90.0(7) 90(1)
Ncyclam-Ni-Ncyclam
85.2(6) 85.9(2) 85.4(1) 86.0(1) 85.2(5)
94.8(6) 94.1(2) 94.6(3) 94.1(1) 94.9(5)
minimum C-M‚‚‚M-C 34.1
90.6
16.7
87.5
11.4
a NCN and Ncyclam indicate N atoms in cyanide and cyclam ligands,
respectively.
The iodide salt of [(Me3tacn)2(cyclam)NiMo2(CN)6]2+ crys-
tallizes from water as [â-(Me3tacn)2(cyclam)NiMo2(CN)6]I2‚
7H2O (9‚H2O), featuring a different conformation of the linear
cluster. The geometry of this â isomer approximates that
depicted in the middle of Figure 5 and differs from the R isomer
observed in 8‚2DMF (Figure 5, upper) by virtue of having its
Me3tacn ligands twisted away from the anti configuration. The
extent of the twist is such that two of the cyanide ligands are
oriented in essentially the same direction, resulting in a
minimum C-Mo‚‚‚Mo-C torsion angle of 16.7°. Accordingly,
the conformation of the â isomer is closer to that of the
chromium-containingclusterin[(Me3tacn)2(cyclam)NiCr2(CN)6]-
(ClO4)2‚2H2O,5b and it exhibits more linear Ni-NCN-C angles
than the R isomer (see Table 3). The magnetic behavior of 9
differs from that of 8 primarily in the magnitude of the zero-
field splitting parameters. The best fit to the magnetization data
gives g ) 1.77, D ) -0.56 cm-1, and E ) 0.0029 cm-1, while
using the exchange Hamiltonian in eq 6, the best fit to the
susceptibility data at T g 14 K gives g ) 1.80 and J ) 17.0
cm-1 35
NiMo2(CN)6]Br2‚6H2O (10) is very similar, with the best fit to
the magnetization data yielding g ) 1.80, D ) -0.72 cm-1
and E ) -0.055 cm-1, and the best fit to the susceptibility
data (T g 12 K) indicating g ) 1.83 and J ) 17.3 cm-1 35
.
Interestingly, the behavior of [R-(Me3tacn)2(cyclam)-
,
.
Thus, it seems that, despite altering the Ni-NCN-C angles, the
different cluster conformations have little effect on the strength
of the magnetic exchange coupling. The conformation does,
however, appear to have an influence on the magnetic anisot-
ropy. If the sign and magnitude of these D values are correct,
then 9 and 10 can be anticipated to behave as single-molecule
magnets with spin reversal barriers of 9 and 12 cm-1, respec-
tively.
Quite distinct magnetic behavior is observed for the perchlo-
rate salt of the linear cluster, which crystallizes from aqueous
solution as [â-(Me3tacn)2(cyclam)NiMo2(CN)6](ClO4)2‚2H2O
(11). With a minimum C-Mo‚‚‚Mo-C torsion angle of 11.4°,
the conformation adopted by the cluster in this compound
Figure 6. Magnetic behavior of [R-(Me3tacn)2(cyclam)NiMo2(CN)6]I2 (8).
Data represented by circles, squares, diamonds, and triangles were measured
in an applied field of 1, 10, 25, and 55 kG, respectively. Solid lines represent
calculated fits to the data; see text for details.
from such powder measurements;34 generally, a comparable fit
with the opposite sign for D can also be obtained. The variation
(35) Figures showing these data together with the corresponding fits are presented
in the Supporting Information.
(34) Kahn, O. Molecular Magnetism; VCH: New York, 1993.
9
2288 J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002

Nickel(II)−Molybdenum(III)−Cyanide Clusters
A R T I C L E S
Neglecting any contribution from zero-field splitting, the fit
matches the data well (see Figure 7) and gives g ) 1.79, J )
14.9 cm-1, and J′ ) -1.9 cm-1. Hence, the ferromagnetic
coupling between MoIII and NiII centers within the cluster
appears to be slightly diminished relative to that in 8-10, and
the reduction in øMT at low temperatures is attributed to the
weak antiferromagnetic coupling between MoIII and NiII centers
situated in neighboring clusters. Hydrogen-bonded pathways
have been invoked to account for long-range magnetic ordering
in other metal-cyanide compounds,6h,36 but, to our knowledge,
this type of supramolecular pairing has not previously been
observed.
If, in the course of preparing [(Me3tacn)2(cyclam)NiMo2-
(CN)6]2+, the reaction solution is allowed to stand in air for an
extended period, partial oxidation of [(Me3tacn)Mo(CN)3]
occurs, leading to contamination of the product with [(Me3tacn)2-
(cyclam)NiMo2(O)2(CN)4]2+. Formation of this oxidized species
is facilitated by using an excess of [(cyclam)Ni(H2O)2]2+, which
potentially aids in the release of cyanide from the molybdenum
complex. As crystallized in [(Me3tacn)2(cyclam)NiMo2(O)2-
(CN)4]I2‚6H2O (12), its structure consists of the usual linear
cluster arrangement, albeit with one terminal cyanide ligand on
each molybdenum center replaced by an oxo group (see Figure
5, lower). The conformation of the cluster is comparable to that
adopted by the R isomer of the NiMo2(CN)6 cluster in 8‚2DMF
(Figure 5, upper). Selected interatomic distances and angles are
listed in the legend of Figure 5; overall, the coordination
geometry of the MoIV centers is similar to that found in [(Me3-
tacn)Mo(O)(CN)2] (see Table 1). The magnetic properties of
12 have not yet been investigated.
Figure 7. Magnetic behavior of [â-(Me3tacn)2(cyclam)NiMo2(CN)6](ClO4)2‚
2H2O (11), as measured at 1000 G. The solid line represents the calculated
fit to the data.
Zigzag Ni3Mo2(CN)6. The presence of terminal cyanide
ligands in the linear [(Me3tacn)2(cyclam)NiMo2(CN)6]2+ cluster
suggests the possibility of utilizing it as a platform for attaching
additional magnetically coupled metal ions. Unfortunately,
however, infrared spectra indicate that the cluster dissociates
upon dissolution. Nonetheless, such constructs can be realized
by increasing the number of equivalents of [(cyclam)Ni-
(H2O)2]2+ employed in eq 5. With bromide as a counterion,
using a large excess of the nickel complex in aqueous solution
prompts formation of a five-metal species, in accord with the
following reaction.
Figure 8. Hydrogen-bonding interactions between two linear clusters in
the structure of [â-(Me3tacn)2(cyclam)NiMo2(CN)6](ClO4)2‚1.5H2O (11).
Black, crosshatched, shaded, large white, and small white spheres represent
Mo, Ni, C, N, and H atoms, respectively. For clarity, only the H atoms
involved in forming the postulated Mo-C-N‚‚‚H-N-Ni exchange
pathways are depicted. Associated with this pathway are the interatomic
distances (Å): N‚‚‚H 2.449, N‚‚‚N 3.144, Mo‚‚‚Ni 7.197. The two clusters
are related by an inversion center in the crystal.
(Figure 5, middle) closely resembles that in the structure of 9‚
H2O. However, as shown in Figure 7, the magnetic susceptibility
data for 11 differ considerably from the results obtained for
8-10. Although the value of øMT at room temperature is nearly
identical for all four compounds, its steady rise with decreasing
temperature is heavily attenuated in 11: a lower maximum value
of 5.96 cm3K/mol is achieved at the higher temperature of 40
K. The origin of this difference likely traces to the crystal
structure of 11, which is the only one to display hydrogen
bonding contacts directly between cluster units. Here, somewhat
long hydrogen bonds between a N-H group of a cyclam ligand
in one cluster and a terminal cyanide ligand in another serve to
pair the clusters up into dimers, as illustrated in Figure 8. By
assuming that the resultant Mo-C-N‚‚‚H-N-Ni connections
provide a second pathway for magnetic superexchange, the
following exchange Hamiltonian was used to generate a fit to
the susceptibility data.
2[(Me3tacn)Mo(CN)3] + 3[(cyclam)Ni(H2O)2]2+
f
[(Me3tacn)2(cyclam)3(H2O)2Ni3Mo2(CN)6]6+ (8)
Approximately an extra 7 equiv of [(cyclam)Ni(H2O)2]2+ is
required to obtain [(Me3tacn)2(cyclam)3(H2O)2Ni3Mo2(CN)6]Br6‚
9H2O (13) as the only molybdenum-containing product. Reduc-
ing the reaction solution to dryness affords an intimate mixture
of 13 and [(cyclam)NiBr2], which, owing to their solubility
properties, are not readily separated. Prior to drying, crystals
of 13‚5H2O are present in the mixture. An X-ray analysis
revealed the zigzag cluster depicted at the top of Figure 9,
(36) (a) Ferlay, S.; Mallah, T.; Vaissermann, J.; Bartolome´, F.; Veillet, P.;
Verdaguer, M. Chem. Commun. 1996, 2481. (b) Kou, H.-Z.; Liao, D.-Z.;
Cheng, P.; Jiang, Z.-H.; Yan, S.-P.; Wang, G.-L.; Yao, X.-K.; Wang, H.-
G. J. Chem. Soc., Dalton Trans. 1997, 1503. (c) Van Langenberg, K.;
Batten, S. R.; Berry, K. J.; Hockless, D. C. R.; Moubaraki, B.; Murray, K.
S. Inorg. Chem. 1997, 36, 5006. (d) Marvilliers, A.; Parsons, S.; Rivie`re,
E.; Audie`re, J.-P.; Mallah, T. Chem. Commun. 1999, 2217. (e) Yan, B.;
Wang, S.; Chen, Z. Monatsh. Chem. 2001, 132, 305.
Hˆ ) -2{J[SˆNi(1)‚(SˆMo(1) + SˆMo(2)) + SˆNi(2)‚(SˆMo(3)
+
SˆMo(4))] + J′(SˆNi(1)‚SˆMo(3) + SˆNi(2)‚SˆMo(2))} (7)
9
J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002 2289

A R T I C L E S
Shores et al.
Figure 10. Magnetic behavior of [(Me3tacn)2(cyclam)3(H2O)2Ni3Mo2(CN)6]-
Br6‚9H2O (13), as measured at 1000 G. The solid line represents the
calculated fit to the data.
NiBr2] under identical conditions were then subtracted to extract
just that component of the data arising from 13. The magnetiza-
tion data indicate the presence of zero-field splitting; however,
attempts at generating a fit were complicated by the apparent
population of low-lying excited states. The magnetic susceptibil-
ity data (see Figure 10) are indeed consistent with a reduction
in the strength of the exchange coupling relative to that observed
in 8-10. At room temperature, the value of øMT lies slightly
below the spin-only value of 6.75 cm3 K/mol expected for three
S ) 1 and two S ) 3/2 ions with g ) 2.00. As the temperature
is lowered, øMT increases monotonically, until reaching a
maximum of 14.11 cm3 K/mol at 9 K. This behavior is
consistent with the presence of ferromagnetic coupling to give
an S ) 6 ground state, which is further supported by the high-
field magnetization data. When assuming that the strength of
the magnetic coupling between each cyanide-bridged MoIII-
NiII pair is identical, attempts to simulate the susceptibility data
failed to yield satisfactory results. Consequently, a model
employing two different coupling constantssone for coupling
with the central Ni atom and the other for coupling with either
of the two outermost Ni atomsswas adopted with use of the
following exchange Hamiltonian.
Figure 9. (Upper) Structure of the zigzag [(Me3tacn)2(cyclam)3(H2O)2-
Ni3Mo2(CN)6]6+ cluster in 13‚5H2O, showing 40% probability ellipsoids.
H atoms are omitted for clarity. The molecule resides on an inversion center
in the crystal. Selected mean interatomic distances (Å) and angles (°):
Mo-C 2.13(5), Ni-NCN 2.103(8), C-NCN 1.17(3), Mo-N 2.24(1), Ni-
Ncyclam 2.072(3), Ni-O 2.221, C-Mo-C 90(3), Mo-C-N 172(3), Ni-
NCN-C 173(3), N-Mo-C 95(2), 173(3), N-Mo-N 79.7(3), Ncyclam-Ni-
NCN 91(1), Ncyclam-Ni-Ncyclam 85.5(2), 94.5(7), NCN-Ni-O 177.4,
Ncyclam-Ni-O 89(3). (Middle and lower) Portions of the one-dimensional
[(Me3tacn)(cyclam)NiMo(CN)3]2+ chains in the structures of 14 (middle)
and 15 (lower). H atoms are omitted for clarity. Black, crosshatched, shaded,
and white spheres represent Mo, Ni, C, and N atoms, respectively. In the
lower structure, crystallographic inversion centers are located at the Ni atoms
running along the middle of the chain.
Hˆ ) -2{J[SˆNi(1)‚(SˆMo(1) + SˆMo(2))] + J′(SˆNi(2)‚SˆMo(1)
+
SˆNi(3)‚SˆMo(2))} (9)
As shown in Figure 10, reasonable agreement with the higher
temperature data is obtained with J ) 4.0 cm-1, J′ ) 8.5 cm-1
,
consisting of a linear [(Me3tacn)2(cyclam)NiMo2(CN)6]2+ unit
capped on either end by a [(cyclam)Ni(H2O)]2+ moiety. With a
minimum C-Mo‚‚‚Mo-C torsion angle of 92.3°, the central
linear unit has a conformation similar to that of the R isomer in
8‚2DMF (Figure 5, upper). A comparison of metric parameters
(see Figure 9 legend and Table 3), however, shows the zigzag
cluster to have a more linear bridging arrangement. No hydrogen
bonding contacts directly between clusters are evident in the
crystal structure.
To probe the magnetic properties of the zigzag cluster,
measurements were carried out on a sample containing 13
together with precisely 7.13 equiv of [(cyclam)NiBr2]. Results
obtained from independent measurements of pure [(cyclam)-
and g ) 1.83. Hence, it appears that attaching two NiII centers
to the [(Me3tacn)Mo(CN)3] unit can cause a substantial reduction
in the strength of the magnetic exchange coupling. Although
the magnitude of the reduction observed in this case is rather
surprising, such a trend might be expected since coordination
of a metal at the nitrogen end of a second cyanide ligand affects
the molybdenum-based orbital that ultimately participates in both
superexchange pathways. In addition, we note that the smaller
coupling constant is associated with the central NiII ion, which
is involved in exchange interactions with two MoIII centers,
rather than just one.
NiMo(CN)3 Chains. Reactions related to eqs 5 and 8 above,
but employing an equimolar ratio of reactants, generate com-
9
2290 J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002

Nickel(II)−Molybdenum(III)−Cyanide Clusters
A R T I C L E S
Table 4. Selected Mean Interatomic Distances (Å) and Angles
(deg) for the One-Dimensional Chains in the Structures of
[(Me3tacn)(cyclam)NiMo(CN)3]I2‚4H2O (14) and
[(Me3tacn)(cyclam)NiMo(CN)3](ClO4)2‚1.5H2O (15)a
14
15
Mo-C
2.14(2)
2.12(1)
1.16(1)
2.227(5)
2.06(1)
89(3)
173(1)
178.1(3)
171.6(2)
95(3)
2.09(8)
2.12(3)
1.18(2)
2.24(1)
2.07(2)
91(2)
173(4)
179(2)
172(3)
94(2)
Ni-NCN
C-NCN
Mo-Ntacn
Ni-Ncyclam
C-Mo-C
Mo-C-NCN
NCN-Ni-NCN
Ni-NCN-C
Ntacn-Mo-C
172.4(2)
79.8(3)
90(1)
85.75(7)
94.3(9)
171(2)
79.4(4)
90(1)
85.1(2)
94.9(5)
Ntacn-Mo-Ntacn
Ncyclam-Ni-NCN
Ncyclam-Ni-Ncyclam
Figure 11. Magnetic behavior of the one-dimensional chain compound
[(Me3tacn)(cyclam)NiMo(CN)3](ClO4)2‚1.5H2O (15), as measured at 1000
G. Simulations are shown for hypothetical, cyclic [(Me3tacn)(cyclam)NiMo-
(CN)3]n2n+ species with n ) 2 (short dashes), 3 (long dashes), and 4 (solid
line).
a NCN, Ntacn, and Ncyclam indicate N atoms in cyanide and Me3tacn, and
cyclam ligands, respectively.
pounds containing one-dimensional [(Me3tacn)(cyclam)NiMo-
ferromagnetic coupling, øMT rises monotonically as the tem-
perature decreases, until achieving a maximum of 34.33 cm3
K/mol at 6 K. Attempts to simulate these data employed the
usual approach of calculating the behavior for a sequence of
cyclic oligomers of increasing size.34 Calculations were per-
formed for cyclic [(Me3tacn)(cyclam)NiMo(CN)3]n2n+ specieswith
n ) 2-4, using an exchange Hamiltonian of the following form.
(CN)3]2+ chains.
[(Me3tacn)Mo(CN)3] + [(cyclam)Ni(H2O)2]2+
f
[(Me3tacn)(cyclam)NiMo(CN)3]2+ (10)
Using iodide as the counterion leads to formation of [(Me3-
tacn)(cyclam)NiMo(CN)3]I2‚4H2O (14), featuring the zigzag
chain displayed in the middle of Figure 9. The structure is a
simple extension of the zigzag cluster shown at the top of Figure
9, with every nickel cyclam complex coordinated axially by
two [(Me3tacn)Mo(CN)3] units. Accordingly, as listed in Table
4, its mean interatomic distances and angles are in close
agreement with those observed in the structure of 13‚5H2O (see
Figure 9 legend). Carrying out reaction 10 with perchlorate as
the counterion in place of iodide produces [(Me3tacn)(cyclam)-
NiMo(CN)3](ClO4)2‚1.5H2O (15), containing an isomeric chain
with the more sinuous structure depicted at the bottom of Figure
9. The essential difference between the two chains is subtle,
lying only in the direction of propagation at every fourth
molybdenum center; as compared in Table 4, they possess very
similar metric parameters. Thus, as for linear [(Me3tacn)2-
(cyclam)NiMo2(CN)6]2+ cluster conformations, the chain struc-
ture adopted appears to be highly sensitive to the packing
influences of the counterions and solvate molecules. Indeed,
although all of the linear NiMo2(CN)6 segments in 14 have the
R isomer conformation, the analogous segments in 15 alternate
between R and â conformations. The latter structure in particular
suggests that, with the right choice of counterion, a cyclized
chain consisting of a discrete [(Me3tacn)4(cyclam)4Ni4Mo4-
(CN)12]8+ square with all edges in a â conformation might be
produced. Note, however, that none of the structures containing
[(Me3tacn)Mo(CN)3] complexes connected through nickel cy-
clam units exhibit Me3tacn ligands in the fully eclipsed
orientation required for an edge-bridged cubic cluster.
Hˆ ) -2J[SˆNi(1)‚(SˆMo(1) + SˆMo(n)) +
n
SˆNi(i)‚(SˆMo(i-1) + SˆMo(i))] (11)
∑
i)2
For the larger cycles, the best agreement with the higher
temperature data was obtained with g ) 1.95 and J ) 13.1 cm-1
suggesting similar parameters for the infinite chain. The
,
corresponding results from simulations of the data for 14 gave
g ) 1.96 and J ) 14.9 cm-1 35 Here again, attaching two NiII
.
centers to the [(Me3tacn)Mo(CN)3] unit appears to cause a
reduction in the strength of the magnetic exchange coupling,
albeit to a much lesser extent than observed in 13.
Outlook
The foregoing results demonstrate the feasibility of replacing
CrIII with MoIII as a means of increasing both the strength of
the magnetic exchange coupling and the magnetic anisotropy
in a metal-cyanide cluster. This type of substitution can likely
be extended to the many other cyanide-bridged clusters and
solids containing magnetically coupled CrIII centers. Indeed,
[(Me3tacn)Mo(CN)3] has already been shown to replace the
[(Me3tacn)Cr(CN)3] units in the trigonal prismatic cluster [(Me3-
tacn)6MnCr6(CN)18]2+ possessing an S ) 13/2 ground state.5d,37
Similar replacements involving WIII or ReIV instead of MoIII
are expected to further increase the exchange coupling and
anisotropy. The possibility of incorporating these and other
paramagnetic ions of second- and third-row transition-metals
into metal-cyanide clusters with a high-spin ground state is
currently under investigation. Ultimately, it is hoped that such
As might be expected, 14 and 15 display similar magnetic
properties. Figure 11 shows the variation of øMT with temper-
ature for 15. At room temperature, it lies slightly above the
spin-only value of 2.875 cm3 K/mol expected for noninteracting
S ) 1 and S ) 3/2 ions with g ) 2.00. Consistent with
(37) Hee, A. G.; Sokol, J. J.; Long, J. R. Work in progress.
9
J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002 2291

A R T I C L E S
Shores et al.
an approach will lead to new single-molecule magnets capable
of storing data at more practical temperatures.
magnetometers, and Prof. J. Arnold for use of the thermogravi-
metric analysis instrument.
Acknowledgment. This research was funded by NSF Grant
No. CHE-0072691, the Camille and Henry Dreyfus Foundation,
the Alfred P. Sloan Foundation, the Hellman Family Faculty
Fund, and the University of California, Berkeley. We thank NSF
for providing J.J.S. with a predoctoral fellowship, Elf-Atochem
for partial support of M.P.S., Dr. C. Crawford and Unilever for
a donation of Me3tacn, Profs. E. Coronado and D. N. Hen-
drickson for supplying software used to simulate magnetic data,
Profs. J. K. McCusker and D. Gatteschi for helpful discussions,
Profs. A. M. Stacy and A. Zettl for use of the SQUID
Supporting Information Available: Cyclic voltammogram
of 2 in DMF. Plots and fits of the magnetization data for 9 and
10 and of the magnetic susceptibility data for 6, 9, 10, and 14.
X-ray structural information for 2-15, including tables of crystal
and refinement data, atomic positional and thermal parameters,
and interatomic distances and angles (PDF). An X-ray crystal-
lographic file (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
JA011645H
9
2292 J. AM. CHEM. SOC. VOL. 124, NO. 10, 2002