A deliberate approach for the syntheses of heterometallic supramolecules containing dimolybdenum Mo24+ species coordinated to other metal units

Article abstract of DOI:10.1039/b617932k

Two compounds with quadruply bonded Mo₂⁴⁺ species having isonicotinate ligands bound through the carboxylate group have been designed to act as anglers by luring metal-containing Lewis acids to bind to the N-pyridyl group. The corner

Full text of DOI:10.1039/b617932k

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A deliberate approach for the syntheses of heterometallic supramolecules
4
+
containing dimolybdenum Mo species coordinated to other metal units†
2
F. Albert Cotton,‡ Jia-Yi Jin, Zhong Li, Chun Y. Liu* and Carlos A. Murillo*a
a
a
a
a,b
Received 12th December 2006, Accepted 12th March 2007
First published as an Advance Article on the web 2nd April 2007
DOI: 10.1039/b617932k
4
+
Two compounds with quadruply bonded Mo
2
species having isonicotinate ligands bound through the
carboxylate group have been designed to act as anglers by luring metal-containing Lewis acids to bind
to the N-pyridyl group. The corner pieces are Mo
2
(DAniF)
3
(O
2
CC
5
H N) (1) and
4
ꢀ
cis-Mo
molecular rods 1-Ni(acac)
and the metal–metal bonded species Rh
mononuclear or a dinuclear species are sandwiched between two molecules of 1. The cisoid compound
has been employed for the synthesis of a molecular rhombus, [2-Zn(Cl )] (5). The successful
2
(DAniF)
2
(O
2
CC
5
H
4
N)
-1 (3) and 1-Rh
(O
2
(2), DAniF = N,N -di(p-anisyl)formamidinate. The heterometallic
2
2
(O
2
CCH
3
)
4
-1 (4) were made by reaction of 1 with Ni(acac)
2
2
2
CCH
)
3 4
, respectively. In these compounds either a
2
2
2
syntheses and isolation of 3–5 show that the use of corner pieces with angler groups is an excellent
approach for making heterometallic supramolecular compounds having a combination of metal–metal
bonded units and other metal species.
Introduction
depends largely on the availability of programmed metal-based
building blocks but these are generally rare.
The use of coordination bonds and weak interactions for the
creation of extended arrays containing metal units connected
by organic linkers is of great importance. In metal-based
In recent years, we have been able to create extended
10,11
supramolecular architectures through convergent synthesis
by
1
employing covalently bonded building blocks having dimetal units
supramolecules and nanostructures, the metal units play an
important role in extending the dimensions of the molecules,
controlling the structural geometries and tuning the chemical
with a hierarchy of ligand labilities, such as those of the types
(4−n)+
[
(
M
2
(DAniF)
n
(NCCH
3
)
2(4−n)
]
and
M
2
(DAniF)
n
(O
2
CCH )
4−n
3
12,13
14
15
ꢀ
M = Mo,
Rh or Ru, and DAniF = N,N -di(p-anisyl)for-
2,3
and physical properties of the compounds. The basic strategy
for the formation of discrete molecules or molecular assemblies
with desirable size, shape and topology is to manipulate the
relationship between the metal unit and organic linker using
mamidinate). In a few of these compounds there are differ-
ent metal units involved, for example, [Mo
2
(DAniF)
3
]
2
(OCH
3
)
2
-
-
16
M(CH
3
O)
2
[Mo
(O MO
2
2
(DAniF)
)[Mo
3
] (M = Zn and Co) and [Mo
2
17
(
DAniF)
3
]
2
2
2
(DAniF)
3
] (M = Mo and W).
4
basic principles of transition metal chemistry with the idea
The latter are examples of rare heterometallic superstructures
of developing functionalized molecules or molecular aggregates.
Indeed, elegant design and synthesis have resulted in metal–ligand
hybrid molecules that show potential applications as electronic
18
that may have potential applications as molecular devices in
addition to their interest in fundamental chemistry. In this
report a deliberate synthesis for compounds having metal–
metal bonded units combined with single metal or other
dimetal units that help increase structural diversity is pre-
sented. In this “ligand-directed” approach, a functionalized
ligand is used to generate various metal nuclearities. In the
5
devices and materials, for example, single molecular transistors
6
and single molecule magnets, which are desirable because of their
7
7c,8
9
conducting, magnetic and optical properties.
Contrary to the synthesis of organic compounds with multiple
functional groups that can be achieved with high specificity by
use of well-defined reactions and reagents, creation of large metal-
based molecules with a high degree of complexity remains highly
challenging because of the dynamic properties and lability of
many coordination bonds. A self-assembly approach could be an
efficient way to achieve an ordered structure, but such an approach
designed corner pieces, Mo
2
(DAniF)
3
(O
2
CC
5
4
H N) (1) and cis-
Mo
2
(DAniF)
2
(O
2
CC
5
H
4
N)
2
(2), either one or two bifunctional
−
isonicotinate ligands, [O
2
CC
5
H
4
N] , are incorporated. The car-
boxylate group binds to the dimolybdenum unit and the tethered
pyridyl nitrogen donor atom acts as the hook in a fishing pole
to attract and then bind to other metal centers (I in Scheme 1).
Thus the isonicotinate group may act as an adapter between
dimetal units and single metal, or other dimetal species. A reported
example that used a similar approach was that of the dirhenium
a
Department of Chemistry and Laboratory for Molecular Structure and
Bonding, P. O. Box 3012, Texas A&M University, College Station, TX
7
7842-3012, USA. E-mail: murillo@tamu.edu
b
Department of Chemistry, Tongji University, 200092, Shanghai, P. R. China.
E-mail: cyliu05@gmail.com
building block cis-[Re
syntheses of heterometallic oligomers.
2
(dppm)
2
(O
2
CC
5
9
H
4
N) ], prepared for the
2
1
†
Electronic supplementary information (ESI) available: Preparation and
(DAniF) (O CC N) ][Ni(acac) . See DOI:
]}
The building blocks 1 and 2 are programmed to incorporate
different metal units through a binary assembly reaction. Be-
cause of geometric constraint in each precursor, the resultant
aggregates have predictable structural motifs. The heterometallic
structure of {[cis-Mo
2
2
2
5
H
4
2
2
n
1
‡
0.1039/b617932k
Dedicated to the memory of Al Cotton, a wonderful friend, brilliant
scientist and caring mentor whose life was cut short.
2
328 | Dalton Trans., 2007, 2328–2335
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the preparation of cis-Mo
2
(DAniF)
2
(O
2
CCH
3
)
2
, made by mixing
21
the precursor with an excess of sodium acetate. For the synthesis
of 2, the isonicotinate anion was generated in situ by addition of
sodium methoxide to a mixture of the dimolybdenum precursor
and nicotinic acid in acetonitrile. The neutral corner piece 2, which
has a low solubility in polar solvents, readily precipitates from the
reaction mixture. Compound 2 appears to be stable and there is
no evidence for a cis to trans isomerization.
The two corner pieces 1 and 2 are isolated in good purity as
1
shown by their H NMR spectra in CDCl
3
. For 1, there are two
singlets at 8.54 and 8.44 ppm in a ratio of 1 : 2 that correspond
to the methine protons from the formamidinate ligands trans and
cis to the isonicotinate group, respectively. The aromatic protons
from the isonicotinate ligands are deshielded, and appear at low
field as two apparent doublets, one centered at 8.78 ppm and the
other one at 8.11 ppm. The aromatic protons from the two types of
hydrogen atoms of the anisyl groups appear as two sets of signals,
one for the groups cis to the isonicotinate group and the other one
for the trans protons. These appear as pseudo doublets centered at
Scheme 1
supramolecules synthesized by self-assembly of 1 with selected
metal complexes include two molecular rods, 1-Ni(acac)
-Rh (O CCH -1 (4). Using the cisoid compound 2 as starting
material, a molecular rhombus, [2-Zn(Cl )] (5) was made. All
these compounds have been structurally characterized using X-
ray crystallography.
2
-1 (3) and
1
2
2
3 4
)
6.51 and 6.28 ppm, and 6.68 and 6.59 ppm, respectively. Finally,
2
2
the signals for the methoxy groups of the anisyl groups appear as
singlets at 3.76 (12 H) and 3.70 (6 H). The UV-vis absorption at
4
−1
−1
4
64 nm (2.4 × 10 M cm ) is within the range of the d → d*
transitions in quadruply bonded compounds of this type. The H
NMR spectrum of 2 in CDCl suggests the presence of a highly
22
1
Results and discussion
3
symmetrical species in solution. There are two signals (centered
at 8.75 and 8.04 ppm) for the two types of hydrogen atoms in the
isonicotinate anion and only one singlet for the methine hydrogen
atom at 8.44 ppm. The aromatic groups of the formamidinate
groups are also equivalent and the signals centered at 6.63 ppm.
A singlet at 3.72 ppm corresponds to the hydrogen atoms in the
methoxy groups.
Syntheses of dimolybdenum building blocks
The mixed-ligand, quadruply bonded paddlewheel complexes 1
and 2 were prepared at room temperature by ligand substitution
reactions from the precursors Mo
Mo (DAniF) (NCCH ](BF , respectively, according to eqn (1)
and (2).
2
(DAniF)
3
(O
2
CCH
3
) and [cis-
2
2
3
)
4
)
4 2
Mo
2
(DAniF)
3
(O
2
CCH
3
) + HO
2
CC
N)
CC
N)
5
H
4
N
(1)
Syntheses of large arrays
NaOCH3/THF
−
−−−− −→ Mo (DAniF)
3
(O
2
C
5
H
4
2
Because of the dangling pyridyl groups, the dimolybdenum build-
ing blocks 1 and 2 may be viewed as monodentate or bidentate
ligands, respectively, capable of binding to another metal unit
through a coordination bond. In both compounds the linker is
rt
2
+
cis-[Mo
2
(DAniF)
2
(NCCH
3
)
4
]
+ 2HO
(O CC
2
5
H
]
4
N
(2)
NaOCH3
preinstalled, e.g., the pyridyl group –C
5
H
4
N → is attached to the
−
−−−− −→ cis-[Mo
2
(DAniF)
2
2
5
H
4
2
rt
4+
Mo
2
unit and is accessible to bind a Lewis acid. With these
The first equation represents a two step process. In this reaction
replacement of the acetate group in Mo (DAniF) (O CCH
by an isonicotinate ligand is needed. Because both of the
leaving and incoming groups are carboxylates, direct ligand
exchange is generally inefficient, as shown for example during
preprogrammed building blocks, heterometallic supramolecules
can be prepared by efficient and straightforward binary self-
assembly reactions. Compound 1 has been used for the preparation
of hybrid molecules having three discrete metal centers, and the
2
3
2
3
)
corner piece 2 in combination with a single metal unit ZnCl for
2
the conversion of cis-ReCl
dppm) (O CC N) , which required reflux of the reaction mix-
ture over a period of two days. The carboxylate replacement
process has now been improved by using NaOCH to remove the
acetate group in a reaction that forms the intermediate compound
2
(l-dppm)
2
(O
2
CCH
3
)
2
into cis-ReCl
2
(l-
the preparation of a molecular rhombus.
2
2
5
H
4
2
By mixing 1 and Ni(acac)
2
in a 2 : 1 stoichiometric ratio at
19
ambient temperature compound 3 is prepared in reasonable yield.
4
+
3
Likewise reaction of 1 with strong Lewis acids having Rh
paddlewheel cores such as dirhodium tetraacetate leads to the
2
20
4+
Mo
2
(DAniF)
3
(OCH
3
)(CH
3
OH), which was then treated with
formation of 4, in which an Rh
2
unit is located between two di-
neutral isonicotinic acid. This intermediary does not have to be
isolated nor purified, and this two-step, one-pot reaction gives the
monodentate building block 1 in good yield.
molybdenum units. Both 3 and 4 are rod-like molecules (vide infra).
Because of its ligand arrangement, the corner piece 2 is expected
to give molecules having different geometries than those from
reactions using 1. In a reaction with the tetrahedrally coordinated
Substitution of acetonitrile molecules in [cis-Mo
2
(DAniF)
by isonicotinate groups for the preparation of 2 is
convenient and straightforward because of the high lability of the
CH CN molecules. In principle, this reaction resembles that for
2
-
2
+
(NCCH
3
)
4
]
ZnCl
2
(THF) species and 2, the labile THF molecules were easily
2
replaced by the dangling N-donor pyridyl groups to generate a
23
3
cyclic heterometallic oligomer 5 having the shape of a rhombus.
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All the assembled molecules (3, 4 and 5) are neutral. Their
solubility is generally low in polar solvents, such as ethanol and
acetonitrile, but fairly high in dichloromethane. This difference
in solubility in polar and non polar solvents is helpful for
product purification and crystal growth, and facilitates product
characterization in both solid state and in solution.
Structures
As shown in Fig. 1a, compound 1 has a quadruply bonded
4
+
Mo
(
2
unit equatorially coordinated by three formamidinate
CC N) group that
DAniF) ligands and one isonicotinate (O
2
5
H
4
is coordinated to the dimetal unit through the carboxylate
terminus. This arrangement leaves a dangling pyridyl moiety
capable of serving as an angler for the capture of metal-
˚
containing Lewis acids. The Mo–Mo bond distance, 2.0906(5) A,
is typical for quadruply bonded dimolybdenum units embraced
2
4
by four, three-atom bridging ligands, such as Mo
2
(DAniF)
As designed, this molecule is closely related to
that of its precursor Mo (DAniF) (O CCH ) by having the same
coordination sphere and a similar Mo–Mo bond length (2.0892(8)
4
and
25
Mo
2
(OCCH ) .
3
4
2
3
2
3
12
˚
A). Upon replacement of the acetate by an isonicotinate group,
the color of the compounds changes from yellow to red as the d →
d* transition is shifted from 439 nm to 464 nm. In the solid state,
the pyridyl group is not in the plane defined by the dimetal unit
◦
and the CO
2
bridging group; the torsion angle is about 24 .
In 2 there are two cisoid DAniF and two isonicotinate anions
4
+
surrounding the Mo
2
unit, as illustrated in Fig. 1b. The Mo–Mo
˚
˚
bond length, 2.115(2) A, is 0.02 A longer than that of 2.092(2)
21
˚
A in cis-Mo
2
(DAniF)
2
(O
2
CCH
3
)
2
,
a molecule with a similar
core. Even though this bond length is slightly elongated, the
distance falls in the range of dimolybdenum quadruply bonded
22,26
distances.
The two orthogonal pyridyl groups are slightly tilted
relative to the five-membered chelating ringsO–Mo–Mo–O–C and
◦
◦
the torsion angles are 5.90 and 14.45 .
The rod-like compound 3 may be described by the formula
4
+
1
-Ni(acac)
2
-1. The two Mo
2
units are connected through ison-
unit as shown in Fig. 2.
icotinate termini to a planar Ni(acac)
2
¯
This compound crystallized in the space group P1 with the
molecule residing on a general position. Because the isonicoti-
nate linkers are slightly bent the molecule is slightly curved.
This hybrid rod is long when compared to other “dimers of
+
dimers” synthesized using the [Mo
2
(DAniF)
3
]
building block.
˚
The distance between the two dimetal centers is about 18 A.
˚
separation, about 16 A, was reported
The longest Mo
in a compound having the conjugated dicarboxylate linker, deca-
2
· · · Mo
2
27
2,4,6,8-trans,trans,trans,trans-octatetraene-1,10-dioate. In 3, the
Fig. 2 Molecular structures of the building blocks 1 (a) and 2 (b).
Displacement ellipsoids are drawn at the 40% probability level. All
hydrogen atoms have been omitted for clarity.
two crystallographically independent Mo–Mo bonds are chemi-
˚
cally equivalent (bond lengths of 2.0927(7) and 2.0923(7) A) and
Fig. 1 Molecular structure of 3 in 3·2CH
2
Cl
2
drawn with displacement ellipsoids at the 40% probability level. All hydrogen atoms have been omitted for
clarity.
2
330 | Dalton Trans., 2007, 2328–2335
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are essentially parallel to each other. The two pyridyl groups on the
apices of the octahedrally coordinated Ni moiety are essentially
˚
The Rh–Rh bond length of 2.402(1) A and the Rh–N distance of
2
+
28
˚
2
.240(4) A are comparable to those in Rh
molecule has a highly symmetrical arrangement having idealized
2h symmetry. The two pyridyl groups have torsion angles of 5.5 ,
much smaller than that of 24 in the building block 1.
2
(O
2
CCH
3
)
4
(py) . The
2
co-planar and mutually define a plane that bisects the NiO
The torsion angles (ca. 2 ) between each of the pyridyl rings
4
square.
◦
◦
D
◦
and the corresponding O–Mo–Mo–O–C groups are significantly
◦
2
+
smaller than in 1 (ca. 24 ).
In compound 5, Zn moieties serve as linkers between the cisoid
4
+
The rod 4, described by the formula 1-Rh
2
(O
2
CCH
3
) -1, crys-
4
Mo
2
units. The compound crystallized in the space group P2 /n.
In each unit cell, there are two crystallographically independent
molecules residing on special positions. This supramolecule is a
distorted rhombus with alternating Zn and Mo
the vertices and four isonicotinate groups serving as edges (Fig. 4).
The formula may be abbreviated as [2-ZnCl . The Mo–Mo
1
¯
tallized in the triclinic P1 space group with Z = 1. This molecule
has an inversion center at the midpoint of the Rh–Rh bond. As
4
+
2
+
4+
shown in Fig. 3, there are two basically parallel Mo
2
units at
unit has the dirhodium
single bond essentially perpendicular to the dimolybdenum units.
2
metal units at
4
+
the ends of the rod. A central Rh
2
]
2 2
4
+
˚
The separation between the two Mo
2
units of about 21 A is
˚
distances of 2.0920(7) A are slightly shorter than in the building
the longest among all dimolybdenum pairs synthesized to date.
The crystallographically independent Mo–Mo bond distance,
block 2 but similar to those in 1, 3 and 4. The Zn · · · Zn separation
˚
˚
of 11.935 A is shorter than the other diagonal length, 13.475 A,
˚
4+
2
.0925(8) A, is almost identical to those in 1 and 3 (Table 1).
measured from the centers of the two Mo
2
units. The geometry
Fig. 3 Molecular structure of 4 in 4·4.5CH
2
Cl
2
·C
6
H14. Displacement ellipsoids are drawn at the 40% probability level. All hydrogen atoms have been
omitted for clarity.
◦
Table 1 Selected bond lengths ( A˚ ) and angles ( ) for1–5
1
2·2CH
2
Cl
2
3·2CH
2
Cl
2
4·4.5CH
2
Cl
2
·C
6
H
14
2 2
5·4CH Cl
Mo(1)–Mo(2)
2.1153(17)
2.0925(8)
2.0926(8)
2.0920(7)
Mo(1)–Mo(1A)
Mo(3)–Mo(4)
Mo(1)–N(1)
Mo(1)–N(3)
Mo(1)–N(5)
Mo(2)–N(2)
Mo(2)–N(4)
Mo(2)–N(6)
Mo(1)–O(1)
Mo(1)–O(3)
Mo(2)–O(2)
Mo(2)–O(4)
2.0905(5)
2.0923(7)
2.109(3)
2.139(3)
2.137(3)
2.138(3)
2.136(3)
2.169(3)
2.144(3)
2.1470(19)
2.123(2)
2.103(11)
2.110(10)
2.142(4)
2.162(4)
2.161(5)
2.133(4)
2.123(4)
2.161(4)
2.137(3)
2.109(4)
2.104(4)
2.105(10)
2.120(10)
2.118(3)
2.114(4)
2.1454(17)
2.127(9)
2.139(8)
2.140(8)
2.138(8)
2.123(3)
2.149(3)
2.136(3)
2.111(3)
2.124(3)
2.148(3)
N(1)–Mo(1)–O(1)
N(3)–Mo(1)–O(1)
N(5)–Mo(1)–O(1)
N(2)–Mo(2)–O(2)
N(4)–Mo(2)–O(2)
N(6)–Mo(2)–O(2)
N(1)–Mo(1)–N(3)
N(1)–Mo(1)–N(5)
N(2)–Mo(2)–N(4)
N(2)–Mo(2)–N(6)
O(1)–Mo(1)–O(3)
O(2)–Mo(2)–O(4)
85.73(7)
175.23(6)
175.4(4)
88.7(4)
174.26(12)
88.02(11)
87.96(14)
175.33(14)
84.04(15)
88.54(14)
174.14(15)
88.26(15)
94.02(15)
170.34(16)
93.62(15)
174.23(17)
174.72(12)
85.26(13)
174.1(4)
89.4(4)
174.24(13)
85.10(11)
86.45(11)
88.60(13)
95.38(13)
90.87(13)
97.19(13)
175.64(12)
87.27(13)
94.6(4)
93.9(4)
88.5(3)
95.32(14)
95.28(13)
85.92(12)
86.49(12)
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absent. Even when the spectral window was opened to cover the
region between −150 ppm and +150 ppm, signals from the acac
methyl groups and from the isonicotinate groups were absent. The
sharpness of the signals from the anisyl groups and the absence of
2
+
those in the Ni units suggest that there is little or no electronic
communication through the isonicotinate bridge, consistent with
the electrochemical data below.
Electrochemistry
Cyclic voltammograms (CVs) and differential pulse voltammo-
grams (DPVs) for 1–5 were measured in CH
2
2
Cl solutions. The
corner pieces 1 and 2 show reversible one-electron redox processes
at 310 and 560 mV vs. Ag/AgCl, respectively (Fig. 5). Previous
studies on dimer of dimers have shown that the separation between
Fig. 4 Molecular structure of 5 in 5·4CH
2 2
Cl drawn with displacement
ellipsoids at the 40% probability level. All hydrogen atoms have been
omitted for clarity.
the two Mo units is a very important factor in determining
2
27
whether electronic communication is efficient or not. As the
intermetal separations increase, it has often been observed that
for the ZnCl
2
N
2
moiety is that of a distorted tetrahedron. The
electronic communication decreases according to an exponential
◦
30
N–Zn–N angle, 102.8 , is slightly smaller than the ideal value
law. Because the separations between the Mo
2
units in 3 and 4
◦
◦
of 109.5 . While the Cl–Zn–Cl angle, 119.63(8) is larger. The
are the longest known for any dimer of dimers compounds of this
type, an extremely weak communication may be anticipated. This
is consistent withthe electrochemicaldata(seeFig. 5). Compounds
3 and 4 show very similar patterns in the CVs and DPVs, a
redox wave was observed for each one of them between 300
and 400 mV. By analogy to the dimer of dimers linked by long
molecule defines a diamond shaped area with an approximate
˚
˚
dimension of 9 A × 9 A and hosts one interstitial dichloromethane
molecule disordered over two orientations.
Information on the structures in solution of these large
molecules has been obtained by H NMR spectroscopy. Com-
pounds 4 and 5 are diamagnetic because of the presence of two
1
31
unsaturated dicarboxylate ligands, this wave can be assigned to
the two unresolved one-electron oxidation processes on each of the
dimolybdenum units. The CV for the rhombohedral compound 5
appears to correspond to a less reversible process. It is possible that
because of a relatively weak N to Zn interaction, the molecule may
decompose upon oxidation.
4
+
4+
quadruply bonded Mo
2
units and the singly bonded Rh
2
unit
in 4 and the d electronic structure of the Zn units in 5.
For the rod-like 4, the spectrum in CDCl shows a singlet at
.59 ppm corresponding to the methine hydrogen atoms from
1
0
2+
3
8
the formamidinate ligands trans to the isonicotinate ligands. The
signals for the cis methine ligands overlap with some of the
isonicotinate signals at 8.46 ppm while the other signals for the
isonicotinate are centered at 9.48 ppm. The rest of the signals,
including the singlet at 1.96 ppm for the methyl groups from
the Rh
2
(O
2
CCH
3
4
) moiety, are in the expected regions of the
spectrum for a highly symmetrical species. Therefore the spectrum
is consistent with the solid state structure. Similarly for 5, the
simple pattern of the spectrum with only two singlets at 8.47 and
3
.72 ppm for the methine and methoxy groups and the expected
pattern for the aromatic hydrogen atoms indicate that the shape
of the molecule in solution resembles that in the solid state.
Unlike 4 and 5, compound 3 is paramagnetic with two unpaired
electrons per molecule (leff = 3.4 BM), as determined from
bulk magnetic susceptibility measurements. The source of the
2
+
paramagnetism is the octahedral coordination of the Ni ions
derived from the coordination of the two pyridyl groups to
the square planar Ni(acac) moiety. Species with octahedral
2
2 2
Fig. 5 CVs and DPVs (potentials vs Ag/AgCl, in CH Cl ) for compounds
trans-Ni(O)
4
(N)
2
units are typically paramagnetic as in trans-
compounds for which the leff have been reported
1–5.
Ni(acac) (amine)
2
2
29
to be in the range of 3.2–3.4 BM. Despite the paramagnetism of
1
3
, its H NMR spectrum in CD Cl shows mostly sharp signals in
3
Conclusions
the expected regions of the spectra. For example, there are singlets
with a ratio of 2 : 1 at 8.31 and 8.45 ppm for the methine and 3.71
and 3.64 ppm for methoxy protons, respectively, from the DAniF
ligands. The signals for the anisyl groups are also as expected
Two
Mo
new
(DAniF)
dimolybdenum-containing
(O N) (1) and cis-Mo
building
(DAniF) (O
blocks
CH N)
2
3
2
C
5
H
4
2
2
2
4
2
(2), each having an angler composed of a pyridyl group capable of
(
6.17–6.60 ppm). However, close inspection of the spectrum shows
binding to metal-containing Lewis acids, have been synthesized.
2
+
that the signals from the ligands directly bound to the Ni unit are
The functionalization by introduction of
a bi-functional
2
332 | Dalton Trans., 2007, 2328–2335
This journal is © The Royal Society of Chemistry 2007

View Article Online
isonicotinate ligand allows incorporation into 1 and 2 of other
metal centers via coordination bonds and the formation of
heterometallic supramolecules. By taking advantage of these two
programmed building blocks, spontaneous self-assemblies with
8.54 (s, 1H, –NCHN–), 8.44 (s, 2H, –NCHN–), 8.11 (d, 2H,
isonicotinate), 6.68 (d, 8H, aromatic), 6.59 (d, 8H, aromatic), 6.51
(d, 4H, aromatic), 6.28 (d, 4H, aromatic), 3.76 (s, 12H, –OCH
3
),
). UV-vis, kmax (e, M cm ): 464 nm (2.4 ×
10 ). Anal. Calcd. for C51 : C, 56.72; H, 4.57; N, 9.08.
Found: C, 56.49; H, 4.86; N, 9.29.
−
1
−1
3.70 (s, 6H, –OCH
3
4
selective metal complexes, e.g., Ni(acac)
Zn Cl , formation of two metal-based molecular rods 1-Ni(acac)
(3), 1-Rh (O CCH -1 (4), and a cyclic oligomer [2-Zn Cl
2
, Rh
2
(O
2
CCH
3
)
4
and
H
49Mo
2
N
7
O
8
2
2
2
-
1
2
2
3
)
4
2
2
]
2
Preparation of cis-Mo
2
(DAniF)
2
(O
2
CC
5
H
4
2
N) , 2. A mixture
(
5) have been synthesized. Compounds 3 and 4 are longer than
of [cis-Mo (DAniF) (NCCH
2
2
3
)
4
](BF
)
4 2
(0.520 g, 0.500 mmol) and
any previously reported dimolybdenum pair. Meanwhile the
isonicotinic acid (0.170 mg, 1.38 mmol) was placed in a Schlenk
flask. With stirring acetonitrile (ca. 20 mL) was added to the solid,
producing a blue solution. After about 10 min, 2.0 mL of a sodium
methoxide solution (0.5 M in methanol) was added. The color
changed from blue to red. The reaction mixture was allowed to
stir at room temperature for 3 h. During this period a dark red
precipitate formed. The supernatant solution was then decanted.
The red solid was washed with 20 mL of ethanol and then dried un-
der vacuum. The crude product was dissolved in dichloromethane
rhombohedral molecule 5 has a large cavity which holds a
CH
2
2
Cl guest molecule. Incorporation of different metal units
into structurally defined architectures is a way to modify the
molecular architecture and tune chemical and physical properties.
The preparative concept and methodology developed here should
have general application for the synthesis of heteronuclear species
having metal–metal corner pieces bound to metal-containing
Lewis acids.
(
15 mL) and the solution was layered with hexanes. Red needle-
Experimental
1
shaped crystals formed after 2 days. Yield: 0.24 g (56%). H NMR
(
)
CDCl
3
, ppm): 8.75 (d, 4H, isonicotinate), 8.44 (s, 2H, –NCHN–
Materials and methods
, 8.04 (d, 4H, isonicotinate), 6.63 (m, 16H, aromatic), 3.72 (s,
−
1
−1
4
All manipulations and procedures were performed under a
nitrogen atmosphere, using either a nitrogen drybox or standard
Schlenk line techniques. Solvents were purified under argon using
a Glass Contour solvent purification system or distilled over
appropriate drying agents under nitrogen. The starting materi-
12H, –OCH
3
). UV-vis, kmax (e, M cm ): 450 nm (1.2 × 10 ).
(2·0.3CH Cl ): C, 52.26;
H, 4.04; N, 8.64. Found: C, 52.23; H, 3.66; N, 8.78.
Anal. Calcd. for C42.3
H
38.6Cl0.6Mo
2
N
6
O
8
2
2
Preparation of [Mo
2
(DAniF)
3
(O
2
CC
5
H
4
N)]
2
Ni(C
5
H
7
O
2
)
2
, 3.
1
2
The dimolybdenum building block Mo
(0.400 g, 0.400 mmol) was dissolved in 20 mL of THF. The
resulting brownish red solution was transferred into a flask
2
(DAniF)
3
(O CC
2
5
H
4
N) (1)
als Mo
2
3
(DAniF)
3
(O
2
CCH
3
)
and [cis-Mo
2
(DAniF)
2
(NCCH
3
)
4
]-
1
(
BF
4
)
2
were prepared following reported procedures. The
dirhodium compound Rh
2
4
(O
2
CCH
3
)
4
(NCCH
3
)
2
was prepared
3
2
containing Ni(acac)
solution. After the reaction mixture was stirred for an additional
h, the solvent was removed under reduced pressure. The red
residue was washed with ethanol (ca. 15 mL) followed by hexanes
ca.10 mL). The dry solid was dissolved in about 15 mL of
2
(0.050 g, 0.20 mmol), generating a bright red
by treating Rh
2
(O
2
CCH
3
)
,
with acetonitrile. Commercially
available chemicals were used as received.
2
Physical measurements
(
Elemental analyses were performed by Robertson Microlit Labo-
ratories, Madison, New Jersey. Electronic spectra were measured
dichloromethane and the solution was layered with 40 mL of
hexanes, affording red block-shaped crystals after a few days.
1
in CH
501PC spectrometer. H NMR spectra were recorded on an
Inova-300 or Mercury NMR spectrometer with chemical shifts (d,
ppm) referenced to CDCl . Cyclic voltammograms and differential
2
Cl
2
solution at ambient temperature on a Shimadzu UV-
Yield: 0.285 g (24%). H NMR (CDCl
3
, ppm): 8.54 (s, 2H, –
1
2
NCHN–), 8.31 (s, 4H, –NCHN–), 6.60 (d, 16H, aromatic), 6.41
(d, 24H, aromatic), 6.17 (d, 8H, aromatic), 3.71 (s, 24H, –OCH ),
). UV-vis, kmax (e, M mol ): 474 nm (2.5 ×
10 ). leff = 3.4 BM. Anal. Calcd. for C115 Mo
(3·3CH Cl ): C, 51.70; H, 4.45; N, 7.34. Found: C, 51.33; H, 4.62;
N, 7.40.
3
−
1
−1
3.64 (s, 12H, –OCH
3
3
4
pulse voltammograms were collected on a CH Instruments
electrochemical analyzer with Pt working and auxiliary electrodes,
H
118Cl
6
4
14
N O20Ni
2
2
−
1
Ag/AgCl reference electrode, scan rate (for CV) of 100 mV s ,
and 0.10 M Bu NPF (in CH Cl ) as electrolyte.
4
6
2
2
Preparation of [Mo
2
(DAniF)
3
(O
2
CC
5
H
4
N)]
2
[Rh
2
(O
2
CCH
3
)
4
],
Preparation of Mo
lution of Mo (DAniF)
of THF, was added 1.0 mL of a NaOCH
methanol). After stirring for about 2 h, a colorless microcrystalline
material, presumably sodium acetate, was removed by filtration.
To the filtrate was added an excess of isonicotinic acid (0.080 g,
2
(DAniF)
3
(O
) (0.512 g, 0.500 mmol) in 15 mL
solution (0.5 M in
2
CC
5
H
4
N), 1. To a yellow so-
4. A solution of purple Rh
2
(O
2
CCH
3
)
4
(NCCH
3
)
2
(0.052 g,
2
3
(O CCH
2
3
0.100 mmol) and red 1 (0.216 g, 0.200 mmol) was prepared in
20 mL of acetonitrile. The reaction mixture was allowed to stir
at room temperature for 4 h. A dark red precipitate formed. The
solvent was then removed under reduced pressure. The dark red
residue was washed with ethanol (2 × 15 mL). The crude product
was dissolved in 15 mL of dichloromethane and the solution
3
0
.650 mmol). Upon stirring, the color of the mixture immediately
changed from yellow to red. After stirring at room temperature
for an additional half hour, the solvent was removed under
vacuum, and the residue was washed with ethanol (2 × 15 mL),
and then dried under vacuum. The red solid was dissolved in
dichloromethane (15 mL) and the solution was layered with
was layered with 40 mL of hexanes, affording dark red crystals
1
after one day. Yield: 0.08 g (31%). H NMR (CDCl
3
, ppm):
9.48 (s, 4H, isonicotinate), 8.59 (s, 2H, –NCHN–), 8.46 (s, 8H,
–NCHN– and isonicotinate) 6.72 (d, 16H, aromatic), 6.62 (d,
16H, aromatic), 6.54 (d, 8H, aromatic), 6.33 (d, 8H, aromatic),
hexanes. Red block-shaped crystals formed after one day. Yield:
3.78 (s, 24H, –OCH
3
), 3.73 (s, 12H, –OCH ), 1.96 (s, 12H, –
3
1
−1
−1
4
0
.380 g (70%). H NMR (CDCl
3
, ppm): 8.78 (d, 2H, isonicotinate),
CH
3
). UV-vis, kmax (e, M cm ): 499 nm (4.1 × 10 ). Anal. Calcd.
This journal is © The Royal Society of Chemistry 2007
Dalton Trans., 2007, 2328–2335 | 2333

View Article Online
Table 2 X-Ray crystallographic data for 1–5
Compound
1
2·2CH
2
Cl
2
3·2CH
2
Cl
2
4·4.5CH
2
Cl
2
·C
6
H
14
2 2
5·4CH Cl
Empirical formula
FW
C
51
H
49Mo
2
N
7
O
8
C
44
H
42Cl
4
Mo
2
N
6
O
8
C
114
H
116Cl
4
Mo
4
N
14
O
20Ni
C
120.5
H
130Cl
9
Mo
4
N
14
O
24Rh
2
88 4 12 2
C H84Cl12Mo N O16Zn
2505.57
1079.85
1116.52
2586.47
3067.02
P1 (No. 2)
¯
¯
Space group
C2/c (No. 15)
17.615(3)
18.492(3)
16.855(3)
90
118.286(4)
90
4834.7(16)
4
213
1.484
0.580
0.0453 (0.0798)
Pbca (No. 61)
13.942(7)
19.406(10)
35.947(18)
90
90
90
9726(8)
8
213
P1 (No. 2)
14.966(5)
17.526(6)
23.141(9)
102.989(7)
98.259(7)
90.533(7)
5848(4)
2
213
1.469
0.738
0.0817 (0.1380)
P2 /n (No. 14)
1
a/A˚
15.260(4)
16.014(5)
16.228(5)
108.216(5)
102.413(5)
106.435(5)
3406.8(17)
1
213
1.495
0.840
0.0847 (0.1588)
10.588(3)
20.103(6)
24.879(8)
90
94.073(5)
90
5282(3)
2
213
b/A˚
c/A˚
◦
a/
b/
◦
◦
c /
V/A˚
3
Z
T/K
d
−
3
calcd/g cm
l/mm
R1 (wR2 )
1.525
0.791
0.1264 (0.1816)
1.575
1.275
0.0625 (0.1194)
−
1
a
b
a
b
2
2
2
2
2
1/2
R1 = RꢁF
o
| − |F
c
ꢁ/R|F
o
|. wR2 = [R[w(F
o
− F
c
o
) ]/R[w(F ) ]] .
for C110
H
110Mo
4
N
14
O
24Rh
2
: C, 50.78; H, 4.26; N, 7.53. Found: C,
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b617932k
50.51; H, 4.10; N, 7.72.
Preparation
The
of
dimolybdenum
(O CC N)
mixed with anhydrous ZnCl
[cis-Mo
2
(DAniF)
building
2
(O
2
CC
5
H
block
4
N)
2
][ZnCl
2
]
2
,
Acknowledgements
5.
cis-
Mo
2
(DAniF)
2
2
5
H
4
2
(2) (0.095 g, 0.100 mmol) was
Funding from the Robert A. Welch Foundation and Texas A&M
University is thankfully acknowledged.
2
(0.050 g, 0.37 mmol) in 20 mL of
THF. The reaction mixture was stirred for 2 h, during which time
a red–purple precipitate formed. The supernatant solution was
decanted and the residue was dried under vacuum. The solid
was then extracted with ca. 15 mL of dichloromethane and the
mixture filtered through a Celite-packed frit. The filtrate was
References
1 See for example: J.-M. Lehn, Supramolecular Chemistry, VCH Publish-
ers, New York, 1995.
See for example:(a) P. J. Stang and B. Olenyuk, Acc. Chem. Res., 1997,
2
layered with 30 mL of hexanes. Dark red needle-shaped crystals
3
1
0, 502; (b) S. Leininger, B. Olenyuk and P. J. Stang, Chem. Rev., 2000,
00, 853; (c) C. A. Schalley, A. L u¨ tzen and M. Albrecht, Chem.–Eur. J.,
1
formed after 4 days. Yield: 0.050 g (25%). H NMR (CDCl
3
,
ppm): 8.96 (s, 8H, isonicotinate), 8.47 (s, 4H, –NCHN–), 8.16
2004, 10, 1072; (d) G. F. Swiegers and T. J. Malefetse, Chem. Rev., 2000,
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1
(
–
s, 8H, isonicotinate), 6.60 (m, 32H, aromatic), 3.72 (s, 24H,
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−
1
−1
4
OCH
3
). UV-vis, kmax (e, M cm ): 508 nm (4.3 × 10 ). Anal.
Calcd. for C86
H
80Cl
8
Mo : C, 44.27; H, 3.45; N, 7.19.
4
N
12
O
16Zn
2
Found: C, 44.27; H, 3.52; N, 7.08.
4
(a) D. Caulder and K. N. Raymond, Acc. Chem. Res., 1999, 32, 975;
X-Ray structure determinations
(
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goniometer of a Bruker SMART 1000 CCD area detector
2
◦
diffractometer and then cooled to −60 C. Cell parameters were
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33
determined using the program SMART. Data reduction and
34
integration were performed with the software package SAINT,
and absorption corrections were applied using the program
2
65, 1054; (b) C. M. Zaleski, E. C. Deperman, J. W. Kampf, M. L. Kirk
and V. L. Pecoraro, Angew. Chem., Int. Ed., 2004, 43, 3912; (c) S. Osa,
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Chem. Soc., 2004, 126, 420.
35
SADABS. In all structures, the positions of the heavy atoms
36
were found via direct methods using the program SHELXTL.
7
(a) O. Ermer, Adv. Mater., 1991, 3, 608; (b) A. Aum u¨ ller, P. Erk, G.
Klebe, S. H u¨ nig, J. U. von Sch u¨ tz and H. P. Werner, Angew. Chem.,
Int. Ed. Engl., 1986, 25, 740; (c) C. S. Campos-Fern a´ ndez, J. R. Gal a´ n-
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Subsequent cycles of least-square refinement followed by differ-
ence Fourier syntheses revealed the positions of the remaining
non-hydrogen atoms. Hydrogen atoms were added in idealized
positions. Non-hydrogen atoms were refined with anisotropic
displacement parameters. Some of the anisyl group in the DAniF
2
003, 988.
8
W. Shi, X.-Y. Chen, B. Zhao, A. Yu, H.-B. Song, P. Cheng, H.-G. Wang,
D.-Z. Liao and S.-P. Yan, Inorg. Chem., 2006, 45, 3939.
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0 (a) F. A. Cotton, C. Lin and C. A. Murillo, Acc. Chem. Res., 2001, 34,
ligands and interstitial CH
and they were refined with soft constraints. Crystallographic data
Cl Cl Cl Cl
2
Cl
2
molecules were found disordered,
1
for 1, 2·2CH
2
2
, 3·2CH
2
2
, 4·4.5CH
2
2
·C
6
H
14 and 5·4CH
2
2
7
59; (b) F. A. Cotton, C. Lin and C. A. Murillo, Proc. Natl. Acad. Sci.
are in Table 2, and selected bond distances and angles in Table 1.
USA, 2002, 99, 4810; (c) M. H. Chisholm and A. M. Macintosh, Chem.
Rev., 2005, 105, 2949.
CCDC reference numbers 628985–628989 for 1–5, respectively.
2
334 | Dalton Trans., 2007, 2328–2335
This journal is © The Royal Society of Chemistry 2007

View Article Online
1
1
1
1 F. A. Cotton, C. Y. Liu, C. A. Murillo and X. Wang, Inorg. Chem.,
006, 45, 2619.
2 F. A. Cotton, C. Y. Liu, C. A. Murillo, D. Villagr a´ n and X. Wang,
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Huffman, S. S. Iyer, C. Lin, A. M. Macintosh and C. A. Murillo,
J. Chem. Soc., Dalton Trans., 1999, 1387.
diffracting but unambiguously showed a zig-zag infinite chain with
alternating dimetal species and single metal units having the formula
2
{[cis-Mo
2
(DAniF)
2
(O
2
CC
2
5
H
4
N)
2
][Ni(acac)
(O CC
2
]}
n
(see ESI†). Crystallo-
N) ][Ni(acac) : space
]}
graphic data for {[cis-Mo
(DAniF)
2
2
5
H
4
2
2
n
˚
¯
group = P1, a = 14.321(16), b = 14.331(16), c = 18.22(2) A, a =
◦
3
92.88(2), b = 110.84(2), c = 97.32(2) ( ), V = 3447(7) A˚ .
24 C. Lin, J. D. Protasiewics, E. T. Smith and T. Ren, Inorg. Chem., 1996,
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1
4 (a) K. V. Catal a´ n, D. J. Mindiola, D. L. Ward and K. R. Dunbar, Inorg.
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1974, B30, 2768.
1
1
1
1
26 (a) F. A. Cotton, L. M. Daniels, E. A. Hillard and C. A. Murillo, Inorg.
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Springer Science and Business Media, Inc., New York, 2005.
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2
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2
229.
8 L. Yu, K. Muthukumaran, I. V. Sazanovich, C. Kirmaier, E. Hindin,
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1
2
9 J. K. Bera, J. Bacsa, B. W. Smucker and K. R. Dunbar, Eur. J. Inorg.
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30 G.-L. Xu, G. Zou, Y.-H. Ni, M. C. DeRosa, R. J. Crutchley and T. Ren,
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31 F. A. Cotton, J. P. Donahue, C. A. Murillo and L. M. P e´ rez, J. Am.
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1972, 13, 90.
33 SMART V 5.05 Software for the CCD Detector System, Bruker
Analytical X-ray System, Inc., Madison, WI, 1998.
34 SAINT. Data, Reduction Software, V 6.36A, Bruker Analytical X-ray
System, Inc., Madison, WI, 2002.
0 In prior work, we had found that addition of NaOCH
Mo (DAniF) (O CCH ) removes the acetate ligand, yielding NaO
and a highly reactive compound Mo (DAniF) (OCH )(CH OH). See:
a) F. A. Cotton, Z. Li, C. Y. Liu, C. A. Murillo and D. Villagr a´ n,
3
to
2
3
2
3
2
CH
3
2
3
3
3
(
Inorg. Chem., 2006, 45, 767; (b) F. A. Cotton, Z. Li, C. Y. Liu and C. A.
Murillo, Inorg. Chem., 2006, 45, 9765.
2
2
1 F. A. Cotton, C. Y. Liu and C. A. Murillo, Inorg. Chem., 2004, 43,
2
267.
2 F. A. Cotton, in Multiple Bonds Between Metal Atoms, ed. F. A. Cotton,
C. A. Murillo and R. A. Walton, Springer Science and Business Media,
Inc., 2005.
35 SADABS. Bruker/Siemens Area Detector Absorption and Other Cor-
rections, V2.03, Bruker Analytical X-ray System, Inc., Madison, WI,
2002.
2
3 When reaction of 2 and Ni(acac)
2
was carried out in THF, a red product
Cl and other solvents were poorly
36 G. M. Sheldrick, SHELXTL. V 6.12, Bruker Analytical X-ray Systems,
was obtained. Crystals from CH
2
2
Inc., Madison, WI, 2000.
This journal is © The Royal Society of Chemistry 2007
Dalton Trans., 2007, 2328–2335 | 2335