Naphthyridine-imidazole hybrid ligands for the construction of multinuclear architecture

Article abstract of DOI:10.1016/j.ica.2011.03.033

Reaction of 2-imidazolyl-5,7-dimethyl-1,8-naphthyridine (L¹) with [Rh(COD)Cl]₂ (COD = 1,5-cyclooctadiene) affords the dinuclear complex [Rh(COD)Cl]₂(μ-L¹) (1). Elimination of chloride from the metal coordination

Full text of DOI:10.1016/j.ica.2011.03.033

Inorganica Chimica Acta 374 (2011) 320–326
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Naphthyridine–imidazole hybrid ligands for the construction
of multinuclear architecture
⇑
S.M. Wahidur Rahaman, Dipak Das, Nabanita Sadhukhan, Arup Sinha, Jitendra K. Bera
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
a r t i c l e i n f o
a b s t r a c t
Reaction of 2-imidazolyl-5,7-dimethyl-1,8-naphthyridine (L1) with [Rh(COD)Cl]2 (COD = 1,5-cyclooctadi-
ene) affords the dinuclear complex [Rh(COD)Cl]2(
-L1) (1). Elimination of chloride from the metal coor-
Article history:
Available online 13 March 2011
l
dination sphere leads to a self-assembled tetranuclear macrocycle [Rh(COD)L1]4[ClO4]4 (2). A subtle
alteration in the ligand framework results in the polymeric chain compound {Rh(COD)(L2)}n(PF6)n (3)
(L2 = 2-imidazolyl-3-phenyl-1,8-naphthyridine). In all these complexes, the imidazole nitrogen and one
of the naphthyridine nitrogen (away from the imidazole substituent) bind the metal. The ‘parallel’ and
‘perpendicular’ dispositions of nitrogens are observed in these compounds contributing to different
RhꢀꢀꢀRh separations. The L1 ligand adopts planar configuration, whereas the naphthyridine–imidazole
rings deviate from planarity in L2 yielding a polymeric structure. The extent of deviation is less in the
polymeric structure {Mo2(OAc)4(L2)}n (4) in which the ligand exhibits weak axial interactions to the
metal.
Dedicated to Professor Wolfgang Kaim
Keywords:
Self-assembly
Metallamacrocycle
Naphthyridine
Rhodium
Coordination polymer
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
of the resultant structure. The present work describes our recent
effort to synthesize multinuclear compounds from a composite
The desire to make new and complex structures has been a
motivating factor for the intensive study of metalla-supramolecular
chemistry. The applications of metal-containing supramolecular
assemblies in gas storage [1–4], catalysis [5–8], single-molecule-
magnetism [9–11], separation [12–14], sensor [15–18] and many
other areas have afforded credence to this chemistry. Numerous
multitopic ligands have been designed and metal components
(including secondary building units, or SBU) have been developed
[19–21]. Pyridine based ligands were one of the first to be used
in the construction of metallamacrocycles [22–24]. Multi-site li-
gands containing multiple imidazole units have also been used in
recent years [25,26]. The general scheme employed for the ligand
design involves the covalent attachment of donor units on a de-
sired organic platform. Ligand systems incorporating different
types of donor moieties have shown prospects for the construction
of homo- and heterometallic metallamacrocycles. Pyridine carbox-
ylic acid has been employed for the construction of Pt and Pd based
molecular squares [27,28]. Dunbar et al. have reported several het-
erobimetallic metallacycles consisting of Re2/Pt and Re2/Zn units
[29,30]. Imidazole carboxylic acids have been employed for the
construction of molecular polygons with ‘Cp⁄Rh’ corners [31].
The disposition of metal-binding sites in the ligand framework
and the directionality of the metal precursor dictate the topology
N-donor ligand.
We have employed naphthyridine–imidazole hybrid ligands
(Scheme 1) for the synthesis of multinuclear compounds. The
naphthyridine and imidazole nitrogens offer prospect for multi-
metal assemblies. The square-planar metal component ‘Rh(COD)’
(COD = 1,5-cyclooctadiene) has been chosen as the metal-contain-
ing unit. By judicious alteration in the ligand framework, and in the
metal coordination sphere as well, dinuclear [Rh(COD)Cl]2(l
-L1)
(1), tetranuclear macrocycle [Rh(COD)L1]4[ClO4]4 (2) and poly-
meric {Rh(COD)(L2)}n(PF6)n (3) have been synthesized (Scheme
2). In this report, we make an attempt to rationalize their struc-
tures based on the ligand conformation and the metal-ion
geometry.
2. Results and discussion
2.1. [Rh(COD)Cl]2(l
-L1) (1)
Addition of L1 to the [Rh(COD)Cl]2 in dichloromethane disrupts
the dimeric structure and affords 1 in high yield. Molecular struc-
ture of 1 consists of two ‘Rh(COD)Cl’ units bridged by L1 (Fig. 1).
0
The terminal nitrogens of imidazolyl (N1) and naphthyridine (N8 )
units bind to two independent Rh centers. The coordinating geom-
etry around each Rh center is square planar and the metrical
parameters are similar to those reported for RhI-COD compounds
[32]. The angle between the naphthyridine (NP) plane and the
⇑
Corresponding author. Tel.: +91 512 259 7336; fax: +91 512 259 7436.
E-mail address: jbera@iitk.ac.in (J.K. Bera).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.03.033

D. Das et al. / Inorganica Chimica Acta 374 (2011) 320–326
321
Scheme 1. Ligands used in the present study and the numbering scheme.
imidazole (Im) plane is 3.9° (u N2–C30–N3–C33 = 2.9(5)°). The
non-bonded RhꢀꢀꢀRh distance is 6.1004(7) Å.
The 1H NMR of 1 reveals a 2:1 composition of ‘Rh(COD)’ and L1.
However, the NMR spectrum exhibits two sets of NP protons in the
ratio 1:0.7, clearly indicating a mixture of compounds in solution
(see Fig. S1). The methyl protons appear as two singlets at d 2.67,
2.71 ppm. In addition, broad signals are observed for COD protons
at d 1.84, 2.49, 4.21, 4.59 ppm. Based on the NMR data, the
Fig. 1. ORTEP diagram (50% probability thermal ellipsoid) of 1 with important
atoms labeled. Hydrogen atoms omitted for the sake of clarity. Selected bond
distances (Å) and angles (°): Rh1–N1 2.124(3), Rh1–Cl1 2.3833(11), Rh1–C1
2.104(4), Rh1–C2 2.106(4), Rh1–C5 2.123(4), Rh1–C6 2.128(4), Rh2–Cl2
2.3910(10), Rh2–N4 2.105(3), Rh2–C9 2.094(4), Rh2–C10 2.103(4), Rh2–C13
2.127(4), Rh2–C14 2.137(4), N1–Rh1–Cl1 86.95(9), N4–Rh2–Cl2 90.64(9), N2–
C30–N3–C33 2.9(5), Rh1ꢀꢀꢀRh2 6.1004(7).
1
N1-L1), Rh(COD)Cl(
j
N8 -L ) and the origi-
0
presence of Rh(COD)Cl(
j
nal dimer [Rh(COD)Cl]2 is proposed. Interestingly, the ESI-MS
exhibits high-intensity signals at 905, 681, 659, 435 attributed to
C12 = 0.1(6)°). The RhꢀꢀꢀRh distance is 8.5652(7) Å, longer than
the corresponding metalꢀꢀꢀmetal distance in 1 by 2.47 Å.
The tetrameric compound 2 is also obtained from the dimer 1.
Treatment of 1 by TlI salt and subsequent addition of one equiva-
lent of L1 provided the cyclic tetramer 2. Evidently, the removal
of chloride allows the propagation of the structure aided by the lin-
ker L1 culminating in a cyclic tetranuclear structure.
{Rh2(COD)2(Cl)(L1)2}+,
{Rh2(COD)2(Cl)(L1)}+,
{Rh(COD)(L1)2}+,
{Rh(COD)(L1)}+, respectively. The assignment is based on mass
and isotropic distribution pattern.
2.2. [Rh(COD)L1]4[ClO4]4 (2)
The iridium analog [Ir(COD)L1]4[OTf]4 has been synthesized fol-
lowing a similar procedure using [Ir(COD)Cl]2, TlOTf and L1. The
ORTEP diagram and the important bond parameters are provided
in the supporting information.
Removal of chlorides from [Rh(COD)Cl]2 by TlClO4 and subsequent
addition of L1 provided a cyclic tetramer [Rh(COD)L1]4[ClO4]4 (2).
Molecular structure of 2 is confirmed by X-ray crystallography.
The tetracationic core consists of four ‘Rh(COD)’ units bridged by
four L1 ligands (Fig. 2(a)). The molecule crystallizes in the tetrago-
nal I41/a space group and only one ‘Rh(COD)L1’ is observed in the
asymmetric unit. Each Rh is connected to the neighboring metal by
L1 ligand through the terminal nitrogens of the Im and NP units.
The four metals form an equilateral quadrangle of 8.5652(7) Å,
each Rh makes an angle of 87.742(1)° with two adjoining metals,
and four metals do not reside on the same plane (see Fig. 2(b)).
Although the coordination motif of the L1 is identical in both di-
mer structure 1 and tetrameric structure 2, some significant differ-
ences are noted. The ‘parallel’ and ‘perpendicular’ disposition of the
coordinating nitrogens are the characteristic features of com-
pounds 1 and 2 (Fig. 3). This results in different metalꢀꢀꢀmetal sep-
arations (6.1004(7) for 1 and 8.5652(7) Å for 2).
All NP and COD protons exhibit broad signals in the 1H NMR
spectrum. The ESI-MS spectrum of complex 2 reveals signal at
The L1 adapts
a
planar configuration
(u
N2–C10–N3–
Scheme 2. Line drawings of metallo-assemblies 1–3.

322
D. Das et al. / Inorganica Chimica Acta 374 (2011) 320–326
Fig. 2. (a) ORTEP diagram (30% probability thermal ellipsoid) of the tetracationic unit [Rh(COD)L1]4 in compound 2 with important atoms labeled. Hydrogen atoms omitted
for the sake of clarity. Selected bond distances (Å) and angles (°): Rh1–N4 2.099(3), Rh1–C18 2.109(5), Rh1–C14 2.124(4), Rh1–C19 2.138(6), Rh1–C15 2.150(4), Rh1–N1
2.165(4), N4–Rh1 2.099(3), N4–Rh1–N1 87.41(14), C18–Rh1–N1 145.21(18), C14–Rh1–N1 96.3(2), C19–Rh1–N1 175.70(18), C15–Rh1–N1 89.92(18), N4–Rh1–C18 90.39(17),
N4–Rh1–C14 158.73(18), N4–Rh1–C19 93.62(17), N4–Rh1–C15 163.25(17). (b) The skeletal arrangement of Rh4 moiety.
Fig. 3. The ‘parallel’ and ‘perpendicular’ dispositions of L1 in compounds 1 (a) and 2 (b).
m/z 1221 (z = 1) corresponding to a species [Rh3(COD)3(L1)2-
The 1H NMR spectrum exhibits well resolved signals indicating
an 1:1 composition of ‘Rh(COD)’ and L2 in CD3CN. ESI-MS spectrum
of complex 3 exhibits signal at m/z 483 and 755 (z = 1) attributed
to [Rh(COD)L2]+ and [Rh(COD)(L2)2]+, respectively. Interestingly,
the signal for the latter complex is the most intense signal
(100%) in the mass spectrum.
(CH3CN)(ClO4)]+.
2.3. {Rh(COD)(L2)}n(PF6)n (3)
X-ray structures of 1 and 2 reveal a planar arrangement of L1 li-
0
gand. We introduced a phenyl ring at C3 position with an intention
to disrupt the planarity, and examine the structural perturbation.
Reaction of [Rh(COD)Cl]2, TlPF6 and L2, following a procedure iden-
tical to that of 2, resulted in an one-dimensional zig-zag chain
structure [Rh(COD)L2]n[PF6]n (3). Molecular structure of 3, deter-
mined by X-ray crystallography, reveals a polymeric chain consist-
ing of alternate ‘Rh(COD)’ and L2 (Fig. 4). The non-bonded RhꢀꢀꢀRh
distance is 8.0110(11) Å. The coordination motif of L2 is the same
as for L1, which is binding through the terminal NP and Im nitro-
gens. The disposition of the coordinating nitrogens is ‘perpendicu-
2.4. {Mo2(OAc)4(L2)}n (4)
The coordination chemistry of L2 was further studied with a
dimolybdenum(II) compound [Mo2(OAc)4]. The strong trans influ-
ence of the Mo–Mo quadruple bond allows weak N coordination at
axial sites with minimum perturbation on the ligand [33,34]. The
polymeric structure of compound
4 of empirical formula
{Mo2(OAc)4L2} consists of alternate ‘Mo2(OAc)4’ and L2 units. Two
neighboring ‘Mo2(OAc)4’ molecules are linked by L2 through the
NP nitrogen and Im nitrogen as depicted in Fig. 6. The ‘parallel’ dis-
position of the coordinating nitrogens is observed in this structure.
The Mo–N distances (2.628(1) and 2.656(1) Å) are characteristi-
cally long. The NP and Im rings deviate from planarity and the in-
ter-planar angle is 24.46°. The extent of deviation is smaller than
lar’. The angle between NP plane and Im plane is 42.2° (
N3–C26 = 34.9°), and the phenyl ring rotates away from the NP
plane (Inter-planar angle = 51.5°; C18–C17–C19–C24 = 51.9°)
u N2–C18–
u
(Fig. 5). The deviation of NP and Im rings from planarity leads to
the open-chain structure.

D. Das et al. / Inorganica Chimica Acta 374 (2011) 320–326
323
Fig. 4. ORTEP diagram (40% probability thermal ellipsoid) of the cationic unit [Rh(COD)L2]n in compound 3 with important atoms labeled. Hydrogen atoms omitted for the
sake of clarity. Selected bond distances (Å) and angles (°): Rh1–C6 2.108(4), Rh1–N4 2.116(3), Rh1–C2 2.119(4), Rh1–N1 2.128(3), Rh1–C1 2.136(4), Rh1–C5 2.138(4). C6–
Rh1–N4 92.11(13), C6–Rh1–C2 99.43(16), N4–Rh1–C2 155.26(13), C6–Rh1–N1 153.82(14), N4–Rh1–N1 88.74(11), C2–Rh1–N1 90.32(14), C6–Rh1–C1 82.84(15), N4–Rh1–C1
166.75(13), C2–Rh1–C1 37.95(14), N1–Rh1–C1 90.45(13), C6–Rh1–C5 38.47(15), N4–Rh1–C5 93.67(12), C2–Rh1–C5 82.35(15), N1–Rh1–C5 167.47(13), C1–Rh1–C5
89.97(15) Rh1ꢀꢀꢀRh1 8.0110(11). Symmetry code: 1/2 + X, 3/2 ꢁ Y, 2 ꢁ Z.
Fig. 5. The configurations of L1 and L2 ligands in compounds 2 (a) and 3 (b), respectively.
that observed in 3. The Ph ring is also rotated away from the NP
plane as reflected in the C18–C17–C22–C27 dihedral angle
45.4(5)°.
and forms dinuclear complex [Rh(COD)Cl]2(l
-L1) (1). Removal of
chloride from the metal coordination sphere allows further
propagation of the structure resulting in a metallamacrocycle
[{Rh(COD)L1}4]4+. Use of L2 under identical condition, however,
afforded an infinite cationic zig-zag chain [{Rh(COD)(L2)}n]n+. A
neutral polymeric chain compound of empirical formula {Mo2
(OAc)4(L2)} is obtained by treating L2 with [Mo2(OAc)4]. In all these
cases, the imidazole nitrogen and one of the naphthyridine nitrogen
3. Summary and conclusions
Table 1 summarizes the relevant details of compounds 1–4.
Addition of L1 to [Rh(COD)Cl]2 disrupts the chloro-bridged structure

324
D. Das et al. / Inorganica Chimica Acta 374 (2011) 320–326
Fig. 6. ORTEP diagram (50% probability thermal ellipsoid) of a fragment in the chain compound [Mo2(OAc)4(L2)]n (4) with important atoms labeled. Hydrogen atoms omitted
for the sake of clarity. Selected bond distances (Å) and angles (°): Mo1–N1 2.628(3), Mo1–Mo2 2.1098(4), Mo1–O1 2.112(3), Mo1–O7 2.117(3), Mo1–O5 2.125(3), Mo1–O3
2.158(3), Mo2–O4 2.101(3), Mo2–O6 2.123(2), Mo2–O2 2.123(3), Mo2–O8 2.132(3), Mo2–Mo1–N1 160.18(7), O1–Mo1–N1 85.93(10), O7–Mo1–N1 90.06(10), O5–Mo1–N1
108.02(10), O3–Mo1–N1 71.31(10).
Table 1
Relevant structural details in compounds 1–4.
Compound
Ligand
Structure
Ligand configuration
RhꢀꢀꢀRh (Å)
ua (°)
[Rh(COD)Cl]2(
l
-L1) (1)
L1
L1
L2
L2
Dimer
Parallel
6.1004(7)
8.5652(7)
8.0110(11)
–
3.9
1.69
42.22
24.46
[Rh(COD)L1]4[ClO4]4 (2)
[Rh(COD)(L2)]n(PF6)n (3)
[Mo2(OAc)4(L2)]n (4)
Equilateral quadrangle
Zig-zag polymer chain
Zig-zag polymer chain
Perpendicular
Perpendicular
Parallel
a
NP–Im inter-planar angle.
(away from the imidazole substituent) bind the metal. These nitro-
gens adopt ‘parallel’ conformation in compounds 1, 4 and ‘perpen-
dicular’ conformation in compounds 2, 3 (Table 1). The free
rotation of NP and Im rings around the C–N single bond allows these
two unique orientations causing different RhꢀꢀꢀRh separations; the
‘parallel’ and ‘perpendicular’ arrangements result in shorter and
longer metalꢀꢀꢀmetal separations. The L1 adopts a planar structure,
whereas L2 is non-planar. The non-planarity of L2 is attributed to
the open-chain structure of 3, whereas a cyclic structure 2 is
obtained for planar L1. In compound 4, the L2 ligand exhibits
‘parallel’ disposition of the coordinating nitrogens, and the NP and
Im rings are non-planar though the extent of deviation is compara-
tively less. In conclusion, the present study illustrates that judicious
alteration in the ligand framework and/or adjustment in the metal
coordination sphere are possible ways to access self-assembled
structures of varied nuclearity and diverse topology.
triple-quadrupole mass spectrometer. The 1H NMR spectrum was
obtained on a JEOL JNM-LA 500 MHz spectrophotometer. Infrared
spectra were recorded on a Bruker Vertex 70 FTIR spectrophotom-
eter in the ranges from 400 to 4000 cmꢁ1 using KBr pellets.
3.3. X-ray data collection and refinement
Single-crystal X-ray studies were performed on a CCD Bruker
SMART APEX diffractometer equipped with an Oxford Instruments
low-temperature attachment. All data were collected at 100(2) K
using graphite monochromated Mo K
a radiation (k ) 0.71073 (Å).
a
The frames were indexed, integrated, and scaled using the SMART
and SAINT software packages [42], and the data were corrected for
absorption using the SADABS programs [43]. Structures were solved
and refined with the SHELX suite of programs [44,45] as imple-
mented in X-seed [46,47]. The ‘‘SQUEEZE’’ option in PLATON program
[48] was used to remove a disordered solvent molecule from the
overall intensity data of compounds 2 and 5. The figures were
drawn using ORTEP [49]. All the hydrogen atoms were included
at geometrically calculated positions in the final stages of the
refinement and were refined according to the ‘‘riding model’’. All
non-hydrogen atoms were refined with anisotropic thermal
parameters unless mentioned otherwise. Pertinent crystallo-
graphic data for compounds 1–4 are summarized in Table 2.
3.1. General procedures and materials
All reactions were carried out under an inert dinitrogen atmo-
sphere with the use of standard Schlenk-line techniques. Solvents
were dried by conventional methods, distilled over nitrogen, and
deoxygenated prior to use. [Ir(COD)Cl]2 [35,36], [Rh(COD)Cl]2
[37], Mo2(CH3COO)4 [38–40], 2-imidazolyl-5,7-dimethyl-1,8-
naphthyridine (L1) and 2-imidazolyl-3-phenyl-1,8-naphthyridine
(L2) [41] were prepared by following literature procedures.
3.4. Synthesis of [Rh(COD)Cl]2(l
-L1) (1)
3.2. Physical measurements
L1 (30 mg, 0.134 mmol) was added to a dichloromethane solu-
tion (10 mL) of [RhCl(COD)]2 (65 mg, 0.132 mmol) and the yellow
mixture was stirred for 12 h at room temperature. The resulting or-
ange solution was concentrated under vacuum and 15 mL of
diethyl ether were added with stirring to induce precipitation.
Elemental analyses were carried out using a Thermoquest CE
instruments model EA/110 CHNS-O elemental analyzer. ESI-MS
spectra were recorded on a Waters Micromass Quattro Micro

D. Das et al. / Inorganica Chimica Acta 374 (2011) 320–326
325
Table 2
Crystallographic data and pertinent refinement parameters for compounds 1–4.
1. CH2Cl2
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
30H38Cl4N4Rh2
C84H96Cl4N16O16Rh4
2139.21
tetragonal
I41/a
16.0732(11)
16.0732(11)
37.675(5)
C25H24F6N4PRh
628.36
orthorhombic
P2(1)2(1)2(1)
9.694(2)
C25H24Mo2N4O8
700.36
orthorhombic
Pna21
802.26
triclinic
P1
ꢀ
10.2847(10)
11.0185(11)
16.3603(16)
92.891(2)
108.210(2)
114.8180(10)
1562.6(3)
2
8.6412(7)
24.883(2)
12.0562(10)
b (Å)
c (Å)
12.358(3)
19.765(4)
a
(°)
b (°)
(°)
90.00
90.00
90.00
c
V (°)
Z
9733.2(15)
4
1.460
0.844
4352
2367.9(9)
4
1.763
0.860
1264
2592.3(4)
4
1.795
1.025
1400
qcalc (g cmꢁ3
)
1.705
1.426
808
l
(mmꢁ1
)
F(0 0 0)
Reflections collected
Independent
13826
7371
43698
5964
20950
5775
22101
6378
Observed [I > 2
r
(I)]
5747
4174
5127
5653
Number of variables
Goodness-of-fit (GOF)
Rint
363
1.075
0.0262
R1 = 0.0369
wR2 = 0.0811
R1 = 0.0553
wR2 = 0.1032
284
334
356
1.110
0.0709
0.0607
0.1668
0.0886
0.1873
1.119
0.0611
0.0338
0.0482
0.0662
0.0784
1.082
0.0471
0.0314
0.0675
0.0460
0.0758
Final R indices [I > 2
r
(I)]a
R indices (all data)a
2
2
1=2
jFoj with F2o > 2
r
ðF2oÞ. wR2 ¼ ½
R
wðjF2oj ꢁ jF2c jÞ =
R
jF2oj ꢂ
a
R1
¼
R
jjFoj ꢁ jFcjj=
R
.
Then it was dried in vacuum. Crystals were grown by layering hex-
ane over dichloromethane solution of the complex. Yield: 86 mg
(91%). Anal. Calc. for C29H36Cl2N4Rh2: C, 48.56; H, 5.06; N, 7.81.
tation. Then it was dried in vacuum. Crystals were grown by layer-
ing hexane over dichloromethane solution of the complex. Yield:
157 mg (88%). Anal. Calc. for C25H24F6N4PRh: C, 47.79; H, 3.85; N,
Found: C, 48.49; H, 4.92; N, 7.80%. IR (KBr pellet):
m
(COD)
8.92. Found: C, 47.49; H, 3.74; N, 8.79%. IR (KBr pellet):
m(COD)
2925 cmꢁ1 1H NMR (CD2Cl2, d, ppm): 9.27, 9.01 (s, 2H, Im), 8.52,
.
2923 cmꢁ1 (PF6ꢁ) 843 cmꢁ1 1H NMR (CD3CN, d, ppm): 9.15 (s,
,
m
.
7.97 (s, 2H, Im), 8.51, 8.46 (d, 2H, NP), 7.69, 7.60 (d, 2H, NP),
7.32, 7.21 (s, 2H, NP) 7.24, 7.05 (s, 2H, Im), 4.59, 4.21 (br, 4H,
COD), 2.71, 2.67 (s, 12H, Me), 2.49 (br, 10H, COD), 1.84 (br, 10H,
COD). ESI-MS: m/z 681 [Rh2(COD)2(Cl)(L1)]+.
1H, NP), 8.52 (s, 1H, NP), 8.45 (d, 1H, NP), 7.68 (br, 1H, Im), 7.68
(br, 1H, NP), 7.41 (s, 3H, Ph), 7.35 (s, 1H, Im), 7.28 (d, 2H, Ph),
6.90 (s, 1H, Im), 4.25 (br, 4H, COD), 2.42 (br, 4H, COD), 1.25 (br,
4H, COD). ESI-MS: m/z 755 [Rh(COD)(L2)2]+.
3.7. Synthesis of [{Mo2(OAc)4(L2)}n] (4)
3.5. Synthesis of [Rh(COD)L1]4[ClO4]4 (2)
L2 (76 mg, 0.28 mmol) was added to an acetonitrile solution
(10 mL) of Mo2(OAc)4 (60 mg, 0.14 mmol) and the yellow mixture
was stirred for 12 h at room temperature. The color was changed
from yellow to reddish brown. The resulting solution was concen-
trated under vacuum and 15 mL of diethyl ether were added with
stirring to induce precipitation. Then it was dried in vacuum. Crys-
tals were grown by layering hexane over dichloromethane solution
of the complex. Yield: 113 mg (83%). Anal. Calc. for C25H24N4O8-
Mo2: C, 42.87; H, 3.45; N, 8.00. Found: C, 42.32; H, 3.21; N,
TlClO4 (86 mg, 0.284 mmol) was added to an acetonitrile solu-
tion (10 mL) of [RhCl(COD)]2 (70 mg, 0.142 mmol) and the yellow
mixture was stirred for 30 min. The TlCl was removed by Schlenk
filtration, then L1 (64 mg, 0.284 mmol) was added to the filtrate
and the mixture was stirred for 16 h at room temperature. The
resulting orange solution was concentrated under vacuum and
15 mL of diethyl ether were added with stirring to induce precipi-
tation. Then it was dried in vacuum. Crystals were grown by layer-
ing hexane over dichloromethane solution of the complex. Yield:
134 mg (88%). Anal. Calc. for C84H96Cl4N16O16Rh4: C, 47.16; H,
4.52; N, 10.48. Found: C, 47.05; H, 4.32; N, 10.31%. IR (KBr pellet):
7.91%. IR (KBr pellet):
m .
(CH3COOꢁ) 1432 cmꢁ1 1H NMR (CD3CN,
d, ppm): 9.13 (dd, 1H, NP), 8.67 (s, H, NP), 8.56 (dd, H, NP), 7.73
(s, H, Im), 7.70 (s, H, NP), 7.43 (br, 3H, Ph), 7.32 (br, 2H, Ph), 7.22
(s, H, Im), 6.93 (s, H, Im), 2.47 (s, 12H, CH3COOꢁ).
m
(COD) 2928 cmꢁ1 (ClO4ꢁ) 1084 cmꢁ1 1H NMR (CD3CN, d,
; m .
ppm): 9.73 (br, 1H, Im), 8.66 (br, 1H, NP), 7.74 (br, 1H, NP), 7.53
(br, 1H, NP), 7.24 (br, 1H, Im), 7.03 (br, 1H, Im), 4.61 (br, 4H,
COD), 4.20 (br, 4H, COD), 2.71 (s, 3H, Me), 2.65 (s, 3H, Me), 2.32
(br, 4H, COD). ESI-MS: m/z 1221 [Rh3(COD)3(L1)2(CH3CN)(ClO4)]+.
Acknowledgements
J.K.B. thanks DST India for support of this research. D.D. thanks
CSIR, India and S.M.W.R. thanks UGC, India for fellowships.
3.6. Synthesis of {Rh(COD)(L2)}n(PF6)n (3)
TlPF6 (99 mg, 0.283 mmol) was added to an acetonitrile solution
(10 mL) of [RhCl(COD)]2 (70 mg, 0.142 mmol) and the yellow mix-
ture was stirred for 30 min. The TlCl was removed by Schlenk fil-
tration, then L2 (77 mg, 0.282 mmol) was added to the filtrate
and the mixture was stirred for 12 h at room temperature. The
resulting orange solution was concentrated under vacuum and
15 mL of diethyl ether were added with stirring to induce precipi-
Appendix A. Supplementary material
CCDC 808933, 808934, 808935 and 808936 contain the supple-
mentary crystallographic data for compounds 1, 2, 3 and 4, respec-
tively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article

326
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