A dynamic open framework exhibiting guest-and/or temperature-induced bicycle-pedal motion in single-crystal to single-crystal transformation

Article abstract of DOI:10.1021/ic102305v

A ligand bis(4-imidazol-1-yl-phenyl)diazene (azim) incorporating an azo moiety at the center and two imidazole groups at the terminals forms two coordination polymers {[Co(azim)₂(DMF)₂]?(ClO ₄)₂?2DMF}_n

Full text of DOI:10.1021/ic102305v

Inorg. Chem. 2011, 50, 1889–1897 1889
DOI: 10.1021/ic102305v
A Dynamic Open Framework Exhibiting Guest- and/or Temperature-Induced
Bicycle-Pedal Motion in Single-Crystal to Single-Crystal Transformation
Manish K. Sharma and Parimal K. Bharadwaj*
Department of Chemistry, Indian Institute of Technology Kanpur, 208016, India
Received November 18, 2010
A ligand bis(4-imidazol-1-yl-phenyl)diazene (azim) incorporating an azo moiety at the center and two imidazole groups
at the terminals forms two coordination polymers {[Co(azim)2(DMF)2] (ClO4)2 2DMF}n (1) and {[Cd(azim)2-
3
3
(DMF)2] (ClO4)2 2DMF}n (2) (DMF = N,N0-dimethylformamide) at room temperature. Both 1 and 2 are isostructural
3
3
with rhombic two-dimensional sheets stacking in ABAB... fashion resulting in large voids that contain DMF and ClOh as
4
guests. In 1, the azo groups and phenyl rings are disordered over two positions and as in usual cases, the pedal motion
cannot be discerned. Upon heating, 1 turns amorphous. In the case of 2, however, heat treatment does not lead to loss
of crystallinity. Thus, when a crystal of 2 (mother crystal) is heated slowly, it causes substantial movement or escape of
both metal-bound and lattice DMF besides movement of ClOh anions to give daughter crystals 2a, 2b, and 2c without
4
losing crystallinity (single-crystal to single-crystal (SC-SC) transformation). Most interestingly, the X-ray structures of
2 and its daughter products reveal stepwise reversible bicycle-pedal or crankshaft motion of the azo group. When a
crystal of 2c is kept in DMF for 10 h, crystal 20 is formed whose structure is similar to that of 2 with slight changes in the
bond distances and angles. Also, crystals of 2 are converted to 3 and 4 upon being kept in acetone or DEF (DEF = N,
N0-diethylformamide), respectively, for 10 h at ambient temperature in SC-SC transformation. In 3, each lattice DMF
molecule is replaced by an acetone molecule, leaving the two coordinated DMF molecules intact. However, in 4, all
lattice and coordinated DMF molecules are replaced by equal number of DEF molecules. Both in 3 and 4, the azo
moieties show bicycle-pedal motion. Thus, bicycle-pedal motion that normally cannot be observed is shown here to be
triggered by heat as well as guest molecules in SC-SC fashion.
Introduction
framework in the solid state. Such motions in crystalline
solidsinresponse to outside stimulisuchaslight, heat, etc. are
particularly intriguing. If the crystallinity of the compound is
maintained, it is possible to observe the effects of molecular
motions in terms of changes in the relative positions of the
atoms via X-ray crystallography.
Molecular motions in crystalline solids have received
attention in recent years due to their potential uses in fabri-
cating nanoscale devices. Particularly, one of the most inter-
esting phenomena is the bicycle-pedal or crankshaft motion.
The pedal motion triggers conformational interconversion
that results in disordered crystal structures if the conformers
In recent years, studies of coordination polymers have
made a paradigm shift with the introduction of flexible and
dynamic coordination polymers with structural1 and functional2
responses to guest sorption and other external stimuli. In
such systems, dynamic behavior arises from the cooperative
action oforganic and inorganic moieties3,4 while the natureof
flexibility depends mainly on the characteristics of the or-
ganic ligands used to build the frameworks. When the ligand
contains mobile parts (for example, groups that undergo
rotation or liberation), dynamic motion may occur inside the
*To whom correspondence should be addressed. E-mail: pkb@iitk.ac.in.
(1) (a) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004,
(2) (a) Chae, H. K.; Siberio-Perez, D. Y.; Kim, J. H.; Go, Y. -B.;
Eddaoudi, M.; Matzger, A. J.; O’Keeffe, M.; Yaghi, O. M. Nature 2004,
427, 523–527. (b) Atwood, J. L.; Barbour, L. J.; Jerga, A.; Schottel, B. L. Science
2002, 298, 1000–1002. (c) Yaghi, O. M.; Li, G. M.; Li, H. L. Nature 1995, 378,
703–706. (d) Hang, J. W.; Hill, C. L. J. Am. Chem. Soc. 2007, 129, 15094–
15095. (e) Wu, C. D.; Lin, W. Angew. Chem., Int. Ed. 2007, 46, 1075–1078. (f)
Alaerts, L.; Seguin, E.; Poelman, H.; Thibault-Starzyk, F.; Jacobs, P. A.; De Vos,
D. E. Chem.;Eur. J. 2006, 12, 7353–7363. (g) Klein, N.; Senkovska, I.;
Gedrich, K.; Stoeck, U.; Henschel, A.; Mueller, U.; Kaskel, S. Angew. Chem.,
Int. Ed. 2009, 48, 9954–9957. (h) Maspoch, D.; Ruiz-Molina, D.; Wurst, K.;
Domingo, N.; Cavallini, N.; Biscarini, F.; Tejada, J.; Rovira, C.; Veciana, J. Nat.
Mater. 2003, 2, 190–195. (i) Beauvais, L. G.; Shores, M. P.; Long, J. R. J. Am.
Chem. Soc. 2000, 122, 2763–2772.
ꢀ
43, 2334–2375. (b) Ferey, G. Chem. Soc. Rev. 2008, 37, 191–214. (c) Batten,
S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460–1494. (d) Eddaoudi,
M.; Moler, D. B.; Li, H. L.; Chen, B. L.; Reineke, T. M.; OKeeffe, M.; Yaghi,
O. M. Acc. Chem. Res. 2001, 34, 319–330. (e) Moulton, B.; Zaworotko, M. J.
Chem. Rev. 2001, 101, 1629–1658. (f) Wang, Z.; Cohen, S. M. Chem. Soc. Rev.
2009, 38, 1315–1329. (g) Xiang, S.; Zhou, W.; Zhang, Z.; Green, M. A.; Liu, Y.;
Chen, B. Angew. Chem., Int. Ed. 2010, 49, 4615–4618. (h) Farha, O. K.; Bae,
Y. -S.; Hauser, B. G.; Spokoyny, A. M.; Snurr, R. Q.; Mirkin, C. A.; Hupp, J. T.
Chem. Commun. 2010, 1056–1058. (i) Kuznicki, S. M.; Bell, V. A.; Nair, S.;
Hillhouse, H. W.; Jacubinas, R. M.; Braunbarth, C. M.; Toby, B. H.; Tspatsis, M.
Nature 2001, 412, 720–724. (j) Halder, G. J.; Kepert, C. J. J. Am. Chem. Soc.
2005, 127, 7891–7900.
r
2011 American Chemical Society
Published on Web 01/21/2011
pubs.acs.org/IC

1890 Inorganic Chemistry, Vol. 50, No. 5, 2011
Sharma and Bharadwaj
have low energy barrier. However, if the energy barrier is
high, the pedal motion does not show any disordering in the
crystal structure due to insignificant population of the minor
conformer.5 This motion has not been widely acknowledged
because it is often difficult to detect and, therefore, easy to
overlook. However, once we recognize the prevalence of the
pedal motion, many dynamic phenomena can be interpreted
on the basis of this motion, irrespective of its detection.
The pedal motion has been shown to be active in several
organic crystals. It has been studied in crystals of bis-
(triarylmethyl)peroxide,6 polyenes,7 and azobenzene.8 Its
role in [2 þ 2] photodimerization of alkene derivatives has
been reported recently.9 The isomerization in butadienes
through the pedal motion is reminiscent of the photoisome-
rization in the visual pigment rhodopsin.10 A recently pro-
posed interpretation of the photocycle of photoactive yellow
protein (PYP) also emphasized the potential importance of
the pedal motion in proteins.11 MacGillivray and co-workers
have reported a rare example of the racklike movement of
alkyl chains that coupled with pinionlike 180° rotation of
olefins in a single crystal.12
Scheme 1. Schematic Representation of Pedal Motion in the Diphe-
nyldiazene Moieties in Ligand (azim)
ditionally, there has been comparatively little attention
directed toward reversible, concerted ligand substitution at
metal sites in PCPs in single-crystal to single-crystal (SC-
SC) fashion, leading to expression of new functionality.13
In compound 2, the guest molecules including the counter-
anions make significant movement, and the counteranions
eventually occupy vacant coordination sites on the metal,
keeping crystallinity intact throughout.
Herein, we report the synthesis of two two-dimensional
(2D) coordination polymers, {[Co(azim)2(DMF)2] (ClO4)2
3
3
2DMF}n (1) and {[Cd(azim)2(DMF)2] (ClO4)2 2DMF}n (2)
3
3
prepared at room temperature by reacting M(ClO4)2 (M(II) =
Co(II) and Cd(II)) with the ligand, bis(4-imidazol-1-yl-phe-
nyl)diazene (azim). The ligand is designed with an azo moiety
in the middle for possible bicycle-pedal motion. Here, the two
phenyl rings are attached to the central NdN moiety. The
relationships among these parts are similar to those of bicycle
pedals (phenyl rings), crank arms (NdN bond), and spindles
(N-Ph bonds) (Scheme 1). The azo bonds and phenyl rings
are disordered in the solid-state structure of 1, over two
positions due to crankshaft motion. Interestingly, this dis-
orderisnotobserved in2. Therefore, wehave chosenpolymer
2 to study heat-/guest-dependent bicycle-pedal motion. Ad-
Results and Discussion
Compounds 1 and 2, once isolated, are found to be air-
stable and slightly soluble in DMF and DMSO, but insoluble
in other common organic solvents or water. Single-crystal
X-ray determination at 100 K reveals that both 1 and 2 are
isostructural and the asymmetric unit of each polymer con-
tains one M(II) ion (half occupancy), two halves of the
ligand, two DMF molecules, and one ClOh anion. Each
4
metal ion is distorted octahedral with equatorial ligation by
imidazole N of four different ligand units and axial ligation
by two DMF molecules (Figure 1) with M-N and M-O
bond distances14,15 within normal ranges. The ligands bridge
metal ions to form a 2D rhombus-grid structure. Both phenyl
rings of the ligand are nearly coplanar, while imidazole rings
are twisted significantly with respect to the phenyl rings. Each
(3) (a) Seo, J.; Matsuda, R.; Sakamoto, H.; Bonneau, C.; Kitagawa, S. J.
Am. Chem. Soc. 2009, 131, 12792–12800. (b) Lee, Y. E.; Jang, S. Y.; Suh, M. P.
J. Am. Chem. Soc. 2005, 127, 6374–638.
(4) (a) Uemura, K.; Kitagawa, S.; Fukui, K.; Saito, K. J. J. Am. Chem.
Soc. 2004, 126, 3817–3828. (b) Matsuda, R.; Kitaura, R.; Kitagawa, S.; Kubota,
Y.; Kobayashi, T. C.; Horike, S.; Takata, M. J. Am. Chem. Soc. 2004, 126,
14063–14070. (c) Kitaura, R.; Seki, K.; Akiyama, G.; Kitagawa, S. Angew.
Chem., Int. Ed. 2003, 42, 428–431.
(5) Harada, J.; Ogawa, K. Chem. Soc. Rev. 2009, 38, 2244–2252.
(6) Khuong, T. -A. V.; Zepeda, G.; Sanrame, C. N.; Dang, H.; Bartberger,
M. D.; Houk, K. N.; Garcia-Garibay, M. A. J. Am. Chem. Soc. 2004, 126,
14778–14786.
(7) (a) Harada, J.; Ogawa, K. J. Am. Chem. Soc. 2004, 126, 3539–3544. (b)
Harada, J.; Harakawa, M.; Ogawa, K. CrystEngComm 2008, 1777–1781. (c)
Galli, S.; Mercandelli, P.; Sironi, A. J. Am. Chem. Soc. 1999, 121, 3767–3772.
(8) (a) Harada, J.; Ogawa, K.; Tomoda, S. Acta Crystallogr., Sect. B 1997,
53, 662–672. (b) Harada, J.; Ogawa, K. J. Am. Chem. Soc. 2001, 123, 10884–
10888.
grid (M4L4) shows the diagonal M M distances of 33.922
3 3 3
˚
˚
and 20.151 A in 1 and 34.759 and 20.275 A in 2 (Table 1,
Figure 2). These 2D layers are stacked in ABAB... fashion.16
Lattice DMF molecules and ClOh anions occupy the void
4
spaces in the grid. In case of 1, diphenyldiazene moiety of the
ligand A and C in the M4L4 macrocyclic unit are disordered
over two positions because of the pedal motion and both con-
formers of the ligand are distributed inthe crystal (Figure 3a).
On the other hand, no such disorder is observed in case of 2
(Figure 3b). Thermal analyses of 1 and 2 show weight losses
of ∼27 and ∼23.4% respectively, in the temperature range
70-150 °C, that correspond to loss of both lattice and
coordinated DMF molecules. The desolvated frameworks
are stable up to ∼340 °C.16 IR spectra of 1 and 2 show a C-H
stretching vibration at ∼2930 cm-1 and a CdO stretching
(9) (a) Bhogala, B. R.; Captain, B.; Parthasarathy, A.; Ramamurthy, V. J.
Am. Chem. Soc. 2010, 132, 13434–13442. (b) Peedikakkal, A. M. P.; Vittal, J. J.
Chem.;Eur. J. 2008, 14, 5329–5334. (c) Chu, Q.; Swenson, D. C.; MacGilliv-
ray, L. R. Angew. Chem., Int. Ed. 2005, 44, 3569–3572.
ꢀ
(10) (a) Gascon, J. A.; Sproviero, E. M.; Batista, V. S. Acc. Chem. Res.
2006, 39, 184–193. (b) Schapiro, I.; Weingart, O.; Buss, V. J. Am. Chem. Soc.
2009, 131, 16–17.
(11) Liu, R. S. H.; Hammond, G. S. Acc. Chem. Res. 2005, 38, 396–403.
(12) Sokolov, A. N.; Swenson, D. C.; MacGillivray, L. R. Proc. Natl.
Acad. Sci. U.S.A. 2008, 105, 1794–1797.
(13) (a) Das, M. C.; Bharadwaj, P. K. J. Am. Chem. Soc. 2009, 131,
10942–10949. (b) Das, M. C.; Bharadwaj, P. K. Chem.;Eur. J. 2010, 16, 5070–
5077. (c) Bradshaw, D.; Warren, J. E.; Rosseinsky, M. J. Science 2007, 315, 977–
980. (d) Halder, G. J.; Keppert, C. J.; Moubaraki, B.; Murray, K. S.; Cashion, J. D.
Science 2002, 298, 1762–1765.
(14) Neogi, S.; Sharma, M. K.; Das, M. C.; Bharadwaj, P. K. Polyhedron
2009, 28, 3923–3928.
~
(15) Lama, P.; Aijaz, A.; Sanudo, E. C.; Bharadwaj, P. K. Cryst. Growth
Des. 2010, 10, 283–290.
(16) See Supporting Information.

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 1891
Figure 1. A perspective view of metal coordination environment in (a) 1, (b) 2.
Table 1. M M Diagonal Distances Comparisons in M4L4 Macrocyclic Units of
M4L4 macrocyclic unit shows bicycle-pedal or crankshaft
motion. Now, the phenyl rings are no longer coplanar but
are twisted, forming a dihedral angle of 24.18°. The
imidazole rings also move away from coplanarity and
make a dihedral angle of ∼15° with respect to each
other. The two phenyl rings in ligand B also move
out of coplanarity to a dihedral angle of 26.83°. The
overall structure of 2a shows two consecutive rows of
channels filled with DMF followed by one row of empty
channels.16 To the best of our knowledge, this is the
first example of guest dependent pedal motion in
SC-SC fashion observed in metal complexes or coor-
dination polymers.
3 3 3
1-4, 2a, 2b, 2c and 20
diagonal distance
between M1 M3 (A)
diagonal distance
between M2 M4 (A)
˚
˚
compounds
3 3 3
3 3 3
1
2
2a
2b
2c
3
33.922
34.759
34.557
34.690
36.328
34.724
34.216
34.749
20.15
20.275
20.004
19.762
16.301
20.495
21.581
20.633
4
20
vibration of DMF at ∼1675 cm-1, whilea broad band centers
around 1095 cm-1 due to ionic ClOh anions.16
Further heating of the crystal 2a at 70 °C for 2 h under
vacuum, affords {[Cd(azim)2(DMF)2] (ClO4)2 (DMF)}n
4
Heat-Induced SC-SC Transformation Studies. In or-
der to investigate the pedal motion, a suitable crystal of 2
(mother crystal) is chosen and used throughout. On
careful heating at 50 °C for 2 h under vacuum, crystal 2
forms the partially desolvated compound, {[Cd(azim)2-
(DMF)2] (ClO4)2 (1.33DMF)}n (2a) without losing crys-
3
3
(2b) still maintaining crystallinity. As before, each Cd-
(II) center exhibits distorted octahedral geometry with
the same coordination mode as in 2 and 2a. Neither the
metal-bound DMF nor the ClOh anions make any
4
significant movement compared to the situation in 2a.
Here, partial expulsion of lattice DMF takes place
although the 2D rhombus grid framework is main-
3
3
tallinity. Each Cd(II) ion remains octahedral with coor-
dination similar to that in 2. While Cd-N bond distances
remain almost the same as in 2, the Cd-O (DMF) bond
distances become longer.16 The rhombic grid framework
tained albeit with slightly different diagonal M
˚
M distances of 34.693 and 19.762 A (Table 1 and
3 3 3
is shortened with the diagonal M M distances of 34.557
3 3 3
Figure 2). Now, the ligand C also undergoes bicycle-
pedal motion (Figure 4) and all phenyl rings of the four
azim ligands (A-D) in the M4L4 unit are twisted away
from coplanarity. The overall structure of 2b shows the
rhombic channels in the grid are empty at alternate
rows.16
˚
and 20.004 A (Table 1, Figure 2). Also, one of the ClOh
4
˚
anions moves toward the nearest Cd(II) from 5.997 A to
˚
˚
5.771 A while the other moves away from 5.997 to 6.639 A
(the distance refers to Cd Cl). Most interestingly, the
3 3 3 3
diphenyldiazene moiety of the ligand A (Figure 4) in the

1892 Inorganic Chemistry, Vol. 50, No. 5, 2011
Sharma and Bharadwaj
Figure 2. Crystal structure showing the M
M diagonal distances in (a) 1, (b) 2, (c) 2a, (d) 2b, (e) 2c, (f) 3, (g) 4, (h) 20.
3 3 3 3
Crystal 2b on further heating at 120 °C for another
2 h gives completely desolvated compound {[Cd(azim)2-
(ClO4)2]}n (2c). Although this crystal is of poor quality
and several cracks can be seen, still an approximate single
crystal X-ray structure is obtained. The framework is
The ClOh anions become highly disordered. Orientations
4
of the azo group remain unaltered with respect to the
situation in 2b. In the IR spectrum of 2c, the bands at 2930
and 1670 cm-1 disappear, suggesting the absence of DMF
molecules in the framework. The broad band at ∼1100
cm-1 corresponding to ionic ClO4- splits into two bands
due to coordination of ClO4- anions to Cd(II) centers.17
Guest-Induced SC-SC Transformation Studies. When
crystal 2c is kept in DMF, it turns shiny and transparent
maintained here with significantly different M M diagonal
˚
distances of 36.328 and 16.301 A (Table 1, Figure 2). Here,
3 3 3
all DMF molecules are lost and the ClOh anions move
4
furtherand occupy both the axial positions on the metal.16

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 1893
Figure 3. View ofM4L4 rhombus grid of (a) 1 showing disordered diphenyldiazenemoieties ofazim (unitsA and C) due todynamic pedal motion, (b) 2 (no
disorder is observed).
Figure 4. Schematic representation of reversible SC-SC pedal motion and twisting of phenyl rings in compound 2 after guest removal by heating (guest
molecules are removed for clarity).
(we call it 20). X-ray structural studies on 20 reveal that the
structure is quite similar to that of 2 with slight differences
in the bond distances and bond angles involving the metal
ion. This also shows removal of DMF molecules from the
framework, and its readmission occurs in SC-SC fash-
ion. Also, the pedal motion of ligands A and C in 20
change to the initial position observed in 2, indicating this
motion to be reversible in nature (Figure 4). To probe the
effect of different solvents on the pedal motion, another
crystal of compound 2 is kept in acetone for 10 h at RT
that affords crystal 3 as {[Cd(azim)2(DMF)2] (ClO4)2
same as that in 2. Each Cd(II) ion is octahedral with
coordination similar to that in 2. However, each lattice
DMF molecule is replaced by an acetone molecule. Most
interestingly, diphenyldiazene moieties of the ligands B
and D in the M4L4 macrocyclic unit have undergone pedal
motion (Figures 5 and 6). When crystal 3 is kept in DMF
for 10 h, the crystal is found to be transformed to the ori-
ginal 2 with slight differences in the bond distances and bond
angles involving the metal ion. The diagonal M M dis-
˚
tances are almost restored (34.749 and 20.633 A compared to
3 3 3
˚
34.759 and 20.275 A in the original (2), and the conforma-
3
3
2acetone}n without losing crystallinity. Its structure re-
veals that the M4L4 macrocyclic framework remains the
tions of the diphenyldiazene moieties are also restored to the
original conformations (as in 2).
When crystal 2 is kept in DEF for 10 h at RT, it gives
crystal 4 without losing crystallinity. Here, each DMF
(17) Wickenden, A. E.; Krause, R. A. Inorg. Chem. 1965, 4, 404–407.

1894 Inorganic Chemistry, Vol. 50, No. 5, 2011
Sharma and Bharadwaj
Figure 5. Schematic representation of reversible SC-SC acetone/DMF exchange in compound 2 (H atoms are removed for clarity).
Figure 6. Schematic representation of reversible SC-SC pedal motion in compound 2 after acetone/DMF exchange (guest molecules are removed for
clarity).
Figure 7. Schematic representation of reversible SC-SC DEF/DMF exchange in compound 2 (H atoms are removed for clarity).
molecule (coordinated or lattice) is replaced by a DEF
molecule retaining the framework with the diagonal
˚
photographs taken (Figure 9) of the mother crystal (2)
and its transformations to 2a, 2b, 2c, 20, 3, or 4 which show
no change in size, morphology, color, and transparency.
M
M distances of 34.724 and 20.495 A. It is found that
3 3 3
diphenyldiazene moieties of ligands A and C in the M4L4
macrocycle have undergone pedal motion (Figures 7 and 8).
To study whether these dynamic pedal motions are re-
versible, the crystal 4 is kept in DMF at RT to get crystal 2
as above. Thus, these pedal motions are completely reversible
in nature. During the substitution reactions, transparency
of the single crystal is retained. The possibility of dissolu-
tion of the mother crystal (2) in the successive liquids
followed by crystallization or renucleation at the surface
and growth of the new phase is excluded as shown by the
Conclusion
In conclusion, we have shown here that the ligand, bis(4-
imidazol-1-yl-phenyl)diazene(L) having two imidazole units
at each end, forms non-interpenetrated rhombus grid net-
works that stack in ABAB... fashion, with two DMF mole-
-
cules and two ClO4 anions occupying the void space. The
coordination polymer 2 shows guest- and heat-induced step-
wise dynamic bicycle-pedal or crankshaft motion in the
ligand moieties without losing crystallinity. To the best of

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 1895
Figure 8. Schematic representation of reversible SC-SC pedal motion in compound 2 after DEF/DMF exchange (guest molecules are removed for
clarity).
Figure 9. Photographs of single crystals of (a) 1, (b) 2, (c) 2a, (d) 2b, (e) 2c, (f) 20, (g) 3, and (h) 4.
our knowledge, this is the first example of guest-/heat-dependent
reversible pedal motion observed in a coordination polymer.
with ice-cold water, and dried in air to get the pure compound
(yield 85%). 1H NMR (CDCl3, 400 MHz): 7.21(s, 1H; HAr), 7.32
(s, 1H; HAr), 7.52(d, J=9.28 Hz, 2H; HAr), 7.94(s, 1H; HAr),
8.31(d, J = 9.28 Hz, 2H; HAr); Anal. Calcd for C9H7N3O2: C,
57.14; H, 3.73; N, 22.21%. Found: C, 57.18; H, 3.71; N, 22.24%.
(ii) Preparation of Bis(4-imidazol-1-yl-phenyl)diazene (L). A
suspension of 1-(4-nitrophenyl)-1H-imidazole (5 g, 26.45 mmol)
in 2-propanol was heated to reflux to obtain a clear solution.
Then aq NaOH (12 g in 30 mL H2O) and Zn powder (30 g) were
added to the mixture. It was then refluxed for 24 h and allowed
to cool to RT, and all insoluble materials present were removed
by filtration. Upon removal of the solvent under reduced
pressure, the product was extracted with chloroform. The
organic layer was washed several times with water, dried over
anhydrous Na2SO4, and finally evaporated under reduced
pressure to obtain a bright-orange solid which was recrystallized
from hexane/chloroform to get the pure compound (yield 70%).
1H NMR (CDCl3, 400 MHz): 7.00 (s, 1H; HAr), 7.31 (s, 1H;
Experimental Section
Materials. The metal salts were obtained from Aldrich and
used as received. All other chemicals were procured from
Aldrich and S.D. Fine Chemicals, India. All solvents were
purified prior to use.
Caution! Perchlorate salts are explosive (especially if they are
dry) and should be handled with extreme caution. We had not
encountered any problem during this work. In order to know the
thermal stability of complexes (1-5 and 10), we had heated 100
mg of each sample separately at 200 °C (heating rate 5 °C/min.)
for 6 h, and we did not face any problem. All the complexes
described herein are stable in air, moisture, and all the solvents
used. To minimize hazards associated with perchlorate com-
plexes the following precautions should be taken: (i) keep reaction
scales to <100 mg, (ii) do not heat the complexes above 200 °C,
not exceeding the heating rate above 5 °C/min, and (iii) carry out
all reactions in an efficient fume hood!
H
Ar), 7.13 (d, J=8.56 Hz, 2H; HAr), 7.56 (s, 1H; HAr), 7.48 (d,
J=8.8 Hz, 2H; HAr); IR (cm-1, KBr pellet): 3103, 1599, 1515,
1305; ESI-MS: m/z [M]þ 315; calculated 314.65; Anal. Calcd for
C18H14N6: C, 68.78; H, 4.49; N, 26.79%. Found: C, 68.82; H,
4.54; N, 26.71%.
Preparation of Ligand. The ligand bis(4-imidazol-1-yl-phe-
nyl)diazene was prepared in two steps as described below.
(i) Preparation of 1-(4-Nitrophenyl)-1H-imidazole. A mixture
of imidazole (2.1 g, 31.18 mmol) and anhydrous K2CO3 (5.8 g,
42.52 mmol) in DMF was heated for 30 min with vigorous stirring.
After that, 4-fluoronitrobenzene (4 g, 28.34 mmol) was added
over a period of 15 min. The mixture was refluxed for 24 h, cooled
to RT, and then added to ice-water. On standing, a yellow-colored
precipitate was formed which was collected by filtration, washed
Preparation of {[Co(L)2(DMF)2] (ClO4)2 (2DMF)}n (1). A
3
3
hot DMF solution (3 mL) of ligand L (50 mg, 0.16 mmol) was
added to MeOH/H2O mixed solution (1:1, 2 mL) of Co(ClO4)2
3
6H2O (58 mg, 0.16 mmol). On slow evaporation of the filtrate at
RT, red crystals were obtained in ∼80% yield. Anal. Calcd for
C48H56CoCl2N16O12: C, 48.90; H, 4.79; N, 19.01%. Found: C,
48.92; H, 4.77; N, 19.03%.

1896 Inorganic Chemistry, Vol. 50, No. 5, 2011
Sharma and Bharadwaj

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 1897
Table 3. Crystal and Structure Refinement Data for 2a, 2b, and 2c
compound
2a
2b
2c
formula
C138H154Cd3Cl6N46O34
3550.97
100
Mo KR
0.71069
triclinic
P1
10.449(5)
15.150(3)
26.857(2)
74.102(2)
87.250(5)
74.714(4)
3943(2)
1
1.495
0.591
1822
C45H49CdCl2N15O11
1159.29
100
Mo KR
0.71069
triclinic
P1
10.453(2)
15.212(5)
17.753(3)
72.53(3)
84.76(2)
74.64(3)
2596.3(12)
2
C36H28CdCl2N12O8
940.00
100
Mo KR
0.71069
monoclinic
C2/m
14.436(6)
16.301(3)
16.996(4)
90.000
92.576(5)
90.000
formula weight
temperature (K)
radiation
˚
wavelength (A)
crystal system
space group
˚
a, A
˚
b, A
˚
c, A
R (deg)
β (deg)
γ (deg)
3
˚
U, A
Z
F
3995(2)
2
0.781
0.374
948
calc g/cm3
1.483
0.596
1188
18273
0.0596
9039
μ, mm-1
F(000)
reflctns collected
Rint
independent reflctns
refinement method
GOF
27818
0.0523
10009
0.0888
13726
full-matrix least-squares on F2
1.043
3599
full-matrix least-squares on F2
1.896
full-matrix least-squares on F2
1.026
final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0660 wR2 = 0.1645
R1 = 0.0937 wR2 = 0.1972
R1 = 0.0846 wR2 = 0.2245
R1 = 0.1348 wR2 = 0.2658
R1 = 0.1874 wR2 =0.4326
R1 = 0.2009 wR2 = 0.4550
Preparation of {[Cd(L)2(DMF)2] (ClO4)2 (2DMF)}n (2). A hot
DMF solution (3 mL) of ligand L(50 mg, 0.16 mmol) was added to
MeOH/H2O mixed solution (1:1, 2 mL) of Cd(ClO4)2 xH2O(49mg,
0.16 mmol). On slow evaporation of the filtrate at RT, orange
crystals were obtained in ∼80% Yield. Anal. Calcd for C48H56-
CdCl2N16O12: C, 46.78; H, 4.58; N, 18.19%. Found: C, 46.82; H,
4.60; N, 18.17%.
X-ray Structural Studies. Single-crystal X-ray data were
collected at 100 K on a Bruker SMART APEX CCD diffract-
ometer using graphite-monochromatized Mo KR radiation (λ,
3
3
3
˚
0.71069 A). The linear absorption coefficients, scattering factors
for the atoms, and anomalous dispersion corrections were taken
from the International Tables for X-ray Crystallography. The
data integration and reduction were processed with SAINT18
software. An empirical absorption correction was applied to the
collected reflections with SADABS19 using XPREP.20 The
structure was solved by the direct methods using SHELXTL21
and refined on F2 by full-matrix least-squares techniques using
the SHELXL-97 program package.22 Each of the C atoms of
(C5-C9) of one benzene ring in the ligand of compound 1 is
disordered over two positions with occupancy of 0.5. Simi-
larly N3 is also disordered over two positions. Only a few H
atoms could be located in the difference Fourier maps in each
structure. The rest were placed in calculated positions using
idealized geometries (riding model) and assigned fixed iso-
tropic displacement parameters. Several DFIX commands
were used to fix the bond distances of lattice DMF molecules.
See Tables 2 and 3 for crystal and structure data for 1, 2, 3, 4,
20, 2a, 2b, and 2c.
Preparation of {[Cd(L)2(DMF)2] (ClO4)2 (1.33DMF)}n (2a).
3
3
Crystal of 2 was heated at 50 °C for 2 h under vacuum to obtain
2a. Anal. Calcd for C46H51.33Cd1Cl2N15.33O11.33: C, 46.68; H,
4.37; N, 18.15%. Found: C, 46.70; H, 4.39; N, 18.12%.
Preparation of {[Cd(L)2(DMF)2](ClO4)2 (DMF)}n (2b). Crystal
3
o
of 2a was heated at 70 C for 2 h under vacuum to obtain 2b.
Anal. Calcd for C45H49CdCl2N15O11: C, 46.62; H, 4.26; N, 18.12%.
Found: C, 46.63; H, 4.24 N, 18.10%.
Preparation of {[Cd(L)2(ClO4)2]}n (2c). Crystal of 2b was
heated at 120 °C for 2 h under vacuum to obtain 2c. Anal.
Calcd for C36H28CdCl2N12O8: C, 45.99 H, 3.00; N, 17.88%.
Found: C, 46.01; H, 2.97; N, 17.91%.
Preparation of {[Cd(L)2(DMF)2] (ClO4)2 (2acetone)}n (3).
3
3
Crystal of 2 on keeping in acetone at room temperature for 10
h affords 3. Anal. Calcd for C48H54CdCl2N14O12: C, 47.95; H,
4.53; N, 16.31%. Found: C, 47.92; H, 4.57; N, 16.29%.
Preparation of {[Cd(L)2(DEF)2] (ClO4)2 (2DEF)}n (4). A new
Acknowledgment. We gratefully acknowledge the financial
support received from the DST, India (Grant No. SR/S5/GC-
04/2008 to P.K.B.) and a SRF (from the CSIR) to M.K.S. We
thank Profs. V. Pedireddi and J. A. R. Navarro for PXRD
measurements.
3
3
crystal of 2 was immersed in DEF (0.1 mL) at room temperature
for 10 h to obtain 4. Anal. Calcd for C56H72CdCl2N16O12: C, 50.02;
H, 5.40; N, 16.67%. Found: C, 50.05; H, 5.39; N, 16.69%.
Preparation of {[Cd(L)2(DMF)2] (ClO4)2 (2DMF)}n (20). Crys-
3
3
tals of 2c, 3, and 4 were immersed in DMF separately at room
temperature for 10 h to obtain 20 in each case. Anal. Calcd for
C48H56CdCl2N16O12: C, 46.78; H, 4.58; N, 18.19%. Found: C,
46.79; H, 4.57; N, 18.16%.
Supporting Information Available: X-ray crystallographic
1
files in CIF format for 1-4, 2a, 2b, 2c, and 20, IR spectra, H
NMR spectra, ESI mass spectra, XRPD, thermogravimetric
analyses, additional figures and tables. This material is available
free of charge via the Internet at http://pubs.acs.org.
Physical Measurements. Spectroscopic data were collected as
follows: IR spectra (KBr disk, 400-4000 cm-1) were recorded
on a Perkin-Elmer model 1320 spectrometer. X-ray powder
patterns (Cu KR radiation, 3 deg/min scan rate, 293 K) were
acquired using a Philips PW100 diffractometer. Thermogravi-
metric analysis (TGA) (5 °C/min heating rate under a nitrogen
atmosphere) was performed with a Mettler Toledo Star System.
1H NMR spectra were recorded on a JEOL JNM-LA500 FT
instrument (400 and 500 MHz) in CDCl3 and DMSO-d6 with
TMS as the internal standard. Microanalysis data for the
compounds were obtained from CDRI, Lucknow.
(18) SAINTþ, version 6.02; Bruker AXS: Madison, WI, 1999.
(19) Sheldrick, G. M. SADABS, Empirical Absorption Correction Pro-
€
gram; University of Gottingen: Germany, 1997.
(20) XPREP, version 5.1; Siemens Industrial Automation Inc.: Madison,
WI, 1995.
(21) Sheldrick, G. M. SHELXTL Reference Manual, version 5.1; Bruker
AXS: Madison, WI, 1997.
(22) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Re-
€
€
finement; University of Gottingen: Gottingen, Germany, 1997.