Indian Journal of Chemistry
Vol. 50A, Sept-Oct 2011, pp. 1410-1417
Synthesis and structural characterization of potassium coordination
polymers based on a copper-bis(dithiolato) complex:
Role of coordinating solvents and counter cation
Ramababu Bolligarlaa, Bharat Kumar Tripuramallua, Vudagandla Sreenivasulub & Samar K Dasa, ∗
a
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
Email: [email protected]/ [email protected]
b
BioPolymer and Thermophysical Lab, Department of Chemistry, Sri Venkateswara University,
Tirupati 517 502, India
Received 11 May 2011; revised and accepted 14 June 2011
We have synthesized two new potassium metal coordination polymers {[K(CH3COCH3)3][Cu(btdt)2]}n (1) and
{[K(CH3CN)2][Cu(btdt)2]}n (2) of diverse dimensionality based on a copper coordination complex [CuIII(btdt)2]1−
({btdt}2– = 2,1,3-benzenethiadiazole-5,6-dithiolate). Recrystallization of the dark brown solid, obtained from the reaction
mixture of H2btdt, KOH and CuCl2·2H2O in MeOH, from the coordinating solvents acetone and acetonitrile results in the
formation of 3-D and 2-D extended networks in compounds (1) and (2) respectively. The crystal structures of (1) and (2)
have been discussed in comparison with those of recently reported sodium coordination polymers
{[Na(CH3OH)4][Au(btdt)2]}n (3), [Na(DMF)2][Au(btdt)2]}n (4) and {[Na(CH3CN)2][Au(btdt)2]}n (5). Compounds (1) and
(2) have additionally been characterized by routine spectroscopy including elemental analyses.
Keywords: Coordination Chemistry, Coordination polymers, Metal-organic frameworks, Crystal structures, Counter cation,
Coordinating solvents, Potassium, Copper
The design and synthesis of coordination polymers or
metal-organic frameworks (MOFs), that involve
careful selection of organic ligands with suitable
functional groups and metal ions, have substantial
interests for producing solid-functional materials.1-7
These materials have applications in the areas of gas
storage and non-linear optical, conducting and
magnetic materials.8-12 In this context, square-planar
metal-dithiolene complexes have drawn considerable
attention, because these coordination complexes have
been used as building blocks for the construction of
polymeric compounds, that have been used as
conducting, magnetic and non-linear optical
materials.13-20 The coordination polymers are generally
described in terms of structural diversity and diverse
dimensionality, that are, in turn, greatly affected/
controlled by the choice of the ligands,21-23 metal/
ligand ratios,24-25 solvents26-29 and counterions.30
Among these factors, influence of solvents and
counter ions are particularly interesting because
simply the variations in solvents and counter ions in
a particular synthesis results in a wide range of
self-assembled structures.26-30 However, influence of
coordinating solvents and counterions on the
coordination networks, based on a square-planar
metal bis(dithiolene) complex, has not been explored.
Also, potassium based coordination polymers
associated with dithiolene complexes are very few in
the literature.31
Recently, we have reported a systematic study of
the solvent effects on the formation of crystalline
coordination networks of diverse dimensionalities
(from 1D to 3D) by employing different coordinating
solvents such as MeOH, DMF and CH3CN through
their coordination to the sodium cation.32 We also
have demonstrated that the geometry of the central
carbon of the crystallizing coordinating solvents plays
an important role in directing the dimensionality of
coordination polymers.32 In the present study, in order
to investigate the effect of counter cation, we have
synthesized two new coordination polymers
{[K(CH3COCH3)3][Cu(btdt)2]}n (1) and {[K(CH3CN)2]
[Cu(btdt)2]}n (2) using potassium ion (K+) as a
counter cation. These compounds have been
characterized unambiguously by single crystal X-ray
crystallography, their spectral characterizations
(IR, NMR and UV-vis) and elemental analyses.
BOLLIGARLA et al.: POTASSIUM COORDINATION POLYMERS BASED ON Cu-BIS(DITHIOLATO) COMPLEX
Materials and Methods
All the reagents for the syntheses were
commercially available and used as received.
2,1,3-Benzenethiadiazole-5,6-dithiol (H2btdt) ligand
was synthesized according to literature procedure.33
Syntheses of metal complexes were performed under
N2 using standard inert-atmosphere techniques.
Solvents were dried by standard procedures.
Elemental analyses were performed on FLASH EA
series 1112 CHNS analyzer. Infrared spectra were
recorded as KBr pellets on a Jasco–5300 FT–IR
spectrophotometer at 298 K. Diffuse reflectance
spectra of solid compounds were recorded on a
UV-3600 Shimadzu UV-Vis-NIR spectrophotometer.
NMR spectra were recorded using Bruker 400 MHz
spectrometer. The chemical shifts (δ) are reported
in ppm.
Synthesis of potassium-based coordination polymers (1) and (2)
Synthesis of the precursor (P)
The btdt dianion is generated, in situ, by treatment
of H2btdt (0.200 g, 1.0 mmol) with excess amount of
KOH (0.2 g, 3.57 mmol) in MeOH (10.0 mL). To the
resulting clear red solution, solid CuCl2·2H2O (0.085 g,
0.5 mmol) was added and the reaction mixture was
stirred for 30 min in open atmosphere. The resulting
dark black micro-crystalline solid was separated by
filtration and air dried. This dark black microcrystalline solid is named as the precursor (P).
Yield: 0.180 g. IR (KBr, cm–1): 3417, 2964, 1597,
1478, 1422, 1384,1361, 1262, 1242, 1080, 853, 799,
701, 618, 525, 475; 1H NMR (400 MHz, δ ppm)
(DMSO-d6): 7.63(s, 4H). Potassium-ion associated
coordination polymers (1) and (2) were prepared
(as described below) by recrystallizing this black
colored solid from the acetone and acetonitrile
solvents respectively.
{[K(CH3COCH3)3][Cu(btdt)2]}n (1)
Black colored crystals of compound (1) were
obtained by the vapor diffusion of diethyl ether into
an acetone solution of the black solid compound (P).
Anal. (%): Calcd. for C21H22N4O3S6KCu: C, 37.45;
H, 3.29; N, 8.32. Found: C, 37.25; H, 3.52; N, 8.19;
IR (KBr, cm–1): 3414, 2963, 1594, 1479, 1420, 1363,
1261, 1242, 1079, 1022, 800, 701, 524, 467;
1
H NMR (400 MHz, δ ppm) (DMSO-d6): 7.63(s, 4H).
{[K(CH3CN)2][Cu(btdt)2]}n (2)
Black solid precursor (P) was recrystallized in
acetonitrile solution by the vapor diffusion of diethyl ether
resulting in black colored crystals of compound (2).
1411
Anal. (%): Calcd. for C16H10N6S6KCu: C, 33.06;
H, 1.73, N, 14.46. Found: C, 33.25; H, 1.67; N, 14.38;
IR (KBr, cm–1): 3405, 2963, 2925, 2833, 1585, 1479,
1419, 1363, 1261, 1242, 1097, 1078, 1022, 862, 844,
825, 800, 524; 1H NMR (400 MHz, δ ppm) (DMSO-d6):
7.63(s, 4H).
Single crystal structure determination
Crystal data for compound (1) was collected on
Oxford Gemini Diffractometer equipped with EOS
CCD detector at 100 K. Monochromatic Mo-Kα
radiation (0.71073 Å) was used for the measurements.
Absorption corrections using multi ψ-scans were
applied. Single crystals suitable for facile structural
determination for the compound (2), were measured
on a three circle Bruker SMART APEX CCD area
detector system under Mo-Kα (λ = 0.71073 Å)
graphite monochromatic X-ray beam. The frames
were recorded with an ω scan width of 0.3°, each for
8 s, crystal-detector distance 60 mm, collimator
0.5 mm. Data reduction was performed by using
SAINTPLUS.34 Empirical absorption corrections were
performed by using equivalent reflections program,
SADABS.34 The structures were solved by direct
methods and least-squares refinement on F2 for the
compounds (1) and (2) by using SHELXS-97.35 All
non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were included in the structure
factor calculation by using a riding model. The
crystallographic parameters, data collection and
structure refinement of the compounds (1) and (2) are
summarized in Table 1. Selected bond lengths and
angles for the compounds (1) and (2) are listed in
Tables 2 and 3 respectively.
Results and Discussion
Synthesis and spectroscopic characterization
The synthetic strategies for the compounds (1) and
(2) are shown in Scheme 1. The black colored solid
(P) is obtained from the reaction of one mole
equivalent of CuCl2·2H2O with two mole equivalents
of H2btdt in MeOH treated with excess amount of
KOH in an open atmosphere as shown in Scheme 1.
Recrystallization of this solid compound (P) from
acetone and acetonitrile/ether diffusions leads to the
formation of 3D and 2D coordination polymers (1)
and (2), respectively. Compounds (1) and (2) have
been characterized by IR, 1H NMR, UV-visible
spectroscopy and elemental analyses. In the solid
state, coordination polymers (1) and (2) show
strong bands over 420-440 nm region in their diffuse
1412
INDIAN J CHEM, SEC A, SEPT-OCT 2011
Table 1—Crystallographic data and structural refinement for compounds (1) and (2)
Empirical formula
Formula weight
Temperature (K)
Crystal size (mm)
Crystal system
Space group
Z
Wavelength (Å)
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
Volume (Å3)
Calc. density (mg/m-3)
Reflections collected/ unique
R(int)
F(000)
Theta range for data collection (deg.)
Refinement method
Data/ restraints/ parameters
Goodness-of-fit on F2
R1/wR2 (I>2sigma(I))
R1/wR2 (all data)
Largest diff. peak and hole (e Å-3)
(1)
C21H22N4O3S6KCu
673.43
100(2)
0.32 × 0.14 × 0.04
Monoclinic
C2/c
4
0.71073
(2)
C16H10N6S6KCu
581.30
100(2)
0.58 × 0.20 × 0.10
Triclinic
P-1
1
0.71073
18.244(4)
7.6325(7)
10.794(2)
7.9361(7)
15.035(3)
9.1797(8)
90.000
81.6030(10)
113.94(3)
78.3720(10)
90.000
80.3500(10)
2723.9(9)
533.28(8)
1.642
1.810
4653/ 2232
5546/ 2092
0.0522
0.0169
1376
292
2.95 – 24.70
2.28 – 26.01
Full-matrix least-squares on F2
2232/ 0/ 169
2092/ 0/ 140
0.871
1.068
0.0454/ 0.1297
0.0238/ 0.0606
0.0571/ 0.1387
0.0244/ 0.0609
1.265 and –1.660
0.340 and –0.354
Table 2—Selected bond lengths and angles for compound (1)
Bond lengths (Å)
Cu(1)-S(1)#1
2.1536(12)
Cu(1)-S(1)
2.1536(12)
Cu(1)-S(2)#1
2.1630(10)
Cu(1)-S(2)
2.1630(10)
S(1)-C(1)
1.747(4)
S(2)-C(6)
1.739(4)
S(2)-K(1)
3.4965(14)
C(1)-C(2)
1.362(5)
K(1)-O(3)
2.599(4)
K(1)-O(1)#2
2.703(3)
K(1)-O(1)
2.703(3)
K(1)-N(2)#3
2.858(3)
K(1)-N(2)#4
2.858(3)
K(1)-S(2)#2
3.4965(14)
N(2)-K(1)#3
2.858(3)
Bond angles (°)
S(1)#1-Cu(1)-S(1)
180.0
S(1)#1-Cu(1)-S(2)#1
91.80(4)
S(1)-Cu(1)-S(2)#1
88.20(4)
S(1)#1-Cu(1)-S(2)
88.20(4)
S(1)-Cu(1)-S(2)
91.80(4)
S(2)#1-Cu(1)-S(2)
180.0
C(1)-S(1)-Cu(1)
105.41(12)
C(6)-S(2)-Cu(1)
105.75(12)
C(6)-S(2)-K(1)
92.85(11)
Cu(1)-S(2)-K(1)
120.34(4)
O(3)-K(1)-O(1)#2
86.26(6)
O(3)-K(1)-O(1)
86.26(6)
O(1)#2-K(1)-O(1)
172.52(13)
O(3)-K(1)-N(2)#3
74.62(6)
O(1)#2-K(1)-N(2)#3
99.14(9)
O(1)-K(1)-N(2)#3
78.85(9)
O(3)-K(1)-N(2)#4
74.62(6)
O(1)#2-K(1)-N(2)#4
78.85(9)
O(1)-K(1)-N(2)#4
99.14(9)
N(2)#3-K(1)-N(2)#4
149.23(13)
O(3)-K(1)-S(2)
148.180(19)
O(1)#2-K(1)-S(2)
111.69(7)
O(1)-K(1)-S(2)
75.01(7)
N(2)#3-K(1)-S(2)
76.64(6)
N(2)#4-K(1)-S(2)
132.99(7)
O(3)-K(1)-S(2)#2
148.180(19)
O(1)#2-K(1)-S(2)#2
75.01(7)
O(1)-K(1)-S(2)#2
111.69(7)
N(2)#3-K(1)-S(2)#2
132.99(7)
N(2)#4-K(1)-S(2)#2
76.64(6)
S(2)-K(1)-S(2)#2
63.64(4)
C(9)-O(1)-K(1)
164.2(3)
C(12)-O(3)-K(1)
180.000(2)
C(3)-N(2)-K(1)#3
134.5(2)
S(3)-N(2)-K(1)#3
118.42(15)
Symmetry transformations used to generate equivalent atoms: #1 -x,-y+1,-z+2; #2 -x,y,-z+3/2; #3 -x+1/2,-y+3/2,-z+2; #4 x-1/2,-y+3/2,z-1/2.
1413
BOLLIGARLA et al.: POTASSIUM COORDINATION POLYMERS BASED ON Cu-BIS(DITHIOLATO) COMPLEX
Table 3—Selected bond lengths and angles for compound (2)
Bond lengths (Å)
Cu(1)-S(2)
Cu(1)-S(1)
S(2)-K(1)
K(1)-N(2)#3
K(1)-N(3)#5
K(1)-C(5)#5
K(1)-S(2)#5
Bond angles (°)
S(2)-Cu(1)-S(2)#1
S(2)#1-Cu(1)-S(1)
S(2)#1-Cu(1)-S(1)#1
C(6)-S(2)-Cu(1)
Cu(1)-S(2)-K(1)
C(3)-N(2)-K(1)#2
N(2)#3-K(1)-N(2)#4
N(2)#4-K(1)-N(3)#5
N(2)#4-K(1)-N(3)
N(2)#3-K(1)-C(5)#5
N(3)#5-K(1)-C(5)#5
N(2)#3-K(1)-C(6)#5
N(3)#5-K(1)-C(6)#5
C(5)#5-K(1)-C(6)#5
N(2)#4-K(1)-S(2)#5
N(3)-K(1)-S(2)#5
C(6)#5-K(1)-S(2)#5
N(2)#4-K(1)-S(2)
N(3)-K(1)-S(2)
C(6)#5-K(1)-S(2)
C(7)-N(3)-K(1)
2.1730(5)
2.1817(5)
3.3795(5)
2.7649(16)
2.7872(17)
3.2917(18)
3.3794(5)
Cu(1)-S(2)#1
Cu(1)-S(1)#1
N(2)-K(1)#2
K(1)-N(2)#4
K(1)-N(3)
K(1)-C(6)#5
2.1730(5)
2.1817(5)
2.7649(16)
2.7649(16)
2.7873(17)
3.2919(18)
180.0
88.034(16)
91.966(16)
104.92(6)
109.589(18)
134.24(12)
180.0
76.88(5)
103.12(5)
79.62(5)
66.49(5)
75.57(4)
90.40(5)
24.08(4)
81.08(3)
75.95(4)
30.51(3)
98.92(3)
104.05(4)
149.49(3)
148.32(16)
S(2)-Cu(1)-S(1)
S(2)-Cu(1)-S(1)#1
S(1)-Cu(1)-S(1)#1
C(6)-S(2)-K(1)
C(1)-S(1)-Cu(1)
S(3)-N(2)-K(1)#2
N(2)#3-K(1)-N(3)#5
N(2)#3-K(1)-N(3)
N(3)#5-K(1)-N(3)
N(2)#4-K(1)-C(5)#5
N(3)-K(1)-C(5)#5
N(2)#4-K(1)-C(6)#5
N(3)-K(1)-C(6)#5
N(2)#3-K(1)-S(2)#5
N(3)#5-K(1)-S(2)#5
C(5)#5-K(1)-S(2)#5
N(2)#3-K(1)-S(2)
N(3)#5-K(1)-S(2)
C(5)#5-K(1)-S(2)
S(2)#5-K(1)-S(2)
91.966(16)
88.034(16)
180.0
71.99(6)
104.96(6)
118.42(8)
103.12(5)
76.88(5)
180.0
100.38(5)
113.51(5)
104.43(4)
89.60(5)
98.92(3)
104.05(4)
47.96(3)
81.08(3)
75.95(4)
132.04(3)
180.0
Symmetry transformations used to generate equivalent atoms: #1-x+1,-y+2,-z-1; #2 x,y-1,z; #3 x,y+1,z; #4 -x+1,-y+1,-z; #5 -x+1,-y+2,-z.
Acetone/ether {[K(CH3COCH3)3][Cu(btdt)2]}n (1)
Diffusion
3-D Coordination polymer
N
SH
N
SH ii) CuCl2.2H2O
iii) Air
S
i) KOH, MeOH
Black solid Recrystallization
Cu-complex
(P)
H2btdt = 2,1,3-Benzene
thiadiazole-5,6-dithiol
CH3CN/ether
{[K(CH3CN)2][Cu(btdt)2]}n
Diffusion
2-D Coordination polymer
(2)
Scheme 1
reflectance spectra as shown in Fig. 1. These spectral
features are similar to the previously reported spectra
for gold coordination polymers,32 {[Na(CH3OH)4]
[Au(btdt)2]}n (3), {[Na(DMF)2][Au(btdt)2]}n (4) and
{[Na(CH3CN)2][Au(btdt)2]}n (5).
Crystal structure of {[K(CH3COCH3)3][Cu(btdt)2]}n (1)
The compound {[K(CH3COCH3)3][Cu(btdt)2]}n (1)
crystallizes in monoclinic space group C2/c. The
asymmetric unit in the crystal structure of the
complex (1) (represented as labeled atoms) contains
one {btdt}2– ligand and one CH3COCH3 molecule in
general positions, while one-half of acetone molecule,
one Cu atom and one K atom are located at symmetry
centers as shown in Fig. 2(a) as thermal ellipsoidal
plot. The structure of the complex shows almost a
square planar geometry around the Cu(III) ion
because the coordination angles are in the range of
88.20(3)°–91.80(3)°, i.e. slightly deviated from 90.0°
while the other coordination angles are 180.0°, and
are not deviated. The Cu–S bond distances are in the
range of 2.1536(12)–2.1630(10) Å. However, there is
a deviation in the planar nature of the dithiolene
ligand (chelate) present in the anionic units of
1414
INDIAN J CHEM, SEC A, SEPT-OCT 2011
Fig. 1—The solid state (diffuse reflectance) spectra (normalized)
of compounds (1) (- - - curve 1), (2) (….. curve 2) and black solid
compound (P) ( ___ curve 3) (See Scheme 1).
complex (1). The bending deviation (η) between the
SMS plane and SCCS plane is characterized by an
angle of 0.90° present in the {Cu1S1S2C1C6} chelate
as shown in Fig. 3(a). In the crystal structure of the
complex (1), two nitrogen and two sulfur donor atoms
of each [Cu(btdt)2]1– anion are coordinated to four
different K+ counter ions. Each K+ ion present in the
crystal structure (1), extends its coordination ability to
the two nitrogen and two sulfur donor atoms of four
different [Cu(btdt)2]1– anions, thus resulting in the
formation of 3D coordination polymeric networks as
shown in Fig. 2(b) and 2(c). The remaining three
coordination sites of hepta-coordinated geometry of
potassium ion are occupied by three oxygen atoms
of three different acetone (solvent) molecules.
In complex (1), the K–N bond distance is 2.858(3) Å
and K–S bond distance is 3.4965(14) Å, which lie in
the range of reported values.31,36-38 The K–O(solvent)
coordination bond distances from acetone molecules
are in the range of 2.599(4) – 2.703(3) Å.
Crystal structure of {[K(CH3CN)2][Cu(btdt)2]}n (2)
Single crystals of the complex {[K(CH3CN)2]
[Cu(btdt)2]}n (2), grown from acetonitrile, crystallize
in the triclinic space group P-1. The asymmetric unit
in the crystal structure of complex (2) (represented as
labeled atoms, Fig. 4(a)) contains one btdt2– ligand
and one acetonitrile (solvent) molecule in general
positions, and one-half Cu and K atoms, located at
symmetry centers as shown in Fig. 4(a). The structure
of complex (2) shows square planar geometry around
the Cu(III) ion (the coordination angles are in the
range of 88.034(16)°–91.966(16)°). The Cu–S bond
distances are in the range of 2.1730(5)–2.1817(5) Å.
Fig. 2—(a) Thermal ellipsoid plot of compound (1) (50%
probability). Extended networks observed in the crystal
structures of compound (1), (b) when viewed down to
crystallographic a axis (hydrogen atoms removed for clarity),
and, (c) when viewed down to crystallographic c axis (hydrogen
atoms and coordinated acetone molecules are removed
for clarity).
BOLLIGARLA et al.: POTASSIUM COORDINATION POLYMERS BASED ON Cu-BIS(DITHIOLATO) COMPLEX
For this structure (complex 2) also, there is a
deviation in the planar nature of the dithiolene ligand
(chelate). The bending deviation (η) between the SMS
plane and SCCS plane is characterized by the angle of
6.91° present in the {Cu1S1S2C1C6} chelate as
shown in Fig. 3(b).
In the crystal structure of the complex (2), two
nitrogen and two sulfur donor atoms of each
[Cu(btdt)2]1– anion are coordinated to four different
K+ counter ions. Geometry around the potassium ion
in this complex, is close to octahedral (the entire
coordination bond angles between S2―K―S2′,
N2―K―N2′ and N3―K―N3′ are 180°). In the
crystal structure, each potassium ion is coordinated to
four nitrogen atoms and two sulfur atoms, in which
two nitrogen and two sulfur atoms are from four
different dithiolene complex [Cu(btdt)2]1− anions and
the remaining two nitrogen atoms are from two
different acetonitrile (solvent) molecules. K–S2,
K–N2 and K–N3(solvent) bond distances are 3.3795(5),
2.7649(16) and 2.7873(17) respectively in the crystal
structure of complex (2), which lie in the range of
reported values.31,36-38 The resulting extended crystal
structure of complex (2) shows 2D coordination
network, as shown in Fig. 4(b).
Fig. 3—Anionic complex units through the side view of
(a) compound (1), and, (b) compound (2).
1415
Influence of counter cations and coordinating solvents on the
structural diversity and dimensionality of coordination polymers
In our recent communication,32 the dimensionality
of a sodium based coordination polymer system,
coupled with a gold(III) bis(dithiolene) complex, has
been shown to be regulated by the type of
hybridization of the central carbon atom of the solvent
coordinating to the sodium ion. From careful crystal
structure analyses, it was generalized that there exists
a relationship between dimensionality of coordination
polymers (based on a square planar gold(III)
bis(dithiolene) complex coupled with an octahedral
sodium complex) and the type of hybridization of the
central carbon atom of the sodium coordinated solvent
molecules. In other words, hybridization of the central
carbon atoms of the solvents (MeOH, DMF and
CH3CN) attached to the coordinating atoms plays an
important role in directing the dimensional-topologies
of the coordination polymers32 (3–5). In continuation
of our systematic investigations of the role of
coordinating solvents and counter cations (i.e., K+ ion
instead of Na+ ion) on the structural diversity and
dimensionality of coordination networks, we have
synthesized these two new potassium-coordination
polymers (1 and 2). As already discussed, the present
systems (compounds 1 and 2) are 3D and 2D
extended networks observed in their crystal structures
obtained from recrystallizations of acetone and
acetonitrile solution of solid precursor (P),
respectively.
We have compared the crystal structures of (2)
(present system) and (5) (reported earlier), since the
recrystallizing solvents are identical in both cases.
Comparison of the crystal structures (mainly
dimensional topologies) of compounds (2) and (5), in
which coordinated acteonitrile solvent is coordinated
Fig. 4—(a) Thermal ellipsoid plot of compound (2) (50% probability), and, (b) extended network observed in the crystal structures of
compound (2) when viewed down to crystallographic a axis (hydrogen atoms have been omitted clarity).
1416
INDIAN J CHEM, SEC A, SEPT-OCT 2011
to the K+ and Na+ ions respectively, shows that
sodium ion is coordinated through four nitrogen
atoms in compound (5), whereas, in compound (2),
potassium ion is coordinated through two nitrogen
and two sulfur atoms, both from four different metal
bis(dithiolene) building blocks. We have argued that
potassium ion can accommodate two sulfur atoms
(and two nitrogen atoms) instead of four nitrogen
atoms (as observed in the case of compound (5),
sodium ion coordinates to four nitrogen donors) due
to the larger size of potassium ion in comparison with
sodium ion. Due to this difference in coordination
environments, the dimensional topologies are
different; thus (2) and (5) are not isomorphous, even
though both sodium and potassium have same
coordination numbers in compounds (5) and (2)
respectively. Thus, compound (5) extends to 3D
network, whereas compound (2) extends into 2D
coordinated network in their crystal structures.
When we compared the crystal structures of
compounds (1) and (2), we found that in both
compounds, the potassium ion coordinates through
nitrogen and sulfur donors. However, in compound
(1) the coordination number of potassium ion is seven
with three coordinated acetone solvent molecules,
whereas in compound (2), the coordination number of
K+ ion is six with two coordinated acetonitrile solvent
molecules. This makes a difference in their
dimensional topologies.
Conclusions
In summary, we have demonstrated here the
synthesis of two new potassium coordination
polymers of diverse dimensionality, based on a
Cu(III) dithiolene complex anion [CuIII(btdt)2]1− by
changing
the
solvents
of
recrystallization.
Recrystallization from the coordinating acetone and
acotonitrile solvents results in the formation of 3D
and 2D extended networks in the crystal structures of
compounds {[K(CH3COCH3)3][Cu(btdt)2]}n (1) and
{[K(CH3CN)2][Cu(btdt)2]}n (2) respectively. We have
compared the structures and dimensionalities of the
present system with previously reported sodium
coordination polymers. We found that the potassium
based polymeric compounds (1) and (2) do not obey
the concept of “dimensionality decided by the type of
hybridization of the central carbon atom of the
coordinating solvent”, as published earlier for sodium
coordination polymers. This is probably due to
difference in size of the counter cations (namely,
sodium and potassium). We believe that in the sodium
based coordination polymeric system, octahedral
geometry of sodium ion (where coordination number
does not vary) plays a role in directing the
dimensionality of the concerned coordination
polymers which is not true for K-based coordination
polymers, where coordination number of potassium
ion varies because of its larger size.
Supplementary Data
CCDC numbers 823820 and 823821 contain the
supplementary crystallographic data for this paper.
These data can be obtained free of charge from
the The Cambridge Crystallographic Data Centre,
12, Union Road, Cambridge CB2 1EZ, UK
via
www.ccdc.cam.ac.uk/data_request/cif
(Email:
[email protected]; Fax: +44 1223 336033).
Acknowledgement
We thank Department of Science and Technology
(DST), New Delhi, Government of India, for financial
support (Project No. SR/SI/IC-23/2007). The National
X-ray Diffractometer facility at University of
Hyderabad, Hyderabad, by the DST, New Delhi, is
gratefully acknowledged. We are grateful to UGC,
New Delhi, for providing infrastructure facility at
University of Hyderabad, Hyderabad, under UPE
grant. RB and BKT thank CSIR and UGC, New
Delhi, and VS thanks UGC Networking Centre for
fellowships.
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