Copper(II) and cobalt(II) coordination polymers with bridging 1,2,4,5-benzenetetracarboxylate and N-methylimidazole: Coordination number-determined sheet topology

Article abstract of DOI:10.1039/b207559h

Two new coordination polymers were synthesized under ambient conditions in water by combining a cobalt(II) or copper(II) metal salt with 1,2,4,5-benzenetetracarboxylate (BTEC) and N-methylimidazole (Meim), forming Co₂(BTEC)(Meim)₄(H₂O)₄·H ₂O (1) and Cu₂(BTEC)(Meim)₄ (2). Compounds 1 and 2 were characterized by X-ray crystallography, powder X-ray diffraction, TGA, FT-IR and elemental analysis. The crystal structures and 2D polymeric structures of compounds 1 and 2 are reported. Coordination polymer 1 crystallizes in the monoclinic space group C2/c. Coordination polymer 2 crystallizes in the triclinic space group P1. Both 1 and 2 are made up of infinite sheets of BTEC ligands and metal ions. The sheets in 1 are puckered, giving an offset zigzag sheet topology, while the sheets in 2 are flat. Significant π-π stacking between Meim rings on adjacent sheets contributes to inter-sheet interactions in both 1 and 2. While hydrogen bonding does not play a role in 2, significant hydrogen bonding between sheets in 1 also stabilizes inter-sheet interactions.

Full text of DOI:10.1039/b207559h

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Copper(II) and cobalt(II) coordination polymers with bridging
1,2,4,5-benzenetetracarboxylate and N-methylimidazole:
coordination number-determined sheet topology†
Deping Cheng, Masood A. Khan and Robert P. Houser*
Department of Chemistry & Biochemistry, University of Oklahoma, 620 Parrington Oval,
Norman, OK 73019, USA. E-mail: houser@ou.edu
Received 2nd August 2002, Accepted 18th October 2002
First published as an Advance Article on the web 7th November 2002
Two new coordination polymers were synthesized under ambient conditions in water by combining a cobalt()
or copper() metal salt with 1,2,4,5-benzenetetracarboxylate (BTEC) and N-methylimidazole (Meim), forming
Co2(BTEC)(Meim)4(H2O)4ؒH2O (1) and Cu2(BTEC)(Meim)4 (2). Compounds 1 and 2 were characterized by X-ray
crystallography, powder X-ray diffraction, TGA, FT-IR and elemental analysis. The crystal structures and 2D
polymeric structures of compounds 1 and 2 are reported. Coordination polymer 1 crystallizes in the monoclinic
¯
space group C2/c. Coordination polymer 2 crystallizes in the triclinic space group P1. Both 1 and 2 are made up of
infinite sheets of BTEC ligands and metal ions. The sheets in 1 are puckered, giving an offset zigzag sheet topology,
while the sheets in 2 are flat. Significant π–π stacking between Meim rings on adjacent sheets contributes to
inter-sheet interactions in both 1 and 2. While hydrogen bonding does not play a role in 2, significant hydrogen
bonding between sheets in 1 also stabilizes inter-sheet interactions.
We and others have synthesized CPs using TMA as a bridg-
Introduction
ing ligand between transition metal ions.4,12,13,16,17 We demon-
strated that a small change in the co-ligand was critical in the
stability of CPs comprised of copper(), TMA, and either imi-
dazole (Him) or N-methylimidazole (Meim).16 In the case of
Him, hydrogen bonding between 2D sheets stabilized the 3D
structure. However, when the co-ligand was Meim, inter-sheet
hydrogen bonding was disrupted, and the 3D structure was
destabilized.16
The design and synthesis of new supramolecular materials have
garnered considerable interest.1 Particularly interesting to
inorganic chemists are coordination polymers (CPs), most
often composed of transition metals and bridging ligands that
form chains, sheets, and 3D networks.2 Many CPs have zeolite-
like structural properties such as large channels or void space,
making them potential candidates for adsorption,3,4 host–guest
chemistry,5 or catalysis.6 Other CPs have been shown to have
unusual magnetic7 or non-linear optical properties.8,9
For the most part, researchers have focussed on altering the
size, shape, and geometry of the ligands to attempt to control
the structure of the CPs.10 One particularly useful family of
ligands that has been used to create a large number of CPs
contain carboxylato functional groups. Ligands with at least
two, and up to four carboxylates can bridge between metal ions
to create 1D chains, 2D sheets, and 3D networks.4,11–14
Recently our laboratory has focussed on the simple aromatic
carboxylates trimesitate (1,3,5-benzenetricarboxylate, TMA)
and pyromellitate (1,2,4,5-benzenetetracarboxylate, BTEC). In
particular, we are interested in using TMA or BTEC and non-
bridging co-ligands with a variety of first-row transition metals
to create CPs. Our goal is to probe the ability of these non-
bridging co-ligands to influence the structures of the CPs. The
synthesis of other mixed ligand CPs and their structures have
been reported in the literature.5,11,15
The BTEC ligand has also been used to create CPs with a
variety of metal ions. The species reported to date can be classi-
fied as bimetallic complexes,18–21 1D polymeric chains,22–24 2D
polymeric sheets,24–28 and 3D polymeric networks.21,29 Several
examples of BTEC complexes created with co-ligands (other
than water) have been reported. Discrete binuclear complexes
bridged by BTEC were prepared with L = 1,4,9-triisopropyl-
[9]aneN3, [Cu2(BTEC)L2];18 L = en, [Ni2(BTEC)L2(H2O)6];19
and L = N-(3-aminopropyl)propane-1,3-diamine, [Cu2(BTE-
C)L2(H2O)2].21 There have been numerous reports of 1D chain
CPs with BTEC and aqua ligands, but only one example with a
co-ligand, [Cu2(BTEC)(Him)6(H2O)4].22 Several structures have
been reported where 2D sheets make up the CP, with L =
2,2Ј-bipy, [Co2(BTEC)L2(H2O)];26 L = phen, [Fe2(BTEC)L2];27
and L = Him, [Mn2(BTEC)L6].28 Finally, one example of a 3D
network CP with BTEC and L = dien has been reported,
[Cu3(BTEC)L3(H2O)](ClO4)2.21
Here we report the structures and characterization of two
new CPs that are synthesized from identical ligand starting
materials (BTEC and Meim) and differ only in the transition
metals used [cobalt() and copper()]. The transition metals’
coordination number and geometry are divergent in each CP,
giving rise to strikingly different 2D structures. To our
knowledge, there have been no reports of CPs that possess
transition metal-dependent structural differences.
Results and discussion
The use of hydrothermal (solvothermal) reaction conditions
wherein starting materials and solvent are combined in a
† Electronic supplementary information (ESI) available: fully labelled
ORTEP figures, TGA, and powder XRD data for 1 and 2. See
http://www.rsc.org/suppdata/dt/b2/b207559h/
DOI: 10.1039/b207559h
J. Chem. Soc., Dalton Trans., 2002, 4555–4560
This journal is © The Royal Society of Chemistry 2002
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Table 1 Selected bond lengths (Å) and angles (Њ) for CP 1a
high pressure vessel and allowed to react at high temperature
and pressure has become quite popular for the synthesis of
CPs.9,13,30 Our strategy for the synthesis of new CPs utilizes
aqueous reaction conditions at room temperature and pressure.
Our reactions generally conform to the following simple
procedure: the pH of an aqueous solution of the carboxylic
acid is adjusted to deprotonate the acid groups, followed by the
addition of aqueous solutions of the co-ligand and the metal
salt. Crystals suitable for X-ray crystallography can then be
obtained via the slow evaporation of solvent.
The CPs reported here were synthesized using BTEC, Meim
and either cobalt() or copper() according to eqn. (1). The pH
of the aqueous BTEC solutions was adjusted to pH ≥ 7.0. Upon
addition of the metal salt, some precipitation was observed and
removed by filtration. Single crystals of Co2(BTEC)(Meim)4-
(H2O)4ؒH2O (1) and Cu2(BTEC)(Meim)4 (2) were isolated
by slow evaporation of filtered solutions. Both 1 and 2 are
insoluble in water and common organic solvents.
Co1–O1
2.093(3)
2.086(3)
2.194(3)
Co1–N1
Co1–N3
Co1–O6(w)
2.097(3)
2.104(3)
2.169(3)
Co1–O3Ba
Co1–O5(w)
O1–Co1–O3Ba
O1–Co1–N1a
O1–Co1–N3
O1–Co1–O5
89.96(11)
91.19(12)
90.66(11)
89.96(10)
172.64(11)
178.77(12)
86.87(12)
90.61(11)
O3B–Co1–O6a
O5–Co1–O6
N1–Co1–N3
N1–Co1–O5
N1–Co1–O6
N3–Co1–O5
N3–Co1–O6
83.35(10)
87.06(10)
92.68(13)
89.82(12)
93.53(12)
177.41(11)
92.03(12)
O1–Co1–O6
O3B–Co1–N1
O3B–Co1–N3a
O3B–Co1–O5a
a Symmetry transformations used to generate equivalent atoms: Ϫx ϩ
3/2, y Ϫ ½, Ϫz ϩ ½.
the four carboxylato groups (O3–C13–O4 and O3A–C13A–
O4A) on each BTEC ligand are twisted out of the plane of the
aromatic ring by approximately 74Њ. The other two carboxylato
groups (O1–C9–O2 and O1A–C9A–O2A) are nearly coplanar
with the aromatic ring, having dihedrals of approximately 5Њ.
The metal–ligand bond lengths and angles are all within
expected limits for cobalt() complexes with carboxylates and
N-heterocycles, and are summarized in Table 1 with hydrogen
bond parameters in Table 2.26
(1)
Each BTEC ligand coordinates to four cobalt atoms,
producing 2D sheets in the (100) plane. These sheets, shown in
Fig. 2, are comprised of folded octagons. The corners of one
octagon are made up of four BTEC ligands and four cobalt
atoms. Each octagon is puckered out of the (100) plane, with
the centers of the BTEC ligands generally in the plane of the
sheets and the cobalt atoms bent above and below.
Co2(BTEC)(Meim)4(H2O)4ؒH2O (1)
CP 1 was isolated as a crimson, crystalline solid and charac-
terized by X-ray crystallography, powder X-ray diffraction
(XRD), TGA, FT-IR and elemental analysis. A single crystal
X-ray diffraction study of 1 revealed that it is made up of
infinite sheets of cobalt atoms connected by BTEC ligands. The
coordination environment around the cobalt() ions illustrated
in Fig. 1 is six-coordinate, with a distorted octahedral geometry.
Fig. 2 Representation of a portion of the 2D sheets of CP 1 as viewed
down the crystallographic a axis (hydrogen atoms, non-coordinated
water molecules, and Meim rings omitted for clarity; carbon = gray;
oxygen = red; nitrogen = blue; cobalt = light blue).
As illustrated in Fig. 3, the puckering produces a wave-like
zigzag structure when the sheets are viewed from the side. The
aromatic rings of the BTEC ligands are canted 60Њ out of the
plane of the sheets. The diamond-shaped void space apparent
in Fig. 3 is actually filled with the Meim ligands. The distance
from crest to crest of the waves in CP 1 is 10.9 Å. The Co–Co
distance between sheets is 5.7 Å, but the aqua ligand O atoms
are separated by 2.8 Å, putting them within hydrogen bonding
distance.
Fig.
1
Representation of a portion of CP 1 highlighting the
asymmetric unit plus the symmetry-derived coordinated BTEC ligands
(50% thermal ellipsoids, non-coordinated solvent water molecules and
hydrogen atoms omitted for clarity).
Two carboxylato oxygen atoms, two aqua ligands and two
Meim ligands in a cis,cis,cis arrangement coordinate to each
cobalt atom. The cis,cis,cis-MA2B2C2 octahedral isomer
exists as an enantiomeric pair, and in the C2/c space group both
enantiomers are present (the Λ-isomer is shown in Fig. 1).
Each carboxylato oxygen atom that coordinates to a cobalt
atom is from a distinct, symmetry-related BTEC ion. Two of
The buckling of the sheets in 1, which creates the zigzag top-
ology observed in Fig. 3, is due principally to the cis disposition
of the carboxylato ligands and the octahedral coordination
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J. Chem. Soc., Dalton Trans., 2002, 4555–4560

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Table 2 Hydrogen bonds (Å and Њ) in the crystal structure of CP 1
D–H ؒ ؒ ؒ A
d(D–H)
d(H ؒ ؒ ؒ A)
d(D ؒ ؒ ؒ A)
Є(DHA)
O5–H5 ؒ ؒ ؒ O2
0.85(2)
0.85(2)
0.85(2)
0.84(2)
0.84(2)
0.85(2)
0.85(2)
1.90(3)
2.66(5)
1.82(3)
1.94(3)
2.51(4)
1.93(3)
2.18(3)
2.714(4)
3.043(4)
2.633(4)
2.775(4)
2.829(4)
2.770(4)
3.023(5)
160(5)
109(4)
161(5)
172(5)
103(3)
171(5)
170(6)
O5–H5 ؒ ؒ ؒ O3Da
O5–H5 ؒ ؒ ؒ O4Da
O6–H6 ؒ ؒ ؒ O2Eb
O6–H6 ؒ ؒ ؒ O3Da
O6–H6 ؒ ؒ ؒ O5Fc
O7–H7 ؒ ؒ ؒ O6
Symmetry transformations used to generate equivalent atoms:a Ϫx ϩ 3/2, y Ϫ ½, Ϫz ϩ ½; b x, Ϫy ϩ 1, z Ϫ ½; c Ϫx ϩ 1, Ϫy ϩ 1, Ϫz.
Table 3 Selected bond lengths (Å) and angles (Њ) for CP 2
Cu1–O1
Cu2–O3
1.9608(17)
1.9734(16)
Cu1–N1
Cu2–N3
1.998(2)
1.971(2)
O1–Cu1–N1
89.66(9)
90.34(9)
180.0
O3–Cu2–N3
91.55(8)
88.45(8)
180.0
O1A–Cu1–N1a
O1–Cu1–O1Aa
N1–Cu1–N1Aa
O3–Cu2–N3Ab
O3–Cu2–O3Db
N3–Cu2–N3Ab
180.0
180.0
Symmetry transformations used to generate equivalent atoms:a Ϫx, Ϫy
ϩ 1, Ϫz; b Ϫx ϩ 1, Ϫy ϩ 1, Ϫz Ϫ 1.
by single crystal X-ray crystallography. Unit cell parameters
identical to those for 1 were obtained. Clearly, the uncoord-
inated water molecules in 1 are held in place very tightly via
hydrogen bonding.
In addition to hydrogen bonding, inter-sheet contacts are
strengthened by π–π interactions between Meim rings. Both
unique Meim rings are parallel with their symmetry-related
partners on adjacent sheets. The Meim ligand containing N3
and N4 has the closest contact with a centroid–centroid vector
of 3.5 Å and an offset angle of 30Њ.‡ Compare for example
the π–π interactions in the Cu3(TMA)2(Him)6(H2O) complex,
which has a centroid–centroid vector of 4.8 Å and an offset
angle of 38Њ.16 A slightly longer interaction is present between
Meim rings containing N1 and N2 (3.9 Å, 42Њ). These π–π
interactions are relatively strong, and presumably contribute to
the structure and stability of 1.
Fig. 3 Representation of CP 1 viewed along the crystallographic c axis
illustrating the buckled sheets (hydrogen atoms, non-coordinated water
molecules, and Meim rings omitted for clarity; carbon = gray; oxygen =
red; nitrogen = blue; cobalt = light blue).
geometry around the cobalt atoms. CPs comprised of cobalt()
and BTEC with trans carboxylato groups have flat 2D sheets
made up of a rhombic grid of BTEC ligands and cobalt
atoms.24 Examples of CPs with wave-like structures have been
reported where the sheets were packed such that the waves are
in phase.31 To our knowledge, 1 is the first example of a CP
where the zigzag sheets are out of phase with each other.
Extensive hydrogen bonding occurs at the interface between
sheets, which corresponds to the crests of the waves. Hydrogen
bonding between aqua ligands and non-coordinating carb-
oxylato oxygen atoms in the same sheet contributes to the
overall topology of the sheets. Hydrogen bonding between
aqua ligands on adjacent sheets contributes to inter-sheet
attractions. One non-coordinated water molecule per formula
unit is held by hydrogen bonding between sheets at the points
of closest contact. Aqua ligand oxygen atom O6 is involved in
hydrogen bonding with the non-coordinated solvent water.
The hydrogen bonding between sheets occurs where the crests
of the wave-like sheets come together. The non-coordinating
water molecules are encapsulated between sheets at these
points. TGA analysis of 1 reveals that water molecules corre-
sponding to approximately 12% of its mass are lost around 100
ЊC (see ESI†). The calculated mass loss for one uncoordinated
water and two aqua ligands per formula unit is 11.5%. Heating
the sample to higher temperatures leads to decomposition at
around 300 ЊC.
Cu2(BTEC)(Meim)4 (2)
CP 2 was synthesized in the same manner as CP 1 (see eqn. (1)).
Deep blue, crystalline 2 was characterized by X-ray crystal-
lography, TGA, powder XRD, FT-IR and elemental analysis.
Like 1, the polymeric structure of 2 is composed of 2D sheets.
Two crystallographically independent copper atoms are each
coordinated by a N2O2 ligand set. The coordination environ-
ment around the copper atoms shown in Fig. 4 is square planar,
with two Meim and two carboxylato ligands in a trans
disposition. The bond distances and angles around the copper
atoms are typical for copper() coordinated by carboxylates
and N-heterocycles and are summarized in Table 3.16,32
The sheets in 2 lie in the crystallographic (111) plane and are
made up of BTEC ligands coordinated to copper() ions. The
BTEC ligands coordinate in a µ4-bridging mode, creating a flat
topology with BTEC ligands on the corners and copper ions on
the edges of a simple rhombic grid (Fig. 5). The carboxylato
groups are twisted slightly out of the plane of the aromatic
rings (dihedral angles of 35 and 60Њ), while the aromatic rings
themselves are askew of the plane of the sheets by about 13Њ.
The Meim ligands, which are canted out of the plane of the
sheets by about 45Њ, occupy the space inside the 10 × 10 Å
rhombic grid, precluding the inclusion of guest molecules.
Since the BTEC ligands coordinate trans to each other, the
structure of the sheets in 2 are composed of four-sided rhombi
A sample of 1 was ground into a powder and dried in a
desiccator. The TGA of the dried sample of 1 is essentially
unchanged, indicating that no water is lost when 1 is dried.†
Furthermore, a comparison of the powder XRD of 1 before
drying with the powder XRD of dried crystals indicates
minimal changes occur upon drying.† Finally, a single crystal
of 1 was dried in a desiccator for one week, and then analysed
‡ The offset angle is defined as the angle between the normal of the
Meim ring plane and the centroid–centroid vector.36
J. Chem. Soc., Dalton Trans., 2002, 4555–4560
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interdigitated Meim ligands are much closer to each other (vide
infra).
Another difference between the structures of 1 and 2 is the
absence of any water molecules, coordinated or uncoordinated,
in 2. The TGA of 2 supports this finding, with no mass change
until decomposition occurs at about 250 ЊC. † As a consequence
of the absence of water in CP 2, there is no hydrogen bonding.
However, π–π contacts between interdigitated Meim ligands on
adjacent sheets does appear to contribute to inter-sheet inter-
actions. A side view of the sheets of CP 2 in Fig. 6 illustrates the
close contacts of the Meim rings on adjacent sheets. Surpris-
ingly, only the Meim rings containing N3 and N4 are in close
enough contact to interact through π–π bonding. The centroid–
centroid distance for these Meim rings is about 3.8 Å and the
offset angle is 23Њ. On the other hand, the centroid–centroid
distance for the Meim rings containing N1 and N2 is greater
than 5 Å. The inter-sheet π–π contacts between Meim ligands
appear to be the only form of stabilization between sheets in
CP 2.
Conclusions
Fig. 4 Representation of a portion of CP 2 highlighting the asym-
metric unit plus the symmetry derived BTEC and Meim ligands
coordinated to the copper ions (50% thermal ellipsoids, hydrogen atoms
omitted for clarity).
The flat sheet topology of CP 2 lies in stark contrast to the
wave-like sheets in CP 1. The difference in coordination
environment between cobalt and copper in CPs 1 and 2, respect-
ively, is the primary reason the sheet topology is so divergent.
Six-coordinate octahedral geometries are common for d7
cobalt() complexes, whereas the Jahn–Teller distortion of d9
copper() favors four-coordinate square planar or tetragonally
distorted geometries.33 This difference in coordination number
and geometry between cobalt and copper leads to significant
differences in polymeric structure. With BTEC as a bridging
ligand and Meim as a co-ligand, the coordination geometry of
the metal ion dictates the structure and topology of the 2D
sheets. The differences between the structures of CPs 1 and 2
illustrate the remarkable influence that the coordination
geometry of individual metal ions may have on the 2D and 3D
structure of coordination polymers.
Experimental
General
All reagents were commercially available and used without
further purification. Elemental analyses were carried out by
Atlantic Microlabs of Norcross, GA. TGA experiments were
performed on a Thermal Analyst 2000 TGA instrument under
a helium atmosphere. The powder XRD data were collected on
a Rigaku DMAX diffractometer at 295 K, operated at 40 kV
and 30 mA, interfaced with an MDI databox and Jade 3.1 soft-
ware, using Cu-Kα (λ = 1.5406 Å) radiation with a scan speed
of 2Њ minϪ1. The IR spectra were recorded on a Nicolet Nexus
470 FT-IR at room temperature using the KBr pellet technique.
Fig. 5 Representation of a portion of the 2D sheets of CP 2 as viewed
perpendicular to the (111) plane (hydrogen atoms omitted for clarity;
carbon = gray; oxygen = red; nitrogen = blue; copper = green).
rather than the folded octagons that give rise to the zigzag
sheets of 1. As a consequence, the topology of the sheets in 2 is
essentially flat. This difference between the topologies of the
sheets in 1 and 2 is a direct result of the difference in coord-
ination number and geometry of the metals. Fig. 6 shows the
flat topology of the sheets in 2. The sheet–sheet separation
measured from copper atoms is about 8.8 Å. However, the
Synthesis
The synthetic methods used to obtain large single-crystal
samples of the compounds, including their initial characteriz-
ation, are described here. All reactions and purification steps
were performed under aerobic conditions at room temperature.
Co2(BTEC)(Meim)4(H2O)4ؒH2O (1). About 5 mmol (1.27 g)
of H4BTEC was slowly added to a 20 mL aqueous solution of
NaOH (0.80 g, 20 mmol) with stirring until pH ≥ 7.0. Cobalt()
sulfate hydrate (2.81 g, 10 mmol) was dissolved in 20 mL of
water and added to the BTEC solution. Meim (1.64 g,
20 mmol) was then slowly added with stirring until the pink
solution turned dark red. The solution was filtered and allowed
to stand at room temperature. Crimson single crystals of
Co2(BTEC)(Meim)4(H2O)4ؒH2O (1) were obtained after six
days (1.13 g, 29%). Found: C, 39.14; H, 4.57; N, 13.90.
Fig. 6 Representation of CP 2 viewed parallel to the sheets and the
(111) plane (hydrogen atoms omitted for clarity; carbon = gray; oxygen
= red; nitrogen = blue; copper = green).
4558
J. Chem. Soc., Dalton Trans., 2002, 4555–4560

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Table 4 Crystallographic data and refinement details for 1 and 2
1
2
Empirical formula
Formula weight
C13H18CoN4O6.5
393.24
C13H13CuN4O4
352.81
Crystal system
Space group
Monoclinic
C2/c
Triclinic
P1
¯
a/Å
b/Å
c/Å
α/Њ
24.148(10)
10.908(6)
12.942(5)
90
107.67(2)
90
3248(2)
8
1.099
8.847(2)
8.985(2)
10.3302(17)
67.817(12)
82.839(17)
75.60(2)
736.0(3)
2
β/Њ
γ/Њ
V/Å3
Z
µ/mmϪ1
1.507
F(000)
Crystal size/mm
Reflections collected
1624
0.40 × 0.18 × 0.08
2963
360
0.48 × 0.32 × 0.22
3534
Independent reflections (Rint
Data/restraints/parameters
)
2829 (0.0481)
2829/10/243
2934 (0.0306)
2934/0/205
Final R [I > 2σ(I )]
R1
wR2
0.0447
0.1061
0.0402
0.1026
R (all data)
R1
wR2
0.0617
0.1160
0.0517
0.1108
C13H18CoN4O6.5 requires C, 39.71; H, 4.61; N, 14.99%. νmax
cmϪ1 (KBr) 3327s, 3136s, 1586s, 1538w, 1484m, 1417s, 1379s,
1321m, 1283m, 1234s, 1138m, 1101s, 1028w, 945m, 829w, 761s,
736w, 675w, 660 m, 617s, 582m, 418w.
/
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Cu2(BTEC)(Meim)4 (2). About 5 mmol (1.27 g) of H4BTEC
was slowly added to a 20 mL aqueous solution of NaOH (0.80
g, 20 mmol) with stirring until pH ≥ 8.0. Copper() sulfate
hydrate (2.52 g, 10 mmol) was dissolved in 20 mL of water and
added to the BTEC solution, immediately resulting in the
formation of a light blue precipitate. Meim (1.64 g, 20 mmol)
was then slowly added with stirring until most of the precipitate
dissolved and the color of the solution turned dark blue. The
solution was filtered and allowed to stand at the room temper-
ature. Deep blue single crystals of Cu2(BTEC)(Meim)4 (2) were
obtained after one week (0.98 g, 28%). Found: C, 44.83; H, 3.69;
N, 15.82. C13H13CuN4O4 requires C, 44.26; H, 3.71; N, 15.88%.
νmax/cmϪ1 (KBr) 3428s, 1603s, 1489w, 1387m, 1353m, 1284w,
1239w, 1010s, 956w, 867w, 820w, 762w, 654w, 619w, 554w.
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X-Ray crystallography
The crystal data and data collection parameters for 1 and 2 are
summarized in Table 4. The intensity data for both crystals
were collected on a Bruker P4 diffractometer with graphite-
monochromated Mo-Kα (λ = 0.71073 Å) radiation in the ω–2θ
scanning mode at 295(2) K. The data were corrected for
Lorentz and polarization effects as well as absorption. All
structures were solved by the Patterson method followed by
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full-matrix least-squares procedures using the SHELXTL
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fixed during structure refinement. All non-hydrogen atoms were
refined anisotropically. Atomic scattering factors were taken
from the International Tables for X-Ray Crystallography.35
CCDC reference numbers 191132 and 191133.
See http://www.rsc.org/suppdata/dt/b2/b207559h/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
This research was supported in part by the donors of the
Petroleum Research Fund, administered by the American
Chemical Society, and the University of Oklahoma.
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