Single-strand molecular wheels and coordination polymers in copper(II) benzoate chemistry by the employment of α-Benzoin oxime and azides: Synthesis, structures, and magnetic characterization

Article abstract of DOI:10.1002/ejic.201101292

The use of α-benzoin oxime (bzoxH₂) in copper(II) benzoate chemistry, in the absence or presence of ancillary azido ligands, is reported. The reaction of Cu(O₂CPh)₂A·2H₂O with one equivalent of bzoxH₂ in N,N-dimethylformamide (DMF) affords the decanuclear complex [Cu₁₀(bzox)₁₀(DMF)₄] (1) in good yield. Dissolution of 1 in CH₂Cl₂ leads to the subsequent isolation of the solvent-free complex [Cu₁₀(bzox) ₁₀] (2) in moderate yields. Complexes 1 and 2 are isostructural and possess a loop or single-strand molecular wheel topology. The bzox^2- dianions behave as I·¹:I·¹: I·²:μ₃ ligands, which give rise to an overall [Cu₁₀(μ-ONR)₁₀(μ-OR')₁₀] core. Both 1 and 2 stack to form nanotubular columns with beautiful supramolecular architectures. The reaction of Cu(O₂CPh)₂A· 2H₂O with bzoxH₂ and NaN₃ in a 1:1:1 molar ratio in MeOH gives the bzoxH₂-free complex [Cu(N₃)(O ₂CPh)(MeOH)]_n (3), which is a 1D chain. The Cu ^II atoms in 3 are linked by a single, end-on N₃ ^- group, a syn,syn-I·¹: I·¹:μ PhCO₂^- ion, and an oxygen atom from the bridging MeOH ligand. The 1D chains are hydrogen bonded into 2D sheets through N_azideA·A·A· H(O_MeOH) interactions. Variable-temperature, solid-state direct-current magnetic studies were carried out on 1-3. The data for 1 and 2 indicate very strong antiferromagnetic exchange interactions and a S = 0 ground state, which is expected for even-membered loop arrays of Cu^II atoms. In contrast, 3 exhibits ferromagnetic exchange interactions; the data were fitted to the appropriate equation derived from the Hamiltonian H = -JI￡(S_iA·S_i+1), which includes a zJ' interchain interaction term. The best-fit parameters were J = +49.6(4) cm^-1, g = 2.067(3), and zJ' = 2.3(1) K. The combined results demonstrate the ligating flexibility of both the bzoxH₂ and azido groups and their usefulness in the synthesis of polynuclear Cu^II clusters and coordination polymers.

Full text of DOI:10.1002/ejic.201101292

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FULL PAPER
DOI: 10.1002/ejic.201101292
Single-Strand Molecular Wheels and Coordination Polymers in Copper(II)
Benzoate Chemistry by the Employment of α-Benzoin Oxime and Azides:
Synthesis, Structures, and Magnetic Characterization
Theocharis C. Stamatatos,[a] Gina Vlahopoulou,[a,b] Catherine P. Raptopoulou,[c]
Vassilis Psycharis,[c] Albert Escuer,*[b] George Christou,*[d] and Spyros P. Perlepes*[a]
Keywords: Copper / Coordination polymers / Single-strand molecular wheels / N,O ligands / Magnetic properties
–
–
The use of α-benzoin oxime (bzoxH2) in copper(II) benzoate
chemistry, in the absence or presence of ancillary azido li-
gands, is reported. The reaction of Cu(O2CPh)2·2H2O with
one equivalent of bzoxH2 in N,N-dimethylformamide (DMF)
affords the decanuclear complex [Cu10(bzox)10(DMF)4] (1) in
single, end-on N3 group, a syn,syn-η1:η1:μ PhCO2 ion, and
an oxygen atom from the bridging MeOH ligand. The 1D
chains are hydrogen bonded into 2D sheets through
N
azide···H(OMeOH) interactions. Variable-temperature, solid-
state direct-current magnetic studies were carried out on 1–
good yield. Dissolution of 1 in CH2Cl2 leads to the subse- 3. The data for 1 and 2 indicate very strong antiferromagnetic
quent isolation of the solvent-free complex [Cu10(bzox)10] (2)
in moderate yields. Complexes 1 and 2 are isostructural and
possess a loop or single-strand molecular wheel topology.
The bzox2– dianions behave as η1:η1:η2:μ3 ligands, which
give rise to an overall [Cu10(μ-ONR)10(μ-ORЈ)10] core. Both
1 and 2 stack to form nanotubular columns with beautiful
supramolecular architectures. The reaction of Cu(O2CPh)2·
2H2O with bzoxH2 and NaN3 in a 1:1:1 molar ratio in MeOH
gives the bzoxH2-free complex [Cu(N3)(O2CPh)(MeOH)]n
(3), which is a 1D chain. The CuII atoms in 3 are linked by a
exchange interactions and a S = 0 ground state, which is ex-
pected for even-membered loop arrays of CuII atoms. In con-
trast, 3 exhibits ferromagnetic exchange interactions; the
data were fitted to the appropriate equation derived from the
Hamiltonian H = –JΣ(Si·Si+1), which includes a zJЈ interchain
interaction term. The best-fit parameters were J = +49.6(4)
cm–1, g = 2.067(3), and zJЈ = 2.3(1) K. The combined results
demonstrate the ligating flexibility of both the bzoxH2 and
azido groups and their usefulness in the synthesis of polynu-
clear CuII clusters and coordination polymers.
Single-strand molecular wheels and closed, cage-like
clusters are the two families of polynuclear 3d-metal com-
plexes that have attracted the most intense interest in recent
years, and both families include complexes of high nu-
clearity with beautiful architectures. Of relevance to this
work are single-strand CuII wheels, which almost always
contain an even number of metal atoms and are antiferro-
magnetically coupled with S = 0 ground states.[7] Such mo-
lecules represent a rare amalgamation of high nuclearity
and high magnetic symmetry, the latter referring to the
(often) single type of M2 (M = 3d-metal ion) pairwise ex-
change couplings that they contain. Thus, they represent
excellent model systems for the study of 1D antiferromag-
netism, magnetic anisotropy,[8] and quantum effects such as
coherent tunneling of the Néel vector.[9] It was recently il-
lustrated for the first time how crystals of Ga10 and Ga18
molecular wheels can be used as nanoporous materials to
control diffusive transport of a gas on micrometer scales.[10]
The prototype wheels were [Cr8F8(O2CtBu)16][11] and
[Fe(OMe)2(O2CCH2Cl)]10,[12] and the largest known to date
is [Ga20(pd)20(O2CMe)20] (H2pd = propane-1,3-diol).[13]
Multiple-strand wheels are also known, which are built
either from repeating metal cluster units or multiple-layer
wheels. These include Ni12,[14] Mn24,[15] Mn16,[16] the giant
Introduction
There are several reasons for the current interest in the
synthesis and study of high nuclearity, molecular clusters
and coordination polymers of 3d-metal ions.[1] Among
these is the search for various nuclearity oxide-bridged
metal carboxylate clusters to model Mx sites in biomole-
cules, which includes understanding the growth of the core
of the ferritin protein,[2] elucidating the Mn site of water
oxidation within the photosynthetic apparatus of green
plants and cyanobacteria,[3] and modeling the Cu site
within the complicated membrane protein (αβγ) methane
monooxygenase.[4] Other reasons for this interest are varied,
and include the aesthetically pleasing structures that many
such molecular clusters possess[5] and the search for com-
pounds with interesting magnetic properties.[6]
[a] Department of Chemistry, University of Patras,
26504 Patras, Greece
Fax: +30-2610-997118
E-mail: perlepes@patreas.upatras.gr
[b] Departament de Quimica Inorganica, Universitat de Barcelona,
Marti Franqués 1-11, 08028 Barcelona, Spain
[c] Institute of Materials Science, NCSR “Demokritos”,
15310 Aghia Paraskevi Attikis, Greece
[d] Department of Chemistry, University of Florida,
Gainesville, Florida 32611-7200, USA
Eur. J. Inorg. Chem. 0000, 0–0
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A. Escuer, G. Christou, S. P. Perlepes, et al.
FULL PAPER
double-decker Mn32,[17] and torus-shaped Mn84,[5a] with various solvents. Our systematic investigation has suc-
[18]
[18]
Mo154
,
and Mo176
;
most of these wheels possess large cessfully led to a family of decanuclear clusters with a sin-
gle-strand wheel topology, which bears the dianionic form
S values and are single-molecule magnets.[5a,14–17]
Coordination polymers are significant from a structural of the ligand, bzox2–, and a new 1D coordination polymer,
chemistry viewpoint with new, intriguing molecular top- which contains bridging benzoato and azido groups. The
ologies being discovered, as well as providing numerous ex- synthesis, structures, and magnetochemical characterization
amples of interesting phenomena such as the interpen- of the products are described here. A small portion of this
etration of networks.[19] To date, scientists have realized work has been previously communicated.[32]
various applications of coordination polymers in catalysis,
electrical conductivity, luminescence, magnetism, nonlinear
optics, molecular electronics, sensing, drug delivery, and ze-
olitic behavior.[20] The ultimate goal is the transformation
of coordination polymers to functional molecular materials.
However, the factors that influence the synthesis of coordi-
nation polymers are still not completely understood and
chemists are always looking for new methods that can lead
to predictable products. The two main trends in the field
are synthesis by design and nonprogrammed assembly. The
former involves the use of rigid, often complicated organic
ligands that force or drive the precipitation of the desired
product. The latter approach involves the use of more flexi-
ble ligands and lacks control over the final product but has
proven to be successful in the synthesis of polymeric com-
pounds with interesting structures and properties.[20,21]
There is a continuing need for new synthetic methods to
prepare clusters and coordination polymers, and one ap-
proach is the development of new reaction systems using
Scheme 1. Structural formula of bzoxH2 (top), and the crystallo-
graphically established coordination modes of its monoanion
bridging organic ligands that can simultaneously chelate
two or more metal ions. One attractive route is to use li-
gands that contain alkoxido[22] or oximato[23] functionalities
as these are good bridging groups that can foster the forma-
tion of polynuclear or polymeric products. In addition, an-
cillary ligands such as carboxylates[24] and/or pseudohalides
(bzoxH–) and dianion (bzox2–) in transition metal complexes (bot-
tom).
Results and Discussion
–
(e.g. N3 , OCN–)[25] can either enhance aggregation, which
favors the isolation of clusters, or act as linkers for polymer
formation. Pseudohalides that bridge in the 1,1-mode (end-
on) give ferromagnetic interactions for a wide range of M–
Syntheses and IR Spectra
Many synthetic procedures[33] for polynuclear 3d-metal
N–M angles,[26] whereas the 1,3-bridging mode (end-to- clusters rely on the reactions of carboxylate starting materi-
end) usually promotes antiferromagnetic interactions and als with a potentially chelating/bridging ligand. In some
leads to multidimensional (1-, 2-, or 3D) coordination poly- cases, pseudohalides are also incorporated in the reaction
mers.[27] In CuII chemistry, for example, we have recently mixtures to obtain magnetically interesting species, i.e.
reported CuII and CuII clusters, and a unique 1D high-spin molecules and single-molecule magnets. From our
7
4
(CuII
)
5 n
coordination polymer,[28] which all bear the previous work, this general route was also known to yield
anion(s) of pyridine-2,6-dimethanol and acetato groups. magnetically and structurally interesting CuII complexes
Furthermore, the employment of various 2-pyridyl oximes upon reaction with various pyridyl alcohol ligands and pyr-
in CuII carboxylate chemistry has afforded a large family of idyl oximes and dioximes.[28–33] In this study we have inves-
antiferromagnetically coupled triangular compounds that tigated the reactions of bzoxH2, a relatively unexplored alk-
show antisymmetric exchange phenomena.[29]
oxide–oximate ligand, with a simple CuII carboxylate
As an extension of this work, we have turned our atten- source, i.e. Cu(O2CPh)2·2H2O, in various solvents and in
tion to a new, mixed alkoxide–oximate ligand in 3d-metal the additional presence of azides. During our synthetic ef-
cluster chemistry as a potential route to molecular and/or forts, it was noticed that the addition of external base, e.g.
polymeric species with unprecedented structural motifs and NEt3, for the deprotonation of the alcohol and oxime
interesting physical properties. The ligand chosen, α-ben- groups of bzoxH2 was unnecessary and yielded the same
zoin oxime (bzoxH2), is shown in Scheme 1. It has been products in lower yields, which were occasionally contami-
sparingly employed in 3d-metal chemistry to yield nated with amorphous precipitates.
[30]
MnIII
,
NiII8, and NiII [31] complexes. In this work, we
A variety of reactions were explored with different sol-
9
6
–
have explored binary (bzoxH2/PhCO2 ) and ternary vents, ratios, and other conditions before the successful pro-
–
–
(bzoxH2/PhCO2 /N3 ) reaction schemes in CuII chemistry cedures were identified. The reaction of Cu(O2CPh)2·2H2O
2
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Coordination Polymers with Copper(II)
with bzoxH2 in a 1:1 molar ratio in N,N-dimethylform- that the reaction solution contains several species in equilib-
amide (DMF) gave a dark green solution and led to the rium, with factors such as concentration, relative solubility,
subsequent isolation of well-formed dark green crystals of lattice energy, crystallization kinetics, and others that deter-
the benzoate-free complex [Cu10(bzox)10(DMF)4] (1) in mine the identity of the isolated products. In any case, the
good yield (ca. 45%). The deprotonation of bzoxH2 was low yield of 3 cannot be explained easily.
achieved solely by the PhCO2– groups and the formation of
With the identity of 3 established, a convenient high-
1 is summarized in Equation (1). Small variations in the yield synthesis of 3 was developed by omitting bzoxH2 from
CuII/bzoxH2 ratio also gave 1 but in lower yields. DMF was the reaction. Thus, the 1:1 reaction between Cu(O2CPh)2·
primarily chosen as the solvent to ensure that both solid 2H2O and NaN3 in MeOH under reflux gave 3 in ca. 80%
reagents were completely dissolved.
yield (Method B). The straightforward formation of 3 is
represented by Equation (3).
As 1 contains four coordinated DMF molecules (vide in-
fra), we wondered if a solvent-free, structurally similar com-
pound could exist. Such a species could be interesting from
supramolecular and chemical reactivity viewpoints. To
achieve this goal, we used nonpolar solvents with poorly
coordinating donor atoms. Thus, dissolution of 1 in CH2Cl2
and layering the resulting green solution with Et2O (Exp.
Section, Method A) led to the subsequent isolation of dark
green crystals of solvent-free [Cu10(bzox)10] (2) in good
yield (ca. 35%). Its formation is summarized in Equation
(2). Complex 2 can also be obtained in higher yield
(ca. 60%) from the 1:1 reaction between Cu(O2CPh)2·2H2O
and bzoxH2 in CH2Cl2 under reflux (Method B). The rela-
tively high temperature employed was necessary to enhance
the solubility of the starting materials and divert the equi-
librium to product formation. Complex 2 can be converted
into 1 by dissolution of the former in DMF.
The use of MeOH as the reaction solvent was crucial for
clean product formation; oily products were obtained when
the reaction was performed in EtOH, DMF, or MeCN,
whereas no significant reaction was observed in CH2Cl2 or
CHCl3.
The IR spectra of vacuum-dried samples of 1 and 2 are
similar and dominated by the stretching and deformation
bands of the aromatic ring. The band at ca. 1115 cm–1 is
tentatively assigned to the ν(NO) vibration of the coordi-
nated oximato groups. Moreover, the IR spectrum of 1 exhi-
bits two very strong bands at 1670 and 696 cm–1, which are
assigned to the ν(C=O) and δ(OCN) vibrational modes of
the coordinated DMF molecules, respectively.[34] Upon co-
ordination, the ν(C=O) and δ(OCN) bands are shifted to
lower and higher wavenumbers, respectively, compared to
the corresponding bands in the spectrum of free DMF.[34]
These bands are absent from the spectrum of 2 as expected.
The presence of a coordinated MeOH molecule in 3 is
manifested by one broad band of medium intensity at
3426 cm–1, assigned to ν(OH); its broadness and relatively
low frequency are indicative of hydrogen bonding.[35] In the
spectrum of 3, the strong bands at 1532 and 1412 cm–1 are
assigned to the νas(CO2) and νs(CO2) modes of the carb-
oxylate groups, respectively. The difference, Δ [Δ = νas-
(CO2) – νs(CO2)], is small (120 cm–1) compared with the Δ
value for NaO2CPh (184 cm–1), which is expected for the
With the identity of 1 and 2 established, and the depen-
dence of the pronounced versatility of their terminal coor-
dination sites on the solvent used (DMF molecules in 1 vs.
none in 2), we undertook the synthetic challenge to link the
Cu10 wheels into multidimensional coordination polymers
using azide ions. Several reactions between 2 and NaN3 in
various molar ratios and solvents were performed but all
were unsuccessful and led to dark green, noncrystalline ma-
terials, which were not characterized. The addition of salts
that contained bulky cations, e.g. Et4N+ or nBu4N+, did
not improve the situation. In contrast, the reaction of
Cu(O2CPh)2·2H2O with bzoxH2 and NaN3 in a 1:1:1 molar
ratio in MeOH (see Exp. Section, Method A) gave a dark
green solution, which led to the subsequent isolation of
dark green crystals of the bzoxH2-free complex [Cu(N3)-
(O2CPh)(MeOH)]n (3) in low yield (ca. 15%) upon layering
–
bidentate bridging PhCO2 group.[36] The intense band at
ca. 2090 cm–1 is assigned to the asymmetric stretching
mode, νas(NNN), of the end-on azide group.[34,37]
Description of Structures
the reaction solution with Et2O. In an attempt to isolate a
Complex 1·12DMF·2H2O crystallizes in the triclinic
–
CuII/PhCO2 /bzoxH2/N3– product, we repeated the reaction space group P1, with the [Cu10(bzox)10(DMF)4] molecule
using different ratios of the reactants (1:2:1, 2:2:1, 1:4:1), in a general position. The structure of the molecule and a
however, all of our efforts led to polymeric 3 in even lower stereopair are shown in Figure 1, and a view of its core is
¯
–
yields. It seems that there is a competition between N3 / presented in Figure 2. Selected interatomic distances and
–
PhCO2 and bzoxH2 for CuII coordination sites. It is likely angles are listed in Table 1.
Eur. J. Inorg. Chem. 0000, 0–0
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Table 1. Selected interatomic distances [Å] and angles [°] for
1·12DMF·2H2O.[a]
Cu1–O1
1.928(3)
1.914(3)
1.902(3)
1.959(3)
1.910(3)
1.897(3)
1.902(3)
1.940(3)
1.935(3)
1.938(3)
1.921(3)
Cu5–O101[b]
Cu5–N41
Cu1···Cu2
Cu2···Cu3
Cu3···Cu4
Cu4···Cu5
Cu5···Cu1Ј
2.343(3)
1.981(4)
3.185(1)
3.154(2)
3.137(1)
3.255(2)
3.269(2)
Cu1–O21
Cu1–O42Ј
Cu1–N21
Cu2–O1
Cu2–O22
Cu2–O81
Cu2–N1
Cu3–O2
Cu1–O1–Cu2
Cu2–O81–Cu3
Cu3–O61–Cu4
Cu4–O41–Cu5
Cu5–O21Ј–Cu1Ј
112.2(1)
111.2(1)
108.7(1)
115.1(1)
115.9(1)
Cu3–O61
Cu3–O81
Cu3–O111[b] 2.457(3)
Cu3–N81
Cu4–O41
Cu4–O61
Cu4–O82
Cu4–N61
Cu5–O21Ј
Cu5–O41
Cu5–O62
1.958(3)
1.925(3)
1.923(3)
1.919(3)
1.962(3)
1.944(3)
1.932(3)
1.929(3)
Torsion angles
Cu1–N21–O22–Cu2
Cu2–N1–O2–Cu3
Cu3–N81–O82–Cu4
Cu4–N61–O62–Cu5
12.2(4)
17.3(4)
25.4(3)
10.6(4)
Cu5–N41–O42–Cu1Ј 14.0(4)
[a] Primed atoms are related to the unprimed ones by the symmetry
transformation 2 – x, 1 – y, –z. [b] O101 and O111 belong to the
coordinated DMF molecules.
Figure 1. The molecular structure of 1 (top) and a stereopair (bot-
tom). Hydrogen atoms are omitted for clarity. Color code: green
CuII, red O, blue N, gray C.
Figure 3. Side view that emphasizes the puckering of the Cu10
wheel in 1. Color scheme as in Figure 1.
Six CuII atoms (Cu1, Cu2, Cu4, Cu1Ј, Cu2Ј, Cu4Ј) are
four-coordinate with distorted square-planar geometry: the
cis and trans angles lie in the 82.4–95.2 and 169.9–174.5°
ranges, respectively, which deviate only slightly from the
Figure 2. Labeled representation of the [Cu10(μ-ONR)10(μ-ORЈ)10]
core of 1.
The structure of 1 comprises ten CuII ions linked through ideal values of 90 and 180°, respectively, of a square. This
the oximate N–O– and alkoxido RO– arms of ten bzox2– deviation is likely due to the formation of a single, five-
groups to form a puckered, single-strand wheel of crystallo- membered chelating ring around each CuII ion, which gives
graphic Ci symmetry (Figure 3). It can also be described as rise to a nonsymmetric CuO3N chromophore. The remain-
a low-symmetry Cu10 loop, with the metal ions bridged by ing four CuII ions (Cu3, Cu5, Cu3Ј, Cu5Ј) are five-coordi-
ten η1:η1:η2:μ3 bzox2– groups, which lie above and below nate with almost ideal square pyramidal geometry (τ = 0.03
the Cu10 plane (Scheme 1). Each bzox2– group chelates a for Cu3 and 0.09 for Cu5, where τ is 0 and 1 for perfect
CuII ion through its Oalkoxido and Noximato atoms and brid- square pyramidal and trigonal bipyramidal geometries,[38]
ges two adjacent CuII centers through its Oalkoxido atom and respectively). The coordinated DMF molecules occupy the
the oximato group. Ligation is completed by four terminal apical positions, and the CuII ions lie 0.114 (Cu3) and
DMF molecules on Cu3, Cu3Ј, Cu5, and Cu5Ј. The com- 0.259 Å (Cu5) above the O3N least-squares planes towards
plex therefore contains a [Cu10(μ-ONR)10(μ-ORЈ)10] core the apical donor atom. The bonds from Cu3 and Cu5 to
(Figure 2), where RNO and RЈO represent the bzox2– the apical DMF oxygen atoms (O101, O111) are longer
group.
than those to basal donor atoms, as expected. The Cu···Cu
4
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Coordination Polymers with Copper(II)
distances are within the 3.137–3.269 Å range, and the Cu– diameter defined by the shortest H···H distance; the corre-
ORЈ–Cu angles and Cu–N–O–Cu torsion angles lie in the sponding values for 2 (Figure 5, bottom) are 23.4 and
108.7–115.9 and 10.6–25.4° ranges, respectively.
3.3 Å, respectively. In 1, a DMF molecule occupies the cen-
Complex 2·8CH2Cl2·2Et2O crystallizes in the monoclinic tral hole of the wheel (Figure 5, top) to form a weak C–
space group P21/n. Selected interatomic distances and H···N hydrogen bond with N61 (N61···C171 3.256 Å). In
angles are listed in Table 2. The molecular structure of 2 contrast, 2 contains a disordered CH2Cl2 molecule at the
(Figure 4) is very similar to that of 1, the major difference center of the wheel, too disordered to be refined. Both
is that all the CuII ions in 2 are four-coordinate with square- wheels 1 and 2 stack to form nanotubular columns (Fig-
planar geometry; the cis and trans angles lie in the 82.2– ure 6).
96.0 and 166.5–172.9° ranges, respectively. The Cu···Cu sep-
arations range from 3.097–3.228 Å, which is slightly shorter
than the corresponding range in 1, and the Cu–ORЈ–Cu
angles and the Cu–N–O–Cu torsion angles lie in the 106.9–
117.0 and 2.9–27.4° ranges, respectively.
Table 2. Selected interatomic distances [Å] and angles [°] for
2·8CH2Cl2·2Et2O.[a]
Cu1–O1
Cu1–O3
Cu1–O10Ј
Cu1–N1
Cu2–O2
Cu2–O3
Cu2–O5
Cu2–N2
Cu3–O4
Cu3–O5
Cu3–O7
Cu3–N3
Cu4–O6
Cu4–O7
Cu4–O9
Cu4–N4
Cu5–O1Ј
Cu5–O8
Cu5–O9
Cu5–N5
1.931(1)
1.924(1)
1.909(1)
1.954(2)
1.898(1)
1.897(1)
1.889(1)
1.953(2)
1.912(1)
1.897(1)
1.905(1)
1.964(2)
1.907(1)
1.910(1)
1.925(1)
1.956(2)
1.933(1)
1.915(1)
1.931(1)
1.956(2)
Cu1···Cu2
Cu2···Cu3
Cu3···Cu4
Cu4···Cu5
Cu5···Cu1Ј
3.228(1)
3.228(2)
3.168(1)
3.097(2)
3.142(1)
Cu1–O3–Cu2
Cu2–O5–Cu3
Cu3–O7–Cu4
Cu4–O9–Cu5
Cu5–O1Ј–Cu1Ј
115.3(6)
117.0(6)
112.3(6)
106.9(6)
108.8(6)
Torsion angles
Cu1–N1–O2–Cu2
Cu2–N2–O4–Cu3
Cu3–N3–O6–Cu4
Cu4–N4–O8–Cu5
13.4(2)
2.9(2)
5.4(2)
20.9(2)
Cu5–N5–O10–Cu1Ј 27.4(2)
Figure 5. Space-filling representations of 1 (top) and 2 (bottom),
which emphasize the position of the DMF molecule in the central
cavity of 1. Color code: green CuII, red O, blue N, gray C, purple
H.
[a] Primed atoms are related to the unprimed ones by the symmetry
transformation 2 – x, –y, 1 – z.
Complexes 1 and 2 join a small family of structurally
characterized 3d-metal complexes that contain a form (neu-
tral, mono- or dianionic) of the α-benzoin oxime li-
gand,[30–32] and are the first in copper(II) coordination
chemistry. The crystallographically confirmed coordination
modes of bzoxH– and bzox2– in the structurally charac-
terized metal complexes to date are shown in Scheme 1.
Complexes 1 and 2 also belong to a relatively undeveloped
family of CuII10 clusters of any structural type with O- and/
or N-ligation.[7c,39] Among these, 1 and 2 are the second
and third examples of CuII10 complexes with a single-strand
wheel or loop conformation after [CuIIClL]10 (L– = amino
alkoxide),[7c] and the first with mixed alkoxide/oximate
ligation. Finally, 1 and 2 join only a handful of structurally
characterized {CuIIx} (x = various) complexes with a wheel
topology.[7]
A partially labeled representation of 3 is shown in Fig-
ure 7. Selected interatomic distances and angles and details
of hydrogen bonding are listed in Table 3.
Figure 4. The molecular structure of 2. Hydrogen atoms are omit-
ted for clarity.
Complex 3 crystallizes in the orthorhombic space group
A space-filling representation (Figure 5, top) shows that P212121. Its structure consists of neutral [Cu(N3)(O2-
1 has a diameter of 23.5 Å, with a central hole of 3.4 Å CPh)(MeOH)]n chains that run along the a axis (Figure 7).
Eur. J. Inorg. Chem. 0000, 0–0
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A. Escuer, G. Christou, S. P. Perlepes, et al.
FULL PAPER
There is one crystallographically independent CuII ion in
the asymmetric unit of 3. Its coordination geometry is well
described as Jahn–Teller distorted octahedral (4+2), with
four short bonds formed by the two azido nitrogen atoms
[Cu–N1 2.007(4), Cu–N1ЈЈ 1.996(4) Å] and two oxygen
atoms from two symmetrically ligated PhCO2– ions [Cu–O1
1.949(3), Cu–O2 1.948(3) Å]. The equatorial bond angles
are only slightly deviated from the ideal value of 90°. The
axial coordination sites are occupied by the oxygen atoms
from two bridging MeOH molecules, and the Cu–O3 and
Cu–O3Ј bond lengths [2.457(4) and 2.425(4) Å, respectively]
are significantly longer than the equatorial ones. Each CuII
center therefore possesses a N2O4 chromophore.
Both end-on azido and carboxylato bridges can be con-
sidered symmetrical within the crystallographic 3σ crite-
rion. These bridges, together with the bridging MeOH
groups, adopt an alternating all trans arrangement through-
out the chains. The azide ions are almost linear with an
N1–N2–N3 angle of 178.3(6)° and exhibit nonsymmetric
N–N bond lengths. The N2–N3 distance [1.145(7) Å] is
shorter than that of N1–N3 [1.211(6) Å].
Figure 6. Wireframe representation of the Cu10 wheels in 2 and
their supramolecular aggregation into ordered nanotubes (exclud-
ing H atoms).
Compound 3 is the second structurally characterized 1D
copper(II) complex in which the CuII ions are exclusively
–
bridged by one end-on μ1,1 N3 group, one η1:η1:μ carbox-
ylato ligand, and one monoatomic bridge from a third li-
gand; the first such complex is [Cu(N3)(L)(DMSO)]n (L– =
2-thiopheneacetato, DMSO = dimethyl sulfoxide).[40] The
combination of these three bridging ligands is also present
in alternating 1D copper systems[40,41] and in the 2D poly-
mer [Cu(N3)(tp)(MeOH)]n, where tp2– is the terephthalato
Figure 7. A plot of a portion of the 1D chain in 3. The aromatic
H atoms are omitted for clarity.
Table 3. Selected interatomic distances [Å] and angles [°] for 3.[a]
Cu–O1
Cu–O2
Cu–O3
Cu–O3Ј
Cu–N1
Cu–N1ЈЈ
Cu–O3Ј–CuЈ
Cu–N1–CuЈ
O1–Cu–O2
O1–Cu–O3
O1–Cu–O3Ј
O1–Cu–N1
1.949(3)
1.948(3)
2.457(4)
2.425(4)
2.006(4)
1.996(4)
80.8(1)
104.5(2)
179.4(1)
85.6(1)
O1–Cu–N1ЈЈ 89.5(1)
O2–Cu–O3
O2–Cu–O3Ј
O2–Cu–N1
94.9(1)
87.3(1)
91.5(2)
O2–Cu–N1ЈЈ 90.8(1)
O3–Cu–O3Ј
O3–Cu–N1
177.7(1)
95.8(2)
O3–Cu–N1ЈЈ 84.3(2)
O3Ј–Cu–N1 85.0(2)
O3Ј–Cu–N1ЈЈ 94.9(2)
N1–Cu–N1ЈЈ 177.7(2)
92.2(1)
88.2(1)
[a] Singly and doubly primed atoms are related to the unprimed
ones by the symmetry transformations: (Ј) = 0.5 + x, 1.5 – y, 2 –
z; (ЈЈ) = –0.5 + x, 1.5 – y, 2 – z.
–
Adjacent CuII ions are bridged by a single end-on N3
–
group, a syn,syn-η1:η1:μ PhCO2 ion, and an oxygen atom
from the neutral bridging MeOH molecule. Thus, three dif-
ferent kinds of bridges are present. The Cu···Cu distance
within the chain is 3.164(1) Å.
Figure 8. A view of the hydrogen bonding (dashed lines) between
chains in 3 along the c axis. The benzoate groups are omitted for
clarity.
6
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Coordination Polymers with Copper(II)
(i.e. a dicarboxylate) ligand.[42] The double (end-on azido)- Cu angles and Cu–N–O–Cu torsion angles), among
(η1:η1:μ-carboxylato) bridging system has also been found others.[44] The very small χMT values at 300 K (relative to
in copper(II) coordination polymers of various (1D, 2D, that expected for ten noninteracting CuII atoms), particu-
3D) dimensionalities.[43]
larly for 1, indicate very strong antiferromagnetic coupling
The 1D chains of 3 are hydrogen bonded into 2D sheets between the CuII atoms in both wheels even at room tem-
(Figure 8) through Nazide···H(OMeOH) interactions. The di- perature.
mensions are: O3#···N2 2.838(7) Å, O3#–H(O3#)···N2
Analysis of the magnetic data was attempted assuming
158.1(6)° (symmetry code: # = 0.5 + x, 0.5 – y, 2 – z). The only one J coupling constant for a ring of ten S = 1/2 spins
closest interchain Cu···Cu separation is 7.432 Å.
with the CLUMAG program[45] by applying the Hamil-
tonian in Equation (4).
H = –J(S1·S2 + S2·S3 + S3·S4 + S4·S5 + S5·S6 + S6·S7 + S7·S8 +
Magnetochemistry
S8·S9 + S9·S10 + S10·S1)
(4)
Solid-state, variable-temperature direct-current (dc) mag-
netic susceptibility (χM) data were collected from vacuum-
dried microcrystalline samples of 1·3DMF·2H2O and 2,
suspended in eicosane to prevent torquing, in the 5.0–300 K
range in a 0.1 T (1000 G) magnetic field. The data are plot-
ted as χMT vs. T in Figure 9, and it can be seen that the
overall magnetic response is similar but not identical for the
two complexes. χMT at 300 K is 0.32 and 0.54 cm3 Kmol–1
for 1·3DMF·2H2O and 2, respectively, much lower than the
value of 4.13 cm3 Kmol–1 (calculated with g = 2.1) expected
for a cluster of ten noninteracting CuII ions, which indicates
the presence of strong antiferromagnetic exchange interac-
tions.
The very strong antiferromagnetic coupling present in 1
with a room temperature χMT value lower than 10% for ten
noninteracting CuII centers makes the procedure extremely
sensitive to the presence of small amounts of paramagnetic
impurities and thus no satisfactory fit was achieved. As an
approximation, a fit of the data for the highest T region
(200–300 K) suggests a J value of ca. –850 cm–1. In con-
trast, a good fit was obtained for the highly pure 2 with
best-fit parameters of J = –765 cm–1 and g = 2.085. The
data indicate that the double (alkoxido)(oximato) bridging
system is an extremely strong antiferromagnetic coupler in
CuII chemistry.
Variable-temperature dc magnetic susceptibility data for
3 were collected on a powdered sample of the compound in
applied fields of 0.5 T (300–30 K) and 0.05 T (30–2.0 K) to
avoid saturation effects. The room temperature χMT value
for 3 is 0.49 cm3 Kmol–1 per formula unit, which is larger
than that expected for one isolated
S = 1/2 spin
(0.41 cm3 Kmol–1 with g = 2.1). Upon cooling, the χMT
value increases continuously to reach
a value of
6.0 cm3 Kmol–1 at 4 K (Figure 10). The room temperature
value and the continuous increase of χMT with decreasing
temperature suggest dominant ferromagnetic interactions in
3.
Figure 9. χMT vs. T plot for 1·3DMF·2H2O (᭿) and 2 (ᮀ) in the
5.0–300 K range. The solid line represents the best theoretical fit
for 2 (see text).
For 1·3DMF·2H2O, χMT gradually decreases with
decreasing temperature to a minimum of 0.02 cm3 Kmol–1
at 30 K and then increases very slightly to 0.03 cm3 Kmol–1
at 5 K. This suggests an S = 0 ground state, as expected for
antiferromagnetic interactions between an even number of
CuII ions in a single-strand wheel arrangement, and the
small increase at the lowest temperature is indicative of a
paramagnetic impurity that arises from polymeric CuII spe-
cies. For 2, χMT also decreases upon cooling, and drops to
a value of 0.02 cm3 Kmol–1 at 5 K, consistent with an S =
0 ground state with negligible evidence for paramagnetic
impurities. The differences in the χMT values between
1·3DMF·2H2O and 2, and consequently in the strength of
Figure 10. χMT vs. T plot for 3. The solid line shows the best-fit
of the experimental data (see text for fitting parameters). Inset:
Magnetization (M) vs. field (H) plot for 3.
Compound 3 shows a regular pattern of interactions
the antiferromagnetic interactions, are likely due to a com- along the 1D chain and thus, analysis of the magnetic data
bination of the different CuII environments (combination of was performed according to the expansion series expression
square pyramidal and square planar in 1 vs. square planar for an homogeneous chain[46] derived from the Hamiltonian
in 2) and differences in the metric parameters (i.e. Cu–ORЈ– in Equation (5).
Eur. J. Inorg. Chem. 0000, 0–0
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A. Escuer, G. Christou, S. P. Perlepes, et al.
FULL PAPER
H = –JΣ(Si·Si+1
)
(5)
architectures. However, when azides were employed in the
reaction mixtures that afforded 1 and 2, the bzoxH2-free
complex [Cu(N3)(O2CPh)(MeOH)]n (3) was obtained.
Compound 3 is a 1D chain, in which the CuII atoms are
This Hamiltonian includes a zJЈ interchain interaction
term. Best-fit parameters were J = +49.6(4) cm–1, g =
2.067(3), and zJЈ = 2.3(1) K. Isothermal magnetization at
2 K tends to a quasisaturated value of Nβ equivalent to 1.06
electrons per copper center under the maximum field of 5 T
(Figure 10, inset).
–
linked by a single, end-on N3 group, a syn,syn-η1:η1:μ
–
PhCO2 ion, and one monoatomic bridge from a neutral
MeOH molecule. The magnetic data for 1 and 2 indicate
strong antiferromagnetic exchange interactions and a S = 0
ground state, which is expected for even-membered loop ar-
rays of CuII atoms. In contrast, 3 exhibits ferromagnetic
exchange interactions due to the presence of end-on azido
ligands with the contribution of countercomplementarity of
the superexchange pathways. We anticipate a variety of new
3d-metal clusters and coordination polymers of different
nuclearities and dimensionalities from the employment of
various ligand combinations that involve bzoxH2, carboxyl-
ates, and/or pseudohalides. Further work is in progress.
From the analysis of the structural data for 3 (Scheme 2)
it is clear that the MeOH molecules link the axial coordina-
tion sites of the copper ions, and therefore the chain could
be considered magnetically as an azido/carboxylato-bridged
system. The net superexchange coupling constant of
+49.6(4) cm–1 for 3 corresponds to the combined interac-
tions due to the single syn,syn carboxylato and the end-on
azido bridges. The single carboxylato bridge is expected to
give moderately weak antiferromagnetic exchange,[40,43a]
whereas the small Cu–N–Cu angle of 104.5(2)° is expected
to lead to weak or moderate ferromagnetic exchange.[40,43a]
The magnetic properties of previously reported examples,
which exhibit the copper environment shown in Scheme 2,
show strong ferromagnetic coupling in all cases, regardless
of the Cu–Nazide–Cu bond angles, which range from 105 to
Experimental Section
Materials and Physical Measurements: All manipulations were per-
formed under aerobic conditions using chemicals and solvents as
131°.[40–43] For such a superexchange pathway, molecular received, unless otherwise stated. Cu(O2CPh)2·2H2O was prepared
orbital calculations have pointed out the countercomple-
as described elsewhere.[48]
mentary character of the superexchange pathways of the
two bridging ligands, a feature that gives rise to or enhances
the ferromagnetic response of the system even for the
largest Cu–Nazide–Cu bond angle of 131°.[43a,47] A few years
ago, the experimental ferromagnetic character was studied
by DFT calculations performed on copper/azide/carboxyl-
ate systems with a Cu–Nazide–Cu bond angle of 103.2° (cal-
culated J = 89 cm–1) and a relatively large bond angle of
116.1° (calculated J = 70 cm–1).[41a]
CAUTION: Azide salts are potentially explosive. Such compounds
should be synthesized and used in small quantities and treated with
utmost care at all times.
IR spectra were recorded from KBr pellets with a Nicolet Nexus
670 FTIR spectrometer in the 400–4000 cm–1 range. Elemental
analyses (C, H, N) were performed in-house at the University of
Florida Chemistry Department. Variable-temperature dc magnetic
susceptibility data for 1 and 2 were collected with a Quantum De-
sign MPMS-XL SQUID magnetometer equipped with a 7 T mag-
net operating in the 1.8–300 K range. Variable-temperature mag-
netic studies for 3 were performed with a DSM5 Quantum Design
SQUID magnetometer at the Magnetochemistry Service of the
University of Barcelona. Samples were embedded in eicosane to
prevent torquing. Pascal’s constants were used to estimate the dia-
magnetic corrections, which were subtracted from the experimental
susceptibilities to give the molar paramagnetic susceptibilities (χM).
[Cu10(bzox)10(DMF)4] (1): To a stirred solution of bzoxH2 (0.23 g,
1.0 mmol) in DMF (30 mL) was added solid Cu(O2CPh)2·2H2O
(0.35 g, 1.0 mmol). The resulting dark green solution was stirred
for 30 min, filtered, and the filtrate was left to evaporate slowly at
room temperature. After 10 d, X-ray quality, dark green crystals of
1·12DMF·2H2O (0.16 g, 45%) were collected by filtration, washed
with cold DMF (2ϫ3 mL) and Et2O (2ϫ 5 mL), and dried under
vacuum over silica gel. 1·3DMF·2H2O: C161H163Cu10N17O29
(3435.69): calcd. C 56.29, H 4.78, N 6.93; found C 56.15, H 4.62,
Scheme 2. Coordination environment of a CuII ion in a triply
bridged N3 /RCO2 /L (L = neutral ligand) system where the axial
bonds exclusively involve the monoatomic bridge of L. L does not
contribute to the magnetic exchange interactions.
–
–
N 7.07. IR (KBr ): ν = 3460 (m br.), 2924 (m), 1670 (vs), 1492 (s),
˜
1442 (m), 1406 (m), 1384 (m), 1254 (m), 1190 (w), 1118 (m), 1090
(vs), 1038 (m), 1016 (s), 918 (w), 844 (s), 792 (w), 744 (s), 696 (vs),
658 (s), 618 (w), 596 (m), 562 (w), 504 (m), 466 (w) cm–1.
Conclusions
The combined use of α-benzoin oxime (bzoxH2), benzo-
ates, and/or azides in copper(II) chemistry has afforded
two new Cu10 molecular wheels and an 1D coordination
polymer. [Cu10(bzox)10(DMF)4] (1) and [Cu10(bzox)10] (2)
contain the bridging dianion of bzox2– with (1) or without
(2) terminal solvate molecules. Wheels 1 and 2 stack to form
[Cu10(bzox)10] (2). Method A: Solid 1·3DMF·2H2O (1.72 g,
0.5 mmol) was dissolved in CH2Cl2 (30 mL) to give a green solu-
tion. The solution was filtered, and Et2O (60 mL) was allowed to
slowly diffuse into the filtrate over a period of 2 d, during which
time green crystals of 2·8CH2Cl2·2Et2O grew. The crystals were
nanotubular columns with interesting supramolecular maintained in the mother liquor for X-ray crystallography and
8
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Coordination Polymers with Copper(II)
other single-crystal studies, or collected by filtration, washed with
CH2Cl2 (2ϫ 3 mL) and Et2O (2ϫ 2 mL), and dried in air to give
solvent-free 2 (0.51 g, 35%). C140H110Cu10N10O20 (2887.99): calcd.
C 58.23, H 3.84, N 4.85; found C 58.02, H 3.76, N 4.97. IR (KBr
during which time the solid dissolved and the solution turned dark
green. Layering of the solution with Et2O (60 mL) gave dark green
crystals of 3 after 2 d. The crystals were collected by filtration,
washed with cold MeOH (2ϫ 5 mL) and Et2O (2ϫ 5 mL), and
): ν = 2920 (m), 1497 (s), 1440 (m), 1401 (m), 1390 (m), 1251 (m), dried in air to give 3 (0.21 g, 80%). The identity of the product was
˜
1184 (w), 1111 (m), 1093 (vs), 1045 (m), 1020 (s), 924 (w), 850 (s),
confirmed by elemental analysis and IR spectral comparison with
790 (w), 747 (s), 714 (vs), 667 (s), 617 (w), 600 (m), 557 (w), 500 the authentic sample prepared according to Method A.
(m), 461 (w) cm–1.
X-ray Crystallography and Structure Solution: Suitable crystals of
1·12DMF·2H2O, 2·8CH2Cl2·2Et2O, and 3 were attached to glass
fibers using silicone grease and transferred to a goniostat where
they were cooled to 180, 173, and 293 K, respectively, for data col-
lection. An initial search of reciprocal space revealed a triclinic cell
for 1·12DMF·2H2O, a monoclinic cell for 2·8CH2Cl2·2Et2O, and
Method B: To a stirred solution of bzoxH2 (0.23 g, 1.0 mmol) in
CH2Cl2 (30 mL) was added solid Cu(O2CPh)2·2H2O (0.35 g,
1.0 mmol). The resulting blue slurry was heated to reflux for 1 h,
during which time the solid dissolved and solution turned green.
Layering of the solution with Et2O (60 mL) gave green crystals of
2·8CH2Cl2·2Et2O after 6 d. The crystals were collected by fil-
tration, washed with CH2Cl2 (2ϫ 3 mL) and Et2O (2ϫ 2 mL), and
dried in air; the yield was 60% (0.17 g). The dried solid analyzed
satisfactorily as solvent-free. The identity of the product was con-
firmed by elemental analysis and IR spectral comparison with the
authentic sample prepared according to Method A.
¯
an orthorhombic cell for 3; the choice of space groups P1, P21/n,
and P212121, respectively, was confirmed by the subsequent solu-
tion and refinement of the structures. Data for 1·12DMF·2H2O
and 3 were collected with a Rigaku R-AXIS SPIDER Image Plate
diffractometer using graphite-monochromated Cu-Kα radiation (λ
= 1.54178 Å). Unit cell dimensions were determined and refined by
using the angular settings of 25 automatically centered reflections
in the range 11° Ͻ 2θ Ͻ 23°. Intensity data were recorded using a
θ–2θ scan to a maximum 2θ value of 130°. Three standard reflec-
tions monitored every 97 reflections showed less than 3% variation
and no decay. Lorentz, polarization, and psi-scan absorption cor-
rections were applied using CrystalClear[52] software. Both struc-
tures were solved by direct methods using SHELXS-97[49a] and re-
fined on F2 by full-matrix least-squares techniques with SHELXL-
97.[49b] All H atoms were either located by Fourier difference maps
and refined isotropically or were introduced at calculated positions
as riding on bonded atoms. All non-H atoms were refined aniso-
tropically. Data for 2·8CH2Cl2·2Et2O were collected with a Siemens
SMART PLATFORM equipped with a CCD area detector and a
graphite monochromator using Mo-Kα radiation (λ = 0.71073 Å).
Cell parameters were refined using up to 8192 reflections. A full
sphere of data (1850 frames) was collected using the ω-scan method
(0.3° frame width). The first 50 frames were remeasured at the end
of data collection to monitor instrument and crystal stability
[Cu(N3)(O2CPh)(MeOH)]n (3). Method A: To a stirred solution of
bzoxH2 (0.23 g, 1.0 mmol) in MeOH (30 mL) was added solid
NaN3 (0.07 g, 1.0 mmol). The mixture was stirred for 15 min before
solid Cu(O2CPh)2·2H2O (0.35 g, 1.0 mmol) was added with vigor-
ous stirring, which caused a rapid color change from blue to dark
green. The resulting solution was stirred for a further 1 h, filtered,
and the filtrate was layered with Et2O (60 mL). After 20 d, X-ray
quality, dark green crystals of 3 were collected by filtration, washed
with cold MeOH (2ϫ 5 mL) and Et2O (2ϫ 5 mL), and dried in
air to give 3 (0.04 g, 15%). C8H9CuN3O3 (258.73): calcd. C 37.14,
H 3.51, N 16.24; found C 37.32, H 3.66, N 16.12. IR (KBr): ν =
˜
3426 (m br.), 2094 (vs), 1592 (m), 1532 (vs), 1412 (s), 1266 (w),
1176 (w), 1090 (w), 1052 (w), 1003 (w), 720 (m), 686 (m), 502 (w),
450 (w) cm–1.
Method B: To a stirred solution of NaN3 (0.07 g, 1.0 mmol) in
MeOH (30 mL) was added solid Cu(O2CPh)2·2H2O (0.35 g,
1.0 mmol). The resulting blue slurry was heated to reflux for 1 h,
Table 4. Crystallographic data for 1·12DMF·2H2O, 2·8CH2Cl2·2Et2O, and 3.
1·12DMF·2H2O
2·8CH2Cl2·2Et2O
3
Formula[a]
C188H226Cu10N26O38
4093.35
C156H146Cu10Cl16N10O22
3715.43
C2H2.25Cu0.25N0.75O0.75
64.68
M [gmol–1][a]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
triclinic
P1
monoclinic
P21/n
16.9401(11)
27.9757(18)
16.9907(11)
90
91.464(1)
90
8049.5(9)
2
orthorhombic
P212121
6.3252(2)
7.4324(1)
22.3233(5)
90
¯
17.6557(3)
17.9324(3)
18.0189(3)
67.520(1)
85.575(1)
65.977(1)
4793.97(14)
1
90
90
γ [°]
V [Å3]
1049.45(4)
16
Z
T [K]
180(2)
1.54178
1.418
1.831
173(2)
0.71073
1.533
1.626
293(2)
1.54178
1.637
λ [Å][b]
ρcalc [gcm–3]
μ [mm–1]
2.907
Measured/independent (Rint); reflections
Observed reflections IϾ2σ(I)
64502/15688; (0.0753)
13346
0.0765
0.1892
1.067
53932/18359; (0.0297)
14412
0.0324
0.0765
1.009
3823/1725; (0.0415)
1428
0.0493
0.1125
1.107
[c,d]
R1
[e]
wR2
GOF on F2
(Δρ)max, min [eÅ–3]
0.858, –0.818
0.356, –0.280
0.590, –0.594
2
2 2
[a] Including solvate molecules. [b] Graphite monochromator. [c] IϾ2σ(I). [d] R1 = Σ(||Fo| – |Fc||)/Σ|Fo|. [e] wR2 = {Σ[w(Fo – Fc ) ]/
Σ[w(Fo2)2]}1/2, w = 1/[σ2(Fo2) + (ap)2 + bp], where p = [max(Fo2, 0) + 2Fc ]/3.
2
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A. Escuer, G. Christou, S. P. Perlepes, et al.
FULL PAPER
Chem. Int. Ed. 2004, 43, 2117; b) T. Liu, Y.-J. Zhang, Z.-M.
Wang, S. Gao, J. Am. Chem. Soc. 2008, 130, 10500; c) Th. C.
Stamatatos, K. A. Abboud, W. Wernsdorfer, G. Christou, An-
gew. Chem. 2007, 119, 902; Angew. Chem. Int. Ed. 2007, 46,
884.
(maximum correction on I was Ͻ 1%). Absorption corrections by
integration were applied based on measured indexed crystal faces.
The structure was solved by direct methods in SHELXTL6,[50] and
refined on F2 using full-matrix least-squares. The non-H atoms
were treated anisotropically, whereas the H atoms were placed in
calculated, ideal positions and refined as riding on their respective
C atoms. The asymmetric unit of 1·12DMF·2H2O consists of half
of the Cu10 cluster, six DMF molecules, and one H2O molecule
of crystallization. None of the water protons could be located in
difference Fourier maps and thus were not included in the final
refinements. A total of 1378 parameters were refined in the final
cycle of refinement using 13346 reflections with IϾ2σ(I). For
2·8CH2Cl2·2Et2O, the asymmetric unit also contains the half of the
Cu10 cluster with four CH2Cl2 molecules and one Et2O molecule
of crystallization. All solvent molecules were disordered and could
not be modeled properly, thus the SQUEEZE[51] program was used
to calculate the solvent disorder area and remove its contribution
to the overall intensity data. It is important to note that one of the
disordered CH2Cl2 molecules was located at the center of the Cu10
wheel cluster. A total of 811 parameters were refined in the final
cycle of refinement using 14412 reflections with IϾ2σ(I). The
asymmetric unit of 3 contains the one-quarter of the repeating,
mononuclear Cu unit, and no solvent of crystallization. A total of
157 parameters were refined in the final cycle of refinement using
1428 reflections with IϾ2σ(I). Unit cell parameters and structure
solution and refinement data for all three complexes are listed in
Table 4.
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Received: November 21, 2011
Published Online: ᭿
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11

Job/Unit: A11292
/KAP1
Date: 09-01-12 16:43:29
Pages: 12
A. Escuer, G. Christou, S. P. Perlepes, et al.
FULL PAPER
Polynuclear Copper(II) Complexes
T. C. Stamatatos, G. Vlahopoulou,
C. P. Raptopoulou, V. Psycharis,
A. Escuer,* G. Christou,*
S. P. Perlepes* ................................. 1–12
Single-Strand Molecular Wheels and Coor-
dination Polymers in Copper(II) Benzoate
Chemistry by the Employment of α-
Benzoin Oxime and Azides: Synthesis,
Structures, and Magnetic Characterization
Keywords: Copper / Coordination poly-
mers / Single-strand molecular wheels /
N,O ligands / Magnetic properties
The reaction illustrated gives the decanu-
clear complexes [Cu10(bzox)10(DMF)4] and
[Cu10(bzox)10] (bzoxH2 = α-benzoin oxime,
DMF = N,N-dimethylformamide), which
have a single-strand wheel topology, and
the 1D chain [Cu(N3)(O2CPh)(MeOH)]n.
The Cu10 clusters are both antiferromag-
netically coupled with S = 0 ground states,
whereas the 1D chain consists of ferromag-
netically coupled S = 1/2 CuII ions.
12
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