Pyrididine-carboxylate ligands as double-bridge spacers in CuI metallacycles

Article abstract of DOI:10.1002/ejic.201402930

The addition of pyridine-3-carboxylic acid (3-PyCOOH), (E)-3-(pyridin-3-yl)acrylic acid (3-PyCH=CHCOOH), or 3-(pyridin-4-yl)benzoic acid (3-PyPhCOOH) to the Lewis acidic [Cu(dppf)(NCMe)₂][BF₄]·2MeCN·2H₂O [1·2MeCN·2H₂O, dppf = 1,1′-bis(diphenylphosphanyl)ferrocene] in the presence of NEt₃ afforded the complexes [Cu₂(dppf)₂(3-PyCOO)₂]·3CHCl₃ (2·3CHCl₃), [Cu₂(dppf)₂(3-PyCH=CHCOO)₂]·CH₂Cl₂·C₆H₁₄ (3·CH₂Cl₂·C₆H₁₄), and [Cu₂(dppf)₂(3-PyPhCOO)₂]·CH₂Cl₂ (4·CH₂Cl₂) with a common metallomacrocycle core and doubly bridging pyridine-carboxylate ligands as spacers. These dinuclear complexes have been structurally characterized by single-crystal X-ray crystallography, and their emission activities have been studied. Pyridine-carboxylate-bridged dinuclear Cu^I complexes capped by 1,1′-bis(diphenylphosphanyl)ferrocene (dppf) exhibit macrocycles with diagonal distances of 6.586, 9.159, and 10.006 ?. Such cavity sizes are formed by the introduction of CH=CH or phenyl units into the original pyridine-3-carboxylic acid (3-PyCOOH) spacer.

Full text of DOI:10.1002/ejic.201402930

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DOI:10.1002/ejic.201402930
Pyrididine–Carboxylate Ligands as Double-Bridge Spacers
in CuI Metallacycles
Xialu Wu,[a] Wenhua Zhang,[b] Xinhai Zhang,[b] Nini Ding,*[b] and
T. S. Andy Hor*[a,b]
Keywords: Metallacycles / N,O ligands / Crystal engineering / Macrocycles / Copper
The addition of pyridine-3-carboxylic acid (3-PyCOOH), (E)-
3-(pyridin-3-yl)acrylic acid (3-PyCH=CHCOOH), or 3-(pyr-
idin-4-yl)benzoic acid (3-PyPhCOOH) to the Lewis acidic
C6H14 (3·CH2Cl2·C6H14), and [Cu2(dppf)2(3-PyPhCOO)2]·
CH2Cl2 (4·CH2Cl2) with a common metallomacrocycle core
and doubly bridging pyridine–carboxylate ligands as spa-
cers. These dinuclear complexes have been structurally char-
acterized by single-crystal X-ray crystallography, and their
[Cu(dppf)(NCMe)2][BF4]·2MeCN·2H2O
[1·2MeCN·2H2O,
dppf = 1,1Ј-bis(diphenylphosphanyl)ferrocene] in the pres-
ence of NEt3 afforded the complexes [Cu2(dppf)2(3-PyCOO)2]· emission activities have been studied.
3CHCl3 (2·3CHCl3), [Cu2(dppf)2(3-PyCH=CHCOO)2]·CH2Cl2·
with pyridine-3-carboxylic acid, which result in triangular
Introduction
topologies.[14–20,24,25] Meanwhile, some CuII dinuclear com-
plexes bridged by pyridine–carboxylate ligands were re-
ported[21,22] in which N-donor ligands such as diethylenetri-
amine were used to end-cap the metal center in combina-
Taking advantage of the abundance of spacers, numerous
metal permutations, and preparative simplicity, the self-as-
sembly of active supramolecular coordination complexes[1]
provides a powerful means to create functional materials
for applications in areas such as photoluminescence,[2,3] gas
storage and separation,[4–7] catalysis,[8–11] and magnet-
ism.[12,13] We are interested in hybrid spacers, such as pyr-
idine–carboxylates, with donating sites that can be easily
stereogeometrically regulated to give assemblies of defined
topologies.[14–23] The synthesis of such structurally defined
materials would pave the way for the creation of functional
molecular materials with targeted applications.
In this paper, we report the synthesis and isolation of an
electroactive CuI precursor with two potential MeCN leav-
ing groups to give it Lewis acidity, namely, [Cu(dppf)-
(NCMe)2][BF4] [1, dppf = 1,1Ј-bis(diphenylphosphanyl)fer-
rocene]. The subsequent addition reactions of 1 with pyr-
idine-3-carboxylic acid (3-PyCOOH), (E)-3-(pyridin-3-yl)-
acrylic acid (3-PyCH=CHCOOH), and 3-(pyridin-4-yl)-
benzoic acid (3-PyPhCOOH) in the presence of NEt3 afford
three dinuclear complexes with a common cyclic central
core. These assemblies from a tetrahedral [Cu(dppf)-
(NCMe)2]+ precursor complement related assemblies of
–
square-planar [Pt(dppf)2(NCMe)2][OTf]2 (OTf– = CF3SO3 )
[a] Department of Chemistry, Faculty of Science, National
University of Singapore,
3 Science Drive 3, 117543, Singapore
E-mail: andyhor@nus.edu.sg
http://staff.science.nus.edu.sg/~andyhor/
[b] Institute of Materials Research & Engineering,
3, Research Link, 117602, Singapore
Scheme 1. Schematic representation of the syntheses of 2, 3, and 4
from 1 and the pyridine–carboxylate ligands.
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402930.
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tion with a short pyridine–carboxylate ligand such as 3-Py- Figure 2, the copper centers in all structures have distorted
COOH as the bridging spacer. Only a small number of di- tetrahedral geometries (Tables S1–S4). Complexes 2–4 are
nuclear complexes bridged by longer pyridine–carboxylate dinuclear and isostructural with doubly bridging pyridine–
ligands such as 3-PyCH=CHCOOH and 3-PyPhCOOH carboxylate ligands coordinated through their O and N
have been reported. Therefore, we wanted to investigate if atoms. They differ only in the size of their central cavity,
such assemblies can provide an easy route to larger func- which is formed as a result of the cyclization of two bridg-
tional metallomacrocycles. As part of our investigations of ing spacers over two metal centers. Complex 2 gives a 12-
self-assemblies with hybrid spacers,[15,17,18,26] we decided to membered metallacycle with a diagonal distance of 6.586 Å
study the complexation of 1 with longer pyridine–carboxyl- (Cu1···Cu1A; Figure 3, top left). The introduction of a
ate ligands.
CH=CH linkage to the spacer (3-PyCH=CHCOOH) re-
The cationic and mononuclear [Cu(dppf)(NCMe)2]+ sulted in a 16-membered metallacycle with the separation
with a chelating ligand (dppf) and two potential leaving extended to 9.159 Å (Figure 3, top middle). The adjustment
groups is a suitable entity to form the corners in squarelike of the cavity size by the spacer is further demonstrated
topologies.[27–31] This paper reports the self-assembly of 1 when a phenyl unit is introduced to the backbone of the
with 3-PyCOOH to give dinuclear metallacycles (Scheme 1) spacer (3-PyPhCOOH), which results in 20-membered
as the only isolated products. By a common methodology, metallacycle with a large separation of 10.006 Å (Figure 3,
we prepared three isostructural metallacycles. The size of
their central cavities can be easily adjusted by the skeletal
dimensions and configurations of the pyridine–carboxylate
spacers 3-PyCOOH, 3-PyCH=CHCOOH, and 3-
PyPhCOOH. The potential of the resultant ensembles as
emissive materials has also been explored.
Results and Discussion
Syntheses and Structures of Heterometallic Dinuclear
Metallacycles
The dinuclear complexes [Cu2(dppf)2(3-PyCOO)2] (2),
[Cu2(dppf)2(3-PyCH=CHCOO)2] (3), and [Cu2(dppf)2(3-
PyPhCOO)2] (4) were prepared in near-quantitative yields
from 1 and 3-PyCOOH, 3-PyCH=CHCOOH, and 3-
PyPhCOOH in CH2Cl2 in the presence of Et3N at ambient
temperature. The disappearance of the 31P NMR spectral
signal at δ = –12.99 ppm of the resultant mixture indicated
the exhaustion of 1, and the sole signal for the product at
ca. δ = –16 ppm suggested high product purity (Supporting
Information, Figure S1).
The structures of 1 (Figure 1) and 2–4 (Figure 2) were
determined by single-crystal X-ray diffraction. As shown in
Figure 2. ORTEP drawings (50% thermal ellipsoids) of 2 (top), 3
Figure 1. ORTEP drawing (50% thermal ellipsoids) of 1 (hydrogen
atoms and solvent molecules are omitted).
(middle), and 4 (bottom); hydrogen atoms and solvent molecules
are omitted.
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Figure 3. Secondary interactions with hydrogen bonds (shown as dashed lines) in 2 (top left), 3 (top middle and bottom), and 4 (top
right).
top right). The packing patterns of 2–4 show narrow 1D shown in Figure 4, all three dinuclear materials at 280 K
solvent-free columns along the a axis (Figure S2).
show strong emissions at λ = 533, 538, and 587 nm upon
An ESI mass spectrometry study of the three complexes excitation by 325 nm laser. The full width at half-maximum
in solution at ambient temperature revealed the mono- is only ca. 2 nm, which is notably much narrower than that
nuclear fragments of the metallacycles (Figure S9–S11) as of the reported CuI emission (ca. 40–60 nm).[32–35] These
[Cu(dppf)(L)] (L = 3-PyCOO–, 3-PyCH=CHCOO–, and 3- three emission peaks can be assigned as Cu electron transfer
PyPhCOO–). This points to a possible mono- and dinuclear of 3P1Ǟ3Fo , 3P2Ǟ3F4, and 3P0Ǟ3Do , respectively.[36]
2
3
interchange in solution, as reported in related work by Shiu Control experiments on 1 and the free acids 3-PyCOOH, 3-
et al.,[23] at least under ESI-MS conditions.
PyC2H2COOH, and 3-PyPhCOOH under similar experi-
Intracyclic H bonding between the C–H group and the mental conditions revealed that 1 showed weaker emission
coordinated carboxy oxygen atom is found in all three dinu- and the latter were nonemissive, as indicated by their poor
clear complexes (Figure 3; the H-bonding distances H···A emission spectra (Figures 4 and S6–S8). These comparisons
of 2.37–2.55 Å and the D–H···A angles of 99–118° are sum-
marized in Table 1). There is also secondary H bonding be-
tween neighboring cycles through a C–H group and the
pendant carboxy oxygen atom in 3, which is different from
2 and 4 (Figure 3; the H···A H-bonding distance of 2.61 Å
and the D–H···A angle of 123° are shown in Table 1). These
H bonds give rise to a series of interconnected cycles in the
crystal packing arrangements.[23]
Table 1. Hydrogen-bonding parameters in 2, 3, and 4.
D–H···A
D–H [Å] H···A [Å] D···A [Å] D–H···A [°]
2
3
C2–H2···O1
C2–H2···O1a
C6–H6···O1
C5–H5···O1a
C7–H7···O2c[a]
C13–H13···O1
C18–H18···O1a
0.951
0.951
0.951
0.950
0.950
0.950
0.950
2.371
2.454
2.452
2.553
2.616
2.394
2.539
2.372
3.021
2.793
3.075
3.240
2.720
2.992
102.006
118.070
100.904
114.815
123.546
99.720
4
109.339
[a] Secondary H bonding between neighboring cycles.
The emission properties of 2–4 in the solid state were
investigated at various temperatures (Figures S3–S5). As emission of 1).
Figure 4. Emission of 2, 3, and 4 excited by 325 nm laser (inset:
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[Cu2(dppf)2(3-PyCOO)2] (2): Complex 1 (78.6 mg, 0.1 mmol) was
dissolved in CH2Cl2 (25 mL), and pyridine-3-carboxylic acid
(12.3 mg, 0.1 mmol) was added to give a suspension. Three drops
of Et3N were added to the suspension to immediately produce a
clear solution. This solution was stirred at ambient temperature for
another 30 min. The solvent and excess Et3N were removed in
vacuo to produce a pale yellow residue of 2 (64.3 mg, 87%). Fur-
ther recrystallization could be carried out from a mixture of
CH2Cl2 and hexane. 1H NMR (CDCl3, 296 K): δ = 9.18 (s, 2 H,
Py), 8.35–8.37 (d, 2 H, Py), 8.22–8.23 (d, 2 H, Py), 7.21–7.48 (m,
42 H, Ph, Py), 4.22 (s, 8 H, Cp), 4.31 (s, 8 H, Cp) ppm. 31P
pointed to the positive optical effect of the pyridine–carb-
oxylate ligands in these materials. Such narrow full width
at half-maximum (2 nm) could point to the possible use of
these materials as sharp-wavelength optical sources.
Conclusions
We have demonstrated a simple and versatile method to
construct isostructural materials with different degrees of
topological cyclic features. The resultant 12-, 16-, and 20-
membered metallacycles prepared from a singular self-as-
sembly method have demonstrated the way forward for
engineering functional materials directly from commercial
reagents. This requires the use of a versatile Lewis acidic
precursor, as evidenced by the synthesis and isolation of the
solvate-coordinated complex [Cu(dppf)(NCMe)2][BF4]. The
isolation of such substrates would pave the way for the cre-
ation of many other systems that demand the use of single
metallic sources. The metallacycles described herein are
strongly emissive at defined wavelengths. Their isolation
demonstrates the possibility for the self-assembly of op-
tically active molecular materials that can be manipulated
optically through the simple choice of spacers at the synthe-
sis level. Although such spacer-dependent emissive wave-
length is not unusual, the preservation of the metallacyclic
structure and nuclearity is particularly valuable. This un-
usual phenomenon gives a rare opportunity for the func-
tional manipulation of molecular materials with a common
or predefined structural framework. We are currently study-
ing the extension of this methodology to related spacers
and metal centers.
NMR (CDCl , 296 K): δ = –16.026 (s) ppm. IR (KBr): ν =
˜
3
1607 (COO)asym
,
1376, 1308 (COO)sym cm–1. C82H68Cl4Cu2-
Fe2N2O4P4 (2·2CH2Cl2, 1649.94): calcd. C 59.69, H 4.15, N 1.70;
found C 59.72, H 4.49, N 1.84. ESI-MS (50 °C, CH2Cl2): m/z (%)
= 617.2 (100) [Cu(dppf)]+, 739.4 (15) [Cu(dppf)(3-PyCOO)]+,
1270.7 (25) [Cu(dppf)2(H2O)(OH)]+, 1357.8 (31) [Cu(dppf)2(3-
PyCOO)(H2O)(NCMe)]+.
[Cu2(dppf)2(3-PyCH=CHCOO)2] (3): The synthetic procedure for
3 was similar to that of 2, except that (E)-3-(pyridin-3-yl)acrylic
acid (14.9 mg, 0.1 mmol) was used instead of pyridine-3-carboxylic
1
acid. Complex 3 was obtained as a yellow solid in 87% yield. H
NMR (CDCl3, 296 K): δ = 9.13 (s, 2 H, Py), 8.34 (s, 2 H, Py),
8.16–8.17 (d, 2 H, Py), 7.84–7.86 (d, 2 H, Py), 7.21–7.48 (m, 42 H,
Ph, CH=CH), 6.49, 6.52 (d, 2 H, CH=CH), 4.19 (s, 8 H, Cp), 4.36
(s, 8 H, Cp) ppm. 31P NMR (CDCl3, 296 K): δ = –16.213 (s) ppm.
IR (KBr): ν = 1605 (COO)asym, 1377, 1307 (COO)sym cm–1.
˜
C86H72Cl4Cu2Fe2N2O4P4 (3·2CH2Cl2, 1702.02): calcd. C 60.69, H
4.26, N 1.65; found C 60.34, H 4.38, N 1.72. ESI-MS (50 °C,
CH2Cl2): m/z (%)
=
617.2 (100) [Cu(dppf)]+, 765.6 (85)
[Cu(dppf)(3-PyCH=CHCOO)]+, 1270.7 (20) [Cu(dppf)2(H2O)-
(OH)]+, 1383.8 (100) [Cu(dppf)2(3-PyCH=CHCOO)(H2O)-
(NCMe)]+.
[Cu2(dppf)2(3-PyPhCOO)2] (4): The synthetic procedure for 4 was
similar to that of 2, except that 3-(pyridin-4-yl)benzoic acid was
used instead of pyridine-3-carboxylic acid. Complex 4 was ob-
Experimental Section
1
tained as a yellow solid in 90% yield. H NMR (CDCl3, 296 K): δ
General Procedures: All reactions were performed under 99.9995%
pure nitrogen by standard Schlenk techniques. All chemicals used
in the synthesis were of reagent grade from commercial sources and
used as received. MeCN, CH2Cl2, CHCl3, MeOH, and hexane were
predried by using an MBraun MB SPS-800 solvent purification
system. [Cu(CH3CN)4][BF4] was prepared as reported pre-
viously.[37]
All 1H [δ (TMS) = 0.0 ppm] and 31P NMR spectra [δ (85% H3PO4)
= 0.0 ppm] were recorded at ca. 296 K at operating frequencies
of 299.96 and 121.49 MHz, respectively, with a Bruker AVANCE
300 MHz spectrometer. The elemental analyses were performed
with a Perkin–Elmer PE 2400 elemental analyzer. The samples used
for the elemental analyses were obtained directly from purified
samples.
= 8.38 (s, 2 H, Ph of 3-PyPhCOO), 8.23–8.24 (d, 4 H, Py), 8.20–
8.21 (d, 2 H, Ph of 3-PyPhCOO), 7.63–7.65 (d, 2 H, Ph of 3-
PyPhCOO), 7.21–7.48 (m, 46 H, Ph, Py), 4.21 (s, 8 H, Cp), 4.33 (s,
8 H, Cp) ppm. 31P NMR (CDCl3, 296 K): δ = –16.174 (s) ppm. IR
(KBr):
ν = 1610 (COO)asym,
˜
1377, 1307 (COO)sym cm–1.
C95H78Cl6Cu2Fe2N2O4P4 (4·3CH2Cl2, 1887.07): calcd. C 60.47, H
4.17, N 1.48; found C 60.34, H 4.38, N 1.72. ESI-MS (50 °C,
CH2Cl2): m/z (%)
=
617.2 (100) [Cu(dppf)]+, 815.6 (75)
[Cu(dppf)(3-PyPhCOO)]+, 1270.7 (95) [Cu(dppf)2(H2O)(OH)]+,
1433.8 (35) [Cu(dppf)2(3-PyPhCOO)(H2O)(NCMe)]+.
Crystal Structure Determinations: The crystals of 1–4 were formed
by the slow diffusion of hexane into solutions of the pure com-
plexes in CH2Cl2 or CHCl3. The diffraction experiments were per-
formed at 100 K with a Bruker SMART CCD diffractometer for
1, 2, and 4 and with a Bruker APEX II diffractometer for 3. The
instruments were both equipped with a graphite-monochromated
Mo-Kα radiation source (λ = 0.71073 Å). The program SMART[38]
was used to collect frames of data, index reflections, and determine
lattice parameters, SAINT was used to integrate the intensity of
[Cu(dppf)(CH3CN)2][BF4] (1):
[Cu(CH3CN)4][BF4] (0.66 g,
2.1 mmol) was dissolved in CH3CN (20 mL), dppf (1.11 g,
2.0 mmol) was added, and the mixture was stirred at ambient tem-
perature for 2 h. Et2O (ca. 120 mL) was then added to the solution
to provide a yellow precipitate of 1, yield 1.43 g, 91%. 1H NMR
(CDCl3, 296 K): δ = 7.43–7.50 (m, 20 H, Ph), 4.37 (s, 4 H, Cp), the reflections and for scaling, SADABS[39] was used for absorption
4.12 (s, 4 H, Cp), 2.19 (s, 6 H, CH3CN) ppm. 31P NMR (CDCl3,
correction, and SHELXTL[40,41] was used for space group and
296 K): δ = –12.99 (s) ppm. C38H34BCuF4FeN2P2 (786.84): calcd. structure determination and least-squares refinements on F2. The
C 58.01, H 4.36, N 3.56; found C 58.37, H 4.30, N 3.38. ESI-MS relevant crystallographic data and refinement details are shown in
(50 °C, CH2Cl2): m/z (%) = 617.2 (100) [Cu(dppf)]+, 1186.9 (20) Table 2. In 1, the asymmetric unit contains one C38H34N2P2FeCu
[Cu(dppf)2(H2O)]+, 1270.7 (20) [Cu(dppf)2(H2O)(OH)]+.
cation, one BF4 anion, two acetonitrile molecules, and two water
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Table 2. Crystallographic data and structure refinement for 1–4.
1
2
3
4
Empirical formula
Temperature [K]
Formula weight
Space group
Crystal system
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C41.50H40.25BCuF4FeN3.50O0.50P2 C80H64Cu2Fe2N2O4P4 C85H71BCl2Cu2F4Fe2N2O4P4 C92H72Cu2Fe2N2O4P4
100(2)
100(2)
123(2)
100(2)
864.16
P21/c
1478.11
P1
1704.81
P1
1630.17
P1
¯
¯
¯
monoclinic
12.6230(11)
22.748(2)
13.7783(13)
90
95.899(3)
90
3935.5(6)
4
triclinic
monoclinic
19.6698(15)
19.8141(16)
20.7723(15)
90
112.112(2)
90
7500.3(10)
4
triclinic
12.2571(11)
13.0080(11)
17.1720(15)
69.889(2)
74.951(2)
64.823(2)
10.020(2)
13.571(3)
14.976(3)
92.454(5)
92.402(5)
92.877(5)
2030.0(8)
1
γ [°]
Volume [Å3]
Z
2305.9(3)
1
Dcalcd [g/cm3]
1.459
1.582
1.510
1.474
μ [mm–1
F(000)
]
1.046
1.404
1.159
1.132
1775
1108
3488
924
Crystal size [mm]
Index ranges
0.50ϫ0.36ϫ0.18
–16Յ hՅ 15
–27Յ kՅ 29
–17Յ lՅ 17
0.0605, 0.1145
0.0473, 0.1084
1.042
0.36ϫ0.22ϫ0.16
–15Յ hՅ 15
–16Յ kՅ 16
–22Յ lՅ 22
0.0842, 0.1481
0.0592, 0.1367
1.034
0.38ϫ0.30ϫ0.28
–24Յ hՅ 25
–25Յ kՅ 25
–26Յ lՅ 23
0.0976, 0.1482
0.0624, 0.1347
1.064
0.54ϫ0.34ϫ0.20
–13Յ hՅ 12
–17Յ kՅ 17
–19Յ lՅ 19
0.0877, 0.1501
0.0603, 0.1383
1.035
[b]
R1 [a], wR2 (all data)
Final R1, wR2
GOF [c]
Largest diff. peak and hole [e/Å3] 0.706 and –0.377
1.470 and –0.865
0.898 and –1.633
1.065 and –0.989
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {Σw(|Fo| – |Fc|)2/Σw|Fo|2}1/2. [c] GOF = {Σw(|Fo| – |Fc|)2/(n – p)}1/2
.
molecules. One of the acetonitrile molecules was 28% replaced by
two water molecules, which makes the empirical formula
the Institute of Materials Research & Engineering (IMRE) for fin-
ancial support as well as Hong Yimian and Tan Geok Kheng for
crystallographic assistance.
C
41.50H40.25BCuF4FeN3.50O0.50P2. In 3, the hydrogen atoms of the
disordered solvate molecules were not located. There is one level A
alert caused by a short O2···O2 (1 – x, 3 – y, 2 – z) contact of
2.450 Å. The ORTEP diagrams indicated no signs of disorder for
O2 or its bonded atoms. This unusual short contact is probably
induced by a pair of complementary hydrogen-bonding interac-
tions between C7–H7···O2 (1 – x, 3 – y, 2 – z; H7···O2 2.616 Å; Є
C7–H7···O2 123.6°), which brings a pair of two symmetry-related
O2 atoms into close proximity.
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CCDC-1004474 (for 1), -1004475 (for 2), -1004476 (for 3), and
-1004477 (for 4) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
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Received: October 8, 2014
Published Online: ᭿
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Metallacycles
X. Wu, W. Zhang, X. Zhang, N. Ding,*
T. S. A. Hor* .................................... 1–7
Pyridine–carboxylate-bridged
dinuclear
CuI complexes capped by 1,1Ј-bis(diphen-
ylphosphanyl)ferrocene (dppf) exhibit
macrocycles with diagonal distances of
6.586, 9.159, and 10.006 Å. Such cavity
sizes are formed by the introduction of
CH=CH or phenyl units into the original
pyridine-3-carboxylic acid (3-PyCOOH)
spacer.
Pyrididine–Carboxylate
Ligands
as
Double-Bridge Spacers in CuI Metall-
acycles
Keywords: Metallacycles / N,O ligands /
Crystal engineering / Macrocycles / Copper
Eur. J. Inorg. Chem. 0000, 0–0
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