New tetracopper(II) cubane cores driven by a diamino alcohol: Self-assembly synthesis, structural and topological features, and magnetic and catalytic oxidation properties

Article abstract of DOI:10.1021/acs.inorgchem.5b00048

Two new coordination compounds with tetracopper(II) cores, namely, a 1D coordination polymer, [Cu₄(μ₄-H₂edte)(μ₅-H₂edte)(sal)₂]_n·10nH₂O (1), and a discrete 0D tetramer, [Cu₄(μ₄-Hedte)₂(Hpmal)₂(H₂O)]·7.5H₂O (2), were easily self-assembled from aqueous solutions of copper(II) nitrate, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (H₄edte), salicylic acid (H₂sal), or phenylmalonic acid (H₂pma). The obtained compounds were characterized by IR and electron paramagnetic resonance spectroscopy, thermogravimetric and elemental analysis, and single-crystal X-ray diffraction. In addition to different dimensionalities, their structures reveal distinct single-open [Cu₄(μ₂-O)(μ₃-O)₃] (in 1) or double-open [Cu₄(μ₂-O)₂(μ₃-O)₂] (in 2) cubane cores with 3M4-1 topology. In crystal structures, numerous crystallization water molecules are arranged into the intricate infinite 1D {(H₂O)₁₈}_n water tapes (in 1) or discrete (H₂O)₉ clusters (in 2) that participate in multiple hydrogen-bonding interactions with the metal-organic hosts, thus extending the overall structures into very complex 3D supramolecular networks. After simplification, their topological analysis revealed the binodal 6,10- or 6,8-connected underlying 3D nets with unique or rare 6,8T2 topology in 1 and 2, respectively. The magnetic properties of 1 and 2 were investigated in the 1.8-300 K temperature range, indicating overall antiferromagnetic interactions between the adjacent Cu^II ions within the [Cu₄O₄] cores. The obtained compounds also act as bioinspired precatalysts for mild homogeneous oxidation, by aqueous hydrogen peroxide at 50 °C in an acidic MeCN/H₂O medium, of various cyclic and linear C₅-C₈ alkanes to the corresponding alcohols and ketones. Overall product yields of up to 21% (based on alkane) were achieved, and the effects of various reaction parameters were studied.

Full text of DOI:10.1021/acs.inorgchem.5b00048

Article
pubs.acs.org/IC
New Tetracopper(II) Cubane Cores Driven by a Diamino Alcohol: Self-
assembly Synthesis, Structural and Topological Features, and
Magnetic and Catalytic Oxidation Properties
†
†
†
‡
,†
̂ ́
Sara S. P. Dias, Marina V. Kirillova, Vania Andre, Julia Kłak, and Alexander M. Kirillov*
†
Centro de Química Estrutural, Complexo I, Instituto Superior Tec
́
nico, Universidade de Lisboa, Avenida Rovisco Pais, 1049-001
Lisbon, Portugal
‡
Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wroclaw, Poland
S Supporting Information
*
ABSTRACT: Two new coordination compounds with tetracopper(II) cores,
namely, a 1D coordination polymer, [Cu (μ -H edte)(μ -H edte)(sal) ] ·
4
4
2
5
2
2 n
1
7
0nH O (1), and a discrete 0D tetramer, [Cu (μ -Hedte) (Hpmal) (H O)]·
2 4 4 2 2 2
.5H O (2), were easily self-assembled from aqueous solutions of copper(II)
2
nitrate, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (H edte), salicylic
4
acid (H sal), or phenylmalonic acid (H pma). The obtained compounds were
2
2
characterized by IR and electron paramagnetic resonance spectroscopy,
thermogravimetric and elemental analysis, and single-crystal X-ray diffraction.
In addition to different dimensionalities, their structures reveal distinct single-
open [Cu (μ -O)(μ -O) ] (in 1) or double-open [Cu (μ -O) (μ -O) ] (in 2)
4
2
3
3
4
2
2
3
2
cubane cores with 3M4-1 topology. In crystal structures, numerous
crystallization water molecules are arranged into the intricate infinite 1D
{
(H O) } water tapes (in 1) or discrete (H O) clusters (in 2) that
2 18 n 2 9
participate in multiple hydrogen-bonding interactions with the metal−organic
hosts, thus extending the overall structures into very complex 3D supramolecular networks. After simplification, their topological
analysis revealed the binodal 6,10- or 6,8-connected underlying 3D nets with unique or rare 6,8T2 topology in 1 and 2,
respectively. The magnetic properties of 1 and 2 were investigated in the 1.8−300 K temperature range, indicating overall
II
antiferromagnetic interactions between the adjacent Cu ions within the [Cu O ] cores. The obtained compounds also act as
4
4
bioinspired precatalysts for mild homogeneous oxidation, by aqueous hydrogen peroxide at 50 °C in an acidic MeCN/H O
2
medium, of various cyclic and linear C −C alkanes to the corresponding alcohols and ketones. Overall product yields of up to
5
8
21% (based on alkane) were achieved, and the effects of various reaction parameters were studied.
6
7
INTRODUCTION
Mn and Fe clusters driven by H edte have been reported, the
4
■
coordination chemistry of H edte toward Cu is still limited to
4
Amino alcohols are recognized N,O building blocks for the
design of coordination compounds that include a diversity of
discrete multinuclear metal complexes, clusters, and molecular
wheels, as well as various coordination polymers and metal−
5a,8
single mono- or dicopper(II) complexes, 1as attested by a
search of the Cambridge Structural Database.
Bearing these points in mind and following our general
interest in the exploration of various amino alcohol building
blocks for the generation, by a simple aqueous medium self-
assembly method, of diverse functional multicopper(II)
complexes and coordination polymers,
objectives of the current work consisted of (i) opening up
1
−3
organic frameworks.
Owing to their different functional
properties, these amino alcohol driven compounds have found
notable applications in areas ranging from molecular magnetism
and catalysis to supramolecular chemistry and crystal engineer-
3
,5
the principal
3
−7
ing.
the application of H edte for the preparation of new discrete
Among the variety of simple amino alcohols (e.g., N,N-
dimethylethanolamine, diethanolamine, and triethanolamine),
4
and polymeric multicopper(II) derivatives, (ii) identifying their
structural and topological features, and (iii) studying their
magnetic and catalytic behavior.
Hence, we report herein the aqueous medium self-assembly
generation, full characterization, crystal structures, topological
analysis, and magnetic and oxidation catalytic properties of two
N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (H edte)
4
represents an interesting multidentate diamine with four ethyl
alcohol groups. However, in spite of its low cost and
commercial availability, water solubility and stability, potential
coordination flexibility and versatility, the application of H edte
4
toward the design of multinuclear metal complexes and, in
particular, coordination polymers has remained underex-
Received: January 7, 2015
1
,6,7
plored.
Although some notable examples of high-nuclearity
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b00048
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Inorganic Chemistry
Article
novel H edte-driven tetracopper(II) compounds, namely, a 1D
bonding interactions, respectively. Crystal data and details of data
collection for 1 and 2 are reported in Table 1.
4
coordination polymer, [Cu (μ -H edte)(μ -H edte)(sal) ] ·
4
4
2
5
2
2 n
1
0nH O (1), and a discrete 0D tetramer, [Cu (μ -
2
4
4
Hedte) (Hpmal) (H O)]·7.5H O (2). Apart from representing
the first multicopper clusters derived from H edte, both
Table 1. Crystal Data and Structure Refinement Details for
Compounds 1 and 2
2
2
2
2
1
4
compounds also display distinct single- or double-open
1
2
[
Cu O ] cubane cores, act as metal−organic matrixes to store
4
4
formula
fw
Cu C H N O
Cu C H N O
4
34 52
4
23
4
38 56
4
23.5
intricate water clusters, reveal the formation of complex 3D
supramolecular networks with undocumented or rare top-
ologies, and function as promising bioinspired precatalysts for
the mild oxidation of different cyclic and linear C −C alkanes
1139
1199
cryst form, color
cryst size (mm)
cryst syst
space group
a, Å
plate, green
plate, blue
0.2 × 0.1 × 0.02
orthorhombic
Pbca
0.2 × 0.15 × 0.04
5
8
triclinic
to produce the corresponding alcohols and ketones.
P1
̅
17.7705(9)
22.3871(12)
23.5210(13)
90
12.838(6)
13.677(4)
15.199(3)
85.959(5)
83.915(6)
69.114(4)
2
EXPERIMENTAL SECTION
b, Å
■
2
General Synthetic Procedure and Characterization for 1 and
. To an aqueous 0.1 M solution of Cu(NO ) ·3H O (10 mL, 1
c, Å
3
2
2
α, deg
mmol) was added an aqueous 1 M solution of N,N,N′,N′-tetrakis(2-
β, deg
90
hydroxyethyl)ethylenediamine (H edte; 0.5 mL, 0.5 mmol) with
4
γ, deg
90
continuous stirring at room temperature. Then, salicylic acid (H sal;
2
Z
8
1
38 mg, 1 mmol) for 1 or phenylmalonic acid (H pmal; 90 mg, 0.5
2
V, Å
9357.4(9)
150(2)
2477.8(15)
293(2)
mmol) for 2 and an aqueous 1 M solution of NaOH (3 mL, 3 mmol;
up to pH ∼8) were added to the reaction mixture. The resulting
solution was stirred for 1 day and then filtered off. The filtrate was left
to evaporate in a beaker at room temperature. Green crystals
T, K
−
3
D , g cm
1.617
1.607
c
μ(Mo Kα), mm−
θ range (deg)
reflns collected
indep reflns
Rint
1
1.878
1.779
2.27−26.37
63901
2.26−26.35
42251
(
including those suitable for single-crystal X-ray diffraction) were
formed in 1 month, then collected, and dried in air to furnish
compounds 1 and 2 in ∼50% yield, based on copper(II) nitrate.
9487
10015
[
Cu (μ -H edte)(μ -H edte)(sal) ] ·10nH O (1). Anal. Calcd for 1 −
0.1308
0.0669
4
4
2
5
2
2 n
2
a
b
3
H O (Cu C H N O ; MW 1121.1): C, 36.43; H, 5.93; N, 5.00.
R1, wR2 [I ≥ 2σ(I)]
0.0943, 0.1671
0.0558, 0.1511
2
4
34 66
4
21
−
1
Found: C, 36.11; H, 5.67; N, 4.87. IR (KBr, cm ): ν(OH) 3362 (s
GOF on F2
1.105
1.010
br), ν(CH) 2864 (s br), ν (COO) 1602 (s), 1566 (s), and 1528 (s),
a
b
2
2 2
as
R1 = ∑||F | − |F ||/∑|F |. wR2 = [∑[w(Fo − F ) ]/
o
c
o
c
ν (COO) 1453 (s) and 1377 (s), 1320 (m), ν(C−X) (X = C, N, O)
2
2
1/2
s
∑
[w(F ) ]] .
o
1
7
253 (s), 1142 (m), and 1066 (s br), 887 (m br), 834 (w), 768 (m),
12 (w), 639 (w), 585 (w), 494 (w). ESI-MS(±) (MeCN/H O):
2
Magnetic Studies. The magnetization of powdered samples 1 and
selected fragments with relative abundance >5%. MS(−): m/z 994
−
2 was measured over the 1.8−300 K temperature range using a
Quantum Design SQUID-based MPMSXL-5-type magnetometer. The
superconducting magnet was generally operated at a field strength
ranging from 0 to 5 T. Sample measurements were made at a magnetic
field of 0.5 T. The SQUID magnetometer was calibrated with the
palladium rod sample. Corrections are based on subtraction of the
sample-holder signal, and the χD contribution was estimated from
(
−
(
100%) [Cu (H edte) (sal) − H] , 949 (15%) [Cu (H edte) (sal)
4
2
2
2
4
2
2
2
−
+
CH CH OH] . MS(+): m/z 858 (5%) [Cu (Hedte) (Hsal)] , 796
15%) [Cu (H edte) (Hsal)] , 641 [Cu (Hedte)(sal)(H O)] , 597
2
2
4
2
+
+
3
2
2
4
2
+
(
100%) [Cu (Hedte)(sal)(H O) − CH CH OH] .
4
2
2
2
[
Cu (μ -Hedte) (Hpmal) (H O)]·7.5H O (2). Anal. Calcd for 2
4 4 2 2 2 2
(
Cu C H N O24.5, MW 1232.2): C, 37.04; H, 5.97; N, 4.55.
4 38 73 4
Found: C, 37.03; H, 5.50; N, 4.54. IR (KBr): ν(OH) 3419 (s br),
ν(CH) 2856 (m), ν (COO) 1624 (s br) and 1597 (s), ν (COO)
15
Pascal’s constants.
as
s
Catalytic Studies. The alkane oxidations were carried out in an air
atmosphere in thermostated Pyrex reactors equipped with a
condenser, under vigorous stirring at 50 °C, and using acetonitrile
MeCN) as the solvent (up to 5.0 mL total volume). In a typical
experiment, a solid precatalyst, 1 or 2 (0.01 mmol), and gas
1
409 (m) and 1395 (m), ν(C−X) (X = C, N, O) 1274 (w), 1059 (m),
and 1034 (w), 906 (w), 730 (m), 637 (w), 504 (w).
X-ray Crystallography. Crystals of 1 and 2 suitable for X-ray
diffraction study were mounted with Fomblin in a cryoloop. Data were
collected on a Bruker AXS-Kappa APEX II diffractometer with
graphite-monochromated radiation (Mo Kα, λ = 0.17073 Å). The X-
ray generator was operated at 50 kV and 30 mA, and the X-ray data
(
chromatography (GC) internal standard (MeNO , 50 μL) were
2
introduced into a MeCN solution, followed by the addition of an acid
promoter (0.01−0.20 mmol) used as a stock solution in MeCN. The
alkane substrate (2 mmol) was then introduced, and the reaction
started upon the addition of hydrogen peroxide (H O ; 50% in water,
0 mmol) in one portion. The reactions were monitored by
withdrawing small aliquots after different periods of time, which
9
collection was monitored by the APEX2 program. All data were
corrected for Lorentzian, polarization, and absorption effects with the
2
2
9
10
11
SAINT and SADABS programs. SIR97 and SHELXS-97 were used
1
1
1
for structure solution, and SHELXL-97 was applied for full-matrix
least-squares refinement on F . These three programs are included in
2
1
6
were treated with PPh (following a method developed by Shul’pin)
for reduction of the remaining H O and alkyl hydroperoxides that are
3
12
the package of programs WINGX, version 1.80.05. Non-H atoms
were refined anisotropically. A full-matrix least-squares refinement was
used for the non-H atoms with anisotropic thermal parameters. All of
the H atoms were inserted in idealized positions and allowed to refine
in the parent C or O atom, except for the hydroxide H atoms in the
amino alcohol ligands, which were located from the electron density
map. It was not possible to locate the water H atoms. In both
structures, there are disordered water molecules (O9w, O10w, O11w,
and O12w in compound 1 and O8w in compound 2) with 0.5
occupancy factors; in the specific case of compound 2, O8w resides
near special positions, and thus both positions are nearby. TOPOS
2
2
typically formed as major primary products in alkane oxidation. The
samples were analyzed by GC using nitromethane as an internal
standard. Attribution of the peaks was made by a comparison with the
chromatograms of authentic samples. Chromatographic analyses were
run on an Agilent Technologies 7820A series gas chromatograph
(helium as the carrier gas) equipped with a flame ionization detector
and a BP20/SGE (30 m × 0.22 mm × 0.25 μm) capillary column.
Blank tests confirmed that alkane oxidation does not proceed in the
absence of a copper precatalyst. Given a possibility of alkane oxidation
1
7
by Cu ions in the presence of trifluoroacetic acid (TFA), control
tests were also performed for the oxidation of cyclohexane by H O
1
3
14
4
.0 and PLATON were used for topological analysis and hydrogen-
2
2
B
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Inorganic Chemistry
Article
1
8
with copper(II) nitrate as a precatalyst (reaction conditions were those
of Table 2), either in the absence or in the presence of a TFA
coordination chemistry, as well as to find out whether the
presence of two aliphatic carboxylic groups in addition to a
phenyl ring can affect the structure of the resulting product.
However, the self-assembly of 1 and 2 appeared to be primarily
Table 2. Mild Oxidation of Different C −C Alkanes by the
5
8
a
1
/TFA/H O and 2/TFA/H O Systems
guided by H edte as a main building block, with both ancillary
2
2
2
2
4
acids acting as terminal ligands. The obtained products were
isolated as air-stable microcrystalline materials and charac-
terized by IR and EPR spectroscopy, thermogravimetric and
elemental analysis, and single-crystal X-ray diffraction (for
discussion of the spectral and thermogravimetric data, see the
Supporting Information, SI).
b
total yield of oxidation products, %
alkane (R−H)
1/TFA/H O
2/TFA/H O2
2
2
2
Structural and Topological Description. Compound 1 is
a 1D coordination polymer, the structure of which is composed
of the repeating tetracopper(II) [Cu (μ -H edte)(μ -H edte)-
cyclopentane
cyclohexane
cycloheptane
cyclooctane
n-pentane
n-hexane
7.2
13.5
21.2
16.0
3.1
8.9
16.2
19.8
19.3
2.8
4
4
2
5
2
(
sal) ] units (Figure 1a) and 10 crystallization water molecules.
2
The adjacent Cu blocks reveal a single-open [Cu (μ -O)(μ -
4
4
2
3
O) ] cubane core and are interconnected via one of the
3
4.2
6.1
hydroxyethyl arms of the μ -H edte ligand, forming an infinite
5
2
n-heptane
10.2
4.4
9.4
metal−organic chain (Figure 1b). The tetracopper(II) blocks
consist of four symmetry-nonequivalent Cu atoms, two
chelating salicylate(2−) ligands, one μ -H edte(2−) moiety,
n-octane
4.5
a
Reaction conditions: precatalyst 1 or 2 (0.01 mmol), TFA (0.05
mmol), alkane (1.0 mmol), H O (50% aq, 5.0 mmol), MeCN (up to
mL total volume), 50 °C, 3 h. Based on an alkane substrate,
calculated from GC analysis after treatment of the reaction mixture
with PPh ; total yields [(moles of products per mole of substrate) ×
00%] correspond to the sum of yields of cyclic alcohols and ketones
in the case of cycloalkane oxidation or to the sum of yields of various
isomeric alcohols and ketones (aldehydes) in the case of n-alkane
oxidation; for yields of each product, see Table S1 in the SI.
4
2
2
2
b
and one μ -H edte(2−) moiety. The five-coordinate Cu1 atom
5
2
5
shows a distorted square-pyramidal {CuO } environment (τ =
5
5
0
.18 in 1; τ = 0 for an idealized square-pyramidal
5
19a,b
3
geometry),
filled by the salicylate O1 and O2 atoms and
1
the amino alcohol O7 and O14 atoms [Cu1−O1 1.927(6) Å;
Cu1−O2 1.890(6) Å; Cu1−O7 1.956(5) Å] in equatorial
i
positions, whereas an axial site is taken by the O8 atom [Cu1−
i
O8 2.432(6) Å]. The five-coordinate Cu2 center is very similar
promoter, resulting in 3.0 or 3.1% total product yield, respectively.
These yields are significantly inferior to those achieved in the 1/TFA/
H O (13.5%) or 2/TFA/H O (16.2%) systems (Table 2), thus
to Cu1 in geometrical terms, with its square-pyramidal {CuO5}
environment (τ = 0.15) occupied by two sal and three H edte
5
2
2
2
2
2
O atoms; the Cu2−O distances are in the 1.902(6)−2.404(6)
Å range. The six-coordinate Cu3 atom exhibits a distorted
octahedral {CuN O } geometry, filled by the N1, N2, O9, and
confirming the influence of ligands and their structural arrangement in
the precatalysts 1 and 2 on the observed catalytic behavior.
2
4
O13 atoms in the equatorial sites [Cu3−N1 2.099(6) Å; Cu3−
N2 1.990(8) Å; Cu3−O10 1.943(6) Å; Cu3−O13 1.941(6) Å],
whereas the apical positions are taken by the remaining O7 and
O9 atoms of the μ -H edte moiety [Cu3−O7 2.395(5) Å;
RESULTS AND DISCUSSION
Synthesis. To probe the use of H edte as a multidentate
■
4
amino alcohol building block for the synthesis of
multicopper(II) coordination compounds, we applied an
aqueous medium self-assembly method. Thus, a simple
combination, in a water solution at ∼25 °C in air, of copper(II)
nitrate with H edte as a main building block, salicylic (H sal) or
4
2
Cu3−O9 2.648(8) Å]. The six-coordinate Cu4 atom is
essentially similar to Cu3, revealing even a more distorted
octahedral {CuN O } environment filled by the equatorial N3,
2
4
4
2
N4, O13, and O14 atoms [Cu4−N3 2.009(8) Å; Cu4−N4
phenylmalonic (H pmal) acid as an ancillary ligand (Scheme
2
2
.071(7) Å; Cu4−O13 1.901(6) Å; Cu4−O14 1.988(6) Å] and
1
), and sodium hydroxide as a pH regulator resulted in the self-
the axial O10 and O12 atoms [Cu4−O10 2.900(6) Å; Cu4−
O12 2.428(8) Å] of the μ -H edte ligand, which possesses one
5
2
Scheme 1. Structural Formulas of Organic Building Blocks
hydroxyethyl arm connected to the Cu1 atom of an adjacent
tetracopper(II) block. Although some of the Cu−O bonds [i.e.,
Cu3−O9 2.648(8) Å and Cu4−O10 2.900(6) Å] are rather
long, these are still inferior to the sum of the van der Waals
19c
radii of the Cu and O atoms (∼2.92 Å). The four Cu centers
are mutually interconnected via three μ -O and one μ -O atoms
3
2
of two H edte moieties to generate a distorted single-open
2
[
Cu (μ -O)(μ -O) ] cubane core (Scheme 2b,e) with the Cu···
4 2 3 3
Cu separations in the 3.129(2)−3.624(1) Å range (avg 3.329
13a,b
Å). From the topological viewpoint,
both regular and open
assembly generation of two new coordination compounds
bearing tetracopper(II) cubane cores, namely, a 1D coordina-
tion polymer, [Cu (μ -H edte)(μ -H edte)(sal) ] ·10nH O
[Cu O ] cubane cores (Scheme 2) can be classified as uninodal
4
4
3-connected motifs with 3M4-1 topology and a point symbol of
3
(3 ). Scheme 2d shows a graph of the Cu skeleton obtained
4
4
2
5
2
2 n
2
4
(
(
1), and a discrete 0D tetramer, [Cu (μ -Hedte)
×
after transforming the μ-O atoms in the [Cu (μ -O)(μ -O) ]
4
4
2
4
2
3
3
Hpmal) (H O)]·7.5H O (2). The choice of H sal was
core to Cu−Cu edges, by applying a method developed for the
2
2
2
2
13a,b,19,20
governed by its recognized application as a simple ancillary
topological analysis of coordination clusters.
1
ligand to stabilize multicopper(II) cores, whereas H pmal was
A notable feature of 1 consists of the presence of numerous
2
selected because of its little explored use in copper(II)
crystallization water molecules that are arranged into intricate
C
DOI: 10.1021/acs.inorgchem.5b00048
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Inorganic Chemistry
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Scheme 2. Schematic Representation of (a) Regular, (b)
Single-Open, and (c) Double-Open [Cu O ] Cubane Cores
4
4
and (d) Their Simplified Topological Graph Showing a
Uninodal 3-Connected Motif with 3M4-1 Topology and a
3
Point Symbol of (3 ) and Ball-and-Stick Representation of
Distorted (e) Single-Open [Cu (μ -O)(μ -O) ] and (f)
4
2
3
3
Double-Open [Cu (μ -O) (μ -O) ] Cubane Cores in 1 and
4
2
2
3
2
a
2, Respectively
a
Color code: Cu centers, green balls; O atoms, red balls.
resulting binodal 6,10-connected net (Figure 1c) has a point
5
7
2
8
12 20
4
symbol of (3 .4 .5 .6) (3 .4 .5 .6 .7) and is topologically
2
1,13,22a
unique, as confirmed by a search of various databases.
The discrete 0D structure of 2 bears a neutral tetracopper(II)
Cu (μ -Hedte) (Hpmal) (H O)] unit (Figure 2a) and 7.5
[
4
4
2
2
2
Figure 1. Structural fragments of 1 showing (a) a tetracopper(II)
crystallization water molecules. Although this Cu4 unit
resembles that of 1, there are a few differences, which consist
of (i) the compound’s dimensionality (0D in 2 vs 1D in 1), (ii)
[
Cu (μ -H edte)(μ -H edte)(sal) ] unit with an atom numbering
4 4 2 5 2 2
scheme, (b) a 1D metal−organic chain with polyhedral representation
of the coordination environments around Cu atoms, and (c) a
topological representation of the underlying binodal 6,10-connected
the presence of two monoprotonated μ -Hedte ligands in 2
4
versus μ - and μ -H edte in 1, and (iii) the existence of three
4
5
2
3
D supramolecular network. Further details: (a and b) H atoms
five-coordinate (Cu1, Cu3, and Cu4) and one six-coordinate
Cu2) Cu atoms in 2 versus a pair of five- and six-coordinate
omitted for clarity [Cu, green; O, red; N, blue; C, gray]; (c) view
(
along the a axis, centroids of 6-connected [Cu (H edte) (sal) ] (green
4
2
2
2
Cu centers in 1. These differences lead to the formation of a
slightly distinct double-open cubane [Cu (μ -O) (μ -O) ] core
balls) and 10-connected (H O) (gray) nodes. Selected distances (Å):
2
18
i
Cu1−O1 1.927(6), Cu1−O2 1.890(6), Cu1−O7 1.956(5), Cu1−O8
4
2
2
3
2
in 2 (Scheme 2c,f) with the Cu···Cu separations ranging from
3.102(1) to 3.548(2) Å (avg 3.309 Å). This core also has 3M4-
1 topology (Scheme 2d). In 2, the Cu1 and Cu4 centers show
2
.432(6), Cu1−O14 1.970(6), Cu2−O4 1.902(6), Cu2−O5 1.908(7),
Cu2−O7 1.975(6), Cu2−O10 1.921(5), Cu2−O14 2.404(6), Cu3−
O7 2.395(5), Cu3−O9 2.648(8), Cu3−O10 1.943(6), Cu3−O13
1
.941(6), Cu3−N1 2.099(6), Cu3−N2 1.990(8), Cu4−O10 2.900(6),
resembling distorted square-pyramidal {CuO } environments
5
19a,b
Cu4−O12 2.428(8), Cu4−O13 1.901(6), Cu4−O14 1.988(6), Cu4−
(
τ5 = 0.16 and 0.12, respectively),
which are filled by two O
N3 2.009(8), Cu4−N4 2.071(7), Cu1···Cu2 3.129(2), Cu1···Cu3
atoms of the chelating monoprotonated phenylmalonate(−)
3
3
.624(1), Cu1···Cu4 3.453(1), Cu2···Cu3 3.156(2), Cu2···Cu4
1 3
ligands [Cu1−O1 1.952(3) Å; Cu1−O3 1.937(3) Å; Cu4−O7
.387(2), Cu3···Cu4 3.322(2). Symmetry code: (i) x + / , y, −z + / .
2
2
1
.931(3) Å; Cu4−O8 1.923(3) Å] and the remaining O atoms
coming from the Hedte moieties [Cu1−O4 1.966(3) Å; Cu1−
O5 1.924(3) Å; Cu1−O12 2.303(3) Å; Cu4−O4 1.942(3) Å;
Cu4−O12 1.946(3) Å] as well as a coordinated water molecule
[only at the Cu4 center, Cu4−O7w 2.498(5) Å]. In contrast,
the Cu3 atom features a {CuN O } geometry that is better
infinite 1D {(H O) } water tapes (Figure S3a in the SI), built
2
18 n
from cyclic (H O) (n = 8, 3) associates. Given the presence of
2
n
some disorder, these water tapes can be roughly classified
within the T8 general type according to the systematization
2
3
21
introduced by Infantes and Motherwell. These water tapes
participate in multiple intermolecular hydrogen-bonding
interactions with the host 1D metal−organic chains, thus
extending the structure into a very complex 3D supramolecular
network (Figure S4a in the SI). To gain further insight into this
network, we have performed its topological analysis by
considered as a highly distorted trigonal-bipyramidal (τ = 0.65
5
19a,b
in 2; τ = 1 for idealized trigonal-bipyramidal geometry),
5
which is filled by the equatorial N4, O6, and O12 atoms and
the axial N3 and O11 atoms of Hedte moieties [Cu3−N4
2.021(4) Å; Cu3−O6 1.917(3) Å; Cu3−O12 2.012(3) Å;
Cu3−N3 2.098(4) Å; Cu3−O11 2.292(3) Å]. The six-
coordinate Cu2 atom exhibits a distorted octahedral
{CuN O } environment filled by the basal N1, N2, O5, and
13
following the concept of a simplified underlying net. The
structure of 1 underwent a significant simplification, namely
involving the contraction of the [Cu (H edte) (sal) ] units and
2
4
O6 atoms and the apical O4 and O14 atoms of Hedte ligands
[Cu2−N1 2.088(4) Å; Cu2−N2 1.990(5) Å; Cu2−O5
1.932(3) Å; Cu2−O6 1.936(3) Å; Cu2−O4 2.439(3) Å;
4
2
2
2
the (H O) fragments of water tapes to the centroids that
2
18
correspond to the 6- and 10-connected nodes, respectively. The
D
DOI: 10.1021/acs.inorgchem.5b00048
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
O4w and O6w) molecules, and tetracopper(II) units leads
to the generation of an intricate 3D supramolecular network
13
(
Figure S4b in the SI). For topological analysis, this network
has been simplified by reducing the 8-connected
Cu (Hedte) (Hpmal) (H O)] and 6-connected (H O) moi-
[
4
2
2
2
2
9
eties to their centroids and eliminating discrete water
molecules. The resulting binodal 6,8-connected net (Figure
1
3,22
2
(
b) features 6,8T2 topology
with a point symbol of
2
12 10
4
2 6 6
3 .4 .5 .6 )(3 .4 .5 .6) . This topological type is rare and was
only identified in one compound.
2
22b
Magnetic Studies. The magnetic properties of 1 and 2
were investigated over the temperature range of 1.8−300 K.
Plots of the magnetic susceptibility χ and χ T product versus
m
m
II
T (χ is the molar magnetic susceptibility for four Cu ions)
m
are given in Figures S5 in the SI and 3a, respectively. At room
Figure 2. Structural fragments of 2 showing (a) a tetracopper(II)
[
Cu (μ -Hedte) (Hpmal) (H O)] unit with atom numbering scheme
4 4 2 2 2
and (b) a topological representation of the underlying binodal 6,8-
connected 3D supramolecular network with 6,8T2 topology. Further
details: (a) H atoms omitted for clarity [Cu, green; O, red; N, blue; C,
gray]; (b) view along the b axis, centroids of 8-connected
[
(
Cu (Hedte) (Hpmal) (H O)] (green balls) and 6-connected
H O)9 (gray) nodes. Selected distances (Å): Cu1−O1 1.952(3),
2
4 2 2 2
Cu1−O3 1.937(3), Cu1−O4 1.966(3), Cu1−O5 1.924(3), Cu1−O12
.303(3), Cu2−N1 2.088(4), Cu2−N2 1.990(5), Cu2−O4 2.439(3),
Cu2−O5 1.932(3), Cu2−O6 1.936(3), Cu2−O14 2.576(8), Cu3−N3
2
2
.098(4), Cu3−N4 2.021(4), Cu3−O6 1.917(3), Cu3−O11 2.292(3),
Figure 3. (a) Temperature dependence of experimental χ T (χ per 4
m
m
Cu3−O12 2.012(3), Cu4−O4 1.942(3), Cu4−O7 1.931(3), Cu4−
II
Cu atoms) for 1 and 2. The solid lines (for 1 and 2) are the
calculated curves derived from eq 1. (b) Schematic representation of
the exchange coupling pattern in the model 2 + 4 [Cu O ] cubane
O7w 2.498(5), Cu4−O8 1.923(3), Cu4−O12 1.946(3), Cu1···Cu2
3
3
.159(1), Cu1···Cu3 3.423(1), Cu1···Cu4 3.102(1), Cu2···Cu3
.352(1), Cu2···Cu4 3.548(2), Cu3···Cu4 3.269(1).
4
4
core.
Cu2−O14 2.576(8) Å]. In 2, most of the bonding parameters
are comparable to those found in 1 and other Cu compounds
5
a,8
3
−1
derived from H edte.
Because the reported Cu-edte
temperature, χ T is 1.52 and 1.59 cm K mol for 1 and 2,
m
4
derivatives are limited to a few mono- and dinuclear
respectively; these values are consistent with the presence of
5
a,8
II
2 2
complexes,
both compounds 1 and 2 not only represent
four uncoupled Cu ions [χ
m
T = 4(Nβ g /3k)S(S + 1) = 1.5]
3
−1
1
the first examples of polynuclear copper clusters derived from
H edte but also bear the first [M O ] cubane cores (Scheme 2)
cm K mol , assuming g = 2.1 and S = /
2
, where N, β, g, k, S,
23
and T have their usual meaning]. Upon cooling, χ T
4
4
4
m
encountered in other transition-metal H edte-driven com-
pounds. Hence, the present work opens up the application
continuously decreases, reaching almost zero at 1.8 K in 1.
These features are characteristic of an overall antiferromagnetic
coupling in 1, which leads to a low-lying spin state (S = 0).
Additionally, the maximum of the magnetic susceptibility is
4
1
of H edte toward the design of copper clusters.
4
Furthermore, several crystallization water molecules in 2 are
assembled into discrete (H O) clusters that comprise a linear
observed in the χ
SI). The increase of χ
presence of a small amount of paramagnetic impurities (S =
m
versus T plot for 1 at 45 K (Figure S5 in the
2
9
(
H O) motif with two branched water groups (Figure S3b in
m
at low temperature indicates the
2
7
21
the SI). These clusters can be classified within the D7 type.
1
An intense pattern of intermolecular hydrogen-bonding
interactions involving such water clusters, discrete water
/ ). The absence of a maximum in the χ curve of 2 may
2 m
indicate that the possible coupling is weaker in this compound.
E
DOI: 10.1021/acs.inorgchem.5b00048
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Inorganic Chemistry
Article
Figure 4. Oxidation of cyclohexane to cyclohexanol and cyclohexanone by H O in the presence of precatalyst 1. (a) Evolution of the total product
2
2
yield with time in the absence and in the presence of different acid promoters (TFA, HNO , H SO , or HCl; 0.1 mmol). (b) Effect of the TFA
3
2
4
amount on the evolution of the total product yield with time (1/TFA molar ratios: 1:0, 1:1, 1:2, 1:5, 1:10, and 1:20). General conditions: C H (2
6
12
mmol), H O (50% aqueous, 10 mmol), 1 (0.01 mmol), TFA (0−0.2 mmol), 50 °C, MeCN (up to 5 mL). For similar data with precatalyst 2, see
2
2
Figure S8 in the SI.
To confirm the nature of the ground state of 1 and 2, we
have investigated variation of the magnetization (M) with
respect to the field (H) at 2 K. The results are shown in Figure
antiferromagnetic coupling is observed for large Cu−O−Cu
bond angles and long Cu···Cu separations, whereas the
ferromagnetic interaction is favored for small Cu−O−Cu
bond angles (<97.5°), which usually imply shorter Cu···Cu
distances. Although the Cu−O−Cu angles and Cu···Cu
distances are the most crucial geometrical parameters, the
coupling constants can also be modulated by other structural
S6 in the SI, where the molar magnetization M (per Cu entity)
4
is expressed in μ units. The magnetization curves for 1 and 2
B
were reproduced by the equation M = gβSNB (x) (S = 4S ),
s
Cu
23
where B (x) is the Brillouin function and x = gβH/kT. The
s
experimental values for 1 and 2 are much lower than those
features. The values of J obtained for 1 and 2 are roughly in
1
calculated using the Brillouin function for four noninteracting
agreement with the earlier reported figures for this parameter in
II
24,26−28
Cu ions. This feature agrees with the global antiferromagnetic
alkoxo-bridged [Cu O ] cubanes.
The presence of
4
4
II
coupling within the four Cu ions in 1 and 2.
antiferromagnetic interactions in 1 and 2 is certainly attributed
to the relatively large Cu−O−Cu angles (mean value above
100°) and rather long Cu···Cu separations (avg 3.329 or 3.309
Å for 1 or 2, respectively). However, the calculated J2
parameters for 1 and 2 have negative values in contrast to
the weakly ferromagnetic interactions generally found in the
II
In compounds 1 and 2, four Cu ions (Cu , Cu , Cu , and
a
b
c
Cu ) occupy alternating cubane vertices and have six Cu···Cu
d
exchange interactions. Considering the presence of two short
(
3.102−3.159 Å) and four rather long (3.269−3.624 Å) Cu···
Cu separations in 1 and 2, their [Cu O ] cubane cores can be
classified within the 2 + 4 type and analyzed using the spin
Hamiltonian given in eq 1:
4
4
24
27
literature. It was proposed that these interactions are
23
24c
practically independent of the geometrical parameters.
In
general, the magnetic behavior of 1 and 2 is in agreement with
the majority of alkoxo-bridged tetranuclear copper(II) com-
pounds. Although 1 and 2 show rather similar magnetic
features, some distinction in their behavior may be caused by
the 1D chain structure of 1 and the different coordination
geometries of Cu atoms in these compounds.
̂
̂
̂
̂
̂
̂
̂
̂
̂
̂
̂
̂
H = −J (S S + S S ) − J (S S + S S + S S + S S )
1
a
b
c d
2
a c
a d
b c
b d
(
1)
where J and J are the intra- and interdinuclear exchange
coupling constants between the local spins within the [Cu O ]
1
2
4
4
cubane core (Figure 3b). The molar magnetic susceptibility for
and 2 is given in the SI. A least-squares fitting of the
experimental data leads to the following values: J = −53.3(3)
Mild Catalytic Oxidation of Alkanes. Following our
1
interest in the oxidative functionalization of alkanes under mild
1
3
,5b−e,29
−
1
−1
conditions catalyzed by multicopper(II) complexes,
probed both compounds 1 and 2 as precatalysts for the
oxidation by H O of various cyclic and linear C −C alkanes to
we
cm , J = −23.7(5) cm , g = 2.09(1), and ρ = 5.4% (R = 2.5 ×
2
−4
−1
−1
1
2
0 ) for 1 and J = −48.3(4) cm , J = −1.2(1) cm , g =
−4
1
2
.24(2), and ρ = 3.4% (R = 2.2 × 10 ) for 2. The criterion
2
2
5
8
the corresponding alcohols and ketones. The oxidation
reactions were carried out in an aqueous MeCN medium at
50 °C and in the presence of an acid promoter (Table 2).
Cyclohexane was studied in detail as a recognized model
applied to determine the best fit was based on the minimization
2
of the sum of squares of the deviation, R = ∑(χ T − χ T) /
(χ T) . The calculated curves for 1 and 2 (solid lines in
Figure 3a) match very well with the experimental magnetic data
in the whole temperature range. The obtained values of J and
exp
calc
2
∑
exp
30
substrate (Figures 4 and S8−S10 in the SI), whereas other
1
II
J indicate an antiferromagnetic coupling between the Cu ions
alkanes were oxidized under optimized conditions.
2
within the tetracopper(II) clusters in 1 and 2.
In the oxidation of cyclohexane to cyclohexanol and
cyclohexanone, both compounds 1 and 2 exhibit rather low
activity (2−4% total yields) unless a small amount of acid
promoter is added (Figures 4 and S9 in the SI), leading to a
pronounced yield growth. To examine whether the type of acid
Magnetostructural correlations for the hydroxo- and alkoxo-
bridged copper(II) compounds were proposed by Hatfield and
2
5
co-workers. They found that the nature and strength of the
magnetic exchange coupling are mainly affected by the Cu···Cu
distance and the Cu−O−Cu bridging angle (α). In general, the
3
,31
promoter affects the efficiency of cyclohexane oxidation,
we
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DOI: 10.1021/acs.inorgchem.5b00048
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
tested the activity of precatalysts 1 (Figure 4a) and 2 (Figure
S9a in the SI) in the presence of various acid promoters,
one carboxylate or one carboxylate along with one amino
alcohol ligand. After the treatment of 1 with TFA and H O ,
2
2
namely, trifluoroacetic (TFA), nitric (HNO ), sulfuric
the obtained ESI-MS(±) patterns still display all of the above-
mentioned fragments, although their intensity has decreased
with the exception of [Cu (Hedte)(sal)(H O) −
3
(
H SO ), and hydrochloric (HCl) acids. Compounds 1 and 2
2 4
show rather similar behavior. Although the type of promoter
affects significantly the reaction rate of cyclohexane oxidation,
the final product yields are comparable when using different
acids. In the C H oxidation, the 1/TFA and 2/TFA systems
4
2
+
CH CH OH] (m/z 597), which continues to be the most
2
2
intense peak in a positive mode. In addition, new [Cu (edte)-
4
−
(sal)(H O) (MeCN)] (m/z 699) and [Cu (Hedte) (H O) −
CH CH OH] (m/z 649) fragments have emerged in the ESI-
6
12
2
2
4
2
2
−
result in total yields of 17 and 18% after 120 min, respectively.
2 2
The kinetic curves of product accumulation in the 1/HNO3
MS(−) spectrum. These data suggest that various tetracopper
species derived from the parent precatalyst 1 upon decoordi-
and 2/HNO systems are very close to those in the presence of
3
TFA promoter, leading to ∼15% yields. Although the oxidation
nation of one H edte and one sal ligands or a pair of salicylate
2
of cyclohexane is slower when using H SO as a promoter, total
moieties can potentially constitute the catalytically active
species.
2
4
yields of 14 and 18% are achieved with precatalysts 1 and 2,
respectively. Interestingly, the oxidation of C H is extremely
The 1/TFA/H
applied for the oxidation of other alkanes, including various
cyclic and linear C −C hydrocarbons (Table 2). Among cyclic
2 2 2 2
O and 2/TFA/H O systems can also be
6
12
fast in the presence of HCl and the reaction is completed in 3
min but results in inferior product yields (13%) in both systems
5
8
3
,29,31
containing 1 or 2. According to the literature background,
alkanes, the oxidation of cycloheptane appears to be the most
efficient, resulting in up to 20−21% total yields of cyclo-
heptanol and cycloheptanone. Cyclooctane and cyclohexane are
slightly less reactive substrates (14−19% total product yields),
followed by cyclopentane, which is the least active cycloalkane
(7−9% total product yield). In contrast to cycloalkanes, linear
the role of an acid promoter consists of its participation in
proton-transfer steps, activation of the precatalyst by
protonation of ligands and unsaturation of the metal centers,
and augmentation of the oxidative properties of H O and
2
2
prevention of its decomposition (i.e., catalase activity).
Given the good promoting behavior of TFA, the effect of its
amount was investigated in the cyclohexane oxidation with
precatalysts 1 (Figure 4b) and 2 (Figure S9b in the SI). A very
small amount of TFA (1−2 equiv relative to the precatalyst) is
enough to promote the activity of both tetracopper(II)
compounds and increase the reaction rate of C H oxidation
C
5
−C alkanes are less reactive, showing the maximum total
8
yields of oxidation products (isomeric alcohols and ketones) of
9−10% in the case of n-heptane, followed by n-hexane (4−6%),
n-octane (4−5%), and n-pentane (3%).
By analogy with other multicopper(II) precatalysts for alkane
oxidation by H O , the determined regioselectivity, bond-
6
12
2 2
(
Figure S10 in the SI). In the case of 1, the maximum value of
selectivity, and stereoselectivity parameters (see Table S2 and
additional discussion in the SI) are comparable to those
the initial reaction rate (W ) was achieved at a 1/TFA molar
0
3,29
ratio of 1:2, corresponding to a total product yield of 14%. A
further increase of the TFA amount up to 10 and 20 equiv
previously reported
for copper-based catalytic systems
operating with hydroxyl radicals, thus suggesting their
involvement as principal oxidizing species. Considering the
results in a decrease of W (Figure S10a in the SI), without
0
3
,29,31
related literature background,
it is possible to assume the
significantly affecting the efficiency of the precatalyst and
leading to comparable total product yields of 17 and 15%,
respectively (Figure 4b). In the cyclohexane oxidation by the 2/
TFA/H O system, the maximum initial rate W is attained at a
following mechanistic steps for alkane oxidation. Thus, an acid
promoter interacts with a copper precatalyst, causing the
formation of labile sites (via an additional protonation and
partial decoordination of amino alcohol and/or carboxylate
ligands) and the generation of active copper(II) species. These
2
2
0
2
/TFA molar ratio of 1:5 (Figure S10b in the SI),
corresponding to a total product yield of 10%. A further
•
3,29c
participate in the formation of HO radicals from H O ,
increase of the TFA loading has almost no effect on W but
2
2
0
which then abstract H atoms from an alkane, generating the
gives a higher product yield (18% at a 2/TFA molar ratio of
•
alkyl radicals (R ). These react further with O (e.g., from air),
1:10; Figure S9b in the SI).
2
•
giving rise to the ROO radicals, which are transformed to alkyl
It should be mentioned that precatalysts 1 and 2 are not
intact during the catalytic experiments and in the presence of an
hydroperoxides (ROOH) as primary intermediate products.
Alkyl hydroperoxides rapidly decompose to furnish the
acid promoter and H O lead to the formation of homogeneous
2
2
3
,29,31,32
corresponding alcohols and ketones as final products.
catalytically active species, eventually via the additional
protonation and partial decoordination of amino alcohol or
3
,16,29,31
CONCLUSIONS
The current study has widened a still very limited application of
H edte as an aqua-soluble, commercially available, and versatile
aromatic carboxylate ligands.
Although a detailed
■
investigation of catalytic intermediates was out of the main
scope of the current work, we performed an electrospray
ionization mass spectrometry (ESI-MS) study of precatalyst 1
4
multidentate building block for the design of new multicopper
compounds, namely resulting in the aqueous medium self-
assembly generation of two tetracopper(II) products, 1 and 2.
The type of ancillary aromatic carboxylate ligand plays an
important structure-driven role in defining the dimensionality
and kind of the tetracopper(II) cubane core in the obtained
compounds. Apart from representing the first polynuclear
in a MeCN/H O medium before and after its treatment with
2
TFA promoter and H O oxidant, using conditions equal to
2
2
those of the catalytic tests. The most characteristic peaks
observed in the ESI-MS(−) spectrum of 1 are due to the
−
tetracopper [Cu (H edte) (sal) − H] (m/z 994) and
4
2
2
2
−
[
Cu (H edte) (sal) − CH CH OH] (m/z 949) fragments,
with the latter corresponding to an ESI-induced cleavage of one
4
2
2
2
2
2
copper clusters derived from H edte, both 1 and 2 also reveal
4
hydroxyethyl group in H edte. The ESI-MS(+) plot of 1 also
the first examples of transition-metal [M O ] cubane cores
driven by this amino alcohol.
Another structural feature concerns the fact that the metal−
organic chains in 1 or discrete clusters in 2 also act as matrixes
2
4
4
+
1
reveals tetracopper fragments, namely, [Cu (Hedte) (Hsal)]
4
2
+
(
m/z 858) and [Cu (Hedte)(sal)(H O) − CH CH OH] (m/
z 597), corresponding to fragmentations with the elimination of
4
2
2
2
G
DOI: 10.1021/acs.inorgchem.5b00048
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Inorganic Chemistry
Article
ACKNOWLEDGMENTS
This work was supported by the Foundation for Science and
Technology (Projects PTDC/QUI-QUI/121526/2010, IF/
■
2
18 n
0
1395/2013/CP1163/CT005, RECI/QEQ-QIN/0189/2012,
PEst-OE/QUI/UI0100/2013, SFRH/BPD/78854/2011, and
REM 2013), Portugal. We thank Dr. M. C. Oliveira and A. Dias
for ESI-MS(±) measurements.
growing family of water assemblies detected in coordination
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3
5,36
■
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(
2
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3,22
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4
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4
4
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3
3
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1
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environment capable of hydroxylating alkanes). In fact, both
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3
2
4
revealing the highest activity in the systems containing TFA.
The substrate versatility and different selectivity parameters
were also investigated.
́
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Further research will be pursued toward the exploration of
H edte and related amino alcohol building blocks in the design
4
of novel multicopper(II) cores, their incorporation into metal−
organic frameworks, and the study of the magnetic and catalytic
properties of the obtained materials. These and other research
directions are currently in progress.
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*
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Supporting Information
Materials and methods, additional discussion of IR and EPR
spectra, thermogravimetric analyses, magnetic and catalytic
studies, as well as thermogravimetric−differential thermal
analysis plots (Figures S1 and S2), structural representations
of water clusters (Figure S3), 3D supramolecular networks
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Figure S4), molar magnetic susceptibility plots (Figure S5),
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(
S8−S10), selectivity parameters (Table S2), and crystallo-
graphic files for 1 and 2 in CIF format (CCDC 1042427−
1
042428). The Supporting Information is available free of
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AUTHOR INFORMATION
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Spagna, R. J. Appl. Crystallogr. 1999, 32, 115−119.
Corresponding Author
E-mail: kirillov@ist.utl.pt.
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Notes
The authors declare no competing financial interest.
Growth Des. 2014, 14, 3576−3586. (b) Blatov, V. A. IUCr CompComm
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