Structural and magnetic properties of dinuclear Cu(II) complexes featuring triazolyl-naphthalimide ligands

Article abstract of DOI:10.1080/00958972.2016.1193168

Naphthalimide-based ligands have received significant attention for their ability to act as secondary building units for metal containing network structures. The potentially bridging 1,2,4-triazole containing N-(1,2,4-triazolyl)-1,8-naphthalimide (L₁) and N-(1,2,4-triazolyl)-4-dimethylamino-1,8-naphthalimide (L₂) were prepared, characterized, and complexed with Cu(II) salts. L₁ resulted in crystallographically characterized dinuclear complexes, [Cu₂(L₁)₄(NO₃)₄] and [Cu₂(L₁)₂(OAc)₄] when reacted with Cu(NO₃)₂ and Cu₂(OAc)₄, respectively. Packing interactions are dominated by π?π and anion?π interactions and gave rise to structure extension through weak supramolecular interactions. Solid state EPR and magnetism measurements on [Cu₂(L₁)₄(NO₃)₄] revealed the expected values for a non-magnetically coupled square-based pyramidal dimer structure, while [Cu₂(L₁)₂(OAc)₄] showed strong anti-ferromagnetic coupling (J_Cu–Cu?=??185.6?cm^?1).

Full text of DOI:10.1080/00958972.2016.1193168

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Structural and magnetic properties of dinuclear
Cu(II) complexes featuring triazolyl-naphthalimide
ligands
Jonathan A. Kitchen, Ningjin Zhang, Anthony B. Carter, Anthony J. Fitzpatrick
& Grace G. Morgan
To cite this article: Jonathan A. Kitchen, Ningjin Zhang, Anthony B. Carter, Anthony J.
Fitzpatrick & Grace G. Morgan (2016): Structural and magnetic properties of dinuclear Cu(II)
complexes featuring triazolyl-naphthalimide ligands, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2016.1193168
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1193168
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Date: 23 June 2016, At: 03:05

Journal of Coordination Chemistry, 2016
http://dx.doi.org/10.1080/00958972.2016.1193168
Structural and magnetic properties of dinuclear Cu(II) complexes
featuring triazolyl-naphthalimide ligands
Jonathan A. Kitchena, Ningjin Zhanga, Anthony B. Cartera, Anthony J. Fitzpatrickb and
Grace G. Morganb
aChemistry, faculty of natural and environmental sciences, highfield Campus, university of southampton,
southampton, uK; bschool of Chemistry, university College dublin, dublin, ireland
ARTICLE HISTORY
ABSTRACT
received 24 february 2016
accepted 5 april 2016
Naphthalimide-based ligands have received significant attention for their
ability to act as secondary building units for metal containing network
structures. The potentially bridging 1,2,4-triazole containing N-(1,2,4-
triazolyl)-1,8-naphthalimide (L1) and N-(1,2,4-triazolyl)-4-dimethylamino-
1,8-naphthalimide (L2) were prepared, characterized, and complexed
with Cu(II) salts. L1 resulted in crystallographically characterized dinuclear
complexes, [Cu2(L1)4(NO3)4] and [Cu2(L1)2(OAc)4] when reacted with Cu(NO3)2
and Cu2(OAc)4, respectively. Packing interactions are dominated by π⋯π and
anion⋯π interactions and gave rise to structure extension through weak
supramolecular interactions. Solid state EPR and magnetism measurements
on [Cu2(L1)4(NO3)4] revealed the expected values for a non-magnetically
coupled square-based pyramidal dimer structure, while [Cu2(L1)2(OAc)4]
showed strong anti-ferromagnetic coupling (JCu–Cu = −185.6 cm−1).
KEYWORDS
naphthalimide; Cu(ii);
magnetism; triazole;
supramolecular
1. Introduction
N-Substituted-1,8-naphthalimide derivatives have been utilized in a range of applications from fluo-
rescent dyes through their more recent use in magnetically interesting, metal containing extended
network structures [1–4]. In this, their π-deficient character has been exploited giving systems where
CONTACT Jonathan a. Kitchen
J.a.Kitchen@soton.ac.uk
supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00958972.2016.1193168.
© 2016 informa uK limited, trading as taylor & francis Group

2
J. A. KITChEN ET Al.
the extension of structure arises through π-based (π⋯π stacking, anion⋯π interactions and C=O⋯π
interactions) contacts and results in frameworks constructed from less traditional weak non-covalent
supramolecular interactions rather than the more typical charge-assisted coordination bonds observed
in coordination polymers and metal-organic frameworks. Reger and co-workers have been instrumental
in this field and have developed many 1,8-naphthalimide transition metal conjugates with a range of
coordinating groups [4–21] whose structures were extended in the solid state by means of the naph-
thalimide groups acting as secondary building units through π-based interactions. Such self-assembled
systems have applications in areas including molecular electronics, porous materials for sensing and gas
storage, supramolecular spintronics, and crystal engineering development [22, 23]. Given our interests
in the development of magnetically interesting transition metal systems [24–31] and our interests in the
development of naphthalimide containing systems [32–34], we have combined 1,2,4-triazole coordi-
nation chemistry with 1,8-naphthalimide chemistry to generate two new ligands (L1 and L2, scheme 1)
that show excellent structure extension through π-based interactions as well as interesting coordination
chemistry. These naphthalimide-triazolyl systems are also ideal for the generation of multi-functional
architectures as the ligand strands also show excellent fluorescent properties (i.e. L2 is highly emissive)
therefore, emissive framework materials, ideal for sensors, can potentially be generated.
herein, we describe the synthesis, characterization, coordination chemistry and structural analysis
of two novel naphthalimide-based ligands L1 and L2. In line with our previous studies [35], our primary
aim was to probe the ability of L1 and L2 to develop higher order supramolecular architectures in
combination with metal salts and here we have employed Cu(II) for this purpose. In doing so, we have
shown that these simple ligands generate systems where structure extension occurs through π⋯π
and anion⋯π interactions.
2. Experimental
2.1. Materials and instrumentation
All chemicals were purchased from commercial sources and used as received. Solvents were hPlC grade
and were used without purification. 4-(Dimethylamino)-1,8-naphthalic anhydride was prepared from
the reaction of 4-bromo-1,8-naphthalic anhydride with dimethylamine using published procedures [33].
Infrared spectra were recorded on a Thermo Scientific Nicolet iS10 spectrometer with Smart ITR acces-
sory between 400 and 4000 cm−1. NMR spectra were recorded on a Bruker DPX400 NMR spectrometer
at 300 K. Chemical shifts are reported in parts per million and referenced to the residual solvent peak
1
((CD3)2SO: h δ 2.50 ppm, 13C δ 39.52 ppm). Standard conventions indicating multiplicity were used:
m = multiplet, t = triplet, d = doublet, s = singlet. Mass spectrometry samples were analyzed using a
MaXis (Bruker Daltonics, Bremen, Germany) mass spectrometer equipped with a time of flight analyzer.
Samples were introduced to the mass spectrometer via a Dionex Ultimate 3000 autosampler and uhPlC
pump [gradient 20% acetonitrile (0.2% formic acid) to 100% acetonitrile (0.2% formic acid) in five min-
utes at 0.6 ml min. Column: Acquity UPlC BEh C18 (Waters) 1.7 micron 50 × 2.1 mm]. high-resolution
mass spectra were recorded using positive/negative ion electrospray ionization. UV–vis absorption
Scheme 1. synthetic protocol for L1 and L2.

JOURNAl OF COORDINATION ChEMISTRy
3
spectra were recorded on an Agilent Technologies Cary100 Spectrometer between 200 and 800 nm.
Fluorescence measurements were carried out using an Agilent Technologies Cary Eclipse fluorescence
spectrophotometer. Variable temperature magnetic susceptibility for polycrystalline powder samples
were recorded on a Quantum Design MPMS® Xl-7 SQUID magnetometer at 0.1T. Magnetic susceptibility
was recorded in the range of 300-4 K cooling at 3 K min−1. The diamagnetism of the sample and sample
holder were accounted for using Pascal constants and by measurement, respectively. The EPR spectra
were collected at 77 K using a Magnetech ms200 X-band EPR working at 9.381 Ghz with magnetic field
centered at 300 mT and a field sweep of 400 mT. A modulation amplitude of 0.5 mT was used in con-
junction with a microwave power of 0.1 mW and a gain of 10. Single-crystal X-ray diffraction data were
either collected at 100 K on a Rigaku AFC12 goniometer equipped with an enhanced sensitivity (hG)
Saturn 724+ detector mounted at the window of an FR-E+ Superbright Mo-Kα rotating anode generator
(λ = 0.71075 Å) with hF or VhF varimax optics, or a Rigaku 007 hF diffractometer equipped with an
enhanced sensitivity Saturn 944+ detector with a Cu-Kα rotating anode generator (λ = 1.5418 Å) with
hF varimax optics [36]. Unit cell parameters were refined against all data and an empirical absorption
correction applied in either CrystalClear [37] or CrysalisPro [38]. All structures were solved by direct
methods using ShElXS-2013 [39] and refined on FO2 by ShElXl-2013 [39] using Olex2 [40]. All hydrogens
were positioned geometrically and refined using a riding model with d(Ch) = 0.95 Å, Uiso = 1.2 Ueq (C)
for aromatic protons. The crystallographic data are summarized below. CCDC entries 1451355-1451358
contain the crystallographic data for the structures reported in this article.
2.2. Synthesis of L1
1,8-Naphthalic anhydride (1.570 g, 8.0 mmol) and 4-amino-4H-1,2,4-triazole (0.706 g, 8.0 mmol) were
added to DMF (16 ml) to give a suspension. The off-white reaction mixture was stirred at 160 °C under
nitrogen for 8 h. The resulting reaction mixture was then cooled and distilled water (20 ml) was added
giving a voluminous white precipitate. The resulting solid was isolated by filtration and washed by
distilled water (2 × 50 ml). The solid was recrystallized from hot methanol and dried to give an off-
white solid, 0.9 g (43%). Mass Spec. (hR, ESI+) m/z: 265.0715 ([L1 + h]+, C14h9N4O2 requires 265.0720),
287.0532 ([L1 + Na]+, C14h8N4O2Na requires 287.0539). IR(neat): v (cm−1): 3134.3, 3059.7, 1719.9 (C=O),
1674.4 (C=O), 1580.1, 1574.8, 1440.2 (C=N), 1390.1 (C=N), 1061.6 (C–N), 1116.3 (C–N), 1175.8 (C–N),
1
1026.6. UV–vis λmax MeCN 340 nm; λmax ChCl3 334 nm h NMR (DMSO-d6, 400 Mhz) δ ppm: 7.98 (dd,
2h, Naphth–h), 8.62 (d, 4h, 2xNaphth–h), 8.82 (s, 2h, Triazole–h). 13C{1h} NMR (DMSO-d6, 101 Mhz) δ
ppm: 122.0, 127.9, 128.0, 132.0, 132.3, 136.3, 143.7, 161.7.
X-ray quality colorless plate-like single crystals (0.12 × 0.07 × 0.04 mm) of L1 were grown by slow
evaporation of DMF. Crystal data: C14h8N4O2 (M = 264.25 g mol−1): monoclinic, space group P21/c (No.
14), a = 11.406(2) Å, b = 15.520(3) Å, c = 6.8292(14) Å, β = 103.97(3)°, V = 1173.2(4) Å3, Z = 4, T = 100 K,
μ(Mo-Kα) = 0.105 mm-1, Dcalc = 1.4960 g cm−3, 8158 reflections measured (5.24° ≤ 2θ ≤ 50°), 2056
unique (Rint = 0.1530, Rσ = 0.2543) which were used in all calculations. The final R1 was 0.0584 (I > 2σ(I))
and wR2 was 0.1331 (all data).
2.3. Synthesis of L2
4-Dimethylamino-1,8-naphthalic anhydride (1.442 g, 6.0 mmol) and 4-amino-4H-1,2,4-triazole (0.520 g,
6.0 mmol) were added to DMF (16 ml) to give a suspension. The orange–brown reaction mixture was
stirred at 160 °C under nitrogen for 8 h. The resulting reaction mixture was then cooled and distilled
water (20 ml) was added. The solid was isolated by filtration and purified by column chromatography
using silica and an acetone–hexane (1:4) solvent mixture to elute the anhydride starting material and
then pure acetone to elute L2. Removal of solvent in vacuo gave pure L2 as an orange solid, 0.500 g
(30%). Mass Spec. (hR, ESI+) m/z: 308.1148 ([L2 + h]+, C16h14N5O2 requires 308.1142). IR: v (cm−1): 3122.9,
2979.2, 2803.2, 1702.9 (C=O), 1657.3 (C=O), 1582.8, 1498.7, 1451.2, 1390.9, 1340.6 (C=N), 1316.7 (C=N),
1242.0 (C–N), 1213.7, 1176.7, 1138.3, 1129.3, 1070.3, 1063.4, 1019.5. UV–vis λmax MeCN 447 nm; λmax

4
J. A. KITChEN ET Al.
ChCl3 443 nm 1h NMR (DMSO-d6, 400 Mhz) δ ppm: 3.19 (s, 6h, N(Ch3)2), 7.27 (br d, 1h, Naphth–h), 7.82
(br dd, 1h, Naphth–h), 8.41 (br d, 1h, Naphth–h), 8.55 (br d, 1h, Naphth-h), 8.65 (br d, 1h, Naphth–h),
8.80 (s, 2h, triazole–h). 13C{1h} NMR (DMSO-d6, 101 Mhz) δ ppm: 44.9, 111.8, 113.2, 122.1, 124.4, 125.4,
130.6, 132.2, 133.7, 133.9, 158.1, 161.0, 161.9.
Orange plate-like crystals (0.4 × 0.3 × 0.1 mm) of L2 were grown by vapor diffusion of diethyl ether
into a DMF solution of L2. The crystal contained non-merohedral twinning [twinned data refine-
ment scales: 0.6741(12), 0.3259(12) where component 2 rotated by 179.9712° around [1.00 −0.00
−0.00] (reciprocal) or [0.98 −0.00 0.18] (direct)]. Crystal data: C16h13N5O2 (M = 307.31 g mol−1): mon-
oclinic, space group P21/c (No. 14), a = 12.0954(4) Å, b = 15.9987(4) Å, c = 7.0636(2) Å, β = 96.094(3)°,
V = 1359.16(7) Å3, Z = 4, T = 100 K, μ(Cu-Kα) = 0.859 mm-1, Dcalc = 1.502 g cm−3, 4481 reflections measured
(13.292° ≤ 2θ ≤ 133.984°), 4481 unique (Rint = 0.0397, Rσ = 0.0203) which were used in all calculations.
The final R1 was 0.0380 (I > 2σ(I)) and wR2 was 0.1099 (all data).
2.4. Synthesis of [Cu2(L1)4(NO3)4]
Copper(II) nitrate trihydrate (0.024 g, 0.1 mmol) and L1 (0.053 g, 0.2 mmol) were dissolved in Ch3CN–
MeOh (1:1 – 10 ml) and heated at 60 °C with continuous stirring for 6 h. The resulting blue solu-
tion was divided into four equal portions and subjected to vapor diffusion of diethyl ether at room
temperature. After three days, blue crystals were obtained (0.021 g, 27%). IR: v (cm−1): 1704, 1590,
1536, 1470, 1397, 1308, 1291, 1230, 1173, 1140, 1118, 1077, 1016, 891, 846, 771, 726, 627, 533. Crystal
data for [Cu2(L1)4(NO3)4]: C56h32Cu2N20O20 (M = 1432.09 g mol−1): triclinic, space group P1 (No. 2),
̄
a = 8.3676(12) Å, b = 13.0331(18) Å, c = 13.773(2) Å, α = 72.508(8)°, β = 80.202(11)°, γ = 79.362(10)°,
V = 1397.4(4) Å3, Z = 1, T = 100(2) K, μ(Mo-Kα) = 0.863 mm−1, Dcalc = 1.702 g cm−3, 15,625 reflections
measured (5.146° ≤ 2θ ≤ 49.998°), 4904 unique (Rint = 0.0261, Rσ = 0.0296) which were used in all calcu-
lations. The final R1 was 0.0307 (I > 2σ(I)) and wR2 was 0.0796 (all data).
2.5. Synthesis of [Cu2(L1)2(OAc)4]
Copper(II) acetate monohydrate (0.041 g, 0.2 mmol) and L1 (0.054 g, 0.2 mmol) were dissolved in Ch3CN–
MeOh (1:1 – 10 ml) and heated at 60 °C with continuous stirring for 8 h. The resulting blue solution
was divided into four equal portions and subjected to vapor diffusion of diethyl ether resulting in
the formation of blue–green crystals (0.012 g, 14%). IR: v (cm−1): 3472, 3369, 3266, 1707, 1600, 1435,
1420, 1354, 1326, 1233, 1222, 1172, 1138, 1114, 1051, 1032, 892, 850, 802, 776, 686, 626, 533. Crystal
data: C36h28Cu2N8O12 (M = 891.74 g mol−1): monoclinic, space group C2/c (No. 15), a = 29.020(6) Å,
b = 8.1450(16) Å, c = 18.711(4) Å, β = 108.42(3)°, V = 4196.1(16) Å3, Z = 4, T = 100 K, μ(Mo-Kα) = 1.081 mm-1,
Dcalc = 1.412 g cm−3, 11,880 reflections measured (5.506° ≤ 2θ ≤ 49.996°), 3673 unique (Rint = 0.0252,
Rσ = 0.0401) which were used in all calculations. The final R1 was 0.0379 (I > 2σ(I)) and wR2 was 0.0991
(all data).
3. Results and discussion
3.1. Ligand synthesis
The ligands, 1,8-naphthalimide-1,2,4-triazole (L1) and 4-(dimethylamino)-1,8-naphthalimide-1,2,4-tri-
azole (L2) were synthesized as shown in scheme 1. The reaction of one equivalent of 1,8-naphthalic
anhydride or 4-dimethylamino-1,8-naphthalic anhydride with one equivalent of 4-amino-4H-1,2,4-tri-
azole in DMF at 160 °C under N2 gave L1 as a pure off-white solid (43%) and L2 as a crude brown solid
on addition of distilled water to the reaction mixtures. L2 required chromatographic purification to give
the pure product as an orange powder (30%). Both ligands were fully characterized using NMR spec-
troscopy, IR spectroscopy, UV–vis spectroscopy, and mass spectrometry (see supporting information).

JOURNAl OF COORDINATION ChEMISTRy
5
1h NMR spectra showed the expected aromatic naphthalimide protons for L1 and L2 (these were
significantly shifted from the corresponding peaks of the starting naphthalic anhydrides) and the char-
acteristic triazole protons at 8.8 ppm. Mass spectrometry confirmed the successful formation of L1 and
L2 with peaks at 265.0715, m/z, and 308.1148, m/z corresponding to the [M + h]+ ions for L1 and L2,
respectively. Additionally, a peak was observed for the [M + Na]+ species of L1 (287.0532 m/z) species.
Colorless crystals of L1 were grown from slow evaporation of a DMF solution and the low temper-
ature (100 K) X-ray structure was determined. L1 crystallized in the monoclinic space group P21/c and
contained one molecule in the asymmetric unit (figure 1(A)). The triazole ring is orthogonal to the naph-
thalimide ring, a feature commonly observed in such ligand species, with an angle of 79° between the
mean planes of the two rings. Packing interactions are dominated by π⋯π stacking interactions between
neighboring naphthalimide rings (figure 1(B)) as well as weaker non-classical Ch hydrogen bonding
from the triazole Ch groups (figure 2(A)). Neighboring molecules of L1 are arranged into alternating
Figure 1. molecular structure of L1 with thermal ellipsoids at 50% probability (a). Packing of L1 showing π⋯π stacking between
molecules (B).
Figure 2. View of C–h based hydrogen-bonding interactions in L1 (a). Packing of L1 showing π-stacked chains in the crystallographic
b direction (B).

6
J. A. KITChEN ET Al.
Figure 3. molecular structure of L2 with thermal ellipsoids at 50% probability (a). Packing of L2 showing π⋯π stacking between
molecules (B).
Figure 4. View of C–h based hydrogen-bonding interactions in L2 (a). Packing of L2 showing π stacked chains in the crystallographic
b direction (B).
stacks through strong π⋯π stacking interactions [centroid⋯centroid = 3.632 Å and centroid⋯central
naphtha-C = 3.414 Å]. These alternating stacks are then linked to neighboring stacks through weaker
Ch⋯O and Ch⋯N hydrogen bonding.
Small orange crystals of L2 were grown from slow evaporation of a DMF solution and the low tem-
perature (100 K) X-ray structure was determined. The crystal contained non-merohedral twinning where
one component was rotated by ca. 180°. L2 crystallized in the monoclinic space group P21/c with one
molecule in the asymmetric unit (figure 3(A)). The triazole ring in L2 is perpendicular to the naphthal-
imide ring plane (81°), and the packing interactions are again dominated by π⋯π stacking interactions
between neighboring naphthalimide rings [centroid⋯centroid = 3.601 Å, figure 3(B)] as well as weaker
non-classical Ch hydrogen bonding from the triazole Ch groups (figure 4(A)).
The solid state packing interactions present in both L1 and L2 involve π⋯π stacking between
neighboring naphthalimide units, and with these being the dominant interaction, we expect this

JOURNAl OF COORDINATION ChEMISTRy
7
Figure 5. emission spectra of L1 (left) and L2 (right) in ChCl3 (blue) and meCn (red) (see http://dx.doi.org/10.1080/00958972.2016.
1193168 for color version).
same interaction to be present in subsequent coordination complexes. Therefore, these ligand spe-
cies should be ideal for the preparation of new metal-based supramolecular architectures where the
structure directing properties of the ligands might influence the physical properties (e.g. magnetism
or photophysical properties) of the metal centers.
The absorption and the emission properties of L1 and L2 were briefly investigated and were typical
for 1,8-naphthalimide-based compounds [1]. Both L1 and L2 displayed high-energy absorptions in the
200–250 nm range, typical for such organic species. L1 displayed a broad absorption band with λmax at
340 nm, while for L2 this broad absorption had λmax at 440 nm (attributed to an ICT band) when recorded
in ChCl3 and MeCN. Upon excitation at λmax, both L1 and L2 show broad fluorescence emission (figure 5).
L1 displayed emission with λmax at 380 nm when excited at 340 nm in both ChCl3 and MeCN, whereas L2
displayed broad emission at 511 and 532 nm when excited at 440 nm in ChCl3 and MeCN, respectively.
3.2. Coordination chemistry of L1 and L2
L1 and L2 were reacted with Cu(II) salts [Cu(NO3)2, Cu(OAc)2, CuSO4] in a range of solvents and with a
range of M:l ratios in order to assess their coordination ability and determine the effect that the naph-
thalimide group has on the packing in the solid state structures. Despite many attempts, the only sets
of reaction conditions that gave bulk samples of single crystals were Cu(NO3)2·3h2O with L1 in a 1:2
ratio in MeCN/MeOh (1:1) and Cu(OAc)2 with L1 in a 1:1 ratio in MeCN/MeOh (1:1). The reaction of
two equivalents of L1 and one equivalent of Cu(NO3)2 at 60 °C in MeCN/MeOh (1:1) for 1 h gave a clear
blue solution that upon cooling to room temperature was subjected to vapor diffusion of diethyl ether.
After 3 days, a number of blue crystals of [Cu2(L1)4(NO3)4] were obtained (27%). Reaction of Cu(OAc)2
with L1 gave a very small number of blue single crystals suitable for diffraction studies. The resulting
molecular structure was found to be a paddle wheel Cu(II) dimer of [Cu2(L1)2(OAc)4]. To date, reactions
involving either CuSO4 or L2 have not resulted in any crystalline samples.
3.3. Crystallographic analysis of [Cu2(L1)4(NO3)4]
̄
1
[Cu2(L1)4(NO3)4] crystallized in the triclinic space group P
and contained half of a molecule in the asym-
metric unit with the other half generated by a center of inversion (figure 6, table 1).
The result is a dimeric complex where each copper(II) is coordinated with two nitrogen atoms from
different triazole groups, two nitrate oxygen atoms, and one naphthalimide carbonyl oxygen atom from
a symmetry generated naphthalimide to give an overall N2O4 coordination sphere (figure 6). Analysis of
the coordination geometry around Cu(II) reveals the degree of trigonality (τ) to be 0.06, which is con-
sistent with a slightly distorted square–pyramidal coordination environment. Bond lengths and angles
are consistent with other axially elongated square-based pyramidal structures where the equatorial
(square base) bond lengths average 1.985(2) Å, whilst the axial bond to the carbonyl oxygen atom is

8
J. A. KITChEN ET Al.
Figure 6. molecular structure of [Cu2(L1)4(no3)4] with thermal ellipsoids set at 50%.
Table 1. selected bond lengths (Å) and angles (°) for [Cu2(L1)4(no3)4].
Cu(1)–o(201)
Cu(1)–o(101)
1.9724(15)
1.9866(15)
1.9891(16)
1.9906(16)
2.3068(15)
6.4799 (11)
169.93(6)
87.88(7)
90.41(6)
93.28(6)
90.70(6)
166.46(7)
82.07(6)
Cu(1)–n(3)
Cu(1)–n(24)a
Cu(1)–o(22)
Cu(1)–Cu(1)a
o(201)–Cu(1)–o(101)
o(201)–Cu(1)–n(3)
o(101)–Cu(1)–n(3)
o(201)–Cu(1)–n(24)a
o(101)–Cu(1)–n(24)a
n(3)–Cu(1)–n(24)a
o(201)–Cu(1)–o(22)
o(101)–Cu(1)–o(22)
n(3)–Cu(1)–o(22)
n(24)a–Cu(1)–o(22)
88.03(6)
90.59(6)
102.94(6)
a−x + 1, −y + 2, −z.
Figure 7. Packing interactions of [Cu2(L1)4(no3)4] showing π⋯π stacking and non-classical interaction between molecules.

JOURNAl OF COORDINATION ChEMISTRy
9
Figure 8. long range order of [Cu2(L1)4(no3)4] showing the chains of dimers along the crystallographic a axis.
Figure 9. molecular structure of [Cu2(L1)2(oac)4] with thermal ellipsoids set at 50%.
2.307(2) Å. The coordination of the carbonyl oxygen atoms in naphthalimides to transition metals is
not a commonly observed occurrence and only three structures are reported in the CSD [19, 41, 42].
The naphthalimide ligand that bridges the two copper(II) centers gives rise to a 14-membered ring
involving the two copper(II) centers and shows strong π⋯π stacking between the neighboring triazole
rings [centroid⋯centroid = 3.517 Å].
Packing interactions in [Cu2(L1)4(NO3)4] are dominated by strong anion⋯π and face-to-face π⋯π
stacking interactions. Anion⋯π interactions exist between two neighboring dimers where the distal
oxygen atoms of the coordinated nitrate anions are involved in anion⋯π interactions to the imide rings
of neighboring dimers (figure 7) with O⋯centroid distances of 2.881 and 2.852 Å for the two different
interactions. The interactions are self-complementary so there are four interactions in total between
two dimers and this extends them into chains of dimers in the direction of the crystallographic a-axis
(figure 8). These anion⋯π linked chains are linked to neighboring chains via offset face-to-face π⋯π
stacking between naphthalene rings where all four naphthalimide ligands are involved in stacking
interactions to link the chains [centroid⋯centroid distances = 3.718].

10
J. A. KITChEN ET Al.
Table 2. selected bond lengths (Å) and angles (°) for [Cu2(L1)2(oac)4].
Cu(1)–o(3)
Cu(1)–o(4)
Cu(1)–o(5)
Cu(1)–o(6)
1.9758(18)
1.9648(18)
1.9657(19)
1.9638(19)
2.181(2)
2.6511(11)
90.95(8)
168.32(8)
90.35(8)
100.72(8)
89.21(8)
93.98(8)
88.76(8)
89.31(8)
168.30(8)
97.58(8)
Cu(1)–n(4)
Cu(1)–Cu(1)a
o(3)–Cu(1)–n(4)
o(4)b–Cu(1)–o(3)
o(4)b–Cu(1)–o(5)
o(4)b–Cu(1)–n(4)
o(5)–Cu(1)–o(3)
o(5)–Cu(1)–n(4)
o(6)–Cu(1)–o(3)
o(6)–Cu(1)–o(4)a
o(6)–Cu(1)–o(5)
o(6)–Cu(1)–n(4)
a1 − x, −y, 1 − z.
Figure 10. Packing of [Cu2(L1)2(oac)4] showing π⋯π stacking between molecules.
Figure 11. Packing of [Cu2(L1)2(oac)4] showing non-classical interaction between molecules.
3.4. Crystallographic analysis of [Cu2(L1)2(OAc)4]
[Cu2(L1)2(OAc)4] crystallized in the monoclinic space group C2/c and contained half of one molecule in
the asymmetric unit with the other half generated by a center of inversion (figure 9, table 2).
The resulting paddle wheel dimer consists of two Cu(II) centers bridged by four acetate molecules
and capped with two L1 molecules to give O4N coordination environments around each copper atom.

JOURNAl OF COORDINATION ChEMISTRy
11
Figure 12. Plot of χmT versus T for [Cu2(L1)4(no3)4] between 4 and 300 K.
Figure 13. Plot of χmT versus T for [Cu2(L1)2(oac)4] between 4 and 300 K.
The Cu(II) ions are 2.651(2) Å apart, similar to other copper paddle wheel complexes [35]. The copper
ions adopt a near perfect square-based pyramidal geometry with the degree of trigonality (τ) being 0
[43]. Bond lengths and angles are also consistent with other axially elongated square-based pyramidal
structures where the equatorial acetate oxygen Cu–O bond lengths average 1.968(2) Å, whilst the axial
triazole nitrogen atom Cu–N bond length is 2.180(2) Å (table 2).
Packing interactions in [Cu2(L1)2(OAc)4] also involve the naphthalimide π-system, as well as Ch hydro-
gen bonding involving the somewhat acidic triazole Ch moiety (a commonly observed packing inter-
action in such structures) [44]. Paddle wheel dimer units are packed into pseudo 1-D chains through
face-to-face π⋯π stacking between neighboring naphthalimide moieties [centroid⋯centroid = 3.806 Å]
(figure 10). These chains are then linked to neighboring chains through weak Ch hydrogen bonding
between triazole Ch and naphthalimide C=O groups [C⋯O = 3.458 Å and <(Ch⋯O) = 147°] (figure 11).

12
J. A. KITChEN ET Al.
Figure 14. solid state X-band ePr spectrum of [Cu2(L1)4(no3)4] measured at 77 K (black) and the calculated fit (red) (seehttp://dx.doi.
org/10.1080/00958972.2016.1193168 for color version).
3.5. Magnetism and EPR studies
Variable temperature magnetic susceptibility measurements were obtained for polycrystalline pow-
der samples of [Cu2(L1)4(NO3)4] and [Cu2(L1)2(OAc)4] and are shown in figures 12 and 13, respectively.
The χMT value of just below 0.8 cm3 mol−1 K for [Cu2(L1)4(NO3)4] across the entire temperature range
is representative of a Cu(II) dimer with negligible magnetic interaction between the Cu(II) centers. In
the plot for [Cu2(L1)2(OAc)4], the χMT value decreases on cooling from 0.8 to 0 cm3 mol−1 K indicative of
antiferromagnetic coupling.
The solid state X-band EPR spectrum of [Cu2(L1)4(NO3)4], measured at 77 K, also showed negligible
interaction between the Cu(II) ions (figure 14). The g factor derived from the data are 2.07 and is in
line with square–pyramidal geometry. There are no obvious hyperfine interactions from the triazole
14N nuclei. There was no EPR signal at 77 K at X-band for [Cu2(L1)2(OAc)4], presumably due to the large
anti-ferromagnetic coupling between the Cu(II) ions coupled with the sensitivity of the X-band EPR used.
Both the magnetic and EPR data for [Cu2(L1)4(NO3)4] and the magnetic data for [Cu2(L1)2(OAc)4] were
fitted using the program PhI [45] utilizing the hamiltonian:
i,j∈N
ꢀ
ꢀ
=
̂
⃗
̂
⃗
̂
⃗ ⃗
B ⋅ S
̂
H = −2
S ⋅ ⋅ Sj − g휇B
JiJ
i
i<j
i
The resulting fit gave a giso of 2.067 and a JCu–Cu = −0.05 cm−1, this correlates well with the very weakly
interacting Cu(II) ion model. This is not unexpected as the Cu(II) centers were shown to be ~6.5 Å apart
(see above).
Conversely, for [Cu2(L1)2(OAc)4], the fit gave giso of 2.07 and JCu–Cu = −185.6 cm−1 consistent with a
strongly anti-ferromagnetic interaction between the Cu(II) centers. [Cu2(L1)2(OAc)4] was EPR silent, fur-
ther emphasizing the strong anti-ferromagnetic coupling between the metal centers.
4. Conclusion
The syntheses of two new 1,8-naphthalimide-1,2,4-triazolyl-based ligands, L1 and L2, were achieved and
the solid state packing revealed significant π-based interactions. Coordination chemistry was attempted
using Cu(II) salts in the hope that the π-based interactions would be the dominant intermolecular
interaction and allow for functional metal-organic networks to be constructed using supramolecular
self-assembly. Cu(NO3)2 when reacted with L1 gave single crystals of a dimeric complex [Cu2(L1)4(NO3)4],
whilst reaction of L1 with Cu2(OAc)4 gave the paddle wheel dimer [Cu2(L1)2(OAc)4]. The expected π-based

JOURNAl OF COORDINATION ChEMISTRy
13
interactions were also present in the complex and resulted in extension of the structure into a supra-
molecular metal-organic network. EPR and magnetism measurements of [Cu2(L1)4(NO3)4] showed very
little coupling between the square-based pyramidal Cu(II) centers, however the interaction between
the Cu(II) centers in [Cu2(L1)2(OAc)4] was strongly anti-ferromagnetic. The use of naphthalimide-based
ligands and triazole coordination sites has resulted in metal-organic supramolecular networks where
interesting dimer complexes were assembled into extended networks through non-covalent π⋯π
and anion⋯π interactions. These initial results suggest that L1 and L2 (and subsequent derivatives)
could be ideal for developing magnetically interesting self-assembled systems, a rapidly expanding
area in molecular electronics research and multi-functional devices. Such research requires modular
ligand design so that a range of functional groups to fine-tune the system or allow for immobilization
of assemblies can be readily incorporated and so that predictable intermolecular interactions can be
generated, all properties that these triazole-naphthalimide systems possess.
Supplementary material
Supporting information is available for this article. CCDC entries 1451355-1451358 contain the crystallographic data for the
structures reported in this article. All data supporting this study are openly available from the University of Southampton
repository at http://dx.doi.org/10.5258/SOTON/390630.
Acknowledgments
The authors are grateful to the University of Southampton and University College Dublin for support of this work. J.A.K
thanks the EPSRC for funding through grant reference EP/K039466/1. In addition G.G.M. and A.J.F. thank Science Foundation
Ireland for an Investigator Project Award 12/IP/1703 (to G.G.M.), the National University of Ireland and the Cultural Service
of the French Embassy in Ireland for scholarships (to A.J.F.) and the Irish higher Education Authority for funding for a
SQUID magnetometer.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the Engineering and Physical Sciences Research Council [grant number EP/K039466/1]; Science
Foundation Ireland [grant number 12/IP/1703].
References
[1] S. Banerjee, E.B. Veale, C.M. Phelan, S.A. Murphy, G.M. Tocci, l.J. Gillespie, D.O. Frimannsson, J.M. Kelly, T. Gunnlaugsson.
Chem. Soc. Rev., 42, 1601 (2013).
[2] C.J. McAdam, B.h. Robinson, J. Simpson. Organometallics, 19, 3644 (2000).
[3] R.M. Duke, E.B. Veale, F.M. Pfeffer, P.E. Kruger, T. Gunnlaugsson. Chem. Soc. Rev., 39, 3936 (2010).
[4] D.l. Reger, A. leitner, M.D. Smith. Cryst. Growth Des., 15, 5637 (2015).
[5] D.l. Reger, J.D. Elgin, R.F. Semeniuc, P.J. Pellechia, M.D. Smith. Chem. Commun., 4068 (2005).
[6] D.l. Reger, A. Debreczeni, M.D. Smith, J. Jezierska, A. Ozarowski. Inorg. Chem., 51, 1068 (2012).
[7] D.l. Reger, R.F. Semeniuc, J.D. Elgin, V. Rassolov, M.D. Smith. Cryst. Growth Des., 6, 2758 (2006).
[8] D.l. Reger, E. Sirianni, J.J. horger, M.D. Smith, R.F. Semeniuc. Cryst. Growth Des., 10, 386 (2010).
[9] D.l. Reger, A. Debreczeni, B. Reinecke, V. Rassolov, M.D. Smith. Inorg. Chem., 48, 8911 (2009).
[10] D.l. Reger, B. Reinecke, M.D. Smith, R.F. Semeniuc. Inorg. Chim. Acta, 362, 4377 (2009).
[11] D.l. Reger, J.D. Elgin, P.J. Pellechia, M.D. Smith, B.K. Simpson. Polyhedron, 28, 1469 (2009).
[12] D.l. Reger, A. Debreczeni, M.D. Smith. Inorg. Chim. Acta, 364, 10 (2010).
[13] D.l. Reger, J.J. horger, M.D. Smith. Chem. Commun., 47, 2805 (2011).
[14] D.l. Reger, J. horger, M.D. Smith, G.J. long. Chem. Commun., 6219 (2009).
[15] D.l. Reger, J.J. horger, M.D. Smith, G.J. long, F. Grandjean. Inorg. Chem., 50, 686 (2011).
[16] D.l. Reger, A. Debreczeni, J.J. horger, M.D. Smith. Cryst. Growth Des., 11, 4068 (2011).

14
J. A. KITChEN ET Al.
[17] D.l. Reger, A. Debreczeni, M.D. Smith. Eur. J. Inorg. Chem., 2012, 712 (2012).
[18] D.l. Reger, A. Debreczeni, M.D. Smith. Inorg. Chim. Acta, 378, 42 (2011).
[19] D.l. Reger, J.J. horger, A. Debreczeni, M.D. Smith. Inorg. Chem., 50, 10225 (2011).
[20] D.l. Reger, A. Debreczeni, M.D. Smith. Inorg. Chem., 50, 11754 (2011).
[21] D.l. Reger, A.P. leitner, M.D. Smith. Cryst. Growth Des., 15, 5637 (2015).
[22] T.R. Cook, y.-R. Zheng, P.J. Stang. Chem. Rev., 113, 734 (2013).
[23] G. Seeber, G.J.T. Cooper, G.N. Newton, M.h. Rosnes, D.-l. long, B.M. Kariuki, P. Kögerler, l. Cronin. Chem. Sci., 1, 62
(2010).
[24] A. Bhattacharjee, V. Ksenofontov, J.A. Kitchen, N.G. White, S. Brooker, P. Gutlich. Appl. Phys. Lett., 92, 174104 (2008).
[25] G.N.l. Jameson, F. Werner, M. Bartel, A. Absmeier, M. Reissner, J.A. Kitchen, S. Brooker, A. Caneschi, C. Carbonera, J.-F.
letard, W. linert. Eur. J. Inorg. Chem., 2009, 3948 (2009).
[26] J.A. Kitchen, S. Brooker. Dalton Trans., 39, 3358 (2010).
[27] J.A. Kitchen, G.N.l. Jameson, V.A. Milway, J.l. Tallon, S. Brooker. Dalton Trans., 39, 7637 (2010).
[28] J.A. Kitchen, N.G. White, G.N.l. Jameson, J.l. Tallon, S. Brooker. Inorg. Chem., 50, 4586 (2011).
[29] J.A. Kitchen, J. Olguín, R. Kulmaczewski, N.G. White, V.A. Milway, G.N.l. Jameson, J.l. Tallon, S. Brooker. Inorg. Chem.,
52, 11185 (2013).
[30] J.P. Byrne, J.A. Kitchen, O. Kotova, V. leigh, A.P. Bell, J.J. Boland, M. Albrecht, T. Gunnlaugsson. Dalton Trans., 43, 196
(2014).
[31] R. Kulmaczewski, J. Olguín, J.A. Kitchen, h.l.C. Feltham, G.N.l. Jameson, J.l. Tallon, S. Brooker. J. Am. Chem. Soc., 136,
878 (2014).
[32] S. Banerjee, J.A. Kitchen, S.A. Bright, J.E. O’Brien, D.C. Williams, J.M. Kelly, T. Gunnlaugsson. Chem. Commun., 49, 8522
(2013).
[33] S. Banerjee, J.A. Kitchen, T. Gunnlaugsson, J.M. Kelly. Org. Biomol. Chem., 11, 5642 (2013).
[34] E.B. Veale, J.A. Kitchen, T. Gunnlaugsson. Supramol. Chem., 25, 101 (2013).
[35] J.A. Kitchen, P.N. Martinho, G.G. Morgan, T. Gunnlaugsson. Dalton Trans., 43, 6468 (2014).
[36] S.J. Coles, P.A. Gale. Chem. Sci., 3, 683 (2012).
[37] CrystalClear-SM Expert 3.1. b27, Rigaku (2012).
[38] CrysAlisPro 1.171.38.41. Rigaku Oxford Diffraction (2015).
[39] G.M. Sheldrick. Acta Crystallogr. Sect. A, 64, 112 (2008).
[40] O.V. Dolomanov, l.J. Bourhis, R.J. Gildea, J.A.K. howard, h. Puschmann. J. Appl. Crystallogr., 42, 339 (2009).
[41] R. García-Bueno, M.D. Santana, G. Sánchez, J. García, G. García, J. Pérez, l. García. Dalton Trans., 39, 5728 (2010).
[42] B.K. Nicholson, P.M. Crosby, K.R. Maunsell, M.J. Wyllie. J. Organomet. Chem., 716, 49 (2012).
[43] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor. J. Chem. Soc., Dalton Trans., 1349 (1984).
[44] R.M. hellyer, J.A. Joule, D.S. larsen, S. Brooker. Acta Crystallogr. Sect. C, 63, 358 (2007).
[45] N.F. Chilton, R.P. Anderson, l.D. Turner, A. Soncini, K.S. Murray. J. Comput. Chem., 34, 1164 (2013).