Design and construction of copper(I) complexes based on flexi-dentate cyclic N2-donor Schiff bases via in situ reduction of copper(II) precursors

Article abstract of DOI:10.1016/j.poly.2014.05.083

Three copper(I) complexes [Cu(μ₂-L¹)I]_n (1), [CuL¹(μ-1,1,3-SeCN)]_n (2) and [Cu ₂(μ₂-I)₂(L²)₂] (3), where L¹ = 5,6-diphenyl-2,3-dihydro

Full text of DOI:10.1016/j.poly.2014.05.083

Accepted Manuscript
Design and construction of copper(I) coordination complexes based on flexi-
dentate cyclic N -donor Schiff bases via in situ reduction of copper(II) precur-
2
sors
Subrata Jana, Shouvik Chattopadhyay
PII:
S0277-5387(14)00414-8
DOI:
http://dx.doi.org/10.1016/j.poly.2014.05.083
POLY 10812
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
10 March 2014
28 May 2014
Please cite this article as: S. Jana, S. Chattopadhyay, Design and construction of copper(I) coordination complexes
based on flexi-dentate cyclic N -donor Schiff bases via in situ reduction of copper(II) precursors, Polyhedron (2014),
2
doi: http://dx.doi.org/10.1016/j.poly.2014.05.083
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Design and construction of copper(I) coordination complexes
based on flexi-dentate cyclic N -donor Schiff bases via in situ
2
reduction of copper(II) precursors
*
Subrata Jana, Shouvik Chattopadhyay
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata – 700 032, India.
e-mail: shouvik.chem@gmail.com Tel. +91-33- 2414-6666-Extn-2941
Abstract
Three copper(I) coordination complexes have been synthesized via the in situ reduction
of copper(II) precursors under ambient conditions and they have been characterized by elemental
analysis, IR and UV-VIS spectroscopy and single-crystal X-ray diffraction studies. The copper(I)
centres have trigonal planar geometries in complexes 1 and 3, whereas the copper(I) centre is
tetrahedral in complex 2. Complex 1 has a 1-D chain structure, whilst complex 2 features a
ladder-like polymeric coordination network with a Cu
2
Se
2
core. Intermolecular C-H⋅⋅⋅π
interactions form 2-D layers in 2. Complex 3 is an iodide bridged dimer. In complexes 1 and 3,
KI reduces the copper(II) centres, but in complex 2, KSeCN acts as the reducing agent.
Complexes 1 and 2 show significant C-H⋅⋅⋅π interactions, but complex 3 has no such C-H⋅⋅⋅π
interactions.
-
Keywords: Copper(I), µ-1,1,3-SeCN , µ-I, Schiff base, Crystal structure, C-H⋅⋅⋅⋅π interaction,
Photoluminescence.

Introduction
Coordination polymers with various architectures, such as 1-D linear chain, zigzag chain,
-D square network, interwoven honeycomb etc., have been widely studied in the last few
2
decades [1-8]. Many properties of coordination polymers arise from these structures and
topologies, and thus the rational design and creation of specific architectures are particularly
important. Pyrazine and substituted pyrazine, in conjugation with other co-ligands, have been
used extensively for the synthesis of homo-polymetallic complexes with interesting supra-
molecular architectures [9-12]. This bridging ligand is also very popular for the construction of
porous organic-inorganic hybrid solids, with potential applications in catalysis, gas adsorption
etc [13-15]. It is found that a slight change in the co-ligands can bring about drastic changes in
the supramolecular architecture [16-18]. The specific oxidation state and the coordination
preference of the metal cation play an important role in determining the final polymeric
9
structure. Thus d copper(II) is normally octahedrally coordinated (distorted) and forms square
1
0
2
D networks with pyrazine or substituted pyrazine [19-22], whereas d copper(I) adopts
tetrahedral or trigonal planar geometries with these ligands [23-25]. The current development in
1
0
coordination polymers based on d metal ions reflects their application in the areas of sensors
and luminescent materials [26-29].
Copper-based luminophores have recently been examined as an inexpensive and less
toxic alternative to the more ubiquitous noble metal emitters in chemical sensors [30-32], probes
of biological systems [33,34] and energy-conversion devices [35-38]. Synthetic simplicity is a
desirable property for luminescent molecular systems as it can make the rapid expansion and
tuning of photophysical properties easy [39-41]. Recently, our group has reported the in situ
synthesis of a highly luminescent copper(I) complex with 5,6-diphenyl-2,3-dihydropyrazine and

thiocyanate by refluxing 1,2-diphenylethane-1,2-dione (benzoin) with 1,2-diaminoethane,
followed by the addition of copper perchlorate and nickel thiocyanate [42], but the details of the
mechanism were not clear. In order to examine the details of the reaction, we repeated the
reaction, but varying the substitution on the pyrazine moiety and varying the pseudohalide.
Surprisingly, new copper(I) complexes with different architectures were produced. Herein, we
report the facile synthesis, characterization and X-ray structures of highly emissive, polymeric,
three/four-coordinate copper(I) complexes with interesting cyclic Schiff bases.
Experimental
Materials
All chemicals used were purchased from Sigma-Aldrich and were of reagent grade. They
were used without further purification.
CAUTION!!!
Although no problems were encountered in this work, perchlorate salts containing organic
ligands are potentially explosive. Only a small amount of the material should be prepared and it
should be handled with care.
Synthesis
1
Synthesis of the precursor complex [Cu(L )
2
4 2
](ClO ) (A)
1
The cyclic Schiff base ligand L (5,6-diphenyl-2,3-dihydropyrazine) was prepared
by the 1:1 condensation of ethylenediamine (2 mmol, 0.14 ml) and benzoin (2 mmol, 0.424 g) in
methanol following the literature method [42]. It was not isolated and a methanol solution (20
ml) of Cu(ClO
4
)
2
·6H O (2 mmol, 0.740 g) was added to it. A deep red crystalline complex was
2

separated instantly and collected by filtration. The complex was characterized by elemental and
spectral analysis and by mass spectrometry. We could not grow suitable single crystals of A for
X-ray diffraction.
Yield: 0.37 g (51%). Anal. Calc. for C32
H
28Cl
2
CuN
4
O
8
(731.04): C, 52.57; H, 3.86; N, 7.66;
CN) m/z: 531.05 (100%,
] ). IR (KBr, cm ): 1625 (νC=N), 1093 (νClO4). Magnetic moment: 1.72 BM. UV-VIS,
Found: C, 52.1; H, 4.0; N, 7.7%; ESI-MS (positive ion mode, CH
3
1
2+
-1
[
Cu(L )
2
3
-1
-1
λ
max (nm) [εmax(dm mol cm )] (acetonitrile): 368 (886), 620 (263).
2
Synthesis of the precursor complex [Cu(L )
2
](ClO
4
)
2
(B)
2
The cyclic Schiff base ligand L (2,3-dihydro-5,6-bis(4-methoxyphenyl)pyrazine) was
prepared in a similar way using 4,4′-dimethoxybenzoin (2 mmol, 0.540 g) instead of benzoin.
The methanol solution (20 ml) of Cu(ClO
4
)
2
·6H O (2 mmol, 0.740 g) was added to the methanol
2
2
solution of the ligand L . A deep red crystalline complex was separated instantly and collected
by filtration. The complex was characterized by elemental and spectral analysis and by mass
spectrometry. Single crystals suitable for X-ray diffraction could not be grown.
Yield: 0.41 g (48%). Anal. Calc. for C36
H
36Cl
2
CuN
4
O
12 (851.14): C, 50.80; H, 4.26; N, 6.58;
CN) m/z: 651.16 (100%,
] ). IR (KBr, cm ): 1607 (νC=N), 1092 (νClO4). Magnetic moment: 1.71 BM. UV-VIS,
Found: C, 51.0; H, 4.3; N, 6.4%; ESI-MS (positive ion mode, CH
3
2
2+
-1
[
Cu(L )
2
3
-1
-1
λ
max (nm) [εmax(dm mol cm )] (acetonitrile): 229 (1220), 294 (579), 411(87).
1
-L )I]
Synthesis of complex [Cu(µ
2
n
(1)
A methanol solution (5 ml) of KI (3 mmol, 0.498 g) was added to an acetonitrile
solution (20 ml) of the precursor complex A (2 mmol, 1.46 g). The solution was stirred for 5 hrs.

Diffraction quality single crystals were obtained after a few days by slow evaporation of the
solution in open atmosphere.
Yield: 0.69 g (81%); Anal. Calc. for C32
H28Cu
2
I
2
N (849.48): C, 45.24; H, 3.32; N, 6.60; Found:
4
1
+
C, 45.3; H, 3.4; N, 6.5%; ESI-MS (positive ion mode, CH
3
CN) m/z: 531.39 (100%, [Cu(L )
2
] );
-1
3
-
IR (KBr, cm ): 1602 (νC=N), Magnetic moment: Diamagnetic. UV-VIS, λmax (nm) [εmax(dm mol
1
-1
cm )] (acetonitrile): 368 (430).
1
Synthesis of complex [CuL ((µ-1,1,3-SeCN)]
n
(2)
A methanol solution of KSeCN (1 mmol, 0.144 g) was added to an acetonitrile
solution of the precursor complex A (1 mmol, 0.731 g). The solution was stirred for 5 hrs.
Diffraction quality single crystals were obtained after a few days by slow evaporation of the
mother liquor in the open atmosphere.
Yield: 0.29 g (72%); Anal. Calc. for C17
H
14CuN
3
Se (402.82): C, 50.69; H, 3.50; N, 10.43;
CN) m/z: 531.25 (100%,
Found: C, 51.3; H, 3.6; N, 10.6%; ESI-MS (positive ion mode, CH
3
1
+
-1
[
Cu(L )
2
] ); IR (KBr, cm ): 1607 (νC=N), 2109 (νSeCN), Magnetic moment: Diamagnetic.
2
(L )
Synthesis of complex [Cu
2
(µ
2
-I)
2
2
] (3)
This was prepared by a similar method to that of complex 1, except that the precursor
complex B (2 mmol, 1.70 g) was used instead of the precursor complex A. The solution was
stirred for 5 hrs. Diffraction quality single crystals were obtained after a few days by slow
evaporation of the solution in the open atmosphere.
Yield: 0.82 g (85%); Anal. Calc. for C36
2
H36Cu I
2
N
4
4
O (969.6): C, 44.59; H, 3.74; N, 5.78;
-1
Found: C, 45.1; H, 3.8; N, 5.9%; IR (KBr, cm ): 1602 (νC=N), Magnetic moment: Diamagnetic.

Physical measurements
Elemental analyses (C, H, N and metal) were carried out using a Perkin-Elmer 2400 II
-1
elemental analyzer. IR spectra in KBr (4000-400 cm ) were recorded using a Perkin Elmer
Spectrum Two FTIR spectrophotometer. Electronic spectra in acetonitrile (800-200 nm) were
recorded with a Hitachi U-3501 spectrophotometer for complexes A, B and 1. UV-visible diffuse
reflectance spectra for complexes 2 and 3 were recorded on a Shimadzu UV 2401PC with an
integrating sphere attachment. BaSO was used as a background standard. The steady state
4
emission spectra were recorded on a Perkin-Elmer LS 55 Luminescence spectrometer at room
temperature. Luminescence lifetime measurements were carried out by using a time-correlated
single photon counting set up from Horiba Jobin-Yvon. EPR spectra of all the complexes were
recorded with a JEOL JES-FA 200 ESR spectrophotometer. Electro-spray ionization mass
spectra were recorded with a Waters QTOF Micro YA263. The magnetic susceptibility
measurements were done with an EG&PAR vibrating sample magnetometer, model 155 at room
temperature and diamagnetic corrections were made using Pascal’s constants. The thermal
−
1
behavior of the complexes was studied in a dynamic nitrogen atmosphere (150 mL min ) at a
−
1
heating rate of 10 °C min using thermogravimetric (TG) techniques in a NETZSCH TG 209F3
instrument.
X-ray crystallography
Single crystals of the complexes 1, 2 and 3, having suitable dimensions, were used for
data collection using a Bruker SMART APEX II diffractometer equipped with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å) at 293 K. The molecular structures were
solved using the SHELX-97 package [43]. Non-hydrogen atoms were refined with anisotropic

thermal parameters. H atoms were placed in their geometrically idealized positions and
constrained to ride on their parent atoms. Multi-scan empirical absorption corrections were
applied to the data using the program SADABS [44]. A summary of the crystallographic data is
given in Table 1. CCDC reference numbers are 931116 (for 2), 931117 (for 1) and 931118 (for
3
). The figures were prepared using ORTEP [45] and MERCURY [46].
3
. Results and discussion
Synthesis
Initially we thought that benzoin was oxidized to benzil with the concomitant reduction
of copper(II) to copper(I), followed by a 1:1 condensation of benzil with ethylenediamine to
produce the 6-membered cyclic Schiff base 5,6-diphenyl-2,3-dihydropyrazine, which then
1
coordinated to the copper(I) to form the red complex [Cu(L )]ClO
4
. However, isolation of the
complex followed by characterization by elemental and mass spectrometric analysis (Figure S1,
1
1
Supplementary Information) suggested the formation of [Cu(L )](ClO
4
)
2
and not [Cu(L )]ClO .
4
We have failed to grow suitable single crystals of this complex from several solvents for an X-
ray diffraction study. However, the EPR spectrum of the complex also supports the presence of
copper(II) in the complex. Thus benzoin is not oxidized to benzil by copper(II), rather a real
oxidation of benzoin occurs in the presence of diamine. Use of benzil instead of benzoin
produces the same complex, as supported by elemental analysis, mass spectrometry and X-ray
single crystal diffraction studies, only the yield increases slightly when benzil is used instead of
benzoin. From these observations, we assume that bezoin is oxidized first under the reaction
conditions to benzil and then it reacts with ethylenediamine to produce the cyclic Schiff base. In
order to decide whether there is any role of copper(II) in the oxidation of benzoin to benzil, we

have refluxed benzoin with ethylenedimine without adding copper(II), and isolated benzil as
supported by elemental analysis, IR and mass spectra and X-ray diffraction studies. The
reduction of copper(II) is therefore facilitated by the addition of iodide/selenocyanide, with the
formation of complexes 1 and 2 respectively. Mass spectra of complexes of 1 and 2 are given in
Figures S2 and S3, Supplementary Information.
-
-
-
Iodide and selenocyanide are converted to I
3
and (SeCN)
+ 2n e ) during the reaction, with the concomitant reduction of the
copper(II) complexes into copper(I) complexes. Keeping these reactions in mind, we have settled
2
respectively (3n I → n I
3
+
-
-
-
2
n e ; 2n SeCN → n (SeCN)
2
-
-
the ratio of copper(II) complexes to I /SeCN . The yields of the reactions are maximized, if this
ratio is maintained.

Scheme 1: Syntheses of complexes 1-3
To confirm the mechanism, we repeated the total synthetic procedure with 4,4′-
dimethoxybenzoin instead of benzoin and have isolated the perchlorate complex
2
[
Cu(L )](ClO
4
2
) , as confirmed by elemental analysis, mass spectrometry (Figure S4,
Supplementary Information) and a spectral study. Addition of KI reduced copper(II) to copper(I),
with the formation of complex 3. The syntheses of the complexes are given in Scheme 1. The
structures of all the complexes were confirmed by an X-ray diffraction study.

Description of the structures
1
-L )I]
[
Cu(µ
2
n
(1)
Complex 1 crystallizes in the monoclinic space group P2
1
/c. It consists of infinite zigzag
1
-D chains of copper(I), the µ -bridging bidentate ligand 5,6-diphenyl-2,3-dihydropyrazine and
2
terminal iodides. The asymmetric unit contains two crystallographically different copper(I) sites,
Cu(1) and Cu(2), both of which possess trigonal planar geometries. A perspective view of the
2
asymmetric unit is shown in Fig. 1. The complex can thus better be represented as [Cu
2
(µ -
1
L )
2
I ] . Each copper(I) centre is coordinated by two nitrogen atoms from two different
2
n
molecules of the ligand {N(1) and N(4) for Cu(1); N(3) and N(2) for Cu(2)} and a terminal
1
iodide {I(1) for Cu(1); I(2) for Cu(2)}. The cyclic Schiff base L acts as a bridging ligand to form
a zigzag chain (Fig. 2). The angles around the copper(I) centres slightly deviate from 120°
(
124.86(9), 128.73(9) and 106.41(12)° for Cu(1); 119.22(9), 133.14(9) and 107.43(12)° for
Cu(2)) and this indicates slight pyramidalization of the trigonal planar geometry, which may be
caused by close copper(I)-ligand contacts. The deviation of Cu(1) from the mean plane passing
through the coordinating atoms I(1), N(1) and N(4) is 0.0026(6) Å. Similarly, the deviations of
Cu(2) from the mean plane passing through the coordinating atoms N(3), I(2) and N(2) is -
0
.0558(6) Å. The minimum Cu(I)-Cu(I) distance in the chain is 6.770(7) Å. The Cu-N and Cu-I
distances are comparable to those reported in the literature [47]. Selected bond lengths and bond
angles are given in Table 2.
The complex shows significant C–H⋅⋅⋅π interactions (Fig. 3). Three methylene hydrogen
atoms, H(9A) attached to C(9), H(10A) attached to C(10) and H(19A) attached to C(19), are
involved in intramolecular C–H⋅⋅⋅π interactions with the phenyl rings [C(3)–C(4)–C(5)–C(6)–

C(7)–C(8)], [C(21)–C(22)–C(23)–C(24)–C(25)–C(26)] and [C(12)–C(13)–C(14)–C(15)–C(16)–
C(17)] respectively. Geometric features of the C–H⋅⋅⋅π interactions are given in Table 3.
1
CuL ((µ-1,1,3-SeCN)]
[
n
(2)
This complex crystallizes in the triclinic space group P-1. It is a polymeric copper(I)
complex, having a tetrahedral geometry around the copper(I) centre. The asymmetric unit
1
contains one copper(I) centre, one SeCN group and one Schiff base ligand, L (Fig. 4). A
i
i
selenium atom (Se1 ) from a symmetry-related ( =1-x,1-y,2-z) selenocyanate coordinates to the
1
copper(I) centre to form a dimer, [Cu
2
(L )
2
(SeCN) ]. The two copper(I) centres in the dimeric
2
unit are linked by two selenium atoms of two SeCN groups, with the formation of a planar four
membered Cu Se cycle. The angles at copper(I) and selenium in the Cu Se cycle are
approximately 107 and 73° respectively. Similar cyclic fragments are known [48-49]. A nitrogen
2
2
2
2
ii
ii
atom (N1 ) from another symmetry-related ( =-x,1-y,2-z) selenocyanate is also coordinated to
-
the copper(I) centre to complete its tetrahedral geometry. Each SeCN thus bridges three
copper(I) centres in the µ-1,1,3 fashion to form a double strand stair polymer of the complex
(
Fig. 5). The complex can thus better be represented as [Cu
2
L
2
(µ-1,1,3-SeCN)
2
n
] . The four-
membered Cu–Se–Cu–Se rings are fused with eight-membered Cu–NCSe–Cu–NCSe rings in the
stair-polymer, thereby causing increased strain in the complex. The increased strain is reflected
in the significant lengthening of the Cu–Se bond length [Cu(1)-Se(1) = 2.7451(5) Å].
Copper(I) in the asymmetric unit has a distorted tetrahedral geometry [angles at
-
copper(I) range from 95 to 135°]. The SeCN group is almost linear [Se(1)–C(17)–N(1) =
1
77.8(3)°]. The shortest inter-atomic distance between two copper(I) centres within the cluster is

3
.117(6) Å, larger than the sum of the van der Waals radii (2.80 Å). Selected bond lengths and
bond angles are given in the Table 4.
The complex forms a 2D layer structure by significant C–H⋅⋅⋅π interactions between the
methylene hydrogen atom H(1A) attached to C(1) of the Schiff base with the phenyl ring [C(4)–
C(5)–C(6)–C(7)–C(8)–C(9)] present in a symmetry related (1-x,1-y,1-z) adjacent moiety (Fig.
6
). Geometric features of the C–H⋅⋅⋅π interactions are given in Table 3.
2
(L )
[
Cu
2
(µ
2
-I)
2
2
] (3)
Complex 3 crystallizes in the triclinic space group P-1.The structural representation is
shown in Fig. 7 and important bond lengths and angles are listed in Table 2. The complex
features a double iodide bridged copper(I) dimer, in which two trigonal planar copper(I) centers
are bridged by two centrosymmetrically related iodide ligands. Within the dimeric units, each of
the two copper(I) centres is tri-coordinated, being bonded to one nitrogen atom, N(1), of the
iv iv
ligand, one iodide, I(1), and another symmetry related iodide, I(1) ( = -x,-y,1-z). The angles
around the copper(I) centres deviate slightly from 120° (120.02(3), 111.31(11) and 128.47(11)°)
and this indicates slight pyramidalization of the trigonal planar geometry. The Cu-N and Cu-I
distances are comparable to those reported in the literature [47].
iv
The intra-dimer Cu(1)⋅⋅⋅Cu(1) distance is 2.573(1) Å, which is much smaller than the sum
of the van der Waals radii (2.80 Å), indicating copper-copper bond formation [50]. The
Cu(I)⋅⋅⋅Cu(I) distance is 2.536(6) Å in a similar complex reported in the literature [47]. The
1
0
attractive interactions between these types of closed-shell d metal ions are receiving great
attention nowadays because of their interesting structural, optical and electronic properties [51-

5
3]. This behavior has been frequently observed for Au, with the term “aurophilicity” being
coined to describe Au(I)-Au(I) interactions [54-57].
IR and electronic spectra
-1
Distinct bands due to the azomethine (C= N) group were observed around 1600 cm in
the IR spectra of all the complexes. Precursor complexes A and B show broad bands at 1093 and
-1
1
092 cm respectively due to the presence of the perchlorate anion (Figures S5 and S6,
-1
Supplementary Information) [58]. In the IR spectrum of complex 2, a strong band at 2109 cm
is observed (νC≡N) due to the presence of the SeCN group.
The electronic spectra of complexes A, B and 1 were recorded in acetonitrile solution
(
Figures S7, S8 and S9, Supplementary Information). All three complexes show absorption
bands in the UV region due to charge transfer transitions [59]. Precursor complex A shows a
broad absorption band in the visible region (620 nm) due to a d-d transition. In the absorption
spectrum of precursor complex B, the d–d transition band cannot be observed as it is obscured by
a strong charge transfer transition. The band at 368 nm in the electronic spectrum of 1 may be
assigned as a MLCT transition. The UV-VIS spectra of complexes 2 and 3 were recorded in the
solid state, as they are insoluble in acetonitrile and in other solvents as well. Solid state diffuse
reflectance UV-VIS spectra of complexes 2 and 3 show broad absorption bands between 300 and
6
00 nm, which may be assigned as copper(I) to ligand charge transfer transitions (Figure S10,
Supplementary Information) [59].
Luminescent properties
The copper(II) complexes A and B show luminescent emission bands at 460 and 418 nm,
respectively, upon excitation at 370 nm in acetonitrile. The excitation and absorption spectra of

both complexes are very similar in nature. (Figures S7 and S8, Supplementary Information). The
luminescence spectra of complexes A and B were also measured in other solvents (Figures 8 and
9
). The positions of the emission bands are given in Table S1 (Supplementary Information). It is
noteworthy that the emission band of complex A is shifted a little towards lower wavelength in
DMSO, THF and ethanol, whereas the emission band of complex B is shifted a little towards
higher wavelength in DMSO, methanol and ethanol.
The relative stabilities of the two neighboring oxidation states of copper(I) [i.e. copper(0)
and copper(II)] allows the direction of charge transfer transitions in copper(I) complexes to
3
depend on the nature of the ligand. As a consequence, emissions from XLCT [halide (X) to
3
3
ligand charge transfer], LMCT [ligand to metal charge transfer] and MLCT [metal to ligand
charge transfer] luminactive states have been observed with the appropriate ligands as well as
from metal centered (d-s) states [60]. Short copper-copper distances also influence the energies
of the luminactive states and thereby constitute the most characteristic photo-physical features of
polynuclear copper(I) complexes [61,62]. Complex 1 shows a luminescent emission band
centered at 445 nm upon excitation at 370 nm in acetonitrile solution. The luminescence
spectrum of complex 1 was also measured in other solvents (Figure 10) and the positions of the
emission bands are gathered in Table S1 (Supplementary Information). It is observed that the
emission is shifted a little towards lower wavelength in DMSO and DMF. Solid-state emission
spectra of powders of 2 and 3 are shown in Figure 11. The emission bands could be assigned to a
combination of ligand-to-metal charge-transfer (LMCT) and d–s transitions due to the Cu···Cu
interaction, according to previous literature [63]. The maxima of the emission band of 2 was
observed at 527 nm (λex = 410 nm) at room temperature. The maxima of the emission band of 3
was measured at 573 nm (λex= 420 nm) in the solid state at room temperature.

The fluorescence lifetimes (τ) of the complexes A, B and 1 have been investigated in
acetonitrile solution at room temperature (Figure 12). The fluorescence lifetimes (τ) of
complexes 2 and 3 have been measured in the solid state at room temperature (Figure 13). Decay
profiles were fitted to a multi-exponential model:
−
t
I
(
t
)
= α exp( )
∑
i
τi
i
2
where bi-exponential functions were used to fit the respective emission, obtaining χ close to 1.0.
We also report the intensity-averaged life times (τav) in Table 5, determined from the results of
the exponential model using:
2
i i
ατ
∑
i
τ =
av
ατ
∑
i i
i
where α
i
and τ are the pre-exponential factors and excited-state luminescence decay times
i
associated with the i-th component, respectively.
EPR spectra and magnetic moment
The X-band EPR spectra of both the precursor complexes A and B at room temperature
(
Figure S11, Supplementary Information) show an isotropic band centered at g = 2.06 (3280 G
for ν = 9.442 GHz). Copper(I) complexes (1, 2 and 3) are EPR inactive as they do not contain a
paramagnetic centre.

Room temperature magnetic susceptibility measurements show that the precursor
complexes A and B have magnetic moments close to 1.73 BM, as expected for a discrete
magnetically non-coupled spin-only copper(II) centre. Complexes 1, 2 and 3 are diamagnetic as
10
expected for d copper(I) species.
Thermogravimetric analysis
Thermogravimetric measurements were performed in a dry nitrogen atmosphere. The TG
plot for complex 1 is shown in Figure 14. There are two zones of weight loss in the ranges 160-
4
2
00 and 400-700 ºC. The first zone of weight loss (~45%) converts complex 1 completely into
CuI (theoretical weight loss = 44.73%). In the second zone, CuI completely loses iodine
(
weight loss ~40%) and transforms to copper (theoretical weight loss ~40.05%). A TG plot of
complex 2 is shown in Figure S12 (Supplementary Information). There are three zones of weight
loss in the ranges 140-250, 250-400 and 400-800 ºC. The first zone of weight loss (~41%)
converts complex 2 completely into CuSeCN (theoretical weight loss = 41.8%). The second zone
of weight loss (~10%) is due to the formation of Cu Se (theoretical weight loss = 10.22%). In
2
the third zone (weight loss~19%), the sample completely loses the selenium and transforms to
copper (theoretical weight loss ~19.5%). A TG plot for complex 3 is shown in Figure S13
(
Supplementary Information). There are again two zones of weight loss, 200-430 and 430-800
ºC. The first zone of weight loss (~42%) converts complex 3 completely into 2CuI (theoretical
weight loss= 42.7%). The second zone of weight loss (~43%) is due to the liberation of iodine
from CuI. In this zone, the sample completely loses the iodine and transforms to copper
(
theoretical weight loss = 42.96%).
Conclusion

The synthesis and characterization of three copper(I) complexes based on two Schiff base
ligands have been described in this paper. The molecular and crystalline architectures of the
three complexes are different. All of the complexes were easily prepared and all were stable in
air. They showed characteristic MLCT transitions, demonstrated by the electronic absorption
spectra. All the complexes gave efficient luminescence at room temperature. Synthetic simplicity
is a desirable property for luminescent molecular systems. The ease of synthesis of these
complexes provides an opportunity to expand the available emission colors and to facilitate a
more detailed study of the photophysical states contributing to their luminescence properties.
Acknowledgement
This work is supported by CSIR, India (Sanction number. 01(2730)/13/EMR-II
dated 18.04.2013). S. J. would like to thank CSIR, Government of India for proving a fellowship
(
Sanction No. 09/096(0659)/2010-EMR-I, dated 18.1.11). Crystallographic data were collected
at the DST-FIST, India funded Single Crystal Diffractometer Facility at the Department of
Chemistry, Jadavpur University.

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6

Table 1: Crystal data and refinement details of complexes 1, 2 and 3
Complex
Formula
1
2
3
C
32
H
28Cu
2
I
2
N
4
C
17
H
14CuN
3
Se
C
36
H
36Cu
2
I
2
N
4
O
4
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
849.48
293
402.82
293
969.59
293
Monoclinic
P2 /c
Triclinic
P-1
Triclinic
P-1
1
10.0065(3)
20.4846(6)
15.6454(4)
90
6.090(2)
7.2761(3)
8.0183(3)
b (Å)
10.5263(4)
12.4493(4)
92.506(2)
102.217(2)
98.667(2)
2
c (Å)
16.5008(7)
76.496(2)
80.033(2)
72.356(2)
1
α (deg)
β (deg)
94.242(1)
90
γ (deg)
Z
4
-3
d
calc (g cm )
1.764
1.740
1.816
-1
µ (mm )
F(000)
3.287
3.786
2.985
1648
400
476
Total reflections
53786
9790
13464
14750
5184
Unique reflections
4570
Observed data [I > 2 σ (I)]
No. of parameters
R(int)
5700
361
3011
199
3864
219
0.040
0.042
0.043
R1, wR2 ( all data)
R1, wR2 [I > 2 σ (I)]
0.0792, 0.1279 0.0677, 0.1049
0.0417, 0.1146 0.0408, 0.0940
0.0623, 0.1604
0.0535, 0.1530

Table 2: Selected bond lengths (Å) and bond angles (°) for complexes 1 and 3
1
3
Cu(1)– I(1)
2.503(6)
-
2.6002(7)
iv
Cu(1)–I(1)
Cu(2)- I(2)
2.5452(7)
2.496(6)
1.999(3)
1.986(3)
2.002(3)
1.990(3)
124.86(9)
128.73(9)
106.41(12)
119.22(9)
133.14(9)
107.43(12)
-
-
Cu(1)-N(1)
1.972(3)
Cu(1) –N(4)
-
Cu(2)-N(2)
-
Cu(2)-N(3)
-
I(1)- Cu(1)- N(1)
I(1) - Cu(1)- N(4)
N(1) - Cu(1) - N(4)
I(2)- Cu(2) - N(2)
I(2)- Cu(2)- N(3)
N(2)- Cu(2)- N(3)
111.31(11)
-
-
-
-
-
iv
Cu(1)- I(1) - Cu(1)
59.99(2)
120.02(3)
128.47(11)
iv
I(1) -Cu(1) -I(1)
-
iv
I(1) –Cu(1) –N(1)
-
iv
Symmetry element, = -x,-y,1-z.

Table 3: Geometric features of the C–H···π interactions of complexes 1 and 2.
Complex
C–H····Cg(Ring)
C(9)–H(9A)···Cg(4)
C(10)–H(10A)···Cg(6)
C(19)–H(19A)···Cg(5)
C(1)–H(1A)···Cg(4)
H····Cg (Å)
2.83
C–H····Cg (°)
C····Cg (Å)
3.684(4)
3.806(4)
3.482(4)
3.514(4)
Symmetry
x,y,z
147
165
147
131
1
2
2.86
x,y,z
2.63
x,y,z
2.80
1-x,1-y,1-z
Cg(4) = Centre of gravity of the 6-membered ring [C(3)–C(4)–C(5)–C(6)–C(7)–C(8)], Cg(5) =
Centre of gravity of the 6-membered ring [C(12)–C(13)–C(14)–C(15)–C(16)–C(17)], Cg(6) =
Centre of gravity of the 6-membered ring [C(21)–C(22)–C(23)–C(24)–C(25)–C(26)] for
complex 1, Cg(4) = Centre of gravity of the 6-membered ring [C(4)–C(5)–C(6)–C(7)–C(8)–
C(9)] for complex 2.

Table 4: Selected bond lengths (Å) and bond angles (°) for complex 2.
Cu(1)-Se(1)
2.7455(5)
2.4882(5)
2.013(2)
i
Cu(1) -Se(1)
Cu(1)-N(2)
ii
Cu(1)-N(1)
1.953(3)
Cu(1)-Se(1)-C(17)
96.01(10)
72.93(1)
i
Cu(1)-Se(1)-Cu(1)
i
Cu(1) - Se(1)-C(17)
104.47(9)
102.70(6)
95.86(6)
Se(1)-Cu(1)-N(2)
ii
Se(1)-Cu(1)-N(1)
i
Se(1)-Cu(1)-Se(1)
107.07(2)
134.69(10)
104.43(7)
108.98(7)
166.6(2)
ii
N(1) -Cu(1)-N(2)
i
Se(1) -Cu(1)-N(2)
i
ii
Se(1) -Cu(1)-N(1)
ii
Cu(1) -N(1)-C(17)
i
ii
Symmetry element, = 1-x,1-y,2-z, = -x,1-y,2-z.

Table 5: Decay parameters of the product monitored at their respective emission maxima using a
3
75 nm LASER:
2
A
1
(%)
τ1 (ns)
2.76
1.64
1.74
0.52
0.43
A
2
(%)
τ2 (ns)
7.62
5.04
4.09
2.16
1.80
τav(ns)
5.14
3.70
2.29
1.84
1.70
χ
Complex A
Complex B
Complex 1
Complex 2
Complex 3
74.19
66.73
88.51
50.32
28.6
25.81
33.27
11.49
49.68
71.4
1.05
1.01
1.09
0.99
1.04

Legends to the Figures
Figure 1: Asymmetric unit of complex 1 with the selective atom numbering scheme.
Hydrogen atoms are omitted for clarity.
Figure 2: Perspective view of the one dimensional chain of complex 1. Hydrogen atoms are
omitted for clarity.
Figure 3: C–H⋅⋅⋅π interactions in complex 1. Cg(4) = Centre of gravity of the 6-membered
ring [C(3)–C(4)–C(5)–C(6)–C(7)–C(8)], Cg(5) = Centre of gravity of the 6-membered ring
[
C(12)–C(13)–C(14)–C(15)–C(16)–C(17)], Cg(6) = Centre of gravity of the 6-membered
ring [C(21)–C(22)–C(23)–C(24)–C(25)–C(26)]
Figure 4: Perspective view of complex 2 with the selective atom numbering scheme.
Figure 5: 1-D stair polymer of complex 2. Hydrogen atoms are omitted for clarity.
i
ii
Symmetry element, = 1-x,1-y,2-z, = -x,1-y,2-z.
iii
Figure 6: (a) C–H⋅⋅⋅π interactions in complex 2. Symmetry element, = 1-x,1-y,1-z. Cg(4) =
Centre of gravity of the 6-membered ring [C(4)–C(5)–C(6)–C(7)–C(8)–C(9)]. (b) 2D array of
the complex containing C–H⋅⋅⋅π interactions.
Figure 7: Perspective view of complex 3 with the atom numbering scheme of the relevant
iv
atoms. Hydrogen atoms are omitted for clarity. = -x,1-y,1-z.
Figure 8: Luminescence spectra of complex A in different solvents.
Figure 9: Luminescence spectra of complex B in different solvents.
Figure 10: Luminescence spectra of complex 1 in different solvents.
Figure 11: Solid state luminescence spectra of complexes 2 and 3.
Figure 12: Luminescence life-time of complexes A, B and 1 in acetonitrile.
Figure 13: Luminescence life-time of complexes 2 and 3 in the solid state.
Figure 14: TG plot of complex 1.

Figure 1