Copper(I) Complexes of N-(2-{[(2E)-2-(4-Nitrobenzylidenyl)Hydrazinyl]Carbonyl}Phenyl)Benzamide and Triphenylphosphine: Synthesis, Characterization and Luminescence Properties

Article abstract of DOI:10.1007/s10895-016-1897-x

Copper(I) complexes of the formula [Cu(L)(PPh₃)₂]X (1–4) (X?=?Cl(1), ClO₄(2), BF₄(3) and PF₆(4)) [where L?=?N-(2-{[(2E)-2-(4-nitrobenzylidenyl)hydrazinyl]carbonyl}phenyl)benzamide; PPh₃?=?triphenylphosphine] have been prepared by the condensation of N-[2-(hydrazinocarbonyl)phenyl]benzamide with 4-nitrobenzaldehyde followed by the reaction with CuCl, [Cu(MeCN)₄]ClO₄, [Cu(MeCN)₄]BF₄ and [Cu(MeCN)₄]PF₆ in presence of triphenylphosphine as a coligand. Complexes 1–4 were then characterized by elemental analyses, FTIR, UV-visible and ¹H NMR spectroscopy. Mononuclear copper(I) complexes 1–4 were formed with L in its keto form by involvement of azomethine nitrogen and the carbonyl oxygen along with two PPh₃ groups. A single crystal X-ray diffraction study of the representative complex [(Cu(L)(PPh₃)₂]CIO₄ (2) reveals a distorted tetrahedral geometry around Cu(I). Crystal data of (2): space group = C2/c, a?=?42.8596 (9) ?, b?=?14.6207 (3) ?, c?=?36.4643 (7) ?, V?=?20,653.7 (7) ?³, Z?=?16. Complexes 1–4 exhibit quasireversible redox behaviour corresponding to a Cu(I)/Cu(II) couple. All complexes show blue-green emission as a result of fluorescence from an intra-ligand charge transition (ILCT), ligand to ligand charge transfer transition (LLCT) or mixture of both. Significant increase in size of the counter anion shows marked effect on quantum efficiency and lifetime of the complexes in solution.

Full text of DOI:10.1007/s10895-016-1897-x

J Fluoresc
DOI 10.1007/s10895-016-1897-x
ORIGINAL ARTICLE
Copper(I) Complexes of N-(2-{[(2E)-2-(4-Nitrobenzylidenyl)
Hydrazinyl]Carbonyl}Phenyl)Benzamide
and Triphenylphosphine: Synthesis, Characterization
and Luminescence Properties
S. S. Chavan1 & S. B. Pawal1 & M. S. More1 & A. C. Willis2
Received: 13 June 2016 /Accepted: 26 July 2016
#
Springer Science+Business Media New York 2016
Abstract Copper(I) complexes of the formula [Cu(L)(PPh3)2]
X (1–4) (X = Cl(1), ClO4(2), BF4(3) and PF6(4)) [where
L = N-(2-{[(2E)-2-(4-nitrobenzylidenyl)hydrazinyl]
carbonyl}phenyl)benzamide; PPh3 = triphenylphosphine]
have been prepared by the condensation of N-[2-
(hydrazinocarbonyl)phenyl]benzamide with 4-
nitrobenzaldehyde followed by the reaction with CuCl,
[Cu(MeCN)4]ClO4, [Cu(MeCN)4]BF4 and [Cu(MeCN)4]PF6
in presence of triphenylphosphine as a coligand. Complexes
1–4 were then characterized by elemental analyses, FTIR,
UV-visible and 1H NMR spectroscopy. Mononuclear
copper(I) complexes 1–4 were formed with L in its keto form
by involvement of azomethine nitrogen and the carbonyl oxy-
gen along with two PPh3 groups. A single crystal X-ray diffrac-
tion study of the representative complex [(Cu(L)(PPh3)2]CIO4
(2) reveals a distorted tetrahedral geometry around Cu(I).
Crystal data of (2): space group = C2/c, a = 42.8596 (9) Å,
b = 14.6207 (3) Å, c = 36.4643 (7) Å, V = 20,653.7 (7) Å3,
Z = 16. Complexes 1–4 exhibit quasireversible redox behav-
iour corresponding to a Cu(I)/Cu(II) couple. All complexes
show blue-green emission as a result of fluorescence from an
intra-ligand charge transition (ILCT), ligand to ligand charge
transfer transition (LLCT) or mixture of both. Significant
increase in size of the counter anion shows marked effect on
quantum efficiency and lifetime of the complexes in solution.
.
.
Keywords Copper(I) complexes Crystal structure
Luminescence properties
Introduction
Copper(I) complexes have attracted considerable attention on
account of their unusual structural features, utility in solar
energy and supramolecular devices, luminescent properties,
catalytic and biological relevance [1–4]. They are environ-
mentally friendly, less expensive and possesses intriguing co-
ordination modes and exhibit a wide range of photochemical
and photophysical properties [5, 6]. Owing to favourable soft
acid-soft base interaction, the chemistry of this closed-shell
d10 metal ion is largely depends upon the mode of coordina-
tion of the ligands. The steric, electronic and conformational
effects imparted by these ligands play an essential role in
stabilizing the copper(I) state and modifying the physical
and chemical properties of the prepared complexes.
Copper(I) complexes with N, S, P potentially donor ligands
have been extensively studied due to their wide variation in
structural motifs and rich photophysical properties [7–9].
However, only a few complexes with O-donor ligands have
been synthesized and structurally characterized [10, 11].
Among the various ligands hydrazone represent as an impor-
tant series of Schiff bases which contain several potential do-
nor sites and so act as major polydentate ligands. They play an
important role in medicinal chemistry and have a wide range
of applications in catalysis, medicine, corrosion and analytical
chemistry as well as in functional materials [12–14]. As they
have a wide range of biological and pharmaceutical activities
and a strong tendency to chelate with transition metals [15],
Electronic supplementary material The online version of this article
(doi:10.1007/s10895-016-1897-x) contains supplementary material,
which is available to authorized users.
* S. S. Chavan
sanjaycha2@rediffmail.com
1
Department of Chemistry, Shivaji University,
Kolhapur, (MS) 416004, India
2
Research School of Chemistry, Australian National University,
Canberra, ACT 2601, Australia

J Fluoresc
lanthanide metals [16] and main group metals [17], the coor-
dination chemistry of hydrazone has been intensively investi-
gated. Acylhydrazone particularly, which contains the keto-
type structure (−O = C-N-N = C-) are useful ligands for the
construction of novel coordination compounds with diverse
structures due to the multiple active coordination sites and rich
coordination modes. Also, they are capable of yielding supra-
molecular architecture and polymeric materials featuring
bridging and oxobridging. Metal complexes of acylhydrazone
have proven to have potential applications as catalysts [18],
luminescent probes [19] and molecular sensors [20]. More
recently hydrazone chelators have been used in the treatment
of iron overload diseases such as β-thalasemia [21].
In this paper, we report the synthesis of some copper(I)
complexes (1–4) derived by the reaction of N-(2-{[(2E)-
2-(4-nitrobenzylidenyl)hydrazinyl]carbonyl}phenyl)
b e n z a m i d e w i t h C u C l , [ C u ( C H 3 C N ) 4 ] C l O 4 ,
[Cu(CH3CN)4]BF4 and [Cu(CH3CN)4]PF6 in the presence
of triphenylphosphine. All the compounds were characterized
by elemental analysis, spectroscopic techniques and com-
pound 2 by X-ray crystallography. The electrochemical and
luminescent properties of the complexes are also reported.
the supporting electrolyte and all measurements were carried
out in CH2Cl2 solution at room temperature with a scan rate of
100 mVs−1.
Synthesis of Ligand (L)
N-(2-{[(2E)-2-(4-nitrobenzylidenyl)hydrazinyl]carbonyl}
phenyl)benzamide (L) was prepared by adopting and modify-
ing the method described in the literature [27]. An intimate
mixture of N-[2-(hydrazinocarbonyl)phenyl]benzamide
(1 mmol, 0.255 g) and 4-nitrobenzaldehyde (1 mmol,
0.151 g) in ethanol (20 ml) was refluxed for 5 h in the presence
of a few drops of acetic acid. On partial removal of the solvent
the product obtained was filtered, washed with ethanol and
dried in vacuo.
Yield: 91 %; Elemental analyses (C, H, N, wt%) Anal.
Calc. for C21H16N4O4: C,64.94; H, 4.15, N, 14.43; found:
C, 64.90; H, 4.05; N, 14.60; IR (KBr; cm−1); 3248, υ(NH);
1
1686, υ(C = O); 1618, υ(HC = N); H NMR (CDCl3;
300 MHz): δ 8.26 (s, 1H, HC = N), δ 10.30 (s, N-NHCO), δ
8.56 (s, C6H5CONH), δ 6.65–8.18 (m, phenyl); MS(EI): m/e
388.12 (M+).
Synthesis of [Cu(L)(PPh3)2]Cl (1)
Experimental
To a 10 ml acetonitrile solution of CuCl (1 mmol, 0.0989 g), 2
equivalent of triphenylphosphine (2 mmol, 0.522 g) were
added and the solution was stirred for 30 min. The solvent
was evaporated under vacuum at room temperature. The crys-
talline product [Cu(MeCN)2(PPh3)2]Cl obtained was added to
a solution of ligand L (1 mmol, 0.388 g) in 10 ml dichloro-
methane and stirred for 2 h at room temperature. The volume
of solvent was reduced under vacuum and the solid product
was produced by diffusion of diethyl ether into the filtrate.
Yield: 82 %; Elemental analyses (C, H, N, wt%) Anal.
Calc. for C57H46CuN4O4P2Cl: C,67.65; H, 4.58, N, 5.54;
found: C, 67.63; H, 4.57; N, 5.58; IR (KBr; cm−1); 3242,
υ(NH); 1657, υ(C = O); 1587, υ(HC = N); 1480, 1436, 696,
518, υ(PPh3); UV-Vis (CH2Cl2) λmax (nm)(ε x103,
General Methods
All chemicals used were of reagent grade and used as re-
ceived. N-(2-Hydrazinocarbonyl-phenyl)-benzamide was pre-
pared as previously reported [22]. The copper(I) compounds
CuCl [23], [Cu(MeCN)4]ClO4 [24] , [Cu(MeCN)4]BF4 [25]
and Cu(MeCN)4PF6 [26] were prepared according to litera-
ture procedures.
Elemental analyses (C, H and N) of the copper(I) com-
plexes were conducted on Thermo Finnegan FLASH EA-
1112 CHNS analyzer. IR spectra were recorded on a Perkin-
Elmer-100 FTIR Spectrometer. 1H NMR spectra of the sam-
ples dissolved in CDCl3 were measured on a Bruker 300 MHz
instrument using TMS [(CH3)4Si] as an internal standard of
chemical shifts (ppm). Electronic spectra were recorded in
dichloromethane (10−4 M) on a Shimadzu 3600 UV-Vis-NIR
spectrophotometer. Emission spectra were recorded using a
Perkin-Elmer LS 55 spectrofluorometer equipped with quartz
cuvettes of 1 cm3 path length at room temperature. Mass spec-
tra were measured on a GCMS Shimadzu-2010.
Luminescence lifetime measurements were carried out by
using time-correlated single photon counting on HORIBA
Jobin Yvon. Thermal analysis of the complexes was carried
out in nitrogen atmosphere at a heating rate of 10 °C/min on a
Perkin-Elmer thermal analyzer. Cyclic voltammetry measure-
ments were performed with a CH-400 A electrochemical an-
alyzer. Tetrabutyl ammonium perchlorate (TBAP) was used as
1
M−1 cm−1): 263 (16.92), 292 (9.44), 368 (2.80); H NMR
(CDCl3; 300 MHz): δ 8.32 (s, 1H, HC = N), δ 10.34 (s, N-
NHCO), δ 8.62 (s, C6H5CONH), δ 6.67–7.88 (m, phenyl).
Synthesis of [Cu(L)(PPh3)2]ClO4 (2)
Complex 2 was prepared by a procedure similar to that used
for the preparation of 1 except that CuCl was replaced by
[Cu(CH3CN)4]ClO4 (0.3335 g, 1 mmol).
Yield: 81 %; Elemental analyses (C, H, N, wt%) Anal. Calc.
for C57H46CuN4O8P2Cl: C,63.63; H, 4.31, N, 5.21; found: C,
63.60; H, 4.28; N, 5.23; IR (KBr; cm−1); 3243, υ(NH); 1661,
υ(C = O); 1593, υ(HC = N); 1481, 1436, 697, 518, υ(PPh3);
1095, 621, υ(ClO4); UV-Vis (CH2Cl2) λmax (nm) (ε x103,

J Fluoresc
1
M−1 cm−1): 267 (22.85), 298 (9.15), 374 (1.78); H NMR
(CDCl3; 300 MHz): δ 8.34 (s, 1H, HC = N), δ 10.31 (s, N-
NHCO), δ 8.68 (s, C6H5CONH), δ 6.65–7.89 (m, phenyl).
Table 1 Crystallographic data and refinement parameters for
complex 2
Empirical formula
C57H46ClCuN4O8P2
Formula weight
Crystal system
Space group
a (Å)
1057.97
Synthesis of [Cu(L)(PPh3)2]BF4 (3)
Monoclinic
C2/c
Complex 3 was prepared by a procedure similar to that used
for the preparation of 1 except that CuCl was replaced by
[Cu(CH3CN)4]BF4 (0.3205 g, 1 mmol).
Yield: 80 %; Elemental analyses (C, H, N, wt%) Anal. Calc.
for C57H46CuN4O4F4BP2: C,64.39; H, 4.36, N, 5.27; found: C,
64.33; H, 4.32; N, 5.30; IR (KBr; cm−1); 3245, υ(NH); 1659,
υ(C = O); 1589, υ(HC = N); 1480, 1436, 696, 518, υ(PPh3);
1057, υ(BF4); UV-Vis (CH2Cl2) λmax (nm)(ε x103, M−1 cm−1):
42.8596(9)
14.6207(3)
36.4643(7)
90.00
b (Å)
c (Å)
α (°)
β (°)
115.3263(6)
90.00
γ (°)
V (A3)
20,653.7(7)
16
1
Z
264 (20.86), 294 (7.53), 372 (1.02); H NMR (CDCl3;
300 MHz): δ 8.31 (s, 1H, HC = N), δ 10.36 (s, N-NHCO), δ
8.65 (s, C6H5CONH), δ 6.71–7.98 (m, phenyl).
Density (g/cm3)
μ (M0Kα)(mm−1
1.384
)
0.71073
F (000)
8896
Synthesis of [Cu(L)(PPh3)2]PF6 (4)
Temperature (K)
200
θ minimum-maximum (deg)
Data set [h, k, l]
Observed data
Refinement
3.0 to 27.5
-55/55,-18/18,-47/42
I > 2.0σ(I)
Full-matrix least-squares on F2
0.0430, 0.0839
0.0787, 0.1038
0.951
Complex 4 was prepared by a procedure similar to that used
for the preparation of 1 except that CuCl was replaced by
[Cu(CH3CN)4]PF6 (0.3799 g, 1 mmol).
Yield: 78 %; Elemental analyses (C, H, N, wt%) Anal.
Calc. for C57H46CuN4O4P3F6: C,61.05; H, 4.13, N, 5.00;
found: C, 60.98; H, 4.02; N, 5.09; IR (KBr; cm−1); 3244,
υ(NH); 1655, υ(C = O); 1588, υ(HC = N); 1481, 1436, 696,
519, υ(PPh3); 842, 556, υ(PF6); UV-Vis (CH2Cl2) λmax
(nm)(ε x103, M−1 cm−1): 262 (23.21), 298 (12.72), 377
(2.73); 1H NMR (CDCl3; 300 MHz): δ 8.32 (s, 1H,
HC = N), δ 10.33 (s, N-NHCO), δ 8.63 (s, C6H5CONH), δ
6.71–7.92 (m, phenyl).
R1, R1
wR2, wR2
Goodness-of-fit
hydrazinyl]carbonyl}phenyl)benzamide (L) was synthesized
by the reaction of N-[2(hydrazinocarbonyl)phenyl]benzamide
with 4-nitrobenzaldehyde. The obtained spectral data, elemen-
tal analysis and mass spectra confirm the formation of L. The
mononuclear copper(I) complexes 1–4 possessing L and
phosphine ligands were prepared via two simple steps. The
complexes [Cu(L)(PPh3)2]X (X = Cl, ClO4, BF4 and PF6)
were firstly afforded by the treatment of [Cu(CH3CN)4]X
(X = Cl, ClO4, BF4 and PF6) with two equivalent of PPh3 then
one equivalent of L was slowly added. All the complexes
were microcrystalline solids that were soluble in common
organic solvents like dichloromethane, chloroform, acetoni-
trile, methanol, ethanol etc. Elemental analyses (C, H and N)
given in section 2 confirm the assigned composition of the
complexes. At room temperature all the complexes are dia-
magnetic, which is characteristic of Cu(I) (d10).
X-Ray Crystallography
A single crystal of [Cu(L)(PPh3)2]ClO4 (2) suitable for X-ray
analysis was obtained by slow evaporation of saturated solu-
tion of complex in dichloromethane. X-ray intensity data were
collected on a Nonius Kappa CCD diffractometer with
graphite-monochromatized MoKα radiation. The details of
crystal data, data collection and the refinement are given in
Table 1. The structure was solved by direct methods using the
SIR 92 program and refined by using CRYSTAL 97 software
[28]. The non-hydrogen atoms were refined with anisotropic
thermal parameters. All of the hydrogen atoms bonded to C
were refined using a riding model and H atoms bonded to N
were allowed to refine freely.
Results and Discussion
Spectroscopic Properties
The synthetic route to the formation of complexes 1–4 is
shown in Scheme 1. N-(2-{[(2E)-2-(4-nitrobenzylidenyl)
The IR spectrum of L exhibits a broad band at 3248 cm−1
which is characteristic of a ν(NH) vibration. This band

J Fluoresc
remains unchanged in 1–4, providing strong evidence for non-
involvement of the NH proton [29]. Another characteristic
band at 1686 cm−1 in L is assigned to ν(C = O) vibration
shifted to lower frequency by 25–31 cm−1 in 1–4 providing
strong evidence of the involvement of a carbonyl oxygen in
the complexation with copper(I) via its keto form [30]. A band
at 1618 cm−1 in the spectrum of free ligand L attributed to
ν(C = N) shifts to 1587–1593 cm−1 upon complexation indi-
cating azomethine nitrogen coordination. This was also con-
firmed by the appearance of a new band at ~530 cm−1 in 1–4
due to ν(C-N). The spectra of all of the copper(I) complexes
exhibit the expected bands due to the PPh3 ligand at around
1480, 1436, 696, 518 cm−1. The perchlorate complex 2 exhibit
a broad band at 1095 cm−1(υ3) and a strong band at 621 cm−1
−
(υ4) which is devoid of any splitting suggesting that the ClO4
Fig. 1 Uv-visible spectra of 1–4
anion is not coordinated to the copper(I) [31]. A broad band at
1057 cm−1 in complex 3 corresponds to presence of BF4
−
−
anion in the complex [32]. The presence of the PF6 anion
imine (HC = N) proton. In the spectra of complexes 1–4, the
signal of the imine proton is considerably deshielded and ap-
pears as a singlet at δ 8.31–8.34 ppm due to positive charge
delocalization on the corresponding C-atom through reso-
nance resulting from the coordination of the ligand [35]. The
downfield shift of –N-NHCO signals in the 1H NMR spectra
of 1–4 indicates participation of the hydrazide >CO group
with the metal ion and observed at δ 10.31–10.36 ppm.
However, the broad multiplet observed in the range δ 6.65–
7.98 ppm for 1–4 can be assigned to the phenyl protons of the
phosphine ligand and the ring protons of L.
in 4 is shown by medium intensity band at 842 cm−1 and
556 cm−1 [33].
The UV-visible absorption spectra of 1–4 in CH2Cl2
(10−4 M) at ambient temperature are depicted in Fig.1. The
ligand L shows two absorptions at λmax ≈ 259 and 286 nm,
attributed to the π-π* transitions within L. Complexes 1–4
exhibit multiple absorption peaks in the range 262–298 nm
region most likely coming from ligand L and PPh3. The red
shift of the π-π* absorption of 1–4 is consistent with better
conjugation of the ligands upon coordination, resulting in a
smaller π-π* energy gap. In addition to the high energy ab-
sorptions, complexes 1–4 also display a comparatively weak
low energy absorption at ca 368–377 nm which can most
likely be assigned to metal to ligand charge transfer transitions
from the dπ orbital of the copper(I) center to the unoccupied
π* orbital of the ligand L [34].
X-Ray Crystal Structure
The crystals of [Cu(L)(PPh3)2]ClO4 (2) were grown by slow
diffusion of diethyl ether into a solution of the complex in
dichloromethane and structure was determined by X-ray crys-
tallography. X-ray analysis reveals that the complex 2 crystal-
lizes in monoclinic space group C2/c with two molecules per
asymmetric unit (molecule A and B) showing some small
1H NMR spectra of 1–4 have been measured in CDCl3 at
1
room temperature. The H NMR spectrum of free ligand L
displayed a singlet at δ 8.26 ppm which can be assigned to the
Scheme 1 Synthetic route
of L and its copper(I) complexes
O
O
NO2
O
N
ethanol
+
NO2
N
H
reflux
H
N
H
NH2
O
N
O
N
H
L
H
Cu[(CH3CN)2(PPh3)2]X
CH2Cl2
+
O
N
H
NO2
X= Cl, ClO4, BF4, PF6
O
NH
N
Cu
Ph3P
PPh3
X

J Fluoresc
Table 2 Selected bond lengths (Ǻ) and bond angles (°) for 2
conformational differences. The molecular structure of 2
along with the atom numbering scheme is illustrated in
Fig. 2 and selected bond lengths and bond angles are collected
in Table 2.
Bond lengths
Bond Angles
Cu(1)-P(1)
Cu(1)-P(2)
Cu(1)-O(1)
Cu(1)-N(4)
Cu(2)-P(3)
Cu(2)-P(4)
Cu(2)-O(101)
Cu(2)-N(104)
2.2363(8)
2.2800(8)
2.1818(18)
2.115(2)
P(1)-Cu(1)-P(2)
122.35(3)
114.16(6)
101.04(6)
125.98(7)
104.56(7)
77.57(8)
Complex 2 contains discrete [Cu(L)(PPh3)2]+ cation and
perchlorate anion with highly distorted tetrahedral geometry
around the copper(I) with CuNOP2 coordination. Ligand L is
bonded to the copper ion in a bidentate manner through
azomethine nitrogen and carbonyl oxygen form a five mem-
bered chelate ring. The distorted four-coordinate geometry of
copper(I) is completed by imine nitrogen atom and one car-
bonyl oxygen atom of L and phosphorous atoms of two
triphenylphosphine groups. The largest deviation from the
ideal tetrahedral geometry is arises from the restricted bite
angle of the chelating ligand. The intra-ligand chelate angles
O(1)-Cu(1)-N(4) in A and O(101)-Cu(2)-N(104) in B are
much less than 109.4°, being 77.57(8) and 76.94(8)°, respec-
tively. In contrast, the P(1)-Cu(1)-P(2) angle in A is
122.35(3)° and the P(3)-Cu(2)-P(4) angle in B is 123.22(3)°
have opened up due to steric effects from the bulky PPh3
ligands. The average distance for Cu-N (2.110 Å), Cu-O
(2.171 Å) and Cu-P (2.262 Å) are comparable to those report-
ed for [Cu(A)(PPh3)2]NO3 (2.061, 2.127 and 2.254 Å) [36].
Torsion angles in the chelating ring and hydrazone group
are listed in Table 3. The chelating ring Cu(1)-N(4)-N(3)-C(2)
in A and Cu(2)-N(104)-N(103)-C(102) in B are near planar
and the sums of the three N atom bond angles are 357.96° in A
and 359.95° in B. The significant deviations from 120°for the
angles about the N atom (A: Cu(1)-N(4)-N(3), 108.66(17)°;
Cu(1)-N(4)-C(5), 136.8(2)° and C(5)-N(4)-N(3), 112.5(2)°;
B: Cu(2)-N(104)-N(103), 109.87(15)°; Cu(2)-N(104)-
N(105), 136.38(18)° and C(105)-N(104)-N(103), 113.7(2)°).
P(1)-Cu(1)-O(1)
P(2)-Cu(1)-O(1)
P(1)-Cu(1)-N(4)
P(2)-Cu(1)-N(4)
O(1)-Cu(1)-N(4)
P(3)-Cu(2)-P(4)
2.2668(8)
2.2664(8)
2.1595(18)
2.105(2)
123.22(3)
106.89(6)
105.30(6)
116.71(6)
115.36(6)
76.94(8)
P(3)-Cu(2)-O(101)
P(4)-Cu(2)-O(101)
P(3)-Cu(2)-N(104)
P(4)-Cu(2)-N(104)
O(101)-Cu(2)-N(104)
characterized by a well defined redox process in the positive
potential side. Complexes 1–4 display oxidative response at
0.672–0.688 V (Epa) which is attributed to Cu(I)/Cu(II) oxida-
tion. The potential appearing in the range 0.536–0.548 V (Epc)
is associated with reduction of Cu(II) to Cu(I). A
quasireversible character is observed for all complexes with
the values of ΔEp (ΔEp = Epa-Epc) ranging from 136 to
140 mV under the conditions of the measurements.
Thermal Studies
In order to understand the thermal stability of the complexes,
thermogravimetric (TG) studies of 1, 3 and 4 were carried out
between 25 and 800 °C under a nitrogen atmosphere. The per-
chlorate complex 2 is potentially explosive and hence not stud-
ied for safety reason. Complexes 1, 3 and 4 showed two decom-
position stages. The first decomposition stage takes place in the
region 166–428(1), 172–431(3) and 168–428°(4) corresponding
to mass loss of 50.23, 51.02 and 51.26 %, respectively and is
attributed to the decomposition of coordinated triphenylphosphine
(theoretical mass loss 51.12 % (1), 51.86 % (3) and 52.01 % (4)).
The DTA curve gives exothermic peaks at 187° for 1, 186° for 3
Electrochemistry
The electrochemical properties of 1–4 were examined by cyclic
voltammetrically in 10−3 M CH2Cl2 solution in the potential
range 1.5 V verses SCE electrode and are presented in
Table 4. The electrochemical potential of 1–4 were
Fig. 2 Single crystal X-ray dif-
fraction structure of
[Cu(L)(PPh3)2]ClO4(2)
a
b

J Fluoresc
Table 3 Torsion angles for chelating ring
Table 5 Emission data of 1–4 in CH2Cl2 solution (10−4 M)
complex λex (nm) λem (nm) ϕ
τ (ns) Kr(s−1/107) Knr(s−1/109)
Cu(1)-O(1)-C(2)-N(3)
12.2(4)
Cu(1)-N(4)-N(3)-C(2)
-4.6(4)
-5.5(5)
7.6(2)
1
2
3
4
318
315
316
317
470
482
475
491
0.072 3.19 2.250
0.290
0.269
0.271
0.265
O(1)-C(2)-N(3)-N(4)
0.085 3.39 2.507
0.078 3.41 2.280
0.091 3.42 2.660
O(1)-Cu(1)-N(4)-N(3)
N(4)-Cu(1)-O(1)-C(2)
10.8(2)
-11.8(4)
-4.6(4)
11.6(5)
1.0(2)
Cu(2)-O(101)-C(102)-N(103)
Cu(2)-N(104)-N(103)-C(102)
O(101)-C(102)-N(103)-N(104)
O(101)-Cu(2)-N(104)-N(103)
N(104)-Cu(2)-O(101)-C(102)
thermal vibration decay [37]. There is a significant increase
in the emission energy as well as the emission wavelength of
1–4 as size of the counter anion increases in the sequence
Cl BF4 < ClO4 PF6 as their counter anion [38].
6.8(2)
The fluorescence quantum yields (ϕ) of the complexes
were determined by using quinine sulphate as a reference with
known ϕR of 0.52 and appeared at 0.072–0.091 (Table 5). The
area of the emission spectrum was integrated using the soft-
ware available on the instrument and the quantum yields were
calculated according to the following equation.
and 189° for 4. The second stage shows further loss of
weight from the range 428–656°, 431–658° and 428–
662° along with strong exothermic DTA peaks at 328,
321 and 324 °C accompanied by a mass loss of 36.24
(1), 37.28 (3), 37.92 % (4) attributed to the decomposition
of ligand L leaving CuCl, CuBF4 and CuPF6 as the final
residue (theoretical mass loss 37.02, 37.48 and 38.15 %).
Â
Ã
Â
Ã
ðAbsÞ
ηS2
½η2RŠ
ϕS ½ASŠ
¼
ðAbsÞRS
Â
Ã
X
X
ϕR ½ARŠ
Fluorescence Spectral Studies
Here ϕS and ϕR are the fluorescence quantum yield of the
sample and reference, respectively. AS and AR are the areas
under the fluorescence spectra of the sample and reference,
respectively, (Abs)S and (Abs)R are the respective optical den-
sities of the sample and the reference solution at the wave-
length of excitation and ηs and ηR are the values of refractive
index for the respective solvent used for the sample and refer-
ence. The results obtained are in good agreement with those
values reported in the literature [39]. The life time data of the
complexes were obtained upon excitation at 320 nm and are
summarized in Table 5. The observed decay of the complexes
The fluorescence emission properties of L and complexes 1–4
have been investigated at room temperature in CH2Cl2 solu-
tion (10−4 M) and the data are displayed in Table 5. The ligand
L exhibits an emission in the blue region centered at
λmax = 428 nm with an excitation maximum at 312 nm attrib-
uted to the fluorescence emission stemming from a ligand-
centered π-π* transition. In contrast, complexes 1–4 show
steady state marked differences in emission behavior in di-
chloromethane solution. As shown in Fig. 3, the spectra of
1–4 exhibit a broad emission profile in degassed CH2Cl2 at
room temperature with λmax at 470–491 nm upon excitation at
315–318 nm. Thus the fluorescence emission observed in 1–4
can be attributed to an intra-ligand charge transition (ILCT), a
ligand to ligand charge transfer transition (LLCT) or mixture
of both. The enhancement of fluorescence efficiency in all the
complexes can be attributed to coordination of the ligands to
copper(I) ion which effectively increases the rigidity of the
ligands and reduced the loss of energy via radiation less
Table 4 Electrochemical data for copper(I) complexes (1–4)
Complex
Epa (V)
Epc (V)
ΔEp (mV)
E1/2 (V)
1
2
3
4
0.688
0.672
0.676
0.683
0.548
0.536
0.539
0.544
140
136
137
139
0.618
0.604
0.607
0.613
Supporting electrolyte: n-Bu4NClO4 (0.05 M); complex: 0.001 M; sol-
vent: CH2Cl2; E1/2 = ½( Epa + Epc); scan rate: 100 mVs−1
Fig. 3 Emission spectra of 1–4

J Fluoresc
spectroscopy and luminescent properties of copper(I) complexes
with mercaptan ligands and triphenylphosphine. J Mol Struct
1062:125–132
fit well with single exponential decay. The average lifetime of
1–4 follow the same sequence described above with respect to
the increase in the size of the counter anion in the complexes.
These results could be attributed to red shifted emission and
decreased emission intensity in the complexes [40].
9. Małecki JG, Łakomska I, Maroń A, Szala M, Fandzloch M, Nycz
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10. Darensbourg DT, Larkins DL, Reibenspies JH (1998) Bis
(triphenylphosphine) copper (I) complexes of Orotate and
L-dihydroorotate. Inorg Chem 37:6125–6128
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Synthesis and crystal structure of photoluminescent copper(I)–
phosphine complexes with oxygen and nitrogen donor ligands.
Inorg Chem Commun 6:469–473
12. Ji YF, Wang R, Ding S, Du CF, Liu ZI (2012) Synthesis, crystal
structures and fluorescence studies of three new Zn(II) complexes
with multidentate Schiff base ligands. Inorg Chem Commun
16:47–50
13. Moraes RS, Aderne RE, Cremona M, Rey NA (2016) Luminescent
properties of a di-hydrazone derived from the antituberculosis agent
isoniazid: potentiality as an emitting layer constituent for OLED
fabrication. Optical. Mater 52:186–191
14. Wu JZ, De Angelis F, Carrell TG, Yap GPA, Sheats J, Car R,
Dismukes GC (2006) Tuning the Photoinduced O2-evolving reac-
tivity of Mn4O47+, Mn4O46+, and Mn4O3(OH)6+ manganese-Oxo
Cubane complexes. Inorg Chem 45:189–195
15. Wen-Xiu Ni, Mian Li, Xiao-Ping Zhou, Zhen Li, Xiao-Chun Huang
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sites. Chem Commun 3479–3481.
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Structural Characterization of Dioxovanadium(V) Complexes with
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In conclusion, a series of copper(I) complexes featuring
N-(2-{[(2E)-2-(4-nitrobenzylidenyl)hydrazinyl] carbonyl}
phenyl)benzamide and triphenylphosphine have been pre-
pared and characterized. It has been demonstrated that the
ligand L is coordinated to copper(I) in its keto form by in-
volvement of azomethine nitrogen and carbonyl oxygen in
coordination. Complex 2 crystallizes in monoclinic space
group C2/c with two molecules per asymmetric unit and as-
sume distorted tetrahedral geometry around copper(I).
Quasireversible redox behavior is observed for all complexes
corresponding to a Cu(I)/Cu(II) couple. All complexes exhibit
blue-green emission as a result of the fluorescence from intra-
ligand charge transitions (ILCT), ligand to ligand charge
transfer transitions (LLCT) or mixture of both. As the size of
the counter anion increases a marked effect on the quantum
efficiency (ϕ) and the lifetime decay (τ) of the complexes is
observed.
17. E. Colacia, M. Ghazi, R. Kivekas, M. Klinga, F. lioret, J. M. Moreno
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