Short-bite PNP ligand-supported rare tetranuclear [Cu4I 4] clusters: Structural and photoluminescence studies

Article abstract of DOI:10.1021/ic500240j

The group 11 metal complexes of two short-bite PNP ligands, C ₆H₅N{P(OC₆H₃(OMe-o)(C ₃H₅-p))₂}₂ (1) and C ₆H₅N{P(OC₆H₄C3H

Full text of DOI:10.1021/ic500240j

Article
pubs.acs.org/IC
Short-Bite PNP Ligand-Supported Rare Tetranuclear [Cu4I4] Clusters:
Structural and Photoluminescence Studies
Susmita Naik,† Joel T. Mague,‡ and Maravanji S. Balakrishna*,†
†Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
‡Department of Chemistry, Tulane University, New Orleans, Lousiana 70118, United States
S
* Supporting Information
ABSTRACT: The group 11 metal complexes of two short-
bite PNP ligands, C6H5N{P(OC6H3(OMe-o)(C3H5-p))2}2 (1)
and C6H5N{P(OC6H4C3H5-o)2}2 (2), are described. Ligands
1 and 2 on treatment with copper(I) halides (CuX, X = Cl, Br,
or I) yielded dimeric, tetranuclear complexes of the type
[(CuX)4{C6H5N(PR2)2}] (R = OC6H3(OMe-o)(C3H5-p), X =
Cl (3), Br (5), I (7); R = OC6H3(C3H5-o), X = Cl (4), Br (6),
I (8)). The chloro-derivative 3 adopts the common “stair-step”
geometry, whereas the bromo- and iodo-derivatives form Cu4
square planes with two tetracoordinating μ4-halides capping
the axial positions to give octahedral geometry with two other
μ2-halides being in the plane. The iodo-derivative 8 with a very
short Cu−Cu distance of 2.568 Å shows photoluminescence in the solid state.
halides.39,40 The different types of copper complexes formed
by mono- and bidentate ligands are shown in Chart 1.
INTRODUCTION
The chemistry of d10 metal systems has attracted considerable
■
Among all copper(I) halide complexes, the iodide derivatives
attention in last few decades due to their structural diversities,
have been investigated extensively due to their peculiar
rich photophysical properties,1−3 and catalytic applications.4,5
photoluminescence properties. The cubane-like structures
The metallophilic interactions in these complexes, especially in
exhibit two distinct emission bands, one at higher energy
the case of gold(I), resulted in the formation of several
around 400−450 nm arising from halide(X)-to-ligand charge
interesting macrocyclic molecules and supramolecular archi-
transfer (3XLCT) and a low-energy band around 550−600 nm
arising from a cluster-centered excited state (3CC). The relative
intensities of these bands depend on the temperature and the
Cu···Cu distance.12,41,42 The high-energy band is dominant at
low temperature, while the low-energy band is dominant at
room temperature in clusters with Cu···Cu distances less than
2.8 Å. However, complexes with the stair-step structure exhibit
luminescence only from the 3XLCT excited state due to longer
Cu···Cu distances.43−47 The planar tetracopper(I) structures
axially capped with tetrabridging halides have shown both types
of bands depending upon the nature of the coordinating ligands
and their substituents.40 The aminobis(phosphonite) C6H5N-
{P(OC6H4OMe-o)2}2 reported earlier by our group on
reactions with copper halides showed a preference to form
only the ladder-step molecules without any photoluminiscent
properties.48 Herein we describe the copper(I) complexes of
aminobis(phosphonites), C6H5N{P(OC6H3(OMe-o)(C3H5-
p))2}2 (1) and C6H5N{P(OC6H4C3H5-o)2}2 (2), and their
photophysical properties. Interestingly aminobis(phosphonites)
1 and 2 on reaction with CuBr and CuI yielded tetranuclear
complexes with planar Cu4 units axially capped by μ4-halides
tectures via intra- and intermolecular aggregations.6−8 The
strong relativistic effects possessed by gold also make it
unique.9 Many studies have shown that the presence of Au···Au
interactions plays an important role in governing the unique
electronic absorption and emission features of these complexes.
Similar to gold(I) complexes, polynuclear copper(I) complexes
are also interesting due to their diverse structural, rich
photoluminescence properties and wide applications in material
science.10−23 The structures of multinuclear copper(I)
complexes depend on the metal-to-ligand ratios as well as the
steric properties of the ligands employed. Treatment of CuI
halides, in particular CuCl, with one equivalent of tertiary
phosphines usually results in cubane-type structures,24−26
whereas a tetranuclear, ladder-type structure was observed
with bulky phosphines, especially in the case of CuBr and CuI.
These ladder structure molecules usually dissociate in solution
in the presence of bridging linkers to form different types of
coordination polymers.24−38 Combinations of copper(I) halides
with bidentate, aromatic imino ligands generally produce 1-D
chains or 2-D layer networks containing rhombic Cu2X2 units
or (CuX)∞ chains. In contrast, ligands such as bis-
(dicyclohexylphosphino)methane (DCPM) and 2-
{(diorganophosphino)methyl}pyridine (P∧N) have produced
coplanar, tetranuclear copper complexes with μ4-bridging
Received: January 30, 2014
Published: March 21, 2014
© 2014 American Chemical Society
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Chart 1. Monodentate (L) and Bidentate (LQL or 2L) Ligands
and with two additional μ2-halides being almost coplanar with
the Cu4 array.
[(CuX)2{C6H5N(PR2)2}]2 (R = OC6H4(OMe-o)(C3H5-p); X
= Cl, 3; Br, 5; I, 7 and R = OC6H4(C3H5-o); X = Cl, 4; Br, 6; I,
8). The analogous reactions of C6H5N(P(OC6H4OMe-o)2)2
with copper halides (CuX, X = Cl, Br, or I) resulted in the
formation of exclusively “stair-step”-type clusters.48 Interest-
ingly, in the present study, the ligands 1 and 2 with allylic
groups in para and ortho position, respectively, yielded “stair-
step”-type complexes in the case of CuCl. But the similar
reactions with CuBr and CuI resulted in the formation of
bicapped “octahedron”-type complexes in which two of the
halide ions are μ2-bridged and the other two halides display μ4-
coordination. The “stair-step”-type complex consists of two
bis(phosphonite)s each bridging a pair of copper(I) centers
along with two μ2-bridged and two μ3-bridged chloride ions as
shown in Scheme 1. All the copper complexes (3−8) are
moderately stable to air and moisture and are soluble in polar
solvents such as dichloromethane, chloroform, and acetonitrile
and insoluble in nonpolar solvents. The 31P{1H} NMR spectra
of all the complexes consist of broad single resonances in the
range 89−103 ppm.
RESULTS AND DISCUSSION
■
The short-bite PNP ligands 1 and 2 were synthesized by
reacting phenylaminobis(dichlorophosphine) with four equiv-
alents of ArOH in the presence of a base using our previously
reported literature procedure.49 The primary objectives of
incorporating dangling olefinic groups at ortho and para
positions on the phosphorus substituents are to involve them
in either inter-50 or intramolecular51 coordination with the
transition metals in addition to those of the trivalent
phosphorus centers as well as to enhance the solubility of the
metal complexes in organic solvents. The present study
includes synthesis, structural characterization, and photo-
luminescence studies of copper(I) complexes containing the
ligands 1 and 2.
Copper(I) Complexes. The reactions of 1 and 2 with one
or two equivalents of CuX (X = Cl, Br, or I) in acetonitrile
resulted in the formation of the tetranuclear complexes
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are equivalent within experimental error (2.1530(8) to
2.1541(8) Å), while the Cu−Cl bond lengths vary appreciably,
ranging from 2.3375(8) Å (Cu1−Cl1) to 2.2565(8) Å (Cu2−
Cl1i). As expected, the Cu−Cl distances involving the triply
bridging chlorine atoms (Cl2 and Cl2i) are longer than those to
the doubly bridging chlorine atoms (Cl1 and Cl1i). The four
copper atoms are precisely coplanar, with Cu···Cu distances
Cu1···Cu2i = Cu1i···Cu2 = 3.0058(5) Å, and Cu1···Cu2 =
Cu1i···Cu2i = 2.9163(6) Å. The Cl−Cu−Cl angles (Cl1−Cu1−
Cl2 = 90.06(3)° and Cl2−Cu2−Cl1i = 91.10(2)°) are larger
than the Cu−Cl−Cu angles, which range from 75.94(2)° to
81.71(3)°. The CuCl complexes of analogous short-bite PNP
ligands such C6H5N{PPh2}2 and CH3N{P(2-C6H4Me)2}2 are
reported to have distorted octahedral geometry with Cu···Cu
distances ranging from 2.75 to 2.89 Å.52,53
Scheme 1. Synthesis of Copper(I) Complexes of PNP
Ligands 1 and 2
The molecular structures of 5, 7, and 8 contain similar
[{Cu4(μ2-X)2(μ4-X)2}] (X = Br or I) cores analogous to that in
complex 3 with two diphosphonites, but possess a different
geometry due to the differences in the Cu−Cu and Cu−X bond
lengths. The complexes 5, 7, and 8, with the Cu4X4 core, are
isostructural with the complexes containing bisphosphines such
as bis(dicyclohexylphosphino)methane and 2-
(diorganophosphino)methylpyridine.39,40 All copper atoms
are tetracoordinated and are arranged in a distorted rectangular
shape. The capping halides are bonded to four copper atoms in
a μ4-fashion and are placed in axial positions above and below
the Cu4-plane, whereas the other two halides are bonded to two
copper atoms in a μ2-fashion. Complex 5 exhibits four different
types of Cu−Cu atom distances ranging from 2.7561 to 2.8484
Å (Cu1−Cu2 = 2.8362(7) Å, Cu1−Cu4 = 2.7561(6) Å, Cu2−
Cu3 = 2.8128(6) Å, Cu3−Cu4 = 2.8485(7) Å). In contrast,
complexes 7 and 8 exhibit two unique Cu−Cu atom distances
(Cu1−Cu2 = 2.6406(11); Cu1−Cu2i = 2.8883(12) Å for 7 and
Cu1−Cu2 = 2.5680(4); Cu1−Cu2i = 2.8327(5) Å for 8)
because of the crystallographically imposed centrosymmetry.
The Cu1−Cu2 distance in 8 is shorter than the same in
complex 7 but is comparable with the equivalent Cu−Cu
distances found in analogous complexes reported in the
literature (see Table 5). The Cu−Cu bond length in complex
8 (2.5680(4) Å) is shorter than those found in the stair-step
structure and Cu2I2 clusters coordinated with bisphosphine
ligands (2.898 Å)54 as well as monodentate N-heteroaromatic
ligands (2.872−3.303 Å)55 but is comparable with those in
bimetallic complexes containing bulky pyridyl ligands (2.557
Å),56 benzimidazoles (2.546 Å),57 imidazolyl pyridines (2.592
Å),58 phenanthroline (2.609 Å),59 1,2,3-triazole (2.530 Å),60
and related nitrogen donor ligands (see Table 4). The steric
crowding imposed by the bridging bis(phosphonite) ligands in
complexes 7 and 8 also influences the separation between the
two fragments in the Cu4I4 cores. The Cu−X bond lengths
involved in the μ4-bridging [2.4906(6)−2.7318(6) Å for 5;
2.7652(10)−2.8636(10) Å for 7; and 2.7035(4)−2.8751(4) Å
for 8] are significantly longer than those participating in μ2-
bridging [2.3780(6) and 2.4350(6) Å for 5; 2.6016(9) and
2.6397(9) Å for 7; 2.5965(4) and 2.6074(4) Å for 8]. The P−
N−P bond angles in all these complexes are in the range 118−
120°.
The molecular structures of complexes 3, 5, 7, and 8 with
atom-numbering schemes are shown in Figures 1 and 2. Crystal
Figure 1. Molecular structure of [Cu2(μ-Cl)(μ3-Cl){C6H5N{P-
(OC6H3(OMe-o)(C3H5-p))2}2}]2 (3). All hydrogen atoms and lattice
solvent have been omitted for clarity.
data and the details of the structure determinations are given in
Table 1, while selected bond lengths and bond angles are given
in Tables 2 and 3. For comparison, Cu−Cu bond distances in
di-, tri-, and teranuclear complexes are presented in Table 4,
whereas Table 5 includes Cu−Cu bond distances for typical
octahedron-type complexes. The molecular structure of 3
consists of a [{Cu4(μ-Cl)2(μ3-Cl)2}] core containing two
bis(phosphonites) and having crystallographically imposed
centrosymmetry. The Cu4Cl4 unit resembles “stair-step”
geometry with each of the 10 edges defined by a Cu−Cl
bond. The Cu1 atom adopts a distorted tetrahedral geometry
coordinated by one phosphorus and three chlorine atoms,
whereas Cu2 is in a distorted trigonal planar environment with
one phosphorus and two chlorine atoms. The Cu−P distances
Photoluminescence Study of Complex 8. The absorp-
tion spectra of 8 recorded in 10−5 M solution of dichloro-
methane, acetonitrile, THF, and acetone are shown in Figure 5.
The spectra are characterized by sharp absorption bands in the
region 220−230 nm and a broad absorption band at 280 nm,
which are assigned to ligand-centered n→π* and π→π*
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Figure 2. Molecular structures of [Cu2(μ-Br)(μ4-Br){C6H5N{P(OC6H3(OMe-o)(C3H5-p))2}2}]2 (5), [{[Cu2(μ-I)(μ4-I){C6H5N{P(OC6H3(OMe-
o)(C3H5-p))2}2]2 (7), and [Cu2(μ-I)(μ4-I){C6H5N{P(OC6H4C3H5-o)2}2}]2 (8). All hydrogen atoms and lattice solvent have been omitted for
clarity.
transitions, respectively. The featureless transitions observed at
longer wavelengths (>300 nm) that gradually decrease in
intensity are assigned to halide-to-ligand charge transfer
transitions except in the case of the acetone solution, which
showed an absorption maximum at 320 nm, but due to the
poor solubility in acetone, this solution showed a maximum
absorbance of only about 0.1. The low-energy transitions in
complex 8 can be observed down to 330 nm in the excitation
spectra recorded from neat solids.
Cu4I4(dcpm)2 (dcpm = bis(dicyclohexylphosphino)methane)
has shown only a low-energy emission band at 596 nm.39
Excitation of dichloromethane solution of 8 at 340 nm
displayed a high-energy emission band at 419 nm correspond-
ing to the halide-to-ligand charge transfer transition
(XLCT).61−64 The emission lifetime is calculated using three-
exponential calculations. The average lifetime of the excited-
state species is around 178 ps. Similar to the complex
Cu4I4(dcpm)2, the emission spectrum of 8 recorded in the
solid state at room temperature showed only a low-energy
emission band at 596 nm when excited at 340 nm. The
emission lifetime is calculated using monoexponential calcu-
lations to be 6.22 μs, implying that the emission is from the
triplet excited state. Complex 8 displayed an orange emission
The emission spectra of similar bare tetragonal complexes
̂
Cu4I4(R2PN)2 recorded in the solid state at room temperature
have shown both dual emission (HE band at 450−470 nm and
LE band at 560−580 nm, R = C6H5, C2H5, or Cy) and only the
40
t
i
high energy emission band (R = Bu or Pr). However,
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Table 1. Crystallographic Information for Compounds 3, 5, 7, and 8
3
5
7
8
emp formula
fw
C92H98Cl4Cu4N2O16P4
2009.62
C92H98Br4Cu4N2O16P4
2193.47
C92H98Cu4I4N2O16P4
2373.41
C84H82Cu4I4N2O8P4
2133.16
cryst syst
space group
a, Å
triclinic
monoclinic
P21/c (No. 14)
16.6114(4)
17.5727(4)
32.0136(6)
90
monoclinic
P21/n (No. 14)
16.5661(8)
15.8160(6)
18.4637(9)
90
triclinic
P1 (No. 2)
̅
P1 (No. 2)
̅
11.8854(3)
14.2961(4)
15.0486(4)
111.404(2)
92.821(2)
100.448(2)
2322.49(11
1
10.3109(6)
14.3055(9)
14.8135(9)
94.458(1)
99.793(1)
101.868(1)
2092.7(2)
1
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
102.268(2)
90
91.059(5)
90
9131.6(4)
4
4836.8(4)
2
Z
D
calc, g cm−3
1.437
1.595
1.630
1.693
μ(Mo Kα), mm−1
1.152
2.805
2.273
2.609
F(000)
1038
4464
2360
1052
cryst size, mm
T (K)
0.24 × 0.29 × 0.32
150
0.16 × 0.21 × 0.28
150
0.14 × 0.18 × 0.23
150
0.10 × 0.11 × 0.18
100
2θ range, deg
total no. reflns
no. of indep reflns
S
3.1, 25.0
19 014
3.0, 25.0
70 165
3.0, 25.0
33 532
2.1, 28.3
37 087
8111 [Rint = 0.018]
1.13
15 992 [Rint = 0.038]
0.91
8501 [Rint = 0.086]
1.12
10 220[Rint = 0.031]
1.04
R1
0.0392
0.0342
0.0634
0.0253
wR2
0.1246
0.0787
0.1777
0.0601
under UV excitation at room temperature analogous to cubane-
type complexes, which are reported to show green to orange
emission under similar conditions. It is reported that, in the
case of octahedral Cu4I4 clusters, the HOMO is composed
primarily of iodide 6p and Cu 3d orbitals, whereas the LUMO
consists of iodide (6s, 6p) and Cu (4s, 4p, 3d) orbitals and the
halide-to-ligand charge transfer transition is the lowest energy
band observed when the complexes are in the ground state.39
be controlled by the steric bulk of the substituents on the
phosphorus atoms.
CONCLUSIONS
■
The reactions of 1 and 2 with copper(I) halides (CuX, X = Cl,
Br, or I) afforded tetranuclear cluster complexes of the type
[(CuX)4{C6H5N(PR2)2}2] (3−8) irrespective of the stoichi-
ometry. The chloro complex adopts the common “stair-step”
geometry, whereas the bromo and iodo complexes of these two
ligands crystallized in a rare octahedron-type structure. The
iodo cluster 8 of ligand 2 has a short Cu−Cu distance of
2.5680(4) Å, due to which it shows a cluster-centered
photoluminescence in the solid state. Although complex 7
has a Cu···Cu distance of 2.6406(11) Å, surprisingly it is
nonfluorescent at room temperature and also at low temper-
ature. The solid-state emission has a lifetime of 6 μs, implying
that the emission is from the triplet excited state. It is
interesting to note that in some papers authors have used Cu−
Cu, whereas the recent papers have referred it as Cu···Cu for
copper−copper interactions in their studies. From the
discussion and the data provided in Tables 4 and 5, the
copper−copper distances below 2.7 Å may be considered as
Cu−Cu bonding interactions, and those with bond distances
more than 2.7 Å may be treated as Cu···Cu nonbonding
interactions. In the present study, these interactions are
considered as Cu−Cu bonding interactions aided by the
photophysical studies.
3
3
However, both XLCT and CC states can be populated upon
irradiation at room temperature according to DFT calculations
on the cubane Cu4I4L4 clusters.18,65 Excitation to the XLCT
3
state leaves the C4I4 cluster unperturbed. The excitation to the
3CC state, which involves transfer of electrons from an
antibonding 3d orbital to the bonding combination of 4s
orbitals, leads to the distortion of the Cu4I4 core compared to
the ground-state geometry, causing a large Stokes shift. Thus
the low-energy emission band is assigned to a cluster centered
excited state. The usual Cu−Cu distances of cubane derivatives
with pyridyl- or phosphine-based ligands are in the range 2.56−
2.90 Å. The octahedron complexes [(CuI)4(Py-2-CH2PtBu2)2]
and [(CuI)4(Py-2-CH2PiPr2)2], having short Cu−Cu distances
of 2.630(1) and 2.620(1) Å, respectively, have shown only a
high-energy emission band at 460 nm, although the band
separation falls within the range of the 3CC transition.
Surprisingly, complexes 5 and 7, having Cu−Cu distances of
2.7561(6) and 2.6406(11) Å, respectively, are nonemissive at
room temperature. It is clear that the Cu−Cu interactions in
cubane as well as octahedron Cu4I4L4 clusters are the key
parameters that influence the luminescence properties of the
3CC transition, and the range of Cu−Cu distances in
octahedron clusters is found to be less (probably <2.60 Å)
than the cubane derivatives. To our knowledge, the maximum
Cu−Cu distance reported for the 3CC transition in octahedron
copper clusters is 2.5760(8) Å.39 As reported, the LE emission
is associated with some kind of structural relaxation, so the
photoluminescence properties of complexes 7 and 8 appear to
EXPERIMENTAL SECTION
■
General Considerations. All experimental manipulations were
performed under an inert atmosphere of dry nitrogen or argon, using
standard Schlenk techniques. All the solvents were purified by
conventional procedures and distilled prior to use. C6H5N(PCl2)2,66
ligand 1,49 and CuX (X = Cl or Br)67 were prepared according to the
published procedures. Other reagents were obtained from commercial
sources and used after purification. The H and 31P{1H} NMR (δ in
1
ppm) spectra were obtained with a Varian VRX 400 spectrometer
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Table 2. Selected Bond Distances and Bond Angles for
Complexes 3 and 5
Table 3. Selected Bond Distances and Bond Angles for
Complexes 7 and 8
bond distances (Å)
bond angles (deg)
bond distances (Å)
bond angles (deg)
[{Cu2(μ-Cl)(μ3-Cl)}{C6H5N{P(OC6H3(OMe-o)(C3H5-p))2}2}]2 (3)
[{Cu2(μ-I)(μ4-I)}{C6H5N{P(OC6H3(OMe-o)(C3H5-p))2}2}]2 (7)
P1−N1
P2−N1
1.691(2)
P2−N1−P1
119.86(15)
122.38(9)
116.14(9)
119.18(3)
121.08(3)
123.97(3)
127.85(3)
136.23(3)
104.48(3)
90.06(3)
P1−N1i
P2−N1
1.685(5)
P1i−N1−P2
N1i−P1−Cu1
N1−P2−Cu2
P1−Cu1−I2
P1−Cu1−I1i
P1−Cu1−I1
P2−Cu2−I2
P2−Cu2−I1
P2−Cu2−I1i
Cu1−Cu2−Cu1i
Cu2−Cu1−Cu2i
120.1(3)
1.677(2)
N1−P1−Cu1
N1−P2−Cu2
P1−Cu1−Cl1
P1−Cu1−Cl2
P1−Cu1−Cl2i
P2−Cu2−Cl2
P2−Cu2−Cl1i
Cl1−Cu1−Cl2
Cl1−Cu1−Cl2i
Cl2−Cu1−Cl2i
Cu2−Cl2−Cu1
Cu2i−Cl1−Cu1
1.702(5)
118.19(18)
119.61(18)
119.58(5)
116.99(6)
120.94(6)
119.72(5)
116.92(6)
119.32(6)
91.79(3)
Cu1−P1
Cu2−P2
Cu1−Cl1
Cu1−Cl2
Cu1−Cl2i
Cu2−Cl2
Cu2−Cl1i
Cu1−Cu2i
Cu2−Cu1i
Cl1−Cu2i
Cl2−Cu1i
2.1541(8)
2.1530(8)
2.3375(8)
2.3732(8)
2.5124(7)
2.3665(8)
2.2565(8)
3.0058(5)
3.0058(5)
2.2565(8)
2.5124(7)
Cu1−P1
Cu1−I2
Cu1−Cu2
Cu1−I1i
Cu1−I1
Cu1−Cu2i
Cu2−P2
Cu2−I1
Cu2−I2
Cu2−I1i
Cu2−Cu1i
I1−Cu1i
I1−Cu2i
2.1891(18)
2.6016(9)
2.6406(11)
2.7652(10)
2.8636(10)
2.8883(12)
2.1977(17)
2.7684(10)
2.6397(9)
2.776(1)
91.10(2)
88.21(3)
75.94(2)
81.71(3)
2.8883(12)
2.7652(10)
2.776(1)
[{Cu2(μ-Br)(μ4-Br)}{C6H5N{P(OC6H3(OMe-o)(C3H5-p))2}2}]2 (5)
P1−N1
P2−N1
P3−N2
P4−N2
1.680(3)
P1−N1−P2
118.70(15)
118.41(10)
118.43(11)
118.80(9)
120.17(10)
128.45(4)
125.94(4)
114.14(3)
120.49(3)
125.39(3)
117.34(3)
128.25(3)
122.11(3)
120.34(3)
122.67(3)
95.19(2)
1.685(3)
N1−P1−Cu1
N1−P2−Cu2
N2−P3−Cu3
N2−P4−Cu4
P1−Cu1−Br4
P1−Cu1−Br1
P1−Cu1−Br2
P2−Cu2−Br3
P2−Cu2−Br1
P2−Cu2−Br2
P3−Cu3−Br3
P3−Cu3−Br2
P4−Cu4−Br4
P4−Cu4−Br1
Cu1−Cu4−Cu3
Cu2−Cu3−Cu4
Cu3−Cu2−Cu1
Cu4−Cu1−Cu2
[{Cu2(μ-I)(μ4-I)}{C6H5N{P(OC6H4C3H5-o)2}2}]2 (8)
1.676(3)
P1−N1
1.683(2)
P1−N1−P2i
N1i−P2−Cu2
N1−P1−Cu1
P1−Cu1−I2
P1−Cu1−I1i
P1−Cu1−I1
P2−Cu2−I2
P2−Cu2−I1i
P2−Cu2−I1
Cu1−Cu2−Cu1i
Cu2−Cu1−Cu2i
120.83(12)
117.61(7)
118.16(7)
119.38(2)
115.34(2)
120.22(2)
119.11(2)
113.43(2)
122.43(2)
90.430(13)
89.569(13)
1.691(3)
P2−N1i
Cu1−P1
I1−Cu1
I1−Cu1i
Cu2−P2
I1−Cu2
I1−Cu2i
I2−Cu1
I2−Cu2
Cu1−I1i
Cu2−I1i
Cu1−Cu2
Cu2−Cu1i
1.687(2)
Cu1−P1
Cu2−P2
Cu3−P3
Cu4−P4
Cu1−Br1
Cu1−Br2
Cu1−Br4
Cu2−Br1
Cu2−Br2
Cu2−Br3
Cu3−Br3
Cu3−Br2
Cu4−Br4
Cu4−Br1
Cu4−Br2
Cu1−Cu2
Cu1−Cu4
Cu2−Cu3
Cu3−Cu4
2.1626(9)
2.1610(9)
2.1597(10)
2.1653(9)
2.7094(6)
2.7304(6)
2.3915(6)
2.4906(6)
2.7318(6)
2.4169(6)
2.3780(6)
2.5101(6)
2.4350(6)
2.5669(6)
2.6476(6)
2.8362(7)
2.7561(6)
2.8128(6)
2.8485(7)
2.1837(6)
2.8751(4)
2.7035(4)
2.1878(7)
2.8142(4)
2.7470(4)
2.5965(4)
2.6074(4)
2.7034(4)
2.7469(4)
2.5680(4)
2.8327(5)
83.258(18)
94.22(2)
Synthesis of [Cu2(μ-Cl)(μ3-Cl){C6H5N{P(OC6H3(OMe-o)(C3H5-
p))2}2}]2 (3). A solution of cuprous chloride (0.0153 g, 0.156 mmol) in
acetonitrile (5 mL) was added to the solution of 1 (0.063 g, 0.078
mmol) in acetonitrile (5 mL). After stirring for 4 h the solvent was
evaporated under vacuum to yield an oily residue, which, on washing
several times with petroleum ether and drying under vacuum, gave 13
as a white solid. Yield: 87% (0.0681 g). Mp: 123−124 °C. 31P{1H}
NMR (CDCl3) δ: 98.4 (br s). 1H NMR (CDCl3) δ: 3.31 (d, CH2, 8H,
3JHH = 8 Hz), 3.63 (s, OCH3, 12H), 5.04−5.10 (m, CH2, 8H), 5.88−
84.510(18)
5.98 (m, CH, 4H), 6.51−7.74 (m, ArH, 17H). Anal. Calcd for
C92H98N2P4O16Cl4Cu4: C, 55.04; H, 4.92; N, 1.39. Found: C, 54.86;
H, 4.71; N, 1.58.
operating at frequencies of 400 and 162 MHz, respectively. The
spectra were recorded in CDCl3 (or DMSO-d6) solutions with CDCl3
(or DMSO-d6) as an internal lock; TMS and 85% H3PO4 were used as
internal and external standards for 1H and 31P{1H} NMR, respectively.
Positive values indicate downfield shifts. Microanalyses were carried
out on a Carlo Erba (model 1106) elemental analyzer. Melting points
of all compounds were determined with a Veego melting point
apparatus and are uncorrected.
Synthesis of [Cu2(μ-Cl)(μ3-Cl){C6H5N{P(OC6H4C3H5-o)2}2}]2 (4).
This compound was prepared analogously to 3 by adding a solution of
CuCl (0.015 g, 0.1604 mmol) in acetonitrile (5 mL) to the solution of
ligand 2 (0.055 g, 0. 0802 mmol) in the same solvent (5 mL). Yield:
87% (0.061 g). Mp: >200 °C. 31P{1H} NMR (CDCl3) δ: 102.9 (br s).
1H NMR (CDCl3) δ: 2.59 (s, CH2, 8H), 4.76 (d, CH2, trans-H, 4H,
Synthesis of C6H5N{P(OC6H4C3H5-o)2}2 (2). To a solution of
C6H5N(PCl2)2 (2.72 g, 9.23 mmol) in diethyl ether (20 mL) was
added dropwise a mixture of 2-allyl phenol (4.96 g, 37.8 mmol) and
triethyl amine (3.294 g, 38.7 mmol) in diethyl ether (15 mL) at 0 °C.
The reaction mixture was warmed to room temperature and stirred
overnight. Triethyl amine hydrochloride formed was filtered through a
frit layered with activated Celite, and the solvent was evaporated under
reduced pressure to give an analytically pure product of 2 as a colorless
oil. Yield: 85% (5.4 g). 31P{1H} NMR (CDCl3) δ: 128.2 (s). 1H NMR
3
3JHH = 17.2 Hz), 4.89 (d, CH2, cis-H, 4H, JHH = 9.5 Hz), 5.56−5.64
(m, CH, 4H), 7.0−7.6 (m, ArH, 21H). Anal. Calcd for
C84H82Cu4Cl4N2O8P4: C, 57.08; H, 4.68; N, 1.58. Found: C, 57.35;
H, 4.58; N, 1.69.
Synthesis of [Cu2(μ-Br)(μ4-Br){C6H5N{P(OC6H3(OMe-o)(C3H5-
p))2}2}]2 (5). This compound was prepared analogous to 3 by adding a
solution of cuprous bromide (0.008 g, 0.055 mmol) in acetonitrile (3
mL) to the solution of 1 (0.022 g, 0.027 mmol) also in acetonitrile (5
mL). Yield: 86% (0.0254 g). Mp: 128−130 °C. 31P{1H} NMR
3
(CDCl3) δ: 3.10 (d, CH2, 8H, JHH = 3.6 Hz), 4.81−4.91 (m, CH2,
8H), 5.69−5.76 (m, CH, 4H), 7.0−7.34 (m, ArH, 21H). Anal. Calcd
for C42H41NO4P2: C, 73.55; H, 6.03; N, 2.04. Found: C, 73.35; H,
5.58; N, 1.89.
(CDCl3) δ: 95.4 (br s). 1H NMR (CDCl3) δ: 3.31 (d, CH2, 8H, 3JHH
=
6.4 Hz), 3.63 (s, OCH3, 12H), 5.04−5.09 (m, CH2, 8H), 5.88−5.96
(m, CH, 4H), 6.6 (m, C6H3, 4H), 6.95 (d, C6H3, 4H, 3JHH = 7.94 Hz),
3869
dx.doi.org/10.1021/ic500240j | Inorg. Chem. 2014, 53, 3864−3873

Inorganic Chemistry
Article
a
Table 4. Cu···Cu Distances in Di-, Tri-, and Tetranuclear
Table 5. Cu···Cu Distances in Octahedron-Type Complexes
a
Copper(I) Complexes
complex
[(CuI)4(dcpm)2]
Cu···Cu distances (Å)
ref
39
complex
Cu···Cu distances (Å)
ref
2.475(1)−2.9846(1)
2.5760(8)−3.005(1)
2.525(2)−2.943(2)
2.574(1)−2.930(1)
2.630(1)−2.839(3)
2.620(1)−2.880(1)
2.562(2)−3.035(2)
2.5516(9)−2.848(1)
2.7861(9)−2.8892(8)
2.7526(13)−2.8726(9)
2.7561(6)−2.8485(7)
[Cu2(μ-I)2(μ-C6H4(o-N-Bn-triazole)2]
[Cu2(μ-I)2(benzimidazole)2]
[Cu2(μ-I)2(2-benzolylpyridine)2]
[Cu2(μ-I)2(imidazolyl pyridine)2]
[Cu2(μ-I)2(phenanthrolene)2]
[Cu2(μ-I)2(FecP)2NHC)]
[Cu2(μ-Cl)2(dppf)2]
2.5303(7)
2.546
60
57
58
58
59
73
74
74
74
75
54
54
54
76
76
77
77
77
78
79
80
81
81
81
82
83
83
83
84
84
84
48
48
48
48
48
48
48
[(CuI)2(dcpm)]2
39
40
40
40
40
40
85
52
53
this
[(CuI)2(Py-2-CH2PPh2)]2
[(CuI)2(Py-2-CH2PCy2)]2
[(CuI)2(Py-2-CH2PtBu2)]2
[(CuI)2(Py-2-CH2PiPr2)]2
[(CuI)2(Py-2-CH2PEt2)]2
[Cu2(μ-I)(μ4-I)(μ-L)]2
[Cu4(dppa)2Cl4]
2.587
2.592
2.609
2.356
3.216(2)
3.331
[Cu2(μ-Br)2(dppf)2]
[Cu2(μ-I)2(dppf)2]
2.5298
[{(2-C6H4Me)2P}2NMe)Cu2Cl2]2
[Cu2(napy)2(ClO4)2]
2.506(2)
2.866
[Cu2(μ-Br)(μ4-Br)
C6H5N{P(OC6H3(OMe-o)(C3H5-
p))2}2]2
work
[Cu2(μ-Cl)2(dppb)2]
[Cu2(μ-Br)2(dppb)2]
2.837
[Cu2(μ-I)(μ4-I)
{C6H5N{P(OC6H3(OMe-o)(C3H5-
p))2}2}]2
2.6406(11)−2.8883(12) this
work
[Cu2(μ-I)2(dppb)2]
2.898
[Cu2(μ-Br)2(μ-1,8-naph)(PPh3)2]
[Cu2(μ-I)2(μ-1,8-naph)(PPh3)2]
[CuBr(PPh3)2(pym)]
2.6271(4)
2.6123(5)
2.8193(16)
2.303
[Cu2(μ-I)(μ4-I)
{C6H5N{P(OC6H4C3H5-o)2}2}]2
2.5680(4)−2.8327(5)
this
work
a
Dcpm = bis(dicyclohexylphosphanyl)methane; L = 2-diphenylphos-
phino-3-methylphosphinine; dppa = bis(diphenylphosphine)aniline.
[CuCl(PPh3)2(pdz)]
[CuBr(PPh3)2(Trz)]
2.8545(8)
3.098(1)
3.066(1)
3.065(1)
3.103(1)
3.109(1)
3.122(1)
3.059(1)
2.525
[(PCy3)2Cu2(μ-Br)2]
[(PCy3)2Cu2(μ-Cl)2]
[(PBn3)2Cu2(μ-Br)2]
[(P(o-tol)3)2Cu2(μ-Cl)2]
[(P(o-tol)3)2Cu2(μ-Br)2]
[(P(o-tol)3)2Cu2(μ-I)2]
[(PPh3)2Cu2(μ-Cl)2(pyrazine)]n
[Cu2(μ-I)2(μ-phz)]n
[Cu2(μ-Br)2(μ-phz)]n
3.141
[Cu2(μ-Cl)2(μ-phz)]n
3.049
[Cu3(dppm)3(μ-Br)2]ClO4
[Cu2(dppm)2(dmcn)Cl2]2(dmcn)
[Cu3(dppm)3(μ3-I)2I]
3.005(3)−3.128(3)
3.293(1)
3.111(3)−3.199
2.721(1)
2.721(1)
2.819(1)-2.939(1)
2.931(1)-2.980(2)
2.708(1)
2.877(1)
2.695(1)
[Cu2(μ-I)2(NCCH3)2(μ-PNP)]
[Cu4(μ-I)2(NCCH3)2(μ-PNP)2]
[Cu4(μ-Br)2(μ3-Br)2(μ-PNP)2]
[Cu4(μ-Cl)2(μ3-Cl)2(μ-PNP)2]
[Cu2(μ-I)2(C5H5N)2(μ-PNP)]
[Cu2(μ-I)I(C10H8N2)(μ-PNP)]
[Cu2(μ-Br)2(μ-PNP)(C10H8N2)]n
[Cu2(μ-Cl)(μ3-Cl){1}]2
Figure 5. UV−visible spectra of complex 8 in different solvents.
to that for 3 using cuprous iodide (0.014 g, 0.074 mmol) and 1 (0.03
g, 0.037 mmol). Yield: 89% (0.0391 g). Mp: 123−125 °C. 31P{1H}
NMR (CDCl3) δ: 86.3 (br s). 1H NMR (CDCl3) δ: 3.30 (d, CH2, 8H,
3JHH = 8 Hz), 3.63 (s, OCH3, 12H), 5.04−5.10 (m, CH2, 8H), 5.9−
2.9163(6)−3.0058(5) this
work
3
5.97 (m, CH, 4H), 6.52 (d, C6H3, 4H, JHH = 6.4 Hz), 6.58 (s, C6H3,
3
a
́
4H), 6.73 (d, C6H3, 4H, JHH = 7.99 Hz), 7.30−7.74 (m, C6H5, 5H).
Anal. Calcd for C92H98N2P4O16I4Cu4: C, 46.56; H, 4.16; N, 1.18.
Found: C, 46.13; H, 4.01; N, 1.19.
(FecP)2NHC) = (SP-4)-[i-1,3-Bis[(R)-1-((S)-2-diphenylphosphino-
́
P-ferrocenyl)ethyl] imidazole-2-i-ylidene]; dppf = 1,1′-bis-
(diphenylphosphine)ferrocene; naph =1,8-naphthyridine; dppb =
1,2-bis(diphenylphosphino)benzene; PNP = C6H5N(P(OC6H4OMe-
o)2)2; pym = pyrimidine; pdz = pyridazine; Trz = triazine; phz =
phthalazine; dmcn = dimethylcyanamide.
Synthesis of [Cu2(μ-I)(μ4-I){C6H5N{P(OC6H4C3H5-o)2}2}]2 (8).
This compound was prepared similarly to 3 by adding a solution of
CuI (0.039 g, 0.2052 mmol) in acetonitrile (5 mL) to the solution of 2
(0.0704 g, 0.1026 mmol) also in acetonitrile (5 mL). Yield: 79%
(0.0864 g). Mp: 190−192 °C. 31P{1H} NMR (CDCl3) δ: 89.7 (s). 1H
NMR (CDCl3) δ: 2.8 (br s, CH2, 8H), 4.78 (d, CH2, trans-H, 4H, 3JHH
= 17.2 Hz), 4.9 (d, CH2, cis-H, 4H, 3JHH = 9.6 Hz), 5.61−5.66 (m, CH,
4H), 7.0−7.5 (m, ArH, 21H). Anal. Calcd for C84H82Cu4I4N2O8P4: C,
47.29; H, 3.87; N, 1.31. Found: C, 47.68; H, 3.70; N, 1.69.
Photophysical Studies. The absorption spectra of 8 were
recorded at 298 K on a Perkin-Elmer UV−vis spectrometer in a
10−5 M solution in dichloromethane, acetonitrile, THF, and acetone
using a quartz cell of 1 cm width. The emission spectra of 8 in a solid
as well as the solution in dichloromethane were recorded at 298 K
with a Perkin-Elmer fluoroscence spectrometer using a quartz cell (1
cm width). The time-resolved fluorescence decay measurements of the
solid and solution were carried out at a magic angle using a
picoseconds diode laser based time-correlated single photon counting
(TCSPC) fluorescence spectrometer from IBH, UK. The emission
6.67 (s, C6H3, 4H), 7.32−7.57 (m, C6H5, 5H). Anal. Calcd for
C92H98N2P4O16Br4Cu4: C, 50.56; H, 4.51; N, 1.28. Found: C, 51.06;
H, 4.46; N, 1.61.
Synthesis of [Cu2(μ-Br)(μ4-Br){C6H5N{P(OC6H4C3H5-o)2}2}]2 (6).
This compound was prepared similarly to 3 by adding CuBr (0.021 g,
0.145 mmol) (in 5 mL) to the solution of ligand 2 (0.050 g, 0. 073
mmol) in the same solvent (5 mL). Yield: 89% (0.0573 g). Mp: >200
°C. 31P{1H} NMR (CDCl3) δ: 97.1 (br s). 1H NMR (CDCl3) δ: 2.94
3
3
(d, CH2, 8H, JHH = 5.2 Hz), 4.77 (d, CH2, trans-H, 4H, JHH = 16.8
3
Hz), 4.9 (d, CH2, cis-H, 4H, JHH = 9.6 Hz), 5.6 (m, CH, 4H), 7.09−
7.45 (m, ArH, 21H). Anal. Calcd for C84H82Cu4Br4N2O8P4: C, 51.86;
H, 4.25; N, 1.44. Found: C, 51.46; H, 4.57; N, 1.43.
Synthesis of [Cu2(μ-I)(μ4-I){C6H5N{P(OC6H3(OMe-o)(C3H5-
p))2}2}]2 (7). This compound was synthesized by a procedure similar
3870
dx.doi.org/10.1021/ic500240j | Inorg. Chem. 2014, 53, 3864−3873

Inorganic Chemistry
Article
Figure 6. Emission spectra and decay lifetime measurement of copper complex 8 in dichloromethane.
Figure 7. Solid-state emission spectra and decay lifetime measurement of copper complex 8.
of 400 scans in ω (0.5° per scan) at φ = 0°, 90°, and 180° plus two
sets of 800 scans in φ (0.45° per scan) at ω = −30° and 210° under
the control of the APEX2 program suite.68 The raw data were reduced
to F2 values using the CrysAlisPro RED (3, 5, and 7) and SAINT+ (8)
software.69 Multiple measurements of equivalent reflections provided
the basis for empirical absorption corrections as well as corrections for
any crystal deterioration during the data collection (SADABS).70 The
structure of 8 was solved by the Patterson method, whereas the rest of
the structures were solved by direct methods, and all were refined by
full-matrix least-squares procedures using the SHELXL-97 program
package.71,72 Hydrogen atoms were placed in calculated positions and
included as riding contributions with isotropic displacement
parameters tied to those of the attached non-hydrogen atoms.
ASSOCIATED CONTENT
* Supporting Information
Crystallogrpahic data in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
■
S
Figure 8. Excitation and emission spectra of copper complex 8 (solid
sample).
AUTHOR INFORMATION
Corresponding Author
*E-mail: krishna@chem.iitb.ac.in; msb_krishna@iitb.ac.in.
Notes
■
lifetime of complex 8 in dichloromethane was calculated using a three
exponential, whereas that of the solid sample was calculated using a
monoexponential. The good fit criteria were low chi-square (1.0) and
random distributions of residuals.
X-ray Diffraction Studies. A crystal of each of the compounds in
the present work suitable for single-crystal X-ray diffraction studies was
mounted in a cryoloop with a drop of paratone oil and placed in the
cold nitrogen stream of the kryoflex attachment of the CCD Oxford
Diffraction XCALIBUR-S diffractometer for complexes 3, 5, and 7 and
Bruker APEX CCD diffractometer for complex 8. The data were
collected by the standard “phi-omega scan technique” using the
CrysAlisPro CCD software for complexes 3, 5, and 7, and for complex
8, a full sphere of data was collected using a combination of three sets
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the Department of Science and Technology
(DST), New Delhi, for financial support (SR/S1/IC-17/2010).
S.N. thanks UGC, New Delhi, for a Senior Research Fellowship
(SRF). We also thank the Department of Chemistry for
instrumentation Facilities and National Single Crystal X-ray
3871
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Inorganic Chemistry
Article
(35) Ganesamoorthy, C.; Mague, J. T.; Balakrishna, M. S. Eur. J.
Inorg. Chem. 2008, 596−604.
Diffraction Facility, IIT Bombay. J.T.M. thanks the Louisiana
Board of Regents through Grant LEQSF-(2002-03)-ENH-TR-
67 for purchasing the CCD diffractometer and the Chemistry
Department of Tulane University for supporting the X-ray
laboratory. We thank Mr. M. Kumaravel and Mr. G. S.
Ananthnag for their assistance in verifying the experimental
data.
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