Structural and electronic properties of luminescent copper(I) halide complexes of bis[2-(diphenylphosphano)phenyl] ether (DPEphos). Crystal structure of [CuCl(DPEphos)(dmpymtH]

Article abstract of DOI:10.1039/c0dt00286k

Heteroleptic copper(i) halide complexes containing the bis[2- (diphenylphosphano)phenyl]ether (DPEphos) ligand and the heterocyclic thioamides pyridine-2(1H)-thione (py2SH), pyrimidine-2(1H)-thione (pymtH) or 4,6-dimethylpyrimidine-2(1H)-thione (dmpymtH) have been synthesized and characterized by ¹H-NMR, IR spectroscopy, elemental analyses and melting point determinations. The complexes can be readily obtained by the addition of the thione ligand to a CuX-diphosphane adduct in dichloromethane-ethanol solution. The molecular structure of [CuCl(DPEphos)(dmpymtH)] complex has been established by single-crystal X-ray diffraction. The structure features a tetrahedral copper(i) center with two phosphorus atoms from the chelating diphos ligand, one halogen atom and the exocyclic sulfur atom of the heterocyclic thioamide unit. The complexes are strongly emissive in the solid state at ambient temperature. DFT and TD-DFT calculations were employed to study the structural, electronic and photophysical properties of the novel complexes. Electronic absorption spectra show two broad bands in the regions 275-290 and 380-398 nm of mixed MLCT/IL character. Intense blue-green emission is observed in the region 500-558 nm for complexes having py2SH or dmpymtH thione ligands. The emitting first triplet excited state, T₁ is mainly localized on the thione ligand. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00286k

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Structural and electronic properties of luminescent copper(I) halide complexes
of bis[2-(diphenylphosphano)phenyl] ether (DPEphos). Crystal structure of
[CuCl(DPEphos)(dmpymtH]†
P. Aslanidis,*a P. J. C ox b and A. C. Tsipis*c
Received 10th April 2010, Accepted 30th July 2010
DOI: 10.1039/c0dt00286k
Heteroleptic copper(I) halide complexes containing the bis[2-(diphenylphosphano)phenyl]ether
(DPEphos) ligand and the heterocyclic thioamides pyridine-2(1H)-thione (py2SH),
pyrimidine-2(1H)-thione (pymtH) or 4,6-dimethylpyrimidine-2(1H)-thione (dmpymtH) have been
synthesized and characterized by 1H-NMR, IR spectroscopy, elemental analyses and melting point
determinations. The complexes can be readily obtained by the addition of the thione ligand to a
CuX–diphosphane adduct in dichloromethane–ethanol solution. The molecular structure of
[CuCl(DPEphos)(dmpymtH)] complex has been established by single-crystal X-ray diffraction. The
structure features a tetrahedral copper(I) center with two phosphorus atoms from the chelating diphos
ligand, one halogen atom and the exocyclic sulfur atom of the heterocyclic thioamide unit. The
complexes are strongly emissive in the solid state at ambient temperature. DFT and TD-DFT
calculations were employed to study the structural, electronic and photophysical properties of the novel
complexes. Electronic absorption spectra show two broad bands in the regions 275–290 and
380–398 nm of mixed MLCT/IL character. Intense blue–green emission is observed in the region
500–558 nm for complexes having py2SH or dmpymtH thione ligands. The emitting first triplet excited
state, T1 is mainly localized on the thione ligand.
to receive particular attention,12,13 with the most intensively
studied and very promising class involving polypyridine and
1. Introduction
phenanthroline luminophores,14,15 newly combined with bis[2-
(diphenylphosphano)phenyl]ether (DPEphos) as a second rigid
chelating ligand.16–20 McMillin et al.21–23 reported that the copper(I)
complex [Cu(dmphen)2]+, where dmphen = bis(2,9-dimethyl-1,10-
phenanthroline) although exhibits photoluminescence in CH2Cl2
it is not emissive in methanol, ethanol or acetonitrile solutions. In
contrast, [Cu(I)(1,10-phenanthroline)2]+ is non-emissive indicating
the key role of the substituents at 2,9-positions of phenanthroline
ligand which prevent large structural distortions of the excited
states.21–23 The impact on luminescence properties upon modi-
fying the molecular structure was demonstrated in the case of
[Cu(dmphen)2]X (X = BF4 , ClO4 , NO3- and Cl-) complexes.24 In
the latter, changing the counteranion, X-, results in a decrease
of the dihedral angle between the two dmphen ligands and
to a concomitant reduction in the emission lifetimes. Mixed-
ligand copper(I) complexes have been synthesized and tested for
their ability to overcome solvent-induced exciplex quenching of
phosphorescence lifetime. Among them the most promising are
copper(I) complexes with polypyridine and phenathroline ligands
of the general formula [Cu(NN)(POP)]+ (NN = phenanthroline,
POP = bis[2-(diphenylphosphano)phenyl]ether).25
In the past two decades, coordination compounds of many
transition metals have attracted considerable interest, stimu-
lated by their real or potential applications as components
for luminescent-based chemical sensors,1–4 in display devices,5,6
as dopants to increase the electroluminescence efficiency of
organic light emitting diodes (OLEDs and PHOLEDs),7–9 as
sensitizers in solar-energy conversion,10,11 as photocatalysts and
photoinitiators. First row transition metal compounds are at-
tractive from an economical viewpoint, while they are less toxic
and more easily available than the currently used third row
noble metal complexes which are expensive, toxic and difficult
to obtain. In particular, copper(I) complexes are beginning
-
-
aAristotle University of Thessaloniki, Faculty of Chemistry, Inorganic
Chemistry Laboratory, P.O. Box 135, GR- 541 24, Thessaloniki, Greece.
E-mail: aslanidi@chem.auth.gr
bSchool of Pharmacy, The Robert Gordon University, Schoolhill, Aberdeen,
AB10 1FR, Scotland. E-mail: p.j.cox@rgu.ac.uk
cLaboratory of Inorganic and General Chemistry, Department of Chemistry,
University of Ioannina, 451 10, Ioannina, Greece. E-mail: attsipis@uoi.gr
† Electronic supplementary information (ESI) available: The structural
parameters of complexes 1–9 in their S0 and T1 states and their differences
are given in Tables S1 and S2 respectively. The principal singlet–singlet
optical transitions for the absorptions of 1–6, 8 and 9 are compiled in
Tables S3–S11. The absorption and emission spectra of complexes 1–9
computed with TD-DFT calculations at the PEB0/Def2-TZVP levels in
the gas phase and in CH2Cl2 solution are given in Fig. S1 and S2. The
cartesian coordinates and energy data of the stationary points on the
potential energy surface of the [CuCl(DPEphos)(thione)] complexes (1–9)
in both the S0 and T1 states (Table S11). The IR and normal modes of
complexes 1–6, 8 and 9 in the S0 and T1 states are shown in Fig. S3–S8.
CCDC reference number 768855. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00286k
Despite the relatively large amount of experimental work
devoted to the luminescence properties of copper(I) complexes,
theoretical studies are rather scarce. An extensive experimental
work accompanied by a detailed theoretical analysis of the
photophysical properties of copper(I) bis(diimine) compounds
was reported by Nozaki et al.26 In a combined experimental–
theoretical study it was shown that for a series of mixed-ligand
copper(I) complexes, [Cu(NN)(POP)]+, the HOMO–LUMO gap
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plays a crucial role in modulating the photophysical properties of
the complexes.25
The yellow to orange coloured microcrystalline solids
are diamagnetic and soluble in dichloromethane, chloroform
and acetone. Their dichloromethane solutions are non-
conducting.
Our interest in exploring the photochemistry of mixed-ligand
copper(I) complexes incorporating chelating phosphanes in the
coordination sphere has evolved from our recent studies on a series
The electronic absorption spectra of complexes 1–9, recorded
in dichloromethane at room temperature, show two intense broad
bands with maxima in the 275–290 and 380–398 nm regions
respectively. With reference to the absorption of the uncoordinated
DPEphos (272 nm), the first one can be attributed to intraligand
p → p* transitions on the phenyl groups of the phosphane ligand,
whereby the lower energy band, which lies in the region where the
free thiones absorb, expressing a small red shift as a consequence
of the coordination to Cu(I), should be considered as a thione-
originating intraligand transition.
The infrared spectra of compounds 1–9 recorded in the
range 4000–250 cm-1 contain, apart from the strong vibrational
phosphane bands, which remain practically unshifted upon co-
ordination, the characteristic four “thioamide bands” due to the
presence of the heterocyclic thione ligands, with shifts indicative
of an exclusive S-coordination mode, as well as a broad band
in the 3430–3460 cm-1 region assigned to the n(NH) stretching
vibration.
3
of Cu(I) compounds formulated as [Cu(k -triphos)(thiolate)].27
Noticeably, the presence of thiolate, acetylide and/or phosphane
ligands favors formation of ligand-linked metal cluster arrays
through metal–metal interactions.28 The emission energy, lifetime
and quantum efficiency of Cu(I) thiolate complexes are tunable
by modifying the ligands as well as introducing electron-donating
or -accepting substituents to the aromatic rings. In this work, we
employed computational (DFT and TD-DFT) methodologies in
conjunction with single crystal X-ray data aiming to contribute
to the understanding of the relationship between structure and
photophysical properties, and in this particular case to evaluate
the impact of the thiolate ligand on the luminescence properties
of the compounds. Accordingly we wish to report on new
luminescent derivatives resulting from the reactions of copper(I)
halides with bis[2-(diphenylphosphino)phenyl]ether (DPEphos)
and some neutral heterocyclic thiones.
Compounds 1–3 and 7–9 exhibit an intense blue–green emission
with lmax values of the broad bands in 500–558 nm range when
excited at l = 350 nm at room temperature in the solid state,
while the emissions observed for compounds 4–6, containing the
pyrimidine-2-thione ligand, are extremely weak. The absorption
and emission spectra of a representative compound 2 are shown in
Fig. 1 while absorption and emission data of the complexes under
investigation are summarized in Table 1.
2. Results and discussion
2.1. General considerations – synthesis and spectroscopic
characterization
Reaction of copper(I) halides with DPEphos and a heterocyclic
thioamide ligand in dry dichloromethane–ethanol mixtures gives
good yields of the complexes [CuX(DPEphos)(thione)] (X = Cl,
Br, I and thione = pyridine-thione, pyrimidine-2-thione and 4,6-
dimethylpyrimidine-2-thione). The diphosphane and heterocyclic
thione ligands along with their abbreviations are given in Scheme 1.
Table 1 Absorption and emission maxima of [CuX(DPEphos)(thione)]
complexes at room temperature
Complex
l
max/nma
l
em/nmb
[CuCl(DPEphos)(py2SH)], 1
[CuBr(DPEphos)(py2SH)], 2
[CuI(DPEphos)(py2SH)], 3
[CuCl(DPEphos)(dmpymtH)], 7
[CuBr(DPEphos)(dmpymtH)], 8
[CuI(DPEphos)(dmpymtH)], 9
275, 390
289, 387
285, 386
278, 393
284, 388
290, 380
513
534
500
549
558
527
Scheme 1 The diphosphane and heterocyclic thiones used as ligands with
their abbreviations.
a Solution in CH2Cl2. b Solid state.
Fig. 1 (a) Room temperature electronic absorption (in CH2Cl2 solution, dashed line, left axis) and emission (solid state, lexc = 350 nm, solid line, right
axis) spectra and (b) emission spectrum in CH2Cl2 solution of [CuBr(DPEphos)(py2SH)], 2 complex.
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2.2 X-Ray structure†
2.3 Computational studies
The single crystal structure of [CuCl(DPEphos)(dmpymtH)]
(complex 7) was resolved. An ORTEP view is depicted in Fig. 2,
and the coordination and geometrical parameters are listed in
Table 2. The molecule adopts a slightly distorted tetrahedral
geometry around the copper center with a P–Cu–P angle of
107.57(3)◦, which is clearly smaller than the values of 111.51(5)◦
2.3.1 Electronic structures at the optimized S0 and T1 geome-
tries. The study of the phosphorescent properties of transition
metal compounds requires knowledge of the degree of structural
distortion on going from the singlet S0 ground state to the
emitting triplet T1 state. This factor along with the energy
difference between these two states, E(T1) - E(S0) are of significant
importance since they are related to the non-radiative decay
rate of a complex. For an effective phosphorescent transition
metal compound the structural distortion accompanying the S0
to T1 transition should be small. In contrast, the T1–S0 energy
gap should be large in order for the non-radiative decay to be
minimized or preferably eliminated according to the energy gap
law which states that the non-radiative decay of a transition metal
complex increases exponentially as the energy gap or emission
energy decreases.37 Therefore, we have employed density functional
theory calculations to optimize the geometry of complexes 1–
9 in their S0 singlet ground state as well as in their T1 triplet
state. The structural parameters of complexes 1–9 along with the
changes of selected structural parameters accompanying the S0
to T1 excitation calculated at the PBEO/Def2-TZVP level are
compiled in Tables S1 and S2 given in ESI.†
and 116.44 (4)◦ observed for [Cu(NCNMe2)2(DPEphos)]BF4
29
30
and [Cu(dmp)(DPEphos)]BF4 complexes respectively.
The two P–Cu bond distances are 2.2966(7) and 2.2829(8) A
˚
respectively, and thus somewhat longer than those found in
[Cu(DPEphos)(acac)],31 or in [Cu(DPEphos)2]BF4 complexes.
32
The two phenyl rings in the backbone of the DPEphos ligand form
an angle of 80.01(9)◦, which is much larger than the corresponding
angle of the free diphosphane [ca. 67◦], but comparable to the val-
ues generally found in other related compounds.27 Furthermore,
˚
the distance of 3.6948(1) A between the two P atoms is significantly
˚
shorter than that found in the free DPEphos [5.741(1) A]. The
˚
Cu–S and Cu–Cl bond distances of 2.3186(8) and 2.3629(7) A
respectively are within the range of values previously found in
complexes with a similar CuClSP2 structural core.33–36
It is worth noting that the ether O atom is located at a non-
˚
bonding distance of 3.3400(19) A from the metal center. As in
The optimized structural parameters of 7 in the S0 ground
state are in good agreement with the X-ray structural analysis
data. However, the PBE0/Def2-TZVP computational protocol
many other copper(I) halide complexes containing heterocyclic
thione ligands, a strong intramolecular hydrogen bridge [N(2)–
˚
˚
˚
H(2) = 0.880 A, NH(1)–Cl(1) = 2.160 A, Cl(1) ◊ ◊ ◊ N(2) = 3.038 A,
Cl(1) ◊ ◊ ◊ H(2)–N(2) = 176◦] contributes to further stabilization of
the molecule in the solid state.
˚
overestimates the coordination bond lengths by 0.04–0.06 A,
while the respective bond angles defining the coordination sphere
of the complex showed a deviation in the range 0.4 to 5.4◦.
It should be noted that the most significant structural changes
accompanying the S0 to T1 transitions of complexes 1–9 are
focused on the coordination sphere of the complexes, i.e. the M–
L bond lengths and L¢–M–L bond angles, while the rest of
the structural parameters remain practically unaffected. The
structural changes on the phenyl rings of the phosphane and
thione ligands present very small or even no changes upon going
from the S0 to the T1 state. Therefore, we will focus our attention
only on the changes in the bond lengths and angles in and near the
copper coordination sphere occurring during the S0–T1 transition.
An inspection of Tables S1 and S2 reveals that in all complexes
there is a shortening of the Cu–X (X = Cl, Br or I), Cu–S and
◦
˚
Table 2 Selected bond lengths [A] and angles [ ] for 7
Cu(1)–Cl(1)
Cu(1)–P(1)
Cu(1)–P(2)
P(1)–Cu(1)–P(2)
P(1)–Cu(1)–S(1)
P(2)–Cu(1)–S(1)
P(1)–Cu(1)–Cl(1)
2.3629(7)
2.2966(7)
2.2829(8)
107.57(3)
109.96(3)
114.34(3)
100.80(3)
Cu(1)–S(1)
S(1)–C(1)
2.3186(8)
1.703(3)
P(2)–Cu(1)–Cl(1)
S(1)–Cu(1)–Cl(1)
C(1)–S(1)–Cu(1)
C(20)–O(1)–C(30)
114.24(3)
109.03(3)
114.09(11)
116.3 (2)
˚
˚
˚
Cu–P2 bond lengths by 0.08–0.15 A, 0.11–0.14 A and 0.02–0.03 A
respectively along the S0 to T1 route.
In contrast, there is an elongation of Cu–P1 bond in the T1 state
˚
by 0.09–0.13 A as compared to that found for the S0 ground state
of complexes 1–9. The same holds true for the S–C1 and C1–N
˚
bonds of the thione ligand which are lengthened by 0.05–0.08 A
˚
and 0.004–0.030 A in the T1 state. Finally, as we move further away
from the copper coordination sphere the changes in bond lengths
between the S0 and T1 states become negligible or even zero (see
Tables S1 and S2, ESI†).
The bond angles mostly affected during the S0–T1 transition
are the <(X–Cu–S) and <(S–Cu–P1). The former becomes more
obtuse while the latter becomes more acute with the changes falling
in the ranges 9–16◦ and 0–7◦ respectively. For the rest of the bond
angles around or near the copper metal center namely the <(P1–
Cu–P2), <(P2–Cu–X), <(Cu–P1–C10) and <(Cu–P2–C12), only
minor changes are observed falling in the range -3–5◦. In addition,
in going from the S0 to the T1 state, significant changes occur in
Fig. 2 A view of [CuCl(DPEphos)(dmpymtH)] (7) with atom labels.
Displacement ellipsoids are shown in the 50% probability level.
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Table 3 Energetic parameters relevant to phosphorescence of complexes 1–9 and differences in Mulliken charges between the S0 and T1 states calculated
at the PEB0/Def2-TZVP level of theory
Parameter
1
2
3
4
5
6
7
8
9
DET /kcal mol-1
Dddocc/eV
DE0–0/eV
DEver/eV
52.9
0.26
2.21
1.81
0.48
0.03
-0.12
-0.05
-0.06
0.00
52.6
0.24
2.20
1.73
0.55
0.03
-0.12
-0.07
-0.06
0.00
51.9
0.19
2.17
1.69
0.56
0.04
-0.11
-0.09
-0.06
0.00
47.2
0.26
1.98
1.20
0.85
0.01
-0.07
-0.07
-0.06
0.00
46.9
0.23
1.96
1.22
0.82
0.03
-0.07
-0.09
-0.06
0.00
46.4
0.20
1.95
1.26
0.75
0.04
-0.06
-0.11
-0.06
0.00
53.6
0.20
2.28
1.66
0.67
0.07
-0.03
-0.03
0.08
0.00
51.6
0.21
2.17
1.48
0.76
0.03
-0.08
-0.09
-0.06
0.00
51.1
0.19
2.14
1.48
0.73
0.05
-0.08
-0.12
-0.05
0.00
1 -S0
l
vib/eV
DQPt
DQS
DQX
DQP1
DQP2
the conformation of the thione and phenyl rings which are twisted
by 5–31◦ and 7–76◦ respectively. On the other hand, the dihedral
angle P1–C12–C13–O changes to a lesser extent by 7–10◦.
T1 states will be, resulting in higher radiative decay rate constant,
kr (faster radiative decay). Therefore, we have calculated the energy
splitting, Dddocc of the highest occupied d orbitals (actually they
are MOs having mainly d orbital character) of complexes 1–9 and
the results are given in Table 3.
The energy difference DET = E(T1) - E(S0) between the singlet
-S
1
0
ground state, S0 and the triplet first excited state, T1, calculated at
the PEB0/Def2-TZVP level of theory is compiled in Table 3. The
Perusal of Table 3 reveals that Dddocc is highest when the halide
ligand is chloride and lowest when it is iodide. Also, amongst
the complexes with the same halide ligand, the lowest Dddocc is
observed for those having dmpymtH as the thione ligand (with
the exception of complexes 3 and 9).
DET1 is taken as the total electronic energy difference between
-S
0
the T1 and S0 states (Scheme 2).
In Table 3 are also given the 0–0 transition energies, DE0–0
,
(Scheme 2) for complexes 1–9 to help rationalize the electronic
origin of peaks in the emission spectra. The 0–0 transition energy
DE0–0 is computed from the difference in total energies of the
optimized S0 and T1 states taking into account the respective zero-
point energies (ZPE) of complexes 1–9.
In addition, two other energetic parameters of interest have
been calculated, namely the vertical transition energy, DEver and
the vibrational reorganization energy, lvib. The former is obtained
by total electronic energy difference between the T1 and the S0
state at the T1 optimized geometry and the latter is taken as the
total electronic energy difference between the S0 and the S0 state
at the T1 optimized geometry (Scheme 2). The calculated values
are also given in Table 3. The vertical transition energy, DEver for
complexes 1–3 and 7–8 correspond to transitions in the visible
region while for complexes 4–6 in the near IR region. Complexes
4–6 show the largest vibrational reorganization energy, lvib while
the lowest ones are observed for complexes 1–3.
Scheme 2 Potential energy curves of S0 and T1 states and energetic
parameters relevant to phosphorescence.
The decrease of the DET
energetic parameter follows the
-S
0
order 1 > 2 > 3 > 8 > 9 > 41> 5 > 6 > 7 and based on the energy
An alternative way to describe the emitting lowest triplet state,
T1 is through Mulliken population analysis allowing the estimation
of the changes of the net atomic charges upon the T1 → S0 de-
excitation process. Perusal of Table 3 reveals that upon the T1 →
S0 de-excitation, charge is transferred from the copper central
metal atom (positive DQCu) to the surrounding donor atoms
(negative DQS, DQX and DQP1) with the exception of P2 donor
atom (DQP2 = 0). However, this does not hold true for complex
7 where in the T1 → S0 de-excitation process the atom losing
electron density is P1 while the atoms gaining electron density are
Cu, S and Cl. It should be noted that the changes in net atomic
charges during the T1 → S0 de-excitation process are relatively
small.
gap law, the non-radiative rate constant, knr of these complexes
is expected to increase in the same order. In general, the DET1
-S
0
energy gap depends on the nature of the thione ligand following
the trend py2SH > dmpymtH > pymtH. The exception is complex
7, which although bears the dmpymtH ligand, exhibits the lowest
DET 0 energy gap and subsequently is expected to have the largest
-S
1
non-radiative decay rate constant, knr. On the other hand, amongst
the copper(I) complexes with py2SH or pymtH thione ligands, the
DET1 energy gap depends on the nature of the halide ligands
-S
0
following the trend Cl- > Br- > I-. However, this is not true for
the copper(I) complexes with dmpymtH thione ligand where the
DET1 energy gap follows the trend Br- > I- > Cl-. Another
-S
0
factor which has been stated as being critical in determining the
phosphorescence efficiency of a transition metal complex38,39 is the
energy splitting, Dddocc of its highest occupied d orbitals.
Accordingly, if the closer in energy the highest d occupied
orbitals are, the larger the Hsoc matrix element between the S1 and
The spin density of a representative complex 1 in its lowest
triplet excited state, T1 obtained as the difference between a and
b spin contributions to the total electron density, is depicted in
Fig. 3 along with the 3D contour plots of the singly occupied
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energy band with a shoulder in the ultraviolet region (250–350 nm)
and a lower energy band of very low intensity in the visible region
(400–450 nm). Noteworthy the simulated absorption spectra of
complexes 1–9 in CH2Cl2 solution are in close resemblance with
the experimentally obtained absorption spectra. An inspection of
Table 4 reveals that the electronic transitions are blue shifted and
gain intensity in the CH2Cl2 solution spectra of the complexes
compared to the simulated spectra in the gas phase.
The low-energy absorption band of very low intensity involves
in all cases, mainly a HOMO → LUMO excitation and in some
cases (2, 3 and 9) involves also a HOMO-1 → LUMO excitation
(Table 4). In Fig. 5 are depicted schematically the 3D contour
surfaces plots of the molecular orbitals involved in the electronic
transitions for a representative complex 7 while analogous are
the MOs involved in the electronic transitions of the remaining
complexes.
Inspection of Fig. 5 reveals that the HOMO and HOMO-1 are
constructed from the out-phase combination of Cu 3d AOs with
p orbitals located on the S atom of the thione ligand and on the
halide ligand as well, while LUMO is mainly located on the thione
ligand. Therefore, the low-energy absorption band exhibits a
composite electronic transition pattern involving both MLCT and
intraligand, IL transitions. The electronic transitions are allowed
under the electric dipole interaction since the corresponding
computed transition dipole moments, m are non-zero while the
% CT values are positive, indicating MLCT character. The charge
transfer, taking place upon the electronic transitions responsible
for the low-energy bands, is reflected on the changes of the electron
density distribution depicted in Fig. 6 in the form of electron
density difference maps (EDDM) for the representative complex 7.
Accordingly, the region comprising the metal and the surrounding
atoms, including the S atom of the thione and the halide ligand, is
depleted from electron density in contrast to the region comprising
the thione ligand where there is an enhancement of the electron
density.
Fig. 3 3D contour plots of SOMO and SOMO-1 along with spin density
isosurface (0.001 au) of complex 1 computed at the PEB0/Def2-TZVP
level.
molecular orbitals (SOMOs). Analogous are the spin densities
and the SOMOs of the remaining complexes.
Inspection of Fig. 3 reveals that the spin density is mainly
distributed on the thione and halide ligands and to a lesser extent
on the Cu metal center as well as on one P donor atom. The spin
density distribution is approximately accounted for by the sum
of the SOMO and SOMO-1. Thus, upon decay from the T1 to
S0 state, polarization of the spin will involve mainly recoupling
of the electron in the SOMO with the electron residing in the
SOMO-1 since in the singlet state spin density is identically zero
at every point in space. Taking into account the shapes of the
molecular orbitals and the spin density in the T1 state, it seems
that the electron is localized mainly on thione ligand while the
hole is localized on the metal.
2.3.2 TD-DFT simulated absorption spectra. The absorption
spectra of complexes 1–9, were computed with TD-DFT calcu-
lations at the PEB0/Def2-TZVP level on the optimized singlet
ground states of the complexes in the gas phase and in CH2Cl2
solution. The simulated absorption spectra of a representative
complex 2 in the gas phase and in CH2Cl2 solution are depicted
schematically in Fig. 4, while those of the remaining complexes
are given in ESI (Fig. S1 and S2).†
Selected TD-DFT principal singlet–singlet electronic transi-
tions, excitation energies and oscillator strengths for the gas phase
and CH2Cl2 solution spectra of the representative complex 2 are
compiled in Table 4. The singlet–singlet electronic transitions,
excitation energies and oscillator strengths of complexes 1–9 are
given in more detail in the ESI (Tables S3–S11).†
The simulated absorption spectra of all complexes 1–9 exhibit
also a broad, very intense high-energy band arising from a
multitude of electronic transitions. The most important electronic
transitions relevant with the high-energy band, involve HOMO,
(HOMO-1 to -3) → LUMO, (LUMO+1 to +9) excitations. As it
has already been mentioned, HOMO and HOMO-1 are located
It should be noted that the absorption spectra are marginally
affected by changing either the halide or the thione ligand, basi-
cally exhibiting the same qualitative features i.e. an intense high
Fig. 4 TD-DFT-PBE0/Def2-TZVP simulated absorption and emission spectra of a representative complex 2 in the gas phase and in CH2Cl2 solution.
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Table 4 Selected principal singlet–singlet optical transitions in the absorption spectra of complex 2 in the gas phase and CH2Cl2 solution calculated at
the TD-DFT-PBEO/Def2-TZVP level
Excitation (% composition)
E/eV
l/nm
OS, f
m
% CT
Gas phase
H-1 → L (19%), H → L (75%)
2.951
3.445
3.692
3.767
3.783
3.885
3.954
4.108
4.273
4.350
4.450
420.2
359.9
335.9
329.2
327.8
319.2
313.6
301.8
290.1
285.0
278.7
0.018
0.016
0.035
0.048
0.053
0.029
0.039
0.051
0.022
0.020
0.030
0.504
0.428
0.621
0.721
0.759
0.553
0.636
0.710
0.453
0.309
0.418
16
16
13
3
15
13
16
14
10
18
16
H → L+1 (94%)
H → L+2 (39%), H → L+3 (40%)
H → L+3 (10%), H → L+4 (10%)
H → L+3 (15%), H → L+4 (61%)
H → L+4 (17%), H → L+5 (60%)
H-1 → L+2 (29%), H-1 → L+3 (53%)
H → L+6 (20%), H → L+7 (64%)
H-5 → L (16%), H-3 → L+1 (72%)
H-1 → L+6 (40%), H-1 → L+7 (32%)
H-3 → L+2 (18%), H-1 → L+8 (70%)
CH2Cl2 solution
H-1 → LUMO (10%), H → L (84%)
3.177
3.620
3.818
3.900
4.012
4.082
4.097
4.173
4.241
4.483
4.517
4.567
4.606
390.3
342.5
325.3
317.9
309.1
303.7
302.6
297.1
292.3
276.6
274.5
271.5
269.2
0.047
0.021
0.057
0.069
0.176
0.022
0.038
0.032
0.075
0.044
0.028
0.034
0.020
0.780
0.487
0.779
0.848
1.339
0.466
0.617
0.556
0.881
0.633
0.493
0.547
0.425
24
30
22
7
10
27
10
8
10
7
13
12
8
HOMO → L+1 (94%)
HOMO → L+2 (81%)
HOMO → L+5 (35%), HOMO → L+3 (31%)
HOMO → L+4 (55%)
H-1 → L+2 (83%)
H-1 → L+3 (33%), H-1 → L+4 (38%)
H-1 → L+3 (44%),
HOMO → L+7 (49%), HOMO → L+6 (26%)
H-3 → L+1 (42%), HOMO → L+10 (31%)
H-1 → L+6 (48%), H-1 → L+7 (34%)
H-2 → L+4 (50%), H-1 → L+7 (23%)
H-1 → L+8 (37%), H-2 → L+5 (23%)
Fig. 5 Molecular orbitals involved in the electronic transitions of complex 7.
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Fig. 6 Electron density difference maps corresponding to electronic transitions with high MLCT character in the absorption spectrum of complex 7.
Green and red colors show the regions of increased and decreased electron density, respectively.
mainly on the metal and the surrounding atoms, including S atom
of thione and the halide ligands while HOMO-2 and HOMO-3
are constructed from out-of-phase combinations of Cu 3d AOs
with p orbitals mainly located on the halide ligand and to a
lesser extent on the S atom of the thione ligand. On the other
hand, LUMO and LUMO+1 are located on the thione ligand
while the rest of the unoccupied orbitals, involved in the electronic
transitions of 1–9, are mainly located in the phosphane ligands
and thus the high-energy band could be assigned as MLL¢CT/IL.
It is worth noting that all the electronic transitions involved in the
high-energy band are electric dipole allowed (non-zero transition
dipole moment) and also that the corresponding %CT character
of the electronic transitions, related to the high-energy band, is
positive which is indicative of metal to ligand charge transfer. The
latter is reflected on the EDDMs depicted in Fig. 6 i.e. clearly there
is electron density depletion in the area comprising the metal and
surrounding atoms and electron density enhancement in the areas
including the phosphane and thione ligands.
matching the experimentally observed broad band (Fig. 2) and
one or two broad high-energy bands within near-IR region (1000–
1600 nm). Practically, changing the halide ligand merely alters the
intensity of the bands. Thus, amongst complexes 1–6 with py2SH
or pymtH thione ligands, the most intense bands are exhibited by
those having chloride ligand while amongst complexes 7–9 with
dmpymtH thione ligand, the iodide one exhibits the most intense
bands. In addition, complexes with py2SH thione ligand show the
most intense bands while the complexes with pymtH or dmpymtH
thione ligands show bands of almost the same intensity. Finally,
the emission spectra of complexes with pymtH ligand show four
sharp low-energy bands in contrast to the emission spectra of the
rest of the complexes which show three.
2.3.4 Vibrational analysis of the ground, S0 and the lowest
triplet, T1 states. In order to help a future analysis of the
vibronic structure of the phosphorescence spectra of complexes 1–
9, possibly with time resolved infrared spectroscopy, we calculated
the vibrational frequencies and simulated the IR spectra for both
their ground, S0 and the lowest triplet, T1 states. The simulated
infrared spectra along with the normal modes of the most intense
absorption bands for a representative complex 7 in both the
ground, S0 and the lowest triplet, T1 states are depicted in
Fig. 7.
The simulated IR spectra and normal modes of the rest of the
complexes 2–9 both in their ground, S0 and the lowest triplet,
T1 states exhibit quite similar features (Fig. S3–S10, ESI†). The
bands at 519, 536, 730, 789 and 1511 cm-1 correspond to the
out-of-plane bending of the atoms of the phenyl rings while
the band at 3203 cm-1 corresponds to a ‘breathing’ mode of
one phenyl ring. The bands at 1289, 1620 and 1679 cm-1 are
related with in-plane deformations of the thione ligand. Finally,
the band at 3115 cm-1 corresponds to N–H stretching vibration.
Generally, the simulated IR spectra of complexes 1–9 are in close
resemblance with the experimental ones. For example compare the
scaled harmonic vibrational frequencies (scaling factor = 0.961)42
of complex 7 with the experimental values given in parentheses:
Noteworthy, is the disappearance of the low-energy band as
well as of the shoulder in the absorption spectra of the iodide
complexes 3, 6 and 9 in contrast to the chloride and bromide
ones.
2.3.3 TD-DFT simulated emission spectra. The emission
spectra of complexes 1–9, were computed with TD-DFT calcula-
tions at the PEB0/Def2-TZVP level on the optimized first excited
triplet state of the complexes both in the gas phase and in CH2Cl2
solution following a previously suggested methodology.40,41 The
simulated emission spectra for a representative complex 2 both in
the gas phase and in CH2Cl2 solution are depicted schematically
in Fig. 4, while those of the remaining complexes are given
in ESI (Fig. S1 and S2).† Noteworthy, the simulated emission
spectra perfectly resemble the experimental ones with respect to
the region of 300–800 nm of the spectra. The simulated emission
spectra of 1–9 exhibit the same qualitative pattern i.e. three or
four sharp low-energy bands within the UV-Vis region (300–
800 nm) which upon overlap afford one broad band perfectly
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Fig. 7 Infrared spectra along with the normal modes of the most intense absorption bands of complex 7 in both the S0 and T1 states computed at the
PEB0/Def2-TZVP level of theory (S0 grey line, T1 black/dashed line).
n9 = 3078.1, 2993.5 (3049 m), n8 = 1613.5 (1614 s), n7 = 1556.8
(1567vs), n6 = 1452.1 (1460 s), n5 = 1238.7 (1229 vs), n4
3. Experimental section
=
758.2 (748 s), n3 = 701.5 (737 s), n2 = 510.3 (511 s). Notice
that the vibrational modes of the unmixed ground, S0 and first
triplet excited state, T1 have almost identical frequencies. The only
remarkable difference is a shift of the N–H stretching vibration to
higher frequencies with a concomitant dramatic intensity decrease.
This is indicative that upon T1 → S0 de-excitation a hydrogen bond
is formed between the H atom of the thione ligand and the halide
ligand.
3.1 Materials and instrumentation
Commercially available copper(I) halides and bis[2-
(diphenylphosphano)phenyl]ether were used as received while
the thiones (Aldrich) were re-crystallized from hot ethanol
prior to their use. All the solvents were purified by respective
suitable methods and allowed to stand over molecular sieves.
Infra-red spectra in the region of 4000–250 cm-1 were obtained
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Table 5 Crystal data and structure refinements for [CuCl(DPEphos)-
(dmpymtH)], 7
3.3 General procedure for the synthesis of complexes 1–9
To a suspension of 0.5 mmol of copper(I) halide (49.5 mg
for CuCl, 71.7 mg for CuBr, 95.2 mg for CuI) in 30 cm3
of dry dichloromethane, 269.3 mg (0.5 mmol) of bis[2-
(diphenylphosphano)phenyl]ether was added and the mixture was
stirred for two hours at 50 ◦C. The resulting clear solution was
filtered of and then treated with the appropriate thione (0.5 mmol)
dissolved in a small amount (~20 cm3) of ethanol and the new
reaction mixture was stirred for additional two hours at 50 ◦C.
Slow evaporation of the clear solution at ambient afforded a
microcrystalline solid, which was filtered off and dried in vacuo.
7
Molecular formula
Formula weight
T/K
C42H36ClCuN2OP2S·0.125C2H5OH
783.48
120(2)
0.71073
Monoclinic
P21/c
15.3542 (2)
16.8655 (4)
14.7534 (3)
90
100.3890 (10)
90
3757.85 (13)
4
1.385
0.830
˚
Wavelength/A
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
3.3.1 [CuCl(DPEphos)(py2SH)]
(1). Yellow
crystals
g /◦
(314 mg, 84%), m.p. 172 ◦C; Anal. Calcd for C41H33NClCuOP2S:
C, 65.77; H, 4.44, N: 1.87%; Found: C, 65.41; H, 4.41; N, 1.69%.
IR (cm-1): 3427 br, 3050 m, 1563 s, 1585 s, 1476 vs, 1459 vs,
1432 vs, 1258 s, 1222 vs, 1180 s, 1132 s, 1092 s, 1068 s, 991 m,
872 s, 800 m, 747 vs, 695 vs, 502 s. UV-Vis [lmax (nm), loge],
(CH2Cl2): 275 (4.69), 390 (2.59).
3
˚
Volume/A
Z
Density (calculated)/Mg m-3
Absorpt. coefficient/mm-1
F(000)
1621
Crystal size/mm
Theta range for data collection
Index ranges
0.18 ¥ 0.11 ¥ 0.08
2.96 to 27.48◦
-19 < = h < = 19
-21 < = k < = 21
-19 < = l < = 19
39 667
8557 [R(int) = 0.0573]
99.4% (theta = 27.48◦)
8557/0/453
0.9366 and 0.8650
Full-matrix least-squares on F2
1.059
3.3.2 [CuBr(DPEphos)(py2SH)]
(2). Yellow
crystals
(396 mg, 91%), m.p. 197 ◦C; Anal. Calcd for C41H33NBrCuOP2S:
C, 62.08; H, 4.19; N, 1.77%; Found: C, 61.87; H, 4.24; N, 1.70%.
IR (cm-1): 3436 br, 3045 m, 1573 vs, 1585 s, 1471 s, 1460 s, 1433 vs,
1258 s, 1205 vs, 1180 s, 1133 vs, 1096 s, 1068 m, 985 s, 872 m, 808
m, 747 vs, 695 vs, 508 s. UV-Vis [lmax (nm), loge], (CH2Cl2): 289
(4.32), 387 (3.85).
Reflections collected
Independent reflections
Completeness
Data/restraints/parameters
Max. and min. transmission
Refinement method
Goodness-of-fit on F2
Final R indices [(I > 2s(I)]
R indices (all data)
R1 = 0.0497, wR2 = 0.01008
3.3.3 [CuI(DPEphos)(py2SH)] (3). Yellow crystals (419 mg,
R1 = 0.0613, wR2 = 0.1070
◦
2
90%), m.p. 259 C; Anal. Calcd for C41H33NCuIOP2S: C, 58.61;
Final weighting scheme
Calc w = 1/[s (Fo2) + (0.0228P)2 +
H, 3.96; N, 1.67%; Found: C, 58.75; H, 4.04; N, 1.64%. IR (cm-1):
3465 br, 3044 m, 1565 vs, 1472 s, 1457 vs, 1361 s, 1256 s, 1203 vs,
1180 m, 1130 vs, 1091 s, 1068 m, 992 m, 870 m, 801 m, 745 vs,
689 vs, 507 vs. UV-Vis [lmax (nm), loge], (CH2Cl2): 285 (4.09),
386 (3.58).
9.1795P] where P = (Fo + 2Fc2)/3
2
3
˚
Largest diff. peak and hole
0.556 and -0.462 e/A
in KBr discs with a Perkin-Elmer 1430 spectrophotometer,
while a Perkin-Elmer-Hitachi 200 spectrophotometer and a
Hitachi F-7000 Fluorescence Spectrophotometer were used
to obtain the electronic absorption and emission spectra
respectively.
Melting points were measured in open tubes with a STUART
scientific instrument and are uncorrected. Molar conductivities,
magnetic susceptibility measurements and elemental analyses for
carbon, nitrogen and hydrogen were performed as described
previously.27
3.3.4 [CuCl(DPEphos)(pymtH)]
(4). Yellow
crystals
(374 mg, 82%), m.p. 232 ◦C; Anal. Calcd for C40H32N2ClCuOP2S:
C, 64.08; H, 4.30; N, 3.74%; Found: C, 63.80; H, 4.28; N, 3.67%.
IR (cm-1): 3435 br, 3046 m, 1603 s, 1575 vs, 1480 s, 1457 s, 1432 vs,
1457 s, 1432 vs, 1324 s, 1218 vs, 1182 vs, 1093 m, 976 s, 875 m,
745 s, 694 vs, 508 s, 466 s. UV-Vis [lmax (nm), loge], (CH2Cl2):
287 (4.35), 398 (3.24).
3.3.5 [CuBr(DPEphos)(pymtH)]
(5). Yellow
crystals
(396 mg, 91%), m.p. 154 ◦C; Anal. Calcd for C40H32N2BrCuOP2S:
C, 60.49; H, 4.06; N, 3.53%; Found: C, 60.36; H, 3.92; N, 3.54%.
IR (cm-1): 3452 br, 3048 m, 1612 vs, 1562 vs, 1459 s, 1433 vs,
1226 vs, 1210 vs, 1157 s, 1093 s, 983 m, 869 m, 747 vs, 738 vs,
696 vs, 511 s, 498 s. UV-Vis [lmax (nm), loge], (CH2Cl2): 286
(4.45), 385 (3.44).
3.2 Crystal structure determination†
Single crystals suitable for crystal structure analysis were ob-
tained by slow evaporation of an acetonitrile–ethanol solution
of the complex at room temperature. X-Ray diffraction data
were collected on an Enraf-Nonius Kappa CCD area-detector
diffractometer. The programs DENZO43 and COLLECT44 were
used in data collection and cell refinement. Details of crystal
and structure refinement are compiled in Table 5. The structures
were solved using program SIR9745 and refined with program
SHELX-97.46 The SQUEEZE option of PLATON is used in
order to remove the disorder of 1/8 of an ethanol molecule from
the calculations. Molecular plots were obtained with program
ORTEP-3.47
3.3.6 [CuI(DPEphos)(pymtH)] (6). Orange crystals (418 mg,
85%), m.p. 208 ◦C; Anal. Calcd for C40H32N2ICuOP2S: C, 57.11;
H, 3.83; N, 3.33%; Found: C, 56.96; H, 3.77; N, 3.34%. IR (cm-1):
3435 br, 3050 m, 1606 s, 1565 s, 1461 s, 1492 vs, 1328 s, 1258 s,
1220 vs, 1189 s, 1093 m, 982 m, 872 m, 748 vs, 694 vs, 508 s, 473 s.
UV-Vis [lmax (nm), loge], (CH2Cl2): 291 (4.46), 390 (3.38).
3.3.7 [CuCl(DPEphos)(dmpymtH)] (7). Yellow crystals
(388 mg, 82%), m.p. 206 ◦C; Anal. Calcd for C42H36ClCuN2OP2S:
C, 64.86; H, 4.66; N, 3.60%; Found: C, 63.53; H, 4.58; N, 3.45%.
10246 | Dalton Trans., 2010, 39, 10238–10248
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IR (cm-1): 3452 br, 3049 m, 1614 s, 1567 vs, 1460 s, 1432 vs,
1229 vs, 1206 vs, 1093 m, 986 m, 748 s, 737 s, 696 s, 511 s, 463 s.
UV-Vis [lmax (nm), loge], (CH2Cl2): 278 (4.09), 393 (3.30).
complexes show two broad bands in the regions 275–290 and 380–
398 nm. According to TD-DFT calculations these bands could
be assigned as having MLL¢CT/IL character. An intense blue–
green emission in the range 500–558 nm is observed for complexes
of py2SH or dmpymtH thione ligands, while complexes of the
pymtH ligand show only weak emission. However, based upon
the TD-DFT simulated emission spectra both in the gas phase
and in CH2Cl2 solution, it is expected to have additional emission
3.3.8 [CuBr(DPEphos)(dmpymtH)] (8). Yellow crystals
(410 mg, 85%), m.p. 197 ◦C; Anal. Calcd for C42H36N2BrCuOP2S:
C, 61.35; H, 4.41; N, 3.41%; Found: C, 61.26; H, 4.50; N, 3.35%.
IR (cm-1): 3436 br, 3052 m, 1608 s, 1564 s, 1547 vs, 1462 s, 1434 vs,
1251 s, 1220 s, 1119 s, 1068 m, 741 s, 694 s, 507 s, 460 s. Vis [lmax
(nm), loge], (CH2Cl2): 284 (4.02), 388 (3.31).
bands in the UV-Vis and near-IR regions. The largest DET1
-S
0
energy gap amongst all complexes under investigation is found for
the complexes with pymtH ligand and therefore it is expected that
they would have the largest nonradiative decay rate constant, knr.
On the other hand, the computed Dddocc energy splitting values
of complexes 1–9 present small variation making this parameter
unsuitable for predicting the magnitude of radiative decay rate
constants, kr and phosphorescence efficiencies. The structural
distortions associated with the T1 to S0 transitions are found to be
relatively small and are also reflected on the computed IR spectra
for these states. The only remarkable structural distortion upon
T1 → S0 de-excitation is a change in the thione conformational
orientation resulting in N–H ◊ ◊ ◊ X hydrogen bond formation.
Concomitantly there is a shift to lower frequencies of the N–H
stretching vibration mode, accompanied by a dramatic intensity
increase.
3.3.9 [CuI(DPEphos)(dmpymtH)]
(9). Yellow
crystals
(434 mg, 82%), m.p. 146 ◦C; Anal. Calcd for C42H36N2ICuOP2S:
C, 58.03; H, 4.17; N: 3.22%; Found: C, 58.06; H, 4.21; N, 3.24; IR
(cm-1): 3434 br, 3035 m, 1622 vs, 1562 vs, 1462 s, 1437 vs, 1219 vs,
1186 vs, 1029 m, 978 s, 746 s, 690 s, 537 m, 505 s, 459 s. Vis [lmax
(nm), loge], (CH2Cl2): 290 (4.40), 380 (3.51).
3.4. Computational details
Full geometry optimization without symmetry constrains were
carried out in the gas phase for both the singlet ground state
(S0) and the lowest triplet excited state (T1) of complexes 1–9,
using the full-range PBE0 non-local hybrid GGA functional48–51
combined with the Def2-TZVP basis set of Ahlrichs et al.52 for
all atoms (the computational protocol is denoted as PBE0/Def2-
TZVP). The attainment of the energy minimum was verified by
calculating the vibrational frequencies that result in the absence
of imaginary eigenvalues (NImag = 0). The computed electronic
energies were corrected to constant pressure and 298 K, for zero
point energy (ZPE) differences and for the contributions of the
translational, rotational and vibrational partition functions. Time-
dependent density functional theory (TDDFT)53–56 calculations
were performed employing the PBE0/Def2-TZVP computational
protocol. The TDDFT calculations were performed in the gas
phase and in CH2Cl2 solution for both the singlet ground state (S0)
and the lowest triplet excited state (T1) of complexes 1–9 including
the lowest 50 singlet–singlet and triplet–triplet excitations. All
calculations were done using the Gaussian03 program suite.56
The Mulliken atomic spin densities were obtained by employing
Mulliken population analysis.57,58
Acknowledgements
We thank the EPSRC X-ray crystallography service at the Univer-
sity of Southampton for collecting the X-ray data. The authors
aknowledge computer time provided by the Center for Scientific
Simulations at the University of Ioannina, Greece.
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10248 | Dalton Trans., 2010, 39, 10238–10248
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