Luminescent mononuclear mixed ligand complexes of copper(i) with 5-phenyl-2,2′-bipyridine and triphenylphosphine

Article abstract of DOI:10.1039/c5dt02755a

Reaction of 5-phenyl-2,2′-bipyridine (L) with a mixture of CuI or [Cu(CH₃CN)₄]BF₄ and PPh₃ leads to mononuclear heteroleptic complexes [CuL(PPh₃)I] (1) and [CuL(PPh₃)₂]BF₄

Full text of DOI:10.1039/c5dt02755a

Dalton
Transactions
View Article Online
View Journal
PAPER
Luminescent mononuclear mixed ligand
complexes of copper(I) with 5-phenyl-
Cite this: DOI: 10.1039/c5dt02755a
2,2’-bipyridine and triphenylphosphine†‡
Damir A. Safin,*a Mariusz P. Mitoraj,*b Koen Robeyns,a Yaroslav Filinchuka and
Christophe M. L. Vande Velde*c
Reaction of 5-phenyl-2,2’-bipyridine (L) with a mixture of CuI or [Cu(CH3CN)4]BF4 and PPh3 leads to
mononuclear heteroleptic complexes [CuL(PPh3)I] (1) and [CuL(PPh3)2]BF4 (2). According to X-ray diffrac-
tion, L crystallizes in the monoclinic space group P21/n, exhibiting a disorder over four orientations. Com-
plexes 1 and 2 crystallize in the monoclinic space groups P21/c and P21, respectively. 1 comprises a
discrete neutral molecule, while 2 has an ionic structure containing [CuL(PPh3)2]+ and BF4–. Both struc-
tures reveal that each tetracoordinated copper(I) atom is linked to two nitrogen atoms of L, one iodide
and one PPh3 in the structure of 1, or two PPh3 in the structure of 2 with the formation of a distorted tetra-
hedral coordination core. The structure of 2 is additionally stabilized by a weak intramolecular π⋯π
stacking interaction formed between two adjacent phenyl rings of two PPh3 ligands. Hirshfeld surface
analysis showed that the structures of both complexes are mainly characterized by H⋯H and C⋯H con-
tacts as well as by I⋯H in the structure of 1 and F⋯H in the structure of 2. The 2D fingerprint plots of two
different molecules in the structure of L showed that both molecules exhibit contacts for π⋯π stacking
interactions. The factors important for the stability of 1 and 2 were further quantitatively and qualitatively
characterized by the charge and energy decomposition method ETS-NOCV. According to diffuse reflec-
tance spectroscopy in the solid state, free L exhibits bands exclusively in the UV region, while the spectra
of 1 and 2 also contain bands in the visible range up to about 500 and 600 nm. All three compounds
were found to be emissive in the solid state. DFT calculations have shown that, while emission of L is due
to the ligand-centered π → π* transition, luminescence of 1 and 2 was assigned to a (M + X)LCT and
MLCT excited states, respectively.
Received 20th July 2015,
Accepted 1st September 2015
DOI: 10.1039/c5dt02755a
www.rsc.org/dalton
sion.1 N-heterocyclic ligands, in particular polypyridine com-
pounds, are known to be an efficient tool to tune the
Introduction
Copper(I) complexes are of ever increasing interest due to their luminescence properties of copper(I) complexes.2 These
attractive photophysical properties for luminescent sensors ligands can be easily modified by introducing different substi-
and probes, electroluminescence, and solar energy conver- tuents, possessing a variety of electronic, steric and confor-
mational impacts on both the coordinated chelate and
coordination core. Furthermore, the nature of additional
aInstitute of Condensed Matter and Nanosciences, Molecules, Solids and Reactivity
(IMCN/MOST), Université catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-
la-Neuve, Belgium. E-mail: damir.a.safin@gmail.com
bDepartment of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University,
R. Ingardena 3, 30-060 Cracow, Poland. E-mail: mitoraj@chemia.uj.edu.pl
cFaculty of Applied Engineering, Advanced Reactor Technology, University of Antwerp,
Salesianenlaan 90, BE-2660 Hoboken, Belgium.
ligands, in particular halides and phosphines, was found to
affect the luminescence properties of copper(I) compounds.3
N-heterocyclic compounds such as 2,2′-bipyridine, 1,10-
phenanthroline and 2,2′:6′,2″-terpyridine seem to be the most
widely used polypyridine luminophore ligands for metal com-
plexes. However, these ligands alone exhibit undesirable
luminescence at short wavelengths due to the emission from
the n–π* excited state.4 Furthermore, since the 2,2′-bipyridine
framework is polarized along the 5,5′-axis,5 introduction of
aromatic substituents into these positions leads to an increase
of the conjugation and, thus, increase of polarization along
E-mail: christophe.vandevelde@uantwerpen.be
†Dedicated to Professor F. Ekkehardt Hahn on the Occasion of his 60th
Birthday.
‡Electronic supplementary information (ESI) available: Fig. S1–S4 and Table S1.
CCDC 1410040–1410042. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c5dt02755a
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
this axis. This, in turn, will lead to higher luminescence as according to the 31P{1H} and 1H NMR spectroscopy, both com-
well as to a red-shift of the emission maximum.6 With this in plexes are dynamic in DMSO-d6. However, the complex 1 is
mind, we have directed our attention to the 5-phenyl-2,2′-bipyr- dynamic with respect to L, while the complex 2 is dynamic
idine (L), which was synthesized according to the known with respect to PPh3.
procedure.7
The crystal structure of L, to the best of our knowledge, has
In this contribution, we describe the synthesis, complete not been reported so far. Furthermore, the Cambridge Struc-
structural investigation and solid state photophysical pro- tural Database10 contains only four L-based structures.7b,11
perties of L and its two novel luminescent mononuclear Thus, every new structure of coordination compounds of L is
heteroleptic copper(I) complexes [CuL(PPh3)I] (1) and of value.
[CuL(PPh3)2]BF4 (2). The experimental results were supported
by detailed quantum chemical calculations.
Compound L (Fig. 1) was refined in the monoclinic space
group P21/n, containing one and a half independent molecules
in the asymmetric unit. The planar molecule of L was found to
be orientationally disordered, without significant positional
disorder. The global shape of the molecules was retained and
positions of the nitrogen atoms were distributed over all poss-
ible sites. All bond lengths and bond angles are typical for the
pyridyl and phenyl fragments.12 The dihedral angles between
the planes formed by the aromatic rings in the crystal structure
are less than 3.0°, making the molecules of L appear comple-
tely planar. The structure of L is stabilized by intermolecular
π⋯π stacking interactions with an interplanar separation of
about 3.6 Å, formed between the corresponding aromatic rings
of adjacent molecules (Fig. 1). The π⋯π stacked molecules
form two types of ribbon-like aggregates almost orthogonal to
each other (∼82.0°) along the a axis (Fig. 1).
Results and discussion
The complexes 1 and 2 were prepared by reacting CuI or
[Cu(CH3CN)4]BF4, respectively, with two equivalents of PPh3, fol-
lowed by addition of one equivalent of L (Scheme 1). The struc-
tures of the intermediate compounds [(Ph3P)2Cu(μ-I)2Cu(PPh3)]8
and [Cu(CH3CN)2(PPh3)2]BF4 (ref. 9) were revealed by single
crystal X-ray diffraction. The obtained orange (1) and yellow (2)
solid materials are soluble in most polar solvents.
The 31P{1H} NMR spectrum of 1 in DMSO-d6 exhibits a
unique sharp (FWHM = 5.2 Hz) signal at 26.0 ppm, while the
31P{1H} NMR spectrum of 2 in the same solvent contains an
extremely broad (FWHM = 167.5 Hz) signal at 2.6 ppm. The
latter broadening can be due to a slow, in the NMR timescale,
equilibrium in DMSO-d6 between the coordinated and non-
coordinated PPh3 ligands in the structure of 2. The resonances
in both spectra show a downfield shift relative to free PPh3,
supporting the fact that the phosphorus atoms coordinate to
the metal ion. In contrast to the 31P{1H} NMR spectrum of 1,
exclusively exhibiting a unique sharp signal, the 1H NMR spec-
trum of the same complex contains two significantly broad-
ened singlets at 8.02–9.16 and 10.62–11.64 ppm, arising from
seven protons of the ligand L. This can be explained by a slow,
in the NMR timescale, equilibrium in DMSO-d6 between the
coordinated and non-coordinated L in the structure of 1. The
signals for the PPh3 and the remaining five protons of L were
observed as two multiplets from 7.31 to 7.78 ppm. The 1H
NMR spectrum of 2 in DMSO-d6 exhibits one multiplet and
two triplets at 7.05–7.20, 7.29 and 7.40 ppm, respectively,
corresponding to the PPh3 protons. The protons of L were
shown as a triplet of doublets at 8.15 ppm and three multiplets
at 7.44–7.59, 8.37–8.49 and 8.61–8.73 ppm, respectively. Thus,
According to the X-ray data, 1 and 2 crystallize in the mono-
clinic space groups P21/c and P21, respectively. Complex 1 com-
Fig. 1 Molecular structure of a π⋯π stacked dimer, constructed from
two independent molecules (top), and crystal packing along the a axis
(bottom) of L. Colour code: C = black, H = grey, N = blue.
Scheme 1 Synthesis of 1 and 2.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
prises a discrete neutral molecule, while 2 exhibits an ionic is about 2.6 Å. The N–Cu–N angles are identical for both com-
structure comprising a discrete cation [CuL(PPh3)2]+ and a plexes and about 79°, while the N–Cu–P angles are almost the
BF4– anion (Fig. 2). Both structures reveal that each tetracoordi- same in the structure of 1 (∼116°) and significantly deviate in
nated copper(I) atom is linked to two nitrogen atoms of L, one the structure of 2 (∼103–124°) (Table 1).
iodide and one PPh3 in the structure of 1, or two PPh3 in the
The structure of 2 is additionally stabilized by a weak intra-
structure of 2, with the formation of a distorted tetrahedral molecular π⋯π stacking interaction with an interplanar separ-
coordination core. This distortion is due to the small bite ation of about 3.9 Å, formed between two adjacent phenyl
angle of L (Table 1). The dihedral angles between the N–Cu–N rings of two PPh3 ligands (Fig. 2). No π⋯π stacking inter-
plane and the P–Cu–I or P–Cu–P plane are about 87.1° and actions were found in the structure of 1.
81.0° for 1 and 2, respectively. Decrease of this angle in the
A closer inspection of both crystal structures revealed no
structure of 2 is due to repulsion between the phenyl frag- classical hydrogen bonds but further H⋯X short contacts.
ments of the two PPh3 ligands. The two pyridine moieties of L However, based on established criteria13 these weak inter-
are almost in the same plane for both complexes, which is actions are not directing the crystal packing or molecular
reflected in the dihedral angles of about 5.1° and 5.6° between structures.
the two cycles (Table 1). However, the phenyl fragments
deviate significantly from the pyridine planes for 1 and 2 X-ray powder diffraction analysis (Fig. 3). The experimental
(Fig. 2 and Table 1). X-ray powder patterns are in agreement with the calculated
The bulk samples of L, 1 and 2 were studied by means of
The Cu–N bond lengths in 1 are slightly longer than in 2, powder patterns obtained from the single crystal X-ray ana-
while the Cu–P distance in 1 are slightly shorter than the lyses, showing that the bulk materials of L, 1 and 2 are free
corresponding bond lengths in 2 (Table 1). The Cu–I bond in 1 from phase impurities.
In order to examine the interactions in the crystal structures
of L, 1 and 2, the Hirshfeld surface analysis14 and the 2D
fingerprint plots15 were obtained using CrystalExplorer 3.1.16
Since the structure of L contains one and a half molecules in
the asymmetric unit, two different pairs of Hirshfeld surfaces
were obtained for two different molecules of L, namely the
“first molecule” in the general position and the “second mole-
cule” for the one on the inversion centre.
According to the Hirshfeld surface analysis, for both mole-
cules of L as well as for 1 and 2, the intermolecular H⋯H con-
Fig. 2 Molecular structures of 1 (left) and 2 (right). Hydrogen atoms
were omitted for clarity. Colour code: C = black, N = blue, B = pink, F =
green, I = purple, P = orange, Cu = magenta.
tacts, comprising 59.2, 57.4, 54.0 and 50.4% of the total
number of contacts respectively, are major contributors to the
crystal packing (Fig. 4). The shortest H⋯H contacts are shown
in the fingerprint plots as characteristic spikes at de + di ≈
2.2 Å (Fig. 5, Fig. S1–S3 in the ESI‡). A subtle feature is evident
in the fingerprint plot for the first molecule of L and it was
also less visible in the corresponding plots of the second mole-
Table 1 Selected bond lengths, bond and dihedral angles for 1 and 2
1
2
Experimental
DFT
Experimental
DFT
2.14
Bond length (Å)
Cu–N
2.086(3)
2.092(3)
2.2030(9)
2.11
2.16
2.24
2.062(4)
2.066(4)
2.2389(13)
2.2619(13)
—
Cu–P
Cu–I
2.28
2.29
—
2.5923(5)
2.67
Bond angle (°)
N–Cu–N
N–Cu–P
78.74(11)
115.46(8)
116.56(8)
77.3
111.2
124.0
79.44(15)
103.44(11)
111.95(11)
113.14(11)
124.45(11)
—
77.5
105.7
107.9
112.9
122.7
—
N–Cu–I
105.13(8)
110.14(7)
122.31(3)
—
110.9
116.7
111.0
—
P–Cu–I
P–Cu–P
—
—
121.7
118.31(5)
Dihedral angle (°)
Py⋯Py
5.14(16)
33.65(17)
36.83(17)
3.2
31.3
5.6(2)
30.0(2)
34.9(3)
10.6
28.3
Fig. 3 Calculated (black) and experimental (red) X-ray powder diffrac-
tion patterns of L (bottom), 1 (middle) and 2 (top).
Py⋯Ph(L)
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
interaction and, as a result, the distinct sawtooth shape on the
upper left and lower right of the plot is observed (Fig. 5,
Fig. S1 in the ESI‡).
It is worth adding that the fingerprint plot of the first mole-
cule of L exhibits a significant number of points at large de
and di, shown as tails at the top right of the plot, when com-
pared to the plot of the second molecule of L (Fig. 5, Fig. S1 in
the ESI‡). These points, similar to those observed in the finger-
print plot of benzene,15 correspond to regions on the Hirshfeld
surface without any close contacts to nuclei in adjacent
molecules.
The structure of the second molecule of L is further charac-
terized by a significant proportion of C⋯C contacts, compris-
ing 18.1%, while a lower proportion (8.9%) of the same
contacts were found in the first molecule of L (Fig. 4). They are
shown on the fingerplots as the areas of pale blue/green color,
and even mixed with yellow and red points on the plot of the
second molecule of L, on the diagonal at de = di ≈ 1.7–1.8 Å
(Fig. 5, Fig. S1 in the ESI‡). These contacts correspond to the
presence of π⋯π stacking interactions in the crystal structure
of L. These interactions are also featured on the fingerplots of
both complexes (Fig. 5, Fig. S2 and S3 in the ESI‡). However,
minor areas (6.5 and 2.5% in 1 and 2, respectively) (Fig. 4) of
pale blue color are present.
Fig. 4 Relative contributions of intermolecular contacts to the Hirsh-
feld surface area in the first and second molecules of L, 1 and 2.
Another significant contribution (16.3%) on the total Hirsh-
feld surface area of 2 arises from F⋯H contacts (Fig. 4) with
the shortest de + di ≈ 2.3 Å (Fig. 5, Fig. S3 in the ESI‡). Close
inspection of other intermolecular contacts also revealed a
negligible proportion of N⋯H (1.7%), C⋯N (0.4%) and C⋯I
(0.4%) contacts in the structure of 1 (Fig. 5, Fig. S2 in the
ESI‡), and N⋯H (0.1%) contacts in the structure of 2 (Fig. 5,
Fig. S3 in the ESI‡). No other contacts were found in the struc-
tures of both molecules of L and both complexes.
To establish the origin of the different colors of L (color-
less), 1 (orange) and 2 (yellow) as well as to study their elec-
tronic properties, diffuse reflectance spectra were recorded on
pure samples (Fig. 6). The spectrum of L exhibits a broad band
Fig. 5 2D fingerprint plots of observed contacts for the first (top row,
left) and second (top row, right) molecules of L (top), and for 1 (bottom
row, left) and 2 (bottom row, right).
cule of L and 2. In each of these cases there is a distinct split-
ting of the short H⋯H fingerprint. This splitting occurs when
the shortest contact is between three atoms, rather than for a
direct two-atom contact.15
The structures of both molecules of L and both complexes
are also dominated by C⋯H contacts, comprising 31.9, 24.5,
25.7 and 30.7% (Fig. 4), respectively, of the total Hirshfeld
surface areas (Fig. 5, Fig. S1–S3 in the ESI‡). It should be
noted that the first molecule of L exhibits a much larger pro-
portion of C⋯H contacts than the second molecule of L. These
contacts in the fingerprint plot of 1 are shown in the form of
clearly pronounced “wings” with the shortest de + di ≈ 2.6 Å
(Fig. 5, Fig. S2 in the ESI‡), which are recognized as character-
istic of a C–H⋯π interaction.15 The first molecule of L exhibits
similar “wings” due to C–H⋯π interactions (Fig. 5, Fig. S1 in
the ESI‡). However, the latter plot contains one more C–H⋯π
Fig. 6 Normalized Kubelka–Munk spectra of L (black), 1 (red) and 2
(orange) at 298 K.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
with several maxima exclusively in the UV region corres-
ponding to intra-ligand π → π* transitions. The spectra of the
complexes exhibit a broad band with several maxima in the
range of 200 to 600 or 500 nm for 1 and 2, respectively. While
the bands in the UV region are coming from intra-ligand π → π*
transitions of L and PPh3, the bands in the visible range are
assigned to a metal-to-ligand charge transfer (MLCT) tran-
sition from the dπ orbital of the 3d10 copper(I) center to the
unoccupied π* orbital of the ligand L. This transition in 1 is
further mixed with a halide-to-ligand charge transfer (XLCT)
transition. The (M + X)LCT transition is significantly red-
shifted in the spectrum of 1 compared to the MLCT transition
in the spectrum of 2. This can be explained by lowering of the
highest occupied molecular orbitals (HOMO) energy upon
coordination of two π-acceptor PPh3 ligands in the structure of
2, compared to one PPh3 ligand in the structure of 1, hence
increasing the energy gap between the HOMO and the lowest
unoccupied molecular orbitals (LUMO).
Fig. 8 Normalized solid-state emission (violet, λexc = 360; and red, λexc
= 525) and excitation (black, λem = 425; and green, λem = 620) spectra of
1 at 298 K.
The emission spectrum of L exhibits a single intense band
centred at 395 nm (Fig. 7), which was assigned to the fluore-
scence emission from ligand-centerd π → π* transition. This
was supported by the excitation spectrum, which reveals a
main contribution from the band centred at 350 nm (Fig. 7).
Surprisingly, the fluorescence spectrum of the iodide
complex 1 shows two bands centered at about 420 and 630 nm
upon excitation at λexc = 360 nm (Fig. 8). The high energy emis-
sion band is obviously due to the fluorescence emission from
ligand-centerd π → π* transition of L, which is revealed from
the excitation spectrum of 1 measured at λem = 425. This is
further supported by comparison with the emission spectrum
of free L (Fig. 7). The latter red-shifted emission band in the
spectrum of 1 can be isolated upon excitation with visible light
at λexc = 525 nm. This emission can be assigned to the mixed
(M + X)LCT excited state.
Complex 2 exhibits an intense emission band centered at
about 575 nm (Fig. 9). Notably, no other emission bands were
observed in the fluorescence spectrum of 2 regardless of the
Fig. 9 Normalized solid-state emission (orange, λexc = 425 nm) and
excitation (black, λem = 580 nm) spectra of 2 at 298 K.
excitation wavelength. The observed emission is about 55 nm
blue-shifted relative to the low energy emission band in the
spectrum of 1 (Fig. 8). This, obviously, can be explained by the
replacement of iodide by an efficient π-acceptor PPh3. This, in
turn, leads to a lowering of the HOMO level and, thus, to a
larger HOMO–LUMO gap.
For 1 and 2, the HOMO is distributed over either the copper(I)
and iodide ions in 1 or the copper(I) ion alone in 2 with
some contribution from the PPh3 ligands. However, the LUMO
for both complexes is mainly on the ligand L.1 The presence of
another PPh3 in 2 would have an insignificant influence on
the LUMO level. Thus, the corresponding emission states at
630 and 575 nm in the fluorescence spectra of 1 and 2 can be
assigned to (M + X)LCT and MLCT excited states, respectively.
In order to further characterize complexes 1 and 2 we have
performed geometry optimization based on DFT/TZP/BLYP-D3
by means of the Amsterdam Density Functional package.17
Fig. 7 Normalized solid-state emission (violet, λexc = 340 nm) and exci-
tation (black, λem = 400 nm) spectra of L at 298 K.
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
The calculated parameters of the optimized structures of 1 and (donation from the lone pair of phosphorus to copper) and
2 are in agreement with the experimental results (Table 1). Fur- back-donations (Δρ2, Δρ3) from the occupied d orbital of
thermore, the calculated HOMO–LUMO gap for 2 is 0.882 eV copper(I) to σ*(P–C), one can clearly see polarizations of the
larger in comparison with that of 1 (Fig. 10). This is fully con- phenyl rings due to the non-covalent π⋯π interactions (Δρ3,
sistent with the experimental blue-shift of the emission band Δρ4 and Δρ5 in Fig. S4 in the ESI‡). It should be noted that a
in the spectrum of 2 (Fig. 9) compared with the spectrum of 1 significant role of the dispersion for the stabilization of 2
(Fig. 8). The HOMO of 1 is built from the lone electron pair of is also visible when comparing [CuPPh3I]–L in
1 with
iodine supported by the copper d orbital, whereas the empty [Cu(PPh3)2]+–L in 2 (Table S1 in the ESI‡). Finally, it can be noted
π*(LUMO) is located entirely on L. Some contributions from that the [CuLPPh3]+–PPh3 bond in 2 is weaker compared with
the lone electron pairs of the phosphorus and nitrogen atoms the [Cu(PPh3)2]+–L bond. This qualitatively explains why 2 is in
are also visible in the shape of HOMO. Similar molecular equilibrium with PPh3 but not with L in solution. The ΔEint
orbital characteristics are valid for 2. However, the HOMO values of [CuLI]–PPh3 and [CuPPh3I]–L in 1 are almost the
comprises a more significant contribution from the lone elec- same (Table S1 in the ESI‡). Accordingly, the feasibility of
tron pairs of the phosphorus atom (Fig. 10). This confirms dissociation of L over PPh3 in 1 observed from NMR should
that luminescence of 1 and 2 originate from the (M + X)LCT rather be related to other factors including, e.g., interactions
and MLCT charge transfers, respectively.
with the solvent.
We have further shed some light on factors that influence
Finally, we have also complemented the Hirshfeld surface
the stability of 1 and 2 by detailed analysis of the Cu–P bonds analysis by the detailed ETS-NOCV-based calculations of inter-
by the means of the charge and energy decomposition method molecular interactions in 1 and 2 with the geometries as in the
ETS-NOCV.18 In 1, the interaction between two neutral frag- crystals (Fig. 11). It was established, that the dispersion contri-
ments, PPh3 and [CuLI], was considered, while in 2, PPh3 bution (ΔEdisp) is the most important for the overall stabiliz-
interacts with the cationic fragment [CuLPPh3]+ (Table S1 in ation of 1, while the electrostatic (ΔEelstat) and orbital (ΔEorb
)
the ESI‡). Similarly, bonding between L and [CuPPh3I] or interaction terms are less significant (Fig. 11). Furthermore,
[Cu(PPh3)2]+ in 1 and 2, respectively, were also characterized the deformation density (Δρorb), corresponding to ΔEorb
(Table S1 in the ESI‡). clearly displays the formation of the intermolecular C–H⋯I
,
It was found, that the overall interaction energy (ΔEint) of and C–H⋯H–C contacts (Fig. 11). On the other hand, similar
[CuLPPh3]+–PPh3 in 2 is significantly lower in comparison with analysis preformed for 2 leads to the conclusion that the most
that of [CuLI]–PPh3 in 1 (Table S1 in the ESI‡). Decomposition crucial stabilizing factor is the electrostatic (ΔEelstat) stabiliz-
of ΔEint into the specific components allows to conclude that ation. It proves a significant ionicity. The dispersion (ΔEdisp
)
it is predominantly due to the weaker steric repulsion term is the least important. The charge-transfer orbital inter-
(measured by ΔEPauli) as well as more significant dispersion action contribution (ΔEorb) describes predominantly the for-
(ΔEdisp) contribution due to π⋯π stacking between the phenyl mation of the C–H⋯F contacts (Fig. 11).
rings (Table S1 in the ESI‡). The orbital interaction term
(ΔEorb) is of the same importance for both [CuLPPh3]+–PPh3 in
2 and [CuLI]–PPh3 in 1. Apart from the dominant dative contri-
butions to the [CuLPPh3]+–PPh3 bond in 2, described by Δρ1
Fig. 11 The contours (0.0001 a.u.) of the overall deformation densities
(Δρorb) together with the corresponding orbital interaction energies
Fig. 10 The contours of molecular orbitals (0.03 a.u.) and the HOMO–
LUMO gaps, obtained from the DFT/TZP/BLYP-D3 calculations, for 1
(left) and [CuL(PPh3)2]+ in 2 (right).
(ΔEorb), describing the interaction between two monomers in 1 (top) and
2 (bottom). Red color shows charge depletion, whereas the blue color
indicates charge accumulation due to bond formation.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
was necessary. Solid-state emission spectra were obtained with
Conclusions
a
Fluorolog-3 (Jobin-Yvon-Spex Company) spectrometer.
We have synthesised two mononuclear heteroleptic copper(I) Kubelka–Munk and emissions spectra were normalized to
complexes, [CuL(PPh3)I] (1) and [CuL(PPh3)2]BF4 (2), with allow meaningful comparisons. Elemental analyses were per-
5-phenyl-2,2′-bipyridine (L) and PPh3, using two different formed on a Thermoquest Flash EA 1112 Analyzer from CE
metal sources, namely CuI and [Cu(CH3CN)4]BF4. The Instruments.
different nature of the iodide and tetrafluoroborate ions,
which are coordinating and non-coordinating ligands respecti-
DFT calculations
vely, allowed to control the coordination core of the com- We have used the ADF2012.01 program17 based on DFT/
plexes. According to X-ray structure determination, complex 1 BLYP-D3/TZP. The charge and energy decomposition scheme
was obtained as a discrete neutral molecule, while 2 exhibits ETS-NOCV18 was applied to describe the bonding situation.
an ionic structure comprising a discrete cation [CuL(PPh3)2]+
–
Synthesis of 1 and 2
and a BF4 counterion. Furthermore, the crystal structure of L
was established for the first time. NMR spectroscopy revealed A solution of L (0.1 mmol, 23.2 mg) in CH2Cl2 for 1 or CH3CN
that 1 is dynamic with respect to L, while 2 is dynamic with for 2 (5 mL) was added dropwise under vigorous stirring to a
respect to PPh3 in DMSO-d6.
mixture of CuI (0.1 mmol, 19.0 mg) and PPh3 (0.2 mmol, 52.5 mg)
According to the Hirshfeld surface analysis, it was found in CH2Cl2 (10 mL) for 1 or a mixture of [Cu(CH3CN)4]BF4
that the structures of both complexes are mainly characterized (0.1 mmol, 31.5 mg) and PPh3 (0.2 mmol, 52.5 mg) in CH3CN
by H⋯H and C⋯H intermolecular contacts as well as by I⋯H for 2 (10 mL). The mixture was stirred at room temperature for
in the structure of 1 and F⋯H in the structure of 2. Although 1 h. The solvent was then removed in vacuo. Complexes were
the decomposed 2D fingerprint plots of two different mole- isolated by recrystallisation from a 1 : 4 mixture of CH2Cl2 and
cules in the structure of L show a very similar major contri- n-hexane.
bution from H⋯H intermolecular contacts, proportions of the
1. Orange crystals. Yield: 64.4 mg (94%). 1H NMR, δ:
remaining C⋯H and C⋯C contacts differ significantly. The 7.31–7.48 (m, 6H, o-H, PPh3), 7.49–7.78 (m, 15H, m-H + p-H,
C⋯H contacts for one of the two independent molecules of L PPh3; L), 8.02–9.16 (br. s, 5H, L), 10.62–11.64 (br. s, 2H, L)
were found mainly in the form of C–H⋯π interactions. Both ppm. 31P{1H} NMR, δ: 26.0 (s) ppm. Anal. Calc. for
independent molecules in the structure of L exhibit contacts C34H27CuIN2P (685.03): C 59.61, H 3.97, N 4.09. Found: C
for π⋯π stacking interactions, which are more pronounced for 59.52, H 4.03, N 4.06%.
the second molecule.
2. Yellow crystals. Yield: 78.9 mg (87%). 1H NMR, δ:
3
The optical and luminescence properties of L, 1 and 2 in 7.05–7.20 (m, 12H, o-H, PPh3), 7.29 (t, JH,H = 7.3 Hz, 12H,
the solid state at ambient temperature were also studied. m-H, PPh3), 7.40 (t, JH,H = 7.3 Hz, 6H, p-H, PPh3), 7.44–7.59
3
3
4
According to diffuse reflectance spectroscopy, free L exhibits (m, 6H, L), 8.15 (t. d, JH,H = 7.8 Hz, JH,H = 1.3 Hz, 1H, L),
bands exclusively in the UV region, while the spectra of 1 and 8.37–8.49 (m, 2H, L), 8.61–8.73 (m, 3H, L) ppm. 31P{1H} NMR,
2 also contain bands in the visible range up to about 500 and δ: 2.6 (br. s) ppm. Anal. Calc. for C52H42BCuF4N2P2 (907.22):
600 nm. This explains why L is colorless, while 1 and 2 are C 68.84, H 4.67, N 3.09. Found: C 68.93, H 4.71, N 3.12%.
orange and yellow, respectively. All three compounds were
X-Ray powder diffraction
found to be emissive in the solid state. DFT calculations
allowed to describe the molecular orbitals involved in the tran- X-Ray powder diffraction for bulk samples was carried out
sitions upon excitation. While emission of L is due to the using a Rigaku Ultima IV X-ray powder diffractometer. The
ligand-centerd π → π* transition, luminescence of 1 and 2 was Parallel Beam mode was used to collect the data (λ = 1.541836 Å).
assigned to (M + X)LCT and MLCT excited states, respectively.
Single crystal X-ray diffraction
The X-ray data of L were collected at 100(2) K on a Bruker
platform goniometer with Smart 1000 detector, using Mo-Kα
radiation (graphite monochromated sealed tube). Diffraction
Experimental
General procedures
images were integrated by SAINT v7.66A, and treated for
NMR spectra in DMSO-d6 were obtained on a Bruker Avance absorption by SADABS.19 The structure of L was solved by
300 MHz spectrometer at 25 °C. H and 31P{1H} NMR spectra SHELXD20 and refined by full-matrix least squares on |F2| with
1
were recorded at 299.948, and 121.420 MHz, respectively. SHELX-201421 and shelXle.22 Non-hydrogen atoms were aniso-
Chemical shifts are reported with reference to SiMe4 (1H) and tropically refined and hydrogen atoms were placed on calcu-
85% H3PO4 (31P{1H}). Diffuse reflectance spectra were obtained lated positions in riding mode with temperature factors fixed
with a Varian Cary 5E spectrometer using polytetrafluoroethyl- at 1.2 times Ueq of the parent atoms.
ene (PTFE) as a reference. Spectra were measured on pure
The asymmetric unit of L consists of 1.5 ligand molecules,
solids. Eventual distortions in the Kubelka–Munk spectra that one being found on an inversion center, amounting to 6 mole-
could result from the study of pure compounds have not been cules in the unit cell. Although the global outline of the per-
considered because no comparison with absorption spectra fectly flat molecule was clearly visible after the structure
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
solution, the structure is orientationally disordered, with the
N-atoms distributed over all possible sites. L can adopt a cis-
Acknowledgements
or trans-conformation and in combination with a pseudo- The Bruker X-ray diffractometer was funded by NSF grant
2-fold axis/pseudo-inversion center this results in 8 possible 0087210, Ohio Board of Regents Grant CAP-491, and by
sites for the N-atoms of the molecule found on a general posi- Youngstown State University. The authors thank Dr. Matthias
tion. These 8 sites are refined as mixed, N or C, with both Zeller (Youngstown State University) for collecting the data set
atoms of each N/C pair constrained to occupy the same posi- of L. D. A. Safin thanks WBI (Belgium) for the post-doctoral
tion with the same thermal ellipsoids. Linear restraints are set position. This work was partly supported by FNRS.
up to ensure the correct chemical composition. For the mole-
cule found on the inversion center a similar procedure was
applied, with the linear restraints adapted in accordance to
the symmetry restraints imposed by the inversion center. From
Notes and references
the refined occupancy factors it was found that the confor-
mations with the N-atoms in a trans-configuration are most
abundantly present (Fig. 12).
1 (a) D. R. McMillin and K. M. McNett, Chem. Rev., 1998, 98,
1201; (b) P. C. Ford, E. Cariati and J. Bourassa, Chem. Rev.,
1999, 99, 3625; (c) N. Armaroli, G. Accorsi, F. Cardinali and
A. Listorti, Top. Curr. Chem., 2007, 280, 69; (d) Z. Liu, W. He
and Z. Guo, Chem. Soc. Rev., 2013, 42, 1568; (e) Z. Liu,
W. Qi and G. Xu, Chem. Soc. Rev., 2015, 44, 3117.
2 (a) V. W. W. Yam and K. K. W. Lo, Chem. Soc. Rev., 1999, 28,
323; (b) Q. Zhang, Q. Zhou, Y. Cheng, L. Wang, D. Ma,
X. Jing and F. Wang, Adv. Mater., 2004, 16, 432;
(c) N. Armaroli, G. Accorsi, M. Holler, O. Moudam,
J.-F. Nierengarten, Z. Zhou, R. T. Wegh and R. Welter, Adv.
Mater., 2006, 18, 1313; (d) M. Nishikawa, K. Nomoto,
S. Kume, K. Inoue, M. Sakai, M. Fujii and H. Nishihara,
J. Am. Chem. Soc., 2010, 132, 9579.
3 (a) D. G. Cuttell, S. M. Kuang, P. E. Fanwick, D. R. McMillin
and R. A. Walton, J. Am. Chem. Soc., 2002, 124, 6;
(b) M. G. Babashkina, D. A. Safin, M. Bolte and A. Klein,
CrystEngComm, 2009, 12, 134; (c) C. S. Smith,
C. W. Branham, B. J. Marquardt and K. R. Mann, J. Am.
Chem. Soc., 2010, 132, 14079; (d) D. A. Safin,
M. G. Babashkina, M. Bolte and A. Klein, Inorg. Chim. Acta,
2010, 363, 1897; (e) M. G. Babashkina, D. A. Safin, A. Klein
and M. Bolte, Eur. J. Inorg. Chem., 2010, 4018;
(f) D. A. Safin, M. G. Babashkina and A. Klein, Croat. Chem.
Acta, 2010, 83, 353; (g) D. A. Safin, M. G. Babashkina,
M. Bolte and A. Klein, CrystEngComm, 2011, 13, 568;
(h) D. A. Safin, M. G. Babashkina, M. Bolte and
M. Köckerling, Inorg. Chim. Acta, 2011, 370, 59;
(i) M. G. Babashkina, D. A. Safin and Y. Garcia, Polyhedron,
2012, 33, 114.
The X-ray data for 1 and 2 were collected at 150(2) K on a
Mar345 image plate detector using Mo-Kα radiation (Xenocs
Fox3D mirror). The data were integrated with the CrysAlisPro
software.23 The implemented empirical absorption correction
was applied. The structures of 1 and 2 were solved by
SHELXS20 and refined by full-matrix least squares on |F2|,
using SHELXL2014/7.21 Non-hydrogen atoms were anisotropi-
cally refined and the hydrogen atoms were placed on calcu-
lated positions in riding mode with temperature factors fixed
at 1.2 times Ueq of the parent atoms.
Figures were generated using the program Mercury.24
Crystal data for L. C16H12N2, C8H6N; Mr = 348.42 g mol−1
,
monoclinic, space group P21/n, a = 5.6180(10), b = 15.682(3),
c = 19.716(3) Å, β = 91.990(2)°, V = 1736.0(5) Å3, Z = 4, ρ =
1.333 g cm−3, μ(Mo-Kα) = 0.080 mm−1, reflections: 20 335 col-
lected, 5657 unique, Rint = 0.021, R1(all) = 0.0801, wR2(all) =
0.1789.
Crystal data for 1. C34H27CuIN2P, Mr = 684.98 g mol−1
,
monoclinic, space group P21/c, a = 9.3666(3), b = 10.2614(3),
c = 30.1047(11) Å, β = 93.907(3)°, V = 2886.76(16) Å3, Z = 4, ρ =
1.576 g cm−3, μ(Mo-Kα) = 1.908 mm−1, reflections: 19 042
collected, 5202 unique, Rint = 0.0491, R1(all) = 0.0417, wR2(all) =
0.0824.
Crystal data for 2. C52H42CuN2P2, BF4; Mr = 907.16 g mol−1
,
monoclinic, space group P21, a = 10.5921(4), b = 13.9695(6), c =
15.0293(5) Å, β = 94.299(3)°, V = 2217.58(15) Å3, Z = 2, ρ =
1.359 g cm−3, μ(Mo-Kα) = 0.620 mm−1, reflections: 16 183
collected, 8086 unique, Rint = 0.0406, R1(all) = 0.0437, wR2(all) =
0.0913.
4 (a) J. Kotlicka and Z. R. Grabowski, J. Photochem., 1979,
413; (b) G. Albano, V. Balzani, E. C. Constable, M. Maestri
and D. R. Smith, Inorg. Chim. Acta, 1998, 277, 225.
CCDC 1410040 (L), 1410041 (1) and 1410042 (2) contain the
supplementary crystallographic data.
5 B. Bosnich, Acc. Chem. Res., 1969, 2, 266.
6 J. C. Loren and J. S. Siegel, Angew. Chem., Int. Ed., 2001, 40,
754.
7 (a) V. N. Kozhevnikov, D. N. Kozhevnikov, O. V. Shabunina,
V. L. Rusinov and O. N. Chupakhin, Tetrahedron Lett., 2005,
46, 1791; (b) D. N. Kozhevnikov, O. V. Shabunina,
D. S. Kopchuk, P. A. Slepukhin and V. N. Kozhevnikov,
Tetrahedron Lett., 2006, 47, 7025.
8 (a) P. G. Eller, G. J. Kubas and R. R. Ryan, Inorg. Chem.,
1977, 16, 2454; (b) K. Paizanos, D. Charalampou,
N. Kourkoumelis, D. Kalpogiannaki, L. Hadjiarapoglou,
Fig. 12 Schematic view of the asymmetric unit of L with possible
N-atom sites shown with their occupancies (%). The major sites are
shown with larger atom labels.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
A. Spanopoulou, K. Lazarou, M. J. Manos, A. J. Tasiopoulos,
M. Kubicki and S. K. Hadjikakou, Inorg. Chem., 2012, 51,
12248.
9 J. Green, E. Sinn, S. Woodward and R. Butcher, Polyhedron,
1993, 12, 991.
M. van Faassen, L. Fan, T. H. Fischer, C. Fonseca Guerra,
A. Ghysels, A. Giammona, S. J. A. van Gisbergen,
A. W. Götz, J. A. Groeneveld, O. V. Gritsenko, M. Grüning,
F. E. Harris, P. van den Hoek, C. R. Jacob, H. Jacobsen,
L. Jensen, G. van Kessel, F. Kootstra, M. V. Krykunov, E. van
Lenthe, D. A. McCormack, A. Michalak, M. Mitoraj,
J. Neugebauer, V. P. Nicu, L. Noodleman, V. P. Osinga,
S. Patchkovskii, P. H. T. Philipsen, D. Post, C. C. Pye,
W. Ravenek, J. I. Rodríguez, P. Ros, P. R. T. Schipper,
G. Schreckenbach, M. Seth, J. G. Snijders, M. Solà,
M. Swart, D. Swerhone, G. te Velde, P. Vernooijs,
L. Versluis, L. Visscher, O. Visser, F. Wang,
T. A. Wesolowski, E. M. van Wezenbeek, G. Wiesenekker,
S. K. Wolff, T. K. Woo, A. L. Yakovlev and T. Ziegler,
Theoretical Chemistry, Vrije Universiteit, Amsterdam.
10 CSD version 5.35 (Update February 2015).
11 (a) A. Tian, Z. Han, J. Peng, B. Dong, J. Sha and B. Li,
J. Mol. Struct., 2007, 832, 117; (b) A.-X. Tian, Z.-G. Han,
J. Peng, J.-L. Zhai, B.-X. Dong and J.-Q. Sha, J. Coord.
Chem., 2007, 60, 1645; (c) S. Cui, M. Zuo, J. Zhang, Y. Zhao,
R. Tan, S. Liu and S. Su, Acta Crystallogr., Sect. E: Struct.
Rep. Online, 2011, 67, m1706; (d) S. Cui, M. Zuo, J. Zhang,
Y. Zhao and H. Wang, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2012, 68, m165.
12 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer,
A. G. Orpen and R. Taylor, J. Chem. Soc., Perkin Trans. 2, 18 (a) T. Ziegler and A. Rauk, Theor. Chim. Acta, 1977, 46, 1;
1987, S1.
(b) M. Mitoraj and A. Michalak, J. Mol. Model, 2007, 13,
347; (c) M. P. Mitoraj, A. Michalak and T. Ziegler, J. Chem.
Theory Comput., 2009, 5, 962.
13 T. Steiner, Angew. Chem., Int. Ed., 2002, 41, 48.
14 M. A. Spackman and D. Jayatilaka, CrystEngComm, 2009,
11, 19.
19 SADABS, Bruker AXS Inc., Madison, Wisconsin, USA, 2008.
15 M. A. Spackman and J. J. McKinnon, CrystEngComm, 2002, 20 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
4, 378. logr., 2008, 64, 112.
16 S. K. Wolff, D. J. Grimwood, J. J. McKinnon, M. J. Turner, 21 G. M. Sheldrick, SHELXL2014/7, University of Göttingen,
D. Jayatilaka and M. A. Spackman, University of Western
Australia, 2012.
17 (a) G. te Velde, F. M. Bickelhaupt, E. J. Baerends,
Germany, 2014.
22 C. B. Hübschle, G. M. Sheldrick and B. Dittrich, J. Appl.
Crystallogr., 2011, 44, 1281.
C. Fonseca Guerra, S. J. A. van Gisbergen, J. G. Snijders and 23 Rigaku Oxford Diffraction, CrysAlisPro Software system,
T. Ziegler, J. Comput. Chem., 2001, 22, 931 and references Version 1.171.37.31, Rigaku Corporation, Oxford, UK, 2014.
therein; (b) E. J. Baerends, J. Autschbach, D. Bashford, 24 I. J. Bruno, J. C. Cole, P. R. Edgington, M. Kessler,
A. Bérces, F. M. Bickelhaupt, C. Bo, P. M. Boerrigter,
L. Cavallo, D. P. Chong, L. Deng, R. M. Dickson, D. E. Ellis,
C. F. Macrae, P. McCabe, J. Pearson and R. Taylor, Acta
Crystallogr., Sect. B: Struct. Sci., 2002, 58, 389.
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.