Higher coordinate gold(I) complexes with the weak Lewis base tri(4-fluorophenyl) phosphine. Synthesis, structural, luminescence, and DFT studies

Article abstract of DOI:10.1016/j.molstruc.2015.12.020

The structures and spectroscopic properties of two high coordinate gold(I) phosphine complexes with the TFFPP=tri(4-fluorophenyl)phosphine ligand are reported. Synthesis in a 1:3 metal to ligand ratio provided the compound [AuCl(TFFPP)₃] (2) th

Full text of DOI:10.1016/j.molstruc.2015.12.020

Journal of Molecular Structure 1108 (2016) 508e515
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Higher coordinate gold(I) complexes with the weak Lewis base tri(4-
fluorophenyl) phosphine. Synthesis, structural, luminescence, and DFT
studies*
,
George Agbeworvi a, Zerihun Assefa a *, Richard E. Sykora b, Jared Taylor b,
Carlos Crawford a
a Department of Chemistry, North Carolina A&T State University, Greensboro, NC 27411, USA
b Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The structures and spectroscopic properties of two high coordinate gold(I) phosphine complexes with
the TFFPP¼tri(4-fluorophenyl)phosphine ligand are reported. Synthesis in a 1:3 metal to ligand ratio
provided the compound [AuCl(TFFPP)3] (2) that crystallize in the P1 space group, where the asymmetric
unit consists of three independent molecules. In all three sites, two sets of bond angles display distinctly
different ranges. The three PeAueP angles have average values of 117.92ꢀ, 117.57ꢀ, and 114.78ꢀ for sites A,
B, and C, with the corresponding PeAueCl angles of 98.31ꢀ, 99.05ꢀ, and 103.38ꢀ, respectively. The
chloride ion coordinates as the fourth ligand, at the corresponding AueCl distance of 2.7337, 2.6825, and
2.6951 Å for the three sites. This distance is longer by 0.40e0.45 Å than the AueCl distance found in the
mono TFFPP complex 1 (2.285 Å) indicating a weakening of the AueCl interaction as the coordination
number increases. In compound 3, [Au(TFFPP)3]Cl$½CH2Cl2$H2O, the structure consists of three phos-
phine ligands bound to the gold(I) atom, but the Clꢁ exists as uncoordinated counter anion. The struc-
tural differences observed in the two complexes are attributable to crystal-packing effects caused by the
Received 4 November 2015
Received in revised form
7 December 2015
Accepted 7 December 2015
Available online 13 December 2015
Keywords:
Gold(I)
Tri(4-fluorophenyl)phosphine
Three coordinate
X-ray crystallography
Photoluminescence
introduction of H-bonding as well as enhanced intra and inter-molecular
p-interaction in 3. The pho-
toluminescence of the complexes compared with that of the ligand show ligand centered emission
perturbed by the metal coordination. Theoretical DFT studies conducted on these complexes supports
assignments of the electronic transitions observed in these systems.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
with coordination numbers ranging from two to four. This result
contrasts with the previously known coordination of sulfur con-
Although molecular gold(I) compounds with a closed shell d10
electronic configuration are in most cases characterized by linear
coordination [1e3], complexes possessing higher coordination
numbers are also known to a lesser degree. Several factors influ-
ence the level of coordination at the gold(I) center including elec-
tronic factors and steric hindrances of the coordinating ligands. For
example, recent work [4] in the use of ferrocene dithiocarboxylates
showed that the ligand coordination to gold(I) center follows ver-
satile modes including monodentate, chelating, or bridging modes
taining ligands as reported for similar systems of dithiocarbamates
[5,6] and xanthates [7], where monodentate coordination modes
were dominant [8,9].
Overall only a small number of ligands have been found capable
of providing high coordination geometries about the gold(I), with
most reports to date involving either bidentate phosphines [10,11]
and/or thiolate ligands [12,13]. Recent progress in four-coordinate
gold(I) chemistry involves bridged diphosphine ligands that have
been characterized structurally and studied computationally [14].
The solid state, vapor induced interconversion of high coordinate
Au(I) complexes has also been observed recently [15,16]. Structur-
ally characterized three- and specifically four-coordinate gold(I)
complexes with monodentate phosphine ligands are still limited.
The tris-2-furyl phosphine [17] and the 1,3,5-triaza-7phosphaada-
mantane (TPA) [18] ligands are noteworthy to mention as they
*
Submission to Journal of Molecular Structure.
* Corresponding author. North Carolina A&T State University, 1601 E. Market St.,
Greensboro, NC 27455, USA. Tel.: þ1 336 285 2255; fax: þ1 336 334 7124.
E-mail address: zassefa@ncat.edu (Z. Assefa).
http://dx.doi.org/10.1016/j.molstruc.2015.12.020
0022-2860/© 2015 Elsevier B.V. All rights reserved.

G. Agbeworvi et al. / Journal of Molecular Structure 1108 (2016) 508e515
509
provided a regular tetrahedral geometry.
Enhance X-ray source, and an Eos area detector. CrysAlisPro [27]
was used for preliminary determination of the cell constants,
data collection strategy, and for data collection control. Following
data collection, CrysAlisPro was also used to integrate the reflection
intensities, apply absorption corrections to the data (semi-empir-
ical), and perform a global cell refinement, while Mercury 3.6 utility
was used for structure visualization and exploration.
The program suite SHELX was used for structure solution (XS)
and least-squares refinement (XL) [28]. The initial structure solu-
tions were carried out using direct methods and the remaining
heavy atom positions were located in difference maps. The final
refinement included anisotropic displacement parameters for all
non-hydrogen atoms. Refinement was performed against F2 by
weighted full-matrix least squares. The molecular structures for 2
and 3 are presented in Figs. 1 and 2, respectively. The crystallo-
graphic and structural refinement data for 2 and 3 are summarized
in Table 1.
A particularly interesting application of high coordination
gold(I) complexes is related to the fact that three-coordinate spe-
cies generally have luminescent properties that can be exploited for
light-emitting diodes [19]. For example, tertiary phosphines with
aromatic substituents have attracted a great deal of attention in the
design and development of chemosensing applications [20]. The
photoluminescent properties of several types of three-coordinate
gold(I) complexes with aromatic substituents in organic solvents
and in the solid state have been reported [21e23].
We have been interested in the coordination of aromatic tertiary
phosphines including tri(4-fluorophenyl)phosphine (TFFPP) li-
gands to gold(I) centers. The steric properties of the TFFPP ligand
are comparable to triphenylphosphine (PPh3) since both have a
similar cone angle of 145ꢀ [24]. Although the two ligands appear
similar sterically, their electronic properties are different because of
the presence of the strong electron withdrawing fluorine groups on
the phenyl ring of the TFFPP ligand. Due to its unique electronic
behavior TFFPP has been used as a flame-retarding additive in
Lieion battery electrolytes [25]. While the electronic properties of
the TFFPP ligand might be interesting, its coordination chemistry
with gold(I) has not been detailed extensively beyond the mono-
coordinated gold(I) chloride system [26].
2.4. Computational studies
All of the theoretical calculations for the TFFPP ligand and the
complexes 1, 2, and 3 were completed using the GAUSSIAN009
software package [29]. Geometry optimization and vibration fre-
quency calculations were performed with the Becke [30] three-
parameter hybrid functional using the PerdeweWang correlation
functional (B3PW91) [31] level of density functional theory (DFT).
The 6e311 G(d, p) basis set was utilized for C, P, Cl, H and F. The
LANL2DZ basis set [32] was used in conjunction with two f-type
polarization functions [33] and p-type functions [34] for the 5s25p6
5d106s1 valence electrons of gold, and one d-type polarization
function for phosphorus. The predicted absorption spectra of the
optimized structures were accomplished by time-dependent den-
sity functional theory (TD-DFT) without consideration of any sol-
vent effects. Molecular orbitals iso-density diagrams (iso-values:
0.02 atomic units) of molecular orbitals were created using the
GaussView 5 software (Gaussian Inc.)
The focus of the current work involves the nature of two
structures containing three TFFPP ligands which show a geomet-
rical transition from a pseudo trigonal pyramidal to a trigonal
planar geometry as a result of inner/outer-sphere complexation of
the fourth Clꢁ ligand. These structural changes are collaborated
with luminescence, 1H NMR, 31P NMR, UVeVis, IR spectroscopy,
and theoretical DFT studies.
2. Experimental
2.1. General method
All reactions were carried out under a modified Schlenk tech-
nique at room temperature. Tetrahydrothiophene gold(I) chloride
[AuCl(tht)] is prepared according to literature [10]. All infrared
spectra were collected with Ge coated on potassium bromide (KBr)
on a Shimadzu IR Affinity-1 Fourier-transform infrared spectro-
2.5. Synthesis
2.5.1. Chloro(tri (4-fluorophenyl)phosphine)gold(I), [AuCl(TFFPP)]
(1)
photometer, over the range 4000e300 cmꢁ1 1H and 31P NMR
.
spectra were recorded on a 300 MHz Varian NMR 300 e 411149 FT-
NMR spectrometer. Chemical shifts ( ppm) were reported relative
TFFPP (0.0200 g, 0.063 mmol) was added to a solution of
[AuCl(C4H8S)] (0.0146 g, 0.063 mmol) in dichloromethane (20 mL)
d
to Me4Si and 0.0485M triphenylphosphate in CDCl3.
2.2. Spectroscopic studies
The UVeVis spectra were collected on a Shimadzu UV-2401 PC
UVeVis recording spectrometer. The luminescence studies were
conducted with a Photon Technology International (PTI) spec-
trometer model QM-7/SE, equipped with a Hamamatsu R928P
photomultiplier. The instrument uses an Ushio 75 W Xe xenon arc
lamp, and a model 101M f/4 0.2-m Czerny Turner with a 4 nm/mm
bandpass monochromator. The instrument operation, data collec-
tion, and handling were all controlled using the advanced FeliX32
software. All samples for the luminescent studies were loaded in
borosilicate capillary tubes and were sealed from the atmosphere
using a micro torch.
2.3. X-ray crystallography studies
Single crystals of the complexes were selected, mounted on
quartz fibers, and aligned with a digital camera on a Varian Oxford
Xcalibur E single-crystal X-ray diffractometer. Intensity measure-
Fig. 1. Thermal ellipsoid diagram of [AuCl(TFFPP)3] (2) showing the asymmetric unit
components consisting of the three independent molecules at sites A, B, and C. The
independent molecules at each site consist of Au1, Au2, and Au3, respectively.
ments were performed using Mo Ka radiation, from a sealed-tube

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G. Agbeworvi et al. / Journal of Molecular Structure 1108 (2016) 508e515
2.5.2. Chloro tris{tri(4-fluorophenyl)phosphine}gold(I),
[AuCl(TFFPP)3] (2)
TFFPP (0.0600 g, 0.189 mmol) was added to a solution of
[AuCl(C4H8S)] (0.0146 g, 0.063 mmol) in dichloromethane (20 mL)
at ꢁ80 ꢀC and the reaction stirred for 3 h. The solvent was removed
by purging nitrogen gas into the solution. The residue was then
recrystallized from CH2Cl2/n-hexane mixture for seven days. Partial
evaporation of the solvent provided quality crystals. Yield is 98%. 1H
NMR [d d (ppm)]: 81.1.
(ppm)]: 7.2(m) and 7.6(m). 31P NMR [
2.5.3. Synthesis of [Au(TFFPP)3]Cl·½CH2Cl2·H2O (3)
Compound 3 was obtained while attempting to synthesize the
tetrakis adduct. TFFPP (0.0800 g, 0.232 mmol) was added to a so-
lution of [AuCl(C4H8S)] (0.0134 g, 0.058 mmol) in tetrahydrofuran
(20 mL) at ꢁ80 ꢀC and the reaction stirred for 2 h. The solvent was
removed by purging nitrogen gas into the solution, until all the
solvent dried up. The residue was then recrystallized from CH2Cl2/
n-hexane mixture. After nine days partial evaporation of the sol-
vent provided x-ray quality crystals. Yield is 94%. 1H NMR [
d (ppm)]:
7.2(m) and 7.7(m). 31P NMR [
d (ppm)]: 81.1.
Fig. 2. Thermal ellipsoid diagram of the [Au(TFFPP)3]Cl$H2O$1=2 CH2Cl2 (3).
3. Results and discussion
Table 1
Crystallographic and structural refinement data for compounds 2 and 3.
3.1. Synthesis and structural characterization
Parameters
2
3
The crystal structure for the TFFPP ligand has been explored
previously by Shawkataly et al. [8]. Muller et al. reported coordi-
nation of the ligand to selenium [35], while Tasker et al. [26], and
Shawkataly et al. [36] studied gold(I) coordination with the ligand.
Although the mono.
TFFPP-gold(I) complex has been reported in that study, higher
coordination number complexes involving the ligand are reported
here for the first time.
In Fig. 1 is shown the thermal ellipsoid plot of compound 2. The
asymmetric unit consists of three crystallographically-independent
molecules which are shown in the figure. The crystallographic
parameters are summarized in Table 1, and selected bond distances
and angles are compared for the three crystallgraphically inde-
pendent molecules in Table 2. Three TFFPP ligands coordinate to the
gold(I) center with the chloride ion representing the fourth inner
sphere ligand. The bond distances and angles in the asymmetric
molecules vary. In all three sites, two sets of bond angles display
distinctly different ranges. The three PeAueP angles have average
values of 117.92ꢀ, 117.57ꢀ, and 114.78ꢀ for sites A, B, and C, while the
three PeAueCl angles have average values of 98.31ꢀ, 99.05ꢀ, and
103.38ꢀ, respectively. In contrast, the average AueP distance in-
creases on going from site A to B, to C with values of 2.3936, 2.3972,
and 2.4063 Å, respectively. Hence, it appears that as the AueP
distance increases the PeAueP angle decreases and approaches
tetrahedral geometry. The AueCl bond has a significantly longer
distance in all three sites when compared with the value for AueP
distances, with values of 2.7337 (9), 2.6825 (7), and 2.6951 (7) Å, for
Empirical formula
Formula weight (amu)
Crystal system
Space group
a (Å)
C54H36AuClF9P3
1181.15
Triclinic
C54.5H39AuCl2F9OP3
1241.64
Triclinic
P1
P1
13.5352 (3)
22.2627 (5)
24.0902 (4)
91.6537 (15)
99.1492 (14)
90.6549 (17)
7162.80(2)
6
180
0.71073
1.643
3.31
9.6589 (2)
12.7081 (3)
21.8364 (6)
84.484 (2)
88.1360 (19)
71.816 (2)
2534.68(13)
2
180
0.71073
1.627
3.175
b (Å)
c (Å)
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
V (Å3)
Z
T (K)
Wavelength (Å)
Density (mg mꢁ3
)
)
m
(Mo K
a
) (mmꢁ1
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
Final R indices
78184
37550
)
26201 (0.030)
26201/0/1837
R1 ¼ 0.0270
wR2 ¼ 0.0583
1.05
9289 (0.034)
9289/3/652
R1 ¼ 0.0238
wR2 ¼ 0.0502
1.04
[I > 2sigma(I)]
Goodness-of-fit on F2
Large diff. peak and hole (eÅꢁ3
)
0.69 and ꢁ0.66
0.65 and ꢁ0.61
at ꢁ80 ꢀC and the reaction, as illustrated in Scheme 1, was stirred
for 2 h. The solvent was removed completely by purging nitrogen
gas into the solution. The residue was then recrystallized from
CH2Cl2/n-hexane mixture within four days. Partial evaporation of
the solvent provided quality crystals. Yield is 97%. 1H NMR [
d
(ppm)]: 7.1(m) and 7.4(m). 31P NMR [
d (ppm)]: 59.01.
Scheme 1. Synthesis of the higher coordinate Au complex.

G. Agbeworvi et al. / Journal of Molecular Structure 1108 (2016) 508e515
511
Table 2
gold(I) center and obtain crystals in the form of the four coordinate
pseudo-trigonal pyramidal geometry or the three coordinate
trigonal planar geometry. This suggests a significant balance be-
tween the electronic factors and steric bulk needed to influence the
geometries and stabilization of higher coordination numbers in
gold(I) chemistry. The interplay of the two conditions has been
analyzed previously [14], where most of the alkyl phosphines with
significantly smaller cone angles are unable to form three or four-
coordinate complexes. One such exception, the water soluble TPA
ligand, has been noted to form a regular tetrahedral geometry
around Au(I) [18]. In contrast, it was possible to coordinate up to
four relatively bulky tri-(hetero) arylphosphine ligands, such as TFP
(trifuryl phosphine, cone angle 133⁰) with ease [17], although ste-
rically it is nearly as demanding as PPh3 (cone angle 145⁰). Never
the less the two ligands (TFP and PPh3) are expected to have
different electronic properties, where TFP consists of electron-
Selected bond distances (Å) and angles (ꢀ) for [AuCl(TFFPP)3] (2)*.
[AuCl(TFFPP)3](2)*
Site
A
B
C
Bond distances (Å)
Au(1,2,3)eP(1,4,7)
Au(1,2,3)eP(2, 5,8)
Au(1,2,3)eP(3, 6, 9)
Au(1,2,3)eCl(1,2,3)
Bond angles (ꢀ)
P(1,4,7)eAu(1,2,3)eP(2,5,8)
P(1,4,7)eAu(1,2,3)eP(3,6,9)
P(2,5,8)eAu(1,2,3)eCl(1,2,3)
P(3,6,9)eAu(1,2,3)eCl(1,2,3)
2.3789 (9)
2.4083 (9)
2.3936 (9)
2.7337 (9)
2.4027 (9)
2.3931 (9)
2.3960 (9)
2.6825 (7)
2.4133 (9)
2.3893 (9)
2.4163 (9)
2.6951 (7)
117.04 (3)
119.32 (3)
94.01 (3)
95.03 3)
116.75 (3)
118.08 (3)
97.99 (3)
99.36 (3)
115.36 (3)
112.69 (3)
106.29 (3)
100.20 (3)
*
Since there are three crystallographically independent molecules in the unit cell
for 2, the bond distances are labeled for each site as follows. Site A corresponds to
distances between Au(1) and P(1), P(2), P(3), and Cl(1). Similarly, the distances
labeled under site B correspond to Au(2) and P(4), P(5), P(6), and Cl(2) etc. The bond
angles are also arranged similarly where P1eAu1eP2 correspond for Site A, while
P4eAu2eP5 correspond to Site B etc.
withdrawing substituents and considered to be a poor
when compared with the PPh3 ligand [37].
s-donor
It is of a continued interest to explore the balance between
steric demand and electronic modifications in terms of - and/or
-donor ability of the ligand. Stabilizing higher coordination in
Au(I) requires a condition that would maintain the balance be-
tween the donor ability of the ligand and the high electron count
on the metal center. Also it is of fundamental interest to explore
the influences of other factors such as H-bonding and piepi in-
teractions in dictating structural stability and inducing changes in
coordination numbers and structural transformations in Au(I)
phosphines complexes.
s
p
sites A, B, and C, respectively. This distance is longer by 0.40e0.45 Å
than the AueCl distance found in the mono TFFPP complex 1
(2.285 Å) indicating a weakening of the AueCl interaction as the
coordination number increases.
The thermal ellipsoid plot of compound 3 is shown in Fig. 2. The
crystallographic details are located in Table 1 and selected bond
lengths and angles can be found in Table 3. The structural mor-
phologies of the two complexes, 2 and 3, are largely different,
although their basic compositions are similar, differing only in the
included solvate molecules in 3. Compound 3 crystallizes in a
triclinic system and the space group is P1 with one molecule in the
asymmetric unit cell. Similar to 2, compound 3 features three TFFPP
ligands coordinated to the Au(I) center. However, unlike the situ-
ation observed in 2, the Clꢁ ion is removed from the inner sphere
coordination and is present as a counter anion in the lattice. The
three PeAueP bond angles in 3 are 116.55⁰ (3), 118.73⁰ (11), and
124.41⁰ (12) with a sum of 359.9⁰ indicating expansion in the an-
gles, as compared with compound 2, as a result of the removal of
the Clꢁ ion. This implies that the resulting geometry is closer to
trigonal planar with an average bond angle of 119.9⁰. The AueP
bond lengths in 3 are 2.366 (3), 2.386 (3), and 2.407 (3) Å providing
an average distance of 2.383 Å. When compared with the AueP
bond lengths in 3, the average AueP distance in 3 is smaller by
0.0307 Å than for site C and by 0.018 Å for site A. In addition, the
average PeAueP angle in 3 is larger by more than 5⁰ when
compared with the value for site C and by more than 2⁰ when
compared with site A. Hence compound 3 appears more planar
around the gold center than 2.
It is intriguing to note that a complete removal of the Clꢁ ion
from the inner sphere coordination has been achieved in 3. Close
analysis of the structural features reveals that co-crystallization of
solvent molecules and the resulting H-bonding interactions appear
to be the main long-range structural difference exhibited in 3 when
compared with that in 2. The H-bonding in 3 involves interaction
between the Clꢁ counter ion and a water molecule co-crystalized in
the lattice at an HOeH/Cl distance of 3.147 Å. Hence, the presence
of H-bonding interaction in 3 appears to stabilize the structure after
the removal of Clꢁ ion from the inner sphere, albeit weak AueCl
interaction exhibited in 2. Concomitantly, the phenyl rings of
neighboring phosphorous atoms show closer interactions in 3 than
in 2.
Hence, the structural difference observed in the two complexes
are attributable to crystal-packing effects caused by the introduc-
tion of H-bonding as well as enhanced intra and inter-molecular p-
interaction in 3. Such enhanced interaction between ligands in the
outer coordination spheres of metal ions is known to contribute to
thermodynamic and kinetic stability of a wide variety of complexes
ranging from antibiotics to gravimetric reagents [38e41]. More-
over, a recent study on copper complexes of the phenolic oxime
family ligands [42] provides further evidence for the existence of H-
bond imposed geometry change in molecular system.
3.2. Structural comparison
In the present study also it can be concluded that the removal of
the Clꢁ ion from the inner sphere coordination of gold(I) with a
concomitant co-crystallization of solvent molecules leads to a
strong H-bond interaction and enhanced stability in the lattice. The
change in coordination number resulted in a readjustment of the
phosphine ligands to a more regular planar geometry around the
gold(I) center. This observation is similar to the behavior reported
by Ziener et al. [43] on recognition-directed supramolecular as-
semblies in complexes of terpyridine derived ligands and self-
complementary hydrogen bonding sites. It is also important to
note that both compounds display identical 31P NMR data
(81.1 ppm) indicating similar structural features in solution. Hence,
the structural differences exhibited in the solid state arise due to
the crystallization procedure of the complexes.
It has been quite easy to coordinate three TFFPP ligands to the
Table 3
Selected bond distances (Å) and angles (ꢀ) for [Au(TFFPP)3]
Cl$½CH2Cl2$H2O (3).
[Au(TFFPP)3]Cl$½CH2Cl2$H2O (3)
Bond distances (Å)
Au(1)eP(1)
Au(1)eP(2)
Au(1)eP(3)
2.3674 (8)
2.3903 (7)
2.3686 (8)
Bond angles (ꢀ)
P(1)eAu(1)eP(2)
P(1)eAu(1)eP(3)
P(2)eAu(1)eP(3)
118.73 (11)
124.41 (12)
116.55 (3)

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G. Agbeworvi et al. / Journal of Molecular Structure 1108 (2016) 508e515
3.3. Spectroscopic studies
The absorption spectral data for the TFFPP ligand, compounds 1,
and 2 reveal similarities in their high-energy broad UV profiles with
strong band at ~260 nm. The spectral similarities between the
ligand and the complexes implies that the 260 nm band is assign-
able to a
observed at 290 nm in the ligand spectrum, but absent in the
complexes. The band is assigned to an n/ * transition as it sug-
p/p* intra-ligand transition. A weaker band is also
p
gests participation of the lone pair electrons in the bonding of the
TFFPP ligand to the metal.
The excitation and emission spectra for the ligand and the
complexes are shown in Fig. 3. A broad excitation band is evident
around 360 nm. Although compounds 1 and 2 have similar exci-
tation features as that of the free ligand, the excitation band of 3
blue shifts slightly to ~340 nm. The emission band maximize at
415 nm with a similar overall profile for the compounds 1, 2, and 3.
In contrast, the spectrum of the ligand shows a sharper shoulder at
382 nm which is absent in the spectra of the compounds. In addi-
tion, a sharper band at 406 nm and a broad shoulder at ~422 nm
characterize the emission feature of the ligand. A shift to longer
wavelength from 406 nm of the TFFPP ligand to ~415 nm for the
complexes indicates some involvement of the metal orbitals in the
electronic transitions. Assignments of the various electronic tran-
sitions are given below after the theoretical analysis of the
complexes.
Fig. 4. UVeVis spectrum of 1 calculated theoretically using Gaussian 09 software
showing the three electronic transitions (X, Y, and Z) with detailed contributions of the
electronic compositions described in Tables 4e6.
the TFFPP ligand, as well as individual atomic participation for the
selected three highest occupied molecular orbitals and lowest three
unoccupied molecular orbitals. The third highest occupied molec-
ular orbital (3rd-HOMO), HOMO-87, has the largest contribution
from the ligand at 89.09% and the metal at 10.91% followed by the
highest occupied molecular orbital, HOMO-89 at 71.71% and 28.29%
contributions, respectively. The contribution of the gold atom in the
3rd HOMO-87 orbital derives from 5s, 5px and 5dxz atomic orbitals
at 4.71%, 2.24% and 3.96% contributions, respectively. The atomic
contribution of the TFFPP ligand is comprised of P, F, and C with
percentage contributions of 4.52s, 36.53px, 19.85py, and 28.19pz
orbitals. However, the gold contribution of the HOMO comes also
from 5.16% of the 5pz and 23.13% of the 5dxz atomic orbitals with
the remaining contribution from the s and p orbitals of the P, F, and
C atoms of the ligand. The table also shows the compositions of the
first three lowest unoccupied molecular orbital (LUMOs), which are
mainly ligand centered contributions. These compositions are
consistent with the absorption and emission assignment given as
ligand centered features.
3.4. Electronic Comparison
The HOMOeLUMO gap calculated by the TDDFT method was
40,366 cmꢁ1 corresponding to 247.7 nm. The calculated spectrum
for 1 obtained using TDDFT with the LANL2DZ basis set to identify
the orbital(s) contributing to the observed absorption is shown in
Fig. 4. The TD-DFT generated ground-state to excited-transitions is
shown in Table 4 which summarizes the orbital that took part most
in the transitions X, Y, and Z. From Table 4, transition Z supports an
assignment of the 3rd-HOMO-87 / LUMO-90, a
p/p* type tran-
sition. The X and Y components reflect transitions from the HOMO-
89 / LUMO-90 and SHOMO-88 / LUMO-90, respectively. Table 5
summarizes the various ground-states to excited-state X, Y and Z
transitions pictorially. The calculated spectrum values are in good
agreement with the experimental UVeVis spectrum of 1, with a
slight red shifting of about 12.3 nm which are within the absorption
range of aromatic derivatives.
3.5. FT-IR analysis
The IR-spectrum of the mono TFFPP complex is compared with
that of the ligand in Fig. 5. A total of thirty three distinct bands are
observed experimentally. The spectrum shows
a moderate
Analysis of the atomic and orbital contributions for 1 is shown in
Table 6. The table lists percentage contributions for the metal and
Table 4
Summary of TD-DFT generated ground-state to excited-state MO transitions
showing percentage contribution of each orbital transition in compound 1.
Transition
Corresponding orbital
Percentage contribution (%)
X
89 / 90
89 / 91
76.48
23.52
Y
Z
87 / 90
87 / 91
88 / 90
88 / 91
88 / 93
88 / 96
89 / 91
13.76
8.58
29.02
16.11
7.79
9.51
15.23
87 / 90
87 / 91
87 / 93
87 / 96
88 / 90
35.37
22.35
10.14
12.48
19.66
Fig. 3. Overlap of excitation and emission spectra of the TFFPP and its metal complexes
collected at liquid nitrogen temperature. Ex e excitation, and Em e emission: a) TFFPP
ligand; b) compound 1; c) compound 2; d) compound 3.

G. Agbeworvi et al. / Journal of Molecular Structure 1108 (2016) 508e515
513
Table 5
Theoretical results showing the contributions of X, Y, and Z transitions of 1.
Excitation
lcalc. (nm)
%Contribution to the transition
Transition energy (cmꢁ1
)
lexp. (nm)
260
X
247.74
Major contribution:
89 / 90
76.48
40,366
Y
244.73
Major contribution:
88 / 90
29.02
40,862
Z
244.47
Major contribution:
87 / 90
35.37
40,906
Table 6
MO contribution in the ground state for compound 1.
Partial molecular orbital contributions in the ground state
Atomic contributions (%)
Atomic orbital (%) contributions
Orbitals
92
Au
9.46
Ligand
90.54
P
F
C
Au
Ligand
P
F
C
10.89s
7.36
3.19
79.99
2.41s
11.94s
1.05s
3.19pz
1.53px
2.12py
4.40pz
2.23s
1.57px
1.52py
3.49pz
1.68s
33.47px
24.35py
20.78pz
11.44s
31.71px
11.71py
36.06pz
9.95s
2.05px
4.26pz
31.42px
24.35py
13.33pz
10.35s
30.57px
11.71py
29.51pz
9.95s
91
90
8.81
7.55
91.19
92.45
6.23
6.83
2.82
2.49
82.14
83.13
1.09s
1.41px
3.73pz
2.82pz
2.49py
1.04py
5.79pz
3.78py
2.09pz
23.93px
45.94py
12.63pz
23.93px
42.41py
6.84pz
HOMOeLUMO GAP
89
88
87
28.29
71.71
70.50
89.09
6.06
5.15
8.02
2.46
4.83
8.86
63.19
60.52
72.21
5.16pz
23.13d
31.93s
6.06pz
4.42py
2.46py
4.15pz
31.93s
22.78py
17.00pz
23.33s
21.34py
24.42pz
4.52s
36.53px
19.85py
28.19pz
20.32py
10.94pz
23.05s
16.92px
20.27pz
1.85s
28.34px
18.29py
23.73pz
29.50
10.91
6.78py
22.72d
4.71s
2.24px
3.96d
2.67s
5.35py
2.84px
1.56py
4.46pz

514
G. Agbeworvi et al. / Journal of Molecular Structure 1108 (2016) 508e515
Appendix A
CCDC 1415993 and 1415994 contains the supplementary crys-
tallographic data for this paper for compounds 2 and 3. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic
Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: þ441223
336033).
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