Mono- and dinuclear luminescent 1,1′-biisoquinoline gold(I) complexes

Article abstract of DOI:10.1016/j.ica.2012.06.024

Mono- and dinuclear, cationic or neutral gold(I) derivatives [(biisoq)(AuL)]ⁿ⁺ (L = PPh₃, n = 1; L = C ₆F₅, n = 0), and [(μ-biisoq)(AuL)₂] ⁿ⁺ (biisoq = 1,1′-biisoquinoline; L = PMe ₃, PPh₃, PMePh₂, n = 2; L = C₆F ₅, n = 0) have been prepared. Aurophilic interactions and steric requirements of the co-ligand L impose the torsion angle between the two isoquinoline units of the flexible, non-planar 1,1′-biisoquinoline ligand, affording different structures. The X-ray molecular structure of the mononuclear complex with PPh₃ confirmed the monodentate mode for the biisoquinoline ligand. In the three X-ray structures solved for dinuclear compounds with bridging biisoquinoline, the torsion angles and the intramolecular gold-gold distances found are, respectively: 65.2° and 3.0739(7) A? for L = PMe₃; 80.10° and 3.785 A? for L = C₆F₅; 95.6° and 4.505 A? for L = PMePh ₂. All the phosphine derivatives are luminescent at room temperature in the solid state, with emission maxima in the range 390-422 nm, and emit from 370 to 438 nm at 77 K. They are also emissive in CH₂Cl₂ at 298 K in the range 381-458 nm, whilst they are luminescent at 77 K in the range 382-550 nm. The fluoroaryl derivatives are not emissive.

Full text of DOI:10.1016/j.ica.2012.06.024

Inorganica Chimica Acta 392 (2012) 91–98
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Inorganica Chimica Acta
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Mono- and dinuclear luminescent 1,10-biisoquinoline gold(I) complexes
⇑
⇑
Manuel Bardají , Ana B. Miguel-Coello, Pablo Espinet
IU CINQUIMA/Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, E-47071 Valladolid, Spain
a r t i c l e i n f o
a b s t r a c t
Mono- and dinuclear, cationic or neutral gold(I) derivatives [(biisoq)(AuL)]n+ (L = PPh3, n = 1; L = C6F5,
Article history:
n = 0), and [(l
-biisoq)(AuL)2]n+ (biisoq = 1,10-biisoquinoline; L = PMe3, PPh3, PMePh2, n = 2; L = C6F5,
Received 29 March 2012
Accepted 13 June 2012
Available online 23 June 2012
n = 0) have been prepared. Aurophilic interactions and steric requirements of the co-ligand L impose
the torsion angle between the two isoquinoline units of the flexible, non-planar 1,10-biisoquinoline
ligand, affording different structures. The X-ray molecular structure of the mononuclear complex with
PPh3 confirmed the monodentate mode for the biisoquinoline ligand. In the three X-ray structures solved
for dinuclear compounds with bridging biisoquinoline, the torsion angles and the intramolecular gold–
gold distances found are, respectively: 65.2° and 3.0739(7) Å for L = PMe3; 80.10° and 3.785 Å for
L = C6F5; 95.6° and 4.505 Å for L = PMePh2. All the phosphine derivatives are luminescent at room temper-
ature in the solid state, with emission maxima in the range 390–422 nm, and emit from 370 to 438 nm at
77 K. They are also emissive in CH2Cl2 at 298 K in the range 381–458 nm, whilst they are luminescent at
77 K in the range 382–550 nm. The fluoroaryl derivatives are not emissive.
Keywords:
Biisoquinoline
Gold
Gold–gold contact
Luminescence
Monodentate ligand
Bridging ligand
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
thought to disfavor its chelating coordination, but in fact this flex-
ible ligand usually acts as chelate in metal complexes, as reported
The study of closed shell gold(I) derivatives has revealed the fre-
quent presence of short gold–gold distances, which have been
attributed to correlation effects reinforced by relativistic effects
and electrostatic contributions. The so-called aurophilic interac-
tion leads to gold–gold distances in the range 2.8–3.6 Å, with
strength similar to some hydrogen bonds, in the order 20–50 kJ/
mol [1]. Gold(I) usually forms two-coordinated complexes display-
ing linear geometry, which facilitates the formation of these gold–
gold contacts, provided the steric requirements of the ligands do
not hinder the interaction. Many gold(I) compounds, with or with-
out gold–gold contacts, are luminescent in the visible region [2],
and some of them have been proposed for applications as chemo-
sensors for cations or anions, or as light-emitting diodes [3].
Ligands incorporating a 1,10-binaphthyl unit, for instance chiral
N-heterocyclic carbenes, have been receiving attention recently
because of their application in catalytic asymmetric reactions [4].
These ligands can show optical activity based on the high barrier
for square planar Rh(I) [6] and Pt(II) [7], or octahedral Os(II) [8],
Ru(II) [8,9], and Ir(III) complexes [10]. Potentially 1,10-biisoquino-
line can also act as bridging bidentate and as monodentate ligand,
although, among the many reported complexes, only two reports
of 1,10-biisoquinoline acting as a bridging ligand (a dinuclear palla-
dium complex [11] and a series of silver(I) compounds recently de-
scribed by us [12]), and only one complex where it is acting as
monodentate ligand (the X-ray crystal structure of a platinum
complex), are found [7a].
The predominant tendency of 1,10-biisoquinoline to behave as a
chelate ligand should be frustrated on metal centers with linear
coordination, thus favoring the occurrence of the other bonding
modes. In effect, in this paper we report mono- and dinuclear
gold(I) compounds with the 1,10-biisoquinoline ligand acting as
monodentate or bridging bidentate, respectively. Most of the com-
plexes are luminescent, both in solution and in the solid state.
to rotation about the C–C
[5]. In particular, 1,10-biisoquinoline is a diamine with a more ex-
tended
-acceptor system than 2,20-bipyridine, while it has a com-
parable N
-donor ability. 1,10-Biisoquinoline is non-planar, as
result of trans-annular steric hindrance between the hydrogen
atoms in positions 8 and 80, one on each isoquinoline subunit
(see labels in Scheme 1 below). Its lack of planarity might be
r-bond, which gives rise to atropisomers
2. Experimental
p
IR spectra were recorded on a FT 1720X Perkin-Elmer spectro-
photometer (4000–400 cmꢀ1
)
using KBr pellets. 1H, 19F and
r
31P{1H} NMR spectra were recorded on Bruker AC-300, ARX-300
or AV-400 instruments in CDCl3 solutions (if no other solvent is
stated); chemical shifts are quoted relative to SiMe4 (external,
1H), CFCl3 (external, 19F) and 85% H3PO4 (external, 31P). 1H NMR la-
bels are in Scheme 1. Elemental analyses were performed with a
Perkin-Elmer 2400 microanalyzer. Emission and excitation spectra
⇑
Corresponding authors. Tel.: +34 983184624; fax: +34 983423013.
E-mail addresses: bardaji@qi.uva.es (M. Bardají), espinet@qi.uva.es (P. Espinet).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.06.024

92
M. Bardají et al. / Inorganica Chimica Acta 392 (2012) 91–98
51.40; H, 3.15; N, 3.24. Found: C, 51.08; H, 3.27; N, 2.92%. 1H
n+
NMR: d 6.9–7.6 (m, 17H, Ph + H8), 7.63 (t, JHH = 7.9 Hz, 2H, H7),
7.87 (t, JHH = 7.6 Hz, 2H, H6), 8.05 (d, JHH = 8.0 Hz, 2H, H5), 8.10 (d,
JHH = 6.2 Hz, 2H, H4), 8.75 (d, JHH = 6.2 Hz, 2H, H3). 19F NMR: d –
N
78.3 (s). 31P{1H} NMR: d 29.7 (s). IR (KBr): 1266, 639 (CF3SO3) cmꢀ1
.
6
3
N
7
1
Au
8
5
4
AuL synton
2.3. Synthesis of [(l-biisoq){Au(C6F5)}2] 2d and [(biisoq){Au(C6F5)}]
1d
L
1
n+
N
N
To
a dichloromethane solution (20 mL) of [Au(C6F5)(tht)]
(81 mg, 0.18 mmol) was added the stoichiometric amount of the
biisoquinoline (23 mg, 0.09 mmol). The resulting solution was stir-
red for 1 h and concentrated to ca. 5 mL. Addition of hexane affor-
ded the mixture of compounds 2d–1d as a light yellow solid in
1:2 M ratio. 1H NMR of 2d: d 7.41 (d, JHH = 8.6 Hz, 2H, H8), 7.69
(t, JHH = 7.8 Hz, 2H, H7), 8.00 (t, JHH = 7.5 Hz, 2H, H6), 8.18 (d,
JHH = 8.3 Hz, 2H, H5), 8.29 (d, JHH = 5.7 Hz, 2H, H4), 8.82 (d,
JHH = 5.7 Hz, 2H, H3). 19F NMR of 2d: d –116.59 (m, 4F, Fo–Au),
ꢀ159.87 (t, N = 18.1 Hz, 2F, Fp–Au), ꢀ163.53 (m, 4F, Fm–Au). 1H
NMR of 1d: d 7.48 (d, JHH = 8.6 Hz, 2H, H8), 7.56 (t, JHH = 7.8 Hz,
2H, H7), 7.85 (t, JHH = 7.5 Hz, 2H, H6), 8.04 (d, JHH = 5.7 Hz, 2H,
H4), 8.06 (d, JHH = 8.3 Hz, 2H, H5), 8.74 (d, JHH = 5.7 Hz, 2H, H3).
19F NMR of 1d: d ꢀ116.59 (m, 4F, Fo–Au), ꢀ160.50 (t, N = 18.1 Hz,
2F, Fp–Au), ꢀ163.86 (m, 4F, Fm–Au).
N
N
Au
Au
2
L
L
Scheme 1.
at 298 and 77 K were measured in the solid state as finely pulver-
ized KBr mixtures, and in deoxygenated CH2Cl2 solutions in quartz
tubes with
a Perkin-Elmer LS-55 spectrofluorimeter. UV–Vis
absorption spectra were recorded at 297 K on a Shimadzu UV-
2550. Literature methods were used to prepare 1,10-biisoquinoline
[9f], [AuCl(PRR02)] [13], and [Au(C6F5)(tht)] [14].
2.4. Crystal structure determination of compounds 1b, 2a, 2c and 2d
2.1. Synthesis of [(l
-biisoq){Au(PRR02)}2](CF3SO3)2; R = R0 = Me 2a, Ph
2b; R = Me, R0 = Ph 2c
Crystals of 1b, 2c and 2d were obtained by slow diffusion of
hexane into a dichloromethane solution, whilst crystals of 2a were
obtained by slow diffusion of diethyl ether/ethanol into a chloro-
form solution, always at ꢀ18 °C. The crystal was mounted on a
glass fiber and transferred to a Bruker SMART CCD diffractometer.
Crystal data and details of data collection and structure refinement
are given in Table 1. Cell parameters were retrieved using SMART
[15] software and refined with SAINT [16] on all observed reflections.
Data reduction was performed with the SAINT software and cor-
rected for Lorentz and polarization effects. Absorption corrections
were based on multiple scans (program SADABS) [17]. The structure
was refined anisotropically on F2 [18]. All non-hydrogen atomic
positions were located in difference Fourier maps and refined
anisotropically. The hydrogen atoms were placed in their geomet-
rically generated positions. In the structure of 2c a water molecule
between two positions was included (their H were not added); the
CF3 of one anion is incipiently disordered. The structure of 2d con-
tains some disordered solvent in the channels, and we were unable
to properly model it.
To an acetone solution (20 mL) of [AuCl(PRR02)] (0.17 mmol;
R = R0 = Me 52 mg, Ph 84 mg; R = Me, R0 = Ph 74 mg) was added
Ag(CF3SO3) (44 mg, 0.17 mmol), and the reaction stirred for
60 min protected from the light. AgCl was filtered off, and the cor-
responding biisoquinoline (22 mg, 0.085 mmol) was added to the
solution. After stirring for 1 h, the suspension was concentrated
to ca. 5 mL. Addition of diethyl ether afforded compounds 2a–2c
as white solids. Yield of 2a: 61 mg, 65%. Anal. Calc. for C, 28.38;
H, 2.75; N, 2.55. Found: C, 28.65; H, 2.67; N, 2.83%. 1H NMR: d
1.45 (d, JHP = 10.5 Hz, 18H, Me), 7.48 (d, JHH = 8.6 Hz, 2H, H8), 7.65
(t, JHH = 7.8 Hz, 2H, H7), 8.11 (t, JHH = 7.5 Hz, 2H, H6), 8.13 (d,
JHH = 8.3 Hz, 2H, H5), 8.20 (d, JHH = 5.7 Hz, 2H, H4), 8.95 (d,
JHH = 5.7 Hz, 2H, H3). 19F NMR: d ꢀ78.3 (s). 31P{1H} NMR: d ꢀ11.2
(s). IR (KBr): 1274, 638 (CF3SO3) cmꢀ1. Yield of 2b: 81 mg, 65%.
Anal. Calc. for C, 45.66; H, 2.87; N, 1.90. Found: C, 45.32; H, 2.77;
N, 1.80%. 1H NMR: d 7.0–7.5 (m, 32H, Ph + H8), 7.75 (t, JHH = 7.9 Hz,
2H, H7), 8.11 (t, JHH = 7.6 Hz, 2H, H6), 8.08 (d, JHH = 8.0 Hz, 2H, H5),
8.27 (d, JHH = 6.1 Hz, 2H, H4), 9.15 (d, JHH = 6.1 Hz, 2H, H3). 19F NMR:
d ꢀ78.3 (s). 31P{1H} NMR: d 28.5 (s). IR (KBr): 1260, 640 (CF3SO3)
cmꢀ1. Yield of 2c: 79 mg, 69%. Anal. Calc. for C, 40.96; H, 2.84; N,
2.08. Found: C, 40.61; H, 2.89; N, 2.0%. 1H RMN: d 2.04 (d,
JHP = 11.3 Hz, 6H, Me), 7.1–7.5 (m, 22H, Ph + H8), 7.70 (t,
JHH = 7.6 Hz, 2H, H7), 7.95 (t, JHH = 7.8 Hz, 2H, H6), 8.08 (d,
JHH = 8.4 Hz, 2H, H5), 8.26 (d, JHH = 6.2 Hz, 2H, H4), 9.2 (d,
JHH = 6.2 Hz, 2H, H3). 19F NMR: d ꢀ78.3 (s). 31P{1H} NMR: d 13.9
3. Results and discussion
3.1. Synthesis and characterization
The reaction of the 1,10-biisoquinoline with appropriate gold(I)
precursors, prepared in situ, yielded compounds of the types 1 or 2,
according to Scheme 1.
(s). IR (KBr): 1260, 637 (CF3SO3) cmꢀ1
.
Thus, using [Au(CF3SO3)(PR2R0)], prepared in situ from
[AuCl(PR2R0)] and Ag(CF3SO3), and an Au:1,10-biisoquinoline 2:1 ra-
tio, the dicationic complexes 2a–c, with CF3SO3 as counter-anion
(2a: R = R0 = Me; 2b: R = R0 = Ph; 2c: R = Ph, R0 = Me), were obtained.
Using an Au:1,10-biisoquinoline 1:1 ratio, the monocationic com-
plex 1b was obtained. Compounds 1b and 2a–c are air-stable white
solids at room temperature and were characterized by elemental
analysis, and by IR and NMR spectroscopy.
2.2. Synthesis of [(biisoq){Au(PPh3)}](CF3SO3) 1b
To an acetone solution (20 mL) of [AuCl(PR3)] (84 mg,
0.17 mmol) was added Ag(CF3SO3) (44 mg, 0.17 mmol), and the
reaction stirred for 90 min protected from the light. AgCl was fil-
tered off, and the corresponding biisoquinoline (44 mg, 0.17 mmol)
was added to the solution. After stirring for 1 h, the suspension was
concentrated to ca. 5 mL. Addition of hexane afforded compounds
1b as a white solid. Yield of 1b: 118 mg, 80%. Anal. Calc. for C,
The dicationic complexes 2a–c show in their 1H NMR spectra a
phosphine:biisoquinoline 2:1 ratio, and only six chemically non-
equivalent biisoquinoline protons, as expected for two equivalent

M. Bardají et al. / Inorganica Chimica Acta 392 (2012) 91–98
93
Table 1
Details of crystal data and structure refinement for complexes 1b, 2a, 2c and 2d.
Compound
1b
2a
2c
2d
Empirical formula
FW
T (K)
C
37H27AuF3N2O3PS
C26H30Au2F6N2O6P2S2
1100.51
298(2)
0.71073
orthorhombic
Pca2(1)
C46H38Au2F6N2O6P2S2.H2O
1364.78
298(2)
C30H12Au2F10N2
984.35
298(2)
0.71073
monoclinic
C2/c
864.60
298(2)
0.71073
triclinic
k (Å)
0.71073
Crystal system
Space group
Unit cell dimensions
a (Å)
triclinic
ꢀ
ꢀ
P1
P1
12.002(4)
12.948(3)
11.769(8)
16.478(5)
b (Å)
c (Å)
12.384(4)
13.753(5)
89.310(7)
68.336(6)
63.986(6)
1679.7(10)
2
1.710
4.546
16.785(4)
16.495(4)
90
90
13.871(10)
16.878(12)
80.849(12)
74.947(11)
67.006(11)
2444(3)
16.319(5)
12.870(4)
90
115.459(5)
90
3124.9(16)
4
2.092
a
(°)
b (°)
v
(°)
90
V (Å3)
3584.7(14)
4
2.039
8.452
2088
Z
2
Dcalc (Mg/m3)
1.854
6.220
1316
Absorption coefficient (mmꢀ1
F(000)
)
9.460
1816
848
Crystal habit
Plate
Needle
Prism
Plate
Crystal size (mm)
0.35 ꢁ 0.14 ꢁ 0.05
1.62 to 28.33
ꢀ16 6 h 6 15, ꢀ16 6 k 6 16,
ꢀ17 6 l 6 18
16942
0.38 ꢁ 0.09 ꢁ 0.07
1.21 to 28.30
ꢀ17 6 h 6 17, ꢀ22 6 k 6 22,
ꢀ22 6 l 6 21
34491
0.38 ꢁ 0.23 ꢁ 0.19
1.25 to 28.46
ꢀ15 6 h 6 15, ꢀ18 6 k 6 18,
ꢀ22 6 l 6 22
24663
0.27 ꢁ 0.19 ꢁ 0.1
1.85 to 28.32
ꢀ21 6 h 6 21, ꢀ21 6 k 6 21,
ꢀ17 6 l 6 17
15212
H
range for data colln
Index ranges
Reflections collected
Independent reflections
Maximum and minimum
transmissions
8253 [Rint = 0.0440]
1 and 0.608606
8728 [Rint = 0.0606]
1 and 0.237895
12068 [Rint = 0.0320]
1 and 0.500817
3889 [Rint = 0.0641]
1 and 0.22177
Data/restraints/parameters
8253/0/433
0.981
8728/1/421
1.020
12068/0/615
1.015
3889/0/199
1.093
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0410, wR2 = 0.0761
R1 = 0.0739, wR2 = 0.0862
1.303 and ꢀ0.509
R1 = 0.0400, wR2 = 0.0867
R1 = 0.0672, wR2 = 0.0982
1.392 and ꢀ0.696
R1 = 0.0395, wR2 = 0.1004
R1 = 0.0660, wR2 = 0.1135
1.625 and ꢀ1.238
R1 = 0.0408, wR2 = 0.1035
R1 = 0.0747, wR2 = 0.1164
1.826 and ꢀ1.129
Largest difference in peak and
hole (e Åꢀ3
)
operating. In addition, a singlet in the 31P{1H} NMR spectra at
29.6 ppm, shifted only by +1.1 ppm compared to derivative 2b,
and a singlet at ꢀ78.3 ppm in the 19F spectra due to the triflate an-
ion, are observed. As for derivatives 2, the H3–H7 resonances are
low-field shifted (the biggest shifts are for H4, and the smallest
one, for H3 is insignificant), whilst H8 is high-field shifted, always
compared to the free ligand. The actual chemical shift values of
1b are midway between those for the related complex 2b and for
the free ligand. These NMR features suggest that the fragment
Au(PPh3) is swinging very fast between N and N0 (Scheme 2).
The reaction of 1,10-biisoquinoline with [Au(C6F5)(tht)]
(tht = tetrahydrothiophene) in Au:biisoquinoline 2:1 ratio yielded
an air-stable light yellow solid which proved to be a mixture of
the neutral fluoroaryl dinuclear compound 2d with a bridging
biisoquinoline, and the mononuclear compound 1d. The 19F NMR
spectrum displays two sets of three resonances of close intensity
due to the Au–C6F5 moiety, in approximately 1:2 ratio, at ꢀ116.6,
ꢀ159.9, and ꢀ163.5 ppm for derivative 2d and at ꢀ116.6,
ꢀ160.5, ꢀ163.9 for derivative 1d, which confirm a mixture of the
two compounds. The 1H NMR spectrum of this mixture displayed
only two sets of signals corresponding to the three kinds of iso-
quinoline moiety in the complexes of Scheme 1, showing that, as
observed for 1b, fast atropisomerization between N and N0 is oper-
ating in the 1d component of the mixture. Taking this into account,
the mixture 2d:1d has an approximate 1:2 ratio, and there is no
fast biisoquinoline exchange between 2d and 1d. This synthesis
was monitored in situ, by mixing the starting materials in CDCl3.
At the end of the reaction the 19F NMR spectrum showed the pres-
ence of 1d:2d:[Au(C6F5)(tht)] in 6.7:1:13 ratio. The 1H NMR spec-
trum displayed the resonances corresponding to 1d, 2d and free
biisoquinoline, and also to free and coordinated tht. During the
workup, the volatility of tht and the different solubility of the com-
ponents of the mixture led to the ratio found for the isolated solid,
Table 2
Summary of 1H NMR resonances of biisoquinoline ligand, either free or coordinated.
Deriv.
H3
H4
H5
H6
H7
H8
biisoq
2a
2b
2c
1b
8.72
8.95
9.15
9.20
8.75
8.82
8.74
7.82
8.20
8.27
8.26
8.10
8.29
8.04
7.95
8.13
8.08
8.08
8.05
8.18
8.06
7.75
8.11
8.11
7.95
7.87
8.00
7.85
7.50
7.65
7.75
7.70
7.63
7.69
7.56
7.70
7.48
7.50
7.42
7.50
7.41
7.48
2d
1d
halves of the biisoquinoline. These aromatic protons (assigned
from COSY experiments) appear low-field shifted by comparison
with the free ligand except H8, which is high-field shifted (see Ta-
ble 2). The biggest shifts are found for H4 and H3, while the smallest
ones are found for H5. The 19F NMR spectra show a singlet at
ꢀ78.3 ppm, due to the triflate anion. A singlet is observed for 2a–
c in the 31P{1H} NMR spectra, at ꢀ11.2 (PMe3), 28.5 (PPh3), or
13.9 (PPh2Me) ppm, respectively.
Compound 1b shows a phosphine:biisoquinoline 1:1 ratio but
the two isoquinoline halves are equivalent in the NMR timescale
even at ꢀ55 °C, revealing that a very fast fluxional process is
n+
n+
n+
N
N
N
N
N
L
N
Au
Au
Au
L
L
Scheme 2.

94
M. Bardají et al. / Inorganica Chimica Acta 392 (2012) 91–98
Table 3
as discussed above. Different attempts at obtaining pure 1d or 2d
were frustrating but some microcrystals of 2d, suitable for X-ray
diffraction studies could be picked up from a mixture enriched in
2d.
Selected bond lengths (Å) and angles (°) for complex 1b.
Au(1)–N(1)
Au(1)–P(1)
N(1)–C(1)
P(1)–C(31)
N(2)–C(11)
2.072(4)
2.2358(13)
1.320(6)
1.805(5)
1.358(8)
N(1)–Au(1)–P(1)
C(31)–P(1)–Au(1)
C(1)–N(1)–C(2)
C(1)–N(1)–C(2)
C(1)–N(1)–Au(1)
175.85(11)
115.54(16)
119.0(4)
120.8(3)
120.2(3)
3.2. X-ray crystal structure determination of compounds 1b, 2a, 2c,
and 2d
ORTEP representations of the structures of the cations of 1b, 2a,
and 2c, and the molecule 2d, are presented below along with rele-
vant distances and angles. The structures of all the complexes are
built around that of the biisoquinoline, which is mostly character-
ized by the N–C1–C10–N0 torsion angle. This angle sufficiently de-
scribes the arrangement of the two halves of the 1,10-
biisoquinoline. On top of this common frame, it is necessary to con-
sider the coordination mode of gold, the possibility of intermolec-
ular Auꢂ ꢂ ꢂAu interactions and, in the dinuclear complexes, the
possibility of Auꢂ ꢂ ꢂAu intramolecular interactions.
A theoretical DFT study of free 1,10-biisoquinoline found that
the most stable structure is the anti isomer, with a N–C1–C10–N0
torsion angle of 129.9°; its syn atropisomer displays a torsion angle
of 26.5°, and the calculated atropisomerization barrier is 123.09 kJ/
mol [19]. Thus the anti atropisomer (dihedral angle > 90°) is pre-
ferred for the ligand itself, as found in similar free ligands
(101.2° for 8,80-dimethyl-1,10-biisoquinoline [20]; 101.6° for 1,10-
biisoquinoline N,N0-dioxide [21]). However, the syn arrangement
(dihedral angle < 90°) is found in metal complexes where the
1,10-biisoquinoline is acting as a chelate, and the N–C1–C10–N0 tor-
sion angles in those complexes are in the range 20–41° [6–10].
None of the structures studied here show chelating biisoquino-
line coordination, nor they show intermolecular Auꢂ ꢂ ꢂAu interac-
tions. Moreover, in all cases the Au coordination is very close to
linear, with normal Au–N [22], Au–P, or Au–C6F5 [23] distances.
Thus the main differential feature of these structures is the N–
C1–C10–N0 torsion angle, as the Au–Au distance is a function of this
angle, which consequently determines the possibility of Auꢂ ꢂ ꢂAu
intradimer aurophilic interactions in the binuclear complexes.
Fig. 2. Structure of the cation of compound 2a. Displacement ellipsoids are at 25%
probability level (H atoms omitted for clarity).
3.2.1. Crystal structure of complex 1b
Suitable crystals for X-ray studies were obtained by slow diffu-
sion of hexane in a solution of dichloromethane at ꢀ18 °C. The cor-
responding cation is shown in Fig. 1, with selected bond lengths and
angles in Table 3. It confirms a mononuclear structure with one
monodentate biisoquinoline, for which there is only one precedent
Fig. 3. Structure of the cation of compound 2c. Displacement ellipsoids are at 25%
probability level (H atoms omitted for clarity).
reported, namely [Pt(biisoq)(dapy)3](ClO4)2 (dapy = 4-(dimethyl-
amino)pyridine), with 77.6° torsion angle [7a]. The torsion angle
between the two isoquinoline moieties in 1b is 100.3°. This torsion
angle is very close to those reported for the free ligands 8,80-di-
methyl-1,10-biisoquinoline and 1,10-biisoquinoline N,N0-dioxide,
and corresponds to an anti arrangement. In contrast, related deriv-
atives with the planar ligand 2,20-bipyridine, [Au(bipy)(PPh3)]PF6
[24] and [(P-P)(Aubipy)2](ClO4)2 [25] (P-P = bis(bis(o-methoxy-
phenoxy)phosphino)(phenyl)amine)) show tricoordinated gold
with torsion angles smaller than 8° and two Au–N bond distances
of 2.167 and 2.404 Å, and 2.247 and 2.250 Å, respectively.
3.2.2. Crystal structure of complexes 2a, 2c, and 2d
Crystals of 2a, 2c and 2d were obtained by slow diffusion of
hexane in a solution of the complex in dichloromethane at
ꢀ18 °C. The studies (Figs. 2–4 and Tables 4 and 5) confirm the
Fig. 1. Structure of the cation of 1b. Displacement ellipsoids are at 50% probability
level (H atoms omitted for clarity).

M. Bardají et al. / Inorganica Chimica Acta 392 (2012) 91–98
95
Fig. 5. View of the crystal packing of 2d from the c axis (axes a and b in the plane).
Spacefill representation.
Fig. 4. Molecular structure of complex 2d. Displacement ellipsoids are at 25%
probability level (H atoms omitted for clarity).
Table 6
Normalized hydrogen bonds for complex 2d (Å and °) [33].
Table 4
C–Hꢂ ꢂ ꢂF
d(C–H)
d(Hꢂ ꢂ ꢂF)
d(Cꢂ ꢂ ꢂF)
<(CHF)
Selected bond lengths (Å) and angles (°) for the complex cations 2a and 2c.
C3–H3ꢂ ꢂ ꢂF1#1
C5–H5ꢂ ꢂ ꢂF2#2
C7–H7ꢂ ꢂ ꢂF1#3
C7–H7ꢂ ꢂ ꢂF5#4
C8–H8ꢂ ꢂ ꢂF4#4
F1ꢂ ꢂ ꢂH3–C3#5
F1ꢂ ꢂ ꢂH7–C7#6
F2ꢂ ꢂ ꢂH5–C5#7
F4ꢂ ꢂ ꢂH8–C8#8
F5ꢂ ꢂ ꢂH7–C7#8
1.089
1.089
1.089
1.089
1.089
1.089
1.089
1.089
1.089
1.089
2.259
2.551
2.500
2.519
2.518
2.259
2.500
2.551
2.518
2.519
3.250
3.302
3.491
3.346
3.557
3.250
3.491
3.302
3.557
3.346
150.20
125.31
150.68
131.89
159.23
150.20
150.68
125.31
159.23
131.89
2a
2c
Au(1)–N(1)
Au(1)–P(1)
Au(1)–Au(2)
N(1)–C(1)
2.116(6)
2.229(2)
3.0739(7)
1.326(11)
1.789(13)
2.115(8)
2.229(3)
1.350(12)
1.772(13)
176.2(2)
175.3(2)
2.090(5)
2.2393(19)
4.505
1.324(7)
1.777(6)
2.091(5)
2.231(2)
1.339(7)
1.798(8)
176.99(13)
175.65(14)
P(1)–C
Au(2)–N(2)
Au(2)–P(2)
N(2)–C(10)
P(2)–C
N(1)–Au(1)–P(1)
N(2)–Au(2)–P(2)
Symmetry transformations used to generate equivalent atoms: #1 x,1 ꢀ y, ꢀ1/2 + z;
#2 ꢀ1/2 + x, ꢀ1/2 + y, ꢀ1 + z; #3 ꢀ1/2 + x, 1/2 ꢀ y, ꢀ1/2 + z; #4 ꢀ1/2 + x, ꢀ1/2 + y, z;
#5 x, 1 ꢀ y, 1/2 + z; #6 1/2 + x, 1/2 ꢀ y, 1/2 + z; #7 1/2 + x, 1/2 + y, 1 + z; #8 1/2 + x, 1/
2 + y, z.
Table 5
Selected bond lengths (Å) and angles (°) for 2d.
Table 7
Electronic absorption data for the biisoquinoline ligand and the gold complexesa.
Au(1)–N(1)
Au(1)–C(11)
N(1)–C(1)
N(1)–C(3)
C(11)–C(12)
C(11)–C(16)
2.062(6)
2.003(8)
1.316(9)
1.388(10)
1.362(11)
1.374(12)
C(11)–Au(1)–N(1)
C(12)–C(11)–Au(1)
C(16)–C(11)–Au(1)
C(1)–N(1)–C(3)
179.0(3)
122.6(7)
123.1(6)
118.4(6)
122.2(5)
Derivative k/nm (e )
/Mꢀ1 cmꢀ1
biisoq
2a
2b
234 (31510), 279 (9110), 311 sh (6540), 322 (7930)
234 (62815), 278 (8123), 325 (7550), 338 sh (6405)
234 (109135), 267 (16705), 275 (14060), 326 (7330), 337 sh
(5890)
C(1)–N(1)–Au(1)
2c
1b
2d–1d
232 (107060), 266 (12775), 274 (11175), 335 (7731)
233 (81060), 268 (11050), 275 (9650), 326 (7140) 336 sh (6165)
228 (66825), 264 sh (17060), 284 sh (12055), 323 (8685), 334 sh
(7150)
expected binuclear structure with a bridging biisoquinoline for
both derivatives. The previous examples of this coordination mode
were: (a) the two enantiomers of [(l-Cl)(l-biisoq){Pd(C-N)}2]ClO4
(C-N = 2-((N,N-dimethylamino)ethyl)phenyl-C,N), which show a
torsion angle of 88.3° [11]; (b) the double biisoquinoline bridged
In CH2Cl2 solution, ca. 5 ꢁ 10ꢀ5 M.
a
silver (I) compounds [(
[( -biisoq)2(AgXL)2] (L = PPh3, PMePh2; X = CF3SO3, ClO4) with
torsion angles in the range 66.0–100.3°; (c) a single bridged silver
(I) polymer [( -biisoq)Ag(OH2)2( -biisoq)Ag]n(CF3SO3)2n with a
torsional angle of 111.8°; (d) and finally, the related single biiso-
quinoline bridge of two phosphino-silver (I) units [( -biisoq)
{Ag(OSO2CF3)(PPh3)}{Ag(OH2)(PPh3)}](CF3SO3) which displays
torsion angle of 113.1° and a long intramolecular silver–silver
distance of 5.1557 Å [12].
The main difference between the three binuclear structures
studied here is the torsion angle between the two isoquinoline
moieties (65.2° for 2a; 95.6° for 2c; 80.1° for 2d) which leads to
l-biisoq)2{Ag(OSO2CF3)(acetone)}2] and
different values for the short intramolecular gold–gold distance:
3.0739(7) Å for 2a; 4.505 Å for 2b; and 3.785 Å for 2d). There is
an almost linear correspondence between the torsion angles and
the gold–gold distances. The later suggest typical aurophilic inter-
actions for 2a; a distance slightly above the limits of aurophilic
interactions (typically in the range 2.8–3.6 Å) for 2d; and a clearly
non-bonding intramolecular gold–gold distance for 2c. These dif-
ferences can be easily explained for 2a and 2c, which bear less ste-
rically demanding phosphines and stabilize the usually less stable
syn atropisomer. In contrast 2c, with the bulkier phosphine, be-
cause of steric hindrance with the bulky phosphine, prefers the anti
arrangement.
l
l
l
l
a

96
M. Bardají et al. / Inorganica Chimica Acta 392 (2012) 91–98
Table 8
Excitation and emission data (in nm) in the solid state and in solution for the 1,10-biisoquinoline and the gold derivatives 2a, 2b, 2c and 1b.
Comp.
Solid
298 K
Solid
77 K
CH2Cl2
298 K
CH2Cl2
77 K
kexc
kemis
kexc
kemis
kexc
kemis
kexc
kemis
biisoq
2a
2b
2c
1b
291, 341a
325
400
292, 340a
295a,325, 340
294a, 326
296, 354a
283a, 322
398
429
370
351
444
283, 336a
341
340, 354
355
388
397a, 422
390
328, 340 sh
367sh, 384(354a, 381)b
332
391a, 514, 545
372, 510a, 548a, 592
382a, 511a, 549a, 594
388, 511a, 550a, 593
389
296, 334a
364
423 sh, 440(419a, 434sh, 511, 546)b
381a, 451, 509
411
–
417
–
426, 438a
351(334)b
458(392, 451)b
334
a
Most intense peak.
b
In parentheses: the second excitation and emission spectrum with less intensity.
Fig. 6. Excitation and emission spectra in dichloromethane of complex 2b: left at 298 K (recorded with two different excitation frequencies); right at 77 K.
A different interplay of forces operates in complex 2d, where
the structure is basically forced by the stacking of C6F5 and
did not emit, neither in solution nor in the solid state, even at
77 K. The later result confirms the electronic differences between
pyridine and biisoquinoline, since a series of intensely luminescent
pyridine halophenyl gold(I) complexes has been reported, with the
emissions assigned to Ligand (halophenyl)–Metal to Ligand (pyri-
dine) Charge Transfer transitions [27].
In the solid state, the emission range goes from 390 to 422 nm
at 298 K, and from 370 to 438 nm at 77 K. The low temperature
emission spectra are slightly blue (for 2b, containing PPh3) or red
(for 2a and 2c, with PMe3 and PPh2Me, respectively) shifted, while
the excitation spectra are similar with some small blue shifts. The
biisoquinoline ligand is luminescent as expected from the presence
of naphthalene-type units. In the solid state it is reasonable to as-
sign the emission observed as ligand-centered modified by the
gold phosphine moiety. The influence of Auꢂ ꢂ ꢂAu interactions in
compound 2a, if any, is not very relevant, contrarily to other pho-
pꢀp
isoquinoline rings, which leads to a N–C1–C10–N0 torsion angle of
80.1°. Moreover, this arrangement gives rise to the formation of
channels in the crystal structure, as shown in Fig. 5. This specific
arrangement can be related to the presence of intermolecular con-
tacts between both ligands. Actually, there are five donor and five
acceptor C–Hꢂ ꢂ ꢂF weak non-classical hydrogen bonds per asym-
metric unit (double for each molecule) as shown in Table 6. This
combination of forces could overcome the alternative possibility
of forming Auꢂ ꢂ ꢂAu interactions at a shorter distance.
3.3. Photophysical studies
The absorption spectra in dichloromethane were measured in
the range 200–600 nm. The results are summarized in Table 7.
The main spectral features for the gold complexes are: (a) an in-
tense absorption at 230 nm due to phenyl rings [26]; (b) an absorp-
tion around 260–280 nm (a tail for mixture 2d–1d) also related
with the aromatic rings of the biisoquinoline, phosphine or penta-
fluorophenyl ligands; (c) a broad peak with intensity maxima in
the range 325–335 nm, which is constituted by one absorption re-
shine–gold dimers as [Au2(l-dcpm)2(ClO4)2] (dcpm = bis(dicyclo-
hexylphosphine)methane) [28]. Dinuclear gold(I) compounds
containing diphosphine and bipyridine ligand have been reported
to show intense luminescence coming from the gold-bipyridine
unit, where the large spin–orbit coupling of the Au 5d electrons
facilitates the emission [29].
Comparing for each compound the spectra in the solid state and
in solution, these are clearly different (Table 8). The typical red
shift on going from solution to the solid state, which is a common
effect in the emission spectra of gold(I) complexes due to intermo-
lecular Auꢂ ꢂ ꢂAu interactions, is not observed. In fact, the spectra in
CH2Cl2 solution are more complicated than in the solid state, with
emission maxima in the range 381–458 nm (or 546 nm consider-
ing low intensity emissions) at 298 K, whereas they are lumines-
cent at 77 K in the range 382–550 nm. The low temperature
lated to p–
p⁄ transitions in the biisoquinoline ligand, and a second
related tentatively to a charge transfer.
The emission and excitation spectra of the free ligand and the
gold complexes were determined in the solid-state and in CH2Cl2
solution, at 298 and 77 K. The results are summarized in Table 8
and the spectra of complex 2b are shown in Fig. 6. All the com-
pounds, including the free 1,10-biisoquinoline ligand, emit at 77
and 298 K in the solid state and in solution, with the only exception
of 1b in the solid state at 298 K; moreover, the mixture of 2d–1d

M. Bardají et al. / Inorganica Chimica Acta 392 (2012) 91–98
97
emission maxima are strongly blue (for biisoquinoline and 1b) or
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