Substituent effects on aurophilicity and π-π interaction in crystals of arylphosphine-Au(I) derivatives. Synthesis and X-ray structural studies of compounds (CX3C6H4)3P-Au-X and {(CF3)2C6H3}3P-Au-X

Article abstract of DOI:10.1016/S0020-1693(01)00543-6

Substituent effects on aurophilic interactions have been explored by single-crystal X-ray diffraction methods for a series of Au(I) complexes of monodentate phosphines, R′₃P-Au-X (X = Cl, Sph, and Spy). When a CF₃ substituent is introduced at a meta position of the phenyl ring in (C₆H₅)₃P, aurophilicity has been accrued in ClAuP(m-CF₃C₆H₄)₃. However, aurophilicity has been weakened by introducing two CF₃ groups at both meta positions. When a CF₃ substituent is substituted for a H atom in the para position or when a CH₃ substituent is introduced in the meta and/or para positions, such an effect has not been observed for R′₃PAuCl and R′₃PAuSph. Most dimers constructed by aurophilicity appear to be reinforced by π-π interactions between the phenyl ring of the Sph ligand or the pyridine ring of the Spy ligand and one of the phenyl rings in the R′₃P ligand. A novel ladder-like supra molecular architecture is created in the crystal of {3,5-(F₃C)₂C₆H₃}₃ PAuSph, and a tetramer is formed in the crystal of (C₆H₅)₃PAuSpy by aurophilic and π-π interactions. Substituent effects on important bond lengths have been discussed.

Full text of DOI:10.1016/S0020-1693(01)00543-6

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 322 (2001) 56–64
Substituent effects on aurophilicity and p–p interaction in crystals
of arylphosphine–Au(I) derivatives. Synthesis and X-ray structural
studies of compounds (CX3C6H4)3PꢀAuꢀX and
{(CF3)2C6H3}3PꢀAuꢀX
Keiko Nunokawa, Satoru Onaka *, Tsutomu Tatematsu, Mitsuhiro Ito, Jyun Sakai
Department of En6ironmental Technology, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku,
Nagoya 466-8555, Japan
Received 16 March 2001; accepted 25 June 2001
Abstract
Substituent effects on aurophilic interactions have been explored by single-crystal X-ray diffraction methods for a series of
Au(I) complexes of monodentate phosphines, R%PꢀAuꢀX (X=Cl, Sph, and Spy). When a CF3 substituent is introduced at a meta
3
position of the phenyl ring in (C6H5)3P, aurophilicity has been accrued in ClAuP(m-CF3C6H4)3. However, aurophilicity has been
weakened by introducing two CF3 groups at both meta positions. When a CF3 substituent is substituted for a H atom in the para
position or when a CH3 substituent is introduced in the meta and/or para positions, such an effect has not been observed for
R3%PAuCl and R%3PAuSph. Most dimers constructed by aurophilicity appear to be reinforced by p–p interactions between the
phenyl ring of the Sph ligand or the pyridine ring of the Spy ligand and one of the phenyl rings in the R%3P ligand. A novel
ladder-like supra molecular architecture is created in the crystal of {3,5-(F3C)2C6H3}3PAuSph, and a tetramer is formed in the
crystal of (C6H5)3PAuSpy by aurophilic and p–p interactions. Substituent effects on important bond lengths have been discussed.
© 2001 Elsevier Science B.V. All rights reserved.
Keywords: Aurophilicity; p–p Interactions; Arylphosphine–gold complexes; Crystal structures; Supramolecular structures
chloride. Literature surveys have shown that au-
rophilicity is manifested without replacement of Cl by
Sph for (AuCl)2(m-diphos) where m-diphos represents a
less bulky diphosphine ligand such as bis(diphenylphos-
phino)propane, bis(diphenylphosphino)hexane, and
bis(diphenylphosphino)octane [5,11], while aurophilic-
ity has not yet been reported for bulky diphosphine
complexes (AuCl)2(m-dppfe) and (AuSPh)2(m-dppfe)
(dppfe=1,1%-bis(diphenylphosphino)ferrocene)) [7,12].
1. Introduction
The use of aurophilicity is a burgeoning strategy for
constructing supramolecular structures in the solid state
[1–7]. Theoretical calculations by Pyykko¨ et al. have
suggested the importance of correlation and relativistic
effects for aurophilicity [8]. They have also pointed out
that aurophilicity is augmented by substituting SR% for
X in R3PꢀAuꢀX. We have observed that aurophilicity is
enhanced by this substitution for (AuꢀSPh)2(m-trans-
dpen) (trans-dpen=trans-1,2-bis(diphenylphosphino)-
ethylene) [7]. Schmidbaur et al. and we have also found
that aurophilicity is induced for Ph3PꢀAuꢀSPh [7,9,10]
when SPh is substituted for Cl in Ph3PꢀAuꢀCl; au-
rophilicity has not yet been reported in the parent
For R3PꢀAuꢀCl where PR3 represents
a simple
monodentate phosphine ligand, a first glance at the
literature has suggested to us that the appearance of
aurophilicity depends on the bulkiness of the R3P lig-
and because aurophilicity is induced by use of the less
bulky Me2PhP and 1,3,5-triaza-7-phosphaadamantane
ligands [13–15], while it is not induced for Ph3PꢀAuꢀCl
[16]. Schmidbaur and coworkers, however, have shown
recently that no Au···Au contact appears in the solid
* Corresponding author. Tel./Fax: +81-52-735 5160.
E-mail address: onklustr@ks.kyy.nitech.ac.jp (S. Onaka).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00543-6

K. Nunokawa et al. / Inorganica Chimica Acta 322 (2001) 56–64
57
state when the (Me2N)3P ligand less bulky than
Me2PhP is employed [17]. Continuing studies described
in previous papers from our laboratory have shown
that the substitution of S-4-py for SPh in
Ph3PꢀAuꢀSꢀAr type compounds induces a similar te-
tramer structure with the aid of aurophilic and p–p
interactions in solid states. These results strongly sug-
gested to us that the appearance of aurophilicity de-
pends on an intricate balance among the electronic and
steric effects of the R3P and/or SꢀAr ligands, and on
the crystal packing force. This idea has prompted us to
explore the electronic and steric effects of monodentate
phosphine ligands R3P and/or SR groups on au-
rophilicity systematically, because it is crucial to grasp
factors which govern the appearance of aurophilicity in
order to construct novel supra structures by use of
crystal engineering. The present paper reports the syn-
thesis and X-ray crystal structure analyses for a series
of (R3CC6H4)3PꢀAuꢀX and {3,5-(F3C)2C6H3}3PꢀAuꢀX
complexes (X=Cl, Sph, and Spy), together with the
results on Ph3PꢀAuꢀS-4-py.
ml) and MeOH (70 ml). The resulting pale yellow
solution was cooled with an ice-bath and a methanol
solution (20 ml) of b-thiodiglycol (3.7 g, 30 mmol) was
added with stirring. After the pale-yellow color disap-
peared, 4.2 g (9 mmol) of (m-F3CC6H4)3P in a mixed
solvent of CH2Cl2 (70 ml) and MeOH (50 ml) was
added and the mixture was stirred in an ice-bath
overnight. A 150 ml portion of MeOH was added and
the mixture was stirred for 1.5 h. Solvents were par-
tially distilled off at reduced pressure to precipitate a
white solid, and the solid was recrystallized from
CH2Cl2–hexane (1:1) two times to give pure needle-like
crystals. The product was vacuum-dried. Yield: 6.25 g
(99%). 31P NMR:
l
34.35. The yield of (p-
F3CC6H4)3PꢀAuꢀCl (2) is 85% (31P NMR: l 31.67) and
that of {3,5-(F3C)2C6H3}3PꢀAuꢀCl (3) is 98.6% (31P
NMR: l 35.67). Three crystal forms were observed for
3 after recrystallization and these crystals were sepa-
rated by use of a needle under a microscope. Methyl
analogues were similarly synthesized; yield of (p-
H3CC6H4)3PꢀAuꢀCl (4) is 52% (31P NMR: l 31.32).
2. Experimental
2.3. Synthesis of R3PꢀAuꢀSꢀAr complexes
2.1. General procedure
The synthesis of (m-F3CC6H4)3PꢀAuꢀSph (5) is de-
scribed below as a typical procedure; 340 mg (0.5
mmol) of 1 was dissolved in a mixed solvent of CH2Cl2
(30 ml) and acetone (25 ml) and to this was added a
methanol solution (30 ml) of PhSH (55 mg, 0.5 mmol)
and KOH (40 mg, 0.6 mmol). The mixture was stirred
at room temperature overnight. Solvent was distilled
off by use of a rotary evaporator to give white and
yellow solids. The yellow solid was extracted with
CH2Cl2 (a white solid was left after extraction) and was
recrystallized from CH2Cl2–hexane to afford pale yel-
low plate-like crystals. Yield: 340 mg, 90%. Anal.
Found: C, 41.82; H, 2.23. Calc. for C27H17AuF9PS: C,
41.98; H, 2.22%. Yellow needle-like crystals of (p-
F3CC6H4)3PꢀAuꢀSph (6) were obtained in 74% yield
similarly. Anal. Found: C, 41.81; H, 2.14. Calc. for
C27H17AuF9PS: C, 41.98; H, 2.22%. The mercapto-pyri-
dine analogue, (m-F3CC6H4)3PꢀAu-4-Sꢀpy (7) (pale
yellow) was obtained in 94% yield. Anal. Found: C,
39.43; H, 2.06. Calc. for C26H16AuF9NPS: C, 40.38; H,
2.09%. Pale-yellow prismatic crystals of {3,5-
(F3C)2C6H3}3PꢀAuꢀSph (8) were obtained in 6% yield
in a form of pure crystals. Anal. Found: C, 36.95; H,
1.41. Calc. for C30H14AuF18PS: C, 36.90; H, 1.45%. The
low yield of 8 is due to instability in ordinary organic
solvents. Ph3PꢀAu-4-Spy (9) (pale yellow) was obtained
in 43% yield. Anal. Found: C, 48.35; H, 3.44. Calc. for
C23H19AuNPS: C, 48.52; H, 3.36%. 31P NMR: l 39.76
(5), 36.18 (6), 38.95 (7), 39.48 (9); instability of 8 in
ordinary organic solvents made it impossible to obtain
31P NMR data.
Syntheses were made under a purified nitrogen or
argon atmosphere using Schlenk and vacuum line tech-
niques. Solvents were dried by standard methods and
distilled under nitrogen. HAuCl4·4H2O was purchased
from Tanaka Precious Metals Co. 4-Mercapto-pyridine
was purchased from Aldrich. (m-H3CC6H4)3P, and (p-
H3CC6H4)3P from Strem Chemicals Inc. (m-
F3CC6H4)3P, (p-F3CC6H4)3P, and {3,5-(F3C)2C6H3}3P
were synthesized by the Grignard method from the
corresponding bromides in THF. (m-F3CC6H4)3P was
purified by distillation at reduced pressure in 67% yield
and the para analogue was purified by recrystallization
from CH2Cl2–hexane in 25% yield. The bis-substituted
phosphine was purified by recrystallization from
CH2Cl2–hexane in 70% yield.
31P{1H} NMR spectra were recorded at 80.984 MHz
on a Varian XL-200 spectrometer at room temperature.
31P{1H} NMR chemical shifts are referenced to external
85% H3PO4.
2.2. Synthesis of R3PꢀAuꢀCl complexes
The synthesis of (m-F3CC6H4)3PꢀAuꢀCl (1) de-
scribed below as a typical procedure was generally
adopted for all other R3PꢀAuꢀCl compounds. The
reaction vessel was covered with black cloth to shield
from room light. To a 500 ml three necked round-bot-
tom flask, 3.7 g (9 mmol) of HAuCl4·4H2O was added
and this was dissolved in a mixed solvent of H2O (15

58
K. Nunokawa et al. / Inorganica Chimica Acta 322 (2001) 56–64
given in Table 1. The structures of these crystals were
2.4. X-ray crystallography
solved by direct methods using SIR92, DIRDIF and/or
SHELXS86 in a CRYSTAN-GM program package and
refined with anisotropic thermal parameters by full-ma-
trix least-squares programs in a CRYSTAL-GM and/or a
CRYSTAN program package provided by MAC Science
except for 5 and 8. The structure of 5 was solved by
SHELXS97 and refined by use of the CRYSTAN program.
The F atoms of 8 were refined with isotropic thermal
parameters because of the paucity of reflection data. An
analytical absorption correction was applied at the final
stage of all refinements [18]. The final R and Rw values
are given in Table 1. The structure of 2 was solved with
a severely disordered CH2Cl2 molecule. The molecular
structure of 4 was previously solved in space group
P21/c by Cookson et al. The crystal which they used for
data collection was grown from a chloroform solution
[19], and presumably the change of solvents for recrys-
tallization is responsible for the different space groups
of the crystals. The molecular structure of 7 was refined
with a severely disordered CH2Cl2 molecule. Tables for
atomic coordinates, thermal parameters, and bond
lengths and angles are available as supplementary mate-
rial. Selected bond lengths and bond angles are tabu-
lated in Table 2.
Crystals suitable for X-ray studies were obtained by
recrystallization from CH2Cl2–hexane and/or benzene–
hexane. For 3, three differently shaped crystals were
precipitated upon recrystallization at one time. These
crystals were separated by use of a needle under a
microscope and subjected to a Laue group determina-
tion. Brilliant-cut shaped crystals (3a) belong to a mon-
oclinic Laue group, hexagon-shaped crystals (3b)
belong to a triclinic Laue group, and distorted pentago-
nal-plate crystals (3c) to a monoclinic Laue group. A
Bravais lattice exchange program was applied to these
crystals, but these three crystal systems were not
interchangeable.
Selected crystals were glued to the top of a fine glass
rod. Accurate cell dimensions were obtained by least-
squares refinements of 20–25 reflections on a MAC
MXC3 diffractometer with graphite-monochromated
Mo Ka radiation. The reflection data were collected at
room temperature for 1, 2, 6, 7, and 8, and those for
3–5, and 9 at −100 °C by use of an Oxford
cryostream cooler. Complete crystallographic data are
3. Results and discussion
3.1. Molecular structure
The molecular structures of 3a, 7, and 9 were solved
and refined as dimers, while that of 8 was solved and
refined for two independent molecules. Although the
structure of 1 was solved as a single molecule, the
ORTEP drawing of 1 shows a dimer to exhibit a weak
Au···Au interaction in Fig. 1. The dimer structure of 3a
is shown in Fig. 2; molecular structures and crystal data
(
of 3b (P1) and 3c (C2/c) will be published elsewhere.
Fig. 1. The ORTEP drawing of Au{(m-F3CC6H4)3P}Cl (1) as a dimer.
F atoms are omitted for clarity.
The molecular structures of R3PꢀAuꢀSꢀAr type com-
pounds, 5 and 7–9, are depicted in Figs. 3–6. An
ORTEP drawing of 8 is made for molecule 1 in Fig. 5 as
a dimer to exhibit the Au···Au interaction; another
Au···Au interaction is formed between two molecules of
2. Most positions of the F atoms for molecules which
have CF3 substituent(s) are disordered.
,
The Au···Au distance in 1 is 3.0738(9) A, which is
,
shorter than that of Ph3PꢀAuꢀSph (10) (3.145(2) A)
suggesting that aurophilicity in 1 is stronger than in 10
,
[7,9]. The Au···Au separation in 2 is 5.584(1) A, which
suggests no Au···Au interaction. The Au···Au distance
,
in 3a is 3.341(1) A, which is close to the upper limit of
the aurophilicity range [8]. This observation indicates
that further introduction of rather bulky CF3 groups to
another meta position is apparently detrimental to the
formation of aurophilic bonding. When the Cl atom in
Fig. 2. The ORTEP drawing of Au[{3,5-(F3C)C6H4}3P]Cl (3a) as a
dimer. F atoms are omitted for clarity.

Table 1
Crystallographic data and structure refinement parameters for compounds 1–9
AuCl-
AuCl-
(2)
AuCl-
(3a)
AuCl-
Au(Sph)-
Au(Sph)-
Au(Spy)-
Au(Sph)-
Au(Spy)-
{P(m-CF3C6H4)3} {P(p-CF3C6H4)3} [P{3,5-(CF3)2C6H3}3] {P(p-CH3C6H4)3} {P(m-CF3C6H4)3} {P(p-CF3C6H4)3} {P(m-CF3C6H4)3} [P{3,5-(CF3)2C6H3}3] {P(C6H5)3}
(1)
Empirical formula C21H12AuClF9P C21H12AuClF9P C24H9AuClF18
(4)
(5)
(6)
(7)
(8)
(9)
P
C21H21AuClP
C27H17AuF9PS
C27H17AuF9PS C26H16AuF9NPS.CC30H14AuF18PS
H2Cl2
C23H19AuNPS
Formula weight
Temperature (K) 298
698.7
698.7
298
902.7
173.2
536.8
173.2
772.4
173.2
698.7
298
818.3
298
976.4
298
569.45
173.2
Crystal system
Space group
Unit cell dimensions
monoclinic
C2/c
triclinic
monoclinic
P21/n
triclinic
monoclinic
A2/a
triclinic
monoclinic
P21/n
monoclinic
C2/c
triclinic
(
(
(
(
P1
P1
P1
P1
,
a (A)
22.573(9)
9.582(4)
22.170(9)
90
93.55(3)
90
4786(3)
8
1.94
11.835(3)
12.804(3)
9.982(2)
107.31(2)
107.11(2)
99.61(2)
1325.5(6)
2
23.624(6)
17.041(5)
13.817(4)
90
95.23(2)
90
5539(3)
8
2.17
10.715(4)
11.413(4)
10.298(3)
116.66(2)
112.83(2)
63.61(2)
979.7(5)
2
24.77(2)
10.196(5)
22.73(2)
90
106.72(7)
90
5496(7)
8
1.87
10.417(2)
14.158(2)
9.951(3)
98.41(2)
93.45(2)
108.88(1)
1364.6(4)
2
33.679(8)
13.887(4)
12.559(4)
90
98.40(3)
90
5822(4)
8
1.87
33.695(7)
15.128(8)
30.734(6)
90
120.83(1)
90
13453(8)
16
1.93
11.556(3)
16.370(4)
10.872(2)
91.40(2)
96.22(2)
96.08(2)
2031.6(7)
4
,
b (A)
/
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (g cm−3
Crystal
)
1.75
1.82
1.88
1.86
0.80×0.50×0.30 0.60×0.30×0.25 0.80×0.70×0.65
0.80×0.70×0.60 0.80×0.45×0.35 0.65×0.45×0.30 0.80×0.70×0.50 0.80×0.65×0.30
0.55×0.45×0.20
dimensions
(mm)
322
v (Mo Ka)
66.02
59.6
58.00
79.57
56.0
57.75
54.0
47.5
76.37
(
(cm−1
)
Scan type
Scan range
Scan speed
2q–ꢀ
2q–ꢀ
2q–ꢀ
2q–ꢀ
2q–ꢀ
2q–ꢀ
2q–ꢀ
2q–ꢀ
2q–ꢀ
1.45+0.35 tan q
6.0
6
1.35+0.35 tan q 1.30+0.35 tan q 1.15+0.35 tan q
6.0
1.07+0.35 tan q 1.15+0.35 tan q 1.15+0.35 tan q 1.20+0.35 tan q 1.10+0.35 tan q
7.0
4
6.0
7.0
6.0
6.0
6.0
7.0
(° min−1
2qmax (°)
)
50.0
55.0
45.0
55.0
50.0
52.0
45.0
45.0
45.0
Unique reflections 5496
Reflections with 3958 (n=3)
ꢀFoꢀ\n|(ꢀFoꢀ)
6079
4067 (n=3)
7263
5200 (n=3)
4881
4069 (n=3)
4856
3423 (n=3)
6074
4380 (n=3
7600
4907 (n=4)
8800
5314 (n=3)
5707
4821 (n=3)
Number of
parameters
R (Rw)
304
376
884
223
430
376
799
809
493
0.075 (0.113)
0.071 (0.063)
0.098 (0.13)
0.062 (0.084)
0.11 (0.167)
0.0592 (0.048) 0.090 (0.090)
0.103(0.114)
0.038(0.043)
2
2 1/2
Mo Ka radiation (u=0.71073 A); R=ꢁꢀꢀFoꢀ−ꢀFcꢀꢀ/ꢀFoꢀ; Rw=[ꢁ(ꢀFoꢀ−ꢀFcꢀ) /ꢁw(Fo) ] where w=1/|2(F).
,

Table 2
Selected bond lengths and bond angles
Compound
AuCl-
{P(m-CF3C6H4)3}
(1)
AuCl-
[P{p-CF3C6H4)3}3]
(2)
AuCl-
AuCl-
{P(p-CH3C6H4)3}
(4)
Au(Sph)-
{P(m-CF3C6H4)3}
(5)
Au(Sph)-
{P(p-CF3C6H4)3}
(6)
Au(Spy)-
{P(m-CF3C6H4)3} (7)
Au(Sph)-
[P{3,5-(CF3)2C6H3}3] (8)
Au(Spy)-
{P(C6H5)3} (9)
{P(3,5-(CF3)2C6H3} (3a)
Molecule 1
Molecule 2
Molecule 1
Molecule 2
Molecule 1
Molecule 2
Molecule 1
Molecule 2
2.271(3)
,
Bond length (A)
Au···Au
AuꢀP
AuꢀCl
AuꢀS
/
3.0738(9)
2.228(3)
2.294(3)
3.341(1)
2.215(6)
2.274(7)
3.028(2)
2.28(1)
3.236(1)
2.256(7)
3.403(3)
2.25(1)
3.325(3)
2.232(8)
3.1906(5)
2.265(3)
2.231(4)
2.277(5)
2.216(6)
2.284(6)
2.228(2)
2.282(2)
2.250(2)
2.258(7)
2.30(1)
1.71(7)
1.77(2)
1.78(6)
1.81(2)
2.301(2)
1.78(1)
1.81(1)
1.82(1)
1.83(1)
2.307(7)
1.73(3)
1.82(2)
1.82(2)
1.83(2)
2.297(7)
1.73(3)
1.82(2)
1.82(2)
1.88(2)
2.29(1)
1.83(3)
1.81(4)
1.83(4)
1.86(3)
2.303(8)
1.74(5)
1.82(3)
1.85(5)
1.88(3)
2.307(3)
1.76(1)
1.81(1)
1.81(1)
1.81(1)
2.318(3)
1.77(1)
1.829(9)
1.82(1)
1.81(1)
SꢀC
PꢀC
1.82(1)
1.82(1)
1.83(1)
1.82(1)
1.82(1)
1.82(1)
1.82(2)
1.85(2)
1.88(2)
1.77(3)
1.79(3)
1.84(2)
1.80(1)
1.81(1)
1.813(9)
Bond angle (°)
AuꢀAuꢀCl
AuꢀAuꢀP
AuꢀAuꢀS
PꢀAuꢀCl
PꢀAuꢀS
80.46(7)
102.88(7)
77.65(2)
105.88(2)
76.32(2)
108.37(2)
104.8(2)
76.3(2)
111.2(2)
72.2(2)
113.6(2)
71.7(2)
109.8(2)
73.8(2)
113.1(3)
70.1(3)
104.68(6)
75.09(6)
102.13(6)
74.22(6)
322
175.9(1)
178.0(1)
173.9(2)
175.0(2)
177.3(1)
)
177.6(2)
110(1)
112(2)
113.4(9)
113(1)
169.6(1)
106.4(3)
109.7(3)
111.9(3)
119.4(3)
175.8(2)
109(1)
115.7(8)
110.5(9)
115.4(9)
174.7(2)
110(1)
116.2(8)
112.5(8)
110.2(8)
176.4(3)
108(1)
118(1)
115(1)
114(1)
176.2(3)
111(1)
116(1)
118(1)
115(1)
178.6(1)
108.0(4)
113.3(4)
112.5(4)
106.7(5)
174.7(1)
108.3(4)
111.7(3)
111.5(3)
116.4(3)
AuꢀSꢀC
AuꢀPꢀC
111.8(4)
112.2(4)
114.5(4)
111.3(5)
112.4(4)
114.9(5)
111.0(8)
114.6(7)
117.2(9)
109.9(8)
112.1(9)
116.1(9)
114.4(4)
111.8(2)
112.3(2)
5
6

K. Nunokawa et al. / Inorganica Chimica Acta 322 (2001) 56–64
61
1 is substituted by a Sph group, the Au···Au distance
,
(3.028(2) A) is slightly shortened in 5. However, such a
substitution does not induce an aurophilicity in 6; the
,
Au···Au separation is 4.092(1) A. The Au···Au length in
,
7 is 3.236(1) A, and therefore elongated upon substitu-
tion of an S-pyridyl group for Cl in 1. This result is
rather contradictory to the theoretical prediction that
aurophilicity should be augmented by introducing a SR
group in XꢀAuꢀPR3 [8]. When the Cl atom in 3 is
replaced by a Sph group, the Au···Au interaction is
,
preserved in 8; the Au···Au lengths are 3.325(3) A
,
(Au2···Au2) and 3.403(3) A (Au1···Au1). Two Au···Au
distances in the crystal of 8 are close to that of the Cl
analogue 3a. As there are two independent Au···Au
interactions in the crystal of 8, that is, one is longer and
the other is shorter than that of 3a, a heuristic discus-
sion on the substitution effect of the Sph group on the
Au···Au interaction is impossible. The Au···Au distance
Fig. 3. The ORTEP drawing of Au{(m-F3CC6H4)3P}(Sph) (5) as a
dimer. F atoms are omitted for clarity.
,
in 9 is 3.1906(5) A, which is slightly longer than that of
,
10 (3.145(3) A). From the comparison of the Au···Au
distances for 5 and 7 and 9 and 10, it is concluded that
the Sph group reinforces the Au···Au interaction more
effectively than the Spy group (4-mercaptopyridine).
The most interesting result for a given series of
R%PꢀAuꢀX compounds is that the aurophilic contact
3
has been shortened by introducing CF3 substituent(s) in
the meta position(s) in the (C6H5)3P ligand; a CH3
substituent in the meta position has not been reported
to have such an effect [20]. When a CF3 substituent is
introduced in the para position (2), however, no such
effect is detected.
Another interesting observation is that aurophilic
contacts are not made upon replacement of Cl by Sph
and/or Spy when the parent R%3PAuCl does not exhibit
aurophilic contact in the crystal. The result clearly is in
contrast to the case of Ph3PAuCl [7]. In Section 1, we
have pointed out that aurophilicity is easily induced for
Au(I) chlorides with a less bulky diphosphine ligand,
while for Au(I) chlorides with a bulky diphosphine such
as dppfe this is not the case. When (m-F3CC6H4)3P is
compared with (p-F3CC6H4)3P, (m-H3CC6H4)3P, and
Fig. 4. The ORTEP drawing of Au{(m-F3CC6H4)3P}(Spy) (7) as a
dimer. F atoms are omitted for clarity.
Fig. 5. The ORTEP drawing of Au[{3,5-(F3C)C6H4}3P](Sph) (8) as a
dimer. F atoms are omitted for clarity.
Fig. 6. The ORTEP drawing of Au{(C6H5)3P}(Spy) (9) as a dimer.

62
K. Nunokawa et al. / Inorganica Chimica Acta 322 (2001) 56–64
(p-H3CC6H4)3P, the former ligand is more bulky than
the latter [21]. The AuꢀP bond lengths for 1, 2, 4, and
tion are formed among Sph and two m-F3CC6H4
groups (two pairs of interaction between rings C1–C6
and C21–C26 and an interaction between two rings
C31–C36). Approximately 1/6 of the area of the phenyl
rings C31–C36 overlap with each other in the crystal,
and the closest atom-to-atom distance between two
(m-H3CC6H4)3PAuCl are 2.228(3), 2.231(4), 2.228(2),
1
,
and 2.235(2) A, respectively [20]. The electronic effect
of the substituent on the Au(I) center for 1, 2, and 4
seems to be quite small as shown below. We surmise
that the advent of aurophilicity depends on the intricate
balance among many factors such as packing force,
steric demand, and complementary weak interactions
such as p–p interactions between aromatic rings as
pointed out in Section 3.2, although Pyykko¨ et al. have
suggested that the steric effect of the ligands is the most
important [8].
,
planes is 3.7(1) A. The phenyl ring of the Sph group is
approximately parallel with the phenyl ring C21–C26
,
(the closest atom-to-atom distance being 3.66(3) A).
The pyridine ring in each 4-pyꢀSꢀAuꢀP(m-F3CC6H4)3
moiety of 7 is parallel to one of the phenyl rings of
(m-F3CC6H4)3P in another pair of molecules. Especially
the angle between the C1N1 pyridine and the C41–C46
phenyl rings is only 14.0°. In addition the closest atom-
to-plane contact between the former pair of rings is
The AuꢀP distances for R3PꢀAuꢀCl (1, 2 and 4) are
1
,
in the range 2.228–2.231 A [19]. As described above, 3
affords three different crystals; 3a belongs to space
group P21/n, 3b to P1, and 3c to C2/c. The molecular
structures of these three crystals are quite similar, and
the geometrical parameters are also quite similar except
for the AuꢀP bond lengths; 3a has the shortest AuꢀP
,
3.290 A (C43 to the C1N1 pyridyl ring), suggesting a
p–p interaction between these rings. As is seen in Fig.
5 for 8, the phenyl ring of the Sph group (C1–C6)
overlaps with the phenyl ring (C13–C18) in the {3,5-
(F3C)2C6H3}3P ligand, and two p–p overlaps are
formed for molecule 1. Similar p–p interactions are
formed between the phenyl ring of the Sph group
(C7–C12) and the phenyl ring (C51–C56) in the {3,5-
(F3C)2C6H3}3P ligand at two places for molecule 2.
Thus aurophilicity is supported by p–p interactions in
each pair of dimers. The C1N1 pyridine ring in 9
overlaps with the C31–C36 phenyl ring. The angle
between these two rings is 10.24° and the closest atom-
,
bond lengths (2.215(6)–2.216(6) A), while that for 3b is
,
,
2.231(4) A and that for 3c is 2.222(4) A. The AuꢀP
distances for R3PꢀAuꢀSꢀR% are in the range 2.250–
,
2.281 A; substitution of SꢀR% for Cl protracts the AuꢀP
distance. Substituent effects on AuꢀP distances are
investigated by comparing the CF3 and CH3 deriva-
tives; the AuꢀP distance of 1 is slightly shorter than
that of the methyl analogue [20], while that of 2 is
slightly longer than that of the methyl analogue 4 [19].1
An electron-withdrawing group at the para-position is
expected to make the AuꢀP bond shorter. This expecta-
,
to-plane contact is 3.417 A (C35 to the pyridyl ring),
which is shorter than that of 10 (3.438 A). These results
,
suggest that there exists a p–p overlap between these
two planes. Thus the dimer structure of 9 (Fig. 6) is
quite similar to that of the phenyl analogue 10 [7]. It is
quite interesting to point out that most compounds
which exhibit aurophilicity have p–p stack(s) in the
dimer structure except 3a. We surmise that complemen-
tary p–p interaction(s) should be important to induce
aurophilicity for Au(I) derivatives with a simple
monodentate phosphine ligand.
,
tion is most explicitly demonstrated in 6 (2.250(2) A)
,
compared to the meta-analogue 5 (2.281(7) A). The
effect of the SꢀAr group on the AuꢀP bond length is
evaluated by comparing the observed AuꢀP bond
lengths for 5 and 7 and for 9 and 10; for the former
pair, the length is shortened from 2.279(8) to 2.256–
,
2.258(7) A by substituting 4-Sꢀpy for 4-SꢀPh, and a
similar trend is observed for the latter pair (as an
,
average from 2.2725 to 2.268 A).
Among these nine derivatives, only 8 and 9 afford
supra structures. As is shown in Fig. 7, a novel supra
structure of an infinite ladder-like architecture is
formed in the crystal of 8 along the b-axis; two
longsides are composed of two columns of p–p stacks
with the sequence of Sph:{3,5-(F3C)2C6H3}:Sph:{3,5-
(F3C)2C6H3} and each step is constructed by au-
rophilicity between Au2 and Au2*. This supra structure
is reinforced by another aurophilicity between Au1 and
Au1* which passes the bc plane perpendicularly. Fig. 8
exhibits a tetrameric structure for 9 in the crystal; two
dimers constructed by aurophilicity described in Section
3.1 are connected by p–p stacks between Spy (C1–
C5N1) and one of the phenyl rings in PPh3 (C11–C16).
This tetrameric structure is quite similar to that of the
Sph analogue (10) [7].
3.2. Crystal structure
Calculations on intermolecular distances were carried
out and ORTEP drawings of the crystal packing for 1–9
were examined. In the dimer of 1, two phenyl rings
(C21–C26) are almost parallel and in close proximity
,
(the closest atom-to-atom contact is 3.36(3) A), suggest-
ing a p–p interaction (Fig. 1). No such p–p interaction
has been detected for 3a. An ORTEP drawing for a pair
of 5 (Fig. 3) indicates that three pairs of p–p interac-
1
,
,
The AuꢀP length (2.228(2) A) and AuꢀCl length (2.282(2) A)
obtained in this work are longer than those (AuꢀP=2.201(3) and
,
,
2.208(3) A and AuꢀCl=2.255(3) and 2.256(3) A) reported by Cook-
son and Tiekink [19].

K. Nunokawa et al. / Inorganica Chimica Acta 322 (2001) 56–64
63
Fig. 9. Correlations between 31P NMR chemical shift and AuꢀP bond
length. Numbers in the graph show the compound in the text. (ꢀ)
chlorides, (ꢁ) thiophenol, (ꢂ) mercaptopyridine. No 11 denotes
Ph3PꢀAuꢀCl.2
Fig. 7. The projection of the crystal structure of Au[{3,5-
(F3C)2C6H3}3P](Sph) (8) along the a-axis. Two phenyl rings of the
phosphine ligand for molecule 1 and two phenyl rings of the phos-
phine ligand and the phenyl ring of the Sph ligand for molecule 2 are
omitted for clarity in addition to F atoms. Hatched rings are under
p–p interactions.
chemical shifts versus AuꢀP bond lengths. A good
correlation is seen for Sph and Spy derivatives, while
an inverse correlation is revealed for chlorides; the
AuꢀP bond length for 3 is taken as an average for
three different phases described in Section 3.1, as the
NMR data are taken from solutions. The inverse cor-
relation for chlorides indicates that the CX3 sub-
stituent in phenyl rings have a more pronounced effect
on the 31P NMR chemical shift than on the AuꢀP
bond length, because the CX3 groups are remote from
the Au center. Sph and Spy ligands clearly make the
AuꢀP bond longer and shift the 31P-resonance to a
lower field. The Sph and Spy anions, which are better
s-electron donors than Cl− are directly coordinated to
the Au center. Thus the substituent effect is clearly
reflected on both AuꢀP bond lengths and 31P NMR
chemical shifts.
Fig. 8. Tetrameric structure of Au{(C6H5)3P}(Spy) (9) as a projection
along the b-axis.
4. Supplementary material
Tables of atomic coordinates, thermal parameters,
and bond lengths and bond angles are available from
the authors upon request.
3.3. The effect of CX3, Sph, and Spy group on the 31P
NMR
31P NMR data described in Sections 2.2 and 2.3
indicate that the position and the kind of CX3 sub-
stituent have a significant effect on the 31P NMR
chemical shifts. Fig. 9 shows the plot of 31P NMR
Acknowledgements
This research was funded by Grants-in-Aid for Sci-
entific research on Priority Areas (Nos. 11136218 and
12023221 ‘Metal-assembled Complexes’) from the
Ministry of Education, Science, Sports, and Culture,
Japan.
2 P NMR chemical shift (l 33.5) is obtained in this laboratory and
r(AuꢀP) is taken from Ref. [22].

64
K. Nunokawa et al. / Inorganica Chimica Acta 322 (2001) 56–64
J.A.K. Bauer, A.E. Bruce, M.R.M. Bruce, J. Am. Chem. Soc.
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