Unsymmetrical Coordination of Bipyridine in Three-Coordinate Gold(I) Complexes

Article abstract of DOI:10.1021/acs.inorgchem.0c00138

The unsymmetrical coordination of gold(I) by 2,2′-bipyridine (bipy) in some planar, three-coordinate cations has been examined by crystallographic and computational studies. The salts [(Ph₃P)Au(bipy)]XF₆ (X = P, As, Sb) form an isomorphic series in which the differences in Au-N distances range from 0.241(2) to 0.146(2) ?. A second polymorph of [(Ph₃P)Au(bipy)]AsF₆ has also been found. Both polymorphs exhibit similar structures. The salts [(Et₃P)Au(bipy)]XF₆ (X = P, As, Sb) form a second isostructural series. In this series the unsymmetrical coordination of the bipy ligand is maintained, but the gold ions are disordered over two unequally populated positions that produce very similar overall structures for the cations. Although many planar, three-coordinate gold(I) complexes are strongly luminescent, the salts [(R₃P)Au(bipy)]XF₆ (R = Ph or Et; X = P, As, Sb) are not luminescent as solids or in solution. Computational studies revealed that a fully symmetrical structure for [(Et₃P)Au(bipy)]⁺ is 7 kJ/mol higher in energy than the observed unsymmetrical structure and is best described as a transition state between the two limiting unsymmetrical geometries. The Au-N bonding has been examined by natural resonance theory (NRT) calculations using the 12 electron rule . The dominant Lewis structure is one with five lone pairs on Au and one bond to the P atom, which results in a saturated (12 electron) gold center and thereby inhibits the formation of any classical, 2 e^- bonds between the gold and either of the bipy nitrogen atoms. The nitrogen atoms may instead donate a lone pair into an empty Au-P antibonding orbital, resulting in a three-center, four-electron (3c/4e) P-Au-N bond. The binuclear complex, [μ₂-bipy(AuPPh₃)₂](PF₆)₂, has also been prepared and shown to have an aurophillic interaction between the two gold ions, which are separated by 3.0747(3) ?. Despite the aurophillic interaction, this binuclear complex is not luminescent.

Full text of DOI:10.1021/acs.inorgchem.0c00138

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Article
Unsymmetrical Coordination of Bipyridine in Three-Coordinate
Gold(I) Complexes
Lucy M. C. Luong, Michael M. Aristov, Alexandria V. Adams, Daniel T. Walters, John F. Berry,*
Marilyn M. Olmstead,* and Alan L. Balch*
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ABSTRACT: The unsymmetrical coordination of gold(I) by 2,2′-
bipyridine (bipy) in some planar, three-coordinate cations has been
examined by crystallographic and computational studies. The salts
[(Ph3P)Au(bipy)]XF6 (X = P, As, Sb) form an isomorphic series in
which the differences in Au−N distances range from 0.241(2) to 0.146(2)
Å. A second polymorph of [(Ph3P)Au(bipy)]AsF6 has also been found.
Both polymorphs exhibit similar structures. The salts [(Et3P)Au(bipy)]XF6
(X = P, As, Sb) form a second isostructural series. In this series the
unsymmetrical coordination of the bipy ligand is maintained, but the gold
ions are disordered over two unequally populated positions that produce
very similar overall structures for the cations. Although many planar, three-
coordinate gold(I) complexes are strongly luminescent, the salts [(R3P)-
Au(bipy)]XF6 (R = Ph or Et; X = P, As, Sb) are not luminescent as solids or in solution. Computational studies revealed that a fully
symmetrical structure for [(Et3P)Au(bipy)]+ is 7 kJ/mol higher in energy than the observed unsymmetrical structure and is best
described as a transition state between the two limiting unsymmetrical geometries. The Au−N bonding has been examined by
natural resonance theory (NRT) calculations using the “12 electron rule”. The dominant Lewis structure is one with five lone pairs
on Au and one bond to the P atom, which results in a saturated (12 electron) gold center and thereby inhibits the formation of any
classical, 2 e− bonds between the gold and either of the bipy nitrogen atoms. The nitrogen atoms may instead donate a lone pair into
an empty Au−P antibonding orbital, resulting in a three-center, four-electron (3c/4e) P−Au−N bond. The binuclear complex, [μ2-
bipy(AuPPh3)2](PF6)2, has also been prepared and shown to have an aurophillic interaction between the two gold ions, which are
separated by 3.0747(3) Å. Despite the aurophillic interaction, this binuclear complex is not luminescent.
molecules such as AuX(PR3)2 (X = halide). For the
symmetrical ions, [Au(PR3)3]+, the excitation involves transfer
INTRODUCTION
■
The coordination chemistry of gold is currently of interest due
to the luminescent behavior1−3 and catalytic activity4−6 of
these complexes. Complexes of gold(I) generally have
coordination numbers of two, three, or four.7,8 The properties
and reactivities of these complexes are intimately connected
with their coordination geometry. Linear, two-coordinate
gold(I) complexes are usually colorless and are frequently
nonluminescent in the absence of aurophilic interactions.9
Such two-coordinate complexes can become luminescent
through aggregation that results from the formation of
aurophillic interactions that induce close Au···Au contacts.
For example, the two-coordinate gold(I) salts
[(C6H11NC)2Au](PF6) and [(C6H11NC)2Au](AsF6) are
colorless, monomeric, and nonluminescent in solution, but
upon crystallization they form two luminescent polymorphs
with extended Au···Au interactions between cations, e.g.,
colorless, blue emitting crystals or yellow, green-emitting
crystals.10,11 Planar, three-coordinate gold complexes are
frequently luminescent as monomeric units.12−20 Examples
include cations of the type [Au(PR3)3]+ as well as neutral
2
2
of an electron from the degenerate filled dxy and dx −y orbitals
to the empty pz orbital where the z axis is perpendicular to the
plane of the AuP3 unit, while the emission involes the reverse
process. Four-coordinate gold complexes are only infrequently
luminescent.21,22
The report of the structure of the planar, three-coordinate
complex [(Ph3P)Au(bipy)]PF6 (bipy = 2,2′-bipyridine)
attracted our attention due to the unusual unsymmetrical
bonding of the bipy ligand with two different Au−N distances
of 2.166(2) and 2.407(2) Å.23 We wondered whether this
compound was luminescent like other planar, three-coordinate
gold(I) complexes and how the unsymmetrical bonding of the
bipy ligand would change if the anion was exchanged or if an
Received: January 14, 2020
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© XXXX American Chemical Society
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Table 1a. Crystal Data for Gold(I) Complexes
c
[(Ph3P)Au(bipy)]PF6
[(Ph3P)Au(bipy)]AsF6
[(Ph3P)Au(bipy)]AsF6 polymorph
[(Ph3P)Au(bipy)]SbF6
color/habit
chemical formula
formula weight
crystal system
space group
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
−
colorless block
C28H23AsAuF6N2P
804.34
triclinic
P1
11.1600(12)
11.2768(12)
11.7071(12)
80.8994(13)
71.9436(13)
72.4764(13)
1332.3(2)
2
colorless needle
C28H23AsAuF6N2P
804.34
monoclinic
P21/c
13.4585(14)
8.4500(9)
23.695(2)
90
95.137(2)
90
colorless block
C28H23AuF6N2PSb
851.17
triclinic
P1
11.343(2)
11.400(2)
11.602(2)
80.994(3)
71.913(3)
72.266(2)
1355.2(5)
2
C28H23AuF6N2P2
676.448
triclinic
P1
11.025(1)
11.248(1)
12.045(2)
81.63(1)
71.98(1)
72.57(1)
1352.9
2
γ (deg)
V (Å3)
Z
2683.8(5)
4
T (K)
295
90(2)
90(2)
90(2)
λ (Å)
0.71069
1.867
5.971
0.0649
0.0771
0.71073
2.005
6.877
0.0152
0.71073
1.991
6.828
0.0199
0.0246
0.71073
2.086
6.525
0.0173
0.0411
ρ (g/cm3)
μ (mm−1
R1 (obsd. data)
wR2 (all data, F2 refinement)
)
a
b
0.0389
a
b
c
2
2
R1 = (Σ||F0| − |Fc||)/Σ|F0| wR2 = ((Σ[w(F0 − Fc2)2])/Σ[w(F0 )2])1/2 Data from ref 23 [Clegg, W. 2,2′-Bipyridyltriphenylphoshine gold(I)
hexafluorophosphate. Acta Cryst. 1976, B32, 2712−2714].
Table 1b. Crystal Data for Gold(I) Complexes
[(Et3P)Au(bipy)]PF6
[(Et3P)Au(bipy)]AsF6
[(Et3P)Au(bipy)]SbF6
[(Ph3PAu)2(μ2-bipy)](PF6)2·2CH2Cl2
color/habit
chemical formula
formula weight
crystal system
space group
a (Å)
b (Å)
c (Å)
α (deg)
colorless block
C16H23AuF6N2P2
616.27
monoclinic
P21/c
14.252(2)
11.2596(19)
13.194(2)
90
colorless block
C16H23AsAuF6N2P
660.22
monoclinic
P21/c
14.3654(19)
11.3778(15)
13.2359(17)
90
colorless block
C16H23AuF6N2PSb
707.05
monoclinic
P21/c
14.5192(14)
11.5278(11)
13.2637(13)
90
colorless plate
C18H42Au2Cl4F12N2P4
1534.45
monoclinic
P21/n
10.9702(4)
31.9777(11)
15.0259(6)
90
β (deg)
γ (deg)
V (Å3)
109.544(2)
90
1995.3(6)
4
109.4450(17)
90
2040.0(5)
4
109.6951(11)
90
2090.1(4)
4
92.0660(10)
90
5267.7(3)
4
Z
T (K)
100(2)
100(2)
100(2)
100(2)
λ (Å)
0.71073
2.051
7.591
0.0369
0.0886
0.71073
2.150
8.956
0.0202
0.0414
0.71073
2.247
8.435
0.0178
0.0428
0.71073
1.935
5.968
0.0359
0.0912
ρ (g/cm3)
μ (mm−1
R1 (obsd. data)
wR2 (all data, F2 refinement)
)
a
b
a
b
2
2
R1 = (Σ||F0| − |Fc||)/Σ|F0| wR2 = ((Σ[w(F0 − Fc2)2])/Σ[w(F0 )2])1/2
alternative phosphine ligand was present. Previous work has
demonstrated that changes in anions can alter the structures
and properties of a variety of cationic gold complexes.24−27
Here, we report structural and computational studies on salts
containing the cations [(Ph3P)Au(bipy)]+ and [(Et3P)Au-
(bipy)]+.
mixture was stirred for an hour, the colorless precipitate of
silver chloride was removed by filtration. Diethyl ether was
added to the colorless filtrate to precipitate the product as very
pale yellow, nearly colorless crystals in yields of 70−90%.
Crystallographic Characterization of [(R3P)Au(bipy)]-
XF6 (R = Ph, Et; X = P, As, Sb). Crystal data are given in
Tables 1a and 1b. The salts [(Ph3P)Au(bipy)]XF6 crystallize in
the triclinic space group P1 as an isostructural series. However,
[(Ph3P)Au(bipy)]AsF6 also crystallizes as a second polymorph
in the monoclinic space group P21/c. Figure 1 shows a drawing
of the structure of [(Ph3P)Au(bipy)]AsF6 and a photograph of
crystals of the two polymorphs that formed concomitantly.
The triclinic P1 polymorph forms nearly colorless plates, while
the monoclinic space group P21/c crystallizes as nearly
RESULTS AND DISCUSSION
■
Preparation of [(R3P)Au(bipy)]XF6 (R = Ph or Et; X = P,
As, Sb). These salts were synthesized following the original
procedure for the preparation of [(Ph3P)Au(bipy)]PF6.23
A
dichloromethane solution of Ag(XF6) (X = P, As, Sb) was
added to a dichloromethane solution containing equimolar
amounts of (R3P)AuCl (R = Ph or Et) and bipy. After the
B
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metrically bonded to the gold ion with two different Au−N
distances. The differences in these two distances range from
0.241(2) to 0.146(2) Å. For example, the Au−N distances in
the triclinic polymorph of [(Ph3P)Au(bipy)]AsF6 are 2.404(2)
and 2.189(2) Å, while they are 2.3846(18) and 2.2121(18) Å
in the monoclinic polymorph. Notice that the Au−N distance
in the linear, two-coordinate [(Ph3P)Au(py)]BF4, 2.073(3)
Å,28 is much shorter than either of the Au−N distances in
either polymorph of [(Ph3P)Au(bipy)]AsF6. The bipy ligand is
somewhat distorted from planarity with the central N−C−C−
N torsional angles ranging from 7.0(3) to 10.6(4)°.
The salts [(Et3P)Au(bipy)]XF6 crystallize in the monoclinic
space group P21/c and form a second isostructural series.
Figure 2 shows the structure of a representative example,
Figure 1. (A) The structure of [(Ph3P)Au(bipy)]AsF6 with 50%
thermal contours. (B) Photograph of crystals of the two polymorphs
(blocks of P1 polymorph, needles of P21/c polymorph) of
[(Ph3P)Au(bipy)]AsF6.
colorless needles. As seen in Table 2, the bond distances and
angles of the cation in the two polymorphs of [(Ph3P)Au-
(bipy)]AsF6 are similar. Thus, the molecular packing, which
differs in the two structures, does not appear to have a major
influence on the structure of the cation. In both polymorphs of
[(Ph3P)Au(bipy)]AsF6 as well as in the hexafluorophosphate
and hexafluoroantimonate salts, the bipy ligand is unsym-
Figure 2. Structure of[(Et3P)Au(bipy)]SbF6 displaying the two
positions for the gold ion drawn with 50% thermal contours.
Hydrogen atoms are omitted for clarity. Au1 has 0.696(7) fractional
occupancy, while Au1A has 0.304(7) fractional occupancy.
Table 2. Comparison of Features of the Au-bipy Bonds
N−Au−N angle
Au−N distance 1
Au−N distance 2
distance difference
N−C−C−N torsional angle
complex Au (occupancy)
(deg)
(Å)
(Å)
(Å)
(deg)
a
[(Ph3P)Au(bipy)]PF6
71.4(1)
2.407(2)
2.3846(18)
2.404(2)
2.370(2)
2.439(4)
2.449(14)
2.166(2)
2.2121(18)
2.189(2)
2.224(2)
2.201(4)
2.172(12)
0.241(2)
0.1725(18)
0.215(2)
0.146(2)
0.238(4)
0.277(3)
8.0
[(Ph3P)Au(bipy)]AsF6
[(Ph3P)Au(bipy)]AsF6
[(Ph3P)Au(bipy)]SbF6
71.24(6)
71.54(8)
71.31(7)
69.99(16)
70.2(3)
7.0(3)
10.6(4)
7.8(3)
2.3(6)
2.3(6)
b
[(Et3P)Au(bipy)]PF6 Au1 (0.903(9))
[(Et3P)Au(bipy)]PF6 Au1A
(0.097(9))
[(Et3P)Au(bipy)]AsF6 Au (0.817(8))
[(Et3P)Au(bipy)]AsF6 Au1A
(0.183(8))
69.62(8)
70.11(12)
2.460(3)
2.429(6)
2.196(2)
2.203(6)
0.264(5)
0.226(6)
3.8(4)
3.8(4)
[(Et3P)Au(bipy)]SbF6 Au1
(0.696(7))
[(Et3P)Au(bipy)]SbF6 Au1A
(0.304(7))
69.40(7)
69.99(9)
2.468(2)
2.422(4)
2.190(2)
2.209(4)
0.278(2)
0.213(4)
3.4(3)
3.4(3)
a
b
Room temperature data from ref 23 [Clegg, W. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1976, 32, 2712]. P21/c polymorph.
C
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1
Figure 3. A portion of the H NMR spectrum from a dichloromethane-d2 solution of [(Et3P)Au(bipy)]PF6 at room temperature showing the
resonances of the bipy ligand.
Figure 4. Top left: Computationally optimized structure of [(Et3P)Au(bipy)]+, 1. Top center: Computationally optimized structure of
[(Et3P)Au(bipy)]+ with the P−Au−N1 angle constrained to be equal to the P−Au−N1 angle in 2′, 2. Bottom left: Computationally optimized
structure of [(Et3P)Au(bipy)]+ with the P−Au−N1 angle constrained to be equal to the P−Au−N1 angle in 1, 1′. Bottom center: Computationally
optimized structure of two-coordinate [(Et3P)Au(bipy)]+, 2′. Center right: Computationally optimized structure of [(Et3P)Au(bipy)]+ with Au−N
distances constrained to be equivalent, 3‡.
[(Et3P)Au(bipy)]SbF6. Again, the bipy ligand is unsymmetri-
cally positioned with respect to the gold ion, but in
[(Et3P)Au(bipy)]SbF6 and the other two members of this
series, there are two fractionally occupied positions for the gold
ion. The fractional occupancy of the major gold site Au1 varies
in each salt, i.e., 0.903(9) for X = P, 0.817(8) for X = As, and
0.696(7) for X = Sb. However, the unsymmetrical coordina-
tion of the bipy ligand is similar for both positions of the gold
ion as seen in the data in Table 2. The differences in the two
Au−N distances in the [(Et3P)Au(bipy)]XF6 series range from
0.278(2) to 0.213(4) Å. In this series the bipy ligands are more
nearly planar than they are in the [(Ph3P)Au(bipy)]XF6 series.
The central N−C−C−N torsional angles in the [(Et3P)Au-
(bipy)]XF6 series range from 2.3(6) to 3.8(4)°.
Spectroscopic Properties of [(R3P)Au(bipy)]XF6 (R =
Ph or Et; X = P, As, Sb). The salts [(R3P)Au(bipy)]XF6 (R =
Ph or Et; X = P, As, Sb) readily dissolve in dichloromethane to
form colorless solutions that lack luminescence. Additionally,
the crystalline solids are also nonluminescent at room
1
temperature or when cooled to 77 K. Figure 3 shows the H
NMR spectrum from a dichloromethane-d2 solution of
[(Et3P)Au(bipy)]PF6 in the region of the bipy resonances.
Four multiplets that resemble those of bipy itself are present.29
The spectrum shows almost no change upon cooling to 200 K.
Consequently, it appears that the complex is fluxional in a
process that renders the two halves of the bipy ligand
1
equivalent (vide infra). The bipy region in the H NMR
D
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Table 3. Experimental and Computational Bond Distances and Angles for 1, 1′, 2, 2′, and 3‡
experimental
computational
crystallographic
1
1′
2
2′
3‡
72°
144°
144°
2.30 Å
2.30 Å
2.34 Å
N1−Au1−N2
N1−Au1−P1
N2−Au1−P1
Au1−N1
Au1−N2
Au1−P1
69.40(8)°
157.63(8)°
132.61(7)°
2.190(2) Å
2.468(2) Å
2.231(1) Å
71°
159°
130°
2.19 Å
2.45 Å
2.35 Å
−
70°
176°
113°
2.13 Å
2.66 Å
2.35 Å
−
159°
176°
−
−
2.12 Å
−
2.36 Å
2.10 Å
−
2.35 Å
spectra of the other five salts are similar (see the Supporting
Information).
A in Figure 5. This structure results in a saturated (12
electron) gold center and thereby inhibits the formation of any
Computational Results. In an effort to understand the
origins of the asymmetric Au−N bond distances in the three-
coordinate [(Et3P)Au(bipy)]+ complexes, five structures were
optimized as shown in Figure 4. The first structure, 1, was
optimized from crystallographic coordinates. In structure 1′
the bipy ligand was forced to be a monodentate ligand by
twisting about the bridging C−C bond. In addition to this
twist, the P−Au−N angle was also constrained to 159.00°,
which was the optimized bent angle found from 1. In structure
2′ a monodentate bipy ligand was also utilized with a twist
about the central C−C bridge, comparable to 1′, but with no
other constraints, and this procedure led to a linear optimized
geometry with only one N atom interacting with the Au center.
In structure 2, bidentate bipy was used with one P−Au−N
angle fixed to 176.20°, as this was the optimized linear angle
found from 2′. In structure 3‡ the two Au−N bonds were both
fixed to a single distance, r1, that itself was optimized. The
resulting structures of 1 and 3‡ maintained a planar bonding
motif about the Au center in an extended Y-shaped geometry,
whereas 2′ was structurally linear about the Au center, as seen
in Figure 4.30 The hypothetical 2 was found to have the distal
N2 atom nearly in the plane formed by P−Au−N1 (deviation
of 0.77°) with a 20.32° twist of N−C−C−N dihedral angle in
the bipy ligand. The hypothetical 1′ was found to have a
distorted geometry with the gold center bending 10.36° away
from the plane of the uncoordinated pyridine ring. The Au−
N1 and Au−P bond distances in 1 were slightly overestimated
by the calculations, Table 3, as is common for DFT
results.31−33 The Au−N2 distance in 1 was ∼0.019 Å shorter
than expected, most likely due to the overestimation of the
stronger Au−P bond. Frequency calculations indicate that 1,
1′, 2, and 2′ occupy local minima, whereas 3‡ was found to
have one imaginary frequency corresponding to an asymmetric
distortion of the two Au−N bonds. From the nature of this
imaginary frequency, the geometry optimization and frequency
calculations strongly imply that 3‡ is best described as a
transition state between the two limiting geometries of 1.
Overall, 3‡ was found to be higher in energy than 1 by 7 kJ/
mol, similar to the 5 kJ/mol estimation of the symmetric form
of [(Ph3P)Au(o-phenanthroline)]+, which involves a rigid
ligand that is constrained to planarity.34 Relative to 1 the free
energy changes at 298.15 K induced by the distortions were 33,
8.5, and 23 kJ/mol for 1′, 2, and 2′, respectively.
Figure 5. Resonance structures of [(Et3P)Au(bipy)]+ as described
from NRT calculations performed on 1.
classical, 2 e− bonds between the gold and either of the bipy
nitrogen atoms. The nitrogen atoms may instead donate a lone
pair into an empty Au−P antibonding orbital, resulting in a
three-center four-electron (3c/4e) P−Au−N bond, Figure 6,
including the resonance forms B and C of Figure 5.39,40 The
3c/4e bonding interaction is maximized when the three atoms
approach a linear geometry, as observed by a 146.1 kJ/mol
stabilization of the lone pair on N1 in 1 due to its donation
Figure 6. Plot showing the 94% probability for electron density of the
filled, nonbonding N1 lone pair and the unfilled, antibonding P−Au
orbitals yielding in the P−Au−N1 3c/4e bond. The green and blue
lobes represent the positive and negative phases for the lone pair on
N1, respectively, and the purple and cyan lobes represent the positive
and negative phases for the empty Au−P antibonding orbital,
respectively. The image was generated with Chimera from NBO
output.12,13
Three-Center Four-Electron (3c/4e) Bond and the anti-
Chelate Effect. We interpret the bonding in [(Et3P)Au-
(bipy)]+ via natural resonance theory (NRT) calculations
using the “12 electron rule” formalism of Landis and Weinhold
taking into account only the 5d and 6s valence orbitals on
Au.35−38 The most dominant Lewis structure for both 1 and 3‡
is one with five lone pairs on Au and one bond to the P atom,
E
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into the P−Au antibonding orbital. This contrasts with the
39.6 kJ/mol stabilization experienced by the donation of the
lone pair on N2, which is significantly diminished due to the
poor orbital overlap. This energetic mismatch is also reflected
in the distinct Au−N bond lengths, with Au−N1 being shorter
as determined crystallographically by 0.278(4) Å as seen in
Table 3.
and the formation of the binuclear complex, [(Ph3PAu)2(μ2-
bipy)](PF6)2·2CH2Cl2, which has been isolated as colorless
crystals. The structure of the cation in [(Ph3PAu)2(μ2-
bipy)](PF6)2·2CH2Cl2 is shown in Figure 7. The cation
The unsymmetrical bidentate binding of the bipy ligand is a
manifestation of the anti-chelate effect, known to occur
between a Au+ center and chelating ligands.41 For this
complex, the anti-chelate effect arises from the combination
of the fixed bite angle of the chelating bipy ligand and the Au
center’s preference for a linear geometry to satisfy the 3c/4e
P−Au−N1 bond. Straightening the N−Au−P bond angle
results in a more favorable 3c/4e interaction and a shorter
N1−Au bond distance. This can be directly observed in both
the computational studies and the crystallographic data, as
shorter N−Au bond lengths are observed in two-coordinate
complexes over their three-coordinate analogs. In the
theoretical 2′ a N−Au bond length of 2.10 Å was predicted,
and this distance agrees well with the Au−N bond length from
the [(Ph3P)Au(py)]BF4 crystal structure, (2.073(3) Å).28
Three additional structures were studied computationally in
addition to 1 and 3‡ in an effort to estimate the energies
associated with bending the P−Au−N1 3c/4e bond and the
dissociation energy of atom N2 from Au. Comparing structures
2′ and 1′, a 10 kJ/mol difference was found, and this
destabilization energy may be attributed to the bending of the
N1−Au−P 3c/4e bond. Distorting structure 1 to 1′ resulted in
a 33 kJ/mol destabilization. When the ∼20 kJ/mol stabilization
energy associated with twisting the N−C−C−N dihedral angle
in bipy42 from 0.14° in 1 to 139.94° in 2′ along with the 10 kJ/
mol stabilization gained from unbending the N1−Au−P
interaction as determined from the 2′ to 1′ transformation is
accounted for, then a total destabilization energy associated
with breaking the Au−N2 bond can be estimated at 53 kJ/mol.
Comparing 2 and 2′ we find a 14.5 kJ/mol destabilization, and
accounting for the bipy torsion, we can estimate a total
destabilization of 34.5 kJ/mol that can be attributed to loss of
the Au−N2 bond. These estimated Au−N2 bond energies are
large enough to be structurally important and thus contribute
to the experimentally observed structure.
Figure 7. Structure of the dication in [(Ph3PAu)2(μ2-bipy)](PF6)2·
2CH2Cl2 showing 50% thermal contours with hydrogen atoms
omitted for clarity. The dashed line shows the aurophillic interaction
between the two gold ions. Selected bond distances: Au1−N1,
2.086(4); Au2−N2, 2.104(5); Au1−P1, 2.2422(13); Au2−P2,
2.2460(14); Au1···Au2, 3.0747(3) Å. Selected bond angles: N1−
Au1−P1, 177.97(13); N2−Au2−P2, 172.81(12)°.
consists of two linear N−Au−PPh3 groups connected through
a bridging bipy ligand. The Au−N and Au−P distances (Au−
N: 2.086(4), 2.104(5). Au−P: 2.2422(13), 2.2460(14) Å) are
similar to those in [(Ph3P)Au(py)]BF4, (2.073(3) and
2.2364(8) Å, respectively).28 The bipy ligand is not planar.
It is twisted due to the presence of the two bulky AuPPh3
groups, but in such a fashion that allows an aurophillic
interaction (with an Au1. . .Au2 distance of 3.0747(3) Å) to
occur between the two gold ions. The N−C−C−N dihedral
angle is 56.3(7)°.
The binuclear complex [(Ph3PAu)2(μ2-bipy)](PF6)2·
2CH2Cl2 dissolves in dichloromethane to produce a colorless
solution that lacks luminescence. Despite the presence of an
aurophilic interaction within this binuclear complex, crystals of
[(Ph3PAu)2(μ2-bipy)](PF6)2·2CH2Cl2 are not luminescent at
room temperature or at 77 K. Other examples of non-
luminescent gold(I) complexes with close Au···Au contacts are
known.43
Luminescence and the Au Atom’s Virtual Orbitals. The
nonluminescence of the asymmetric three-coordinate gold
complexes presented herein contrasts with the observed
luminescence of previously reported three-coordinate gold(I)
phosphine complexes.15 Computational studies performed on
these previously reported gold(I) complexes revealed their
luminescence to be a result of an excitation from the filled Au
2
2
5dx −y orbital into the Au 6pz orbital that is stabilized by Au−P
back bonding. The 6pz virtual orbital on the Au atom in the
asymmetric three-coordinate gold complexes presented in this
work is located ca. 72000 cm−1 higher in energy than the
highest occupied Au orbital and is therefore computationally
predicted to be inaccessible for a visible light excitation/
emission. This result highlights the importance of π-acceptor
ligands in promoting luminescence involving a 6pz excited
state.
Preparation and Structure of the Binuclear Complex,
[(Ph3PAu)2(μ2-bipy)](PF6)2·2CH2Cl2. The addition of two
molar equivalents of Ph3PAuCl to one equivalent of bipy in
dichloromethane solution followed by the addition of two
molar equivalents of AgPF6 results in the precipitation of AgCl
CONCLUSIONS
■
The unsymmetrical coordination of gold by 2,2′-bipyridine
(bipy) in [(R3P)Au(bipy)]XF6 (R = Ph or Et; X = P, As, Sb) is
an intrinsic property that results from the mismatch of the
ligand’s bite size and the availability of orbitals on gold to
accept electrons. Computational studies demonstrated that a
hypothetical symmetrical structure of [(Et3P)Au(bipy)]+, with
two equal Au−N bond lengths, is 7 kJ/mol higher in energy
than the observed unsymmetrical structure. This symmetrical
structure is best described as a transition state between the two
unsymmetrical structures, similar to those seen in the
disordered structures of [(Et3P)Au(bipy)]SbF6 shown in
Figure 2.
F
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Article
gold. Five structures were examined, i.e., an asymmetric structure, 1,
based on crystallographic coordinates; a 2-coordinate bent structure,
1′; a distorted T-shaped structure, 2; a 2-coordinate linear structure,
2′; and a symmetric structure, 3‡, as shown in Figure 4. Structures 1,
2, and 3‡ contain a planar bidentate bipy ligand with a N−C−C−N
dihedral angle of <50°, and structures 1′ and 2′ contain a twisted
monodentate bipy ligand with a N−C−C−N dihedral angle of <180°
but >60°. Structures 1, 1′, 2, and 2′ were optimized to have no
imaginary frequencies. Structure 3‡ was optimized using a modified z-
matrix to constrain the two Au−N bond distances to the same, freely
refining variable. Structure 3‡ as optimized was found to have one
imaginary frequency of −17 cm−1 that interconverts 3‡ to 1.
Structures 1′ and 2 were optimized with the N−Au−P angle
constrained to 159.00° and 176.20°, respectively.
Single Point and Natural Resonance Theory (NRT) Calculations.
Single-point and NRT calculations were carried out using ORCA ver.
4.0.0.2.56 For the single-point calculations, the CAM-B3LYP49
exchange-correlation functional was used. The Stuttgart−Dresden
effective core potential (ECP), def2-SVP,57 was used along with the
valence basis sets def2-TZVPP58 and density fitting basis set def2-
TZVPP/C54 for Au. The def2-SVP53 basis set, def2/J59 auxiliary basis,
and def2-SVP/C60 density fitting basis set were used for all other
atoms. The atom-pairwise dispersion corrections were accounted for
with the Becke−Johnson damping scheme (D3BJ).61,62 Normal
optimization and normal self-consistent field convergence criteria
were employed with grid4 and finalgrid5 for all calculations.
Visualizations of the orbitals were carried out with the UCSF
Chimera package.63 The relative contributions of the resonance
structures were determined from NRT using NBO 7.0.1.64,65
Such unsymmetrical coordination of bipy is not restricted to
these gold(I) complexes reported here and related o-
phenanthroline gold complexes.34 For example, the silver(I)-
containing cation, [μ2-bipy(Agbipy)2]2+,44 the copper(I)
cation, [μ2-1,4-bipy{Cu(2,2′-bipy)}2]2+,45 and the mercury(II)
complex, (1,3-dimethyluracil-5-yl)Hg(bipy),46 all display
nearly planar, three-coordinate structures with unsymmetrical
coordination of the bipy ligand. Additionally, the gold
complexes [(Ph3P)Au{(i-Pr)2ATI}] and [(Ph3P)Au-
{(cyclohexyl)2ATI}] (ATI = aminotroponiminate)47 and
28
[(Ph3P)Au(Me2NCH2CH2NMe2)]BF4 also exhibit struc-
tures with two distinctly different Au−N bond distances.
However, the coordination of the fluorine-substituted bipy
ligand is nearly symmetrical (Au−N, 2.178(2) and 2.210(2)
Å) in the cation, (C2H4)Au(5,5′-difluoro-2,2′-bipyridine),
which also involves an ethylene ligand in place of the tertiary
phosphine.48
EXPERIMENTAL SECTION
■
Preparation of [(Et3P)Au(bipy)]PF6. In the dark, 0.0279 g
(0.110 mmol) of silver hexafluorophosphate was dissolved in 2.0 mL
of dichloromethane. Separately, 0.0357 g (0.102 mmol) of Et3PAuCl
and 0.0163 g (0.104 mmol) of bipy were dissolved in 4.0 mL of
dichloromethane. The silver solution was transferred to the gold
solution to produce a white precipitate of AgCl. The suspension was
stirred for 1 h and then filtered to give a colorless solution. A 6.0 mL
portion of diethyl ether was then added and allowed to slowly diffuse
into the dichloromethane solution. Colorless crystals (0.0492 g) of
[(Et3P)Au(bipy)]PF6 formed in 78% yield. The other salts [(R3P)-
Au(bipy)]XF6 (R = Ph or Et; X = P, As, Sb) were prepared similarly.
Preparation of [(Ph3PAu)2(μ2-bipy)](PF6)2·2CH2Cl2. In the
dark, 0.0345 g (0.136 mmol) of silver hexafluorophosphate was
dissolved in 2.0 mL of dichloromethane. Separately, 0.0655 g (0.132
mmol) of Ph3PAuCl and 0.0104 g (0.0663 mmol) of bipy were
dissolved in 4.0 mL of dichloromethane. The silver solution was
transferred to the gold solution to produce a white precipitate of
AgCl. The suspension was stirred for 30 s and then filtered to give a
colorless solution. A 6.0 mL portion of diethyl ether was then added
and allowed to slowly diffuse into the dichloromethane solution.
Colorless crystals of a dichloromethane solvate formed in 48% yield.
These crystals lost crystallinity when removed from the mother liquor
due to the loss of the solvate molecules.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00138.
■
sı
1
Infrared and H NMR data for [(R3P)Au(bipy)]XF6 (R
= Ph, Et; X = P, As, Sb) and [(Ph3PAu)2(μ2-
bipy)](PF6)2·2CH2Cl2 (PDF)
Accession Codes
CCDC 1977743−1977749 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
X-ray Crystallography and Data Collection. All crystals were
transferred with a small amount of mother liquor to a microscope
slide and immediately coated with a hydrocarbon oil. A suitable
crystal of each [(Et3P)Au(bipy)]XF6 compound and of
[(Ph3PAu)2(μ2-bipy)](PF6)2·2CH2Cl2 was mounted in the 100 K
nitrogen cold stream provided by an Oxford Cryostream low-
temperature apparatus on the goniometer head of a Bruker D8
Venture Kappa DUO diffractometer equipped with Bruker Photon
100 CMOS detector. A suitable crystal of each [(Ph3P)Au(bipy)]XF6
compound was mounted in the 90 K nitrogen cold stream provided
by a Cryo Industries low-temperature apparatus on the goniometer
head of a Bruker APEX II sealed-tube diffractometer and CCD
detector. All data were collected with the use of Mo Kα (λ = 0.71073
Å) radiation. A multiscan absorption correction was applied with the
program SADABS.49 The structure was solved by a dual space
method, (SHELXT)50 and refined by full-matrix least-squares on F2
(SHELXL-2017).51 Further information on the structure determi-
nation is available in the deposited CIF, CCDC numbers 1977743−
1977749.
AUTHOR INFORMATION
Corresponding Authors
■
John F. Berry − Department of Chemistry, University of
Wisconsin-Madison, Madison, Wisconsin 53706, United States;
orcid.org/0000-0002-6805-0640; Email: berry@
chem.wisc.edu
Marilyn M. Olmstead − Department of Chemistry, University of
California-Davis, Davis, California 05616, United States;
orcid.org/0000-0002-6160-1622; Email: mmolmstead@
ucdavis.edu
Alan L. Balch − Department of Chemistry, University of
California-Davis, Davis, California 05616, United States;
orcid.org/0000-0002-8813-6281; Email: albalch@
ucdavis.edu
Computational Methods. Geometry Optimization and Fre-
quency Calculations. Initial coordinates of [(Et3P)Au(bipy)]+ for
the calculations were obtained from the crystallographic data with the
counterion removed. Geometry optimizations and frequency calcu-
lations were carried out using Gaussian 09.52 The CAM-B3LYP53
functional and the SDD54,55 basis set were used for all atoms, and
these included relativistically contracted effective core potentials for
Authors
Lucy M. C. Luong − Department of Chemistry, University of
California-Davis, Davis, California 05616, United States
Michael M. Aristov − Department of Chemistry, University of
Wisconsin-Madison, Madison, Wisconsin 53706, United States
G
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Article
́
(17) Visbal, R.; Lopez-de-Luzuriaga, J. M.; Laguna, A.; Gimeno, M.
C. Three-coordinate gold(I) N-heterocyclic carbene complexes: a
new class of strongly luminescent derivatives. Dalton Trans. 2014, 43,
328−334.
Alexandria V. Adams − Department of Chemistry, University of
California-Davis, Davis, California 05616, United States
Daniel T. Walters − Department of Chemistry, University of
California-Davis, Davis, California 05616, United States
(18) Osawa, M.; Aino, M.; Nagakura, T.; Hoshino, M.; Tanaka, Y.;
Akita, M. Near-unity thermally activated delayed fluorescence
efficiency in three- and four-coordinate Au(I) complexes with
diphosphine ligands. Dalton Trans. 2018, 47, 8229−8239.
(19) Lim, S. H.; Olmstead, M. M.; Balch, A. L. Molecular
Accordion: Vapoluminescence and Molecular Flexibility in the
Orange and Green Luminscent Crystals of the Dimer, Au2(μ-bis-
(diphenylphosphino)ethane)2Br2. J. Am. Chem. Soc. 2011, 133,
10229−10238.
(20) Lim, S. H.; Olmstead, M. M.; Balch, A. L. Inorganic
topochemistry. Vapor-induced solid state transformations of lumines-
cent, three-coordinate gold(I) complexes. Chem. Sci. 2013, 4, 311−
318.
(21) Osawa, M.; Kawata, I.; Igawa, S.; Tsuboyama, A.; Hashizume,
D.; Hoshino, M. Phosphorescence Color Alteration by Changing
Counter Anions on Tetrahedral Gold(I) Complexes; Intra- and
Interligand π-π Interactions. Eur. J. Inorg. Chem. 2009, 3708−3711.
(22) Osawa, M.; Kawata, I.; Igawa, S.; Hoshino, M.; Fukunaga, T.;
Hashizume, D. Vapochromic and Mechanochromic Tetrahedral
Gold(I) Complexes Based on the 1,2-Bis(diphenylphosphino)-
benzene Ligand. Chem. - Eur. J. 2010, 16, 12114−12126.
(23) Clegg, W. 2,2′-Bipyridyltriphenylphoshinegold(I) hexafluor-
ophosphate. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem.
1976, 32, 2712−2714.
(24) Ecken, H.; Olmstead, M. M.; Noll, B. C.; Attar, S.; Schlyer, B.;
Balch, A. L. Effects of anions on the solid state structures of linear
gold(I) complexes of the type (o-xylyl isocyanide)gold(I) (mono-
anion). J. Chem. Soc., Dalton Trans. 1998, 3715−3720.
(25) White-Morris, R. L.; Olmstead, M. M.; Jiang, F.; Tinti, D. S.;
Balch, A. L. Remarkable Variations in the Luminescence of Frozen
Solutions of [Au{C(NHMe)2}2](PF6)·0.5(Acetone). Structural and
Spectroscopic Studies of the Effects of Anions and Solvents on
Gold(I) Carbene Complexes. J. Am. Chem. Soc. 2002, 124, 2327−
2336.
(26) Rios, D.; Pham, D. M.; Fettinger, J. C.; Olmstead, M. M.; Balch,
A. L. Blue or Green Glowing Crystals of the Cation [Au{C-
(NHMe)2}2]+. Structural Effects of Anions, Hydrogen Bonding, and
Solvate Molecules on the Luminescence of a Two-Coordinate Gold
(I) Carbene Complex. Inorg. Chem. 2008, 47, 3442−3451.
(27) Saitoh, M.; Balch, A. L.; Yuasa, J.; Kawai, T. Effects of Counter
Anions on Intense Photoluminescence of 1-D Chain Gold (I)
Complexes. Inorg. Chem. 2010, 49, 7129−7134.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c00138
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the ARCS Foundation for two awards to L.M.C.L.,
the National Science Foundation (CHE-1807637) for partial
support of this project, and grant CHE-1531193 for the dual-
source X-ray diffractometer. J.F.B. thanks the National Science
Foundation for funding under CHE-1664999.
REFERENCES
■
(1) Yam, V. W.-W.; Au, V. K.-A.; Leung, S. Y.-L. Light-Emitting Self-
Assembled Materials Based on d8 and d10 Transition Metal
Complexes. Chem. Rev. 2015, 115, 7589−7728.
(2) Zhao, Q.; Li, F.; Huang, C. Phosphorescent chemosensors based
on heavy-metal complexes. Chem. Soc. Rev. 2010, 39, 3007−3030.
(3) Zhang, X.; Chi, Z.; Zhang, Y.; Liu, S.; Xu, J. Recent advances in
mechanochromic luminescent metal complexes. J. Mater. Chem. C
2013, 1, 3376−3390.
(4) Hashmi, A. S. K. Homogeneous Gold Catalysis Beyond
Assumptions and Proposals-Characterized Intermediates. Angew.
Chem., Int. Ed. 2010, 49, 5232−5241.
(5) Rudolph, M.; Hashmi, A. S. K. Gold catalysis in total synthesis-
an update. Chem. Soc. Rev. 2012, 41, 2448−2462.
(6) Wang, Y.-M.; Lackner, A. D.; Toste, F. D. Development of
Catalysts and Ligands for Enantioselective Gold Catalysis. Acc. Chem.
Res. 2014, 47, 889−901.
(7) Balch, A. L. Remarkable Luminescence Behaviors and Structural
Variations of Two-Coordinate Gold(I) Complexes. Struct. Bonding
(Berlin, Ger.) 2007, 123, 1−40.
(8) Gimeno, M. C.; Laguna, A. Three- and Four-Coordinate Gold(I)
Complexes. Chem. Rev. 1997, 97, 511−522.
(9) Schmidbaur, H.; Schier, A. Aurophilic interactions as a subject of
current research: an up-date. Chem. Soc. Rev. 2012, 41, 370−412.
(10) White-Morris, R. L.; Olmstead, M. M.; Balch, A. L. Aurophilic
Interactions in Cationic Gold Complexes with Two Isocyanide
Ligands. Polymorphic Yellow and Colorless Forms of [(Cyclohexyl
Isocyanide)2AuI](PF6) with Distinct Luminescence. J. Am. Chem. Soc.
2003, 125, 1033−1040.
(28) Thwaite, S. E.; Schier, A.; Schmidbaur, H. The auration of 2-
hydroxy-pyridine (2-pyridone): preparative and structural studies and
a comparison with reactions of related aliphatic O;N-donors. Inorg.
Chim. Acta 2004, 357, 1549−1557.
(11) Malwitz, M. A.; Lim, S. H.; White-Morris, R. L.; Pham, D. M.;
Olmstead, M. M.; Balch, A. L. Crystallization and Interconversions of
Vapor-Sensitive, Luminescent Polymorphs of [(C6H11NC)2AuI]-
(AsF6) and [(C6H11NC)2AuI](PF6). J. Am. Chem. Soc. 2012, 134,
10885−10893.
(29) Shen, W.-Z.; Trotscher-Kaus, G.; Lippert, B. 1H NMR
̈
spectroscopic identification of binding modes of 2,2’-bipyridine
ligands in complexes of square-planar d8 metal ions. Dalton Trans.
2009, 8203−8214.
(12) King, C.; Khan, M. N. I.; Staples, R. J.; Fackler, J. P., Jr.
Luminescent Mononuclear Gold(I) Phosphines. Inorg. Chem. 1992,
31, 3236−3238.
(30) Davis, T. L.; Watts, J. L.; Brown, K. J.; Hewage, J. S.; Treleven,
A. R.; Lindeman, S. V.; Gardinier, J. R. Structural Classification of
Metal Complexes with Three-Coordinate Centres. Dalton Trans.
2015, 44, 15408−15412.
(13) Forward, J. M.; Assefa, Z.; Fackler, J. P., Jr. Photoluminescence
of gold(I) phosphine complexes in aqueous solution. J. Am. Chem.
Soc. 1995, 117, 9103−9104.
(31) Boom, D. H. A.; Ehlers, A. W.; Nieger, M.; Devillard, M.;
Bouhadir, G.; Bourissou, D.; Slootweg, J. C. Gold(I) Complexes of
the Geminal Phosphinoborane tBu2PCH2BPh2. ACS Omega 2018, 3,
3945−3951.
(32) Schwerdtfeger, P.; Hermann, H. L.; Schmidbaur, H. Stability of
the Gold(I)-Phosphine Bond. A Comparison with Other Group 11
Elements. Inorg. Chem. 2003, 42, 1334−1342.
(33) Shawkataly, O. b.; Goh, C.-P.; Tariq, A.; Khan, I. A.; Fun, H.-
K.; Rosli, M. M. Synthesis, Spectral Characterization and Crystals
Structure of some Arsane Derivatives of Gold (I) Complexes: A
(14) McCleskey, T. M.; Gray, H. B. Emission Spectroscopic
Properties of l,2-Bis(dicyclohexylphosphino)ethane Complexes of
Gold(I). Inorg. Chem. 1992, 31, 1733−1734.
(15) Barakat, K. A.; Cundari, T. R.; Omary, M. A. Jahn-Teller
Distortion in the Phosphorescent Excited State of Three-Coordinate
Au(I) Phosphine Complexes. J. Am. Chem. Soc. 2003, 125, 14228−
14229.
(16) Sinha, P.; Wilson, A. K.; Omary, M. A. Beyond a T-Shape. J.
Am. Chem. Soc. 2005, 127, 12488−12489.
H
https://dx.doi.org/10.1021/acs.inorgchem.0c00138
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
Comparative Density Functional Theory Study. PLoS One 2015, 10,
No. e0119620.
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar,
S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox,
J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09, rev. B.01; Gaussian, Inc.: Wallingford, CT, 2016.
(53) Yanai, T.; Tew, D. P.; Handy, N. C. A New Hybrid Exchange-
Correlation Functional Using the Coulomb-Attenuating Method
(CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51−57.
(34) Yang, Y.; Eberle, L.; Mulks, F. F.; Wunsch, J. F.; Zimmer, M.;
Rominger, F.; Rudolph, M.; Hashmi, A. S. K. Trans Influence of
Ligands on the Oxidation of Gold(I) Complexes. J. Am. Chem. Soc.
2019, 141, 17414−17420.
(35) Weinhold, F.; Landis, C. Lewis-like structures for the d-block
elements. Valency and Bonding: A Natural Bond Orbital Donor-
Acceptor Perspective 2005, 365−367.
(36) Landis, C. R.; Hughes, R. P.; Weinhold, F. Bonding Analysis of
TM(cAAC)2 (TM = Cu, Ag, and Au) and the Importance of
Reference State. Organometallics 2015, 34, 3442−3449.
(37) Landis, C. R.; Weinhold, F. 18-electron rule and the 3c/4e
hyperbonding saturation limit. J. Comput. Chem. 2016, 37, 237−241.
(38) Landis, C. R.; Weinhold, F. Valence and extra-valence orbitals
in main group and transition metal bonding. J. Comput. Chem. 2007,
28, 198−203.
̈
(54) Andrae, D.; Haußermann, U.; Dolg, M.; Stoll, H.; Preuß, H.
Energy-Adjusted ab initio Pseudopotentials for the Second and Third
Row Transition Elements. Theor. Chim. Acta 1990, 77, 123−141.
(55) Schwerdtfeger, P.; Dolg, M.; Schwarz, W. H. E.; Bowmaker, G.
A.; Boyd, P. D. W. Relativistic Effects in Gold Chemistry. I. Diatomic
Gold Compounds. J. Chem. Phys. 1989, 91, 1762−1774.
(56) Neese, F. Software Update: The Orca Program System, Version
4.0. Wiley Interdiscip. Rev. Comput. Mol. Sci. 2018, 8, No. e1327.
(57) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence,
Triple Zeta Valence and Quadruple Zeta Valence Quality for H To
Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys.
2005, 7, 3297−3305.
(39) Cheung, Y.-S.; Ng, C.-Y.; Chiu, S.-W.; Li, W.-K. Application of
Three-Center-Four-Electron Bonding for Structural and Stability
Predictions of Main Group Hypervalent Molecules: The Fulfillment
of Octet Shell Rule. J. Mol. Struct.: THEOCHEM 2003, 623, 1−10.
(40) Berry, J. F. The Role of Three-Center/Four-Electron Bonds in
Superelectrophilic Dirhodium Carbene and Nitrene Catalytic
Intermediates. Dalton Trans. 2012, 41, 700−713.
(41) Weinhold, F.; Landis, C. Vertical trends in transition-metal
bonding. Valency and Bonding: A Natural Bond Orbital Donor-Acceptor
Perspective 2005, 526−530.
(58) Peterson, K. A.; Puzzarini, C. Systematically Convergent Basis
Sets for Transition Metals. II. Pseudopotential-Based Correlation
Consistent Basis Sets for the Group 11 (Cu, Ag, Au) and 12 (Zn, Cd,
Hg) Elements. Theor. Chem. Acc. 2005, 114, 283−296.
̈
(42) Goller, A.; Grummt, U.-W. Torsional Barriers in Biphenyl, 2,2′-
Bipyridine and 2-Phenylpyridine. Chem. Phys. Lett. 2000, 321, 399−
(59) Weigend, F. Accurate Coulomb-Fitting Basis Sets for H to Rn.
Phys. Chem. Chem. Phys. 2006, 8, 1057−1065.
405.
(43) Walters, D. T.; England, K. R.; Ghiassi, K. G.; Semma, F. Z.;
Olmstead, M. M.; Balch, A. L. Steric effects and aurophilic
interactions in crystals of Au2(μ-1,2-bis(diphenylphosphino)ethane)-
X2 and Au2(μ-1,2-bis(dicyclohexylphosphino)ethane)X2 (X = Cl, Br,
I). Polyhedron 2016, 117, 535−541.
(44) Lu, Y.; Xiao, L.-N.; Hao, X.-R.; Cui, X.-B.; Xu, J.-Q. A series of
organic-inorganic hybrid compounds formed by [P2W18O62]6− and
several types of transition metal complexes. Dalton Trans. 2017, 46,
14393−14405.
(45) Yuan, L.; Qin, C.; Wang, X.; Wang, E.; Chang, S. Two
Extended Organic-Inorganic Assemblies Based on Polyoxometalates
and Copper Coordination Polymers with Mixed 4,4-Bipyridine and
2,2-Bipyridine Ligands. Eur. J. Inorg. Chem. 2008, 4936−4942.
(46) Zamora, F.; Sabat, M.; Lippert, B. Synthesis and structure of
(1,3-dimethyluracil-5-yl)mercury(II) complexes with aromatic nitro-
gen donor ligands. Inorg. Chim. Acta 1998, 282, 237−242.
(47) Meiners, J.; Herrmann, J.-S.; Roesky, P. W. Three-Coordinated
Aminotroponiminate and Aminotroponate Complexes of Gold(I).
Inorg. Chem. 2007, 46, 4599−4604.
(48) Harper, M. J.; Arthur, C. J.; Crosby, J.; Emmett, E. J.; Falconer,
R. L.; Fensham-Smith, A. J.; Gates, P. J.; Leman, T.; McGrady, J. E.;
Bower, J. F.; Russell, C. A. Oxidative Addition, Transmetalation, and
Reductive Elimination at a 2,2′-Bipyridyl-Ligated Gold Center. J. Am.
Chem. Soc. 2018, 140, 4440−4445.
̈
̈
(60) Hellweg, A.; Hattig, C.; Hofener, S.; Klopper, W. Optimized
Accurate Auxiliary Basis Sets for RI-MP2 And RI-CC2 Calculations
for the Atoms Rb to Rn. Theor. Chem. Acc. 2007, 117, 587−597.
(61) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the Damping
Function in Dispersion Corrected Density Functional Theory. J.
Comput. Chem. 2011, 32, 1456−1465.
(62) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and
Accurate ab initio Parametrization of Density Functional Dispersion
Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys. 2010,
132, 154104.
(63) Pettersen, E. F.; Goddard, T. D.; Huang, C. C.; Couch, G. S.;
Greenblatt, D. M.; Meng, E. C.; Ferrin, T. E. UCSF Chimera-A
Visualization System for Exploratory Research and Analysis. J.
Comput. Chem. 2004, 25, 1605−1612.
(64) Glendening, E. D.; Landis, C. R.; Weinhold, F. NBO 7.0: New
Vistas in Localized and Delocalized Chemical Bonding Theory. J.
Comput. Chem. 2019, 40, 2234−2241.
(65) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J.
E.; Bohmann, J. A.; Morales, C. M.; Karafiloglou, P.; Landis, C. R.;
Weinhold, F. NBO 7.0; Theoretical Chemistry Institute, University of
Wisconsin: Madison, WI, 2018.
(49) Krause, L.; Herbst-Irmer, R.; Sheldrick, G. M.; Stalke, D.
Comparison of silver and molybdenum microfocus X-ray sources for
single-crystal structure determination. J. Appl. Crystallogr. 2015, 48,
3−10.
(50) Sheldrick, G. M. SHELXT - Integrated space-group and crystal-
structure determination. Acta Crystallogr., Sect. A: Found. Adv. 2015,
71, 3−8.
(51) Sheldrick, G. M. Crystal structure refinement with SHELXL.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8.
(52) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
I
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