Structures and photoluminescence of Silver(I) and Gold(I) cyclic trinuclear complexes with aryl substituted pyrazolates

Article abstract of DOI:10.1246/cl.190145

The 4-aryl substituted pyrazolate ligands, L1(Ph)H and L1(Naph)H, were synthesized by SuzukiMiyaura cross-coupling and combined with metal sources to give cyclic trinuclear structures [AgL1(Ph)]₃, [AuL1(Ph)] ₃, [AgL1(Naph)] ₃, and [AuL1(Naph)]3. The aryl group determined the crystal packing of these cyclic trinuclear complexes with the phenyl systems exhibiting stair type solid state structures and the naphthyl complexes exhibiting irregular structures with spaces occupied with some solvent molecules. These differences in solid-state structures were accompanied by differences in MN stretching frequencies and temperature dependent photoluminescence.

Full text of DOI:10.1246/cl.190145

Advance Publication Cover Page
Structures and Photoluminescence of Silver(I) and Gold(I) Cyclic Trinuclear Complexes
with Aryl Substituted Pyrazolates
Mai Saotome, Daichi Shimizu, Ayaka Itagaki, David James Young, and Kiyoshi Fujisawa*
Advance Publication on the web May 9, 2019
doi:10.1246/cl.190145
© 2019 The Chemical Society of Japan
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Publication manuscripts.

1
Structures and Photoluminescence of Silver(I) and Gold(I) Cyclic Trinuclear Complexes with
Aryl Substituted Pyrazolates
Mai Saotome,1 Daichi Shimizu,1 Ayaka Itagaki,1 David James Young,2 and Kiyoshi Fujisawa*1
1Department of Chemistry, Ibaraki University, Mito, Ibaraki 310-8512
2 College of Engineering, IT & Environment, Charles Darwin University, Darwin, NT 0909, Australia
(E-mail: kiyoshi.fujisawa.sci@vc.ibaraki.ac.jp)
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The 4-aryl substituted pyrazolate ligands, L1(Ph)H and
49 butyl-1-pyrazole). The electronegativity and bulkiness of
50 halogens introduced at the 4-position of L1(H)H and 3,5-
51 Ph2pzH (= 3,5-diphenyl-1-pyrazole) influenced both the
52 geometry and physiochemical properties of the resulting
53 complexes.5 To explore this relationship further, we herein
54 report new aryl ligands substituted at the 4-position of
55 L1(H)H, viz 4-phenyl-3,5-diisopropyl-1-pyrazole (denoted
56 as L1(Ph)H) and 4-naphthyl-3,5-diisopropyl-1-pyrazole
57 (denoted as L1(Naph)H) and their silver(I) and gold(I)
58 complexes, [AgL1(Ph)]3, [AuL1(Ph)]3, [AgL1(Naph)]3, and
59 [AuL1(Naph)]3 (Scheme 1).
L1(Naph)H, were synthesized by Suzuki–Miyaura cross-
coupling and combined with metal sources to give cyclic
trinuclear
structures
[AgL1(Ph)]3,
[AuL1(Ph)]3,
[AgL1(Naph)]3, and [AuL1(Naph)]3. The aryl group
determined the crystal packing of these cyclic trinuclear
complexes with the phenyl systems exhibiting stair type solid
state structures and the naphthyl complexes exhibiting irregular
structures with spaces occupied with some solvent molecules.
10 These differences in solid-state structures were accompanied by
11 differences in M–N stretching frequencies and temperature
12 dependent photoluminescence.
13 Keywords: Silver(I) complexes, Gold(I) complexes,
14 Pyrazole
15
Cyclic trinuclear complexes of monovalent coinage
N N
N N
16 metal ions are of current interest in inorganic and
17 coordination chemistry because of their diverse structures
18 and structure dependent photoluminescence.1 We chose
19 pyrazole as a bidentate ligand for these systems because they
20 can be easily obtained with various substituents from the
21 reaction of β-diketones with hydrazines or by aryl cross-
22 coupling.2 Pyrazoles are weak bases and the nucleophilicity
23 of N2 can be modified by introduction of the appropriate
24 substituents at the 3-, 4- or 5-positions of the heterocyclic
25 ring (Chart 1).1–3
26
27
28
29
H
H
L1(Ph)H
L1(Naph)H
X
X
Ag2O
C6H5CH3
N N
M
N
N
M
N N
[AuCl(tht)]
THF
N
H
M
N
L1(X)H
X = Ph or Naph
X
X
[ML1(X)]3
M = Ag(I) or Au(I)
60 Scheme 1. Ligands and preparation of the complexes.
61
62
4
3
We employed Suzuki–Miyaura cross-coupling to
5
63 introduce the aryl groups on to the pyrazole ring1d,6 rather
64 than reaction of a modified β-diketone with hydrazine.7 This
65 involved palladium catalyzed coupling of L1(Br)Ts with
66 phenyl- or naphthyl-boronate to give L1(Ph)H and
67 L1(Naph)H in 82% and 66% yields, respectively (see
68 supporting information, Figures S1-S4).1d,6,8 Homo-coupled
69 by-products, biphenyl and 1,1-dinaphthyl were also obtained
70 as confirmed by X-ray crystallography (Figures S1-S2).9–10
71 Successful single-crystal X-ray structural determinations
72 were performed on all of the complexes [AgL1(Ph)]3,
73 [AuL1(Ph)]3, [AgL1(Naph)]3, and [AuL1(Naph)]3,
74 revealing cyclic trinuclear complexes (Tables S1–S2, Figures
75 1 and S5–S6). The perspective drawings of these complexes
76 are shown in Figure 1. The related copper(I) complexes were
77 reported in 2010 by Gong and coworkers.7c These authors
78 synthesized [Cu{μ-3,5-Me2-4-Phpz}]3, [Cu{μ-3,5-Me2-4-
N1
2N
30
31
32
H
33 Chart 1. Pyrazole ligand.
34
35
We are interested in the coordination geometry of
36 monovalent coinage metal ions with pyrazolate, viz
37 {M(pz*)}n (M = Cu(I), Ag(I), and Au(I); n = 3, 4, or 6, and
38 particularly in their luminescent properties. Trinuclear and
39 tetranuclear complexes of monovalent coinage metal ions
40 have been reported and their structures depends on the
41 metal(I) ion used and the bulkiness of the substituent on the
42 pyrazolate ring.4–5 For example, by using 3,5-diisopropyl
43 substituted pyrazole, trinuclear complexes {M(μ-3,5-
44 iPr2pz)}3 (M = Cu(I), Ag(I), and Au(I); 3,5-iPr2pzH = 3,5-
45 diiropropyl-1-pyrazole, denoted as L1(H)H) were obtained.4
46 On the other hand, introduction of a bulkier substituent
47 resulted in the tetranuclear complexes {M(μ-3,5-tBu2pz)}4
48 (M = Cu(I), Ag(I), and Au(I); 3,5-tBu2pzH = 3,5-di-tertiary
79 Naphpz}]3 and [Cu{μ-3,5-Me2-4-Anthpz}]3 (Anth
80 anthranyl group), but only [Cu{μ-3,5-Me2-4-Phpz}]3 was
81 characterized by X-ray crystallography, while the structures
=

2
1
2
3
4
5
Figure 1. Molecular structures of [AgL1(Ph)]3 (upper left, 50% displacement ellipsoids), [AuL1(Ph)]3 (upper right, 50%
displacement ellipsoids), [AgL1(Naph)]3 without solvent (bottom left, 30% displacement ellipsoids) and [AuL1(Naph)]3
without solvent (bottom right, 30% displacement ellipsoids) and the atom labeling scheme. Hydrogen atoms are omitted for
clarity.
6
7
8
9
of the other complexes were optimized by DFT calculations.
The crystal structures of L1(Ph)H and L1(Naph)H
were very similar to each other (Figure S3). Intermolecular
and intramolecular hydrogen bonding interactions resulted in
30 177.83(5) deg in [AgL1(Ph)]3, av. N–Au–N, 178.52(7) deg
31 in [AuL1(Ph)]3, av. N–Ag–N, 177.7(2) deg in
32 [AgL1(Naph)]3, and av. N–Au–N, 178.5(5) deg in
33 [AuL1(Naph)]3,) indicate that each metal(I) ion is
34 coordinated by two pyrazolyl nitrogen atoms with an almost
35 linear coordination mode. These structural observations are
36 similar to that of previously reported cyclic trinuclear
37 pyrazolato complexes.4b,5 Packing diagrams for all complexes
38 are shown in Figures S7-S10. Pseudo dimeric structures were
39 observed in the L1(Ph)H system, without any evidence of
40 intermolecular M···M interactions as indicated by metal–
41 metal distances greater than twice the Bondi’s van der Waals
42 radii (Ag: 3.44 Å and Au: 3.32 Å)13 in Figures S7–S8. Cyclic
43 trinuclear structures were slipped relative to one another to
44 give an overall stepwise structure. The averaged dihedral
45 angles between the phenyl group and pyrazole planes were
46 78.1 deg, ranging from 56.5 deg to 89.1 deg in [AgL1(Ph)]3,
47 and 78.3 deg ranging from 57.0 deg to 89.3 deg in
48 [AuL1(Ph)]3. These values are larger than those in the
49 corresponding ligand (61.14(5) deg) because of the trinuclear
50 formation. No common, irregular pattern was observed in the
51 lattices of complexes involving the L1(Naph)H ligand
52 (Figures S9–S10). Averaged dihedral angles between
10 pseudo dimer structures (Figure S4). The dihedral angles
11 between the aryl group and pyrazole planes were 61.14(5)
12 deg in L1(Ph)H and 60.63(4) deg in L1(Naph)H.
13
On complexation, cyclic trinuclear structures were
14 obtained and their solid-state structures analyzed by X-ray
15 crystallographic analysis. A comparison of the averaged M–
16 N bond distances and the averaged intramolecular M···M
17 interaction (av. Ag–N, 2.064(1) Å and av. Ag···Ag,
18 3.4331(6) Å in [AgL1(Ph)]3 (Figure 1), av. Au–N, 2.002(2)
19 Å and av. Au···Au, 3.3500(7) Å in [AuL1(Ph)]3 (Figure 1),
20 av. Ag–N, 2.065(5) Å and av. Ag···Ag, 3.4302(7) Å in
21 [AgL1(Naph)]3 (Figures 1 and S5), and av. Au–N, 1.987(3)
22 Å and av. Au···Au, 3.3447(8) Å in [AuL1(Naph)]3 (Figures
23 1 and S6)) revealed an interesting trend resulting from the
24 differences in the M–N distances (Au–N < Ag–N) and in the
25 ionic radii (Au(I) < Ag(I)) due to relativistic effects.11,12 The
26 intramolecular M···M interactions were almost twice the
27 Bondi’s van der Waals radius (Ag: 3.44 Å and Au: 3.32 Å),13
28 indicating only very weak metallophilic intramolecular
29 interactions. The bond angles of N–M–N (av. N–Ag–N,

3
250
200
150
100
50
200
150
100
50
83K
173K
298K
83K
173K
298K
0
0
300
350
400
450
500
550
600
650
300
350
400
450
500
550
600
650
Wavelength / nm
Wavelength / nm
1
2
3
Figure 2. Temperature dependent photoluminescence spectra at 83 K, 173 K, and 298 K in [AuL1(Ph)]3 (left) at 280 nm
excitation wavelength and [AuL1(Naph)]3 (right) at 320 nm excitation wavelength.
45 were observed on complexation. The bands for the silver(I)
4
5
6
7
8
9
the 1-naphthyl group and pyrazole planes were 84.4 deg
ranging from 78.1 deg to 87.1 deg in [AgL1(Naph)]3 and
80.9 deg ranging from 73.3 deg to 87.9 deg in
[AuL1(Naph)]3. The averaged dihedral angles in the
L1(Naph)H system were more obtuse than those in the
46 complexes were higher in energy than those of the gold(I)
47 complexes for both ligand systems.
48
Photoluminescence spectra from powdered samples of
49 the two ligands and four complexes are shown in Figures 2,
50 S15–S20. Spectra were acquired at variable excitation
51 wavelengths and at three different temperatures (83, 173,
52 ands 298 K). Aryl based photoluminescent emissions were
53 observed for L1(Ph)H (~330 nm at 280 nm excitation) and
54 L1(Naph)H (~345 nm at 290 nm excitation) Vibrational fine
55 structure was observed at lower temperatures (Figures S15
56 and S18). Lower energy emissions at room temperature were
57 observed for the L1(Ph)H complexes at 645.5 nm (λex 280
58 nm) in [AgL1(Ph)]3 and 573 nm (λex 280 nm) in [AuL1(Ph)]3.
59 These lower energy emissions were attributed to metal-based
60 phosphorescence arising from closed shell d10-d10
61 intramolecular M···M interactions.4b,7c,15 Stepwise structures
62 were observed for the L1(Ph)H complexes and therefore
63 very weak intermolecular M···M interactions were expected
64 at low temperature. From this interaction, on cooling to lower
65 temperature, the maximum peaks were more intense and
66 shifted to higher energy, 400.5 nm in [AgL1(Ph)]3 and 396.5
67 nm in [AuL1(Ph)]3 with vibrational fine-structure. More
68 intense, higher energy emissions of 354.0 nm in
69 [AgL1(Naph)]3 and 345.0 nm in [AuL1(Naph)]3 were
70 observed at room temperature. Both bands grew more intense
71 at lower temperature without any change in wavelength.
72 These bands had some vibrational structure arising from
73 coordination of the L1(Naph)H ligand to the metal centers.
74 The irregular pattern structure in the lattice of the
75 L1(Naph)H complexes does not permit intermolecular
76 M···M interactions. Therefore, ligand-based emissions in the
77 higher energy region were more intense, arising from the
78 highly luminescent naphthyl group. At lower temperature,
79 very weak bands at 527.5 nm in [AgL1(Naph)]3 and 524.0
80 nm in [AuL1(Naph)]3 were observed.
10 L1(Ph)H system due to the bulkier 1-naphthyl group. Void
11 spaces were found in the irregular type lattice, and some
12 solvent molecules were incorporated in the unit cell (Figures
13 S5–S6).
14
15 metal complexes were quite different in chemical shift to
16 those of the corresponding ligands, indicating that M–N
17 coordination is retained in solution.
1
The H- and 13C- NMR signals of the cyclic trinuclear
18
In the L1(Ph)H system, the C=N stretching vibrations
19 in the cyclic trinuclear metal complexes were shifted to 1542
20 cm–1 from 1568 cm–1 in the corresponding pyrazole (Table
21 S3). The same tendency was observed in the L1(Naph)H
22 system, shifting the same stretching vibration to 1534 cm–1
23 (1533–1535 cm–1) from 1565 cm–1. These changes indicate
24 weakening of the C=N pyrazolyl bonds on complexation of
25 the two pyrazolyl nitrogens, with relative bond energies
26 L1(Ph)H system < L1(Naph)H system due to the larger aryl
27 group of the latter. Almost the same C=N bond energies were
28 observed between the silver(I) and gold(I) analogues bearing
29 the same ligand. Far–IR and FT–Raman spectra of the two
30 ligands and four complexes are shown in Figures S11–S12.
31 M–N stretching vibrations were observed in the 546 cm–1 to
32 512 cm–1 region as expected.4–5,14 The M–N stretching
33 vibrations were ~512 cm–1 for [AgL1(Ph)]3 and ~528 cm–1
34 for [AuL1(Ph)]3, consistent with the M–N bond lengths
35 discussed above. The corresponding values for the naphthyl
36 substituted complexes were ~538 cm–1 for [AgL1(Naph)]3
37 and ~546 cm–1 for [AuL1(Naph)]3, reflecting the greater
38 steric bulk of this substituent.
39
All electronic absorption bands measured in both
40 solution (cyclohexane) and the solid-state (nujol) were very
41 broad, mainly due to overlapping π-π* transition bands
42 associated with the aryl substituents and the pyrazolyl rings
43 (Table S4, Figures S13–S14). Higher energy absorption
44 bands due to metal to ligand charge transfer (MLCT) bands
81
In summary, we have designed and prepared new 4-aryl
82 substituted pyrazole ligands and the corresponding silver(I)
83 and gold(I) complexes, bearing luminescent phenyl and
84 naphthyl groups. The coordination environments were
85 different from previously reported analogues, with no

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1
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intermetallic interactions. Photoluminescent spectra were
dominated by ligand-based emissions. We are now preparing
other ligand systems towards new, highly luminescent
materials including some with metal–metal intermolecular
interactions.
6
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8
This work was supported by a JSPS KAKENHI grant
and by an Ibaraki University Priority Research Grant (K. F.).
9
10
Supporting
Information
is
available
on
11 http://dc.doi.org/10.1246/cl.xxxxxx.
12
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