Gold(I) and silver(I) mixed-metal trinuclear complexes: Dimeric products from the reaction of gold(I) carbeniates or benzylimidazolates with silver(I) 3,5-diphenylpyrazolate

Article abstract of DOI:10.1021/ic060792j

Trinuclear mixed-metal gold-silver compounds are obtained by the reaction of gold(I) carbeniate [Au(μ-C(OEt)= NC₆H₄-P-CH ₃)]₃, TR(carb), or gold(I) imidazolate [Au-μ-C,N-1-benzyl-2-imidazolate]₃, TR(bzim), with silver(I) pyrazolate [Ag(μ-3,5-Ph₂pz)]₃. The crystalline products are mixed-ligand, mixed-metal dimeric products [Au(carb)Ag₂(μ-3, 5-Ph₂pz)₂], [Au₂(carb)₂Ag(μ-3,5- Ph₂pz)]·CH₂Cl₂, [Au(bzim) ₂Ag₂(μ-3,5-Ph₂pz)], and [Au ₂(bzim)₂Ag(μ-3,5-Ph₂pz)]. They have been characterized by elemental analysis and ¹H NMR and mass spectrometry. The X-ray structure of [Au-(carb)Ag₂(μ-3,5-Ph₂pz) ₂] shows it to be a dimer with two Ag...Au contacts between the trinuclear units of 3.083(2) and 3.310(2) A and with average intramolecular Ag...Ag and Au...Ag distances of ～3.3 and 3.2 A, respectively. The structure of [Au₂(carb) ₂Ag(μ-3,5-Ph₂pz)]·CH₂Cl₂ is a dimer with one intermolecular Au...Au attraction of 3.3354-(10) A and a short Ag...Au distance of ～3.42 A and intramolecular Ag...Au and Au...Au contacts of ～3.2 and ～3.3 A, respectively. Packing diagrams of both complexes show that the dimeric units are independent, similar to their parent molecules. The dimers of trinuclear [Au(carb)Ag₂(μ-3,5-Ph₂pz)₂] and [Au₂(carb)₂Ag(μ-3,5-Ph₂pz)]·CH ₂-Cl₂ crystallize in the triclinic space group P1 (Z = 2), a = 9.688(3) A, b = 15.542(4) A, c = 23.689(6) A, α = 82.560(5)°, β = 87.887(6)°, γ = 78.060(5)°, and the orthorhombic space group Pca2₁ (Z= 4), a = 29.644(4) A, b = 7.4582(10) A, c = 30.473(4) A, respectively. The structure of [Au(bzim)Ag₂(μ-3,5-Ph₂pz)₂] is a dimer with two metallophilic Ag...Au interactions of 3.14 A. The complex crystallizes in the monoclinic space group C2/c (Z = 4), a = 26.368(5) A, b = 15.672(3) A, c = 17.010(3) A, β = 102.206(3)°.

Full text of DOI:10.1021/ic060792j

Inorg. Chem. 2006, 45, 7770−7776
Gold(I) and Silver(I) Mixed-Metal Trinuclear Complexes: Dimeric
Products from the Reaction of Gold(I) Carbeniates or
Benzylimidazolates with Silver(I) 3,5-Diphenylpyrazolate†
Ahmed A. Mohamed,‡ Rossana Galassi,§ Fabrizio Papa,§ Alfredo Burini,*,§ and John P. Fackler, Jr.*,‡
Laboratory for Molecular Structure & Bonding, Department of Chemistry, Texas A&M UniVersity,
College Station, Texas 77843-3255, and Dipartimento di Scienze Chimiche, UniVersity of
Camerino, Via S. Agostino, 1-62032 Camerino, Italy
Received May 9, 2006
Trinuclear mixed-metal gold
NC6H4-p-CH3)]3, TR(carb), or gold(I) imidazolate [Au-
[Ag( -3,5-Ph2pz)]3. The crystalline products are mixed-ligand, mixed-metal dimeric products [Au(carb)Ag2(
Ph2pz)2], [Au2(carb)2Ag( -3,5-Ph2pz)] CH2Cl2, [Au(bzim)2Ag2( -3,5-Ph2pz)], and [Au2(bzim)2Ag(
have been characterized by elemental analysis and 1H NMR and mass spectrometry. The X-ray structure of [Au-
(carb)Ag2( -3,5-Ph2pz)2] shows it to be a dimer with two Ag‚‚‚Au contacts between the trinuclear units of 3.083(2)
and 3.310(2) Å and with average intramolecular Ag‚‚‚Ag and Au‚‚‚Ag distances of 3.3 and 3.2 Å, respectively.
The structure of [Au2(carb)2Ag( -3,5-Ph2pz)] CH2Cl2 is a dimer with one intermolecular Au‚‚‚Au attraction of 3.3354-
(10) Å and a short Ag‚‚‚Au distance of 3.42 Å and intramolecular Ag‚‚‚Au and Au‚‚‚Au contacts of 3.2 and
3.3 Å, respectively. Packing diagrams of both complexes show that the dimeric units are independent, similar to
their parent molecules. The dimers of trinuclear [Au(carb)Ag2( -3,5-Ph2pz)2] and [Au2(carb)2Ag( -3,5-Ph2pz)] CH2-
Cl2 crystallize in the triclinic space group P1 (Z 2), a 9.688(3) Å, b 23.689(6) Å, R )
82.560(5) â ) 87.887(6) γ ) 78.060(5) , and the orthorhombic space group Pca21 (Z 4), a 29.644(4)
Å, b 7.4582(10) Å, c 30.473(4) Å, respectively. The structure of [Au(bzim)Ag2(
two metallophilic Ag‚‚‚Au interactions of 3.14 Å. The complex crystallizes in the monoclinic space group C2/c (Z
4), a 26.368(5) Å, b 15.672(3) Å, c 17.010(3) Å, â ) 102.206(3)
−
silver compounds are obtained by the reaction of gold(I) carbeniate [Au(
µ
-C(OEt)
d
µ-C,N-1-benzyl-2-imidazolate]3, TR(bzim), with silver(I) pyrazolate
µ
µ
-3,5-
µ
‚
µ
µ-3,5-Ph2pz)]. They
µ
∼
µ
‚
∼
∼
∼
µ
µ
‚
h
°
)
)
)
15.542(4) Å, c
)
)
°
,
°
,
)
)
)
µ-3,5-Ph2pz)2] is a dimer with
)
)
)
)
°.
Introduction
their increased activity, resistance to poisoning, and selectiv-
ity.4 Recently, molecular materials with gold and silver
nanoclusters and nanowires have been synthesized. These
Attention has been given to the syntheses and properties
of bimetallic clusters because of their unique catalytic,1
optical, and electronic properties.2 Small gold-silver clusters
(nanomaterials) have been found to be highly effective in
catalysis and medicine.3 The silver-gold clusters proved to
be more effective catalysts than the pure metals because of
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* To whom correspondence should be addressed. E-mail:
fackler@mail.chem.tamu.edu (J.P.F.).
† Dedicated to the memory of Prof. Bianca Rosa Pietroni.
‡ Texas A&M University.
§ University of Camerino.
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7770 Inorganic Chemistry, Vol. 45, No. 19, 2006
10.1021/ic060792j CCC: $33.50
© 2006 American Chemical Society
Published on Web 08/19/2006

Au(I) and Ag(I) Mixed-Metal Trinuclear Complexes
Chart 1. Trinuclear Carbeniate, TR(carb) (1), Benzylimidazolate, TR(bzim) (2), and Pyrazolate (3), Starting Materials
materials are considered to be good candidates for electronic
nanodevices and biosensors.5
We have shown that trinuclear gold(I) compounds such
as 1 and 2 interact with Lewis acid salts such as silver(I)
and thallium(I) to form chains in which the cation interacts
with the trinuclear gold(I) compounds in a [(Au3Au3MAu3-
Au3)M]n (M ) Tl+ or Ag+, Au3 ) TR(carb) or TR(bzim))
pattern.12 Treatment of the TR(carb) or TR(bzim) with AgBF4
or TlPF6 results in the formation of yellow crystals of these
sandwich compounds in which the trinuclear units surround
the silver or thallium ion with M‚‚‚Au distances ranging from
2.7 to 3.0 Å.
Current understanding of the chemistry of neutral trinuclear
cyclic gold complexes6 includes the synthesis and structure
of complexes that contain ancillary ligands, [Au(C,N)]3 or
[Au(N,N)]3, where [Au(C,N)]3 is a carbeniate, TR(carb), such
as 1, or a benzylimidazolate, TR(bzim), such as 2, and [Au-
(N,N)]3 is a pyrazolate, like the [Ag(N,N)]3 shown as 3, Chart
1.7-10 The structure of {[Au{µ-C(OMe)dN(CH3)}]3}n was
reported first as an infinite trigonal column with extensive
intermolecular Au‚‚‚Au interactions, not known to exist in
other related structures.11 The material now is known to show
several crystalline oligomeric polymorphs. Balch reported
that the columnar {[Au{µ-C(OMe)dN(CH3)}]3}n also dis-
plays a novel phenomenon he has described as solvolumin-
escence.11a Crystals of this material show a long-lived
photoluminescence that is readily detected by the human eye
for tens of seconds after cessation of irradiation. Addition
of a drop of dichloromethane or chloroform to previously
irradiated crystals produces a bright burst of light. This
phenomenon does not occur with the other polymorphs of
this gold(I) carbeniate.11b,c
The reaction of trinuclear gold(I) compounds TR(carb) or
TR(bzim) with trinuclear Hg(II) complex [Hg(C6F4)]3 forms
a repeat pattern of [Au3Hg3Au3Hg3] (Au3 ) TR(carb) or TR-
(bzim), Hg3 ) [Hg(C6F4)]3), with Hg‚‚‚Au distances of ∼3.2
Å.13 The trinuclear gold(I) units are isolated from each other
with no intermolecular Au‚‚‚Au interactions. A similar
arrangement has been found in π acid A, π base B
14
compounds, isolated with C6F6 and C10F8 intercalated
between trinuclear carbeniate or benzylimidazolate units.
With the organic π-acid TCNQ, an AB2AB2 pattern of acid-
base interaction is observed. With nitrofluorenones, Balch
also observed both patterns, i.e., ABAB and AB2AB2.8d
Unpublished DFT calculations from our laboratory suggest
that the π basicity of [TR(carb)]2 is about 50% greater than
for the [TR(carb)] alone.
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Inorganic Chemistry, Vol. 45, No. 19, 2006 7771

Mohamed et al.
acquisition of the data was performed by scanning in ranges from
100 to 1500 and 1400 to 3000 amu. Attempts to obtain good spectra
using electrospray techniques were not as successful. Elemental
analyses were carried out with a Carlo Erba 1106 elemental
microanalyzer. 1H NMR spectra were performed in CD3CN solution
on Varian VXR-300 spectrometers. Referencing is relative to TMS
(1H). Emission spectra were recorded on a SLM AMINCO model
8100 spectrofluorometer equipped with a xenon lamp. Spectra were
corrected for instrumental response. Solid-state low-temperature
measurements were made using a cryogenic sample holder of local
design. Powder samples were attached to the holder with a mixture
of copper powder, cryogen oil (used for mounting crystals for X-ray
structures), and collodion (an ether- and alcohol-soluble transparent
nitrocellulose). The glue was scanned for a baseline subtraction.
Liquid nitrogen was used to obtain the 77 K measurements.
Various bimetallic gold-silver clusters have been syn-
thesized during the past decade.15-23 AunAgm, AunPtm, and
even AunAgmPto carbonyl clusters21 have been prepared and
characterized crystallographically. Fackler et al.22 reported
the bridged mixed-metal [AuAg(mtp)2] (mtp ) diphenyl-
methylenethiophosphinate) several years ago. Unbridged,
base-free gold-silver polymeric chains such as [{AgAu-
(C6F5)2(THT or benzene)}n],19 [{Au3(µ-bzim-N3,C2)3}2Ag],12
[Ag2Au2(CH2PPh3)4(ClO4)4],20 and the base-stabilized com-
plex23 [AgAu4(CH2SiMe3)4(µ-dppm)2][CF3SO3] are known.
A Au-Ag complex that is three-coordinate at each metal
center, [AuAg(dpim)3]2+ (dpim ) 2-(diphenylphosphino)-
1-methylimidazole), has been reported by Catalano.21c
In this paper, we describe the synthesis of mixed-metal
trinuclear gold-silver complexes by the direct reaction of
gold(I) carbeniate (1) and gold(I) benzylimidazolate (2) with
the silver(I) pyrazolate complex (3). The complexes [Au-
(carb)Ag2(µ-3,5-Ph2pz)2] (4), [Au2(carb)2Ag(µ-3,5-Ph2pz)]‚
CH2Cl2 (5), and [Au(bzim)Ag2(µ-3,5-Ph2pz)2] (6) have been
characterized by X-ray crystallography. A communication
describing these mixed-metal complexes has appeared.24
Synthesis of [Au(carb)Ag2(µ-3,5-Ph2pz)2] (4). An 80 mg (0.40
mmol) sample of 3 is dissolved in 5 mL of dichloromethane. A 44
mg (0.20 mmol) sample of 1 is added to the solution of 3, and the
mixture is stirred for 1 h at room temperature. The colorless solution
forms a white precipitate after layering the sample with hexanes
or ether. Yield: 106 mg, 86%. X-ray quality crystals are grown by
very slow evaporation from dichloromethane over a few weeks.
Layering the solution with ether or hexanes gives thin crystals of
a lower crystallographic quality. Mp: 207-210 °C. Anal. Calcd
for C80H68N10Ag4Au2O2: C, 47.41; H, 3.38; N, 6.91. Found: C,
46.72; H, 3.39; N, 6.72. APCI-MS (m/z, positive field): 1046.9,
301.1, 221.1; (m/z, negative field) 1047.8, 1080.9, 863.7. 1H NMR
(CDCl3, 293 K): δ 1.05 (m, 3H), 2.3 (s, 3H), 4.13 (m, 2H), 6.8 (s,
1H), 6.95 (s, 1H), 7.0-7.4 (m, 17 H), 7.6-7.83 (m, 7H).
Experimental Section
General. Unless otherwise noted, all reactions and manipulations
were carried out under an inert atmosphere with a positive nitrogen
gas flow, using standard Schlenk techniques. Dichloromethane was
distilled over P4O10. Chemicals were purchased from Aldrich
Chemical Co. and used as received. The mass spectrometer used
in all the analyses involving APCI, atmospheric pressure chemical
ionization, was the Hewlett-Packard 1100 MSD; the software
employed was that included in the Work-Station HP package. The
experimental conditions are as follows: organic phase flow, 300
µL/min; drying gas flow (N2), 10 L/min; nebulization pressure, 30
psig; temperature of the drying gas, 350 °C; capillary potential,
4000 V. The value for the fragmentor was fixed to 30 and the
Synthesis of [Au2(carb)2Ag(µ-3,5-Ph2pz)]‚CH2Cl2 (5). We used
a procedure similar to that used for 4 but with a 2:1 stoichiometry
of 1:3. X-ray quality crystals are grown by slow evaporation from
a dichloromethane solution. Yield: 122 mg, 83%. Mp: 120-122
°C and changed to brown at 140 °C. Anal. Calcd for C71H72N8-
Ag2Au4O4Cl2: C, 39.19; H, 3.34; N, 5.15. Found: C, 39.26; H,
3.52; N, 5.16. APCI-MS (m/z, positive field): 1298.1, 1164.0,
1119.1, 1078.1, 1046.9, 1001.0, 221.1; (m/z, negative field) 1168.8,
1
1111.9, 1080.9, 1034.9, 865.8. H NMR (CDCl3, 293 K): δ 1.15
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P.; Beurskens, G.; Smits, J. M. M.; Beurskens, P. T.; Steggerda, J. J.
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(m, 6H), 2.32 (s, 6H), 4.24 (m, 4H), 6.82-7.2 (m, 8H), 7.26-7.41
(m, 7H), 7.78-7.95 (m, 4H).
Synthesis of [Au(bzim)Ag2(µ-3,5-Ph2pz)2] (6). Following a
procedure analogous to the synthesis of 4, we obtained compound
6 in 51% yield. Mp: 248-250 °C. Anal. Calcd for C80H62N12Ag4-
Au2: C, 47.64; H, 3.1; N, 8.33. Found: C, 46.56; H, 3.07; N,
7.97.1H NMR (CDCl3, 293 K): δ 4.94 (s, 1.5H), 5.16 (s, 0.5H),
6.0-8.0 (m, 29H).
Synthesis of [Au2(bzim)2Ag(µ-3,5-Ph2pz)] (7). Following a
procedure analogous to the synthesis of 5, we obtained compound
7 in 32% yield. Mp: 163-166 °C. Anal. Calcd for C70H58N12Ag2-
Au4: C, 40.6; H, 2.82; N, 8.12. Found: C, 40.36; H, 2.87; N,
7.89.1H NMR (CDCl3, 293 K): δ 5.08 (s, 1.5H), 5.16 (s, 0.5H),
5.21 (s, 1.5H), 5.39 (s, 0.5H), 6.78-7.5 (m, 21H), 7.9-8.0 (m,
4H).
(19) (a) Uso´n, R.; Laguna, A.; Laguna, M.; Manzano, B. R.; Jones, P. G.;
Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1984, 285. (b) Uso´n,
R.; Laguna, A.; Laguna, M.; Jones, P. G.; Sheldrick, G. M. J. Chem.
Soc., Chem. Commun. 1981, 1097.
Data Collection. Data for 4-6 were collected using a Siemens
(Bruker) SMART CCD (charge-coupled device)-based diffracto-
meter equipped with an LT-2 low-temperature apparatus operating
at 110 K. A suitable crystal was chosen and mounted on a glass
fiber using grease. Data were measured using ω scans of 0.3E per
frame for 60 s, such that a hemisphere was collected. A total of
1271 frames were collected, with a final resolution of 0.75 Å. The
first 50 frames were recollected at the end of data collection to
monitor for decay. Cell parameters were retrieved using SMART
(20) Uso´n, R.; Laguna, A.; Laguna, M.; Jones, P. G.; Erdbru¨gger, C. F.
Organometallics 1987, 6, 1778.
(21) (a) Tran, N. T.; Powell, D. R.; Dahl, L. F. Dalton Tans. 2004, 209.
(b) Tran, N. T.; Powell, D. R.; Dahl, L. F. Dalton Tans. 2004, 217.
(c) Catalano, V. J.; Horner, S. J. Inorg. Chem. 2003, 42, 8430.
(22) Rawashdeh-Omary, M. A.; Omary, M. A.; Fackler, J. P., Jr. Inorg.
Chim. Acta 2002, 334, 376.
(23) Contel, M.; Garrido, J.; Gimeno, M. G.; Laguna, M. J. Chem. Soc.,
Dalton Trans. 1998, 1083.
(24) Mohamed, A. A.; Burini, A.; Fackler, J. P., Jr. J. Am. Chem. Soc.
2005, 127, 5012.
7772 Inorganic Chemistry, Vol. 45, No. 19, 2006

Au(I) and Ag(I) Mixed-Metal Trinuclear Complexes
Table 1. Crystal Data, Data Collection, and Structure Refinement for
4-6
Table 3. Selected Bond Distances and Angles of Complex 5
Bond Distances (Å)
4
5
6
Au(1)‚‚‚Au(2)
Au(1)‚‚‚Au(3)
Au(3)‚‚‚Ag(2)
Au(4)‚‚‚Ag(2)
Au(1)-N(1)
3.2746(11) Au(1)‚‚‚Ag(1)
3.3354(10) Au(2)‚‚‚Ag(1)
3.2169(17) Au(3)‚‚‚Au(4)
3.2456(17) Au(1)-C(32)
2.065(15) Ag(2)-N(8)
3.2803(16)
3.2427(16)
3.3411(11)
1.982(18)
2.057(15)
empirical formula
C80H68Ag4Au2- C71H72Ag2Au4- C80H62Ag4-
N10O2
2026.87
110(2)
0.71073
Triclinic
P1h
9.688(3)
15.542(4)
23.689(6)
82.560(5)
87.887(6)
78.060(5)
3460.4(16)
2
Cl2N8O4
2175.89
Au2N12
2016.84
fw
T (K)
wavelength (Å)
cryst syst
space group
a (Å)
110(2)
110(2)
Bond Angles (deg)
0.71073
Orthorhombic
Pca21
29.644(4)
7.4582(10)
30.473(4)
0.71073
Monoclinic
C2/c
26.368(5)
15.672(3)
17.010(3)
C(32)-Au(1)-N(1)
Ag(1)‚‚‚Au(2)‚‚‚Au(1) 60.44(3)
Au(2)‚‚‚Ag(1)‚‚‚Au(1) 60.26(3)
177.5(6)
Au(2)‚‚‚Au(1)‚‚‚Ag(1) 59.30(3)
N(2)-Ag(1)-N(3) 173.7(6)
Ag(2)‚‚‚Au(3)‚‚‚Au(1) 93.98(3)
b (Å)
c (Å)
Table 4. Selected Bond Distances and Angles of Complex 6
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
Bond Distances (Å)
102.206(3)
Ag(1)‚‚‚Ag(2)
Ag(1)-N(3)
Au(1)-N(1)
3.3516(8)
2.085(5)
2.060(5)
Au(1)‚‚‚Ag(1A)
Au(1)-C(31)
3.1423(8)
1.995 (6)
6737.3(16)
4
6870(2)
4
D
calcd (mg/m3)
1.944
5.390
0.764
2.145
9.382
1.019
1.950
5.428
1.082
Bond Angles (deg)
abs coeff (mm-1
)
C(31)-Au(1)-N(1)
Ag(2)-N(4)-N(3)
174.7(2)
116.8(3)
N(2)-Ag(1)-N(3)
170.27(19)
GOF on F2
R1, wR2 [I > 2σ(I)] 0.0721, 0.1249 0.0597, 0.1332 0.0433, 0.0781
Table 2. Selected Bond Distances and Angles of Complex 4
stoichiometric ratios of 1:2 and 2:1 produced complexes 4-7.
A colorless solution forms from the mixing of 1 or 2 with
3, whereas a yellow suspension forms when a solution of
Ag[PF6] reacts with 1. Reactions occur rapidly, and evapora-
tion of a drop from the reaction mixture on a filter paper
within a few minutes of mixing produces a spot that gives a
strong green or orange luminescence under a hand-held UV
lamp. Crystals were grown by slow evaporation from a CH2-
Cl2 solution over a few weeks. The crystalline products were
not the expected acid-base adducts but rearranged dimeric,
trinuclear products. Thus [Ag(µ-3,5-Ph2pz)]3 behaves dif-
ferently from the π-acid complex [Hg(C6F4)]3 reported by
Gabbai.30 It is suspected that the lability of the M-N bond
(M ) Au, Ag) in these complexes results in the subsequent
cleavage of the cyclic complexes to produce the product
statistically expected from the stoichiometry of materials
used. Thus the mixed metal products [Au(carb)Ag2(µ-3,5-
Ph2pz)2] (4), [Au2(carb)2Ag(µ-3,5-Ph2pz)]‚CH2Cl2 (5), [Au-
(bzim)Ag2(µ-3,5-Ph2pz)2] (6), and [Au2(bzim)2Ag(µ-3,5-
Ph2pz)] (7) crystallize from the medium.
Bond Distances (Å)
Au(1)-C(38)
Au(1)-N(1)
Au(1)‚‚‚Ag(2)
Au(1)‚‚‚Ag(4)
Au(2)‚‚‚Ag(1)
1.960(18)
2.011(17)
3.2663(19) Ag(1)‚‚‚Ag(2)
3.311(2)
3.082(2)
Au(2)‚‚‚Ag(4)
3.2136(19)
2.003(15)
3.285(2)
2.099(17)
3.283(2)
Ag(1)-N(2)
Ag(2)-N(4)
Ag(3)‚‚‚Ag(4)
Bond Angles (deg)
N(4)-Ag(2)-N(5)
174.9(6)
Au(1)‚‚‚Ag(2)‚‚‚Ag(1) 62.62(4)
C(38)-Au(1)-N(1) 176.2(7)
C(78)-Au(2)-N(9) 176.9(7)
Ag(2)‚‚‚Au(1)‚‚‚Ag(4) 65.96(5)
N(2)-Ag(1)-N(3)
171.8(6)
N(7)-Ag(3)-N(8)
N(6)-Ag(4)-N(10) 164.5(6)
172.9(7)
Au(2)‚‚‚Ag(4)‚‚‚Ag(3) 63.41(5)
N(5)-C(38)-Au(1) 121.4(13)
software and refined using SAINT on all observed reflections.25
Data reduction was performed using the SAINT software, which
corrects for Lp and decay.26 Absorption corrections were applied
using SADABS, supplied by George Sheldrick.27 The structures
are solved by the direct method using the SHELXS-97 program
and refined by the least-squares method on F2, SHELXL-97,
incorporated in SHELXTL-PC V 5.03.28,29
The structures of 4-6 were solved in the triclinic, orthorhombic,
and monoclinic space groups P1h, Pca21, and C2/c, respectively,
by analysis of systematic absences. The Flack parameter for 5 is
0.000(9). All non-hydrogen atoms are refined anisotropically.
Hydrogen atoms were calculated by geometrical methods and
refined as a riding model. The crystallographic details are given in
Table 1, and bond distances and angles are listed in Tables 2-4.
The products also were analyzed using X-ray powder
diffraction, and the patterns were compared with the patterns
generated from the single-crystal data. The compounds are
stable in the solid state at room temperature. The IR spectra
do not show major changes from the starting materials in
the range 4000-600 cm-1. The complexes are very soluble
in most organic solvents, which make them very good
candidates for catalytic studies. Preliminary catalysis results
show that these complexes form nanoclusters on a TiO2
surface upon reduction and calcination.31 Resulting mixed-
metal clusters have been found to be active to room-
temperature CO oxidation in air. Most of the molecular
gold-silver complexes reported to date contains metal
centers coordinated to phosphorus and sulfur-donor ligands.
These ancillary ligands are often poisonous to catalysis,
making their applications limited.
Results and Discussion
Synthesis. On the basis of the fact that π-acids interact
with trinuclear gold(I) pi-bases TR(carb) and TR(bzim), we
reacted trinuclear 3,5-diphenylpyrazolate silver(I) complex
3 with each of them. Mixing 1 or 2 with 3 in CH2Cl2 in
(25) SMART Software for the CCD Detector System, version 4.043; Bruker
Analytical X-ray Systems: Madison, WI, 1995.
(26) SAINT Software for the CCD Detector System, version 4.035; Bruker
Analytical X-ray Systems: Madison, WI, 1995.
(27) Blessing, R. H. SADABS Program for Absorption Corrections Using
Siemens CCD Based on the Method of Robert Blessing. Acta
Crystallogr., Sect. A 1995, 51, 33.
(28) Scheldrick, G. M. SHELXS-97, Program for the Solution of Crystal
Structure; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(29) SHELXTL 5.03 (PC Version), Program Library for Structure Solution
and Molecular Graphics; Bruker Analytical X-ray Systems: Madison,
WI, 1995.
(30) Haneline, M. R.; Gabbai, F. P. Angew. Chem., Int. Ed. 2004, 43, 5471.
(31) Chusuei, C. C.; Lai, X.; Davis, K. A.; Bowers, E. K.; Fackler, J. P.;
Goodman, D. W. Langmuir 2001, 17, 4113.
Inorganic Chemistry, Vol. 45, No. 19, 2006 7773

Mohamed et al.
The stability of compounds 4 and 5 in solution is also
highlighted by APCI mass spectrometry. The parent ions
have been observed for both compounds as adducts with
solvents, protons, and chloride ions, both as positive and
negative ions. The metallocyclic rings are incompletely
rearranged in methylene chloride/acetonitrile solutions, which
yield evidence for the starting compounds. Also, traces of
the dimer of trimers are detected in the range 1500-3000
1
amu. The H NMR spectra demonstrate the stability of the
heterometallocyclic rings, although the NMR patterns are
more complex than expected from the individual trinuclear
species. The ethoxy group of the carbeniate ligand in
complex 4 should exhibit a quartet and a triplet, and the
methylene group of the benzylimidazolate ligand in 6 should
be a singlet. What is observed is the superimposition of two
quartets and two triplets of different intensity for the ethoxy
of 4 and two singlets of different intensities for the methylene
group of 6. In complexes 5 and 7, the two carbeniate or
benzylimidazolate ligands are not magnetically equivalent.
The spectra for the ethoxy groups are a superimposition of
at least three quartets and three triplets of different intensities
resulting in resolved but crowded multiplets (assigned as
multiplets in the Experimental Section). For 7, four singlets
of different intensities are observed for the methylene groups
(CH2-Ph). By comparing these data and ruling out the
presence of starting materials, we can attribute the complexity
of the signals (in addition to the nonequivalences) to the
presence of dimeric structures in solution, as described in a
previous NMR study on analogous substrates.12c
Figure 1. ORTEP diagram of [Au(carb)Ag2(µ-3,5-Ph2pz)2]2, 4.
Gold(I) carbeniate-silver(I) pyrazolate complexes 4 and
5 give a green luminescence under a UV lamp, whereas gold-
(I) benzylimidazolate-silver(I) pyrazolate complexes 6 and
7 show an orange luminescence under UV lamp excitation
at room temperature. The emission spectra of 6 and 7 in the
solid state at 77 K show a strong emission centered at ∼460
nm with vibronic structure. It is an emission typical of ligand-
based excited-state spectra of Au(I) pyrazolates and ben-
zylimidazolates with a large Stokes’ shift. The excitation
centers around 275 nm. The vibronic separations are sug-
gestive of CdN and NdN stretching modes. The emission
spectra of these four complexes will be reported and
discussed in a future paper.
Molecular Structures. X-ray Structure of 4. The struc-
ture of [Au2(carb)2Ag4(µ-3,5-Ph2pz)4] (4; Figure 1) is not
32
unlike that reported for the dimer of 3, [Ag3(µ-3,5-Ph2pz)3]2,
but it crystallizes with a different space group and a different
dimeric arrangement. The hairlike crystals of 4 belong to
the triclinic space group Pjı (Z ) 2), whereas [Ag3(µ-3,5-
Ph2pz)3]2 crystallizes in the monoclinic space group C2/c.
The two trinuclear moieties of the dimer of 3 are rotated
anti to each other, but this arrangement is less apparent in
4. The shortest Ag‚‚‚Ag interactions within the metallocycle
rings of the dimer of 3 are ca. 3.4 Å, whereas between the
trinuclear units. the Ag‚‚‚Ag distance is 2.9712(14) Å. The
Au‚‚‚Ag distances between trinuclear units in 4 are 3.311-
(2) and 3.082(2) Å (Table 2). There are no short Au‚‚‚Au
Figure 2. Top: ORTEP diagram of an asymmetric unit of [Au2(carb)2-
Ag(µ-3,5-Ph2pz)]2, 5. Bottom: Packing diagram.
or Ag‚‚‚Ag interactions. The metallocycles in 4 are irregular
and puckered, similar to those in the dimer of 3, with a mean
deviation of 0.469 Å of the trinuclear units from a plane.
The packing diagrams of the dimer of 3 and 4 show
structurally independent dimeric units.
X-ray Structure of 5. The hairlike crystals of 5 crystallize
in the orthorhombic space group Pca21. The structure of 5
(Figure 2) shows one intermolecular interaction between the
trinuclear gold units, with a Au‚‚‚Au distance of 3.33 Å.
This is slightly longer than the Au‚‚‚Au distances, 3.224-
(32) Mohamed, A. A.; Perez, L. M.; Fackler, J. P., Jr. Inorg. Chim. Acta
2005, 358, 1657-1662.
7774 Inorganic Chemistry, Vol. 45, No. 19, 2006

Au(I) and Ag(I) Mixed-Metal Trinuclear Complexes
units similar to the distance observed6 in 1, 3.824 Å. The
N-M-N angle in 5 is 173.7°, with a lesser deviation from
linearity at the N-Au-C angle, 177.5°.
X-ray Structure of 6. The inter-trinuclear Au‚‚‚Ag
interaction in 6 is 3.1423(8) Å. The two benzyl groups are
perpendicular to the planes of the trinuclear units and hinder
further interactions between them, Figure 3. The intermo-
lecular distances in 6, Au‚‚‚Ag ) 3.53 and 3.38 Å and Ag‚
‚‚Ag ) 3.35 Å, are longer than those in the dimer of 4.
A few additional structural comparisons between the
homonuclear gold and silver complexes and the mixed gold
and silver complexes are of interest. In the dimer of the
trinuclear silver(I) 3,5-diphenylpyrazolate (3) the six silver
atoms are arranged as two triangles connected by only one
short interaction, Chart 2. This drastically changes when a
gold atom is introduced into the trinuclear unit as in 4. An
irregular square is formed by two Ag and two Au atoms
with M-M distances in the range 3.08-3.40 Å. The other
two silver atoms are above and below the plane of the square.
A metallophilicity is observed in 4 in which each of the two
gold atoms interact with three silver atoms. In 5, three Au
and one Ag form a nearly regular square with distances
ranging from 3.21 to 3.42 Å. The homonuclear, trinuclear
Au compounds generally form dimers with nearly perfect
squares, Au-Au ca. 3.2 Å, as seen in the structure of the
dimer of 1.
The Ag-Au distance in the trinuclear [{Au-µ-mesityl)-
AsPh3}2Ag]ClO4 is 2.7758(8) Å,15g which is shorter than all
Au-Ag distances in 3-5. In the bridged Ag-Au complex
{Ag(µ-dppm)2{Au(mesityl)}2]ClO4, the distances are 2.944-
(2) and 2.946(2) Å.15h The structure of the complex [Au2-
Ag2(C6F5)4(OCMe2)2]n forms infinite chains by repetition of
the Au2Ag2 core through short Au‚‚‚Au contacts of 3.1674-
(11) Å.15j The silver atoms in the main unit are bonded to
two gold atoms with Au-Ag distances of 2.7903(9) and
2.7829(9) Å. The two silver centers make a close contact of
3.1810(13) Å. The Au-Ag separations in the dinuclear
complexes are 2.8635(15) Å in the three-coordinate [AuAg-
(dpim)3]2+ (dpim ) 2-(diphenylphosphino)-1-methylimi-
dazole),21c 2.9124(13) Å in AgAu(MTP)2 (MTP ) diphen-
ylmethylenethiophosphinate),22 and 2.820(1) Å in [AuAg-
(dppy)2(ClO4)2] (dppy ) 2-(diphenylphosphino)pyridine).33
Laguna and Pyykko¨ studied theoretically the interactions in
the unsupported [Ag(pyridine)3][Au(C6F5)2]pyridine gold-
Figure 3. Top: ORTEP diagram of an asymmetric unit of [Au(TRbz)-
Ag2(µ-3,5-Ph2pz)2]2, 6. Bottom: Packing diagram.
3.299 Å, in the irregular and puckered nine-membered ring6
of the dimer of 1. The Au‚‚‚Ag distances in 5 are 3.22-
3.28 Å (Table 3). The average distance of the two closest
Au atoms between the trinuclear units of each dimer is 3.2
Å.
The metallocycles in 5 are irregular and puckered, similar
to those in the dimer of 1, but with a puckering smaller than
that in 4. The deviation from the mean plane of one of the
trinuclear units is 0.342 Å. A packing diagram (Figure 2)
shows a Au‚‚‚Au interaction, 3.857 Å, between the dimer
Chart 2 Intermetallic Arrangements of the Metal Atoms in the Dimers of 1, 3, 4, and 5
Inorganic Chemistry, Vol. 45, No. 19, 2006 7775

Mohamed et al.
silver chains.15i Here, the Ag‚‚‚Au bonding is largely formed
by electrostatic attraction and dispersion-type correlation
effects. The Ag‚‚‚Au interactions when the naked Ag(I) is
sandwiched between 1 or 2 are 2.73-2.92 Å.12
A series of vertex-sharing polyicosahedral phosphine Au-
Ag halide clusters have been reported by Teo.16 The general
synthesis of these “clusters of clusters” involves the reduction
of a mixture of PPh3AuX and PPh3AgX with NaBH4. The
metal-metal distances in the tri-icosahedral structure of
cluster [(PPh3)12Au12Ag13Cl6]m+ follow the trend of Au-Au
< Au-Ag < Ag-Ag.16a
The sum of the covalent radii of metallic gold and silver
is 2.89 Å. In the complexes reported here, the shortest
unbridged Ag-Au distance is 3.08 Å, and the shortest
bridged Ag-Au distance is 3.21 Å, in agreement with the
reported values of many other Ag-Au complexes.
dimers of planar, trinuclear complexes are readily formed
by mixing gold(I) carbeniates or gold(I) benzylimidazolates
with silver(I) pyrazolate in stoichiometric ratios. The com-
plexes retain the ligands associated with the metal atoms of
the starting materials. The clusters produced are similar in
their crystalline structure to the starting materials. Ligand-
bridged metal-metal distances display longer M-M dis-
tances than in the unbridged complexes. In the compounds
studied, the nonbridged intermolecular M-M distances
follow the order: Ag-Ag < Au-Ag < Au-Au, whereas
the intrametallocycle M-M distances with bridging-ligand
bonding follow the order Au-Au < Au-Ag < Ag-Ag.
The synthesis of these mixed gold-silver compounds
represents a new approach to cluster mixed-metal synthesis
with potential use in mixed-metal catalysis.
Acknowledgment. The Robert A. Welch Foundation of
Houston, Texas, and the University of Camerino, Italy, are
acknowledged for financial support.
Conclusions
As a result of the lability of Au-N and Ag-N bonds and
the stability of Au-C bonds, mixed-metal gold-silver
Supporting Information Available: X-ray crystallographic files
for 4-6 (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
(33) Olmos, M. E.; Schier, A.; Schmidbaur, H. Z. Naturforsch., B: Chem.
Sci. 1997, 52, 203.
IC060792J
7776 Inorganic Chemistry, Vol. 45, No. 19, 2006