Luminescent coordination polymers with extended Au(I)-Ag(I) interactions supported by a pyridyl-substituted NHC ligand

Article abstract of DOI:10.1016/j.jorganchem.2005.07.109

Reaction of [Ag(CH₃impy)₂]PF₆, 1, with Au(tht)Cl produces the monometallic Au(I)-species [Au(CH₃impy) ₂]PF₆, 2. Treatment of 2 with excess AgBF₄ in acetonitrile, benzonitrile or benzylnitrile produces the polymeric species {[AuAg(CH₃impy)₂(L)](BF₄)₂} _n, (L = CH₃CN,3; L = C₆H₅CN, 4; L = C₆H₅CH₂CN, 5) where the Au(I) centers remain bound to two carbene moieties while the Ag(I) centers are coordinated to two alternating pyridyl groups and a solvent molecule (L). Reaction of 2 with AgNO₃ in acetonitrile produces the zig-zag mixed-metal polymer {[AuAg(CH₃impy)₂(NO₃)]NO₃} _n, 6, that contains a coordinated nitrate ion in place of the coordinated solvent species. All of these polymeric materials are dynamic in solution and dissociate into their respective monometallic components. Compounds 2-6 are intensely luminescent in the solid-state and in frozen solution. All of these complexes were characterized by ¹H, ¹³C NMR, electronic absorption and emission spectroscopy and elemental analysis.

Full text of DOI:10.1016/j.jorganchem.2005.07.109

Journal of Organometallic Chemistry 690 (2005) 6041–6050
www.elsevier.com/locate/jorganchem
Luminescent coordination polymers with extended Au(I)–Ag(I)
interactions supported by a pyridyl-substituted NHC ligand
*
Vincent J. Catalano , Anthony O. Etogo
Department of Chemistry, University of Nevada, Reno, NV 89557, United States
Received 10 June 2005; accepted 29 July 2005
Available online 15 September 2005
Abstract
Reaction of [Ag(CH
3 2 6 3 2 6
impy) ]PF , 1, with Au(tht)Cl produces the monometallic Au(I)-species [Au(CH impy) ]PF , 2. Treatment of 2
with excess AgBF4 in acetonitrile, benzonitrile or benzylnitrile produces the polymeric species {[AuAg(CH impy) (L)](BF ) } ,
3
2
4 2 n
(
L = CH
Ag(I) centers are coordinated to two alternating pyridyl groups and a solvent molecule (L). Reaction of 2 with AgNO
produces the zig-zag mixed-metal polymer {[AuAg(CH impy) (NO )]NO } , 6, that contains a coordinated nitrate ion in place of the
3
CN,3; L = C
6
H
5
CN, 4; L = C
6
H
5
CH
2
CN, 5) where the Au(I) centers remain bound to two carbene moieties while the
3
in acetonitrile
3
2
3
3 n
coordinated solvent species. All of these polymeric materials are dynamic in solution and dissociate into their respective monometallic
components. Compounds 2–6 are intensely luminescent in the solid-state and in frozen solution. All of these complexes were character-
1
13
ized by H, C NMR, electronic absorption and emission spectroscopy and elemental analysis.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Coordination Polymer; Luminescence; Aurophilic; Carbene; Crystal Structures
1
. Introduction
these interactions, prominent among which are dispersion
forces and relativistic effects [6].
Attractive interactions between closed-shell metals have
The role of the former as the primary attractive force in
metallophilic interactions has only been recently clarified,
[7] whereas the latter has been known to play a significant
role in maintaining the aurophilic attraction between Au(I)
centers for quite some time [2,8]. In the case of mixed-metal
interactions, the dispersion forces are enhanced by the
introduction of dipolar interactions between dissimilar
metals, resulting in shorter metal–metal separations than
their respective homometallic species [9].
The luminescence attributed to these metal–metal inter-
actions makes complexes with such properties very attrac-
tive towards potential applications such as luminescent
display devices [10] and luminescent sensors for volatile
organic compounds (VOC)[1b,c,11]. Because of goldꢀs
strong affinity for phosphorus we and others have exten-
sively used chelating phosphines in the past as supports
for metallophilic interactions, [12,13] either by encapsulat-
ing closed-shell metal ions or atoms in metallocryptands,
received considerable attention in recent years [1]. Among
the most well-studied are the aurophilic attractions found
1
0
between d Au(I) centers [2]. To a lesser degree mixed-me-
tal interactions involving Ag(I)–Au(I) centers termed arg-
ento-aurophilic have been reported in the literature [3].
These non-bonding interactions are sufficiently strong to
overcome the anticipated Coloumbic repulsion between
like-charged metals, and extensive networks of cationic
complexes can be formed in the solid-state [4]. Short auro-
philic Au(I)–Au(I) interactions are also achievable through
aggregation of linear, two-coordinate gold monomers in
the solid-state or by the incorporation of bridging ligands
[
5]. Several theories have been advanced to rationalize
*
Corresponding author. Tel.: +1 775 784 1329; fax: +1 775 784 6804.
E-mail address: vjc@unr.edu (V.J. Catalano).
0
022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.109

6042
V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
2
+
or by forming multinuclear molecules with discrete auro-
philic Au(I)–Au(I) or argento-aurophilic Ag(I)–Au(I)
interactions. More recently we [9] and others [14] have
turned out attention to the now ubiquitous N-heterocyclic
carbene ligands [15] as possible supports for maintaining
group in each py im unit of the [AuAg(py im) ] coor-
2 2 2
dination core. In order to assess if the dynamic behavior
was a result of the silver exchanging between these two
sets of pyridyl in solution, we have now extended this
chemistry to the closely related, yet unsymmetrical,
mono-pyridyl-substituted ligand, [HCH impy]PF .
1
0
10
d –d interactions.
3
6
Earlier, we reported [16] the formation of a chiral
coordination polymer, using the NHC ligand precursor,
2. Results
1
,3-bis(2-pyridyl)-1H-imidazolium tetrafluoroborate [H-
(
py) im]BF as a support for stabilizing a Ag(I)–Au(I)
As shown in Scheme 2, the imidazolium salt [HCH im-
2
4
3
interaction. The simple reaction (Scheme 1) of the gold
monomer, [Au((py )im) ]BF with AgBF in acetonitrile
py]PF6, obtained by modifying a known procedure, [17]
was deprotonated with Ag O in CH Cl , readily forming
2
2
4
4
2
2
2
at room temperature or under reflux affords the helical
coordination polymer {[AuAg(py im) (CH CN)](BF ) }
4 2 n
the homoleptic [Ag(CH impy) ]PF complex, 1, in very
3 2 6
good yield and purity. Metathesis to the analogous
2
2
3
with extended and short metal–metal separations of
Au(I)-species [Au(CH impy) ]PF , 2, was accomplished
using a simple carbene transfer reaction with Au(tht)Cl in
3
2
6
˚
2
.8–2.9 A. In the solid-state this species is intensely lumi-
nescent; however, in solution this material dissociates
into its monometallic components. One notable feature
of this helical polymer is the uncoordinated pyridyl
either CH Cl or CH CN. Further treatment of 2 with ex-
2
2
3
cess AgBF in acetonitrile, benzonitrile and benzylnitrile
4
coordinates a metal to the uncoordinated pyridyl moieties
producing the polymeric species {[AuAg(CH impy) (L)]-
3
2
(
BF ) } , (L = CH CN,3; L = C H CN, 4; L = C H CH -
4 2 n 3 6 5 6 5 2
CN, 5). In these polymers the Au(I) centers remain bound
to two carbene moieties while the Ag(I) centers are coordi-
nated to two alternating pyridyl groups and a solvent mol-
ecule (L). Similarly, further treatment of 2 with AgNO in
3
acetonitrile results in the zig-zag mixed metal polymer
{
[AuAg(CH impy) (NO )]NO } , 6, that contains a coor-
3 2 3 3 n
dinated nitrate ion in place of the coordinated solvent spe-
cies. The formation of 3–6 is independent of reaction
temperature and stoichiometry; however, in solution these
materials dissociate into their respective monomeric com-
ponents (vide infra). Polymers 3–5 can be interconverted
by dissolving the solids in the appropriate nitrile solvent
and followed by precipitation with diethyl ether.
1
All of the aforementioned complexes were studied by H
NMR spectroscopy. In CD CN [H(CH impy)]PF displays
3
3
6
seven resonances, with the diagnostic singlet attributed to
the proton on the carbene carbon appearing at 9.26 ppm.
The remaining two protons on the backbone imidazole ring
Scheme 1.
Scheme 2.

V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
6043
resonate at 8.06 and 7.55 ppm while the methyl resonance
is observed at 3.96 ppm. Coordination to Ag(I) to form
Ag(CH impy) ]PF , 1, eliminates the downfield resonance
[
3
2
6
and shifts the imidazole backbone resonances to 7.82 and
.39 ppm. The methyl resonance, observed at 3.95 ppm is
nearly unchanged. Replacing the Ag(I) for Au(I) to form
Au(CH impy) ]PF 2, further shifts the imidazolium reso-
7
[
3
2
6
nances to 7.76 and 7.48 ppm, but only minimally affects the
methyl resonance which is now observed at 3.94 ppm. The
room temperature solution spectra (CD CN) of 3, 4, 5, and
3
6
are identical to that of 2 indicating that these polymers
readily dissociate the silver ion in solution at room temper-
ature leaving the pyridyl resonance unchanged relative to 2.
This exchange is facilitated by the presence of a donor sol-
vent like CH CN, and unfortunately, none of these poly-
3
mers are soluble enough in non-coordinating solvents to
acquire a spectrum. Low temperature NMR experiments
were equally disappointing, as the polymers precipitated
out of solution as the temperature was reduced.
Complexes 1–6 were additionally characterized by single
crystal X-ray diffraction. Crystallographic data are pre-
sented in Table 1. The colorless complex, [Ag(CH im-
3
ꢀ
py) ]PF , 1, crystallizes in the triclinic space group P1,
2
6
with one and one-half each of the cation and the hexaflu-
orophosphate anion residing in the asymmetric unit. The
remainder is related by a crystallographic center of inver-
sion. The structure of the cationic portion containing
Ag(1) is shown in Fig. 1 while selected bond distances
and angles are tabulated in Table 2. Metrically, these two
cations are nearly identical except for the relative orienta-
tions of the pyridyl rings and a small difference in the
C–Ag–C angles. Each Ag(1) center is nearly linearly coor-
dinated to two carbene ligands with C(10)–Ag(1)–C(1) and
C(19)–Ag(2)–C(19)#1 angles of 173.09(16)° and 180.00
(
19)°, respectively. The NHC ligands are oriented to oppo-
site sides of the Ag(I) cation with the imidazole portions
being nearly coplanar. The Ag(1)–C(1) and Ag(1)–C(10)
˚
separations measure 2.091(4) and 2.098(4) A, respectively,
while the corresponding Ag(2)–C(19) bond length is
˚
˚
2
.090(4) A. The Ag(1)Á Á ÁAg(2) contact is long at 7.329 A.
The analogous Au(I)-monomer [Au(CH impy) ]PF , 2,
3
2
6
crystallizes in the monoclinic space group P2 /c with one-
1
half of the cation and hexafluorophosphate counterion in
the asymmetric unit each of which resides on a crystallo-
graphic inversion center. As displayed in Fig. 2 this symme-
try makes the Au(I) center rigorously linear and the two
imidazole rings coplanar. The Au(1)–C(1) separation of
˚
2
.0184(14) A is slightly shorter the corresponding distance
in 1. Like 1 the two NHC ligands in 2 are oriented in a
head-to-tail fashion with the pyridyl groups rotated about
3
8.8 ° relative to the NHC portion of the ligand. There are
no short aurophilic contacts in 2, and the shortest
˚
Au(I)Á Á ÁAu(I) separation is very long at 7.24 A (see Table
3
).
Addition of AgBF to 2 in acetonitrile produces the
4
mixed-metal, zig-zag polymer, {[AuAg(CH impy) (NC-
3
2
CH )](BF ) } , 3, shown in Figs. 3 and 7. This material
3
4 2 n

6044
V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
Table 3
˚
Selected bond distances (A) and angles (°) for [Au(CH
3 2
impy) ]PF
6
, 2
Au(1)–C(1)
C(1)–N(1)
C(1)–N(2)
N(1)–C(2)
N(2)–C(3)
C(2)–C(3)
2.0184(14)
1.3632(17)
1.3506(18)
1.3830(17)
1.3844(18)
1.345(2)
C(1)–Au(1)–C(1A)
N(1)–C(1)–N(2)
Au(1)–C(1)–N(1)
Au(1)–C(1)–N(2)
C(1)–N(1)–C(4)–C(5)
180.0
104.37(11)
128.87(10)
126.71(10)
41.7(2)
crystallizes in the monoclinic space group P2 /c with the
1
Fig. 1. X-ray structural drawing (50%) showing the cationic portion of
Ag(CH impy) ]PF , 1, with hydrogen atoms removed for clarity. Only the
Ag(1) containing cation is shown.
asymmetric unit containing four metal atoms, four tetra-
fluoroborate anions and one acetonitrile solvate. Selected
bond distances and angles are presented in Table 4. The
[
3
2
6
1
0
10
d –d metal–metal separations are short with Au(1)–
Ag(1), Ag(1)–Au(2) and Au(2)–Ag(2) separations of
˚
2
.9239(6), 2.8912(6), and 2.8633(6) A, respectively. This
Table 2
˚
Selected bond distances (A) and angles (deg) for [Ag(CH
3
impy)
2
]PF
6
, 1
metallo-chain repeats into the next symmetric unit with
˚
an Ag(2)–Au(1A) separation of 2.8873(6) A. Three of the
Ag(1)–C(1)
Ag(1)–C(10)
Ag(2)–C(19)
C(1)–N(1)
2.091(4)
2.098(4)
2.090(4)
1.355(5)
1.368(5)
1.345(5)
1.370(5)
1.337(5)
1.367(5)
four intermetallic angles deviate significantly from linearity
with Au(1)–Ag(1)–Au(2) and Ag(1)–Au(2)–Ag(2) measur-
ing 175.37(3)° and 144.06(2)°, respectively, while the
Au(2)–Ag(2)–Au(1A) and Ag(1)–Au(1)–Ag(2A) measure
C(1)–N(2)
C(10)–N(4)
C(10)–N(5)
C(19)–N(7)
C(19)–N(8)
1
66.85(2) and 135.20(2)° each. Each Au(I) center is coordi-
nated to two NHC ligands in a nearly linear fashion
with typical separations (Au(1)–C(1) = 2.017(7),
C(10)–Ag(1)–C(1)
C(19)–Ag(2)–C(19A)
N(1)–C(1)–N(2)
N(4)-C(10)-N(5)
N(7)-C(19)-N(8)
C(1)–N(2)–C(4)–N(3)
C(10)–N(5)–C(13)–C(14)
C(19)–N(8)–C(22)–C(23)
173.09(19)
180
104.1(3)
103.7(3)
104.2(3)
0.4(6)
Au(1)–C(28) = 2.013(7), Au(2)–C(10) = 2.015(8), and
Au(2)–C(19) =2.007(7) A) while each Ag(I) center is three-
coordinated with two pyridyl moieties and one-coordinated
solvent molecule. Because of ring strain imposed by the
˚
6-membered dimetallacycle, the Ag–pyridyl separation are
41.4(6)
37.8(6)
slightly longer than the Ag–acetonitrile separation. The
Ag(1)–N(3) and Ag(1)–N(6) distances measure 2.306(6)
Fig. 3. X-ray structural drawing (40%) of the cationic portion of
Fig. 2. Thermal ellipsoid drawing (50%) of cationic portion of
Au(CH impy) ]PF , 2, with hydrogen atoms removed for clarity. Only
the crystallographically unique portion is labeled.
3 2 3 4 2 n
{[AuAg(CH impy) (NCCH )](BF ) } , 3, with carbon atoms drawn as
circles and hydrogen atoms removed for clarity. Only the asymmetric unit
is displayed. The extended polymer structure is presented in Fig. 7.
[
3
2
6

V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
6045
Fig. 6. X-ray structural drawing (50%) of the cationic portion of
[AuAg(CH impy) (NO )]NO , 6, with carbon atoms drawn as circles
and hydrogen atoms removed for clarity. Only the asymmetric unit is
displayed. The extended polymer structure is presented in Fig. 7.
{
3
2
3
3 n
}
Fig. 4. X-ray structural drawing (40%) of the cationic portion of
[AuAg(CH impy) (NCC )](BF , 4, with carbon atoms drawn as
circles and hydrogen atoms removed for clarity. Only the asymmetric unit
is displayed. The extended polymer structure is presented in Fig. 7.
{
3
2
6
H
5
4 2 n
) }
Fig. 5. X-ray structural drawing (40%) of the cationic portion of
{
3 2 2 6 5 4 2 n
[AuAg(CH impy) (NCCH C H )](BF ) } , 5, with carbon atoms drawn
as circles and hydrogen atoms removed for clarity. Only the asymmetric
unit is displayed. The extended polymer structure is presented in Fig. 7.
˚
and 2.376(7) A while the Ag(1)–N(13) is shorter at
˚
2
.193(7) A. Likewise, the Ag(2)–N(9) and Ag(2)–N(12) sep-
˚
arations are 2.304(6) and 2.245(7) A, respectively, and the
Ag(2)–N(14) bond distance is shorter at 2.238(7) A. The
˚
metal–ligand angles around Ag(1) and Ag(2) range from
1
00.7(2)° to 138.3(2)° but sum to 359.9° and 359.5°, respec-
tively indicating a planar environment.
Replacing the acetonitrile solvent with benzonitrile pro-
duces a similar polymer {[AuAg(CH impy) (NCC H )]
3
2
6
5
(
BF ) } , 4, whose structure is depicted in Figs. 4 and 7.
4 2 n
Fig. 7. Crystal structure drawing of the extended polymeric chains of 3
Selected bond distances and angles are shown in Table 5.
(top)–6 (bottom) with carbon atoms drawn as circles and hydrogen atoms
Unlike 3 this material crystallizes in the chiral space group
removed for clarity.

6046
V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
Table 4
Selected bond distances (A) and angles (°) for {[AuAg(CH
NCCH )](BF , 3
Table 5
Selected bond distances (A) and angles (°) for {[AuAg(CH
(NCC )](BF , 4
˚
˚
3
impy)
2
-
3 2
impy) -
(
3
4
)
2
}
n
6
H
5
4 2 n
) }
Au(1)–Ag(1)
Ag(1)–Au(2)
Au(2)–Ag(2)
2.9239(6)
2.8912(6)
2.8633(6)
2.8873(6)
2.017(7)
2.013(7)
2.015(8)
2.007(7)
2.306(6)
2.376(7)
2.193(7)
2.304(6)
2.245(7)
2.238(7)
Au(1)–Ag(1)
Ag(1)–Au(1A)
Au(1)–C(1)
Au(1)–C(10)
Ag(1)–N(3)
Ag(1)–N(6)
Ag(1)–N(7)
2.835(1)
2.833(1)
2.011(8)
2.021(8)
2.265(7)
Au(1)–Ag(2A)
Au(1)–C(1)
Au(1)–C(28)
Au(2)–C(10)
Au(2)–C(19)
Ag(1)–N(3)
Ag(1)–N(6)
Ag(1)–N(13)
Ag(2)–N(9)
Ag(2)–N(12)
Ag(2)–N(14)
2.268((7)
2.273(10)
C(1)–Au(1)–Ag(1)–N(3)
C(1)–N(2)–C(4)–N(3)
Ag(1A)–Au(1)–Ag(1)
Au(1)–Ag(1)–Au(1A)
C(1)–Au(1)–C(10)
N(3)–Ag(1)–N(6)
67.7(3)
48.1(10)
162.429(8)
179.86(4)
174.3(3)
137.1(2)
112.0(4)
110.9(5)
73.6(3)
105.3(2)
78.83(18)
101.22(19)
90.0(3)
N(3)–Ag(1)–N(7)
N(6)–Ag(1)–N(7)
C(1)–Au(1)–Ag(1)–N(3)
N(6)–Ag(1)–Au(2)–C(10)
C(19)–Au(2)–Ag(2)–N(9)
C(1)–N(2)–C(5)–N(3)
C(10)–N(5)–C(14)–N(6)
C(19)–N(8)–C(23)–N(9)
Au(1)–Ag(1)–Au(2)–Ag(2)
Au(1)–Ag(1)–Au(2)
Ag(1)–Au(2)–Ag(2)
Au(2)–Ag(2)–Au(1A)
Ag(2A)–Au(1)–Ag(1)
C(1)–Au(1)–C(28)
C(10)–Au(2)–C(19)
N(3)–Ag(1)–N(6)
N(3)–Ag(1)–N(13)
N(6)–Ag(1)–N(13)
N(9)–Ag(2)–N(12)
N(9)–Ag(2)–N(14)
N(12)–Ag(2)–N(14)
C(1)–Au(1)–Ag(1)
C(28)–Au(1)–Ag(1)
N(3)–Ag(1)–Au(2)
N(6)–Ag(1)–Au(2)
N(13)–Ag(1)–Au(2)
C(10)–Au(2)–Ag(2)
C(19)–Au(2)–Ag(2)
N(9)–Ag(2)–Au(2)
N(12)–Ag(2)–Au(2)
N(14)–Ag(2)–Au(2)
66.6(3)
62.8(3)
66.8(3)
C(1)–Au(1)–Ag(1)
C(10)–Au(1)–Ag(1)
N(3)–Ag(1)–Au(1)
N(6)–Ag(1)–Au(1)
N(7)–Ag(1)–Au(1)
44.1(9)
40.0(10)
41.4(10)
145.9(3)
175.37(3)
144.06(3)
166.85(2)
135.20(2)
178.03(3)
176.6(3)
100.7(2)
121.8(2)
137.4(2)
138.3(2)
102.1(3)
119.1(3)
74.0(2)
106.7(2)
101.99(15)
74.32(16)
93.28(16)
109.5(2)
73.84(19)
77.15(14)
106.05(17)
91.42(18)
N(7) angles of 137.1(2)°, 112.0(2)° and 110.9(5)°. The
Ag–N separations are more regular with Ag(1)–N(3),
Ag(1)–N(6), and Ag(1)–N(7) distances of 2.265(7),
˚
2.268(7), and 2.273(10) A respectively with very little differ-
ence between the separations of the coordinated benzonit-
rile and the pyridyl groups. The C(19)–N(7) separation at
˚
1.105(13) A is typical of a triple bond and is linearly coor-
dinated to the Ag(1) center with a Ag(1)–N(7)–C(19) angle
of 178.7(14)°.
The benzylnitrile adduct only minimally perturbs the
polymeric structure relative to 4. The coordination polymer
{
[AuAg(CH impy) (NCCH C H )](BF ) } , 5, crystallizes
3 2 2 6 5 4 2 n
in the centrosymmetric space group P2 /c with one repeat-
1
ing Ag–Au unit, two tetrafluoroborate anions and one-half
of a benzylnitrile in the asymmetric unit. A view of the cat-
ionic portion is shown in Fig. 5 while selected bond dis-
tances and angles are presented in Table 6. The structural
representation of the extended polymer chain is presented
in Fig. 7. The Au(1)–Ag(1) separation is short at
˚
P2 with the cationic potion containing only a dimetallic
2.8448(5) A and connects to the next repeating unit with
1
˚
repeating unit, two tetrafluoroborate anions and a benzo-
nitrile solvent of crystallization. Although this crystal is
chiral the bulk material is racemic and contains a statistical
a separation of 2.8940(5) A. This chain zig-zags with
Ag(1)–Au(1)–Ag(1A) and Au(1)–Ag(1)–Au(1A) angles of
148.919(9)° and 170.87(2)° respectively. The NHC ligands
are nearly linearly coordinated to Au(1) with a C(1)–
Au(1)–C(10) angle of 174.7(3)° and Au(1)–C(1) and
Au(1)–C(10) separations of 2.014(9) and 2.038(8) A respec-
tively. Similar to 3 the nitrile moiety is more tightly bound
mixture of chiral crystals. The Au(1)–Ag(1) separation at
˚
2
.835(1) A is slightly shorter than the corresponding sepa-
˚
ration in 3. This chain is connected to the next with a
Au–Ag separations of 2.833(1) A. The angles between these
˚
metals are more regular than those in 3 with alternating
Ag(1A)–Au(1)–Ag(1) and Au(1)–Ag(1)–Au(1A) angles of
than the pyridyl groups. The Ag(1)–N(3) and Ag(1)–N(6)
˚
separations measure 2.327(6) and 2.283(5) A while the
˚
1
62.429(8)° and 179.86(4)°, respectively. The Au(I) center
Ag(1)–N(7) separation is shorter at 2.226(9) A. These
is nearly linear with the C(1)–Au(1)–C(10) angle of
groups are arranged around Ag(1) in a trigonal planar
fashion with N(3)–Ag(1)–N(6), N(3)–Ag(1)–N(7), and
N(6)–Ag(1)–N(7) angles of 126.3(2)°, 108.0(3)° and
125.5(3)° respectively. The benzylnitrile group protrudes
away from the metallic core and fills the void between
1
2
74.3(3)° and Au(1)–C(1) and Au(1)–C(10) separations of
˚
.011(8) and 2.021(8) A, respectively. The Ag(I) center
maintains a nearly trigonal planar environment with
N(3)–Ag(1)–N(6), N(3)–Ag(1)–N(7), and N(6)–Ag(1)–

V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
6047
Table 6
Selected bond distances (A) and angles (°) for {[AuAg(CH
NCCH )](BF , 5
Table 7
Selected bond distances (A) and angles (°) for {[AuAg(CH
NO , 6
˚
˚
3
impy)
2
-
3 2 3
impy) (NO )]-
(
2
C
6
H
5
4
)
}
2 n
3 n
}
Au(1)–Ag(1)
2.8448(5)
2.8940(5)
2.014(9)
2.038(8)
2.327(6)
2.283(5)
2.226(9)
1.124(13)
Ag(1)–Au(1)
Au(1)–Ag(2)
Ag(2)–Au(2)
Au(2)–Ag(1A)
Au(1)–C(10)
Au(1)–C(19)
Au(2)–C(28)
Au(2)–C(1A)
Ag(1)–O(1)
Ag(1)–N(3)
Ag(1)–N(6)
Ag(2)–O(4)
Ag(2)–N(9)
Ag(2)–N(12)
Ag(1)–O(1)
Ag(1)–O(3)
Ag(2)–O(5)
2.8125(2)
2.8460(2)
2.8397(2)
2.9428(2)
2.012(3)
2.010(3)
2.022(3)
2.022(2)
2.451(2)
2.273(2)
2.290(2)
2.564(2)
2.302(2)
2.297(2)
2.451(2)
3.093(3)
2.696(2)
Au(1)–Ag(1A)
Au(1)–C(1)
Au(1)–C(10)
Ag(1)–N(3)
Ag(1)–N(6)
Ag(1)–N(7)
N(7)–C(19)
C(1)–N(2)–C(5)–N(3)
42.0(9)
61.5(3)
C(1)–Au(1)–Ag(1)–N(3)
Ag(1)–Au(1)–Ag(1A)
Au(1)–Ag(1)–Au(1A)
C(1)–Au(1)–C(10)
N(3)–Ag(1)–N(6)
N(3)–Ag(1)–N(7)
N(6)–Ag(1)–N(7)
Ag(1)–N(7)–C(19)
N(7)–C(19)–C(20)
C(19)–C(20)–C(21)
C(1)–Au(1)–Ag(1)
C(10)–Au(1)–Ag(1)
N(3)–Ag(1)–Au(1)
N(6)–Ag(1)–Au(1)
N(7)–Ag(1)–Au(1)
148.919(2)
170.87(2)
174.7(3)
126.3(2)
108.0(3)
125.5(3)
174.9(12)
176.7(18)
114.6(12)
80.1(2)
Ag(1)–Au(1)–Ag(2)
Au(1)–Ag(2)–Au(2)
Au(1)–Ag(1)–Au(2A)
Ag(2)–Au(2)–Ag(1A)
C(10)–Au(1)–C(19)
C(28)–Au(2)–C(1A)
N(3)–Ag(1)–N(6)
140.915(7)
131.321(8)
146.883(9)
143.053(7)
177.74(11)
173.39(10)
150.21(8)
121.50(8)
88.24(8)
97.08(19)
76.59(14)
97.77(13)
97.86(19)
N(3)–Ag(1)–O(1)
N(6)–Ag(1)–O(1)
the polymer chains. The nitrile group is linear with a N(7)–
N(9)–Ag(2)–N(12)
N(9)–Ag(2)–O(4)
N(12)–Ag(2)–O(4)
C(1)–N(2)–C(5)–N(3)
C(10)–N(5)–C(14)–N(6)
C(28)–N(11)–C(32)–N(12)
Ag(1)–Au(1)–Ag(2)–Au(2)
161.43(8)
87.50(8)
110.64(8)
49.5(4)
52.0(4)
47.8(4)
C(19)–C(20) angle of 176.7(18)° and a N(7)–C(19) separa-
˚
tion of 1.124(13) A.
In an attempt to turn off the dynamic behavior of these
polymers in solution, the coordinated nitriles were replaced
with a coordinating nitrate anion. Accordingly, the
colorless mixed-metal polymer {[AuAg(CH impy) (NO )]-
120.006(12)
3
2
3
NO } , 6, readily crystallizes in the P2 /n space group with
Ag(1)–N(6), Ag(2)–N(9) and Ag(2)–N(12) distances mea-
sure 2.273(2), 2.290(2), 2.302(2), and 2.297(2) A respec-
3
n
1
˚
a repeating four-metal zig-zag chain bridged by NHC li-
gands, one-coordinated nitrate anion and one uncoordi-
nated nitrate anion. Views of the cationic portion of 6
are presented in Figs. 6 and 7 while selected bond distances
and angles are tabulated in Table 7. The metal–metal sep-
arations in 6 are similar to the other coordination polymers
with Ag(1)–Au(1), Au(1)–Ag(2), and Ag(2)–Au(2) separa-
tively. The angles around each Ag ion deviate from the
other coordination polymers with N(3)–Ag(1)–N(6),
N(3)–Ag(1)–O(1), and N(6)–Ag(1)–O(1) angles of
150.21(8)°, 121.50(8)° and 88.24(8)° respectively. Similarly,
the corresponding angles around the second silver center,
N(9)–Ag(2)–N(12), N(9)–Ag(2)–O(4), and N(12)–Ag(2)–
O(4), measure 161.43(8), 87.50(8) and 110.64(8)° each. Also
noteworthy in 6 are the relatively large torsion angles
between the imidazole and pyridyl groups. The C(1)–N(2)–
C(5)–N(3), C(10)–N(5)–C(14)–N(6), and C(28)–N(11)–
C(32)–N(12) angles at 49.5(4)°, 52.0(4)°, and 47.8(4)° are
nearly 10° larger than the corresponding angles in 3–5.
The electronic absorption spectra of 1 and 2 are nearly
identical to that of [HCH impy]PF with p–p* bands be-
˚
tions of 2.8125(2), 2.8460(2) and 2.8397(2) A, and these
chains are connected to each other with Ag–Au separations
˚
of 2.9428(2) A. The angles between these metals are more
acute than those in the other polymers with Au(1)–
Ag(2)–Au(2) and Ag(1)–Au(1)–Ag(2) angles of 131.321(8)
and 140.915(7)°. In between the chains angles of
1
46.883(9) and 143.053(7)° are observed for Au(1)–
Ag(1)–Au(2A) and Ag(2)–Au(2)–Ag(1A) respectively.
Each Au(I) center is linearly bound to the NHC ligands
with Au(1)–C(10), Au(1)–C(19), Au(2)–C(1A) and Au(2)–
3
6
tween 260 and 270 nm. Because the polymeric complexes
dissociate into their respective monomers, in solution the
electronic absorption spectra of 3 to 6 are nearly identical
to 2. All of the polymers are noticeably photoluminescent
C(28) distances of 2.012(3), 2.010(3), 2.022(2) and
˚
2
.022(3) A respectively. The corresponding angles are close
to linear with C(10)–Au(1)–C(19) and C(28)–Au(2)–C(1A)
angles of 177.74(11)° and 173.39(10)° each. Coordination
of the nitrate anions distorts the environment around the
silver centers. The Ag(1)–O(1) and Ag(2)–O(4) separations
when excited with a hand-held UV lamp (k = 336 nm).
x
Both solutions and solid-state samples of the carbene pre-
cursor are photo-luminescent with a band appearing at
435 nm. Likewise, excitation of a solid samples of the
monometallic Au containing species, 2, produces a broad
˚
are long at 2.451(2) and 2.564(2) A while the Ag(1)–N(3),

6048
V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
lene spacer between the pyridyl group and the imidazole
ring relieves this strain and only discrete dimetallic mole-
cules are formed [18]. All the complexes reported are air
stable, yet the polymers 3–6 readily dissociate Ag(I) ions
in solution but reform the respective polymer chains upon
precipitation. Replacement of the coordinated solvent mol-
ecule with a coordinating anion (nitrate in 6) does not stop
this dissociation. The loss of Ag(I) in solution is confirmed
by the NMR spectroscopy which shows no change in four
pyridyl resonances relative to 2.
The observation of short Au–Ag separations is particu-
larly interesting with both the shortest and longest Au(I)–
˚
Ag(I) separations of 2.8125(2) and 2.9482(2) A found in
the nitrate containing polymer, 6. The changes in metal–
metal separation within the different polymers, though sub-
tle, demonstrates the significant impact of changing the
coordinating solvent or anion on the basic structure of
the polymer, and subsequently on its optoelectronic prop-
erties. This variation is even more striking considering
the rigidity imposed by the constrained ligand backbone.
While there are numerous reports in the literature on li-
gand-supported metal–metal interactions, [19] and clearly
the strained scaffolding imposed by the rigid ligand back-
Fig. 8. Room temperature emission spectra of solid samples of the nitrile
containing polymers 3–5. The nitrate containing polymer has a spectrum
nearly identical to that of 4.
1
0
10
bone influences the short d –d interactions observed in
3–6, recent reports have attributed shorter metal–metal
interactions in mixed-metal species to an introduction of
attractive dipolar interactions between the dissimilar met-
als [20]. For example, Fackler and coworkers [21] described
the structures of three isomorphous M (MTP) compounds
band at 541 nm (kex = 348 nm). Cooling the solid to 77 K
blue shifts this broad band to an emission maximum of
2
2
5
06 (kex = 340 nm ). At room temperature the solid-state
where M2 is Au , Ag or AuAg and MTP is diph-
2 2
emission spectra (Fig. 8) of the nitrile containing polymers
show intense bands at 480, 474 and 522 nm (kex = 360 nm)
for the acetonitrile, benzonitrile and benzylnitrile contain-
ing polymers (3–5) respectively. The nitrate containing
polymer 6 similarly has band that appears at 469 nm
enylmethylenethiophosphinate and attributed the reduc-
˚
tion in the mixed-metal separation (2.912 A) relative to
˚
the homometallic separations (>3.0 A) to an attractive
dipolar interaction. Fernandez et al. [3a] also recently syn-
thesized and structurally characterized the mixed Au(I)–
Ag(I) ion pair complex, [Ag(py) ][Au(C F ) ], with an
(
kex = 383). These spectra are independent of excitation
3
6 5 2
wavelength. Cooling these solids to 77 K, sharpens and
shifts these bands to 450, 480, 453 and 466 nm for 3–6,
respectively. Dissolving the polymers in acetonitrile dis-
rupts the multimetallic framework, and emission spectra
similar to that of 2 are observed. Freezing these solutions
to 77 K produces intense emission bands around 500 nm
similar to that of the [Au(CH impy) ]PF , 2, indicating
extended unsupported one-dimensional chain of alternat-
ing gold and silver atoms. According to their theoretical
studies, the short Au(I)–Ag(I) interactions arise from both
an attractive ionic(dipolar) contribution and from disper-
sion-type correlation effects. We recently reported the
mixed-metal metallocryptands [AuPdTl(P phen) ](PF )
6 2
2
3
3
2
6
and [AuPtTl(P phen) ](PF ) , where dipolar interactions
2 3 6 2
that the polymer is no longer intact.
shorten the M–Tl separations relative to those of their
homometallic counterparts [22].
3
. Discussion
From a structural standpoint, the polymers 3–6 are par-
ticularly interesting. Although silver containing coordina-
tion polymers are well-known [23], 4 along with the
previously reported {[AuAg((py) im) (CH CN)](BF ) }
4 2 n
The present study provides additional evidence for the
versatility of N-heterocyclic carbenes as ligands in coordi-
2
2
3
1
0
nation chemistry, and as supports for d metallophilic
interactions. It also further illustrates the generality of
one-dimensional Au(I)–Ag(I) coordination polymer forma-
tion using the simple the pyridyl-imidazolium linkage of
these NHC ligands. The propensity for polymer formation
may be a consequence of the constrained Ag(I) coordina-
tion environment imposed by the rigid pyridyl-substituted
carbene framework. In contrast, the insertion of a methy-
polymer are two rare examples of single-handed mixed-me-
tal species derived from achiral ligands. Polymers 3, 5 and 6
each contain helical one-dimensional multi-metallic chains
but crystallize in a racemic fashion as dictated by their cen-
trosymmetric space groups. Spontaneous resolution of
racemic Ag-containing polymers from achiral components,
although rare, has been reported elsewhere [24]. One of the
more interesting features of the polymers reported here is

V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
6049
their differential luminescence. The origin of this difference
is not well-understood. The trend of increasing energy of
emission (5 < 3 < 4) does not correlate to decreasing
Ag(I)–Au(I) separation or to the nitrile donor ability as
measured by the nitrile–Ag separation. The origin likely re-
sides in a combination of metal chain geometry and ancil-
lary ligand electronic and steric properties. However, the
significant changes in emission behavior reported here sug-
gest that further substitution would lead to even more var-
ied emission behavior. The photoluminescence of these
materials and their potential applications [25] in optoelec-
tronics and material science are also exciting avenues to ex-
plore in further detail in the near future.
(C H N AgPF Æ H O) C, 36.69; H, 3.42; N, 14.26.
18 18 6 6 2
1
Found: C, 36.02; H, 3.25; N, 14.02.
H NMR
(499.8 MHz, CD CN, 25 °C) d = 8.36 (m, 4.5 Hz, 2H),
3
7.93 (m, 8.5 Hz, 2H), 7.85(m, 2H), 7.82 (d, 2H), 7.42 (m,
1
3
1
2H), 7.93 (d, 2H), 3.95 (s, 6H).
C { H} NMR
(125.7 MHz, CD CN, 25 °C) d = 150.50, 147.86, 141.48,
3
135.58, 126.37, 125.74, 120.23, 114.99, 37.48. UV (CH CN)
3
kmax, nm (e): 265 (33,300), 358 (2000), 487 (2000).
4.3. Preparation of [Au(CH impy) ]PF , 2
3
2
6
A 50 ml round bottom flask was charged with 0.094 g
(0.16 mmol) of 2 in 20 mL of CH CN. To this was added
3
0.052 g (0.16 mmol) of Au(tht)Cl dissolved in 10 mL of
4
. Experimental
CH CN. The mixture was protected from light and stirred
3
for 15 min after which solution was filtered through celite
to remove the precipitated AgCl. The clear filtrate was re-
duced to minimum volume under vacuum and precipitated
Solvents were used as received without purification or
drying. The preparation of the imidazolium salt, [HCH im-
3
py]PF , was modified from a published procedure. [17] The
using Et O affording 0.098 g (0.10 mmol) of 2 as a white
6
2
preparation of Au(tht)Cl was described elsewhere [26].
UV–Vis spectra were obtained using a Hewlett–Packard
powder (90.0%). Anal. Calc. (%). (C H N AuPF ) C,
1
8
18
6
6
32.74; H, 2.75; N, 12.73. Found: C, 32.42; H, 2.79; N,
1
8
453 diode array spectrometer (1 cm path-length cells).
12.62. H NMR (499.8 MHz, CD CN, 25 °C) d = 8.51 (d,
3
Emission data were recorded using a Spex Fluoromax
steady-state fluorimeter.
4.5 Hz, 2H), 8.01 (d, 8.5 Hz, 2H), 7.88 (m, 8.5 Hz, 2H),
7.76 (d, 1.5 Hz, 2H), 7.48 (m, 4.5 Hz, 2H), 7.37 (d,
1
3
1
1.5 Hz, 2H), 3.94 (s, 6H). C { H} NMR (125.7 MHz,
4
.1. Preparation of 1-methyl-3-(2-pyridinyl)-1H-
Imidazolium hexafluorophosphate ([HCH impy]PF )
CD CN, 25 °C) d = 183.57, 151.67, 150.16, 140.34,
3
125.73, 125.43, 124.87, 121.98, 39.49. (CH CN) kmax, nm
3
6
3
(e): 210 (22,000), 264 (16,000).
A mixture of 2-bromopyridine (3.8 mL, 40.0 mmol) and
-methyl imidazole (3.2 mL, 40.0 mmol) was heated neat at
60 °C for 24 h. After cooling the resulting dark red oil was
1
1
4.4. Preparation of {[AuAg(CH impy) (NCCH )]-
3
2
3
(BF ) } , 3
4 2 n
diluted with 30 mL of water, followed by addition of a sat-
urated aqueous solution of 40.0 mmol NH PF . The pre-
A 100 mL round bottom flask was charged with 0.071 g
4
6
cipitated solid was filtered and washed with two 30 mL
(0.10 mmol) of 3 and 0.021 g (0.13 mmol) of AgBF in
4
portions of anhydrous Et O to afford 4.080 g (13.4 mmol)
30 mL CH CN. The colorless mixture was removed from
2
3
of 1-methyl-3-(2-pyridinyl)-1H-imidazolium hexafluoro-
phosphate as an off white powder (33.4%). This material
can be recrystallized from CH CN/Et O to afford a white
light and stirred at room temperature for 1.5 h. The mix-
ture was filtered through bulk celite, reduced to minimum
volume under vacuum and precipitated with Et O afford-
3
2
2
1
powder. H NMR (499.8 MHz, CD CN, 25 °C) d = 9.25
ing 0.075g (0.04 mmol) of 3 as a white powder. (43.8%).
3
(
(
{
1
4
s, 1H), 8.59 (m, 1H), 8.10 (m, 1H), 8.06 (m, 1H), 7.73
Anal. Calc. (%) (C H N AuAgB F ) C, 28.67; H,
2
0
21
7
2 8
1
3
d, 1H), 7.56 (m, 1H), 7.55 (d, 1H), 3.96 (s, 3H).
C
2.52%; N, 11.70%. Found: C, 27.66; H, 2.19; N, 12.29.
1
H} NMR (125.7 MHz, CD CN, 25 °C) d = 155.03,
3
51.96, 146.04, 140.12, 130.92, 130.30, 124.76, 119.53,
2.01.
4.5. Preparation of {[AuAg(CH impy) (NCC H )-
3
2
6
5
(BF ) } , 4
2 n
4
4
.2. Preparation of [Ag(CH impy) ]PF , 1
3
Made analogously to 3 except benzonitrile is used in
2
6
place of acetonitrile (57.7%). Anal. Calc. (%) (C H -
2
5
23
A 100 mL round bottom flask was charged with 0.107 g
0.35 mmol) of [HCH impy]PF in 25 mL CH Cl , 0.020 g
N AuAgB F Æ 0.5 C H CN) C, 35.97; H, 2.70; N, 11.04.
7 2 8 6 5
Found: C, 36.04; H, 2.42; N, 11.04.
(
(
3
6
2
2
0.088 mmol) Ag O, and a catalytic amount of Bu NPF .
2
4
6
The mixture was protected from light and stirred for 1.5
hr at room temperature. NaOH (1 N, 3 mL) was then
added, and stirring was continued for a further 15 min.
The mixture was filtered through celite. The bright yellow
filtrate was reduced to minimum volume under vacuum
4.6. Preparation of {[AuAg(CH impy) (NCCH C H )]-
3
2
2
6
5
(BF ) } , 5
4 2 n
Made analogously to 3 except benzylnitrile is used in
place of acetonitrile (57.4%). Anal. Calc. (%) (C H -
2
6
25
and precipitated with Et O affording 0.1700 g (0.27 mmol)
N AuAgB F Æ 0.5 C H CH CN) C, 37.05; H, 2.95; N,
7 2 8 6 5 2
2
of 2 as a white powder (75.3%). Anal. Calc. (%)
10.80. Found: C, 36.64; H, 2.46; N, 10.8.

6050
V.J. Catalano, A.O. Etogo / Journal of Organometallic Chemistry 690 (2005) 6041–6050
4
.7. Preparation of {[AuAg(CH impy) (NO )]NO } , 6
3
(c) R.L. White-Morris, M.M. Olmstead, A.L. Balch, J. Am. Chem.
Soc. 125 (2003) 1033.
2
3
3 n
[
[
5] F.A. Cotton, B. Hong, Prog. Inorg. Chem. 40 (1992) 179.
6] P. Pyykk o¨ , M. Straka, Phys. Chem. Chem. Phys. 2 (2000) 2489.
Made analogously to 3 except AgNO is used in place of
3
AgBF (58.8%). Anal. Calc. (%) (C H N O Au Ag ) C,
4
36 36 16 12
2
2
[7] (a) F. Mendizabal, P. Pyykk o¨ , A. Runeberg, Chem. Phys. Lett. 370
(2003) 733;
2
8.93; H, 2.43; N, 14.99. Found: C, 29.30; H, 2.52; N, 14.65.
(
7
b) N. Runeberg, M. Sch u¨ tz, H.-J. Werner, J. Chem. Phys. 110 (1999)
210.
5
. X-ray crystallography
[
[
8] P. Pyykk o¨ , F. Mendizabal, Chem. Eur. J. 3 (1997) 1458.
9] V.J. Catalano, M.A. Malwitz, Inorg. Chem. 42 (2003) 548.
Suitable crystals were coated in a hydrocarbon oil and
[
[
10] (a) J.M. Forward, J.P. Fackler Jr., Z. Assefa, in: D.M. Roundhill,
J.P. FacklerJr. (Eds.), Optoelectronic Properties of Inorganic Com-
pounds, Plenum Press, New York, 1999, p. 195;
mounted on a glass fiber. X-ray crystallographic data were
collected at low temperature (100 K) using a Bruker
SMART Apex CCD diffractometer with Mo Ka radiation
and a detector-to-crystal distance of 4.94 cm. Data were
collected in a full sphere using four set of frames with
(
b) Y. Ma, C.-M. Che, H.-Y. Chao, X. Zhou, W.-H. Chan, J. Shen,
Adv. Mater. 11 (1999) 852.
11] (a) C.E. Buss, K.R. Mann, J. Am. Chem. Soc. 124 (2002) 1031;
(
b) M.A. Mansour, W.B. Connick, R.J. Lachicotte, H.J. Gysling, R.
0
.3° scans in x and an exposure time of 10s per frame.
Eisenberg, J. Am. Chem. Soc. 120 (1998) 1329;
(c) L.G. Beauvais, M.P. Shores, J.R. Long, J. Am. Chem. Soc. 122
The 2h range extended from 3.0 to 64°. Data were cor-
rected for Lorentz and polarization effects using the SAINT
program and corrected for absorption using SADABS or
TWINABS. Unit cells were indexed using up to 9999 reflec-
tions harvested from the data collection. The structures
were solved by direct methods and refined using the
SHELXTL 5.12 software package [27].
(
(
2000) 2763;
d) E. Cariati, X. Bu, P.C. Ford, Chem. Mater. 12 (2000) 3385.
[
12] V.J. Catalano, B.L. Bennett, M.A. Malwitz, R.L. Yson, H.M.
Kar, S. Muratidis, S.J. Horner, Comments Inorg. Chem. 24 (2003)
39.
[13] (a) R.J. Puddephatt, Coord. Chem. Rev. 216–217 (2001) 313;
b) V.W.-W. Yam, K.K.-W. Lo, Chem. Soc. Rev. 28 (1999) 323.
(
[
14] P.J. Barnard, M.V. Baker, S.J. Berners-Price, B.W. Skelton, A.H.
White, Dalton Trans. 7 (2004) 1038.
15] (a) T. Weskamp, V.P.W. B o¨ hm, W.A. Herrmann, J. Organomet.
Chem. 600 (2000) 12;
6
. Supporting information available
[
CCDC 273792–273797 contains the supplementary
(b) W.A. Herrmann, T. Weskamp, V.P.W. B o¨ hm, Adv. Organomet.
Chem. 48 (2001) 1;
crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
(
c) I.J.B. Lin, C.S. Vasam, Comments Inorg. Chem. 25 (2004)
5;
d) D. Bourissou, O. Guerret, F.P. Gabba ¨ı , G. Bertrand,
Chem. Rev. 100 (2000) 39;
7
(
(
(
e) W.A. Herrmann, C. K o¨ cher, Angew. Chem., Int. Ed. 36
1997) 2162.
Acknowledgment
[
[
16] V.J. Catalano, M.A. Malwitz, A.O. Etogo, Inorg. Chem. 43 (2004)
714.
5
This work and the X-ray diffractometer purchase were
supported by the National Science Foundation (CHE-
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