Effect of anion and ligand ratio in self-assembled silver(I) complexes of 4-(diphenylphosphinomethyl)pyridine and their derivatives with bipyridine ligands

Article abstract of DOI:10.1016/j.ica.2008.04.032

An efficient procedure for the synthesis of the novel bidentate ligand 4-(diphenylphosphinomethyl)pyridine (PMP-41, 1) has been developed and its coordination behavior with Ag(I) has been studied. Reaction of the PMP-41 ligand with the silver(I) salts of

Full text of DOI:10.1016/j.ica.2008.04.032

Inorganica Chimica Acta 362 (2009) 426–436
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Inorganica Chimica Acta
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Effect of anion and ligand ratio in self-assembled silver(I) complexes of
4-(diphenylphosphinomethyl)pyridine and their derivatives with bipyridine ligands
*
Fernando Hung-Low, Kevin K. Klausmeyer , John Brannon Gary
Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient procedure for the synthesis of the novel bidentate ligand 4-(diphenylphosphinomethyl)pyr-
idine (PMP-41, 1) has been developed and its coordination behavior with Ag(I) has been studied. Reaction
of the PMP-41 ligand with the silver(I) salts of tetrafluoroborate ðBF4ꢀÞ, trifluoromethanesulfonate (Otfꢀ),
and trifluoroacetate (tfaꢀ) produces discrete molecules and polymeric structures that depend on the
varying degrees of interaction of the corresponding anion with the metal centers. When the proportion
of ligand to metal is 1:1, a bimetallic box conformation is obtained with AgBF4 and AgOtf (2 and 5, respec-
Received 13 March 2008
Received in revised form 18 April 2008
Accepted 18 April 2008
Available online 24 April 2008
Keywords:
ꢀ
tively). Varying the ratio to 2:1, a polymeric chain of bimetallic boxes is constructed when the BF4 salt is
Bimetallic box
p–p interaction
Silver
used (3). With Agtfa two distinct structural motifs are formed (8A and 8B), arising from the crystallization
process of using two different solvent systems. Further reaction of the AgBF4/PMP-41 and AgOtf/PMP-41
adducts with the chelating 5,50-dimethyl-2,20-bipyridine or the bridging 4,40-bipyridine ligands affords
dimeric and bridged structural motifs, depending upon the coordination ability of the corresponding
bipyridine fragment. Addition of the 5,50-dimethyl-2,20-bipyridine ligand to a solution containing AgBF4
and PMP-41 results the capping of the silver atoms by the bipyridine fragment 4, and the disruption of
the bimetallic box in the AgOtf(PMP-41) structure to generate an infinite chain in a 1:1:1 ratio of the reac-
tants 6. As expected, the 4,40-bipyridine acts as a bridging ligand by connecting [AgOtf(PMP-41)]2 mole-
cules, which results in the formation of compound 7. Low-temperature luminescence spectra were also
collected for all compounds and are compared.
Coordination modes
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
[23–27]. In this paper we report the synthesis and coordinative
behavior of 4-(diphenylphosphinomethyl)pyridine (Fig. 1) with
Pyridyl-substituted phosphines [1–5], which were first reported
more than 60 years ago, have been extensively used in metal ion
coordination chemistry for their ease of functionalization and the
electronic properties that they impart to metal complexes used
for catalysis purposes [6–15]. The presence of both hard and
soft-donating atoms make it easy to coordinate as a multidentate
ligand, as seen for the series of 2-(phosphinomethyl)pyridyl of
the type PPhxCH2py3ꢀx (x = 0, 1, 2). From this family of ligands,
the coordination chemistry of the 2-(diphenylphosphino-
methyl)pyridine [16–20] (PPh2CH2py, PMP-21) and the phen-
ylphosphino-bis-2-methylpyridyl [21,22] (PPh(CH2py2)2, PMP-22)
have been widely studied in our group using different Ag(I) salts
of both interacting and non-interacting anions. Interesting struc-
tural variations within the series AgX/PPhxCH2py3ꢀx (x = 1 or 2)
result from the different coordination modes of the anions, as well
as supramolecular interactions such as hydrogen-bonding, p–p
stacking, electrostatic and van der Waals interactions, which are
determinant in the construction of such coordinative structures
different silver salts. No reports have been published that involve
the use of this bidentate ligand, except for the structurally similar
related 4-pyridyldiphenylphosphine ligand [28], that have been
seen to form bimetallic complexes with transition metals like W,
Fe, Ru, and Rh [29–31]. The incorporation of a methyl group be-
tween the P atom and the pyridyl group increases the variety of
conformations for the ligand. This structural feature has allowed
the synthesis of discrete molecules and very complex coordination
polymers of various silver(I) salts. Despite the variety of coordina-
tive environments encountered around the metal centers, except-
ing one of all metal complexes reported herein present one
structural feature in common in that the phosphine ligand coordi-
nates head-to-tail, P–Ag–N, which accounts for the symmetric
coordinating mode of the PMP-41 ligand.
The preparation of mixed-ligand complexes has also been
achieved by addition of the 5,50-dimethyl-2,20-bipyridine or 4,40-
bipyridine ligands to reaction mixtures containing equivalent
amounts of AgX (X = BF4 or Otfꢀ) and PMP-41. The use of a pre-
ꢀ
dominantly chelating bipyridine ligand [32,33] and a rigid connec-
tor with two binding sites in a divergent fashion [34–37], allowed
the formation of polymeric structures and multidimensional
* Corresponding author. Fax: +1 254 710 4272.
E-mail address: Kevin_Klausmeyer@baylor.edu (K.K. Klausmeyer).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.04.032

F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
427
>97% in 78% yield. If necessary, purification of the ligand can be
achieved by precipitation with CH2Cl2/hexanes mixtures. 1H NMR
(CDCl3, 298 K) d: 3.40 (s, 2H), 6.96 (m, 2H), 7.39 (m, 10H), 8.41
(d, 2H). 31P NMR (CDCl3, 298 K) d: (ꢀ8.81, s).
N
2.2.2. Synthesis of [AgBF4(PMP-41)(CH3CN)2]2 (2)
To a stirred solution of AgBF4 (0.077 g, 0.396 mmol) in CH3CN
(5 mL) was added 1 (0.109 g, 0.396 mmol) in CH3CN (5 mL). The
resulting solution was allowed to stir for 5 min and then dried in
vacuo to leave a brownish solid. This was then re-dissolved in a
small amount of CH2Cl2 and precipitated with ether to obtain com-
P
pound
2 as a white powder upon drying in 57% (0.125 g,
0.225 mmol) yield. Colorless blocks were obtained by slow diffu-
sion of ether into a CH3CN solution of 2 at 5 °C. 1H NMR (CD3CN,
298 K) d: 3.88 (m, 2H), 7.05 (m, 2H), 7.72 (m, 10H), 8.09 (m, 2H).
31P NMR (CD3CN, 243 K) d: 15.7, d. Anal. Calc. for C22H22AgBF4N3P
(554.08): C, 46.82; H, 3.73; N, 5.46. Found: C, 46.91; H, 3.65; N,
5.25.
Fig. 1. Structure of PMP-41 ligand.
coordination networks, most of which were obtained by control-
ling functionality of the corresponding ligand, ratio of reactants
or solvent system. Herein, we describe the variations in the coordi-
native environments of the silver(I) centers that results from the
coordination of the bipyridine ligand to the corresponding
AgX:PMP-41 complex, and the changes in luminescence properties
exhibited from the different Ag–P interactions in the presence of a
bipyridine ligand. The PMP–nm naming convention that we have
adopted in here and in different reports, allows for simplicity in
discussion of these phosphinomethylpyridines, as there are many
substitutions that can be made and systematic nomenclature can
be cumbersome. As such, PMP indicates the phosphinomethylpyri-
dine ligands, where n is the position of substitution on the pyridyl
ring and m is the number of substitutions by methylpyridine on
the phosphorus.
2.2.3. Synthesis of AgBF4(PMP-41)2 (3)
This reaction used 2 equiv. of 1 (0.222 g, 0.801 mmol) in CH3CN
(5 mL) added to 1 equiv. of AgBF4 (0.078 g, 0.402 mmol) in CH3CN
(5 mL). After stirring for 5 min, the solution was dried in vacuo and
a light yellow solid was obtained. This was then dissolved in a
small amount of CH2Cl2 and precipitated with ether to obtain com-
pound 3 as a white solid upon drying in 58% (0.175 g, 0.233 mmol)
yield. Crystallization formed colorless blocks obtained by slow dif-
fusion of ether into a CH3CN solution of 3 at 5 °C. 1H NMR (CD3CN,
298 K) d: 3.78 (m, 2H), 6.85 (m, 2H), 7.57 (m, 10H), 8.07 (m, 2H).
31P NMR (CD3CN, 243 K) d: 9.01, d. Anal. Calc. for C36H32AgBF4N2P2
(748.87): C, 57.71; H, 4.30; N, 3.94. Found: C, 57.24; H, 4.12; N,
4.34.
2. Experimental
2.2.4. Synthesis of [AgBF4 (PMP-41)(5,50-dimethyl-2,20-bipyridine)]2
(4)
2.1. General remarks
This reaction used 1 equiv. of 1 (0.110 g, 0.402 mmol) in CH3CN
(5 mL) added to 1 equiv. of AgBF4 (0.079 g, 0.406 mmol) in CH3CN
(5 mL). After stirring for 5 min, a solution of 5,50-dimethyl-2,20-
bipyridine (0.073 g, 0.396 mmol) in CH3CN (5 mL) was added to
the reaction mixture. After stirring for 10 min, a white solid precip-
itated, which was then isolated by removing the solvent. Upon
evaporation, a light yellow powder was obtained in 69% yield
(0.185 g, 0.282 mmol). Crystallization formed colorless blocks ob-
tained by slow diffusion of hexane into a CH2Cl2 solution of 4 at
5 °C. 1H NMR ((CD3)2CO, 298 K) d: 2.47 (s, 6H), 4.13 (m, 2H), 7.23
(m, 2H), 7.63 (m, 6H), 7.95 (m, 4H), 8.05 (m, 2H), 8.28 (m, 2H),
8.45 (m, 2H), 8.50 (s, 2H). 31P NMR ((CD3)2CO, 243 K) d: 11.03, d.
Anal. Calc. for C30H28AgBF4N3P1 (656.22): C, 54.01; H, 4.30; N,
6.40. Found: C, 53.97; H, 4.33; N, 6.25.
All syntheses and handling were carried out under a nitrogen
atmosphere using a Schlenk line and standard Schlenk techniques.
All silver salt reagents were stored in an inert-atmosphere glove-
box; solvents were distilled under nitrogen from the appropriate
drying agent immediately before use. n-Butyllitium, chlorodiphen-
ylphosphine, 5,50-dimethyl-2,20-bipyridine, and 4,40-bipyridine
were purchased from Aldrich and used as received. Silver(I) tetra-
fluoroborate, silver(I) trifluoromethanesulfonate, and silver(I) tri-
fluoroacetate were purchased from Strem Chemicals Inc. and
used as received. 1H, 31P and variable-temperature 31P NMR spec-
tra were recorded at 360.13 MHz with a Bruker Spectrospin
300 MHz spectrometer. Elemental analyses were performed by
Atlantic Microlabs Inc. in Norcross, Georgia. Excitation and emis-
sion spectra were recorded with an Instruments S.A. Inc. Fluoro-
max-2 model spectrometer using band pathways of 5 nm for
both excitation and emission and are presented uncorrected.
2.2.5. Synthesis of AgOtf(PMP-41) (5)
To a stirred solution of AgOtf (0.109 g, 0.399 mmol) in CH3CN
(5 mL) was added 1 (0.109 g, 0.399 mmol) in CH3CN (5 mL). The
resulting solution was allowed to stir for 5 min and then dried in
vacuo to leave an off-white powder. The compound was re-crystal-
lized with CH2Cl2/ether solutions upon drying in 83% (0.177 g,
0.331 mmol) yield. Colorless blocks were obtained by slow diffu-
sion of ether into a CH3CN solution of 5 at 5 °C. 1H NMR (CD3CN,
298 K) d: 3.88 (d, 2H), 7.03 (m, 2H), 7.63 (m, 10H), 8.09 (m, 2H).
31P NMR (CD3CN, 243 K) d: 15.75, d. Anal. Calc. for C19H16AgF3-
NO3PS (534.23): C, 42.72; H, 3.02; N, 2.62. Found: C, 42.92; H,
2.86; N, 2.53.
2.2. Synthesis
2.2.1. Synthesis of 4-(diphenylphosphinomethyl)pyridine, PMP-41 (1)
n-Butyllitium (17 mmol, 5.86 mL, 2.9 M in hexane) was added
over a period of 10 min to 4-picoline (17 mmol, 1.67 mL) in dry
THF (20 mL) at ꢀ41 °C. After stirring for 1 h, the mixture was added
dropwise to
a solution of chlorodiphenylphosphine (3.0 g,
17 mmol) in dry THF (20 mL) at ꢀ84 °C. Water (20 mL) was then
added over 10 min and the mixture stirred for 30 min. The product
was obtained by first extracting with 0.3 N HCl(aq), then neutraliz-
ing with a NaHCO3 solution, and extracting with dichloromethane.
The solvent and any un-reacted 4-picoline were removed under
vacuum (oil pump) and a light yellow solid resulted with purity
2.2.6. Synthesis of AgOtf(PMP-41)(5,50-dimethyl-2,20-bipyridine) (6)
To a stirred solution of AgOtf (0.107 g, 0.392 mmol) in CH3CN
(5 mL) was added 1 (0.109 g, 0.399 mmol) in CH3CN (5 mL). The

428
F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
resulting solution remained clear and colorless, and after stirring
for 5 min a solution of 5,50-dimethyl-2,20-bipyridine (0.073 g,
0.396 mmol) in CH3CN (5 mL) was added to the mixture. After stir-
ring for 10 min, the solution was dried in vacuo and a light yellow
solid was obtained. This was then washed several times with ace-
tone to obtain compound 6 as a white solid upon drying in 65%
(0.183 g, 0.255 mmol) yield. Colorless block crystals were obtained
by slow diffusion of hexane into a CH2Cl2 solution of 6 at 5 °C. 1H
NMR (CD3CN, 298 K) d: 2.13 (s, 6H), 3.89 (d, 2H), 7.02 (m, 2H),
7.61 (m, 6H), 7.77 (m, 4H), 7.94 (m, 2H), 8.21 (m, 4H), 8.35 (s,
2H). 31P NMR (CD3CN, 243 K) d: 18.39, d. Anal. Calc. for C31H28AgF3-
N3O3PS (718.46): C, 51.82; H, 3.93; N, 5.85. Found: C, 51.58; H,
3.94; N, 5.93.
can be preserved for a period up to 3 months. Pure 1 can be sepa-
rated, if necessary, from its decomposition products by precipita-
tion of the ligand with CH2Cl2/hexanes mixtures. 1H and 31P NMR
spectra of 1 in CDCl3 verify the formation of the PMP-41 ligand,
with a phosphorus singlet at ꢀ8.81 ppm, which is in the region ex-
pected for aromatic-substituted phosphines.
The reaction under ambient conditionꢀs in an iꢀnert atmosphere
of three different silver(I) salts (BF4ꢀ, Otf , or tfa ) with 1 affords
compounds 2, 5, 8A, and 8B in a 1:1 ligand to metal ratio, and com-
pound 3 in a 2:1 proportion. Under the same conditions, reaction of
1 equiv. of 5,50-dimethyl-2,20-bipyridine in a reaction mixture con-
taining AgBF4 and PMP-41 yields compound 4. Reaction of the
AgOtf/PMP-41 adduct with 1 equiv. of 5,50-dimethyl-2,20-bipyri-
dine and 1/2 equiv. of 4,40-bipyridine yields compounds 6 and 7
respectively. No further reaction of the [Agtfa(PMP-41)]2 complex
with any of the bipyridine ligands is observed, due to corroborated
evidences that demonstrate the silver centers are sterically and
electronically crowded when using a coordinating anion like tfa
[20]. Upon coordination, all of the silver compounds reported here-
in are stable in air and room temperatures, with little sign of
decomposition within several hours upon exposure to light. In
solution, the metal compounds tend to undergo decomposition
to form an oily black product.
2.2.7. Synthesis of [AgOtf(PMP-41)](4,40-bipyridine)1/2 (7)
This reaction used 1 equiv. of 1 (0.110 g, 0.401 mmol) in CH3CN
(5 mL) added to 1 equiv. of AgOtf (0.109 g, 0.399 mmol) in CH3CN
(5 mL). This was stirred for 5 min, and then a solution of 4,40-bipyr-
idine (0.031 g, 0.201 mmol) in CH3CN (5 mL) was added to the
solution. This mixture was stirred for 10 min, and the solvent
was removed in vacuo to leave a white powder in 73% isolated
yield (0.178 g, 0.097 mmol). Colorless block crystals were obtained
by slow diffusion of hexane into a solution of 8 in CH2Cl2 at 5 °C. 1H
NMR (CD3CN, 298 K) d: 3.82 (m, 2H), 6.99 (m, 2H), 7.62 (m, 18H),
8.73 (m, 2H). 31P NMR (CD3CN, 243 K) d: 13.06, br, s. Anal. Calc.
for C72H60Ag3F9N6O9P3S3 (1836.96): C, 47.08; H, 3.29; N, 4.57.
Found: C, 47.23; H, 3.32; N, 4.60.
The 1H and 31P NMR spectra of all compounds were collected in
CD3CN, excepting 4 and 8, which were recorded in deuterated ace-
tone and methanol respectively, due to the solubility of each com-
pound. The 1H NMR spectra of compounds 2–8 are, as expected,
generally similar. At room temperature, 31P NMR spectra show a
doublet of broad peaks and only in compound 7 a broad singlet ow-
ing to the phosphorous-silver coupling. This indicates at least some
degree of coordination of the ligand to silver in room temperature
solutions, though the process does appear to be dynamic on the
NMR time scale. Variable temperature 31P NMR were collected at
ꢀ30 °C for all compounds to observe the dissociation of the Ag–P
bond. In most of the compounds it was observed a sharpening of
the doublet peaks, and in the case of a broad singlet, the corre-
sponding splitting into doublet peaks. The coupling of the separate
isotopes of Ag was not observed in any of the metal complexes.
2.2.8. Synthesis of Agtfa(PMP-41) (8A and 8B)
This reaction used 1 (0.109 g, 0.398 mmol) in CH3CN (5 mL)
added to a stirred solution of Agtfa (0.880 g, 0.398 mmol) in CH3CN
(5 mL). After stirring for 5 min a white solid precipitated out of the
solution to leave a fluffy off-white powder upon evaporation of the
solvent. The compound was purified by washing with CH3CN since
it is only slightly soluble in the solvent. Upon drying the com-
pound, the product was obtained in 81% (0.160 g, 0.322 mmol)
yield. Colorless blocks of 8A were obtained by slow diffusion of
ether into a CH3CN solution of the compound at 5 °C, and colorless
blocks of 8B by layering ether into a DMF solution of the same so-
lid. 1H NMR (CH3OD, 298 K) d: 3.96 (d, 2H), 7.17 (m, 2H), 7.60 (m,
6H), 7.85 (m, 4H), 8.09 (m, 2H). 31P NMR (CH3OD, 243 K) d: 15.77
br, d. Anal. Calc. for C20H16AgF3N1O2P (498.18): C, 48.22; H, 3.24;
N, 2.81. Found: C, 48.03; H, 3.24; N, 2.78.
3.2. Description of the crystal structures
Single X-ray diffraction data were collected on crystals with
approximate dimensions of 0.280 ꢁ 0.180 ꢁ 0.120 mm for 2,
0.250 ꢁ 0.150 ꢁ 0.140 mm for 3, 0.361 ꢁ 0.231 ꢁ 0.152 mm for 4,
0.190 ꢁ 0.120 ꢁ 0.110 mm for 5, 0.220 ꢁ 0.170 ꢁ 0.160 mm for 6,
0.210 ꢁ 0.164 ꢁ 0.157 mm for 7, 0.200 ꢁ 0.120 ꢁ 0.100 mm for 8,
and 0.294 ꢁ 0.216 ꢁ 0.214 mm for 8B. Data were collected at
3. Results and discussion
3.1. General characterizations
110 K on
a
Bruker X8 Apex using Mo Ka radiation
(k = 0.71073 Å). All structures were solved by direct methods after
correction of the data using SADABS [38,39]. Details of the crystal
parameters, data collection, and refinement are summarized in
Tables 1 and 2. The molecular structure of the compounds is dis-
played in Figs. 2–10. Summary of selected bond lengths, angles,
and interatomic distances are given in Tables 3 and 4. All data were
processed using the Bruker AXS SHELXTL software, version 6.10 [40].
Hydrogen atoms were placed in calculated positions and all non-
hydrogen atoms were refined anisotropically, unless specified.
Compound 3 has a volume of 998 Å3/unit cell volume, which con-
tains several solvent molecules. We were unable to satisfactorily
model these solvent molecules and therefore they were removed
from the structure using the SQUEEZE procedure implemented in PLA-
TON [41].
3.1.1. Synthesis and NMR spectra
The novel 4-(diphenylphosphinomethyl)pyridine ligand, syn-
thesized by a procedure similar to that reported for the PMP-21
ligand [19,20], is made by the reaction of the corresponding 4-lith-
iomethylpyridine with Ph2PCl at low temperature to afford 1 in
high yield and purity. Care must be taken during the formation
of the pyridyllithium prior to the addition to the phosphorus
halide, since it was observed that this stage of the reaction is
responsible for the formation of several unidentified phosphine
oxide byproducts. Experimental observations indicate that inter-
mediates of the reaction are sensitive to parameters such as tem-
perature, addition rate, and solvent. High temperatures, rapid
addition rates, and non-polar solvents, such as ether, reduce dra-
matically the formation of 1, and enhance the production of other
phosphine compounds. Decomposition of 1 is observed when ex-
posed to air, observing the transition from a light to dark yellow
solid. By refrigeration under an inert atmosphere, compound 1
3.2.1. Structure of compound 2
The coordination of the silver centers in compound 2 is charac-
terized by a pair of head-to-tail coordinated PMP-41 ligands bound

F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
429
Table 1
Crystallographic data for complexes 2–5
Compound
2
3
4
5
Empirical formula
Formula mass
a (Å)
b (Å)
c (Å)
a (°)
b (°)
C48H50Ag2B2F8N8P2
1190.26
C116H108Ag3B2F8N10P6
2325.17
18.203(3)
28.542(4)
23.783(3)
90
104.008(7)
90
11989(3)
4
C64H64Ag2B2Cl8F8N6P2
1652.11
C19H16AgF3NO3PS
534.23
8.6060(9)
10.9368(11)
14.4667(16)
80.640(5)
79.864(5)
81.467(5)
1312.4(2)
1
11.4103(19)
13.537(2)
13.744(2)
92.193(8)
113.884(8)
111.568(7)
1760.9(5)
1
8.7089(4)
11.1276(5)
11.2426(5)
87.816(3)
83.551(3)
70.806(3)
1022.43(8)
2
c (°)
V (Å3)
Z
Crystal system
Space group
T [K]
triclinic
P1
110(2)
1.506
0.877
monoclinic
C2/c
110(2)
1.288
0.626
triclinic
P1
110(2)
1.558
0.970
triclinic
P1
110(2)
1.735
1.213
ꢀ
ꢀ
ꢀ
DCalc (g cmꢀ3
)
l (mmꢀ1
2hmax (°)
)
25.00
26.37
26.47
26.44
Reflections measured
38810
4607 (0.0408)
10/356
0.0346
0.0877
0.0373
0.0911
1.041
56690
12276 (0.0480)
0/656
0.0412
0.1128
0.0556
0.1186
1.083
37315
7167 (0.0364)
0/417
0.0247
0.0578
0.0279
0.0599
1.025
9971
4151 (0.0421)
0/262
0.0385
0.0831
0.0498
0.0905
1.030
Reflections used (Rint
Restraints/parameters
R1 [I > 2r(I)]
)
wR2 [I > 2r(I)]
RðF2oÞ (all data)
RwðF2oÞ (all data)
Goodness-of-fit (GOF) on F2
Table 2
Crystallographic data for complexes 6–8
Compound
6
7
8A
8B
Empirical formula
Formula mass
a (Å)
b (Å)
c (Å)
a (°)
b (°)
C31H28AgF3N3O3PS
718.46
17.163(4)
10.560(3)
17.885(3)
90
112.344(9)
90
2998.1(11)
4
C72H60Ag3F9N6O9P3S3
1836.96
C22H19AgF3N2O2P
539.23
7.7386(8)
27.933(3)
10.4527(9)
90
97.830(3)
90
2238.4(4)
4
C20H16AgF3NO2P
498.18
24.3039(11)
9.1146(4)
17.9687(8)
90
108.306(2)
90
3779.0(3)
8
10.7913(7)
15.3140(9)
24.5005(15)
74.212(2)
89.7100(10)
75.7750(10)
3768.4(4)
2
c (°)
V (Å3)
Z
Crystal system
Space group
T (K)
monoclinic
P21/n
110(2)
1.592
0.852
triclinic
P1
110(2)
1.619
1.000
monoclinic
P21/c
110(2)
1.600
1.017
monoclinic
C2/c
110(2)
1.751
1.196
ꢀ
DCalc (g cmꢀ3
)
l (mmꢀ1
2hmax (°)
)
27.18
25.73
26.43
26.46
Reflections measured
27095
53351
14070 (0.0598)
0/946
0.0367
0.0750
0.0563
0.0849
1.049
22429
4585 (0.0494)
0/281
0.0364
0.0716
0.0523
0.0783
1.043
17515
3824 (0.0468)
0/253
0.0333
0.0747
0.0469
0.0820
1.033
Reflections used (Rint
Restraints/parameters
R1 [I > 2r(I)]
)
6640 (0.0524)
19/424
0.0422
0.0922
0.0584
wR2 [I > 2r(I)]
RðF2oÞ (all data)
RwðF2oÞ (all data)
0.1022
1.023
Goodness-of-fit (GOF) on F2
to the two symmetry equivalent silvers. This bimetallic box is the
common unit relating all structures with PMP-41, where the para
substitution of the nitrogen on the pyridyl ring makes it ideal for
this type of conformation. In this arrangement the pyridyl p-sys-
tems of the opposing ligands are conveniently oriented to interact
with one another, forming a rather rectangle. A thermal ellipsoid
plot of the discrete molecule of 2 is presented in Fig. 2, and selected
bond lengths and angles are given in Table 3. Adjacent molecules
are perfectly aligned in one dimension down the crystallographic
b-axis, as observed in the packing structure of 2 shown in Fig. 3,
with no apparent p–p interactions between the aromatic rings.
The geometry around the metal centers consists of a distorted tet-
rahedron with two CH3CN molecules completing the coordination
sphere of the Ag atoms. The angles around Ag1 range between
89.96(11) and 125.55(8)°, and the Ag–P and Ag–N distances fall
in the range of reported values. The angle formed between the P
and the pyridyl arm of the PMP-41 ligand allows for an easy
approach of the N-donor atom to the metal center, with a value
of 110.54(19)° for C(2)#1–C(1)–P(1). The BF4 anion is disordered
about the position of the boron, and is refined isotropically. The
center of the bimetallic box lies on a crystallographic inversion
center. (See Table 5)
3.2.2. Structure of compound 3
The molecular structure of compound 3 consists of a polymeric
array in a 2:1 ligand to metal ratio, which results from the substi-
tution of the two CH3CN molecules observed in 2, by another
equivalent of PMP-41 to afford the polymeric chain. A view of

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F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
3.2.3. Structure of compound 4
Given the labile nature of the two CH3CN molecules coordinated
to the silver centers in compound 2, design of mixed-ligand com-
plexes using additional electron donating ligands appeared to be
feasible. Reaction of the bidentate 5,50-dimethyl-2,20-bipyridine
with a solution containing AgBF4 and PMP-41 in a 1:1:1 ratio of
the reactants, gave rise to the formation of compound 4 (Fig. 5).
As expected, the chelating bipyridine preferentially binds the sil-
ver(I) cation, displacing the solvent molecules from its coordina-
tion sphere to form a discrete bimetallic molecule. The metal
centers are in distorted tetrahedral environments with angles
ranging between 71.58(5) and 133.61(4)°. The high deformation
of the tetrahedral bond angles in this compound results from the
small bite angle of the coordinated bipyridine ligand. The aromatic
rings of the bipyridine fragment are twisted from planarity at an
angle of 14.1(1)°. The Ag–P and Ag–N distances are comparable
with those reported for compound 2, and therefore no large vari-
ances in electron donation to the Ag centers is obvious by substi-
tuting the CH3CN molecules with bipyridine ligands. Molecules of
compound 4 display weak p–p interactions in the crystal system
between the aromatic rings of the bipyridine ligands. The distance
between the planes of the p-systems averages around 3.6 Å from
one molecule to the next in the crystal structure, as shown in the
supplementary material (Fig. S1). The center of the molecule lies
on a crystallographic inversion center.
Fig. 2. Thermal ellipsoid of the cationic portion of 2 with an atomic numbering
scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms and two CH3CN
molecules have been removed for clarity.
the infinite chain of this structure and the thermal ellipsoid plot of
the unique portion of 3 are shown in Fig. 4. The metal centers are
repeated in one dimension, each one constituting an axis of two
bimetallic boxes which are in a zigzag conformation. The planes
of two consecutive bimetallic boxes present an approximate angle
of 90°, from which it can be seen as an infinite ladder. Each Ag
atom is coordinated to two N and P atoms belonging to four differ-
ent PMP-41 ligands. A distorted tetrahedral geometry is observed
for the silver ions in compound 3, with little variances in the angles
when moving from one metal center to another. The Ag–P dis-
tances display an average value of 2.4549(9) Å, which is consider-
ably longer than the reported value of 2.3701(8) Å for Ag(1)–P(1) in
compound 2. This observation reflects the increase in electron
donation to the silver atom in compound 3, when another pyridyl
group of a PMP-41 ligand is coordinated to the metal center, thus
resulting in elongated distances due to the weakening of the Ag–
P interactions.
3.2.4. Structure of compound 5
The X-ray crystal structure of compound 5 reveals the triflate
anion playing an integral part in deciding the geometry of the sil-
ver ions and the connectivity with adjacent molecules. A thermal
ellipsoid plot of the molecular structure of 5 is shown in Fig. 6b,
where the bimetallic box motif is conserved, based upon the sym-
metric bidentate ligand. Compound 5 consists of a polymeric struc-
ture in a 1:1 ligand to metal ratio, where the bimetallic boxes are
held together by the triflate anions through a single oxygen, thus
acting as a bridging connector between the silver atoms (Fig. 6a)
[42–46]. Although the sulfonate oxygen is connected to two iden-
tical atoms, the bridging is quite asymmetric, as denoted by the
Ag1–O distances varying from 2.489(2) to 2.607 Å with the longer
value represented by the bridging contact. The molecular structure
of this polymeric chain is obtained by growing the unique part of
Fig. 3. Packing structure of complex 2 showing the 3-D growth of the molecule. H atoms, tetrafluoroborates, and all the solvent molecules have been removed for clarity.

F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
431
Fig. 4. (a) Ball-and-stick view of the extended cationic polymer of 3. (b) Thermal ellipsoid of the unique cationic portion of 3 with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms and two CH3CN molecules have been removed for clarity.
a four-coordinate arrangement in a distorted tetrahedral geometry,
due to the bridging interaction that distorts the symmetry of the
angles. The Ag–P distance falls in the range of reported values,
although the Ag–N distance (2.237(3) Å) corresponding to the
pyridyl-metal contact is reported to be shorter when compared
to the values in previous molecules discussed herein.
3.2.5. Structure of compound 6
Compound 6 was obtained by addition of 1 equiv. of 5,50-di-
methyl-2,20-bipyridine into a reaction mixture containing AgOtf
and PMP-41 in a 1:1 ratio. The growth molecular structure of 6 is
shown in Fig. 7a, and corresponds to the first example of the
AgX/PMP-41 structures where the bimetallic box unit, commonly
seen in these molecules, is disrupted by addition of an additional
electron donating ligand. The unique portion of this structure is
shown in Fig. 7b, and a view of the packing structure in Fig. S2.
The extended view of the cationic portion of 6 (Fig. 7a) reveals a
Fig. 5. Thermal ellipsoid plot of the cationic portion of 4 with an atomic numbering
scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms and two CH2Cl2
molecules have been removed for clarity.
polymeric chain linked by PMP-41 ligands, displaying a zigzag con-
formation due to the reported angle of 110.5(2)° for C(2)–C(1)–
P(1). The angles around the metal center describe a tetrahedron,
slightly more distorted than in previous structures with N–Ag–N
and P–Ag–N angles ranging from 70.41(10) to 118.95(8)° (Table
4). The aromatic rings of the bipyridine ligand are twisted from
planarity at an angle of 16.5(1)°, probably due to the steric effects
imparted by the phenyl rings of the PMP-41 ligands. The Otf anion
in this instance acts non-coordinating, and is disordered about the
position of the sulfur; therefore it was refined isotropically, and the
two sulfur positions restrained to have the same thermal
parameters.
the molecule through an inversion center, where the long bridging
interaction between the Ag and O atoms are shown in dashed lines.
The formation of 5 is independent of the ratio of reactants from
which the reaction is carried out. Accordingly, a 3:2 ratio com-
pound of PMP-41 and AgOtf is not feasible because of the coordi-
nating ability of the Otfꢀ ions to act either as a mono or
bidentate ligand, when compared to the non-connectivity of the
BF4 anion. The metal centers in the molecular structure of 5 exhibit

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F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
Fig. 6. (a) Ball-and-stick plot of the growth molecular structure of 5. (b) Thermal ellipsoid of 5 with an atomic numbering scheme. Ellipsoids are shown at the 50% level.
Hydrogen atoms have been removed for clarity.
Fig. 7. (a) Expanded view of the two-dimensional growth of the cationic polymer of 6. (b) Thermal ellipsoid plot of the unique cationic portion of 6 with an atomic numbering
scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms have been removed for clarity.
3.2.6. Structure of compound 7
work by linking together [AgOtf(PMP-41)]2 units through the Ag
atoms (Fig. S3). The rings of the bipyridine ligand are highly
twisted with an angle of 30.4(1)°, that results from the free rota-
tion along the central C–C bond. The molecule presents three
non-equivalent silver atoms, although each metal center displays
Compound 7 shown in Fig. 8 is obtained by addition of 1/
2 equiv. of 4,40-bipyridine to a reaction mixture containing a 1:1
ratio of PMP-41 ligand to AgOtf. The use of a bridging connector
such as the 4,40-bipyridine provides an extended coordination net-

F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
433
Fig. 8. Thermal ellipsoid plot of the unique portion of 7 with an atomic numbering
scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms have been removed
for clarity.
the same connectivity of one P atom, one N from a PMP-41 ligand
and one from the bipyridine unit, and one O atom of the coordi-
nated Otf anion. Accordingly, the silver atoms are four-coordi-
nated, where the angles around the metal centers describe a
distorted tetrahedron for each Ag. All Ag–P, Ag–N, and Ag–O
distances present little variances when moving from one silver
atom to another, falling in the range of reported values. The center
of the bimetallic box lies on a crystallographic inversion center.
Fig. 9. Thermal ellipsoid of 8A with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms and a CH3CN molecule have been removed
for clarity.
Fig. 10. (a) Ball-and-stick plot of the growth molecular structure of 8B. (b) Thermal ellipsoid of the unique portion of 8B with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms have been removed for clarity.

434
F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
Table 3
Table 4
Selected bond lengths (Å), angles (°), and distances for the compounds [AgBF4(PMP-
41)(CH3CN)2]2 (2), (AgBF4)(PMP-41)2 (3), [AgBF4(PMP-41)(5,50-dimethyl-2,20-bipyri-
dine)]2 (4), and AgOtf(PMP-41) (5)a
Selected bond lengths (Å), angles (°), and distances for the compounds AgOtf(PMP-
41)(5,50-dimethyl-2,20-bipyridine) (6), [AgOtf(PMP-41)](4,40-bipyridine)1/2 (7), and
Agtfa(PMP-41) (8)a
Compound 2
Compound 6
Ag(1)–P(1)
Ag(1)–N(2)
2.3701(8)
2.318(3)
Ag(1)–N(1)
Ag(1)–N(3)
2.304(2)
2.394(3)
Ag(1)–P(1)
Ag(1)–N(2)
2.3771(9)
2.412(3)
Ag(1)–N(1)#1
Ag(1)–N(3)
2.280(3)
2.362(3)
N(1)–Ag(1)–N(2)
N(2)–Ag(1)–P(1)
N(2)–Ag(1)–N(3)
C(2)#1–C(1)–P(1)
94.04(10)
125.55(8)
89.96(11)
110.54(19)
N(1)–Ag(1)–P(1)
N(1)–Ag(1)–N(3)
P(1)–Ag(1)–N(3)
121.72(6)
106.74(9)
113.21(7)
N(1)#1–Ag(1)–N(3)
N(3)–Ag(1)–P(1)
N(3)–Ag(1)–N(2)
C(2)–C(1)–P(1)
101.82(10)
118.95(8)
70.41(10)
110.5(2)
N(1)#1–Ag(1)–P(1)
N(1)#1–Ag(1)–N(2)
P(1)–Ag(1)–N(2)
70.41(10)
100.27(10)
109.59(7)
Compound 3
Compound 7
Ag(1)–P(1)
Ag(1)–N(2)
Ag(2)–P(2)
Ag(2)–N(1)
N(3)#1–Ag(1)–N(2)
N(2)–Ag(1)–P(1)
N(2)–Ag(1)–P(3)
N(1)#2–Ag(2)–N(1)
N(1)–Ag(2)–P(2)
N(1)–Ag(2)–P(2)#2
C(2)–C(1)–P(1)
C(38)–C(37)–P(3)
2.4600(9)
2.360(3)
2.4465(9)
2.352(3)
103.16(9)
110.67(7)
101.32(7)
101.28(13)
115.11(7)
99.74(7)
Ag(1)–P(3)
Ag(1)–N(3)#1
Ag(2)–P(2)#2
Ag(2)–N(1)#2
N(3)#1–Ag(1)–P(1)
N(3)#1–Ag(1)–P(3)
P(1)–Ag(1)–P(3)
N(1)#2–Ag(2)–P(2)
N(1)#2–Ag(2)–P(2)#2
P(2)–Ag(2)–P(2)#2
C(20)–C(19)–P(2)
2.4667(8)
2.343(3)
2.4465(9)
2.352(3)
106.90(7)
111.25(6)
121.95(3)
99.74(7)
115.11(7)
124.20(4)
110.1(2)
Ag(1)–P(1)
Ag(1)–N(3)
Ag(2)–P(2)
Ag(2)–N(6)
Ag(3)–P(3)
Ag(3)–N(5)
N(3)–Ag(1)–N(2)
N(2)–Ag(1)–P(1)
N(2)–Ag(1)–O(1)
N(6)–Ag(2)–N(1)
N(1)–Ag(2)–P(2)
N(1)–Ag(2)–O(4)
N(4)–Ag(3)–N(5)
N(5)–Ag(3)–P(3)
N(5)–Ag(3)–O(7)
C(2)–C(1)–P(1)
C(48)–C(47)–P(3)#1
2.3647(9)
2.323(3)
2.3579(9)
2.304(3)
2.3639(9)
2.356(2)
96.58(9)
121.61(7)
86.88(9)
94.84(9)
125.84(7)
87.91(9)
91.02(9)
123.22(7)
87.87(8)
110.3(2)
110.2(2)
Ag(1)–N(2)
Ag(1)–O(1)
Ag(2)–N(1)
Ag(2)–O(4)
Ag(3)–N(4)
Ag(3)–O(7)
N(3)–Ag(1)–P(1)
N(3)–Ag(1)–O(1)
P(1)–Ag(1)–O(1)
N(6)–Ag(2)–P(2)
N(6)–Ag(2)–O(4)
P(2)–Ag(2)–O(4)
N(4)–Ag(3)–P(3)
N(4)–Ag(3)–O(7)
P(3)–Ag(3)–O(7)
C(20)–C(19)–P(2)
2.347(3)
2.456(2)
2.347(3)
2.454(2)
2.289(3)
2.522(2)
128.07(7)
80.49(9)
130.45(6)
133.96(7)
83.33(9)
115.14(6)
141.64(7)
82.76(8)
112.48(5)
110.0(2)
110.4(2)
112.7(2)
Compound 4
Ag(1)–P(1)
Ag(1)–N(2)
N(2)–Ag(1)–N(3)
N(3)–Ag(1)–P(1)
N(3)–Ag(1)–N(1)#1
C(2)–C(1)–P(1)
2.3523(6)
2.3363(16)
71.58(5)
133.61(4)
95.06(6)
Ag(1)–N(1)#1
Ag(1)–N(3)
N(2)–Ag(1)–P(1)
N(2)–Ag(1)–N(1)#1
P(1)–Ag(1)–N(1)#1
2.3850(16)
2.3444(15)
127.29(4)
102.34(6)
116.27(4)
Compound 8A
Ag(1)–Ag(1)#2
Ag(1)–N(1)#1
N(1)#1–Ag(1)–O(1)
O(1)–Ag(1)–P(1)
O(1)–Ag(1)–Ag(1)#2
C(2)–C(1)–P(1)
110.98(12)
3.1084(6)
2.262(3)
93.17(9)
125.18(6)
79.31(6)
108.4(2)
Ag(1)–P(1)
Ag(1)–O(1)
N(1)#1–Ag(1)–P(1)
N(1)#1–Ag(1)–Ag(1)#2
P(1)–Ag(1)–Ag(1)#2
2.3743(9)
2.359(2)
137.87(7)
65.20(7)
Compound 5
Ag(1)–P(1)
Ag(1)–O(1)
N(1)#1–Ag(1)–P(1)
P(1)–Ag(1)–O(1)
2.3564(9)
2.489(2)
139.69(8)
122.85(6)
Ag(1)–N(1)#1
2.237(3)
132.11(2)
N(1)#1–Ag(1)–O(1)
C(2)–C(1)–P(1)
94.01(10)
109.2(2)
Compound 8B
Ag(1)–P(1)
Ag(1)–O(1)
N(1)–Ag(1)–P(1)
P(1)–Ag(1)–O(1)#1
P(1)–Ag(1)–O(1)
C(2)–C(1)–P(1)#2
a
Symmetry transformations used to generate equivalent atoms. For 2:
#1 = ꢀx + 1, ꢀy + 2, ꢀz. For 3: #1 = ꢀx + 1, ꢀy, ꢀz + 1; #2 = ꢀx + 2, y, ꢀz + 3/2. For 4:
#1 = ꢀx + 1, ꢀy + 2, ꢀz + 1. For 5: #1 = ꢀx, ꢀy + 1, ꢀz + 1.
2.3630(9)
2.408(2)
116.29(7)
146.42(6)
125.34(5)
111.0(2)
Ag(1)–N(1)
Ag(1)–O(1)#1
N(1)–Ag(1)–O(1)#1
N(1)–Ag(1)–O(1)
O(1)#1–Ag(1)–O(1)
2.343(3)
2.401(2)
87.77(9)
90.51(9)
73.91(8)
3.2.7. Structure of compounds 8A and 8B
According to the molecular structures of 8A and 8B, the confor-
mation of the PMP-41 ligand is seen to be quite sensitive to coun-
terion effects due to the presence of a strong coordinating anion. In
addition, the silver environment is just as susceptible, if not more
so, to change when using different crystallization solvent systems.
The molecular structure shown in Fig. 9 was obtained by layering
ether into a solution of compound 8 in CH3CN, while in Fig. 10b
is shown the thermal ellipsoid of 8B, formed by layering ether into
a solution of compound 8 in DMF. Both correspond to polymeric
structures displaying notable differences in connectivity even
when they were obtained by using the same starting materials.
The crystal structure of 8A displays an uncommon Ag–Ag interac-
tion for compounds involving the bidentate PMP-41 ligand. The
structure conserves the same bimetallic box conformation
observed in the other compounds, where the infinite chain is sup-
a
Symmetry transformations used to generate equivalent atoms. For 6:
#1 = ꢀx + 3/2, y ꢀ 1/2, ꢀz + 1/2; #2 = ꢀx + 3/2, y + 1/2, ꢀz + 1/2. For 7: #1 = ꢀx + 3,
ꢀy ꢀ 1, ꢀz; #2 = ꢀx, ꢀy + 1, ꢀz + 1. For 8A: #1 = ꢀx + 1, ꢀy + 1, ꢀz + 1; #2 = ꢀx,
ꢀy + 1, ꢀz + 1. For 8B: #1 = ꢀx + 1/2, ꢀy + 5/2, ꢀz; #2 = ꢀx + 1/2, ꢀy + 3/2, ꢀz.
of 90° with respect to the plane of the bimetallic box, thus resulting
in a polymeric structure with a zigzag conformation (Fig. 10a). The
silver atoms have a distorted tetrahedral geometry with a Ag1–
Ag1A distance of 3.8686(9) Å. Each Ag is also bound to two phos-
phine ligands with opposing ends facing each other in a head-to-
tail fashion, as observed in all other AgX/PMP-41 structures. The
Ag(1)–O(1)#1 distance displays a value of 2.401(2) Å, which is
longer than the observed in compound 8A with a value of
2.359(2) Å, due to weaker interactions when the O atom displays
a bridging mode.
ported by the metal–metal interactions with
a distance of
3.1084(6) Å that falls in the range of reported values. The metal
center displays a distorted tetrahedral geometry, bound to a P
and a N atom of two different PMP-41 ligands, an O from the tfa
anion, and the already mentioned Ag–Ag bond. The metallophilic
interaction only observed in this structure is probably favored by
the electronegative effect imparted by the O atom of the tfa anion,
which is better stabilized by a metal-metal interaction than by the
electronic contribution from a pyridyl group of another PMP-41
ligand. The crystal structure of compound 8B reveals a diamond
like binuclear silver center with each Ag bridged by two tfaꢀ ions.
This type of conformations has been reported before in our group
when oxygen-containing counteranions were used [47,48]. The
4-center bimetallic interaction exhibit an approximate separation
3.3. Luminescence properties
Self-assembled coordination complexes that present high lumi-
nous efficiency are currently of great interest due to their potential
in microelectronics, sensor technologies, non-linear optics, porous
materials, and other applications [48–53]. Organometallic com-
plexes associated with ligands that contain aromatic nitrogen het-
erocycles have been extensively studied as they can be used as
light-emitting devices. According to this, the absorption and emis-
sion properties of these materials may be adjusted by varying the
metal environment and employing ligands that can effectively
enhance luminescence properties. In this work, can be seen dra-

F. Hung-Low et al. / Inorganica Chimica Acta 362 (2009) 426–436
435
Table 5
the bimetallic box conformation of the PMP-41 structures. The
complexes, according to their structures and luminescent charac-
teristics, are seen to be highly dependent on the bipyridine ligand
used in the reaction, which is also responsible for the enhancement
of the excitation and emission spectra intensities. To date, we are
continuing to study the coordination properties of 1 with other
metals and are also actively pursuing the bisubstituted pyridyl
PMP-42 ligand. Studies of phosphine-substituted ligands of the
type PPhxCH2py3ꢀx (x = 0, 1, 2) will be continued, as well as substi-
tuted and non-substituted bipyridines in mixed ligand systems.
Luminescent spectral data for compounds 2–8 at 77 K and 1 ꢁ 10ꢀ4 M in CH3CN
Compound
Excitation kmax (nm)
Emission local kmin (nm)
2
3
4
5
6
7
8
393, 408
398, 418
448, 481
382, 393
446, 473
412, 438, 462
387, 396
283, 288
289
318
279
314
297
282
matic changes in the luminescence properties of the metal com-
plexes by introducing in the coordination sphere of the metal addi-
tional electron donating ligands, as they are the 5,50-dimethyl-2,20-
bipyridine and the 4,40-bipyridine. Here we report the excitation
and emission spectra of the metal complexes; all spectra were re-
corded at concentrations of 1 ꢁ 10ꢀ4 M in acetonitrile glasses at
77 K, and shown in Figs. S4 and S5.
Acknowledgements
This research was supported by funds provided by a Grant from
the Robert A. Welch Foundation (AA-1508). The Bruker X8 APEX
diffractometer was purchased with funds received from the
national Science Foundation Major Research Instrumentation
Program Grant CHE-0321214.
According to the intensity of the emission and excitation max-
ima of the compounds discussed herein, these can be separated
into two groups. Molecules that present only metal-PMP-41 inter-
actions and metal complexes obtained by adding 5,50-dimethyl-
2,20-bipyridine or 4,40-bipyridine to reaction mixtures containing
AgX/PMP-41, which show a clear difference in intensity of the
emission and excitation spectra. Excitation maxima of all com-
pounds are presented in Table 4 along with the local emission
maxima. Excitation maxima for 2, 3, 5 and 8 are 283, 289, 279
and 282 nm, respectively, with intensities that reach up to the
4.2 ꢁ 106 cps units. As expected the excitation spectra of these
compounds are very similar, given the same structural conforma-
tion of the phosphine ligand with the silver metal in the com-
plexes. The emission spectra of the mentioned compounds show
two maximums for each case, illustrating the decay transitions
associated with each system, and covering a small range of the
spectrum with local maxima that range between 283 and
289 nm. Comparing the emission data of the compounds based
on the AgBF4 salt, a red shift of the maximum of approximately
30 nm is observed for the [AgBF4(PMP-41)]2 complex with respect
to the same compound coordinated to the 5,50-dimethyl-2,20-
bipyridine. The same luminescent behavior is observed for the ser-
ies of compounds obtained with the AgOtf salt, where the maxi-
mum in the emission spectrum of the AgOtf(PMP-41) compound
is red shifted with respect to compounds 6 and 7. However, the
most noticeable difference between the [AgX(PMP-41)]2 com-
pounds and their corresponding analogous coordinated to either
the 5,50-dimethyl-2,20-bipyridine or 4,40-bipyridine, is the in-
creased intensity in which the latter group of compounds emit,
observing differences up to 1 ꢁ 106 units of cps. This high lumines-
cent efficiency of compounds containing bipyridine type ligands
have been reported before [54,55], particularly in complexes of
some transition metals of the group VII and VIII, where the
metal-bipyridine interactions illustrates the complexity of the
decay transitions associated with the more complicated system.
Appendix A. Supplementary data
CCDC 682322, 680324, 680327, 680320, 680325, 680326,
680321 and 680323 for contain the supplementary crystallo-
graphic data for 2, 3, 4, 5, 6, 7, 8A and 8B. These data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2008.04.032.
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