Silver coordination complexes of 2-(diphenylphosphinomethyl)pyridine and their bipyridine derivatives

Article abstract of DOI:10.1016/j.ica.2007.08.015

Reaction of 2-(diphenylphosphinomethyl)pyridine (PMP-21) with the silver(I) salts of tetrafluoroborate (BF₄^-), triflate (Otf^-), and trifluoroacetate (tfa^-) affords dinuclear complexes (2-4), where the ligand bridges the two silver centers, and the anions interact with the metal centers to varying degrees. Further reaction of AgBF₄ and AgOtf with reaction solutions containing PMP-21 and either the bidentate 5,5′-dimethyl-2,2′-bipyridine or 4,4′-bipyridine ligands produce dimeric and bridged structural motifs. The ability of 5,5′-dimethyl-2,2′-bipyridine to chelate and the 4,4′-bipyridine to serve as a connector between metal centers, allows the construction of coordinative structures where the effect of ligand ratio and either interacting or non interacting anions influence the silver coordination environment, allowing it to take on several geometries including trigonal bipyramidal, 5, both T-shaped and tetrahedral in a single structure, 6 and 8, trigonal pyramidal, 7, and trigonal planar, 9. Structures 2, 3, and 4 display comparable Ag-Ag contacts ranging from 2.7979(10) to 3.0538(4) ?, with a corresponding weakening of the metallophilic interaction when a bipyridine ligand is coordinated. Low-temperature luminescence spectra were collected for all compounds and are compared.

Full text of DOI:10.1016/j.ica.2007.08.015

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 1298–1310
www.elsevier.com/locate/ica
Silver coordination complexes of 2-(diphenylphosphinomethyl)
pyridine and their bipyridine derivatives
*
Fernando Hung-Low, Kevin K. Klausmeyer
Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, United States
Received 13 July 2007; accepted 18 August 2007
Available online 25 August 2007
Abstract
Reaction of 2-(diphenylphosphinomethyl)pyridine (PMP-21) with the silver(I) salts of tetrafluoroborate ðBF4ꢀÞ, triflate (Otfꢀ), and
trifluoroacetate (tfaꢀ) affords dinuclear complexes (2–4), where the ligand bridges the two silver centers, and the anions interact with
the metal centers to varying degrees. Further reaction of AgBF4 and AgOtf with reaction solutions containing PMP-21 and either
the bidentate 5,50-dimethyl-2,20-bipyridine or 4,40-bipyridine ligands produce dimeric and bridged structural motifs. The ability of
5,50-dimethyl-2,20-bipyridine to chelate and the 4,40-bipyridine to serve as a connector between metal centers, allows the construction
of coordinative structures where the effect of ligand ratio and either interacting or non interacting anions influence the silver coordination
environment, allowing it to take on several geometries including trigonal bipyramidal, 5, both T-shaped and tetrahedral in a single struc-
ture, 6 and 8, trigonal pyramidal, 7, and trigonal planar, 9. Structures 2, 3, and 4 display comparable Ag–Ag contacts ranging from
˚
2.7979(10) to 3.0538(4) A, with a corresponding weakening of the metallophilic interaction when a bipyridine ligand is coordinated.
Low-temperature luminescence spectra were collected for all compounds and are compared.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: N,P ligands; Metal–metal interaction; Silver; Coordination modes
1. Introduction
ambidentate ligand 2-(diphenylphosphinomethyl)pyridine
(PMP-21, Fig. 1), which can act in a chelating fashion
for metal centers that easily adopt L–M–L angles of 90ꢁ
[8,9]. With metals that do not easily adopt an octahedral
environment such as silver(I) it was anticipated that the
ligand would act as a bridge suitable for the formation of
dinuclear complexes in which the metal ions are held in
close proximity, thus allowing direct metal–metal
interactions.
The coordination behavior of phosphine ligands which
also contain a pyridine moiety has been studied for many
years [1–3]. The incorporation of harder pyridyl substitu-
ents in conjunction with a softer phosphorus center alters
and augments the coordination flexibility of the ligand
and leads to multidentate hemilabile ligands [4,5]. Free
rotation about the P–Cipso bond of pyridyl and 2-methyl-
pyridyl derivatives allows the nitrogen to obtain the correct
orientation to coordinate metals of different radii, and in
addition to the geometrical flexibility, they provide
electronic adaptability as well [6,7]. The multidentate
2-(phosphinomethyl) pyridines of the type PPhx-
(CH2py3ꢀx)(x = 0, 1, 2) are potentially interesting ligands
in this respect. Of particular interest to this study is the
The study of d10 ‘‘closed-shell’’ interactions that exist
between the monovalent elements of group 11 has been
active for many years [10–12]. These interactions are typi-
cally associated with ligand-bridged, hydrogen-bonded,
electrostatically-attracted, or p–p stacked effects, though
unsupported M–M interactions have been described as well
[13–18]. With silver in particular, crystal engineering of
coordination architectures has emerged as a promising field
of investigation for the design and construction of novel
discrete and polymeric metal–organic coordination
*
Corresponding author. Fax: +1 254 710 4272.
E-mail address: Kevin_Klausmeyer@baylor.edu (K.K. Klausmeyer).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.08.015

F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
1299
glovebox; solvents were distilled under nitrogen from the
appropriate drying agent immediately before use. n-Butylli-
thium and chlorodiphenylphosphine were purchased from
Aldrich and used as received. Silver(I) trifluoroacetate, sil-
ver(I) trifluoromethanesulfonate, and silver(I) tetrafluoro-
borate were purchased from Strem Chemicals Inc. and
P
1
used as received. H were recorded at 360.13 MHz with a
Bruker Spectrospin 300 MHz spectrometer and 31P and var-
iable-temperature 31P NMR spectra were recorded at
202.31 MHz on a Varian 500 MHz NMR spectrometer. Ele-
mental analyses were performed by Atlantic Microlabs Inc.
in Norcross, Georgia. Excitation and emission spectra were
recorded with an Instruments S.A. Inc. Fluoromax-2 model
spectrometer using band pathways of 5 nm for both excita-
tion and emission and are presented uncorrected.
N
Fig. 1. Structure of PMP-21 ligand.
complexes, with potential use as functional materials [19–
23]. The many silver coordination architectures reported
are demonstrative of the influence that slight variations in
ligand and/or anion imparts on the formation of unique
and discrete molecules, supramolecular arrays, and 1-, 2-,
and 3-dimensional coordination networks [15–18,24–30].
To date, several reports of the PMP-21 ligand coordinated
to transition metals such as Rh [9], Fe, and Ru [31–33] with
potential application in the catalysis arena have been pub-
lished [34], but no systematic investigation of the interac-
tion between this P,N-donor and silver salts has been
reported. In this report, we fill the void by the synthesis
2.2. Synthesis
2.2.1. Synthesis of 2-(diphenylphosphinomethyl)pyridine,
PMP-21 (1)
n-Butyllithium (17 mmol, 5.86 mL, 2.9 M in hexane)
was added over a period of 10 min to 2-picoline (17 mmol,
1.67 mL) in dry THF (20 mL) at ꢀ41 ꢁC. After stirring for
1 h, the mixture was added to a solution of chlorodiphenyl-
phosphine (3.0 g, 17 mmol) in dry THF (20 mL) at ꢀ84 ꢁC
over a period of 30 min. Water (20 mL) was then added
over 10 min and the mixture stirred for 30 min. The prod-
uct was obtained by first extracting with 0.3 N HCl (aq.),
then neutralizing with a NaHCO3 solution, and extracting
with dichloromethane. The solvent and any un-reacted 2-
picoline were removed under vacuum (oil pump) and a yel-
low oil resulted. The yield of the crude product was 81%.
Purification of the ligand was carried out by several extrac-
tions with dry hexane. After removing the solvent a white
solid of >98% purity in 70% yield was obtained. 31P
NMR (CDCl3, 298 K) d: (s, ꢀ13.73).
and spectroscopic characterization of
AgX:PMP-21 complexes supported by single-crystal X-
ray studies.
a number of
Additionally the use of bipyridine ligands (5,50-
dimethyl-2,20-bipyridine and 4,40-bipyridine) in the coordi-
nation chemistry associated with the AgX:PMP-21 adducts
for the formation of mixed ligand coordination complexes
is reported. The complexes described in this paper were
obtained by varying the ligand/metal ratio and by changing
the counterion of the system. Herein, we describe the
changes that are brought about in the flexible coordination
sphere of the silver(I) cation by the coordination of the
bipyridine ligand to the corresponding AgX:PMP-21 com-
plex, and the luminescence that results from the different
Ag–P interactions encountered in each metal compound.
The PMP–nm naming convention that we have adopted
allows for ease in discussion of these phosphinomethylpyri-
dines, as there are many substitutions that can be made and
systematic nomenclature can be cumbersome. As such,
PMP indicates the PhosphinoMethylPyridine ligands,
where n is the position of substitution on the pyridyl ring
and m is the number of substitutions by methylpyridine
on the phosphorus.
2.2.2. Synthesis of [AgBF4(PMP-21)]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 an off-white
powder. This was then dissolved in a small amount of
CH2Cl2 and precipitated with hexane. The recrystallization
was repeated until compound 2 was obtained as a white
powder upon drying in 63% (0.117 g, 0.124 mmol) yield.
Colorless blocks were obtained by slow diffusion of hexane
1
into a CH2Cl2 solution of 2 at 5 ꢁC. H NMR (CDCl3,
298 K) d: 4.05 (m, 4H), 6.65 (d, 2H), 7.48 (m, 8H), 7.60
(m, 16H), 8.89 (d, 2H). 31P NMR ((CD3)2CO, 238 K) d:
14.8, dd, J(107Ag–P) = 715 Hz, J(109Ag–P) = 629 Hz,
C36H32Ag2B2F8N2P2 (943.94): Anal. Calc. C, 45.81; H,
3.42; N, 2.97. Found: C, 46.04; H, 3.53; N, 3.19%.
2. Experimental
2.1. General remarks
All experiments were carried out under a nitrogen atmo-
sphere using a Schlenk line and standard Schlenk techniques.
All silver salts reagents were stored in an inert-atmosphere
2.2.3. Synthesis of [AgOtf(PMP-21)]2 (3)
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

1300
F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
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-crystallized with CH3CN/
ether solutions upon drying in 71% (0.151 g, 0.141 mmol)
yield. Colorless blocks were obtained by slow diffusion of
hexane into a CH2Cl2 solution of 3 at 5 ꢁC. 1H NMR
(CDCl3, 298 K) d: 4.36 (s, 4H), 7.08 (d, 2H), 7.54 (m,
10H), 7.61 (m, 4H), 7.81 (m, 10H), 8.92 (d, 2H). 31P
NMR ((CD3)2CO, 238 K) d: 13.17, dd, J(107Ag–
P) = 725 Hz, J(109Ag–P) = 628 Hz, C38H32Ag2F6N2O6P2S2
(1068.46): Anal. Calc. C, 42.72; H, 3.02; N, 2.62. Found: C,
42.77; H, 3.16; N, 2.55%.
(0.292 g, 140 mmol). Crystallization formed colorless
blocks obtained by slow diffusion of hexane into a THF
solution of 6 at 5 ꢁC. H NMR (CDCl3, 298 K) d: 4.51
(s, 8H), 7.22 (m, 4H), 7.50 (m, 31H), 7.82 (m, 21H), 8.28
(m, 4H), 8.91 (m, 4H). 31P NMR ((CD3)2CO, 238 K) d:
14.3, dd, J(107Ag–P) = 719 Hz, J(109Ag–P) = 623 Hz,
C93H88Ag4B4F16N6O3P4 (2240.29): Anal. Calc. C, 45.04;
H, 3.16; N, 3.66. Found: C, 44.55; H, 3.49; N, 3.07%.
1
2.2.7. Synthesis of (AgOtf)2(PMP-21)(5,50-dimethyl-2,20-
bipyridine)2 (7)
To a stirred solution of AgOtf (0.217 g, 0.798 mmol) in
CH3CN (5 mL) was added a solution of 5,50-dimethyl-2,20-
bipyridine (0.147 g, 0.798 mmol) in CH3CN (5 mL). The
resulting solution remained clear and colorless, and after
stirring for 5 min a solution of 1/2 equiv. of 1 (0.109 g,
0.398 mmol) in CH3CN (5 mL) was added to the mixture.
Upon drying, a light yellow powder in 63% isolated yield
(0.304 g, 0.125 mmol) was reclaimed. Colorless blocks crys-
tals were obtained by slow diffusion of hexane into a
2.2.4. Synthesis of [Agtfa(PMP-21)]2 (4)
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) to leave a fluffy off-white
solid upon evaporation of the solvent. The compound
was purified by washing with CH2Cl2 since it is insoluble
in the solvent. Upon drying the compound, the product
was obtained in 82% (0.325 g, 0.163 mmol) yield. Colorless
blocks were obtained by slow diffusion of hexane into a
1
CH2Cl2 solution of 4 at 5 ꢁC. H NMR (CDCl3, 298 K)
d: 2.38 (s, 12H), 4,67 (m, 2H), 7.23 (m, 1H), 7.69 (m,
7H), 7.97 (m, 9H), 8.18 (m, 8H), 9.03 (m, 1H). 31P NMR
((CD3)2CO, 238 K) d: 16.5, br. s. C90H85Ag4Cl4F12-
N10O13P2S4 (2506.14): Anal. Calc. C, 44.31; H, 3.26; N,
5.04. Found: C, 43.82; H, 3.33; N, 4.84%.
1
CH2Cl2 solution of 4 at 5 ꢁC. H NMR (CDCl3, 298 K)
d: 4.04 (d, 4H), 6.87 (d, 2H), 7.37 (m, 2H), 7.47 (m, 8H),
7.57 (m, 4H), 7.70 (m, 10H), 8.69 (d, 2H). 31P NMR
((CD3)2CO, 238 K) d: 11.5, dd, J(107Ag–P) = 700 Hz,
J(109Ag–P) = 608 Hz, C83H70Ag4Cl6F12N4O8P4 (2247.49):
Anal. Calc. C, 48.22; H, 3.24; N, 2.81. Found: C, 48.09;
H, 3.25; N, 2.83%.
2.2.8. Synthesis of [AgOtf(PMP-21)]4(4,40-bipyridine)
(8)
To a stirred solution of 2 equiv. of AgOtf (0.217 g,
0.798 mmol) in CH3CN (5 mL) was added 2 equiv. of 1
(0.221 g, 0.798 mmol) in 5CH3CN (5 mL). This was stirred
for 5 min, and then a solution of 4,40-bipyridine (0.031 g,
0.199 mmol) in CH3CN (5 mL) was added. This mixture
was stirred for 10 min, and then the solvent was removed
in vacuo to leave a light yellow powder in 63% isolated
yield (0.296 g, 0.125 mmol). Colorless block crystals were
obtained by slow diffusion of hexane into a solution of 8
2.2.5. Synthesis of [AgBF4(PMP-21)(5,50-dimethyl-2,20-
bipyridine)]2 (5)
To a stirred solution of AgOtf (0.109 g, 0.399 mmol) was
added 1 equiv. of 5,50-dimethyl-2,20-bipyridine (0.074 g,
0.401 mmol) in CH3CN (5 mL). This was stirred for
5 min, and then a solution of 1 (0.109 g, 0.398 mmol) in
CH3CN (5 mL) was added to the reaction mixture. The
solution was stirred for 10 min, and then the solvent was
removed in vacuo to leave a light yellow powder in 65%
isolated yield (0.170 g, 0.129 mmol). Crystallization formed
colorless blocks obtained by slow diffusion of hexane into a
1
in CH2Cl2 at 5 ꢁC. H NMR (CDCl3, 298 K) d: 4.35 (s,
8H), 7.15 (m, 4H), 7.53 (m, 30H), 7.63 (m, 8H), 7.82 (m,
18H), 8.81 (m, 4H). 31P NMR ((CD3)2CO, 238 K) d:
13.0, dd, J(107Ag–P) = 714 Hz, J(109Ag–P) = 631 Hz,
1
CH2Cl2 solution of 5 at 5 ꢁC. H NMR (CDCl3, 298 K) d:
2.41 (s, 12H), 4.51 (d, 4H), 7.31 (m, 2H), 7.51 (m, 2H), 7.63
(m, 11H), 7.99 (m, 14H), 8.25 (d, 7H), 8.46 (s, 2H) 8.70 (m,
2H). 31P NMR ((CD3)2CO, 238 K) d: 12.4, br. s,
C62H60Ag2B2Cl4F8N6P2 (1482.26): Anal. Calc. C, 50.24;
H, 4.08; N, 5.97. Found: C, 50.65; H, 4.17; N, 6.55%.
C102H104Ag4F12N6O16P4S4(2581.51): Anal. Calc. C, 45.04;
H, 3.16; N, 3.66. Found: C, 44.43; H, 3.31; N, 2.99%.
2.2.9. Synthesis of [AgOtf(PMP-21)2]2(4,40-bipyridine)
(9)
To a stirred solution of 2 equiv. of AgOtf (0.217 g,
0.798 mmol) in CH3CN (5 mL) was added 4 equiv. of 1
(0.442 g, 1.596 mmol) in CH3CN (5 mL). This was stirred
for 5 min, and then a solution of 4,40-bipyridine (0.062 g,
0.399 mmol) in CH3CN (5 mL) was added. Upon drying,
a light yellow powder in 70% isolated yield (0.496 g,
0.279 mmol) was obtained. Crystallization formed colorless
blocks of obtained by slow diffusion of hexane into a solu-
2.2.6. Synthesis of [AgBF4(PMP-21)]4(4,40-bipyridine)
(6)
This reaction used 1 equiv. of AgBF4 (0.077 g,
0.396 mmol) in CH3CN (5 mL) added to 1 equiv. of 1
(0.109 g, 0.398 mmol) in CH3CN (5 mL). After stirring
for 5 min,
a
solution of 4,40-bipyridine (0.031 g,
0.198 mmol) in CH3CN (5 mL) was added, and the mixture
was then stirred for 10 min. Upon evaporation of the sol-
vent, a light yellow powder was isolated in 71% yield
1
tion of 9 in CH2Cl2 at 5 ꢁC. H NMR (CDCl3, 298 K) d:
4.32 (s, 8H), 7.16 (m, 4H), 7.54 (m, 30H), 7.63 (m, 8H),

F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
1301
7.86 (m, 18H), 8.82 (m, 4H). 31P NMR ((CD3)2CO, 238 K)
d: 12.5, dd, J(107Ag–P) = 718 Hz, J(109Ag–P) = 631 Hz,
C84H72Ag2F6N6O6P4S2 (1779.22): Anal. Calc. C, 56.58; H,
4.30; N, 4.71. Found: C, 56.05; H, 4.03; N, 5.00%.
strongly binding 5,50-dimethyl-2,20-bipyridine which satu-
rates the metal center in solution and only allows signifi-
cant binding of the phosphorus moiety upon
crystallization or precipitation. Chemical shifts and cou-
pling constants are provided in the experimental section.
3. Results and discussion
3.2. Description of the crystal structures
3.1. General characterizations
Crystallographic data were collected on crystals with
dimensions 0.094 · 0.062 · 0.055 mm for 2, 0.303 · 0.247 ·
0.161 mm for 3, 0.281 · 0.201 · 0.188 mm for 4, 0.209 ·
0.153 · 0.102 mm for 5, 0.334 · 0.181 · 0.156 mm for 6,
0.268 · 0.158 · 0.094 for 7, 0.320 · 0.160 · 0.100 for 8, and
0.296 · 0.287 · 0.176 for 9. Data were collected at 110 K
on a Bruker X8 Apex using Mo Ka radiation (k = 0.710
3.1.1. Synthesis and NMR spectra
The ligand 2-(diphenylphosphinomethyl)pyridine (PMP-
21) 1, synthesized by a modified procedure [9], has been
effectively purified with several hexane extractions, produc-
ing a white powder with >98% purity in 70% yield, as
opposed to the creamy colored oil with purity >90% previ-
ously reported. Pure 1 is thermally stable and is not found
to be readily oxidized in comparison to the less pure creamy
yellow oil.ꢀThe reꢀaction of three different silver(I) salts
˚
73 A). All structures were solved by direct methods after
correction of the data using SADABS. Crystallographic data
and refinement details for the complexes mentioned herein
are found in Tables 1 and 2. The molecular structure of
the compounds is displayed in Figs. 2–9. Summary of
selected bond lengths, angles, and interatomic distances
are given in Tables 3–5. All data were processed using the
Bruker AXS SHELXTL software, version 6.10. Hydrogen
atoms were placed in calculated positions and all non-
hydrogen atoms were refined anisotropically except for the
disordered solvent molecules and anions of compound 8.
(BF4ꢀ, Otf , or tfa ) with an equimolar quantity of 1 gave
ꢀ
rise to the compounds [AgX:PMP-21]2 (1:1) (X ¼ BF4
,
Otfꢀ, or tfaꢀ) 2–4. Under the same conditions, reaction of
an equivalent of 5,50-dimethyl-2,20-bipyridine and 1/
2 equiv. of 4,40-bipyridine in a reaction mixture containing
AgBF4 and PMP-21 yield compounds 5 and 6, respectively.
Reaction of two equivalents of the 5,50-dimethyl-2,20-bipyr-
idine ligand with a reaction mixture of 2 equiv. AgOtf and
1 equiv. PMP-21 directs the formation of compound 7. Con-
trolling the PMP-21/Ag ratio in the reaction involving 4,40-
bipyridine, allows the formation of compounds 8 and 9. No
further reaction of the [Agtfa(PMP-21)]2 complex with any
of the bipyridine ligands was observed, likely due to the elec-
tronically and sterically crowded silver centers of 4. Altering
the reaction sequence to add the bipy first to the Ag salt and
with subsequent addition of the PMP-21 ligand yielded only
compound 4 upon crystallization.
3.2.1. Crystal and molecular structure of compounds 2, 3,
and 4
The crystal structure of complex 2 is shown in Fig. 2 and
is demonstrative of the bridging effect that the PMP-21
ligand displays, forming a 6-membered ring fragment with
two interconnecting silver ions. The silver coordination
environments that are seen in structures 2–4 do not differ
greatly from one structure to the next, demonstrating coor-
dination independence of the counterion present (Scheme
1). As shown in Figs. 2–4 the metal centers in 2 exhibit a
T-shape geometry and in 3 and 4 capped T-shaped environ-
ments since interaction with the respective counterion is
encountered, the exception being one of the silver atoms
in compound 4, where the tfaꢀ counterion has only a
Solutions of the silver compounds 2–4 readily decompose
to leave metallic silver and unidentified black byproduct. A
light brown color appears almost immediately upon mixing
and is indicative of the reaction of 1 with the various silver
salts. However, the powders of each complex have proven
themselves to be quite robust, withstanding long exposure
to air and room temperatures with little sign of decomposi-
tion, provided they are shielded from light. Compounds 5–8
were isolated from the respective reaction mixture by imme-
diate precipitation of the corresponding white product with
ether once the bipyridine ligand is reacted with the AgX and
PMP-21 solution. Compound 9 was purified with simple
dichloromethane washings of the remaining solid, since
the resulting product was insoluble in the solvent.
˚
weakly interacting Ag1–O(4) distance of 2.661(3) A. In 2,
ꢀ
although the BF4 ions are displayed as non coordinative,
˚
the Ag1–F2 and Ag2–F8 distances of 2.692(2) A and
˚
2.693(3) A, respectively, suggest a weak interaction. All
three complexes display M–M distances in the typical
range values for Ag–Ag interactions, varying from
˚
2.7979(10) to 3.0538(4) A. The bifunctional phosphine
ligand bridges the Ag–Ag axis, acting as a bridging biden-
tate allowing the metals to come close to one another. A
repetitive structural feature in common is that the two
PMP-21 ligands coordinate head-to-tail, P–Ag–N across
the Ag–Ag axis, rather than head-to-head.
Compounds 3 and 4 both display a 1:1 ratio of PMP-21
ligand to metal with only small variances between the two
likely arising from the difference in basicity of Otfꢀ versus
tfaꢀ. According to Table 3, the Ag–P and Ag–N distances
The 1H NMR spectra of compounds 2–9 are, as
expected, generally similar. The 31P NMR spectra at
ꢀ40 ꢁC were recorded in deuterated acetone for all com-
pounds. At this temperature the dissociation of the Ag–P
bond is slowed to a time scale where a doublet of doublets
signal, due to the two isotopes of Ag, is observed for all
compounds except 5 and 7. The lack of observed coupling
for complexes 5 and 7 is likely due to the presence of the

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Table 1
Crystallographic data for compounds 2–5
2
3
4
5
Empirical formula
Formula mass
C36H32Ag2B2F8N2 P2
C38H32Ag2F6N2 O6P2S2
1068.46
9.046(3)
10.393(3)
10.612(3)
86.744(16)
87.096(16)
80.804(16)
982.4(5)
C83H70Ag4Cl6F12N4O8P4
2247.49
19.2216(19)
11.6882(14)
19.809(3)
90
102.160(3)
90
4350.5(9)
2
C62H60Ag2B2Cl4F8N6P2
1482.26
11.284(2)
20.890(4)
14.498(3)
90
112.210(4)
90
3164.1(9)
2
943.94
12.0138(14)
22.4294(18)
13.6037(14)
90
97.885(3)
90
3631.0(6)
4
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
1
Crystal system
Space group
T (K)
Monoclinic
P21/n
110(2)
1.727
1.238
Triclinic
Monoclinic
P21/n
110(2)
1.716
1.228
Monoclinic
P21/c
110(2)
1.556
0.907
ꢀ
P1
110(2)
1.806
1.263
Dcalc (g cmꢀ3
)
l (mmꢀ1
2hmax (ꢁ)
)
27.63
25.68
26.28
33.18
Reflections measured
Reflections used (Rint
Restraints/parameters
R1 [I > 2r(I)]
28310
8408 (0.0596)
0/469
0.0415
0.0712
0.0690
0.0812
1.036
13967
3637 (0.0525)
0/262
0.0479
0.1219
0.0544
0.1270
1.034
41440
8624 (0.0483)
0/556
0.0335
0.0763
0.0465
0.0836
1.009
26111
10882 (0.0350)
0/390
0.0376
0.0849
0.0520
0.0942
1.027
)
wR2 [I > 2r(I)]
RðF 2oÞ (all data)
RwðF 2oÞ (all data)
Goodness-of-fit on F2
Table 2
Crystallographic data for compounds 6-9
6
7
8
9
Empirical formula
Formula mass
C
93H88Ag4B4F16N6O3P4
C90H85Ag4Cl4F12N10O13P2S4
C102H104Ag4F12N6O16P4S4
2581.51
9.9341(5)
27.9506(16)
19.8545(12)
90
103.234(3)
90
5366.5(5)
2
C84H72Ag2F6N6O6P4S2
1779.22
15.9418(16)
15.4521(14)
16.1046(16)
90
93.856(3)
90
3958.1(7)
2
2240.29
17.5712(7)
11.3796(4)
23.4529(10)
90
101.292(2)
90
4598.7(3)
2
2506.14
29.5902(15)
12.6772(7)
27.3150(16)
90
108.079(2)
90
9740.6(9)
4
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Crystal system
Space group
T (K)
Monoclinic
P21/n
110(2)
1.618
0.995
Monoclinic
C2/c
110(2)
1.709
1.110
Monoclinic
P21
110(2)
1.598
0.943
Monoclinic
P21/c
110(2)
1.493
0.700
Dcalc. (g cmꢀ3
)
l (mmꢀ1
2hmax (ꢁ)
)
26.53
31.90
26.36
28.36
Reflections measured
88127
16120
48692
49846
Reflections used (Rint
Restraints/parameters
R1 [I > 2r(I)]
)
9501 (0.0579)
30/614
0.0490
0.1279
0.0600
0.1355
1.054
11012 (0.0348)
0/627
21138 (0.0431)
344/1266
0.0475
0.0935
0.0657
9890 (0.0527)
0/496
0.0363
0.0895
0.0494
0.0482
0.0983
0.0822
0.1140
1.014
wR2 [I > 2r(I)]
RðF 2oÞ (all data)
RwðF 2oÞ (all data)
Goodness-of-fit on F2
0.1049
1.024
0.0975
1.047
are in the range of the typical values, with no significant
differences in the bond distances or angles.
the Otfꢀ ion in 3, design of coordination complexes using
additional electron donor ligands appeared to be feasible.
Reaction of the bidentate 5,50-dimethyl-2,20-bipyridine
with a solution containing AgBF4, and the subsequent
addition of the PMP-21 gave rise to the formation of com-
pound 5. Formation of the product is not achieved when
3.2.2. Crystal and molecular structure of compound 5
Given the coordinatively unsaturated environment of
the silver centers in compound 2 and the labile nature of

F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
1303
Fig. 2. Thermal ellipsoid plot of 2 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms have been removed for
clarity.
Fig. 3. Thermal ellipsoid plot of 3 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms have been removed for
clarity.
the bipyridine ligand is added to a reaction mixture con-
taining the silver salt and the phosphine ligand, which
is indicative that in solution the AgBF4:PMP-21 adduct
contains a saturated environment that prevents the coordi-
nation of another donor ligand. On the other hand, forma-
tion of a AgBF4:5,50-dimethyl-2,20-bipyridine adduct is

1304
F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
Fig. 4. Thermal ellipsoid plot 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.
Fig. 5. Thermal ellipsoid plot of the cationic portion of 5 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms have
been removed for clarity.
more susceptible to coordination of a P,N-donor ligand.
The crystal structure shown in Fig. 5 displays a 1:1:1 ratio
of PMP-21 ligand to metal to bipyridine fragment. The
expansion of the silver coordination environment from tri-
gonal into a five-coordinate setting was as expected. A dis-
torted trigonal bipyramidal geometry is observed for the

F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
1305
Fig. 6. Thermal ellipsoid plot of the cationic portion of 6 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms and
solvent molecules have been removed for clarity.
ligands weakens the metal–metal interaction. The rings of
the bipyridine ligand are twisted from planarity at an angle
of 17.8(1)ꢁ. The center of the Ag–Ag axis lies on a crystal-
lographic inversion center.
3.2.3. Crystal and molecular structure of compound 6
Using the bifunctional connector, the crystal structure
of compound 6 reveals a linked structure supported by
the coordination of the 4,40-bipyridine to two discrete
[AgBF4(PMP-21)]2 molecules. 4,40-Bipyridine is an ideal
connector between metal atoms for the prolongation of
coordination networks, due to two binding sites which
are arranged in a divergent (exo) fashion. It also has a rigid
structure which will help in the predictability of the net-
work geometries, and the length of the ligand is appropri-
ate to create cavities of molecular dimensions upon the
formation of the networks with metal atoms [35]. Com-
pound 6 shown in Fig. 6 is obtained by addition of 1/2
equiv. of 4,40-bipyridine to a reaction mixture containing
a 1:1 ratio of PMP-21 ligand to AgBF4. Ag1 has a slightly
distorted T-shaped geometry, confirmed by the approxi-
mately perpendicular angles of 90.8(3)ꢁ and 82.6(1)ꢁ and
the closely linear conformation in N2–Ag1–P1 with a value
Fig. 7. Thermal ellipsoid plot of the cationic portion of 7 with an atomic
numbering scheme. Ellipsoids are shown at the 50% level. Hydrogen
atoms and a CH2Cl2 molecule have been removed for clarity.
of 164.4(1)ꢁ. The coordination sphere of Ag2 displays a dis-
torted tetrahedral conformation due to the coordination of
the bipyridine ligand, with angles ranging between 84.2(1)ꢁ
and 122.3(1)ꢁ. The Ag–Ag interaction in the typical lengths
˚
at 2.9989(5) A, is rather less affected by the presence of the
4,40-bipyridine ligand compared with the silver interaction
silver ions in compound 5. The equatorial angles range
in compound 5. The conformation of the phosphine ligand
in compound 6 is analogous to compound 5, displaying
torsion angles with values of 78.4(4)ꢁ for P1–C1–C2–N1
and 79.2(4)ꢁ for P2–C19–C20–N2. The middle of the bipy
connecting ligand lies on a crystallographic inversion
center.
from 115.6(4)ꢁ to 127.5(4)ꢁ, where the Ag1–N1, Ag1–N3,
and Ag1–P1 bonds conform the equatorial plane, and the
axial angle is close to 180ꢁ with a value of 163.29(4)ꢁ corre-
sponding to the N2–Ag1–Ag1#1 angle. An expected longer
Ag–Ag distance is observed (3.2645(5) A) compared to
compound 2, since electron donation of the bipyridine
˚

1306
F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
Fig. 8. Thermal ellipsoid plot of 8 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms have been removed for
clarity.
Fig. 9. Thermal ellipsoid plot of the cationic portion of 9 with an atomic numbering scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms have
been removed for clarity.
3.2.4. Crystal and molecular structure of compound 7
Compound 7 presents a different ligand/metal ratio
where there are one PMP-21 ligands, two silvers and two
5,50-dimethyl-2,20-bipyridines as shown in Fig. 7. With
the other bipyridine connected to Ag2, which is N-bound
by the PMP-21 displays a larger twisting angle of
18.2(8)ꢁ. Angles around the silver ions indicate a capped
trigonal planar geometry, ranging from 73.2(1)ꢁ to
141.9(9)ꢁ for Ag1 and 73.4(1)ꢁ to 153.4(1)ꢁ for Ag2.
˚
the shortest Ag–O distance being 4.5894(3) A (Ag2–O1)
there is no interaction of the Ag centers with the anions.
The cationic portion of 7 does however have p–p interac-
tions from adjacent molecules which results in the forma-
tion of a chain of cations down the crystallographic
b-axis. The pyridyl rings of the bipyridine ligand bound
to Ag1 which is P-bound by the PMP-21 remains nearly
coplanar, evidenced by the small angle of 6.18(5)ꢁ, while
3.2.5. Crystal and molecular structure of compounds 8 and 9
Compounds 8 and 9 show the result of the reaction of
the PMP-21 ligand with AgOtf in a 1:1 and 2:1 ratio respec-
tively, with subsequent addition of 1/2 equiv. of 4,40-bipyr-
idine. The crystal structure of compound 8 is analogous to
compound 6 where two [AgOtf(PMP-21)]2 units are linked

F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
1307
Table 3
Selected bond lengths (A), angles (ꢁ), and distances for the compounds [AgBF4(PMP-21)]2 (2), [AgOtf(PMP-21)]2 (3), and [Agtfa(PMP-21)]2 (4)a
˚
2
Ag(1)–Ag(2)
Ag(1)–P(1)
Ag(1)–N(2)
2.9219(4)
2.3752(11)
2.198(3)
Ag(2)–P(2)
Ag(2)–N(1)
2.3649(10)
2.187(3)
N(2)–Ag(1)–P(1)
N(2)–Ag(1)–Ag(2)
P(1)–Ag(1)–Ag(2)
163.2(8)
86.8(7)
86.0(3)
N(1)–Ag(2)–P(2)
N(1)–Ag(2)–Ag(1)
P(2)–Ag(2)–Ag(1)
160.4(8)
92.2(8)
87.9(3)
3
Ag(1)–Ag(1)#1
Ag(1)–N(1)
2.7979(10)
2.201(4)
Ag(1)–P(1)
Ag(1)–O(1)
2.3860(15)
2.456(3)
N(1)–Ag(1)–P(1)
N(1)–Ag(1)–O(1)
P(1)–Ag(1)–O(1)
144.0(1)
100.3(1)
114.8(9)
N(1)–Ag(1)–Ag(1)#1
P(1)–Ag(1)–Ag(1)#1
O(1)–Ag(1)–Ag(1)#1
103.4(1)
84.50(4)
91.17(8)
4
Ag(1)–Ag(2)
Ag(2)–P(1)
Ag(2)–N(2)
3.0538(4)
2.3796(9)
2.253(3)
Ag(1)–P(2)
Ag(1)–N(1)
Ag(2)–O(1)
2.4010(9)
2.282(3)
2.449(2)
N(1)–Ag(1)–P(2)
N(1)–Ag(1)–Ag(2)
P(2)–Ag(1)–Ag(2)
N(2)–Ag(2)–P(1)
N(2)–Ag(2)–O(1)
a
155.2(7)
76.1(7)
86.5(2)
153.2(8)
91.9(9)
P(1)–Ag(2)–O(1)
N(2)–Ag(2)–Ag(1)
P(1)–Ag(2)–Ag(1)
O(1)–Ag(2)–Ag(1)
114.7(6)
80.1(7)
88.5(2)
105.9(6)
Symmetry transformations used to generate equivalent atoms. For 3: #1 = ꢀx + 1, ꢀy + 1, ꢀz + 1.
Table 4
0
0
0
˚
Selected bond lengths (A), angles (ꢁ), and distances for the compounds [AgBF4(PMP-21)(5,5 -dimethyl-2,2 -bipyridine)]2 (5) and [AgBF4(PMP-21)]4(4,4 -
bipyridine) (6)a
5
Ag(1)–Ag(1)#1
Ag(1)–N(1)
Ag(1)–N(3)
3.2645(5)
2.2995(16)
2.3979(16)
Ag(1)–P(1)
Ag(1)–N(2)
2.3808(6)
2.4211(17)
N(1)–Ag(1)–P(1)
P(1)–Ag(1)–N(3)
P(1)–Ag(1)–N(2)
127.50(4)
115.54(4)
112.79(4)
N(1)–Ag(1)–N(3)
N(1)–Ag(1)–N(2)
N(2)–Ag(1)–Ag(1)#1
116.53(6)
91.57(6)
163.29(4)
6
Ag(1)–Ag(2)
Ag(2)–P(2)
Ag(2)–N(1)
2.9989(5)
2.3623(11)
2.254(4)
Ag(1)–P(1)
Ag(1)–N(2)
2.3624(11)
2.172(4)
N(2)–Ag(1)–P(1)
P(1)–Ag(1)–Ag(2)
N(1)–Ag(2)–N(3)
N(1)–Ag(2)–Ag(1)
N(3)–Ag(2)–Ag(1)
a
164.43(10)
90.78(3)
91.36(13)
91.21(9)
N(2)–Ag(1)–Ag(2)
N(1)–Ag(2)–P(2)
P(2)–Ag(2)–N(3)
P(2)–Ag(2)–Ag(1)
82.58(10)
145.44(9)
122.25(10)
85.08(3)
84.20(10)
Symmetry transformations used to generate equivalent atoms. For 5: #1 = ꢀx + 1, ꢀy, ꢀz + 2.
together by coordination of the 4,40-bipyridine. The molec-
ular structure of compound 8, displayed in Fig. 8, shows
different coordination geometries for the different silver
atoms. Ag1 has a distorted tetrahedral geometry where
the previously binding triflate from 3 has been replaced
by the 4,40-bipyridine. Ag2 which is coordinated with a
Otf anion presents a distorted tetrahedral geometry with
angles varying between 84.6(2)ꢁ and 159.2(2)ꢁ. Ag3 has a
distorted trigonal bipyramidal geometry, where the axis is
formed by the interaction of Ag3 with Ag4 and O7. In
Ag4 a highly distorted tetrahedral geometry is encountered
with angles ranging between 84.6(2)ꢁ and 157.2(2)ꢁ. The X-
ray crystal structure of compound 8 also has four THF
molecules, two of which are disordered, and one unbound
Otf anion. The Otf anion bound to Ag3 is disordered such
that only 54% of the time it is actually bound to the silver,
the other 46% of the time it is slightly further away and
outside bonding distance. The Ag–Ag interactions are seen

1308
F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
Table 5
0
0
Selected bond lengths (A), angles (ꢁ), and distances for the compounds (AgOtf)2(PMP-21)(5,5 -dimethyl-2,2 -dipyridyl)2 (7) [AgOtf(PMP-21)]4(4,40-
˚
bipyridine) (8), and [AgOtf(PMP-21)2]2(4,40-bipyridine) (9)
7
Ag(1)–Ag(2)
Ag(2)–N(1)
Ag(1)–N(3)
Ag(2)–N(5)
3.1430(5)
2.155(3)
2.280(4)
2.328(3)
Ag(1)–P(3)
Ag(1)–N(2)
Ag(2)–N(4)
Ag(2)–O(1)
2.3402(10)
2.301(3)
2.245(3)
4.589(3)
N(3)–Ag(1)–N(2)
N(2)–Ag(1)–P(3)
N(2)–Ag(1)–Ag(2)
N(1)–Ag(2)–N(4)
N(4)–Ag(2)–N(5)
N(4)–Ag(2)–Ag(1)
73.2(1)
141.9(1)
95.2(9)
153.4(1)
73.4(1)
79.7(9)
N(3)–Ag(1)–P(3)
N(3)–Ag(1)–Ag(2)
P(3)–Ag(1)–Ag(2)
N(1)–Ag(2)–N(5)
N(1)–Ag(2)–Ag(1)
N(5)–Ag(2)–Ag(1)
141.9(9)
73.5(9)
86.1(3)
132.8(1)
83.3(9)
114.7(1)
8
Ag(1)–Ag(2)
Ag(1)–P(1)
Ag(3)–P(3)
Ag(1)–N(2)
Ag(2)–N(1)
Ag(3)–N(6)
3.0816(8)
2.375(2)
2.3633(19)
2.283(6)
2.191(7)
2.285(7)
Ag(3)–Ag(4)
Ag(2)–P(2)
Ag(4)–P(4)
Ag(1)–N(3)
Ag(3)–N(4)
Ag(4)–N(5)
3.0538(9)
2.3642(19)
2.3730(19)
2.341(7)
2.367(6)
2.216(6)
N(2)–Ag(1)–N(3)
N(3)–Ag(1)–P(1)
N(3)–Ag(1)–Ag(2)
N(1)–Ag(2)–P(2)
P(2)–Ag(2)–O(5)
P(2)–Ag(2)–Ag(1)
N(6)–Ag(3)–P(3)
P(3)–Ag(3)–N(4)
N(5)–Ag(4)–P(4)
P(4)–Ag(4)–O(10)
P(4)–Ag(4)–Ag(3)
92.2(2)
120.8(2)
73.3(2)
159.2(2)
110.4(1)
86.5(5)
140.8(2)
123.1(2)
157.2(2)
114.3(1)
85.7(5)
N(2)–Ag(1)–P(1)
N(2)–Ag(1)–Ag(2)
P(1)–Ag(1)–Ag(2)
N(1)–Ag(2)–O(5)
N(1)–Ag(2)–Ag(1)
O(5)–Ag(2)–Ag(1)
N(6)–Ag(3)–N(4)
O(7A)–Ag(3)–Ag(4)
N(5)–Ag(4)–O(10)
N(5)–Ag(4)–Ag(3)
O(10)–Ag(4)–Ag(3)
143.7(2)
89.3(2)
86.52(5)
88.9(2)
84.6(2)
135.9(1)
92.2(2)
148.6(2)
86.4(2)
84.6(2)
138.3(1)
9
Ag(1)–P(1)
Ag(1)–N(3)
2.4384(6)
2.3924(19)
Ag(1)–P(2)
2.4274(6)
N(3)–Ag(1)–P(2)
P(2)–Ag(1)–P(1)
105.2(5)
139.1(2)
N(3)–Ag(1)–P(1)
112.7(5)
X
X
P
Ag
N
P
P
N
Ag
Ag
N
P
P
N
Ag
N
P
N
Ag
Ag
X
2
3
4
Scheme 1.
˚
to be weakened by the coordination of the bipyridine
ligand, compared to the metallophilic interactions encoun-
tered in compound 3. All Ag–P and Ag–N distances fall in
the range of reported values.
Compound 9 is representative of an intermediate struc-
tural compound when moving from the 1:1 to 2:1 ratios of
PMP-21 ligand to metal. The PMP-21 ligands are monod-
entate as shown in Fig. 9, with the Ag1 atom too far
removed from the N1 and N2 atoms (2.6575(2) and
3.2591(2) A, respectively) to describe any strong interac-
tion. The angles around the metal center indicate a dis-
torted trigonal planar geometry, with angles ranging
between 105.18(5)ꢁ and 139.08(2)ꢁ. The center of the bipyr-
idine ligands sits on a crystallographic inversion center.
Attempts to prepare the analogous compound with tri-
phenylphosphine in place of the PMP-21 ligand resulted
only in the crystallization of AgOtf(PPh3)4 as the main
product of the reaction. This leads to the conclusion that

F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
1309
not only steric, but also electronic factors provided by the
pyridyl group contribute to the formation of compound 9.
plex with respect to any of the species coordinated either
with the 5,50-dimethyl-2,20-bipyridine or 4,40-bipyridine.
Also the emission spectrum of complex 2 is noticeably
more intense than 5 and 6. The same luminescent behavior
is observed for the series of compounds synthesized with
the AgOtf salt, where the maximum in the emission spec-
trum of the [AgOtf(PMP-21)]2 compound is red shifted
with respect to compounds 7, 8, and 9. A stronger shift
occurs between 3 and 7 in the presence of the 5,50-
dimethyl-2,20-bipyridine. Comparing the emission spectra
of compounds 8 and 9, which differ in the coordination
of two PMP-21 ligands to the silver atom in 9 and only
one through the phosphorus atom in compound 8, no
major differences in maxima location and intensity is
observed. The excitation maxima of the compounds substi-
tuted with a bipyridine ligand cover a short range of wave-
lengths between 291 and 323 nm. As described also for the
emission spectra, compounds 5 and 7 exhibit the largest
excitation maxima shift to the red compared to the corre-
sponding [AgBF4(PMP-21)]2 and [AgOtf(PMP-21)]2
complexes.
3.3. Luminescence properties
Coordination complexes that present luminescent prop-
erties have attracted increasing attention because of their
potential applications as light-emitting devices, in areas
of optoelectronic devices and chemical sensors [36–38].
Organic compounds with aromatic nitrogen heterocycles,
which can be receptors for metal ions, have been studied
extensively because they are capable of performing useful
light- and/or redox-induced tasks [39–41]. Particularly,
luminescence complexes of some transition metals of the
group VII and VIII containing bipyridine type ligands have
attracted much attention because of their high luminescent
efficiency [42–45]. However, the low yields and higher costs
of these complexes are disadvantages for their use as opto-
electronic materials. The lower cost of d10 metal complexes
with nitrogen and phosphorous containing ligands are of
interest because of their photoluminescent properties [42–
46]. Here, we report the excitation and emission spectra
of the metal complexes, all spectra were recorded at con-
centrations of 1 · 10ꢀ4 M in acetonitrile glasses at 77 K.
In solution at room temperature there is no observable
fluorescence.
The similarity of the excitation spectra of compounds 2–
4 is not surprising, given the same structural conformation
of the phosphine ligand with the silver metal in the com-
plexes, which is the result of a ligand-to-metal charge trans-
fer. Excitation maxima for 2, 3, and 4 are 300, 297, and
295 nm, respectively. The emission spectra show a single
maximum for each case, illustrating the decay transitions
associated with each system. Excitation maxima of all com-
pounds are presented in Table 6 along with the local emis-
sion maxima. The emission spectra of all the compounds
cover a wide range of the spectrum with local maxima
spanning approximately 200 nm, showing in the case of
the bipyridine substituted complexes multiple maxima,
illustrating the complexity of the decay transitions associ-
ated with the more complicated system. Comparing the
emission data of the series of compounds obtained with
the AgBF4 salt, a red shift of the maximum of approxi-
mately 100 nm is observed for the [AgBF4(PMP-21)]2 com-
4. Conclusions
We have demonstrated in this study the ability of the
PMP-21 ligand to act as a bridging bidentate ligand for
the formation of Ag coordination complexes containing a
Ag–Ag arꢀgentophꢀilic interaction. Structures formed with
BF4ꢀ, Otf , or tfa as the counterion show little structural
dependence on the interactionꢀof the anion when reacted in
a 1:1 ratio. For both the BF4 and Otfꢀ derivatives, addi-
tional reactivity at the silver center has been demonstrated
by the formation of complexes containing 5,50-dimethyl-
2,20-bipyridine or 4,40-bipyridine. Which result in highly
in crowded metal centers for the 5,50-dimethyl-2,20-bipyri-
dine derivatives and linked dimers for the 4,40-bipyridine
derivatives. A unique structure containing a bridging
4,40-bipyridine has been found when the ratio of PMP-21
to silver is 2:1. As expected, all of the compounds reported
exhibit luminescence at 77 K.
Work continues on the synthesis and coordination
chemistry of interesting pyridyl-containing phosphines.
A new ligand PMP-41, where the pyridine is substituted
in the 4-position, has been synthesized and its coordination
behavior with silver salts studied. The chemistry of the
PMP-21 ligand has also been extended to the doubly
substituted phenylphosphino-bis-2-methylpyridine (PMP-
22) which can act as a chelate and a pincer ligand at the
same time. Manuscripts concerning the results of the coor-
dination chemistry of these ligands are currently in
preparation.
Table 6
Luminescent spectral data for compounds 2–9 at 77 K and 1 · 10ꢀ4 M in
CH3CN
Compound
Excitation, kmax (nm)
Emission local, kmin (nm)
2
3
4
5
6
7
8
9
300
297
295
323
313
329
291
299
392, 402
389
392
455, 483, 507
438, 468, 493
451, 483
410, 435
411, 438
Acknowledgements
This research was supported by funds provided by grant
from the Robert A. Welch Foundation (AA-1508). The
Bruker X8 APEX diffractometer was purchased with funds

1310
F. Hung-Low, K.K. Klausmeyer / Inorganica Chimica Acta 361 (2008) 1298–1310
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1460.
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received from the national Science Foundation Major Re-
search Instrumentation Program Grant CHE-0321214.
Baylor University’s Varian 500 MHz NMR was funded
by the National Science Foundation’s Major Research
Instrumentation program, Award # CHE-0420802.
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Appendix A. Supplementary data
CCDC 648315, 648316, 648317, 648318, 648319,
648320, 648321 and 648322 for 2, 3, 4, 5, 6, 7, 8 and 9.
These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-
mail: deposit@ccdc.cam.ac.uk. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2007.08.015.
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