First halogen anion-bridged (MMX)n-type one-dimensional coordination polymer built upon d10-d10 dimers

Article abstract of DOI:10.1021/ic101619y

The complex [Ag₂(PhPPy₂)₂(NCCH ₃)₂](ClO₄)₂ [PhPPy₂ = bis(2-pyridyl)phenylphosphine] reacts with NH₄Cl to form an insoluble one-dimensional polymer of the type (MMX)_n, {[Ag ₂(PhPPy₂)₂Cl](ClO₄)}_n. The binuclear unit, Ag₂(PhPPy₂)₂²⁺, exhibits two PhPPy₂ tridentate ligands bridging the two Ag atoms in a head-to-tail fashion with C_2h symmetry, and the Ag...Ag distance [3.0942(11) A, X-ray] suggests argentophilic interactions. Each Ag center adopts a distorted trigonal-bipyramidal geometry, coordinated by one P atom and two pyridyl arms at the equatorial positions and interacting with one Cl ion and one Ag ion at the axial positions. The short Ag-Cl bond length [2.5791(7) A] indicates the presence of some covalent character. The solid-state absorption bands spread all the way to 600 nm have been interpreted by means of density functional theory (DFT) and time-dependent DFT (B3LYP), and the lowest-energy excited states are assigned to metal/halide-to-pyridyl charge transfer, consistent with the d¹⁰ electronic configuration of Ag. The calculated oscillator strengths are low because of the poor molecular orbital overlaps in the charge-transfer components. The novel material exhibits a luminescence band centered at about ～520 nm.

Full text of DOI:10.1021/ic101619y

Inorg. Chem. 2010, 49, 11069–11076 11069
DOI: 10.1021/ic101619y
First Halogen Anion-Bridged (MMX)n-Type One-Dimensional Coordination Polymer
Built upon d10-d10 Dimers
Tianle Zhang,*,† Changpeng Ji,† Kaili Wang,† Daniel Fortin,‡ and Pierre D. Harvey*,‡
†College of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan,
‡
ꢀ
ꢀ
Hubei 430074, People’s Republic of China, and Departement de Chimie, Universite de Sherbrooke, Sherbrooke,
Quebec J1K, 2R1, Canada
Received August 9, 2010
The complex [Ag2(PhPPy2)2(NCCH3)2](ClO4)2 [PhPPy2 = bis(2-pyridyl)phenylphosphine] reacts with NH4Cl to
form an insoluble one-dimensional polymer of the type (MMX)n, {[Ag2(PhPPy2)2Cl](ClO4)}n. The binuclear unit,
Ag2(PhPPy2)22þ, exhibits two PhPPy2 tridentate ligands bridging the two Ag atoms in a head-to-tail fashion with C2h
˚
symmetry, and the Ag Ag distance [3.0942(11) A, X-ray] suggests argentophilic interactions. Each Ag center
adopts a distorted trigonal-bipyramidal geometry, coordinated by one P atom and two pyridyl arms at the equatorial
3 3 3
˚
positions and interacting with one Cl ion and one Agion at the axial positions. The short Ag-Cl bond length [2.5791(7) A]
indicates the presence of some covalent character. The solid-state absorption bands spread all the way to 600 nm
have been interpreted by means of density functional theory (DFT) and time-dependent DFT (B3LYP), and the lowest-
energy excited states are assigned to metal/halide-to-pyridyl charge transfer, consistent with the d10 electronic
configuration of Ag. The calculated oscillator strengths are low because of the poor molecular orbital overlaps in the
charge-transfer components. The novel material exhibits a luminescence band centered at about ∼520 nm.
Introduction
magneticproperties. Froma structuralpoint of view, the con-
struction of these materials is based upon the square-planar
geometry about the metal, with the remaining axial positions
occupied by the bridging halide and neighboring metal.11-20
Moreover, species belonging to this same family of halogen-
bridged polymers of dimers is a mixed-metal (Pt6Rh2Cl)n
polymer in which two dimers are bridged by a Cl ion and two
others are not.21,22 The metal atoms in the (MMX)n polymers
Unidimensional halide-bridged coordination oligomers1,2
and polymers3-10 built upon dimetallic fragments, (MMX)n,
are of current interest primarily because of their metallic and
*To whom correspondence should be addressed. E-mail: tlzhang@mail.
hust.edu.cn (T.Z.), Pierre.Harvey@USherbrooke.ca (P.D.H.). Tel: 1-819-
821-7092 (P.D.H.). Fax: 86-27-87543632 (T.Z.), 1-819-821-8017 (P.D.H.).
(1) Yin, C.-X.; Huang, G.-C.; Kuo, C.-K.; Fu, M.-D.; Lu, H.-C.; Ke,
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S.-M. J. Am. Chem. Soc. 2008, 130, 10090–10092.
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r
2010 American Chemical Society
Published on Web 11/10/2010
pubs.acs.org/IC

11070 Inorganic Chemistry, Vol. 49, No. 23, 2010
Zhang et al.
Chart 1
Table 1. Crystal Data and Collection Parameters for Polymer {[Ag2(PhPPy2)2-
Cl](ClO4)}n
empirical formula
fw
temp/K
C32H26N4O4P2Cl2Ag2
879.15
293(2)
monoclinic
C2/m
18.263(4)
13.911(3)
8.236(2)
90
100.237(4)
90
2059.1(9)
2
1.444
888
1.197
7423
2108 [R(int) = 0.0254]
2108/10/132
0.0491
0.1610
1.258
cryst syst
space group
˚
a/A
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
are those capable of forming square-planar or octahedral
complexes, and to our knowledge, these are exclusively
limited to Ni, Ru, Rh, and Pt.
3
˚
volume/A
Z
density(calcd)/g cm-3
F(000)
3
Recently, one of the authors developed a convenient syn-
thetic route to preparing the tridentate ligand bis(2-pyridyl)-
phenylphosphine (PPhPy2)23 and studied its coordination to
transition metals such as Pd, Cu, and Ag.24-26 In these cases,
homo- and heterobimetallic complexes were reported where
PPhPy2 acts as a bridging ligand supporting either M-M
μ/mm-1
reflns collected
unique reflns [R(int)]
data/restraints/param
final R1 [F > 4σ(F)]
wR2 (all data)
GOF
bonds or M M interactions. In some cases, luminescence
3 3 3
was also detected. We now report a new one-dimensional
293 K. The structure was solved by direct methods and refined
by full-matrix least squares using the SHELXTL crystallo-
graphic software package.27 Anisotropic displacement param-
eters were applied to all non-H atoms. The H atoms were
included and were generated geometrically. A summary of
crystallographic data and refinement parameters is given in
Table 1.
(1D) coordination polymer of the type (MMX)n, built upon
2þ
the dimetallic fragment Ag2(PPhPy2)2 (i.e.,
Ag2(PPh-
3 3 3
2þ
2þ
Py2)2
Cl- Ag2(PPhPy2)2
Cl- ; Chart 1). This
3 3 3
3 3 3
3 3 3
3 3 3
new luminescent material differs from the examples cited
above by the fact that the Ag environment is a distorted
triangular plane (not a square-planar geometry), where the
axial positions are occupied by a Ag atom and a Cl ion. The
solid-state photophysical data are supported by density func-
tional theory (DFT) and time-dependent DFT (TDDFT)
computations.
Computations. The electronic structure was calculated using
Gaussian09 software,28 at Universite de Sherbrooke’s Mammouth
ꢀ
ꢀ
ꢀ ꢀ
supercomputer, supported by Reseau Quebecois de Calcul de
Haute Performance. DFT and TDDFT29-35 were calculated
using the B3LYP33-35 method with 3-21G* basis sets on C, H,
N, Cl, and P atoms36-41 and SBKJC effective-core potentials
with VDZ valence double-ζ electrons for Ag.42-45 All of the
geometries were taken directly from the single-crystal structure
coordinates; a single-point calculation was performed on each
asymmetric unit number in the polymerization direction. The
UV-vis spectrum was also computed using Gaussian software46
Experimental Section
Materials. [Ag2(PhPPy2)2(CH3CN)2](ClO4)2 was prepared
according to a literature method.26 Ammonium chloride, aceto-
nitrile, methanol, and diethyl ether were purchased from com-
mercial sources and used without further purification.
{[Ag2(PhPPy2)2Cl](ClO4)}n. Solid [Ag2(PhPPy2)2(CH3CN)2]-
(ClO4)2 (0.0046 g, 0.0045 mmol) was dissolved in 0.4 mL of
acetonitrile, to which a 1 mL methanolic solution of ammonium
€
€
(27) (a) Sheldrick, G. M. SADABS; University of Gottingen: Gottingen,
Germany, 1997. (b) Sheldrick, G. M. SHELXS97 and SHELXL97; University of
chloride (0.0095 mol L-1, 0.0095 mmol) was added with stirr-
3
€
€
Gottingen: Gottingen, Germany, 1997.
ing. After 0.5 h, the cloudy solution was filtered to remove the
precipitate. The polymer was obtained in about 51% yield as
colorless crystals in about 3 weeks by diffusion of diethyl ether
onto the filtrate (0.0020 g). Elem anal. Calcd for C32H26N4O4P2-
Cl2Ag2: C, 43.72; H, 2.96; N, 6.37. Found: C, 43.28; H, 2.87; N,
6.15. IR: 1088 cm-1 [vs, ν(ClO4-)].
(28) Gaussian09; Gaussian, Inc.: Wallingford, CT, 2009.
(29) Hohenberg, P.; Kohn, W. Phys. Rev. 1964, 136, B864–B871.
(30) Kohn, W.; Sham, L. J. Phys. Rev. 1965, 140, A1133–A1138.
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American Chemical Society: Washington, DC, 1989.
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Molecules; Oxford University Press: Oxford, U.K., 1989.
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Phys. 1988, 785–789.
Physical Measurements. Fourier transform IR spectra were
recorded on a Bruker Vertex 70 spectrometer. UV and emission
spectra were measured on Perkin-Elmer Lambda 35 and
Jasco FP-6500 spectrometers, respectively. Elemental analysis
(C, H, N) was determined on a Perkin-Elmer elemental analyzer.
X-ray Structure Determinations. A suitable single crystal with
dimensions of 0.30 ꢀ 0.20 ꢀ 0.15 mm was selected and mounted
on the end of a thin glass fiber. Diffraction data were collected
on a Bruker SMART APEX CCD-based diffractometer with
(35) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,
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(36) Binkley, J. S.; Pople, J. A.; Hehre, W. J. J. Am. Chem. Soc. 1980, 102,
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J. Am. Chem. Soc. 1982, 104, 2797–2803.
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Binkley, J. S. J. Am. Chem. Soc. 1982, 104, 5039–5048.
(39) Dobbs, K. D.; Hehre, W. J. J. Comput. Chem. 1986, 7, 359–378.
(40) Dobbs, K. D.; Hehre, W. J. J. Comput. Chem. 1987, 8, 861–879.
(41) Dobbs, K. D.; Hehre, W. J. J. Comput. Chem. 1987, 8, 880–893.
(42) Basis Set Exchange Library https://bse.pnl.gov/bse/portal.
(43) Stevens, W. J.; Basch, H.; Krauss, M. J. Chem. Phys. 1984, 81, 6026–
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(44) Stevens, W. J.; Krauss, M.; Basch, H.; Jasien, P. G. Can. J. Chem.
1992, 70, 612–630.
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(46) O’Boyle, N. M.; Tenderholt, A. L.; Langner, K. M. J. Comput. Chem.
2008, 29, 839–845.
˚
graphite-monochromated Mo KR radiation (λ = 0.710 73 A) at
(23) Zhang, T.-L.; Qin, Y.; Wu, D.-Y.; Zhou, R.; Yi, X.-W.; Liu, C.-L.
Synth. Commun. 2005, 35, 1889–1895.
(24) Zhang, T.-L.; Qin, Y.; Wu, D.-Y.; Wang, C.-G.; Liu, C.-L. J. Coord.
Chem. 2005, 58, 1485–1491.
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C.-G. Inorg. Chim. Acta 2007, 360, 1609–1615.

Article
Inorganic Chemistry, Vol. 49, No. 23, 2010 11071
Figure 1. (a) Linear chain structure in the {[Ag2(PhPPy2)2Cl](ClO4)}n polymer (50% thermal ellipsoids). (b) Linear chain viewed along the c direction
(50%thermalellipsoids). Perchlorate groupsare omittedfor clarity. Symmetry codes:A, 2- x, y, 1- z; B, 2- x, y, 2- z; C, 2- x, 2- y, 1- z. Selected bond
˚
distances (A) and angles (deg): Ag1-Ag1A 3.0942(11), Ag1-Cl1 2.5791(7), Ag1-N1A 2.378(4), Ag1-N1C 2.378(4), Ag1-P1 2.3834(16), H2 Cl1
3 3 3
2.5957(6); Ag1A-Ag1-Cl1 172.48(2), Ag1-Cl1-Ag1B 180.000, P1-Ag1-N1A 133.38(10), P1-Ag1-N1C 133.38(10), N1A-Ag1-N1C 80.65(18),
P1-Ag1-Ag1A 73.47(4), P1-Ag1-Cl1 114.04(4), N1A-Ag1-Ag1A 83.01(10), N1C-Ag1-Ag1A 83.01(10), N1A-Ag1-Cl1 91.28(10),
N1C-Ag1-Cl1 91.28(10), C2-H2-Cl1 176.645(13), H2-Cl1-H2B 180.000.
with a full-width at half-maximum (fwhm) of 1000 cm-1. The
number of Cl[Ag2(PhPPy2)2Cl]n units was limited to 7 in the
DFT computations and 3 in the TDDFT calculations. Attempts
to compute larger oligomers failed on our supercomputer.
Results and Discussion
Synthesis. The reaction of the dicationic binuclear com-
plex [Cu2(PhPPy2)2(NCCH3)2](ClO4)2 with 2 equiv of
ammonium chloride produces the neutral dinuclear com-
plex [Cu2(PhPPy2)2Cl2].47 However, when one uses the
silver analogue [Ag2(PhPPy2)2(NCCH3)2](ClO4)2 as the
starting material, a similar reaction takes place but,
unexpectedly, leads to a new polymer with the formula
{[Ag2(PhPPy2)2Cl](ClO4)}n as determined by X-ray crys-
tallography (see below). This material crystallizes as the
sole product, instead of the anticipated binuclear com-
plex [Ag2(PhPPy2)2Cl2]. Upon reduction of the relative
amount of ammonium chloride, the colorless title poly-
mer and starting material are always found to cocrystal-
lize as colorless blocks and needles, respectively. The
solid-state IR spectrum does not exhibit the characteristic
absorption band for coordinated acetonitrile molecules
at 2017 cm-1 in the starting material, indicating that
these coordinated CH3CN molecules are completely sub-
stituted by Cl anions. The strong peak at 1088 cm-1 is
consistent with the presence of perchlorate counterions in
this new material.
Figure 2. Space-filling plot showing the C-H Cl interactions in
{[Ag2(PhPPy2)2Cl](ClO4)}n.
3 3 3
the two Ag centers in a head-to-tail fashion (Figure1a).
Each Ag center adopts a distorted trigonal-bipyramidal
geometry, coordinated by one P atom and two pyridyl
groups in the equatorial positions and by a Cl ion and a
Ag ion in the axial positions. The Ag Ag distance is
˚
3 3 3
3.0942(11) A, indicative of the existence of argentophilic
interactions.48 The Ag-Cl bond length [2.5791(7) A]
˚
The difference in reactivity between the copper and
silver binuclear complexes is at first glance difficult to
explain. The new polymer, {[Ag2(PhPPy2)2Cl](ClO4)}n,
precipitates out of solution during the reaction and is
insoluble in most common solvents. We propose that the
poor solubility of the mixed-anion-containing polymer
causes precipitation to occur before anion exchange is
proves to be short when compared to that cited in the
literature,49 hence suggesting the presence of covalent
interactions. These stronger interactions in comparison
with a purely ionic bonding may explain the insolubility
of the polymer.
The most interesting structural feature of this com-
pound is that these dinuclear units are connected by Cl
anions as bridging ligands to generate a 1D chain of the
type (MMX)n (Figure 1a,b). This structural 1D polymer
completed. Consequently, the Ag Cl interactions ap-
pear strong (see the comment on the short Ag-Cl dis-
tance).
3 3 3
Structural Analysis. Crystallographic studies revealed
that the dinuclear complex unit in the polymer is retained,
where two bis(2-pyridyl)phenylphosphine ligands bind
€
(48) (a) Pyykko, P. Chem. Rev. 1997, 97, 597–636. (b) Che, C.-M.; Tse,
M.-C.; Chan, M. C. W.; Cheung, K.-K.; Phillip, D. L.; Leung, K.-H. J. Am. Chem.
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m3494–3495.

11072 Inorganic Chemistry, Vol. 49, No. 23, 2010
Zhang et al.
Figure 3. (a) Crystalpackingdiagram showingthe 1Dchannel along thec direction. (b) Packing diagram showingthe disorder ofthe perchlorate groups in
the channels. Four possible locations for the perchlorate group in the channel are divided by a turquoise cross.
feature is usually found for nickel, ruthenium, rhodium,
and platinum complexes but has never been observed for
copper(I) and silver(I) compounds to the best of our knowl-
edge. The closest and only other example is a gold(I) tetra-
mer reported about 2 decades ago, in which two dimeric
units were found to be bridged by a Br or an I anion.50 In
the title polymer, the Cl anion is centered between two Ag
ions (Ag1-Cl1-Ag1B = 180.00°). However, the angle of
Ag1A-Ag1-Cl1 [172.48(2)°] indicates that the polymer
chain just slightly deviates from perfect linearity. Finally,
the trigonal-bipyramidal geometry about the metal atoms
in this type of coordination is also unique because all
other reported literature examples exhibit an octahedral
geometry for the metal in the (MMX)n polymers.
Figure 4. UV spectrum of {[Ag2(PPhPy2)2]Cl(ClO4)}n in the solid state
at 298 K.
Recently, it was demonstrated that weak hydrogen
bonds are important in crystal engineering and supra-
molecular chemistry.51 In this polymer, the Cl anion inter-
acts with two o-H atoms H2 and H2B of the two phenyl
groups belonging to neighboring dinuclear silver complex
Photophysical Study. The polymer exhibits lumines-
cence in the 500 nm region (below). This observation
prompted us to analyze the electronic spectrum. Figure 4
shows the solid-state absorption spectrum of this new
{[Ag2(PhPPy2)2Cl](ClO4)}n polymer at 298 K. The ab-
sorption spectrum is characterized by a series of stronger
features in the 250-350 nm region and a long tail expand-
ing from 350 to 600 nm.
The colorless nature of the insoluble polymer is surpris-
ing considering the presence of absorption features in
the 400 nm region. A possible reason for this is the low
absorptivity of the electronic transitions, supported by
TDDFT calculations (see below). This is addressed by
first establishing an electronic structure using DFT com-
putations and then calculating the electronic transitions
using the TDDFT approach. Selected molecular orbital
(MO) representations for Cl[Ag2(PhPPy2)2Cl]n oligomers
(n = 1, 2, 7) are shown in Figures 5 and 6 and were
calculated using the X-ray data as input files. The cases
with n = 3 and 5 are included with the Supporting
Information (Figures S1 and S2).
˚
units (Figure 1a). The H Cl distance is 2.5957(6) A,
3 3 3
which is much shorter than the sum of the van der Waals
52
radii (2.95 A). Figure 2 clearly shows that two phenyl
˚
groups and one Cl anion are arranged in a quasi-perfect
straight line [C2-H2-Cl1=176.645(13)°], and the close
contact between the H and Cl anions appears to play
an important role in the construction of this unusual
{[Ag2(PhPPy2)2Cl](ClO4)}n polymer.
In the solid state, the 1D polymer chains are placed
parallel to each other, and no interaction between these
chains is observed. Four polymer chains aggregate to
form a 1D channel (Figure 3a). Crystallographic studies
reveal that these channels are filled by the perchlorate
anions. The four positions allowing an anion to be placed
in these channels are present. These disordered perchlo-
rate anions in these channels are depicted in Figure 3b.
(50) Jaw, H.-R. C.; Savas, M. M.; Rogers, R. D.; Mason, W. R. Inorg.
Chem. 1989, 28, 1028–1037.
In all cases, the lowest unoccupied MOs (LUMOs) are
π* orbitals primarily localized on the pyridine rings of the
PhPPy2 ligands. For the highest occupied MO (HOMO)
in the monomeric species, a mixture of σ*(Ag-Cl) and
(51) (a) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311–2327.
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10315–10326. Wu, J.-S.; Leung, K. C.-F.; Benítez, D.; Han, J.-Y.; Cantrill, S. J.;
Fang, L.; Stoddart, J. F. Angew. Chem., Int. Ed. 2008, 47, 7470–7474.
(52) (a) Chandrasekhar, V.; Baskar, V.; Kingsley, S.; Nagendran, S.;
Butcher, R. J. CrystEngComm 2001, 17, 1–3. (b) Bondi, A. J. Phys. Chem.
1964, 68, 441–451.
σ*(Ag Ag) are computed as the major and minor
3 3 3
contributions, respectively (Figure 5). In the monomer,
the σ*(Ag Ag) MO is built upon the dx2-y2-dx2-y2
3 3 3

Article
Inorganic Chemistry, Vol. 49, No. 23, 2010 11073
Figure 5. Selected frontier MO representations for the Cl[Ag2(PhPPy2)2Cl]n units [n = 1 (left), 2 (right)].
Figure 7. Variation of the MO energy for the frontier orbitals of the
Cl[Ag2(PhPPy2)2Cl]n oligomers (n = 1-3, 5, 7). In HOMO-x, x takes
the values of 1-4 for n=1 and of 1-5 for n=2, 3, 5, and 7. The square,
round, and star dots correspond to the surface MOs issued from anti-
bonding Ag dx2-y2-Cl px, Ag dxy-Cl py, and Ag dxz-Cl pz interactions,
respectively.
Figure 6. Selected frontier MO representations for the Cl[Ag2-
(PhPPy2)2Cl]n units (n = 7).
Below the HOMO, we find two other series of MOs
built upon antibonding Ag dxy-Cl py (quasi-degenerated
HOMO-1 and HOMO-2) and antibonding Ag dxz-
Cl pz interactions (quasi-degenerated HOMO-3 and
HOMO-4). HOMO-5 is a mixture of σ*(Ag-Cl) and
antibonding interactions, whereas the σ*(Ag-Cl) MO is
constructed with Ag dx2-y2-Cl px interactions (the
Ag-Ag vector is placed along the x axis).

11074 Inorganic Chemistry, Vol. 49, No. 23, 2010
Zhang et al.
Table 2. Computed Frequency and Wavelength of the 20 First Pure Electronic Transitions for the Monomeric Species ClAg2(PhPPy2)2Cl, along with Their Major
Individual Contributions
no.
ν (cm-1
)
λ (nm)
f
major contributions (%)
1
2
3
4
5
6
7
8
21 504
24 085
24 643
24 667
24 974
25 030
25 125
25 207
25 814
26 797
26 892
27 412
27 466
27 868
27 874
27 967
28 020
28 106
28 343
28 385
465.0
415.2
405.8
405.4
400.4
399.5
398.0
396.7
387.4
373.2
371.9
364.8
364.1
358.8
358.8
357.6
356.9
355.8
352.8
352.3
0.0427
0
0.0037
HOMO f LUMO (99)
HOMO f Lþ1 (93)
H-1 f LUMO (93)
H-2 f LUMO (93)
0
0
0.0163
0
0.0005
H-3 f LUMO (12), HOMO f Lþ2 (86)
HOMO f Lþ3 (90)
H-3 f LUMO (81), HOMO f Lþ2 (13)
H-4 f LUMO (85)
H-5 f LUMO (91)
9
0
10
11
12
13
14
15
16
17
18
19
20
0
0.0029
0
0.0034
0
0
0.0001
0
0
0.0017
0.0086
HOMO f Lþ4 (97)
HOMO f Lþ5 (96)
H-1 f Lþ1 (92)
H-2 f Lþ1 (92)
H-3 f Lþ1 (50), H-2 f Lþ2 (21), H-1 f Lþ3 (21)
H-4 f Lþ1 (22), H-2 f Lþ3 (26), H-1 f Lþ2 (44)
H-3fLþ1 (42), H-2fLþ2 (31), H-1fLþ3 (23)
H-4 f Lþ1 (56), H-2 f Lþ3 (13), H-1 f Lþ2 (12), HOMO f Lþ6 (12)
H-5 f Lþ3 (10), H-4 f Lþ1 (14), HOMO f Lþ6 (67)
H-5 f Lþ2 (17), H-2 f Lþ2 (14), H-1 f Lþ3 (14), HOMO f Lþ7 (52)
H-5 f Lþ1 (54), H-4 f Lþ3 (18), H-3 f Lþ2 (23)
Table 3. Computed Frequency and Wavelength of the 20 First Pure Electronic
Transitions for the Dimeric Species Cl[Ag2(PhPPy2)2Cl]2, along with Their Major
Individual Contributions
Table 4. Computed Frequency and Wavelength of the 20 First Pure Electronic
Transitions for the Trimeric Species Cl[Ag2(PhPPy2)2Cl]3, along with Their Major
Individual Contributions
ν
λ
(nm)
ν
λ
(nm)
no. (cm-1
)
f
major contributions (%)
no. (cm-1
)
f
major contributions (%)
1
2
3
4
5
6
7
8
9
21 162 472.5
0
H-1 f LUMO (36), HOMO f Lþ1 (56)
1
2
3
4
5
6
7
8
9
17 239 580.1 0.0003 HOMO f LUMO (94)
17 260 579.4 H-1 f LUMO (95)
17 830 560.9 0.0001 H-2 f LUMO (96)
21 189 471.9 0.0452 H-1 f Lþ1 (35), HOMO f LUMO (58)
22 288 448.7 0.0024 H-3 f Lþ1 (34), H-2 f LUMO (40)
22 289 448.6 0.0005 H-3 f LUMO (35), H-2 f Lþ1 (39)
0
17 840 560.5
18 166 550.5
18 175 550.2
19 691 507.8
0
0
0
0
H-3 f LUMO (96)
H-4 f LUMO (100)
H-5 f LUMO (100)
HOMO f Lþ1 (94)
22 717 440.3
22 714 440.3
0
0
H-4 f LUMO (40), H-4 f Lþ1 (40)
H-5 f LUMO (40), H-5 f Lþ1 (40)
23 652 422.8 0.0002 H-1 f Lþ1 (52), HOMO f LUMO (40)
23 658 422.7
0
H-1 f LUMO (53), HOMO f Lþ1 (42)
19 713 507.3 0.0014 H-1 f Lþ1 (95)
24 267 412.1 0.0112 H-1 f Lþ5 (34), HOMO f Lþ4 (56)
20 258 493.6 0.0112 H-2 f Lþ1 (13), H-2 f Lþ6 (10),
H-1 f Lþ6 (15), HOMO f Lþ6 (40)
10 24 293 411.6
11 24 498 408.2
0
0
H-1 f Lþ4 (41), HOMO f Lþ5 (51)
H-1 f Lþ3 (32), HOMO f Lþ2 (61)
10 20 273 493.3 0.0196 H-3 f Lþ1 (17), H-1 f Lþ6 (12),
H-1 f Lþ7 (29), HOMO f Lþ7 (21)
12 24 518 407.9 0.0001 H-3 f Lþ1 (40), H-2 f LUMO (43)
13 24 519 407.8
0
H-3 f LUMO (42), H-2 f Lþ1 (41)
11 20 286 493.0 0.0016 H-2 f Lþ1 (83)
12 20 297 492.7 0.0065 H-3 f Lþ1 (79)
14 24 534 407.6 0.0109 H-1 f Lþ2 (37), HOMO f Lþ3 (56)
15 24 900 401.6 0.0002 H-3 f Lþ4 (37), H-2 f Lþ5 (38)
16 24 902 401.6 0.0016 H-3 f Lþ5 (34), H-2 f Lþ4 (41)
13 20 615 485.1
14 20 625 484.9
15 20 854 479.5
16 20 862 479.3
0
0
0
0
H-4 f Lþ1 (99)
H-5 f Lþ1 (99)
17 24 924 401.2
18 24 925 401.2
0
0
H-4 f LUMO (43), H-4 f Lþ1 (40)
H-5 f LUMO (42), H-5 f Lþ1 (40)
H-1 f Lþ3 (22), HOMO f Lþ2 (71)
H-1 f Lþ2 (62), HOMO f Lþ3 (32)
19 25 341 394.6 0.0011 H-5 f Lþ5 (16), H-4 f Lþ4 (44),
H-4 f Lþ5 (25)
17 21 020 475.7 0.0002 H-1 f Lþ2 (32), HOMO f Lþ3 (62)
18 21 029 475.5
0
H-1 f Lþ3 (72), HOMO f Lþ2 (22)
20 25 342 394.6 0.0004 H-5 f Lþ4 (44), H-5 f Lþ5 (25),
H-4 f Lþ5 (16)
19 21 055 474.9 0.0009 H-2 f Lþ6 (61), H-2 f Lþ7 (13)
20 21 079 474.4 0.0009 H-3 f Lþ6 (14), H-3 f Lþ7 (60)
σ(Ag Ag). For the dimeric species, the HOMO be-
the Supporting Information), hence indicating that the
polymer is obviously unconjugated, which is consistent
with the closed shell of the Ag and Cl ions, Figure 7
illustrates that the addition of supplementary units in the
oligomers has a stabilizing effect.
One other important issue that is noted upon further
examination of Figures 5 and 6 is that again the MOs
appear to be localized on one unit or another. Second,
the atomic contributions on the frontier LUMOs and
HOMOs are very different in nature (i.e., very poor
orbital overlap). From these two observations, the oscil-
lator strengths for the electronic transitions are predicted
to be very weak on the basis of orbital overlaps. This is
indeed the case as depicted in Tables 2-4 where about
half of the first electronic transitions exhibit calculated
oscillator strengths ( f ) of zero. The others are small.
Together, the absence of a transition and the weakness
3 3 3
comes the degenerate HOMO and HOMO-1 (Figure 5)
and the lower-energy MOs exhibit the same relative
energy order, atomic contribution, and MO character.
The same trend is computed for the trimer (Figures S1 in
the Supporting Information), but the two sets of HOMO
and HOMO-1 and of HOMO-2 and HOMO-3 are
closely placed in the energy MO diagram (i.e., nearly
accidently degenerated). For the pentamer and heptamer,
the reversal of order between these two sets of MOs is then
computed and the quasi-degenerated nature of these
series remains, as plotted in Figure 7. The energy gap
between the LUMO and HOMO decreases with n, sug-
gesting that the lowest-energy electronic transitions
should be more shifted to the red as n is increased.
Noteworthy, despite the appearance of localized atomic
contributions in the MOs (Figures 5, 6, and S1 and S2 in

Article
Inorganic Chemistry, Vol. 49, No. 23, 2010 11075
of the others make the overall predicted spectrum of weak
intensity. This observation would explain why the solid is
colorless.
Through calculation of enough pure electronic (0,0)
transitions (here 100 is the maximum), a graph of the
absorptivity or oscillator strengths as a function of the
wavelength generates a bar graph (see the green bars in
Figure 8). When a thickness assigned to the bar, a
calculated spectrum can be generated (see the red trace
in Figure 8). The calculated spectrum does not include
vibronic components, so they will appear narrow. In
reality, they should be broadened by these vibronic
features on the high-energy side of the 0-0 component.
Nonetheless, the resemblance between the experimental
and calculated spectra suggests that the calculations are
valid.
The calculated spectrum for one unit, ClAg2(PhPPy2)2-
Cl, exhibitsstrongerabsorptionsbelow 300 nm and weaker
ones above 300 nm. These features lead to a resemblance
with the experimental solid-state absorption spectrum
(Figure 4). The computed strongest-intensity feature in
the low-energy region is found at 465 nm (calculated f =
0.043). For the dimer Cl[Ag2(PhPPy2)2Cl]2, this feature is
calculated at 472 nm (f = 0.045). The computed spectrum
for the trimer Cl[Ag2(PhPPy2)2Cl]3 exhibits the computed
strongest-intensity feature in the low-energy region at
493 nm ( f=0.020). The red shift is consistent with the
expected trend based on the reduction of the HOMO-
LUMO gap seen in Figure 7. However, an extra new
feature (of a much lower intensity; f = 0.0003) is also
computed at 580 nm.
The decrease in the calculated oscillator strength on
going from 2 to 3 units and the appearance of a weak
feature in the 580-nm region are also consistent with the
experimental spectrum (Figure 4). Overall, we find that
the computed spectra are consistent with the experimen-
tal data, and metal/halide-to-pyridyl charge-transfer
(M/XLCT) assignments for the lowest-energy absorption
bands are made on the basis of the DFT and TDDFT
calculations.
Although complexes containing phosphorus and nitro-
gen ligands are numerous,53 only a few have been reported
to be luminescent.54,55 The {[Ag2(PhPPy2)2Cl](ClO4)}n
polymer is found to be luminescent in the solid state at
room temperature (Figure 9). The most striking feature is
that the emission is localized between 400 and 600 nm
(with a maximum at ∼520 nm), a range where absorption
features are still present. The presence of luminescence
in this specific range is consistent with what has been
reported for other phosphorus- and nitrogen-ligand-
containing binuclear silver and copper complexes.54,55
The presence of shoulders on the high-energy side of
the emission suggests that it may be ligand-localized. This
was verified using the pure ligand in the solid state (Figure
S3 in the Supporting Information), and indeed shoulders
are also observed on the high-energy side as well. The
overall shape of these emissions for both ligands is con-
sistent with the proposed assignment of the absorption
Figure 8. Computed absorption spectra of the monomer and trimer of
Cl[Ag2(PhPPy2)2Cl]n [n = 1 (top), 2 (middle), 3 (bottom)]. Green = bar
graph; red = spectrum with an assigned thickness of 1000 cm-1
.
bands (i.e., M/XLCT). The polymer emission is red-
shifted with respect to the uncoordinated ligand. This
behavior is common, and numerous examples where
coordination of a ligand onto a transition metal with a d10
electronic configuration exist.56
(53) Maggini, S. Coord. Chem. Rev. 2009, 253, 1793–1832.
(54) Catalano, V. J.; Horner, S. J. Inorg. Chem. 2003, 42, 8430–8438.
(55) Crespo, O.; Gimeno, M. C.; Laguna, A.; Larraz, C. Z. Naturforsch.
2009, 64b, 1525–1534.
(56) Guyon, F.; Hameau, A.; Khatyr, A.; Knorr, M.; Amrouche, H.;
Fortin, D.; Harvey, P. D.; Strohmann, C.; Ndiaye, A. L.; Huch, V.; Veith,
M.; Avarvari, N. Inorg. Chem. 2008, 47, 7483–7492.

11076 Inorganic Chemistry, Vol. 49, No. 23, 2010
Zhang et al.
Cl(ClO4)}n polymer may explain this notable difference, a
difference that may be associated with the covalent nature of
the Ag-Cl bond. The strong Ag-Cl interaction could also be
noted in the frontier MO representations. During the course
of this study, the presence of luminescence for this colorless
polymer prompted us to examine the electronic spectra and
their interpretation by means of DFT and TDDFT calcula-
tions. M/XLCT assignments were made to explain the pres-
ence of weak absorptions in the visible region of the spec-
trum, electronic transitions that exhibit strong forbidden
character. The striking featureisthe presence of luminescence
centered at 500 nm, which is blue-shifted with respect to the
absorption bands. Because the Ag2(PhPPy2)2Cl2 binuclear
complex representing a monomer unit could not be isolated,
the explanation of this luminescence could not be confidently
explained experimentally. This recently synthesized new
ligand, PhPPy2, has led us to the preparation of new com-
plexes and now a new and unusual 1D coordination polymer,
which exhibits unusual absorption and luminescence proper-
ties. Further works are in progress.
Figure 9. Comparison of the solid-state absorption (black), excitation
(blue), and emission spectra (red) of ([Ag2(PPhPy2)2]Cl(ClO4))n at 298 K.
The emission spectrum curiously begins at 400 nm,
which is significantly blue-shifted with respect to the
absorption (Figure 9). We considered the possibility that,
in the bulk, small oligomers may be present and may be
responsible for the observed blue-shifted luminescence.
Because of the poor solubility of the bulk material, this
could not be verified. No other emission was noted be-
tween 700 and 850 nm, which is the limit of the instrument.
Acknowledgment. This research was supported by the
National Natural Science Foundation of China (Grant
20871049), the Analytical and Testing Center, Huazhong
University of Science and Technology (to T.Z.), the
Natural Sciences and Engineering Research Council of
ꢀ ꢀ
Canada, le Fonds Quebecois de la Recherche sur la
ꢀ
Nature et les Technologies, and the Centre d’Etudes des
Conclusion
ꢀ
Materiaux Optiques et Photoniques de l’Universite de
Sherbrooke (to P.D.H.).
ꢀ
An original new 1D coordination polymer of the type
(MMX)n has been synthesized and characterized. Its novelty
arises from the use of silver, and its structure exhibits a
trigonal-bipyramidal geometry about the metal. Surpris-
ingly, the monomeric bimetallic complex has never been
prepared, conversely to its congener Cu2(PhPPy2)2Cl2.51
The particularly poor solubility of the {[Ag2(PPhPy2)2]-
Supporting Information Available: X-ray crystallographic
data file in CIF format, excitation (black) and emission spectra
(red) of the PPhPy2 ligand in the solid state at 298 K, and
selected frontier MO representations for the Cl[Ag2(PhPPy2)2-
Cl]n units (n=3, 5). This material is available free of charge via
the Internet at http://pubs.acs.org.