Synthesis, structure and luminescence of new dinuclear cyanido-bridged AgI-AuI one-dimensional coordination polymer

Article abstract of DOI:10.1016/j.inoche.2012.03.005

A new alternating chain compound consisting of gold(I) and silver(I) bridged by cyanides is reported. The Ag(I) ion is functionalized by 2 triphenyl phosphane ligands, resulting in the formula [Au(CN)₂(PPh ₃)₂Ag]_n. The compound has been prepared by room temperature reaction of triphenyl phosphane with the cyanide salts of silver(I) and gold(I). The product has been characterized and its single crystal X-ray structure was determined. In the molecular structure of the complex, the Au(I) centers exhibit the expected linear, two-coordinate geometry with C-bound cyanides, whereas the Ag(I) centers adopt a tetrahedral geometry in a AgN ₂P₂ chromophore. The shortest hetero intermetallic separation distance is 4.94(7) ?. No aurophilic interactions are observed, but only the non-conventional CH...Au hydrogen interactions are present. Upon excitation at 325 nm, a quite intense luminescence at 475 nm, assigned on the basis of DFT calculations to MMLCT, is observed, which amounts to ca. 10% of the luminescence intensity of the best known luminescent compounds.

Full text of DOI:10.1016/j.inoche.2012.03.005

Inorganic Chemistry Communications 20 (2012) 188–190
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, structure and luminescence of new dinuclear cyanido-bridged AgI–AuI
one-dimensional coordination polymer
a
Mohamed Ghazzali a, , Mohammed H. Jaafar , Khalid Al-Farhan a,b, Sebastiaan Akerboom c, Jan Reedijk a,c
⁎
a
Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, 11451 Riyadh, Saudi Arabia
Hydrogen Energy Research Group, SET, King Saud University, 11451 Riyadh, Saudi Arabia
Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A new alternating chain compound consisting of gold(I) and silver(I) bridged by cyanides is reported. The Ag(I)
ion is functionalized by 2 triphenyl phosphane ligands, resulting in the formula [Au(C`N)2(PPh3)2Ag]n. The
compound has been prepared by room temperature reaction of triphenyl phosphane with the cyanide salts of
silver(I) and gold(I). The product has been characterized and its single crystal X-ray structure was determined.
In the molecular structure of the complex, the Au(I) centers exhibit the expected linear, two-coordinate geom-
etry with C-bound cyanides, whereas the Ag(I) centers adopt a tetrahedral geometry in a AgN2P2 chromophore.
The shortest hetero intermetallic separation distance is 4.94(7) Å. No aurophilic interactions are observed, but
only the non-conventional C\H…Au hydrogen interactions are present. Upon excitation at 325 nm, a quite
intense luminescence at 475 nm, assigned on the basis of DFT calculations to MMLCT, is observed, which amounts
to ca. 10% of the luminescence intensity of the best known luminescent compounds.
Received 13 January 2012
Accepted 6 March 2012
Available online 15 March 2012
Keywords:
Bimetallic
Single-crystal X-ray diffraction
One-dimensional coordination polymer
Ag(I)–Au(I) complex
Luminescence
DFT
© 2012 Elsevier B.V. All rights reserved.
The design and construction of coordination polymers have been
evolved as an important cornerstone in supramolecular chemistry [1].
Since the venerable Prussian Blue coordination polymers [2,3] and
due to their strong bonds with transition-metal ions, the hexa-, tetra-
and di-cyanidometallate anions have been effectively employed as
molecular tectons in homo- and hetero-metallic multi-dimensional
coordination polymers [4–7]. Meanwhile, the construction of new com-
pounds employing the linear anions [Au(CN)2]−, for the synthesis of
new functional materials with the advantage of closed-shell metal ions
electronic interaction, continues to generate a great interest [8–10]. In
addition, Leznoff and others also demonstrate a moderate to strong
anti-ferromagnetic coupling, in materials synthesized using [Au(CN)2]−
with capping diamine ligands, for a variety of CuII [11–16], NiII and MnII
[17–19] scaffolds, and also with bi- and tri-pyridine-based donor ligands
[20–24]. Moreover, Real and coworkers have described functional mate-
rials in a series of FeII complexes, by employing the [Au(CN)2]− building
units, revealing solid state three-dimensional coordination polymers
showing Hoffman-like spin crossover and reversible ligands exchange
[25–28]. According to CSD version 5.33 [29], the combination of AgI com-
plexes with the linear [Au(CN)2]− has been yet unexplored.
By stirring AuCN, AgCN and PPh3 in toluene at a 1:1:3 molar ratio
under ambient aerobic conditions, the dinuclear AgI–AuI complex (I)
is formed. Details of synthesis and characterization are available in
[30]. Details of the X-ray crystallography are summarized in [31–34].
A thermal ellipsoid plot of the structure is depicted in Fig. 1 and a pack-
ing diagram is given in Fig. 2. Figs. 1 and 2 were created with DIAMOND
package [35]. Luminescence experimental details are described in [36]
and the spectrum is depicted in Fig. 3.
The AgI ion adopts a distorted tetrahedral geometry (main angles are:
103.55(2), 111.47(2), 98.94(2) and 117.69(2)°). The AuI ions are two-
coordinated in an almost linear geometry (174.95(4)°). See Fig. 1. The
hetero intermetallic separation distances are 4.94(7) and 5.366(6) Å.
The Ag–Ag intermetallic node length is 9.935(9), while that of Au–Au
is 9.546(7) Å.
The molecular array is best described as a zig-zag like chain along
the crystallographic [101] vector, with the chain nodes propagation
angle of 146.93 (7)°. See Fig. 2.
Although clearly-defined now as either agostic bonds or non-
conventional hydrogen bonds; the electrostatic interactions involving
hydrogen bond donor and metal empty d-orbitals acceptor have been
investigated during the last decade [37–39]. The C\H…Au interactions
in (I) arise from the phenyl ring hydrogen atoms, are in short contacts
(D–A (Å): 3.668, 3.662 and 3.645) to the gold(I) ions, with apparently
no aurophilic interactions are visible, which may be ascribed to the
bulky phosphane ligand on AgI.
In the current communication, we describe a new compound with
the formula [AgAu(CN)2(PPh3)2]n (I) and we report the synthesis,
structure and luminescence of the first example of a AgI–AuI cyanido-
bridged one-dimensional coordination polymer.
Excitation of the solid-state compound of (I) with UV radiation
results in the appearance of a rather intense blue luminescence band
centered around 475 nm and a shoulder near 450 nm. The compound
⁎
Corresponding author. Tel.: +966 14674743; fax: +966 14673734.
E-mail address: mghazzali@ksu.edu.sa (M. Ghazzali).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.03.005

M. Ghazzali et al. / Inorganic Chemistry Communications 20 (2012) 188–190
189
Fig. 3. Excitation (left) and emission (right) spectrum of the compound (I).
Fig. 1. Thermal ellipsoidal of 50% probability level with atomic numbering scheme for a
part of the polymeric structure of (I). Hydrogen atoms are presented as spheres of arbi-
trary radii. Selected bond distances (Å); Au1–C1:1.983(10), Au1–C2: 1.987(9), Ag1–P1:
2.473(2), Ag1–P2: 2.474(2), Ag1–N1: 2.402(7), Ag1–N2i: 2.280(7), P1–C3: 1.824(8),
P1–C9: 1.822(7), P1–C15: 1.829(7), P2–C21: 1.820(7), P2–C27: 1.827(8),P2–C33:
1.832(8), N1–C1: 1.143(12), N2–C2: 1.134(11). Selected bond angles (°); C1–Au1–C2:
175.0(4), P1–Ag1–P2: 123.73(7), P1–Ag1–N1: 98.94(19), P2–Ag1–N: 111.5(2),
Ag1–P1–C3: 114.2(3), Ag1–P1–C9: 112.3(3), Ag1–P1–C15: 115.5(3), C3–P1–C9:
103.3(3), C3–P1–C15: 105.1(4), C9–P1–C15: 105.3(3), Ag1–P2–C21: 1116.9(2),
Ag1–P2–C27: 116.0(2), Ag1–P2–C33: 111.6(2), C21–P2–C27: 101.2(3), C21–P2–C33:
105.8(3), C27–P2–C33: 103.9(3), Ag1–N1–C1: 128.8(7), C2–N2–Ag1ii:169.2(7),
Au1–C1–N1: 174.4(8), Au1–C2–N2: 176.2(9). P1–Ag1–N2i: 117.7(2), P2–Ag1–N2i:
103.6(2), N1–Ag1–N2i: 98.6(3). Symmetry codes: (i) −1/2+x, 1/2−y, −1/2+z (ii)
1/2+x, 1/2−y, 1/2+z.
features a broad excitation spectrum ranging from 220 to 350 nm with
two maxima at 240 and 325 nm. Excitation of the compound at these
maxima results in a luminescence intensity that is about 10% of that
obtained for one of the best known luminescent coordination com-
pounds, triethylammonium tetrakis(dibenzoylmethanate)europate
[40]. In order to assign the electronic transitions associated with
these emission bands, we carried out DFT calculation on the dinuclear
[AgI(PPh3)2AuI(CN)] molecular fragment [41,42]. The relevant HOMOs
and LUMOs are depicted in Fig. 4.
Fig. 4. Isodensity surface diagrams of LUMO with LUMO{+1} (a) and HOMO with
HOMO{−1} (b) for the compound cationic fragment. HOMO/LUMO are in solid,
HOMO{−1}/LUMO{+1} are in mesh.
Fig. 2. a-axis projection of the molecular chains in (I), with hydrogen atoms are omit-
ted for clarification purpose.

190
M. Ghazzali et al. / Inorganic Chemistry Communications 20 (2012) 188–190
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The d10 cyanidometallate luminescence is frequently attributed to
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Stanica, Dalton Trans. (2005) 1195.
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Inorg. Chem. 47 (2008) 8143.
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In. Ed. 42 (2003) 3760.
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MLCT or MMLCT transitions [43–45]. In the 1D-chain compound of I,
The two lowest singlet excitations are dominated by the combination
of HOMO–LUMO and HOMO{−1}–LUMO{+1} transitions, in which
both HOMO{−1} and HOMO are containing the character of Ag(I)
d-orbitals. The HOMOs are localized on the silver metal center (namely
2
the dxy orbital), mixing with ð-(Ag–P) and (C`N) bondings as well as
π-orbital contribution from phenyl rings on the PPh3 chromophore. The
last one can be also relevant with the existence of C\H…Au interaction.
The cyanide π*-orbital mixes with an Au p*-orbital in bonding fashion to
form the LUMOs. The small HOMO/LUMO gap of ca. 0.031 a.u. can be
attributed to the HOMO's and LUMO's large metallic characters. It is
expected that during a MLCT transition, the mixing of the π*(C`N)
with the empty p-orbitals of Au and the phenyl π-orbitals is capable of
defining the direction of the structural variations along the chain com-
pound. This is also similar to recent results of others [45].
[28] G. Agusti, M.C. Muñoz, A.B. Gaspar, J.A. Real, Inorg. Chem. 47 (2008) 2552.
[29] The Cambridge Crystallographic Data Centre 12 Union Road, Cambridge, UK.
ConQuest ver 1.14 with CSD ver 5.33 November 2011 update.
[30] The starting chemicals were commercially available (BDH-Analar grade). Hexane
was dried and distilled before use; toluene and dichloromethane were kept over
molecular sieves and used without distillation. The elemental analysis was
performed by Perkin Elmer Series II-2400 analyzer. The FT-IR spectrum was
recorded by Shimadzu FT-IR prestige-21 spectrophotometer. Triphenyl phosphane
(0.786 g, 3 mmol) was added to yellow suspension of gold cyanide AuCN (0.223 g,
1 mmol) in toluene (30 ml). Stirring continued for 20 min till a clear solution is
obtained. Silver cyanide AgCN (0.134 g, 1 mmol) was added then stirring continues
for one day. The white precipitate is filtered off, washed with toluene (10 ml) and
collected. The recrystallisation with dichloromethane/hexane gives crystals suitable
for X-ray single crystal diffraction. Yield of [AgAu(C`N)2(PPh3)2]n (0.820 g, ca.
93%), m.p. 218 °C, Elemental Analysis for C38H30AgAuN2P2; Found (calc.): 52.05
(51.78) %C, 3.40 (3.43) %H, 3.18 (3.19) %N νmax cm−1 (KBr disk) 503 (s), 515 (s)
cm−1 (Au–C), 2170 (m), 2141 (m) cm−1 (C`N).
In conclusion, the structure of new bimetallic AuI–AgI one dimen-
sional coordination compound is presented, and its luminescence is
ascribed as due to MMLCT.
Acknowledgments
[31] X-ray crystallography: Crystal Data: C38H30AgAuN2P2, Monoclinic, P21/n, a=9.7145(6)
Å, b=20.4203(13) Å, c=17.3735(12) Å, β=95.666(2)º, V=3429.6(4) Å3,
D
The authors are indebted to the deanship of scientific research,
college of Science research center for supporting this work. The Distin-
guished Scientist Fellowship Program (DSFP) at King Saud University is
gratefully acknowledged. Mohamed Ghazzali is grateful for the National
Plan for Science and Technology (NPST Grant 09-ENE909-02).
calc =1.707 g cm−3, A total of 39826 reflections were collected, of which 7809 were
independent. Rint=0.099, Dataset (h;k;l)=−12;12; −26:26; −22:22, Observed
data [I>2σ(I)]=4715, 398 parameters, R(F) [I>2σ(I)]=0.0518, w=0.1444,
R
S=0.99, min. and max. Residual density (e/Å3)=−2.48 and 1.26 (0.90 Å from Au1
and 1.18 Å from C1 or 1.4 Å from Au1, respectively). A colorless plate was selected,
mounted and glued on a thin capillary tip. Diffraction data were collected using Rigaku
R-axis RAPID diffractometer equipped with an imaging plate area detector utilizing
Mo-Kα radiation (λ=0.71075 Å) with graphite monochromator. The data were
collected using ω-scans at a temperature of 294 2 K to a maximum 2θ of 55.0°. The
intensity data were corrected for Lorentz and polarization effects, for absorption and
extinction. The structure was solved by direct method [33] and refined by the SHELX
package [34]. All non-hydrogen atoms were refined anisotropically. All hydrogen
atoms were geometrically fixed and refined by riding atom approximation.
[32] Rigaku and Rigaku Americas, 9009 New Trails Dr., The Woodlands TX 77381
(2007) USA.
Appendix A. Supplementary material
Supplementary data to this article can be found online at doi:10.
1016/j.inoche.2012.03.005.
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