Silver(I) complexes of 2-(diphenylphosphano)benzaldehyde: Synthesis, structure and luminescence

Article abstract of DOI:10.1016/j.poly.2011.12.020

Reactions of silver(I) chloride or nitrate with 2-(diphenylphosphano) benzaldehyde (dppbza) in 1:2 molar ratio afforded mononuclear complexes of the type [AgX(dppbza)₂], whereas treatment of these compounds with equimolar amounts of pyridine-2-thione or 4,6-dimethylpyrimidine-2-thione gave rise to the formation of mixed-ligand complexes of the formula [Ag(dppbza) ₂(thione)₂]NO₃ and [AgCl(dppbza)(thione)] ₂, respectively. The molecular structure of [Ag(dppbza) ₂(NO₃)] has been established by single-crystal X-ray diffraction. The complex features a strongly distorted tetrahedral Ag(I) center surrounded by two phosphane P atoms and two O atoms from the nitrate anion. The new compounds show intense emission in the solid state and in solution at ambient temperature.

Full text of DOI:10.1016/j.poly.2011.12.020

Polyhedron 34 (2012) 171–175
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Silver(I) complexes of 2-(diphenylphosphano)benzaldehyde: Synthesis,
structure and luminescence
C. Ntoras a, P.J. Cox b, P. Aslanidis a,
⇑
a Aristotle University of Thessaloniki, Faculty of Chemistry, Inorganic Chemistry Laboratory, P.O. Box 135, GR-541 24 Thessaloniki, Greece
b School of Pharmacy and Life Sciences, The Robert Gordon University, Schoolhill, Aberdeen AB10 1FR, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of silver(I) chloride or nitrate with 2-(diphenylphosphano)benzaldehyde (dppbza) in 1:2 molar
ratio afforded mononuclear complexes of the type [AgX(dppbza)2], whereas treatment of these compounds
with equimolar amounts of pyridine-2-thione or 4,6-dimethylpyrimidine-2-thione gave rise to the forma-
tion of mixed-ligand complexes of the formula [Ag(dppbza)2(thione)2]NO3 and [AgCl(dppbza)(thione)]2,
respectively. The molecular structure of [Ag(dppbza)2(NO3)] has been established by single-crystal
X-ray diffraction. The complex features a strongly distorted tetrahedral Ag(I) center surrounded by two
phosphane P atoms and two O atoms from the nitrate anion. The new compounds show intense emission
in the solid state and in solution at ambient temperature.
Received 12 November 2011
Accepted 22 December 2011
Available online 2 January 2012
Keywords:
Silver(I)
2-(Diphenylphosphano)benzaldehyde
Heterocyclic thioamides
Luminescence
Ó 2011 Elsevier Ltd. All rights reserved.
Crystal structure
1. Introduction
standing of the impact of the thione ligand on their luminescence
properties. In this work we report on the synthesis and characteriza-
Owing to the favorable soft acid–soft base interaction, there is a
rich chemistry of monovalent group 11 metal ions based upon coor-
dination to ligands containing phosphorus and sulfur donor atoms.
In this respect, phosphane containing silver(I) complexes have re-
ceived a great deal of attention during the past few decades, mainly
because of their applications in certain homogenous catalytic
processes [1], while some of them showed antitumor, antifungal
and antibacterial properties [2,3] as well. As far as the sulfur contain-
ing ligands are concerned, considerable amount of work has been
performed on the synthesis and characterization of silver(I) com-
plexes containing heterocyclic thioamides, a class of compounds
with close relevance to biological systems [4,5]. In a series of studies
[6] we have explored the mixed-ligand complexes blending both ter-
tiary arylphosphanes and heterocyclic thioamides as ligands. In
these complexes the coordination number has been found to be re-
lated to the steric requirements on the part of the phosphane ligand
only, thus we recently focused on phosphanes that may introduce
imposed steric effects around the metal center. Recently, group 11
d10 metal complexes are becoming more and more popular with
respect to their potential use as photocatalysts and photoinitiators
[7], as components for luminescent-based chemical sensors [8], or
as sensitizers in solar-energy conversion [9]. Thus, we recently have
turned our interest to the photochemistry of these phosphane/thione
ligated group 11 metal complexes, aiming to contribute to the under-
tion of some new luminescent silver(I) complexes formed upon
reacting silver(I) salts with 2-(diphenylphosphano)benzaldehyde
(dppbza), a sterically demanding phosphane that bears, besides the
‘‘soft’’ phosphorus donor, a ‘‘hard’’ oxygen atom, thus being capable
of behaving as a potential P,O-chelate [10].
2. Experimental
2.1. Materials and instrumentation
Commercially available silver(I) chloride and nitrate and 2-
(diphenylphosphano)benzaldehyde (Aldrich) were used as received
while the thiones (Merck) were re-crystallized from hot ethanol
prior to their use (Scheme 1). All the solvents were purified by
respective suitable methods and allowed to stand over molecular
sieves. Infra-red spectra in the region of 4000–250 cmÀ1 were
obtained in KBr disks with a Nicolet FT-IR spectrophotometer. Elec-
tronic absorption spectra were measured with a Perkin-Elmer-Hit-
achi 200 spectrophotometer while a Hitachi F-700 fluorescence
spectrophotometer was used to obtain the emission spectra. Melt-
ing points were measured in open tubes with a STUART scientific
instrument and are uncorrected.
2.2. Crystal structure determination
Single crystals of [Ag(dppbza)2(NO3)] suitable for crystal struc-
ture analysis were obtained by slow evaporation of a saturated
acetonitrile solution of the complex at room temperature. X-ray
⇑
Corresponding author.
E-mail addresses: ext.cox1@rgu.sc.uk (P.J. Cox), aslanidi@chem.auth.gr
(P. Aslanidis).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.12.020

172
C. Ntoras et al. / Polyhedron 34 (2012) 171–175
CH3
NH
3.94; N, 1.82%. IR (cmÀ1): 3050m, 2854m, 1693s, 1669vs, 1584m,
1562s, 1480s, 1435vs, 1408vs, 1288vs, 1203vs, 1098s, 844vs,
752vs, 694vs, 573s, 530s, 463vs; UV–Vis (kmax, log e): 237 (4.27),
H3C
O
NH
N
272 (3.11).
S
S
PPh
2
2.3.2. [AgCl(dppbza)2] (2)
dmpymtH
py2SH
dppbza
Yellow powder (145 mg, 80%), m.p. 201 °C; Anal. Calc. for
C
38H30AgClO2P2: C, 63.95; H, 4.18. Found: C, 63.68; H, 4.24%. IR
Scheme 1. The phosphane and the heterocyclic thiones used as ligands with their
abbreviations.
(cmÀ1): 3050w, 2996w, 1696vs, 1674vs, 1583 m, 1568s, 1481s,
1435vs, 1393 m, 1295s, 1204s, 1094s, 1027m, 998m, 917m, 846s,
diffraction data were collected on an Enraf-Nonius Kappa CCD area-
detector diffractometer. The programs DENZO [11] and COLLECT [12]
were used in data collection and cell refinement. Details of crystal
and structure refinement are shown in Table 1. The structure were
solved using program SIR97 [13] and refined with program SHELX-97
[14]. Molecular plots were obtained with program ORTEP-3 [15].
749vs, 696vs, 677s, 529vs, 508s, 462m; UV–Vis (kmax, log e): 247
(4.25), 299.5 (3.65), 363 (2.91).
2.4. Synthesis of complexes 3–6
To a suspension of 0.25 mmol of the silver(I) salt (36 mg for
AgCl, 42.5 mg for AgNO3) in 30 cm3 of dry acetonitrile, a solution
of 145 mg (0.5 mmol) of 2-(diphenylphosphano)benzaldehyde in
25 cm3 of dry acetonitrile was added and the mixture was stirred
for 4 h at 50 °C. The resulting solution was then treated with
0.5 mmol of the appropriate thione (55.5 mg for py2SH, 70 mg
for dmpymtH) dissolved in a small amount (ꢀ20 cm3) of methanol.
The new reaction mixture was stirred for additional 4 h at 50 °C
and then was filtered off and left several days at ambient to pro-
vide the colored powdery product.
2.3. Synthesis of complexes 1 and 2
To a suspension of 0.25 mmol of the silver(I) salt (36 mg for
AgCl, 42.5 mg for AgNO3) in 30 cm3 of dry acetonitrile, a solution
of 145 mg (0.5 mmol) of 2-(diphenylphosphano)benzaldehyde in
25 cm3 of dry acetonitrile was added and the mixture was stirred
for 4 h at 50 °C. The resulting bright yellow solution was filtered
off and left to evaporate at ambient. The microcrystalline yellow
solid, which was deposited upon standing for several days, was
filtered off and dried in vacuo.
2.4.1. [Ag(dppbza)2(py2SH)2]NO3 (3)
Yellow powdery solid (102 mg, 42%), m.p. 105–107 °C; Anal.
Calc. for C48H40N3AgO5P2S2: C, 59.26; H, 4.14; N, 4.32. Found: C,
60.01; H, 4.27; N, 4.17%. IR (cmÀ1): 3049m, 2850m, 1694vs,
1669s, 1574vs, 1540s, 1480s, 1434vs, 1384vs, 1205vs, 1133vs,
2.3.1. [Ag(dppbza)2(NO3)] (1)
Yellow crystals (142 mg, 76%), m.p. 234 °C; Anal. Calc. for
C38H30NAgO5P2: C, 60.82; H, 4.03; N, 1.87. Found: C, 60.52; H,
1096s, 844s, 749s, 726vs, 694vs, 543vs; UV–Vis (kmax, log e): 234
(4.27), 277 (3.93), 351 (3.53).
Table 1
Crystal data and structure refinement for [Ag(dppbza)2(NO3)].
Molecular formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C38H30AgNO5P2
750.44
120(2)
0.71073
monoclinic
P21/c
2.4.2. [Ag(dppbza)2(dmpymtH)2]NO3 (4)
Pale yellow microcrystalline solid (152 mg, 59%), m.p. 119–
120 °C; Anal. Calc. for C50H46N5AgO5P2S2: C, 58.26; H, 4.50; N,
6.79. Found: C, 59.01; H, 4.56; N, 6.83%. IR (cmÀ1): 3185w, 3045m,
2915m, 1613vs, 1562vs, 1474s, 1437vs, 1381vs, 1307s, 1233vs,
1177s, 1094s, 1019m, 982s, 890m, 843m, 746vs, 695vs, 547s,
9.7154(4)
38.8873(18)
9.9009(5)
90
117.1020(10)
90
3329.9(3)
4
1.497
505s, 454s; UV–Vis (kmax, log
e): 240 (4.41), 279 (4.22), 350 (3.70).
b (Å)
c (Å)
a
(°)
2.4.3. [AgCl(dppbza)(py2SH)] (5)
b (°)
Yellow powdery solid (76 mg, 56%), m.p. 179 °C; Anal. Calc. for
c
(°)
V (Å3)
C
24H20NAgClOPS: C, 52.91; H, 3.70; N, 2.57. Found: C, 52.80; H,
3.69; N, 2.68%. IR (cmÀ1): 3050m, 2996w, 1697vs, 1674vs, 1583s,
1562s, 1393s, 1295s, 1204vs, 1094s, 998m, 846vs, 749vs, 696vs,
Z
Dcalc (Mg/m3)
Absorption coefficient
0.747
677s, 526s, 502vs; UV–Vis (kmax, log e): 236 (4.16), 282 (4.20),
357 (3.83).
(mmÀ1
)
F(000)
1528
Crystal size (mm)
Theta range for data
collection (°)
0.09 Â 0.07 Â 0.06
3.12–27.45
2.4.4. [AgCl(dppbza)(dmpymtH)] (6)
Yellow powdery solid (69 mg, 62%), m.p. 114–116 °C; Anal. Calc.
for C25H23N2AgClOPS: C, 52.33; H, 4.04; N, 4.88. Found: C, 52.68; H,
4.22; N, 4.41%. IR (cmÀ1): 3047m, 2846m, 1691s, 1616vs, 1561vs,
1479m, 1435s, 1229vs, 1184s, 1095s, 843m, 748s, 726vs,
695vs, 545s, 507s; UV–Vis (kmax, log e): 234 (4.16), 283 (4.09),
332 (3.77).
Index ranges
À12 6 h 6 12, À50 6 k 6 50, À12 6 l 6 12
Reflections collected
Independent reflections
Completeness to
theta = 27.54°
Maximum and minimum
34773
7639 [Rint = 0.0887]
99.4%
0.9566 and 0.9358
transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
full-matrix least-squares on F2
7639/0/424
1.023
3. Results and discussion
Final R indices [I > 2
R indices (all data)
Final weighting scheme
r
(I)]
R1 = 0.0529, wR2 = 0.1082
R1 = 0.0916, wR2 = 0.1213
3.1. Synthesis
calc w = 1/r
2[(Fo2) + (0.0426P)2 + 5.3092P]
where P = (Fo2 + 2Fc2)/3
0.720 and À0.651
Treatment of 2-(diphenylphosphano)benzaldehyde and AgX
(X = Cl, NO3À) resulted in the formation of orange-yellow colored
crystalline compounds formulated as [AgX(dppbza)2] (compounds
Largest difference in peak
and hole (e ÅÀ3
)

C. Ntoras et al. / Polyhedron 34 (2012) 171–175
173
1–2), regardless of the molar ratio (1:1 or 2:1) applied. Aiming to
obtain phosphane/thione mixed-ligand complexes, we further
treated the solutions of these precursors, skipping their isolation,
with a methanolic solution of two equivalent of a heterocyclic thi-
one. Stirring of such a mixture at 50 °C gradually caused slight
darkening of the solution, from which, on slow evaporation, micro-
crystalline or powdery solids were deposited. These proved, how-
ever, to correspond to the desired pure compounds only in a few
cases, although the described one-top two-step synthetic proce-
dure has been applied successfully on copper(I) halides, in combi-
nation with virtually any heterocyclic thioamide. In particular,
solutions that contained pyridine-2-thione (py2SH) and 4,6-dim-
ethylpyrimidine-2-thione (dmpymtH) yielded small amounts of
yellow to orange colored solids, which could be satisfactory de-
fined as compounds 4–6, but inseparable mixtures of two or more
products resulted in all the other cases. All prepared compounds
are air stable diamagnetic solids, moderately soluble in acetoni-
trile, chloroform or acetone. Solutions of compounds 1, 2, 5 and 6
in common organic solvents are non-conducting, whereas 3 and
4 behave as 1:1 electrolytes.
Fig. 1. A view of [Ag(dppbza)2(NO3)] with atom labels. Displacement ellipsoids are
shown in the 50% probability level.
3.2. Spectroscopy
The infrared spectra of compounds 1–6, recorded in the range
4000–250 cmÀ1 display strong vibrational phosphane bands, which
remain practically unshifted upon coordination. In addition, the spec-
tra of the mixed-ligand complexes 4–6 contain the expected charac-
teristic ‘‘thioamide bands’’, with shifts due to coordination indicative
of an exclusive S-coordination mode. As expected, upon coordination
Table 2
Selected bond lengths (Å) and angles (o) for [Ag(dppbza)2(NO3)].
Ag(1)–O(3)
Ag(1)–O(4)
Ag(1)–P(2)
Ag(1)–P(1)
P(1)–C(14)
P(1)–C(8)
2.413(3)
2.619(4)
2.4239(10)
2.4353(11)
1.818(4)
1.826(4)
1.839(4)
1.815(4)
P(2)–C(33)
P(2)–C(20)
O(1)–C(7)
O(2)–C(26)
O(3)–N(1)
O(4)–N(1)
O(5)–N(1)
1.833(4)
1.841(4)
1.216(5)
1.209(5)
1.255(4)
1.233(5)
1.240(5)
no significant shift is noticed for the m(C@O) vibration of the dppbza
ligand. The presence of non-coordinated NO3À in the spectra of com-
P(1)–C(1)
P(2)–C(27)
pounds 3 and 4 is indicated by the presence of a very strong band at
ꢀ1380 cmÀ1 assigned to the N–O asymmetric stretching mode (m1
)
P(1)–Ag(1)–P(2)
O(3)–Ag(1)–P(1)
O(3)–Ag(1)–P(2)
O(4)–Ag(1)–P(1)
O(4)–Ag(1)–P(2)
O(3)–Ag(1)–O(4)
C(1)–P(1)–Ag(1)
C(8)–P(1)–Ag(1)
C(14)–P(1)–Ag(1)
127.38(4)
108.30(9)
122.78(9)
123.39(12)
100.31(11)
49.73(11)
114.19(13)
110.63(13)
117.82(13)
C(20)–P(2)–Ag(1)
C(27)–P(2)–Ag(1)
N(1)–O(3)–Ag(1)
C(33)–P(2)–Ag(1)
O(4)–N(1)–O(5)
O(4)–N(1)–O(3)
O(5)–N(1)–O(3)
O(1)–C(7)–C(2)
O(2)–C(26)–C(21)
112.64(13)
120.85(14)
101.2(3)
110.16(13)
122.1(4)
117.3(4)
120.6(4)
[16], however the bands associated with coordination of the nitrate
unit could not be certainly identified in the spectrum of 1 due to
the fact that the region in question is masked by strong phosphane
bands.
The UV–Vis spectra of all compounds are dominated by intense
absorption bands at ꢀ240 and ꢀ280 nm, which are assigned to the
124.2(4)
124.2(4)
p–
p⁄ transition of the phosphine. Moreover, a third broad band of
lower intensity in the 350–360 nm region in the spectra of com-
pounds 3–6 can be ascribed to thione originating intraligand tran-
sitions, which may possess partial CT character.
ligands are almost parallel oriented to each other, the dihedral an-
gle between them being 10.8(2)°. The respective stacking distance
between ring centroids is 3.921(2) Å, suggesting the presence of
3.3. Molecular structure of [Ag(dppbza)2(NO3)]
p p interaction [18], which may be considered to significantly
Á Á Á
The structure of [Ag(dppbza)2(NO3)] (1), was established by sin-
gle crystal X-ray diffraction. Details of crystal and structure refine-
ment are given in Table 1. The ORTEP drawing for the molecule is
illustrated in Fig. 1, whereas selected interatomic distances and an-
gles are listed in Table 2. The structure consists of discrete mole-
cules containing the Ag+ ion in a strongly distorted tetrahedral
environment, surrounded by two P atoms of two dppbza units
and two O atoms of the chelating nitrate anion. The angular devi-
ations from the ideal tetrahedral value are remarkable but not at
all unexpected, at least regarding the appropriate opening up of
the angle between the sterically demanding groups of the dppbza
units.
Interestingly, the formyl groups of the two dppba ligands have
both their oxygen atom oriented toward the silver atom to a dis-
tance of 3.036(3) and 3.204(3) Å, respectively. These AgÁ Á ÁO con-
tacts are slightly shorter than the sum of the respective van der
Waal radii (3.24 Å) and can be considered as a dipole–ion interac-
tion [17]. Moreover, the formyl groups are both essentially copla-
nar with the C atoms of the attached phenyl rings. Further, the
formylated phenyl rings C1–C6 and C20–C25 of the two phosphane
contribute to the alignment of the molecule in the crystalline state.
The Ag–P bond distances of 2.4239(10) and 2.4353(11) Å are
within the range of values observed in other tetrahedrally coordi-
nated Ag(I) complexes [19]. Likewise, the Ag–O distances of
2.413(3) and 2.619(4) Å are comparable to those found in
phosphane ligated Ag(I) complexes bearing coordinated nitrate
[19b,c].
3.4. Luminescence
The RT luminescence spectra of the complexes in the solid state
and in CH2Cl2 solution have been studied. The absorption and
emission spectra of compound 1 together with the emission spec-
tra of compounds 3 and 4 are shown in Fig. 2 while absorption and
emission data of all the complexes under investigation are summa-
rized in Table 3. After excitation at 380 nm, the RT emission spec-
trum of dppba in CH2Cl2 consists of a broad band with maximum at
447 nm, whereas in the spectrum of [Ag(dppbza)2(NO3)] (com-
pound 1) the emission maximum appears significantly red-shifted,

174
C. Ntoras et al. / Polyhedron 34 (2012) 171–175
4. Conclusion
The aim of this work was the study of the coordination behavior
of 2-(diphenylphosphano)benzaldehyde (dppbza) toward silver(I).
We have found that dppbza acts as a monodentate, coordinating to
the metal exclusively via the ‘‘soft’’ phosphorus atom, whereas no
bonding interaction could be proposed for the formyl group, de-
spite the observed marked orientation of its oxygen atom towards
the copper center. Thus, the resulting complexes of composition
[AgX(dppbza)2] (X = ClÀ, NO3À), are monomers with the silver atom
in a fairly trigonal (for X = ClÀ) or strongly distorted tetrahedral (for
X = NO3À) environment, respectively. These compounds proved to
be good precursors for the preparation of other derivatives; in
the course of the present study these are chosen for the synthesis
of phosphane/thione mixed-ligand mononuclear cationic com-
plexes of type [Ag(thione)2(dppbza)2]NO3 and dimeric complexes
of type [AgCl(thione)(dppbza)]2, the later proposed to contain the
halides as bridging ligands between the two metal centers. The
complexes show intense room temperature luminescence in both
the solid state and in solution, originating probably from LMCT
transition. There is strong evidence for a participation of S ? Ag
charge transfer in the emissive excited state, thus complexes of
this type may provide a possibility for fine tuning the emission en-
ergy by the choice of the thione ligand.
Fig. 2. Room temperature excitation (a) and emission (b) spectrum of [Ag
(dppbza)2(NO3)] (1) and emission (c and d) spectra of 3 and 4, respectively, in
CH3Cl2 solution.
Table 3
Excitation and emission maxima of the complexes at room temperature.
Compound
kex (nm)
kem (nm)a
[Ag(dppbza)2(NO3)], 1
[AgCl(dppbza)2], 2
[Ag(dppbza)2(py2SH)2]NO3, 3
[Ag(dppbza)2(dmpymtH)2]NO3, 4
[AgCl(dppbza)(py2SH)2], 5
[AgCl(dppbza)(dmpymtH)2], 6
330
320
330
300
280
280
473, 500
457, 525
437, 455
444, 465
480, 494
461, 477
Acknowledgment
We thank the EPSRC X-ray crystallography service at the Uni-
versity of Southampton for collecting the X-ray data.
a
Solid state (first entry), 10À5 M solution in CH2Cl2 (second entry).
Appendix A. Supplementary material
at 500 nm. It is noteworthy that a solid sample of 1 emits at clearly
higher energies (473 nm).
CCDC 851806 contains the supplementary crystallographic data
for complex 1. 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.
The emission spectra of the heteroleptic complexes [Ag(dppb-
za)2(py2SH)2]NO3 (3) and [Ag(dppbza)2(dmpymtH)2]NO3 (4) are
simple, with kmax(em) at 455 and 465 nm, respectively, expressing
significant shifting towards higher energies, as compared to the
[Ag(dppbza)2(NO3)] value. This result may be considered as evi-
dence for participation of S ? Ag charge transfer in the emissive
excited state [20]. In a similar manner, the emission maximum in
the spectrum of [AgCl(dppbza)2] (compound 2) appears notably
red shifted in comparison with that of free dppa (by 76 nm),
whereas in the respective heteroleptic complexes [AgCl(dppbza)(-
py2SH)] (5) and [AgCl(dppbza)(dmpymtH)] (6) the presence of the
thione also causes strong hypsochromic shift (Table 3).
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