Di- and polynuclear silver(I) derivatives with a new multitopic pyrimidine-base tri-thioether ligand

Article abstract of DOI:10.1016/j.inoche.2012.07.019

Four novel silver(I) derivatives containing a new flexible multitopic ligand L, incorporating both the pyrimidine and the thioether linkages, have been synthesized and characterized. The X-ray crystal structure of the ligand L shows that two of the three arms of the free ligand adopt an anti geometry about the CH₂-S bonds, while the third one is in a distorted gauche conformation. [(L)Ag(BF₄)] and [(L)Ag(PF₆)] are insoluble likely polymeric species, with a cationic network and uncoordinated anions. However, soluble derivatives are obtained with AgNO₃ and AgCF ₃SO₃, where the counter-ions in the solid state are coordinated to the Ag(I) ion. The X-ray crystal structure of derivative [(L)Ag(NO₃)] is composed by dinuclear molecules in which each L bridges two silver ions through the coordination of the nitrogen atoms of two pyrimidine rings. All silver(I) derivatives emits bluish-green light with a maximum emission at 517 nm, when excited at 370 nm source. The quite low emission increases by five times for derivative [(L)Ag(CF₃SO ₃)] on cooling to 50 K.

Full text of DOI:10.1016/j.inoche.2012.07.019

Inorganic Chemistry Communications 24 (2012) 20–23
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Di- and polynuclear silver(I) derivatives with a new multitopic pyrimidine-base
tri-thioether ligand
b,
Archana Mizar a, , Claudio Pettinari , Fabio Marchetti c,1, Ivan Timokhin c, Alessandra Crispini d,2
⁎
⁎
a
Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Avenida Rovisco Pais, 1049–001 Lisboa, Portugal
School of Pharmacy, Inorganic Chemistry Section, Via S. Agostino 1, Università degli studi di Camerino, 62032 Camerino (MC), Italy
School of Science and Technology, Chemistry Section, Via S. Agostino 1, Università degli studi di Camerino, 62032 Camerino (MC), Italy
Department of Pharmaceutical Sciences, Università della Calabria, I-87030 Arcavacata di Rende (CS), Italy
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Four novel silver(I) derivatives containing a new flexible multitopic ligand L, incorporating both the pyrim-
idine and the thioether linkages, have been synthesized and characterized. The X-ray crystal structure of the
ligand L shows that two of the three arms of the free ligand adopt an anti geometry about the CH2-S bonds,
while the third one is in a distorted gauche conformation. [(L)Ag(BF4)] and [(L)Ag(PF6)] are insoluble likely
polymeric species, with a cationic network and uncoordinated anions. However, soluble derivatives are
obtained with AgNO3 and AgCF3SO3, where the counter-ions in the solid state are coordinated to the Ag(I)
ion. The X-ray crystal structure of derivative [(L)Ag(NO3)] is composed by dinuclear molecules in which
each L bridges two silver ions through the coordination of the nitrogen atoms of two pyrimidine rings. All
silver(I) derivatives emits bluish-green light with a maximum emission at 517 nm, when excited at 370 nm
source. The quite low emission increases by five times for derivative [(L)Ag(CF3SO3)] on cooling to 50 K.
© 2012 Elsevier B.V. All rights reserved.
Received 28 May 2012
Accepted 9 July 2012
Available online 17 July 2012
Keywords:
Trithioether pyrimidine-based ligand
Ag compounds
Crystal structure
Luminescence
The rational design of coordination polymer networks based on
multitopic ligands and metal centers represents one of the most exciting
and rapidly developing field in current coordination and supramolecular
chemistry due to their potential applications in many areas [1]. One of
the interesting challenges in supramolecular chemistry and crystal engi-
neering is the development of methods for the design and synthesis of
topologically interesting architectures with increasing dimensionality.
AgI is a favourable and fashionable building block or connecting node
for coordination polymers [2], as the lack of crystal field stabilization at
the d10 configuration monovalent silver cation allows different coordi-
nation environments depending on the particular steric and electronic
requirements of the employed tethering ligands, thereby allowing a
variety of coordination polymer morphologies. Thioether ligands pos-
sess unusual potential for the construction of coordination architectures
[3]. The rigid ligands tends to facilitate the formation of highly ordered,
crystalline extended networks [4] apparently because the multiple
equivalent positions allow the ligand to achieve more readily the re-
quired orientation in the growing lattice. However recent developments
on multitopic ligands incorporating flexible spacers between the donor
atoms have demonstrated new and unexpected opportunities in the
self-assembly of inclusion coordination polyhedra, such as, for example,
open and closed metallacages obtained with ligands designed to be
semiflexible in order to promote structures that will maximize both
the covalent and noncovalent forces [5]. Here we report the rational
design and synthesis of a new multitopic ligand incorporating both the
pyrimidine and the thioether linkages (Scheme 1), and its interaction
with selected silver(I) salts.
From the reaction of pyrimidine-2-thiol with 1,3,5-tris(bromomethyl)
benzene in the presence of base the ligand L was obtained in good yield
[6]. Its IR spectrum displays the typical weak absorptions above
3000 cm−1 assigned to C\Haromatic stretching and strong bands in the
range 1500–600 cm−1 due to C_C and C_N stretching modes. The
ESI-MS spectrum of L in MeCN displays a unique peak at 415 m/z due to
protonated L. Re-crystallization from hot ethanol afforded yellow crystals
of L, suitable to be analysed by single crystal X-ray diffraction [7]. Fig. 1a
shows a perspective view of the structure of L. Bond distances and angles
are similar to those observed in analogous multitopic ligands containing
thioether linkages [8]. Two of the three arms adopt an anti geometry
about the CH2-S bonds, while the third on is in a distorted gauche confor-
mation [torsion angle C(18)-S(3)-C(17)-C(4) of 84.1(1)°] probably due to
packing effects. Indeed, the molecules pack in the crystal with the central
benzene ring of one molecule forming π-π stacking interaction with the
one of an adjacent molecule, showing a face-to-face displaced arrange-
ment with interplanar distance of 3.4 Å and transversal slip of 1.51 Å.
⁎
Corresponding authors. Tel.: +39 0737 402234; fax: +39 0737 637645.
E-mail addresses: archana.mizar@gmail.com (A. Mizar),
claudio.pettinari@unicam.it (C. Pettinari), a.crispini@unical.it (A. Crispini).
1
Tel.: +39 0737 402217; fax: +39 0737 637345.
Tel.: +39 0984 492888; fax: +39 0984 492067.
2
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.07.019

A. Mizar et al. / Inorganic Chemistry Communications 24 (2012) 20–23
21
Scheme 1. Synthesis of the multitopic ligand L.
Moreover, one nitrogen atom of the pyrimidine ring of the S(3) arm inter-
acts through a weak N\H\C hydrogen bond with the above S(1) arm
(Fig. 1b).
coordination to silver centres. In detail, the IR of 1 contains two strong
bands at 1377 and 1309 cm−1 due to coordinated NO3− and the pres-
ence of two overtones at 1747 and 1737 cm−1 in accordance with
O-NO3 coordination [13]. The IR spectrum of 4 shows several strong
bands in the range 1100–1250 cm−1 due to the CF3SO3− stretching
modes. The presence of fine splitting is indicative of coordination of
the counterion to silver through the oxygen atoms [14]. The ESI-MS
spectra (MeCN) of 1 and 4 show two peaks corresponding to
From the reaction of L with AgX in 1:1 molar ratio in refluxing eth-
anol, 1:1 adducts [(L)AgX] 1–4 (1: X=NO3, 2: X=BF4, 3: X=PF6, 4:
X=CF3SO3) were obtained [9]. Derivatives 1 and 4 are slightly solu-
ble in acetonitrile and DMSO, while 2 and 3 are completely insoluble
in all solvents. Conductance measurements in acetonitrile of 1 and 4
exhibits values of ca. 190 S cm2 mol−1 which are typical of 1:1 elec-
trolytes [10]. IR spectroscopy is a powerful technique in inferring
some structural features, especially with insoluble compounds. The
1
[L+Ag]+ and [2 L+2Ag+X]+ species. The H NMR spectra of 1
IR spectra of 2 and 3 contain sharp bands at 1045 and 834 cm−1
,
which are due to noncordinated fluorinated counter-ions BF4 [11]
and PF6 [12], respectively. This evidence, together with the insolubil-
ity of 2 and 3 seems to support a polynuclear nature where L acts as
di- or even tri-topic bridging ligand connecting two or more Ag+
ions, while the anions are dispersed within the cationic lattice. On
the other hand the IR spectra of 1 and 4 display evidence anion
Fig. 1. Perspective view of L with thermal ellipsoids (40% probability) and numbering
scheme (a) and representation of association of molecules of L with formation of π–π
and CH/N interactions (b).
Fig. 2. Perspective view of derivative 1 with thermal ellipsoids (40% probability) and
numbering scheme (a) and representation of the interlocking of two chair conforma-
tion molecules and their intermolecular interactions (b).

22
A. Mizar et al. / Inorganic Chemistry Communications 24 (2012) 20–23
below, with the generation of a CH/π interaction characterized by a
separation between the hydrogen atom (H(16a)) and the centroid
of the phenyl ring of 2.82 Å [15].
The interpenetration of the two macrocycles is reinforced by hy-
drogen bond interactions between the oxygen atoms of the pendent
nitrate anions involved in the interlocking and the -CH2 groups of
two arms of the bridging L ligand lying above and below [C(17)\O(1)i
3.540(6) Å, H(17)\O(1)i 2.585 Å, C(17)\H(17)\O(1)i 168.5(3)°;
C(12)\O(3)ii 3.418(6) Å, H(12)\O(3)ii 2.567 Å, C(17)\H(17)\O(1)ii
146.6(3)°, i=1−x, 2−y, 1−z; ii=x−1, y, z ] (Fig. 2b). The remaining
two pendent anions, one for each interlock chair, establish hydrogen
bond interactions with symmetrically related structural motives approx-
imately along the b direction generating the ribbon like aggregation
shown in Fig. 2b [C(14)\O(2)iii 3.383(8) Å, H(14)\O(2)i 2.697 Å,
C(14)\H(14)\O(2)i 131.3(4)°, iii=1−x, 1−y, 1−z].
It is well known that some silver(I) compounds have great lumi-
nescence properties due to the energy transfer from the d10 metal
centre to π-acceptor ligands [16]. They usually exhibit weak lumines-
cence at low temperatures, whereas those exhibiting luminescent
properties at room temperature being very limited [17]. When excit-
ed by a 370 nm source at 300 K, derivative 4 emits bluish-green light
with a maximum emission at 517 nm. Such emission is however
quite low, but increases ca. five times on cooling to 50 K (Fig. 3).
The AgI derivatives 1–2 display a very weak luminescence at low
temperature, with a maximum emission at ca. 517 nm, as shown in
Fig. 4.
In summary, we have reported the synthesis of a new flexible
multitopic ligand, incorporating both the pyrimidine rings and the
thioether linkages, which has been shown suitable to coordinate
silver(I) through its nitrogen atoms, affording both di- and polynucle-
ar metal systems, some of them exhibiting interesting luminescence
properties. The coordinative potentials of such ligand through its sul-
fur atoms will be explored and further studies are actually on going.
Fig. 3. Intensity variation upon temperature of the emission maximum of derivative 4.
and 4 (CD3CN) containing all the expected resonances in accordance
with the formulation proposed exhibit the proton resonances of the
central aromatic ring and of methylene groups of L unchanged with
respect to those of free ligand, whereas the absorption due to the py-
rimidine rings are only slightly shifted upon coordination.
The X-ray crystal structure of derivative [(L)Ag(NO3)]2. CH3CN, 1,
(Fig. 2a) is composed of centrosymmetric molecules in which each L
ligand bridges two silver ions through the coordination of the nitro-
gen atoms of two pyrimidine rings [bond distances Ag(1)\N(3)
and Ag(1)\N(5) of 2.217(3) and 2.215(3) Å, respectively]. The linear
coordination around the AgI ion is slightly distorted [bond angle
N(3)\Ag(1)\N(5) of 164.5(1)°] by the proximity of the NO3− ion,
interacting in an asymmetrical chelating mode with the metal center, as
proved by the Ag(1)\O(1) and Ag(1)\O(2) distances of 2.626(5) and
2.766(7) Å, respectively. The AgI macrocycle formed by the bidentate co-
ordination mode of ligand L adopts a chair conformation with the central
benzyl rings coplanar to each other and the two 2-pyrimidinylthiomethyl
groups bearing the silver ion laying above and below the central mean
plane (Fig. 2b).
Acknowledgements
This work was supported by the University of Camerino and
COOPERLINK AF 2007.
The two arms not involved in the formation of the macrocycle
adopt an anti geometry about the CH2-S bonds, with the pyrimidinyl
rings nearly orthogonal to the central benzyl rings (dihedral angle be-
tween the mean planes of 63.2(2)°). In the 3D space the two chairs
interlock approximately along the a axis, with the Ag(I) ion of one
molecule facing towards the S(3) atom of the neighbor one, at an
intermolecular distance of 3.260(2) Å. The facing of the two frag-
ments is such that the aromatic hydrogen atom of the N(3)/N(4)
pyrimidinyl ring points towards the C(1)/C(6) central benzyl ring
Appendix A. Supplementary data
CCDC 880936 & 880937 contain the supplementary crystallo-
graphic data for L and 1. The data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via http://www.
ccdc.cam.ac.uk/conts/retrieving.html. Supplementary data to this ar-
ticle can be found online at http://dx.doi.org/10.1016/j.inoche.2012.
07.019.
Fig. 4. Emission spectra of derivatives 1 and 2 at 50 K.

A. Mizar et al. / Inorganic Chemistry Communications 24 (2012) 20–23
23
geometrical calculations and the graphical manipulations were performed using the
XP utility of the SHELXTL system and the Mercury program.
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19
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,
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.
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β=93.553(15)°. V=2113.6(15) Å3. Z=4, R(int)=0.0398, R1=0.0410, wR2=
0.0958, GOF=1.014. Crystal data for [(L)AgNO3]2.CH3CN (1): triclinic, P-1, a=
9.2888(8) Å, b=11.3706(11) Å, c=14.1304(13) Å, α=112.714(3)° β=104.961(4)°
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GOF=1.050. The X-ray data were collected on a Bruker-Nonius X8APEXII CCD area de-
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through the SAINT reduction and SADABS absorption software. The structures were
solved with the SHELXTL software package by standard direct methods and subse-
quently completed by Fourier recycling. All non-hydrogen atoms were refined aniso-
tropically and hydrogen atoms were included as idealized riding atoms. The final
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