Synthesis and crystal structures of three novel coordination polymers constructed from Ag(I) thiocyanate and nitrogen donor ligands

Article abstract of DOI:10.1016/j.poly.2009.01.005

Three supramolecular coordination polymers (SCPs) [(AgSCN)₂L] {L = 4,4′-bipyridine (bpy) (1), trans-1,2-bis(4-pyridyl)ethylene (tbpe) (2) and phenazine (phenz) (3)} have been synthesized and structurally characterized by single-crystal X-ray di

Full text of DOI:10.1016/j.poly.2009.01.005

Polyhedron 28 (2009) 1001–1009
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and crystal structures of three novel coordination polymers
constructed from Ag(I) thiocyanate and nitrogen donor ligands
*
Safaa El-din H. Etaiw , Dina M. Abd El-Aziz, Moustafa Sh. Ibrahim, Ahmed S. Badr El-din
Chemistry Department, Faculty of Science, Tanta University, El-gash Street, Tanta 31527, Egypt
a r t i c l e i n f o
a b s t r a c t
Three supramolecular coordination polymers (SCPs) [(AgSCN)2L] {L = 4,40-bipyridine (bpy) (1), trans-1,2-
bis(4-pyridyl)ethylene (tbpe) (2) and phenazine (phenz) (3)} have been synthesized and structurally
characterized by single-crystal X-ray diffraction. Synthesis was affected in H2O/acetonitrile/NH3 media
at room temperature. The bpy, tbpe and phenz bipodal ligands adopt different conformations which
would affect the skeleton of the (AgSCN)n building blocks that allow the interconnection of the (AgSCN)n
fragments and propagation of the network structure in three dimensions. Supramolecular interactions
Article history:
Received 29 August 2008
Accepted 5 January 2009
Available online 25 February 2009
Keywords:
Supramolecular
Silver(I) thiocyanate
Coordination polymers
Nitrogen donor ligands
such as hydrogen-bonding, argentophilic interaction and
assembly of these coordination polymers.
p–
p
stacking play an important role in the
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
bond length is usually longer than the M–N bonds while the M–
N–C angle is approximately linear and the M–S–C is bent which
in agreement with the mesomeric structure of the thiocyanate
group [21]. Silver(I) is good candidate as a soft acid favoring coordi-
nation to soft bases such as ligands containing sulfur and nitrogen
atoms. The simple silver(I) thiocyanate salt was suggested to have
a chain structure [22], however its adducts with pyridine and other
ligands have been shown to be mono- and di-meric complexes
[23,24], as well as one- and two-dimensional networks containing
AgSCN fragments as building blocks [25]. In this report the reac-
tions of the ternary system; thiocyanate as a potential bridging li-
gand, rigid linear or angular bipodal ligands, e.g. phenz, bpy, tbpe
and AgNO3 are utilized to obtain high dimensional supramolecular
coordination AgSCN polymers with unique topologies. Argentophil-
ic interaction and formation of the minicycle Ag2S2 motif should re-
sult in assemblies of the 3D-networks.
In recent years there has been considerable interest in the devel-
opment of the rational synthetic routes to coordination polymers
by self assembly due to their potential applications in the areas
such as magnetism, nonlinear optics, electronics, catalysis and
molecular topologies such as honeycomb, brick wall, grid, ladder,
herringbone diamondoid polycatenanes and polyrotaxanes [1–5].
Self-assembly is heavily influenced by many factors such as the sol-
vent systems [6], template [7,8], pH value of the solution [8] and
counter ions [9]. Therefore, much work is required to extend knowl-
edge of the relevant structural types and establish proper synthetic
strategies leading to the desired species. So far, considerable atten-
tion has been paid to synthesis and characterization of adducts of
silver(I) pseudo-halides with nitrogen bases [10–17]. On the other
hand, polytopic ligands incorporating multiple oligopyridine me-
tal-binding domains are important components in the development
of metallosupramolecular chemistry [18,19]. The importance of
these components comes from the fact that they can be used in
material science and as double helical supramolecular array which
is an attractive geometric motif in nature [20]. However, little re-
search has been reported on the complexes of pseudo-halogen spe-
cies in particular the thiocyanate ion with bidentate nitrogen
ligands [14–17]. With its ambidextrous character the thiocyanate
anion is expected to show a rich variety of coordination modes.
The elements acting as hard Lewis acid form mainly thiocyanate-
N complexes (isothiocyanate) while the electron rich metal acting
as soft Lewis acid usually form thiocyanate-S-complexes. The M–S
2. Experimental
2.1. Materials and general methods
All the reagents for the syntheses were commercially available
and employed without further purification. Elemental analysis was
performed with a Perkin–Elmer 2400 automatic elemental ana-
lyzer. The IR spectra were recorded on a Brucker Vector 22 Spectro-
photometer as KBr discs. Thermogravimetric analysis was carried
out on a Shimadzu AT 50 thermal analyzer (under N2 atmosphere).
Electronic absorption spectra were measured on Shimadzu (UV-
310PC) spectrometer. Luminescence spectra were carried out using
Perkin–Elmer (LS 50 B) spectrometer.
* Corresponding author. Tel.: +20 2222601379.
E-mail address: safaaetaiw@hotmail.com (S.E.-d.H. Etaiw).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.01.005

1002
S.E.-d.H. Etaiw et al. / Polyhedron 28 (2009) 1001–1009
The SCPs 1–3, were prepared by the same procedure under the
were obtained. Anal. Calc. for 2 (C14H10N4S2Ag2): C, 32.67; H,
1.94; N, 10.89. Found: C, 32.63; H, 1.97; N, 10.75%. IR (KBr,
cmꢁ1): 3047w, 2925w, 2862w, 2099s, 1599m, 1419s, 1319m,
1295m, 1250m, 1207m, 980s, 827s, 754s, 552s, 448m. Brown nee-
dle crystals of 3 were formed after one week and filtered off then
after washed with small portions of water and MeCN and dried
overnight. Sixty-two milligrams of [(AgSCN)2 ꢀ phenz], 3, were ob-
tained. Anal. Calc. for 3 (C14H8N4S2Ag2): C, 32.80; H, 1.56; N, 10.93.
Found: C, 32.64; H, 1.55; N, 11.09%. IR (KBr, cmꢁ1): 3048w, 3006w,
2867w, 2131s, 1513s, 1466m, 1432m, 1360m, 1119m, 905m,
823m, 748s, 654m, 594m, 439m.
same conditions. A solution of 85 mg (0.5 mmol) of AgNO3 in
10 mL H2O was being added at room temperature to the mixture
of (0.5 mmol) of the bipodal ligand; L, in 10 mL MeCN and of
48 mg (0.5 mmol) of KSCN in 10 mL H2O. White turbidity appeared
then after concentrated ammonia solution was added to the hot
mixture dropwise with stirring till clearness. The mixture was fil-
tered off and the filtrate was left to stand for some days. Prismatic
colorless crystals of 1 appeared after two weeks. After filtration,
subsequent washing with small portions of water and MeCN and
overnight drying, about 109 mg of [(AgSCN)2 ꢀ bpy] 1 were ob-
tained. Anal. Calc. for 1 (C12H8N4S2Ag2): C, 29.50; H, 1.63; N,
11.47. Found: C, 29.32; H, 1.60; N, 11.55%. IR (KBr, cmꢁ1):
3045w, 2117s, 2090s, 1597s, 1528m, 1409s, 1372m, 1214m,
1067m, 799s, 622s, 562m, 508s, 452w and 431w. Also, brown pris-
matic crystals of [(AgSCN)2 ꢀ (tbpe)], 2, were formed after two
weeks and filtered off then after washed with small portions of
water and MeCN and dried overnight. Ninety-six milligrams of 2
2.2. X-ray structural determination
Structural measurements for the SCPs 1–3 were performed on a
Kappa CCd Enraf Nonius FR 90 four cycle geniometer with graphite
monochromatic Mo
Ka radiation {[kMo Ka] = 0.71073 Å} at
25 2 °C. All structures were resolved using direct-methods and
Table 1
Table 3
Crystal data and structure refinement parameters of the SCPs 1–3.
Selected bond distances (Å) and bond angles (°) for the SCP 2.
1
2
3
Ag1–S2
Ag1–S2a
Ag1–N3
Ag1–N5
2.7534 (8)
2.7722 (8)
2.248 (2)
2.173 (3)
S2–H6
2.9547 (7)
1.154 (3)
1.652 (3)
3.3638 (6)
C10–N5
S2–C10
Ag1–Ag1a
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
C12H8Ag2N4S2
488.072
298
C14H10Ag2N4S2
514.110
298
C14H8Ag2N4S2
512.114
298
monoclinic
C2/c
18.3525 (7)
6.2310 (3)
12.1581 (4)
90.00
99.836 (3)
90.00
1369.89 (10)
4
triclinic
P1
monoclinic
P21/c
4.1453 (2)
20.6722 (9)
9.3478 (4)
90.00
110. 00(18)
90.00
760.36 (6)
2
S2–Ag1–S2a
S2–Ag1–N3
S2–Ag1–N5
S2a–Ag1–N3
S2a–Ag1–N5
N3–Ag1–N5
Ag1–S2–Ag1a
Ag1–S2–N5
Ag1–S2–C10
S2-C10-N5
105.00 (2)
103.72 (6)
100.08 (7)
95.27 (6)
103.02 (8)
144.95 (10)
75.00 (2)
96.58 (6)
96.37 (10)
179.1(3)
Ag1a–S2–C10
Ag1–N3–C4
Ag1–N3–C7
Ag1–N3–C8
Ag1–N3–C9
Ag1–N3–C11
Ag1–N5–S2
Ag1–N5–C10
Ag1a–S2–N5
98.57 (10)
173.91 (12)
154.34 (14)
145.69 (12)
125.3 (2)
117.5 (2)
155.98 (13)
155.6 (2)
ꢀ
5.9315 (2)
7.3747 (3)
9.6990 (4)
99.676 (2)
106.843 (2)
97.072 (2)
393.59 (3)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
98.91 (6)
Z
l
(Mo K
a
) (mmꢁ1
)
3.16
2.75
2.85
R1
wR2
Rint
0.044
0.212
0.024
925/0/91
2.367
0.029
0.060
0.022
1251/0/100
2.169
0.033
0.079
0.026
1085/0/106
2.237
Hydrogen-bonding
Inter-layer
S2–H6
Intra-layer
N5–H11c
C10–H11c
2.9547 (7)
3.0761 (7)
3.202 (7)
3.292 (7)
2.838 (3)
2.927 (3)
2.869 (3)
S2–H7b
Data/restraints/parameters
Calculated density (mg/m3)
Goodness-of-fit on F2
N5–H7b
2.506
1.026
1.316
N5–H6b
C10–H7b
Symmetry codes: (a) ꢁx, ꢁy, 1ꢁz; (b) ꢁx, ꢁy, ꢁz; (c) 1 ꢁ x, ꢁy, 1 ꢁ z.
Table 2
Selected bond distances (Å) and bond angles (°) for the SCP 1.
Table 4
Ag1–S2
2.7742 (6)
3.0637 (6)
2.247 (2)
2.158 (2)
3.3939(6)
92.95 (2)
99.45 (4)
98.98 (5)
88.88 (4)
91.53 (4)
161.52 (7)
87.05 (2)
103.30 (4)
172.81 (9)
172.2 (2)
S2–N15
S2–C14
2.797 (2)
1.660 (2)
1.138(2)
Ag1–S2a
Selected bond distances (Å) and bond angles (°) for the SCP 3.
Ag1–N8
C14–N15
Ag1–S2
S2–C6
Ag1–N4
2.6020 (8)
1.652 (3)
2.438 (2)
Ag1–N11a
C6–N11
2.219 (3)
1.141 (3)
2.5942 (8)
Ag1–N15b
Ag1–Ag1a
3.2431 (5)
Ag1a–S2
Ag1–S2a
S2–Ag1–S2a
S2–Ag1–N8
S2–Ag1–N15b
S2a–Ag1–N8
S2a–Ag1–N15b
N8–Ag1–N15b
Ag1–S2–Ag1a
Ag1–S2–N15
Ag1c–N15–S2
Ag1c–N15–C14
Ag1–S2–C14
Ag1a–S2–N15
Ag1a–S2–C14
Ag1–N8–C10
Ag1–N8–C12
Ag1–N8–C9
Ag1–N8–C11
Ag1–N8–C13
S2–C14–N15
103.06 (7)
94.34 (4)
94.73 (6)
153.18 (9)
145.15 (9)
125.21 (12)
170.53 (8)
116.99 (13)
178.9 (2)
S2–Ag1–S2
105.82 (3)
115.69 (5)
108.30 (7)
87.82 (5)
121.83 (7)
116.26 (9)
105.82 (3)
110.23 (10)
100.18 (6)
178.5 (3)
Ag1–N4–C3
Ag1–N4–C3b
Ag1–N4–N4b
Ag1–N4–C5
Ag1–N4–C8
Ag1–N4–C8b
Ag1–N4–C9
Ag1c–N11–S2
Ag1c–N11–C6
122.1 (2)
150.78 (12)
179.2 (2)
90.95 (10)
120.4 (2)
152.51 (11)
89.49 (10)
176.83 (13)
177.7 (3)
S2–Ag1–N4
S2–Ag1–N11a
S2–Ag1–N4
S2–Ag1–N11a
N4–Ag1–N11a
Ag1–S2–Ag1
Ag1–S2–C6
Ag1–S2–N11
S2–C6–N11
Interlayer H-bonding
S2–H9a
2.8667 (5)
3.0163 (4)
2.657 (2)
2.907 (2)
Hydrogen-bonding
S2–H5
S2–H13a
2.84 (3)
2.97 (3)
3.037 (3)
N11–H7
N11–H9c
N11–H9d
3.014 (3)
2.997 (3)
2.728 (3)
N15–H13d
S2–H10b
C14–H13d
C6–H7
Symmetry codes: (a) 1/2 ꢁ x, 1/2 ꢁ y, ꢁz; (b) x, ꢁy, z ꢁ 1/2; (c) x, ꢁy, 1/2 + z;
(d) 1/2 ꢁ x, ꢁ1/2 ꢁ y, ꢁz.
Symmetry codes: (a) x ꢁ 1, 1/2 ꢁ y, z ꢁ 1/2; (b) ꢁx, ꢁy, 1 ꢁ z; (c) 1 + x, 1/2 ꢁ y, 1/
2 + z; (d) 1 + x, 1/2 ꢁ y, 1/2 + z.

S.E.-d.H. Etaiw et al. / Polyhedron 28 (2009) 1001–1009
1003
all of the non-hydrogen atoms were located from the initial solu-
3. Results and discussion
tion or from subsequent electron density difference maps during
the initial stages of the refinement. After locating all of the non-
hydrogen atoms in each structure the models were refined against
F2, first using isotropic and finally using anisotropic thermal dis-
placement parameters. The positions of the hydrogen atoms were
then calculated and refined isotropically, and the final cycle of
refinements was performed. The cyano groups of all structures
were ordered. Crystallographic data for the SCPs 1–3 are summa-
rized in Table 1. Selected bond distances and bond angles are given
in Tables 2–4.
3.1. Crystal structures
3.1.1. Crystal structure of [(AgSCN)2 ꢀ bpy] (1)
The ORTEP plot of the novel SCP 1 shows one half of the chem-
ical formula; Fig. 1a, while the formula unit contains two crystallo-
graphically identical silver atoms, two thiocyanate ligands and one
bpy ligand. Each silver atom is bound to one S atom and one N
atom of two thiocyanate ligands and one N atom of bpy ligand
forming distorted trigonal planar geometry with N8–Ag1–N15
Fig. 1. (a) An ORTEP view of the asymmetric unit of the SCP 1. (b)View of the ribbon structure of the SCP 1 along the b-axis; H-atoms are omitted for clarity.
Fig. 2. View of the 3D-structure of the SCP 1 along the b-axis showing the crossing of the 2D-layers.

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S.E.-d.H. Etaiw et al. / Polyhedron 28 (2009) 1001–1009
Fig. 3. View of the 3D-structure of the SCP 1 along the c-axis showing the Ag–Ag, Ag–S interactions and hydrogen-bonding.
angle equals to 161.52°, Table 2 and Fig. 1b. The thiocyanate ligand
acts as 2-1,3-ligand connecting the silver atoms, Ag1–
l
N15 = 2.158 Å, Ag1–S2 = 2.774 Å, which are in the range of the re-
ported values [10,14]. On the other hand, the AgNC angle is nearly
linear, while AgSC angle is nearly perpendicular; Table 2. The
AgSCN building blocks create infinite parallel zig-zag chains with
S2–Ag1–N15 = 98.99° and Ag1–S2–C14 = 103.06°. These zig-zag
chains are bridged by the bpy bipodal ligand forming extended
vertical 2D-ribbons along the b-axis, Fig. 1b. In this case, a polygon
consisting of [(Ag4(SCN)2(bpy)2], of dimensions of 6.096 Å ꢂ
16.632 Å, is recognized as a typical fragment of 1. These polygons
are arranged in unique way that one pyridyl ring of the bpy ligand
in one polygon is parallel to another pyridyl ring of bpy in the adja-
cent polygon with a separation distance of 3.74 Å suggesting the
presence of weak but not negligible stacking interactions, between
the pyridine rings, as well as Ag–p interaction between the silver(I)
ion and the neighboring pyridyl ring; 3.695 Å; Fig. 1b. It is worth
mentioned here that one pyridyl ring in each bpy ligand is tilted
out of the plane defined by the other bpy ring by an angle of
43.93°. Alternatively, these ribbons can be considered as infinite
non-interpenetrating 2D-layers that cross each other along the b-
axis via the AgSCN fragments, Fig. 2. On the other hand, each rib-
bon can be considered as a compressed spring along the c-axis cre-
ating a unique shape, Fig. 3.
The ribbons are arranged parallel in unique way where one
layer connect two ribbons above and two ribbons below by Ag–
Ag interactions; Ag–Ag = 3.242 Å and by H-bonds between H-
atoms of the pyridyl rings in one layer and thiocyanate groups in
the neighboring layers; H–S = 2.867 and 3.016 Å, C–H = 2.907 Å
and N–H = 2.657 Å, as well as considerable contacts between Ag
atoms and S2 atoms in the adjacent layers Ag–S2a = 3.0627 and
3.393 Å forming 3D-network structure; Fig. 3. The Ag–Ag and
Ag–S2 contacts cause pyramidalisation of Ag(I) sites.
Fig. 4. (a) An ORTEP plot of the asymmetric unit of the SCP 2. (b) The basic building
block of the SCP 2; H-atoms are omitted for clarity.

S.E.-d.H. Etaiw et al. / Polyhedron 28 (2009) 1001–1009
1005
Fig. 5. (a) Stair-case-like ribbon of the SCP 2 along the a-axis. (b) View of the 2D-layer of the SCP 2 along the b-axis; H-atoms are omitted for clarity.
Fig. 6. View of the layer stacking of the SCP 2 along the a-axis showing H-bonding and p–p stacking.

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S.E.-d.H. Etaiw et al. / Polyhedron 28 (2009) 1001–1009
3.1.2. Crystal structure of [(AgSCN)2 ꢀ tbpe] (2)
The crystal structure of 2 consists of silver(I) thiocyanate and
tbpe fragments in a 2:1 molar ratio creating a three-dimensional
3
3
network formulated as 1 [(AgSCN)2 ꢀ tbpe] ꢃ 1 [Ag2(
l3-SCN)2(l-
tbpe)]. The asymmetric unit of 2 consists of only one Ag(I) ion,
one SCN group and half of the tbpe ligand, Fig. 4a. Each Ag(I) ion
is pseudo-tetrahedrally four-coordinated by a tbpe nitrogen atom;
Ag1–N3 = 2.248 Å, two thiocyanate sulfur atoms Ag1–S2 = 2.753 Å,
Ag1–S2a = 2.772 Å and one nitrogen atom of another thiocyanate li-
gand; Ag1–N5 = 2.173 Å, with the bond angles at the silver atom in
the range of 95.27–144.95°; Fig. 4b, Table 3. The extended structure
of 2 consists of infinite parallel AgSCN zig-zag chains bonded at the
sulfur atom; Ag1–S2–C10 = 96.37° and contains the unusual bifur-
cated cyanide fragment which exhibits bent AgCN angle, where
Ag1–N5–C10 = 155.6°; Table 3. Each two close parallel AgSCN zig-
zag chains are connected via two silver atoms and two sulfur atoms
forming an array of fused polymer rings containing the unique qua-
dro minicycle (Ag2S2) motif, in addition to the usual hexagonal rings
of Ag2(SCN)2 with dimensions of 3.776 Å ꢂ 5.577 Å; Fig. 4b. These
1
fused rings create stair-case like 1 [Ag2(SCN)2] ribbons in which
the minicycle (Ag2S2) motif represents the steps along the a-axis,
Fig. 5a. The S–S distance in the minicycle is equal to 4.383 Å while
the Ag–Ag distance is equal to 3.364 Å which is shorter than the
sum of the van der Waals radii of two silver atoms (3.44 Å [26]),
Fig. 7. (a) An ORTEP plot the asymmetric unit of the SCP 3. (b) The basic building
block of the SCP 3; H-atoms are omitted for clarity.
Fig. 8. (a) View of the parallel zig-zag (AgSCN)n chains showing the hexagonal Ag3(SCN)3 rings. (b) 3D-dimensional structure of the SCP 3 along the a-axis. H-atoms are
omitted for clarity.

S.E.-d.H. Etaiw et al. / Polyhedron 28 (2009) 1001–1009
1007
Table 5
Absorption and emission bands for bpy, tbpe, phenz and the SCPs 1–3.
Ligand
SCP
kabs (nm)
Assignment
kem (nm)
kabs (nm)
Assignment
kem (nm)
bpy
218
278
390
1La
1Lb
1A
1A
400
452
481
516
660
1
219
278
345
1La
1Lb
CT
1A
1A
430
450
487
528
n–p*
tbpe
232
265
325
450
1La
1Lb
1A
1A
390
478
529
2
3
214
272
352 b
1La
1Lb
CT
1A
1A
425
450
490
519
543
428
493
528
583
p
–
p*
n–p*
phenz
220
275
340
394
414
510
1Cb
1Bb
1La
1A
1A
1A
390
464
490
522
218
252
366
412
442
1Cb
1Bb
1La
1Lb
CT
1A
1A
1A
1A
1Lb
1A
n–p*
*
b, broad.
indicating argentophilic interaction. The bifurcated silver-SCN frag-
ment can be considered as a consequence of the formation of the
minicycle (Ag2S2) motif which represents the essential building
block in the structure of 2.
gles of the thiocyanate ligand are almost linear while the Ag1–
S2–C6 acquires bent conformation, 110.80°; Table 4. These parallel
zig-zag chains are bridged by the sulfur atoms where each S atom
connects two silver atoms, one from its own chain and the other
silver atom is from the adjacent chain, creating 2D-sheet contain-
ing fused hexagonal rings, 4.145 Å ꢂ 7.194 Å, that adopt chair con-
formation leading to the formation of corrugated layers consisting
of Ag3(SCN)3 fragments, Fig. 8a. These hexagonal rings are interwo-
ven along the b-axis.
The 2D-sheets of (AgSCN)n are further linked by the planar
phenazine ligands creating distorted polygons consisting of
[Ag6(SCN)4(phenz)2] with enough space to accommodate the phe-
nyl rings of the phenazine ligand forming 3D-network structure. It
is worth noting here that the phenazine ligands as well as the thio-
cyanate bridges are completely parallel assuming weak stacking
interactions; 3.618 Å, while hydrogen bonds with S2; 2.84 and
2.97 Å, and the CN unit; 2.728–3.014 Å; Table 4, as well as short
contacts between silver atom and carbon atoms of phenz and
SCN ligands, 3.347 and 3.339 Å, lead to further stabilization of
the 3D-network of 3, Fig. 8b.
These infinite parallel stair-case-like ribbons are arranged in a
quasi-parallel fashion in the cell and separated by a distance of
13.606 Å. They are bridged by the tbpe ligands via silver atoms
along the diagonal of the unit cell, forming infinite two-dimen-
sional layered structure; Fig. 5b. In this case, one tbpe is directed
to the space of the hexagonal ring Ag2(SCN)2 and the ethylenic
moiety locates toward the quadro minicycle (Ag2S2) motif while
the other pyridyl ring is directed to the next hexagonal ring in
the adjacent stair-case chain. The bridging tbpe molecules are ar-
ranged in a parallel way with a distance between two successive
tbpe ligands equal to 5.932 Å forming distorted polygon structure
consisting
of
[Ag4(SCN)2(tbpe)2]
with
dimensions
of
5.415 Å ꢂ 18.348 Å. It is interesting that the network structure of
2 consists of adjacent parallel infinite 2D-layers which are all re-
lated by translation in the a-axis direction in the solid state, being
stacked in an . . .AAAA. . . fashion to build up the three-dimensional
structure with the inter-layer separation of about 6.5 Å; Fig. 6. The
3D-network structure of 2 is stabilized by extensive p–p stacking
between the pyridyl rings, 3.360 Å, as well as hydrogen bonds be-
tween H-atoms of the ethylenic group and the sulfur atoms,
2.955 Å, and between the H-atom of the pyridyl rings and C10 of
the thiocyanate group, 2.838 Å; see Table 3.
3.1.3. Crystal structure of [(AgSCN)2 ꢀ phenz] (3)
The reaction of in situ prepared AgSCN with phenazine in aque-
ous ammonical solution affords the brown needle crystals
3
1 [(AgSCN)2 ꢀ phenz], 3. The crystal structure of 3 confirms the
assignment of 2:1 stoichiometry for the silver(I) thiocyanate phen-
azine complex while the asymmetric unit of 3 comprises half of the
formula unit, Fig. 7a. The asymmetric unit consists of one type of
silver(I) which is four-coordinated assuming distorted tetrahedral
geometry with angles in the range of 87.82–121.83°; Table 4. The
silver site is coordinated to two sulfur atoms; Ag–S = 2.594 and
2.602 Å,
a nitrogen atom of the thiocyanate ligand; Ag–
N = 2.219 Å and nitrogen atom of the phenazine ligand; Ag–
N = 2.438 Å, Fig. 7b. In this case, two silver atoms are bridged al-
most symmetrically by the S atom of the
l3-1,1,3-SCN ligand.
The structure of 3 is best described as AgSCN infinite chains which
significantly perturbed at S atom to assume zig-zag conformation
arranged parallelly to the crystallographic c-axis, Fig. 8a. The an-
Fig. 9. Emission Spectra of the SCPs 1–3; (kex is 300 nm for 1, 270 nm for 2 and
300 nm for 3).

1008
S.E.-d.H. Etaiw et al. / Polyhedron 28 (2009) 1001–1009
Table 6
Thermogravimetric analysis data of the SCPs 1–3.
Compound First step
Second step
Assignment Transition
(%) temperature observed
Third step
Residue
Transition
temperature observed
D
m%
D
m%
Assignment Transition
D
m%
Assignment Formation
D
m%
Assignment
(%)
(%)
temperature observed
(%)
temperature observed
(°C)
(calculated)
(°C)
(calculated)
(°C)
(calculated)
(°C)
(calculated)
1
2
3
180–250
200–300
150–250
32.5 (31.9) 1 bpy
35.5 (35.4) 1 tbpe
35.5 (35.6) 1 phenz
380–480
350–450
270–350
6.5 (6.5)
6.0 (6.22)
6.4 (6.19)
1 S
1 S
1 S
500–750
480–750
400–750
10.5 (10.5) 1 (CN)2
10.5 (10.1) 1 (CN)2
10.0 (10.0) 1 (CN)2
750
750
750
50.5 (50.7) Ag2S
47.5 (48.1) Ag2S
48.0 (48.0) Ag2S
3.3. Thermogravimetric analysis of the SCPs 1–3
Table 7
Geometry of the thiocyanate group in the SCPs 1–3.
The SCPs 1–3 are thermally stable until 150–200 °C, then after
they start decomposition with the loss of ligand in the temperature
range 150–300 °C, Table 6. The second decomposition step in-
volves removal of one sulfur atom in the temperature rang 350–
480 °C, for the SCP 1 and 2 and at 270–360 °C for the SCP 3. The
third step occurs at slow rate and over relatively large temperature
range, 400–750 °C, where two cyanide groups are lost as cyanogen,
Table 6. Finally above 750 °C the residue is obtained which is coin-
cident with the silver sulfide. The relatively high temperature at
which the SCN groups are released supporting the bridging capa-
bility of this group forming stable (AgSCN)n chains.
Angle (°)/bond (Å)
1
2
3
Ag–N–C
Ag–S–C
S–C–N
S–C
172.2
103.6–94.73
178.9
1.660
1.138
155.6
96.37–98.53
179.1
1.652
1.154
177.7
110.23–100.17
178.5
1.652
1.150
C–N
3.2. Electronic absorption spectra and emission spectra of SCPs 1–3
The electronic absorption spectra of the ligands and the SCPs 1–
3 were measured in the solid state at room temperature as reflec-
tance spectra. The absorption spectra of the SCPs 1–3 display, gen-
erally, the absorption bands of ligands in addition to the CT bands.
Thus, investigating the absorption spectra of the bpy and tbpe li-
gands reveals that the spectra display mainly three absorption
bands at 218–232 nm (1La 1A), 265–278 nm (1Lb 1A), and
4. Conclusions
The general features of the structure of the SCPs 1–3 are the
formation of AgSCN-L adducts in a 2:1 molar ratio forming 3D-
networks containing the AgSCN building blocks connected via
*
*
l2-1,3-SCN in 1 and l3-1,1,3-SCN in 2 and 3. These AgSCN building
325 nm (p–p ), in addition to a band at 390–450 nm (n–p ), Table
blocks form zig-zag AgSCN chains which are bridged by the bipodal
ligands creating polygons consisting of [Ag4(SCN)2(L)2]; L = bpy or
tbpe, and [Ag6(SCN)4(phenz)2]. However, the parallel zig-zag
chains assume different modes of interaction where in 1 they are
bridged by Ag–Ag bonding interactions, in 2 via the formation of
quaro minicycle Ag2S2 motif with weaker Ag–Ag interaction and
in 3 by S atoms creating hexagonal rings which adopt chair confor-
mation without any interaction between the silver atoms. The
mode of bridging depends on the nature of the bipodal ligand,
whereas the longest bipodal ligand tbpe; 9.412 Å, acquire wide
space in the network structure of 2 which should be achieved by
the formation of the minicycle motif and the bifurcated AgNC frag-
ment which assumes quasi-linear fashion in 1; 172.2° while it is al-
most linear in 2; 177.7°. In the same direction, the AgSCN zig-zag
chains are more puckered in 2 than in 1 and 3; Table 7. The S–C–
N fragment tends to be linear in all cases, whereas the Ag–N–C–S
fragment is quasi-linear in 1 and 3 but nonlinear in 2. On the other
hand, the Ag–S distances in 1 and 2 are longer than that in molec-
ular AgSCN (2.648 Å) [22], while they assume shorter distance in 3.
Thus, using bipodal ligands which would not be constrained to a
planar conformation like bpy and tbpe which exhibit the two pyr-
idyl rings in two parallel planes separated by ethylenic bond or the
bulky planar phenazine ligand, would change the shape and geom-
etry of the (AgSCN)n chains and allow the interconnection of chains
and propagation of the microstructure in three dimensions.
5. On the other hand, the spectrum of phenazine shows several
bands at 220, 275, 340, 394, 414, 510 nm; Table 5. It is a matter
of fact that replacement of the methine group in anthracene by
nitrogen atom in phenazine ligand results in relatively little
changes in the spectrum of phenazine. This is especially true due
to the fact that the replacement of N for CH of anthracene occurs
at positions that it does not seriously affect the symmetry of
anthracene. Thus, the phenz and anthracene are isoelectronic. In
spite of the fact that transition (1Cb 1A) in anthracene is forbid-
den the (1Cb 1A) band in phenz is observed at 220 nm which is
surprisingly intense for a forbidden transition [27]. The band at
270 nm exhibits red shift than 1Bb 1A band of anthracene [27].
The bands at 340 and 394 nm should be assigned to 1La 1A tran-
sition, whereas the band of phenz at 414 nm should be assigned to
1Lb 1A transition. The relatively low intensity band at the long
*
wavelength side is assigned to n–
n–
p
transition. The bands due to
*
p transitions disappear in the spectra of SCPs 1–3 due to partic-
ipation of the bipodal ligands in the coordination sphere of silver(I)
ions. The absorption spectra of the SCPs 1–3 exhibit an additional
broad band at 345, 352 and 442 nm, respectively, corresponding
to metal-to-ligand charge transfer (MLCT) where the charge is
*
p -orbital
transferred from the silver(I) center to the unoccupied
of the ligand.
The emission spectra of the SCPs 1–3, Fig. 9, together with the
emission spectra of their ligands were measured using the same
excitation wavelength in each case. The emission spectra of the
bipodal ligands display structural bands, Table 5, which correspond
Appendix A. Supplementary data
*
*
to the lowest (
p
,
p
) and close lying (n,
p
) states. On the other
hand, the emission spectra of the SCPs 1–3 display structural peaks
of the bipodal ligands as well as additional bands which may as-
signed to MLCT or metal-centered transitions of the type
4d10 ? 4d9 5s1 and 4d10 ? 4d9 5p1 on the silver(I) center. The
emission spectra of the SCPs 1–3 exhibit red shift compared to
those of the corresponding ligands.
CCDC 682261–682263 contain the supplementary crystallo-
graphic data for SCPs 1–3. 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: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this

S.E.-d.H. Etaiw et al. / Polyhedron 28 (2009) 1001–1009
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