Unprecedented μ-1,2,3κS : 4,5κN coordination mode of the thiocyanate anion in two new double salts of silver(I), AgSCN·2AgNO3 and AgSCN·AgClO4

Article abstract of DOI:10.1039/a901876j

The double salts AgSCN·2AgNO₃ and AgSCN·AgClO₄ both feature an unprecedented μ₅-1,2,3κS : 4,5κN coordination mode of the thiocyanate ligand, which generates a two- or three-dimensional network according to the relative coordinating capability of the co-existing nitrate or perchlorate anion.

Full text of DOI:10.1039/a901876j

Unprecedented m-1,2,3kS:4,5kN coordination mode of the thiocyanate anion in
two new double salts of silver(i), AgSCN·2AgNO and AgSCN·AgClO
3
4
Guo-Cong Guo and Thomas C. W. Mak*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
E-mail: tcwmak@cuhk.edu.hk
Received (in Cambridge, UK) 9th March 1999, Accepted 31st March 1999
The double salts AgSCN·2AgNO
3
and AgSCN·AgClO
4
both
The crystal structures‡ of both 1 and 2 feature a common
centrosymmetric, nearly planar eight-membered (AgSCN)
ring that has angularly distorted hexagonal geometry, which can
be regarded as a basic architectural unit for constructing the
coordination network. In each planar heterocycle, there are two
‘substituent’ silver atoms bonded to each sulfur atom and one
feature an unprecedented m
5
-1,2,3kS:4,5kN coordination
2
mode of the thiocyanate ligand, which generates a two- or
three-dimensional network according to the relative coor-
dinating capability of the co-existing nitrate or perchlorate
anion.
‘
substituent’ silver atom bonded to each nitrogen atom, as
shown in Fig. 2. To our knowledge the nearly planar (AgSCN)
ring moiety with six additional silver atoms attached to it and
With the advent of supramolecular chemistry, the coordination
concept as applied to metal ions has been extended to
polyatomic species such as neutral molecules, organic cations,
2
the resulting m -1,2,3kS:4,5kN coordination mode of the
5
1
and anions of various types. In the design of polynuclear metal
thiocyanate ligand are both unprecedented.
2
complexes and the crystal engineering of coordination net-
In the crystal structure of 1, the basic architectural units share
the S-bonded ‘substituent’ silver atoms of type Ag2 and Ag3
3
works, the possible coordination modes of anionic ligands
¯
have to be considered in the synthetic strategy. In this context,
it is of interest to determine the highest ligation number (HLN)
of simple inorganic polyatomic anions, namely the largest
number of coordination bonds that a particular anion can form
with neighboring metal centers in its complexes. For example,
along the [110] and [110] directions to generate a corrugated
4
layer (Fig. 3), with the nitrate anions located between adjacent
2
layers. One of the two independent NO
3
anions functions as a
tightly bridged ligand to silver atoms of type Ag1 and Ag4
[average Ag–O 2.445(3) Å], and the other as a loosely bridged
one to silver atoms of type Ag2 and Ag4 [average Ag–O
the HLN of the m
oxovanadium(iv) cluster [(VO)
The group 11 metal(i) ions, each having a spherical d
6
-carbonato group in the hexanuclear
5+
is six.5
6
(CO
3
)
4
(OH)
9
]
10
electronic configuration, can in principle serve as ideal probes
for obtaining the HLN of small inorganic anions. The synthesis
of suitable complexes for such investigations is favored by the
tendency of the monovalent coinage metal ions to form
10
10
6,7
aggregates through homoatomic d –d interactions. Fur-
thermore, silver(i) has distinct advantages over the other
members of the coinage triad, as copper (i) is easily oxidized to
the +2 oxidation state, and gold(i) has a strong tendency to adopt
linear digonal coordination geometry and is also susceptible to
disproportionation into Au(iii) and Au(0). Our recent studies on
the crystal structures of double salts of silver have shown that
8
the cyanide ion has a HLN of four in 3AgCN·2AgF·3H
2
O, and
9
the azide ion has a HLN of six in AgN
The coordination modes of the ambident thiocyanate ligand
in their metal complexes exhibit considerable diversity (Fig. 1),
and modes F, H and K are hitherto unknown. Thus far the
maximum coordinating capacity of SCN involves the forma-
3 3
·2AgNO .
10
Fig. 2 Basic architectural units in 1 and 2, each consisting of a nearly planar
eight-membered (AgSCN) ring with six ‘substituent’ silver atoms.
2
11
2
tion of two coordination bonds by its nitrogen atom, or three
coordination bonds by its sulfur atom, but not simultaneously.
Here, we report two novel double salts AgSCN·2AgNO
AgSCN·AgClO 2† in which the thiocyanate group exhibits an
-1,2,3kS:4,5kN coordination mode K with a
3
1 and
4
unprecedented m
5
HLN of five.
Fig. 3 Corrugated layer formed by linkage of basic architectural units in 1.
2
Fig. 1 Possible coordination modes of the thiocyanate ligand.
The interlayer NO
3
ligands have been omitted for clarity.
Chem. Commun., 1999, 813–814
813

This work is supported by Hong Kong Research Grants
Council Earmarked Grant CUHK 4022/98P and Direct Grant
A/C 2060129 of The Chinese University of Hong Kong.
Notes and references
†
Synthesis: AgSCN was prepared by mixing aqueous solutions of
ammonium thiocyanate and silver nitrate at room temperature. The white
precipitate was filtered, washed several times with de-ionized water, and
temporarily stored in wet form in the dark.
Synthesis of AgSCN·2AgNO
concentrated MeCN solution of AgNO
saturated at 40 °C. The excess amount of AgSCN was filtered off, and the
solution was placed into a desiccator charged with P . In the course of
two days colorless crystals of AgSCN·2AgNO were obtained in nearly
3
1: wet AgSCN was added to 2 mL of a
3
(ca. 40%) with stirring until
2 5
O
3
quantitative yield. The compound is stable when immersed in its mother
liquor; it is hygroscopic and slowly decomposes in air.
Synthesis of AgSCN·AgClO 2: the above procedure was repeated using
4
EtOH and silver perchlorate instead of MeCN and silver nitrate,
respectively. The distinct difference between the two preparations is that the
filtrate of 2 turned from colorless to pale purple and the cyrstals of 2 are pale
purple.
‡
Crystal data: 1: colorless prism, Siemens P4/PC diffractometer, Mo-Ka
radiation (l = 0.71073 Å), 2275 unique reflections (Rint = 0.0247), 1423
of which with I > 2s(I) were considered as observed, triclinic, space group
P1 (no. 2), Z = 2, D
¯
23
c
= 4.256 g cm , a = 6.569(5), b = 7.732(1), c =
3
8
.031(2) Å, a = 104.09(1), b = 93.94(4), g = 90.04(3)°, V = 394.6(3) Å ,
Fig. 4 Crystal structure of 2 viewed along the b direction (top), and a
hexagonal channel viewed along the a direction showing it as a ladder-like
chain of fused (SCN) rings.
2
2
1
m = 76.41 cm , R1 = 0.0394, GOF = 0.990.
: pale purple plate, Rigaku RAXIS IIC diffractometer, Mo-Ka radiation
l = 0.710 73 Å), 1086 unique reflections (Rint = 0.0862), 1032 of which
with I > 2s(I) were considered as observed, Monoclinic, space group C2/c
2
(
2
3
c
(No. 15), Z = 8, D = 3.958 g cm , a = 15.294(4), b = 4.766(1), c =
2
.579(4) Å], thus linking adjacent layers along the c direction
3
21
1
0
8.278(4) Å,b = 109.89(2)°, V = 1252.7(5) Å , m = 69.55 cm , R1 =
.0642, GOF = 1.116. The structures of 1 and 2 were solved by the direct
into a three-dimensional framework. Interestingly, there co-
exist four kinds of coordination modes of silver atoms in 1,
2
method (SHELXS-86) and refined by full-matrix least squares on F using
the Siemens SHELXTL-93 (PC Version) package of crystallographic
software. All non-hydrogen atoms were refined with anisotropic thermal
parameters. Results of the crystal structure determination (CSD-410622 and
410623) have been deposited at the Fachinformationszentrum Karlsruhe,
D-76344, Eggenstein-Leopoldshafen, Germany (fax: (+49)7247-808-666;
e-mail: crysdata@fiz-karlsruhe.de). CCDC 182/1206. See http://
www.rsc.org/suppdata/cc/1999/813/ for crystallographic files in .cif for-
mat.
¯
namely linear coordination for type Ag3 atoms at 1 [Ag3–S1
.571(1) Å], nearly coplanar triangular coordination for type
Ag1 atoms [Ag1–N1 2.392(4), Ag1–O2 2.479(3), Ag1–S1
.748(2) Å, sum of bond angles at Ag1 358.5°], distorted square
2
2
¯
coordination for type Ag2 atoms at 1 [Ag2–O6 2.566(4), Ag2–
S1 2.672(1) Å] and distorted tetrahedral coordination for type
Ag4 atoms [Ag4–N1 2.269(4), Ag4–O3 2.411(3) Ag4–O5
2.591(4), Ag4–S1 2.861(2) Å].
In the crystal structure of 2, fusion of the basic architectural
1
Supramolecular Chemistry of Anions, ed. A. Bianchi, K. Bowman-
James and E. Garcia-Espa n˜ a, Wiley–VCH, New York, 1996; P. D. Beer
and D. K. Smith, Prog. Inorg. Chem., 1997, 46, 1; A. Clearfield, Prog.
Inorg. Chem., 1998, 47, 371; J.-M. Lehn, Angew. Chem., Int. Ed. Engl.,
1988, 27, 89.
units along the b direction generates a ladder-like chain, which
takes the appearance of a hexagonal column when viewed in the
b direction (Fig. 4). The hexagonal columns are connected by
sharing the S-bonded Ag2 atoms (site symmetry 2) along the c
¯
2 P. J. Stang, Chem. Eur. J., 1998, 4, 19; P. J. Zapf, R. C. Haushalter and
J. Zubieta, Chem. Commun., 1997, 321; M. Fujita, Chem. Soc. Rev.,
direction and the N-bonded Ag3 atoms (site symmetry 1) along
the a direction to form a three-dimensional channel-type
network, as shown in Fig. 4. The perchlorate anions are stacked
as a double column within each channel. In contrast to the
nitrate anions in 1, the perchlorate anions in 2 do not directly
bond to silver atoms, leading to lower coordination numbers,
namely linear coordination for type Ag2 [Ag2–S1 2.521(2) Å]
and Ag3 [Ag3–N1 2.270(6) Å] atoms, and trigonal pyramidal
coordination for the type Ag1 atom [Ag1–S1 2.583(2)
and 2.651(2), Ag1–N1 2.505(6) Å].
1
998, 27, 417.
3
4
S. R. Batten and R. Robson, Angew. Chem. Int. Ed., 1998, 37, 1460;
K. R. Dunbar and R. A. Heintz, Prog. Inorg. Chem., 1997, 45, 283.
The term ‘ligation number’ is used here in preference to ‘coordination
number’ which generally to refers to the number of ligand around an
atomic center, normally a metal ion.
5 T. C. W. Mak, P.-J. Li, C.-M. Zheng and K.-Y. Huang, J. Chem. Soc.,
Chem. Commun., 1986, 1597.
6 M. Jansen, Angew. Chem. Int. Ed. Engl., 1987, 26, 1098; M. Jansen and
C. Linke, Angew. Chem., Int. Ed. Engl., 1992, 31, 653.
7
8
The sulfur and nitrogen atoms of the thiocyanate unit in both
and 2 are asymmetrically bonded to silver atoms. The Ag–S
H. Schmidbaur, Chem. Soc. Rev., 1995, 391.
G. C. Guo and T. C. W. Mak, Angew. Chem., Int. Ed. Engl., 1998, 37,
1
and Ag–N distances are significantly longer than those found in
AgSCN [Ag–S 2.428(11), Ag–N 2.223(28) Å],12 respectively,
but still fall within the range found in many transition metal
thiocyanate complexes.13 The thiocyanate units in both 1 and 2
are essentially linear. The S–C and C·N distances of the
thiocyanate ligands in 1 [S–C 1.669(4), C–N 1.148(5) Å] and 2
3
183.
G. C. Guo and T. C. W. Mak, Angew. Chem., Int. Ed., 1998, 37,
268.
9
3
1
0 R. G. Pearson, J. Am. Chem. Soc., 1963, 85, 3533; R. G. Pearson,
J. Chem. Educ., 1968, 45, 643; M. K. Kroeger and R. S. Drago, J. Am.
Chem. Soc., 1981, 103, 3250.
[
S–C 1.666(2), C–N 1.160(3) Å] are in good agreement with
11 A. M. Golub, H. Kohler and V. V. Skopenko, in Chemistry of
Pseudohalides, ed. R. J. H. Clark, Elsevier, New York, 1986, p. 239; M.
Kabe sˆ ov a´ , R. Boca, M. Meln ´ı k, D. Val `ı gura and M. Dunaj-Jurco,
Coord. Chem. Rev., 1995, 140, 115.
12
those found in AgSCN [S–C 1.64(3), C–N 1.19(7) Å] and
many transition metal thiocyanates.11 In contrast to AgSCN, in
which the cations and anions are arranged alternately to form an
infinite zigzag chain such that each silver atom is only bound to
one nitrogen and one sulfur atom,12 the thiocyanate unit bridges
five silver atoms in both double salts 1 and 2 to form two- and
three-dimensional networks, respectively, resulting in a variety
of coordination environments around individual silver atoms.
1
1
2 I. Lindqvist, Acta Crystallogr., 1957, 10, 29.
3 N. K. Mills and A. H. White, J. Chem. Soc., Dalton Trans., 1984, 229;
H. Krautscheid, N. Emig, N. Klaassen and P. Seringer, J. Chem. Soc.,
Dalton Trans., 1998, 3071.
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814
Chem. Commun., 1999, 813–814