Order of the coordinating ability of polyatomic monoanions established from their interaction with a disilver(I) metallacyclophane skeleton

Article abstract of DOI:10.1039/b505919d

An ordered sequence of the coordinating ability of a series of polyatomic monoanions has been established on the basis of structural parameters derived from their interaction with a disilver(i) metallacyclophane skeleton in isostructural complexes. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b505919d

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Order of the coordinating ability of polyatomic monoanions established
from their interaction with a disilver(I) metallacyclophane skeleton{
Xu-Dong Chen and Thomas C. W. Mak*
Received (in Cambridge, UK) 29th April 2005, Accepted 6th June 2005
First published as an Advance Article on the web 24th June 2005
DOI: 10.1039/b505919d
An ordered sequence of the coordinating ability of a series of
polyatomic monoanions has been established on the basis
of structural parameters derived from their interaction
with a disilver(I) metallacyclophane skeleton in isostructural
complexes.
Complexes 1–6 constitute an isomorphous series, all crystallizing
in space group Pbca. The dimeric skeletons in complexes 1–4 are
stabilized by weak interactions between silver(I) and the anionic
ligand atoms, as exemplified by 3 in Fig. 1a. In complexes 5–7, the
counter anions are bound to the silver atoms of the metallacycles
by coordination bonds, as shown in Fig. 1b with 5 as an example.
Both above-mentioned metal–ligand binding modes exist in
complex 8 (Fig. 1c). The anions in complexes 5–8 also serve as
The study of anions in connection with host–guest chemistry,
including the development of cationic receptors for anion
1
,2
22+
recognition and the design of anionic hosts for the entrapment
3
of cations, has drawn a great deal of interest during the past two
bridging ligands, linking the Ag
2
L
units into one- or two-
dimensional polymeric structures. Notably, in complex 9 the silver
atom does not interact with the hexafluorophosphate anion but is
coordinated by two acetonitrile molecules (Fig. 1d).
4a,b
decades. Anion coordination chemistry as applied to catalysis,
4c–e
templated reactions,
4f,g
4h,i
ionic liquids,
lithium batteries,
4l,m
4j,k
…
…
biological processes, industrial chemical processing,
4m–o
mental pollution,
environ-
4m
and health-related perspectives has also
Intramolecular Ag p and p p interactions also contribute to
the stabilization of the dinuclear metallacycles (see Supplementary
Information for details{) Our attempts at preparing similar
metallacyclophane complexes with pseudo-halide and heavier
halide ions (Y) were unsuccessful owing to the ready precipitation
of AgY, and the use of fluoride did not lead to crystallization.
An anionic ligand with stronger coordinating ability interacts
with the silver atom at a shorter distance, and vice versa. For the
series of monoanions in the present study, the weighted averages of
closest Ag…anion contacts within 2.8 s in the complexes decrease
witnessed enormous progress. Some notable recent papers have
4c–e,5,6
addressed the issue of anion-controlled self-assembly.
However, thus far only a few attempts have been made to
assess and compare the coordinating ability of commonly used
6
anions, a detailed knowledge of which is a prerequisite for
precise control over the course and outcome of supramolecular
assembly.
The coordination diversity of di-2-pyridinylmethanone (di-2-
7
pyridyl ketone) in transition metal and supramolecular chemistry
in the sequence 1 . 2 . 8 y 3 . 4 . 5 y 6 . 7 (Chart 1). In the
2
6
has prompted us to investigate the ligand behavior of its positional
isomer 2-pyridinyl-4-pyridinylmethanone (L). Noting that the
case of complex 9 (space group P2 /n), the absence of PF
1
in the
1
0
spherical d electronic configuration of silver(I) does not impose a
preferred coordination geometry and number in its interaction
8
9
with anionic ligands, we have prepared a series of isostructural
dimeric silver(I) complexes classified into three types: [Ag(L)]
X 5 BF 1; ClO 2; NO 3; ClO 4), {[Ag(L)(X)] } (X 5 NO 5;
2 2
X
(
4
4
3
3
2 ‘
2
2 3 2 3 3 3 2 2 2
HCO 6; CF CO 7; CF SO 8) and [Ag(L)(CH CN) ] X
(
X 5 PF6 9). All nine compounds possess the same flexible
10
metallacyclophane skeleton, to which
2
2
+
centrosymmetric Ag
2
L
various polyatomic monoanions are attached to the silver atom
through coordination bonds or weak electrostatic interactions,
with the lone exception of 9. With the structural parameters
obtained from single-crystal X-ray analysis of this series of
isostructural dinuclear silver(I) complexes,{ together with competi-
tion experiments conducted in solution, we are able to rank the
commonly used polyatomic monoanions according to their
coordinating ability.
{
Electronic supplementary information (ESI) available: experimental and
crystallographic details. See http://dx.doi.org/10.1039/b505919d
Department of Chemistry, The Chinese University of Hong Kong, New
Territories, Hong Kong SAR, P. R. China.
2+
Fig. 1 Parts (a) to (d) show the cyclic Ag
2
L
2
skeleton stabilized by
2
2
2
interaction of Ag(I) with NO
anions and CH CN molecules (9), respectively. Color codes: purple: Ag;
light gray: C; red: O; turquoise: N; green: F; deep blue: S.
3
(complex 3), NO
2
(5), CF
3
SO
3
(8)
E-mail: tcwmak@cuhk.edu.hk
*tcwmak@cuhk.edu.hk
3
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Chem. Commun., 2005, 3529–3531 | 3529

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2
and Chart 1, it can be inferred that NO
3
is about the same or
2
3 3
slightly superior to CF SO . However, one can only conclude
2
2
2
2
that CF CO has a similar coordinating ability to HCO and
3
2
NO
2
2
2
, since Table 1 indicates the order HCO
2
2
y NO
2
.
2
2
2
CF CO while Chart 1 suggests that CF CO . HCO2
3
2
NO .
2
y
3
2
Based on the X-ray structural parameters, the coordinating
ability of the whole series of nine polyatomic monoanions can be
arranged in the order:
2
2
2
2
2
2
3
Chart 1 Trend of Ag…anion distances (s) in complexes 1–9 based on
the structural data listed in Table S1. A line is drawn through the
weighted average values.
NO2 y HCO2 . CF CO . ClO . NO . CF SO
3
2
2 2 2
3
3
3
.
ClO4 . BF4 . PF6
.
The trends of N–Ag–N bond angles (Table 1) and intramole-
…
…
coordination sphere of the silver atom indirectly indicates that it is
the weakest coordinating ligand in the list, since acetonitrile was
used as a solvent in the preparation of all nine complexes. On the
other hand, stronger coordination ability of the anions can reduce
the plus charge on the silver atom within the metallacycle and
hence increase Ag–N bond distances, being consistent with the
trend 1 , 2 , 8 , 3 , 4 , 7 , 5 , 6 , 9 shown in Table 1 and
Chart S1. By the same token, attachment of various anionic
ligands to the metallacycle affects its geometry to different extents,
so that the measured structural parameters can also be used for
ranking them in the order of increasing coordinating ability. The
shape of the dinuclear skeleton in complexes 1–9 gradually changes
from a sharply angled parallelogram towards a rectangle (Table S2
and Chart S4), reflecting the effect of the different coordinating
abilities of the complementary ligands (counter anions in 1–8 and
cular Ag p and p p interactions (Table S2) also support
this sequence but only to a more limited degree (Chart S2
and S3).
Complexes 1–9 are soluble in water and common organic
solvents such as methanol and acetonitile, so we performed
11
crystallization experiments with co-existing anions under the
same conditions used for preparing these complexes (Table S4),
anticipating that competition between anions for preferential
incorporation into the resulting crystal may provide complemen-
tary information on their relative coordinating ability.
Notwithstanding the easy decomposition of {[Ag(L)(HCO )] }
2
2 ‘
6, the results of competition experiments involving isomor-
phous complexes 1–6 (space group Pbca) are in accord with
the proposed sequence. However, poor agreement was
2
2
3
obtained with CF CO and CF SO as competing anions,
3
3
2
2+
CH CN in 9). These results indicate that the Ag
3
2
L
2
system is
which may be attributed to their bulk and the crystallization of
complexes 7 and 8 in a different space group P 1¯ with low
quite malleable and responsive to minor variation in the
coordinating ability of the anionic ligands.
symmetry.
For the monoanions in isomorphous complexes 1–6 which
belong to space group Pbca, taking all structural information into
consideration, an ordered sequence of decreasing coordinating
The rapid development in supramolecular coordination chemi-
stry over the past twenty years has witnessed great achievement in
the generation of both discrete molecular and extended solid-state
2
2
2
2
12
ability can be arranged as HCO y NO2 . ClO3 . NO3
.
ClO4 . BF4 . Although complexes 7 and 8 both crystallize in
architectures through crystal engineering. Strategies of rational
2
2
2
design have mainly focused on spontaneous assembly by metal–
ligand coordination and non-covalent interactions that include
2
3
2
2
¯
space group P1, the large anions CF SO and CF CO do not
3
3
1
3
fit into adjacent positions in the sequence. Judging from Table 1
hydrogen bonding and weak electrostatic interactions. In view of
the crucial role of anions in supramolecular organization, the
establishment of an ordered sequence of their coordinating ability
is useful not only in the context of anion recognition but also in the
rational construction of perceived supramolecular aggregates and
infinite frameworks with diverse architectures and structure-related
properties.
Table 1 List of Ag–N distances and N–Ag–N angles in 1–9
The present ordered sequence of polyatomic monoanions is
6
a
quite different from that put forward by Jung et al., which was
deduced mainly from the crystal data of non-identical systems and
2
2
experiments on anion exchange: NO
3
2
. CF CO
3
2
3 3
. CF SO
˚
Bond lengths/A and angles/u
2
2
PF6 . ClO4 . BF4 . Our ordering encompasses a wider
2
.
Complex
Anion
Ag–N1A
Ag–N2
N1A–Ag–N2
range of anions and is based on a self-consistent set of X-ray
structural data of nine isostructural crystalline silver(I) complexes,
of which six constitute an isomorphous series.
2
1
2
8
3
4
5
6
7
9
BF
4
2.217(4)
2.235(3)
2.258(3)
2.281(4)
2.313(4)
2.327(2)
2.347(2)
2.321(4)
2.401(3)
2.180(4)
2.200(2)
2.234(3)
2.249(4)
2.248(4)
2.304(2)
2.303(2)
2.276(4)
2.248(3)
160.2(2)
158.9(1)
144.9(1)
149.4(1)
153.5(2)
139.0(1)
142.6(1)
140.9(1)
123.8(1)
2
ClO
CF SO
4
2
3
3
The generality and reliability of the present ordered sequence of
coordinating ability of commonly used polyatomic monoanions
should be of value in future development of the coordination and
supramolecular chemistry of anions.
2
NO
ClO
3
2
3
2
NO
HCO
CF CO
2
2
2
2
2
3
We gratefully acknowledge financial support from the Hong
Kong Research Grants Council (Ref. No. CUHK 402003).
2
PF
6
3
530 | Chem. Commun., 2005, 3529–3531
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{
8 4 2
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3
2
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a 5 7.9427(5), b 5 15.078(1), c 5 20.808(1) s, V 5 2492.0(3) s , Z 5 8,
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for 2606 observed reflections [I . 2s(I)].
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a 5 7.5654(5), b 5 15.162(1), c 5 20.531(1) s, V 5 2355.1(3) s , Z 5 8,
819 unique MoKa reflections (Rint 5 0.0496), R 5 0.0467, wR 5 0.1241
for 2014 observed reflections [I . 2s(I)].
, C11 ClN Ag, M 5 375.51, orthorhombic, space group Pbca,
a 5 7.279(2), b 5 15.972(3), c 5 21.400(4) s, V 5 2487.9(9) s , Z 5 8,
246 unique MoKa reflections (Rint 5 0.0691), R 5 0.0596, wR 5 0.1733
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, C11 Ag, M 5 338.07, orthorhombic, space group Pbca,
a 5 7.1774(4), b 5 15.4432(9), c 5 20.659(1) s, V 5 2289.8(2) s , Z 5 8,
950 unique MoKa reflections (Rint 5 0.0286), R 5 0.0278, wR 5 0.0749
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, C12 Ag, M 5 337.08, orthorhombic, space group Pbca,
a 5 7.0155(3), b 5 15.5043(7), c 5 21.059(1) s, V 5 2290.6(2) s , Z 5 8,
961 unique MoKa reflections (Rint 5 0.0328), R 5 0.0303, wR 5 0.0816
for 2345 observed reflections [I . 2s(I)].
, C13 Ag, M 5 405.08, triclinic, space group P1, a 5 7.711(2),
R
1
2
2
H
8
2 5
O
3
3
1
2
3
8 3 4
H N O
3
2
1
2
4
H
8
2 4
O
3
2
1
2
5
8 3 3
H N O
3
2
1
2
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6
9 2 3
H N O
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8
b 5 9.289(1), c 5 10.193(1) s, a 5 88.633(3), b 5 70.997(2), c 5 64.430(2) u,
3
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9
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H
14
F
6
N
4
1
7
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1 Competition experiments were performed under the same conditions as
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1
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3
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4
3
1
resulting solution was allowed to stand overnight to give 20 mg yellow
crystals which were identified as complex 5.
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(
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Chem. Commun., 2005, 3529–3531 | 3531