Supramolecular isomerism of a metallocyclic dipyridyldiamide ligand metal halide system generating isostructural (Hg, Co and Zn) porous materials

Article abstract of DOI:10.1039/c2cc16691g

We show how crystallisation of supramolecular isomers of a dynamic coordination system generates a series of isostructural porous materials. These mercury, cobalt and zinc metallocyclic materials show permanent porosity and exhibit single-crystal-to-singl

Full text of DOI:10.1039/c2cc16691g

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Supramolecular isomerism of a metallocyclic dipyridyldiamide ligand
metal halide system generating isostructural (Hg, Co and Zn) porous
materialsw
a
b
a
Christopher D. Jones, Jin Chong Tan and Gareth O. Lloyd*
Received 28th October 2011, Accepted 14th December 2011
DOI: 10.1039/c2cc16691g
5
We show how crystallisation of supramolecular isomers of a dynamic
coordination system generates a series of isostructural porous
materials. These mercury, cobalt and zinc metallocyclic materials
show permanent porosity and exhibit single-crystal-to-single-crystal
transformations.
properties. Thus, we also highlight a series of isostructural
porous molecular materials in which only the metal is varied.
1f,3a
The synthesis of 1 was performed as reported in the literature.
In studying the formation of the metallocycles of 1 we aimed to
form solvates other than those already reported (THF and
dichloroethane), specifically focusing our studies on the polar
alcohols. As a result we isolated three new forms of Hg halides
The relationship between the solid-state products of crystalli-
sation and the dynamic processes within the originating
solution are not fully understood. Yet, to produce sustainable
and recyclable materials, scientists and engineers need to be
able to control the reversible supramolecular interactions that
lead to the myriad of crystals forms produced by dynamic
systems. Polymorphism and supramolecular isomerism are
indicators of the processes at play in nucleus formation from
dynamic species in solution, the selection of preferred nuclei
and the growth of crystals; moreover, stability towards trans-
formations can be inferred from the structures of favoured
with 1: material A, Hg Cl
2
4 2
1
ꢀnMeOH or EtOH (where n varies
from 1–2); material B, [HgCl 1] ; and material C, [Hg Br 1 ]ꢀ
2
n
4
8 4
MeOH). Two forms were also obtained from CoCl and
2
1
: material D, Co Cl 1 ꢀEtOH, and ZnCl and 1: material E,
2
4
2
2
Zn Cl 1 ꢀEtOH (Fig. 1; see S.I. for exact synthesis conditions
2
4 2
for all materials). Materials A, D and E are isostructural and
metallocyclic in nature. While investigating the formation of
Hg Cl 1
2 4 2
2 n
we obtained a polymeric form of [HgCl 1]
(
material B, Fig. 1b) by performing the crystallisation in a mixture
of methanol (0.5 ml) and dichloromethane (1.5 ml). Within B the
1
ligand with the HgCl forms a helical 1D coordination polymer
2
materials. With this in mind, we investigated a metal halide
0
1f
1
(following the 2 screw axis running along [010], Fig. S13–S14).
and dipyridyldiamide ligand, (Compound 1) N,N -(1,2-phenylene)
There is no ligand-based intramolecular hydrogen bonding
between amides: instead, two amide groups form a hydrogen-
bonded dimer and an N–H group forms a further hydrogen
bond to a chloride ligand. The remaining two hydrogen bond
acceptors, the chloride ligand and carbonyl group, interact with
C–H groups in the pyridyl groups, forming an intramolecular
motif in the latter case. The carbonyl group hydrogen bond is
diisonicotinamide, system which was known to form macrocyclic
2
complexes. We noted that Puddephatt and coworkers had used
1
to synthesise metallocycles with a series of mercury halides
1f,3
which have the potential to be porous.
By studying the
crystallisation of 1 with transition metals and varying conditions
such as solvent, metal, concentration and gel formation, we show
that the supramolecular isomerism of metallocyclic compounds
can allow for the formation of porous materials. These materials
utilise the intrinsic porosity of the assembled metallocyclic
species; notably, control over crystallisation of such intrinsically
porous compounds has recently been highlighted as an important
6
similar to those found in urea pyridyl compounds. Upon
establishing the solvent-induced supramolecular isomerism
2 4 2
of Hg Cl 1 , we performed experiments to understand the
influence of the halogen anion on the structure. In particular,
since Puddephatt and coworkers reported that macrocyclic
4
scientific target. There has also been recent interest in developing
3
forms of Hg Br 1 and Hg2I41 could be crystallised, we
a
isostructural materials as a means of tuning important
2
4
2
2
attempted to synthesise Hg Br 1 macrocycles isostructural
2 4 2
with A from methanol or ethanol, but instead obtained
Hg Br
a
[
4
1
8 4
]ꢀMeOH, material C (Fig. 1e, S15). This compound
Department of Chemistry, University of Cambridge, Lensfield Road,
Cambridge, United Kingdom CB2 1EW. E-mail: gol20@cam.ac.uk;
Fax: +44 1223 336362; Tel: +44 1223 763989
Department of Materials Science and Metallurgy, University of
Cambridge, Pembroke Street, Cambridge, United Kingdom
CB2 3QZ
is not a 2 ꢁ 2 macrocycle but rather a 4 ꢁ 4 macrocycle. The
coordination spheres of the two Hg centres of material C are
tetrahedral and the intramolecular hydrogen bonding is
present in both instances of 1 in the asymmetric unit (Fig. 1e).
This indicates the geometry of the metal and ligand does not
play a part in selecting for the 4 ꢁ 4 metallocycle.
b
w Electronic supplementary information (ESI) available: Crystallo-
graphic details and powder diffraction patterns, analytical data of
synthesised materials and compounds, TGA and DSC analyses.
CCDC 851192–851197 and 857511. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c2cc16691g
The influence of the metal on the crystalline form of the
materials with 1 was also tested: specifically, CoCl and ZnCl
2
2
2
110 Chem. Commun., 2012, 48, 2110–2112
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Fig. 1 Ligand 1 and the formation of materials A to E. (i) HgCl
MeOH/CHCl gives the 1D helical coordination polymers in B. (iii) A gel forms upon mixing of solutions of 1 and CoCl
metallocycles in material E. (v) HgBr .1 gel material converts to material D.
in MeOH gives C which contains 4 ꢁ 4 metallocycles. (vi) The CoCl
2
in MeOH or EtOH gives A which contains 2 ꢁ 2 metallocycles. (ii) HgCl
2
in
2
2
. (iv) ZnCl in EtOH gives
2
2
2
were utilised in place of HgCl in the reaction with 1. When a
2
packed structure down [100], it becomes apparent that
there are one-dimensional channels running along this axis
(Fig. 2, S10–S11, S20–S22, S26).
hot filtered ethanol solution of 1 (22 mg in 10 ml) was added to
2
an ethanol solution of CoCl (16 mg in 7 ml) a blue coloured
gel formed (Fig. 1c); this immediately began to break down
through crystallisation of a blue material, providing an example
The packing of metallocycles one on top of another is
stabilised by continuous p–p stacking interactions of alternating
pyridyl and phenylene rings (the separation distance between
rings being half the a axis). The p–p stacking of the metallo-
cycles results in two-dimensional layers which interact with each
other via the hydrogen bonding of amide groups to chloride
ligands; such bonding influences the orientation of the layers in
relation to each other. The solvent of crystallisation is included
in the channels of the stacking metallocycles, as evidenced by
thermal gravimetric analysis (TGA) (Fig. S7–S9; S18–S19) and
7
of a sol–gel process in molecular materials synthesis. There has
been considerable interest lately in the use of metal-containing
gels and crystal growth from and/or in low molecular weight
7
gelators. Due to the transient nature of the gel we did not aim
to characterise it; however, it does appear to influence the
crystal morphology of D (Fig. S23). One important aspect of
this sol–gel process is that it gives a near quantitative synthesis
of D via the gel. When ZnCl was utilised in the synthesis of the
2
1
0
metallocycle, material E formed from the crystallisation of an
Squeeze experiments. The TGA results indicate that the
solvent can be easily removed. Desolvation of bulk samples
was monitored by hot-stage microscopy and PXRD, and
2
ethanol solution (8 ml) of 1 (6.0 mg) and ZnCl (3.0 mg), with
no indication of gel formation.
As A, D and E are isostructural, the structural description
that follows essentially describes all three (A understandably
being largest metallocycle). The 2 ꢁ 2 metallocycle (half the
metallocycle being the asymmetric unit) is conformationally
different to the reported metallocycles due to the intramolecular
hydrogen bonding of the ligand (Fig. S27). This contributes to the
difference in packing observed in comparison to the previously
2
,3,8
reported structures, a type of supramolecular isomerism.
The ligands within A, D and E have significantly different
conformations to all but one of the reported structures of
ligand 1, in which only intermolecular hydrogen bonds are
8
,9
observed (Fig. S27). Importantly, the planes of the pyridyl
groups of the ligand are approximately orthogonal to each
other. This is in strong contrast with the known structures
of 1, in which amide hydrogen-bonding tapes are the norm and
the planes of the pyridyl groups are approximately parallel. The
influence of the conformational change in the metallocycle on the
supramoleuclar isomerism becomes clear once the interactions
between metallocycles are investigated. When viewing the fully
Fig. 2 One-dimensional channels found in material A, which is
isostructural to D and E, formed by the p–p stacking of the metallo-
cycles. Yellow semi-transparent surface represents the solvent-accessible
˚
volume of a sphere of radius 1.5 A.
This journal is c The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 2110–2112 2111

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13
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(
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112 Chem. Commun., 2012, 48, 2110–2112
This journal is c The Royal Society of Chemistry 2012