Networking of tribenzo-O2S2-macrocycles with mercury thiocyanate: Effect of macrocyclic isomers

Article abstract of DOI:10.1021/cg100687v

Tribenzo-O₂S₂-macrocyclic isomers incorporating a xylyl group in the ortho (o-L), meta (m-L), and para (p-L) positions were employed to examine the effect of ligand isomers on supramolecular networking assembly with mercury(II) thioc

Full text of DOI:10.1021/cg100687v

DOI: 10.1021/cg100687v
Networking of Tribenzo-O2S2-Macrocycles with Mercury Thiocyanate:
Effect of Macrocyclic Isomers
2010, Vol. 10
3850–3853
Hyun Jee Kim,† Leonard F. Lindoy,*,‡ and Shim Sung Lee*,†
†Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University,
Jinju 660-701, S. Korea, and ‡School of Chemistry, The University of Sydney, NSW 2006, Australia
Received May 22, 2010; Revised Manuscript Received July 16, 2010
ABSTRACT: Tribenzo-O2S2-macrocyclic isomers incorporating a xylyl group in the ortho (o-L), meta (m-L), and para (p-L) positions were
employed to examine the effect of ligand isomers on supramolecular networking assembly with mercury(II) thiocyanate. o-L and p-L afforded
1-D linear [Hg2(o-L)(SCN)4]n (1) and 1-D zigzag [Hg( p-L)(SCN)2]n (3) coordination polymer networks, respectively, while m-L gave a brick-
wall type 2-D network polymer of type [Hg2(m-L)(SCN)4]n (2). All three polymeric structures show different thiocyanate binding motifs.
The structural modification of macrocyclic ligands has been an
important strategy for the construction of novel supramolecular
coordination species and has led to a very considerable variety of
coordination geometries and metal bonding modes that are con-
trolled to varying degrees by the conformational flexibility of the
ligand.1 In particular, the versatility of thioether-containing macro-
cycles makes them useful for generation of a range of network
products because the sulfur donor is expected to favor binding to
softer metals such as Ag(I) and Hg(II) in either an exo- or an endo-
cyclic mode.2,3 The nature of such network coordination polymeric
structures incorporating thiamacrocycles quite often displays a
strong dependence on the ring rigidity of the macrocyclic unit.4
In the course of our ongoing studies of the thiamacrocycles,2,4,5
we explore the possibility of generating novel metallosupramolecu-
lar architectures through the structural modification of the macro-
cycles. Recently, we reported the influence of the use of positional
isomers of three NS2-macrocycles on the formation of their exo-
coordination-based silver(I) and mercury(II) complexes that were
shown to exhibit flower-, leaf-, and tree-shaped patterns.5f
Motivated by these results, we were interested in extending these
studies employing the use of the (17- to 19-ring) O2S2 tribenzoma-
Figure 1. Crystal structure of 1, [Hg2(o-L)(SCN)4]n: (a) core
coordination unit and (b) 1-D “looped” network.
crocycle isomers o-L, m-L, and p-L. These tribenzomacrocycle
isomers contain two sulfur donors in the crown rings as possible
bridging positions for proposed exocoordination-based network
formation.6 Since the order of their conformational ring flexibility
is o-L > m-L > p-L, reflecting the position of the xylyl constituent,4
we reasoned that the use of these positional isomers may also induce
the formation of different (flexibility-controlled) products when
reacted with a soft metal ion, such as the mercury(II) ion. Further,
we have coupled this approach with the use of thiocyanate as a
commonly bridging anion in an endeavor to achieve the construc-
tion of a new family of infinite networks. In particular, the different
linker anions can induce different structural networking, and thus,
this and the use of exosulfur coordination effects will most likely play
important roles in forming resulting supramolecular architectures.7
that involve the networking of the macrocycles by means of exo-
cyclic coordination. In this work, an investigation of the effect of
changing the macrocyclic ring flexibility across o-L, m-L, and p-L
on the products obtained with mercury(II) thiocyanate was
carried out. Using this strategy, we obtained the self-assembled
supramolecular networks 1-3, exhibiting different topologies
(Scheme 1); all three structures were characterized by X-ray
analysis (Figures 1-3).
Synthesis of o-L involved four steps starting from salicylalde-
hyde, with each step proceeding smoothly (Scheme 2). Dichloride
precursor 6 was prepared through dialdehyde 4 and dialcohol 5
using a known procedure.8 The target macrocycle o-L was ob-
tained by coupling reactions involving dichloride 6 and 1,2-ben-
zenedimethanethiol in the presence of Cs2CO3 under high dilu-
tion conditions in a yield of 65%. The 1H and 13C NMR spectra
together with elemental analysis and mass spectra were clearly in
agreement with the proposed structures. m-L was synthesized as
reported previously by us.9 p-L was synthesized similarly except
the use of 1,4-benzenedimethanethiol and its synthetic detail will
be reported elsewhere.
Reaction of o-L in dichloromethane with Hg(SCN)2 in acetoni-
trile afforded the colorless crystalline product 1, suitable for X-ray
analysis. Interestingly, compound 1 features a 1-D polymeric array
of formula [Hg2(o-L)(μ1,3-SCN)2(SCN)2]n, in which the three
anions contribute to the coordination sphere of each Hg center
Herein, we present the synthesis and structural characteriza-
tion of three supramolecular complexes for o-L, m-L, and p-L
*Corresponding authors. E-mails: sslee@gnu.ac.kr, lindoy@chem.usyd.
edu.au.
r
pubs.acs.org/crystal
Published on Web 07/21/2010
2010 American Chemical Society

Communication
Crystal Growth & Design, Vol. 10, No. 9, 2010 3851
Scheme 1. Mercury(II) Thiocyanate Complexes Prepared
Scheme 2. Synthesis of o-L
(Figure 1). The asymmetric unit of 1 contains one o-L, two mercury
ions, and four thiocyanate ions. An unusual feature of 1 is the
presence of two types of thiocyanato groups: one is acting as a
S-terminal ligand, and the other has a μ1,3-SCN bridging coordina-
tion mode through its N and S atoms. The macrocycle coordinates
in a bidentate fashion toward two different metal centers via two
exodentate S donors, with the two ring oxygen donors remaining
uncoordinated. Consequently, the 1-D polymeric array of 1consists
of alternating linkages of one o-L and one eight-membered metal-
lacycle, Hg1-(μ1,3-SCN)2-Hg2, with the end-to-end thiocyanate

3852 Crystal Growth & Design, Vol. 10, No. 9, 2010
Kim et al.
Figure 2. Crystal structure of 2, [Hg2(m-L)(SCN)4]n: (a) core coordination unit, (b) single brick unit, and (c) 2-D brick-wall type network.
bibridge in a “chair” conformation, with a Hg1 Hg2 distance of
3 3 3
Reaction of m-L with Hg(SCN)2 under similar conditions to
those employed for o-L afforded the colorless crystalline product 2,
which proved suitable for X-ray analysis. Unlike 1, compound 2
features a 2-D polymeric arrangement of formula [Hg2(m-L)-
(SCN)4]n (Figure 2). The asymmetric unit of 2 contains one
m-L, two mercury ions, and four thiocyanate ions. The gross geo-
metry of 2 can be described as an infinite brick-wall pattern
(Figure 2c). The network of 2 is made up of the 1-D “looped”
backbones composed of Hg1-(μ1,3-SCN)2-Hg2 repeating units.
These linear “looped” chains are further cross-linked by m-L
macrocycle via Hg-S(thioether) bonds, yielding the 2-D frame-
work. The Hg-S(thioether) bond lengths [Hg1-S1 2.631(2),
˚
5.852(4) A.
The bond distances to the thioether sulfur donors (Hg1-S1,
˚
2.577(3); Hg2-S2A, 2.528(3) A) are reasonably similar and com-
pare well with those found in other mercury(II)-thiamacrocyclic
complexes.10 Both of the Hg centers (Hg1 and Hg2) are four-coordi-
nate and show similar coordination environments, being coordi-
nated by one sulfur donor from one o-L, two bridging thiocyanate
ions, and one terminal thiocyanate ion. The coordination sphere of
each Hg center is distorted tetrahedral, with the “tetrahedral” angles
falling in the range 93.4(2)-130.9(1)ꢀ for Hg1 and 91.7(1)-137.7-
(1)ꢀ for Hg2. The distortions from a regular tetrahedron result, in
part, from the formation of the mercury(II) thiocyanate metalla-
cycle with its presumably rigid NCS-Hg-NCS bond angles.
The eight-membered metallacycle formed by two mercury
atoms and two bridging thiocyanate ions is nonplanar, with the
˚
Hg2-S2C 2.585(2) A] agree well with the corresponding values
10
˚
[2.5-2.8 A] for related systems; they are slightly shorter than
˚
those for Hg-SSCN (avg 2.431 A).
Each Hg(II) ion is five-coordinate, being bound to one sulfur
atom of m-L and four thiocyanate ions via two Hg-SSCN and two
Hg-NSCN bonds. The coordination geometry can best be described
as a distorted trigonal bipyramid with one S donor of m-L, two S
atoms from two thiocyanate ions defining the trigonal plane, and the
˚
˚
mercury atoms being displaced 0.675 A (Hg1) and 0.890 A (Hg2)
above and below the plane determined by the two coplanar
thiocynate groups. The thiocynate groups show small distortions
[175.0(6) and 177.3(6)ꢀ] from linearity, as is usually observed.

Communication
Crystal Growth & Design, Vol. 10, No. 9, 2010 3853
stereochemical demand of any types of the bridging coordination
modes for thiocyanate ion. Instead, the two thiocyante ions in the
coordinationsphereof 3 simplyact as terminalligands. The phase
purities of the bulk materials for 1-3 were confirmed by XRPD
(Figure S1 of the Supporting Information).
In summary, the present paper reports the assembly and
structural characterization of three new mercury thiocyanate
metallo-supramolecular structures with 1-D and 2-D coordination
polymers. From these results, it is concluded that a combination of
the binding behavior of the thiocyanate anion and the influence of
the ring-rigidity of the macrocycles in complexation coupled with
the tendency for the exocoordination of sulfur donors of the
thiamacrocycle alters ligand behavior and has important conse-
quences of the ligand binding modes for constructing new Hg(II)-
supramolecular systems exhibiting different architectures.
Acknowledgment. This work was supported by a grant from a
WCU project (R32-2008-000-20003-0) of MEST, Korea. L.F.L.
thanks the Australian Research Council for support.
Supporting Information Available: Experimental details, crystal
data, XRPD patterns, selected bond distances and angles, and a cif
file. This material is available free of charge via the Internet at http://
pubs.acs.org.
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