Hydrothermal synthesis and crystal structure of a metal-organic coordination polymer with double-helical structure: [Fe(phen)(ipt)]n (ipt = isophthalate, phen = 1,10-phenanthroline)

Article abstract of DOI:10.1016/j.inoche.2003.08.015

A novel metal-organic coordination polymer [Fe(phen)(ipt)]_n 1 has been hydrothermally synthesized and structurally characterized. Compound 1 exhibits a novel neutral cross double-helical structure composed of left-handed and right-handed helical chains.

Full text of DOI:10.1016/j.inoche.2003.08.015

Inorganic Chemistry Communications 6 (2003) 1347–1349
www.elsevier.com/locate/inoche
Hydrothermal synthesis and crystal structure of a
metal–organic coordination polymer with double-helical structure:
[Fe(phen)(ipt)]n (ipt ¼ isophthalate, phen ¼ 1,10-phenanthroline)
*
Yu Hou, Enhong Shen, Shutao Wang, Enbo Wang , Dongrong Xiao, Yangguang Li,
Lin Xu, Changwen Hu
Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun 130024, PR China
Received 4 June 2003; accepted 21 August 2003
Published online: 11 September 2003
Abstract
A novel metal–organic coordination polymer [Fe(phen)(ipt)]n 1 has been hydrothermally synthesized and structurally charac-
terized. Compound 1 exhibits a novel neutral cross double-helical structure composed of left-handed and right-handed helical
chains.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Coordination polymer; Helical structure; Hydrothermal synthesis; Crystal structure
Over the past decade, helical metal complexes have
been extensively concerned not only in coordination
chemistry but also in materials chemistry because of
their similarities to nucleic acids and proteins and their
potential applications in asymmetric catalysis and non-
linear optical materials [1]. Since the early pioneering
work of Lehn and co-workers [2–12] on double-helical
Cu(I) complexes, a lot of helicates have been synthesized
using different ligands and metal cations through self-
assembly process. These helicates have been assembled
by coordinate-covalent bonding, hydrogen bonding, p–p
aromatic stacking interaction or the combination of the
two [13,14]. Usually, exo-bidentate ligands composed of
2; 20-bipyridine and 2; 20:60; 200-terpyridine, combined
with metal ions that adopt appropriate coordination
geometry, tetrahedron or octahedron, are used to syn-
thesize double-stranded helicates [15]. But double-
stranded helicates constructed from asymmetrically
dicarboxylate ligands have far been unexplored.
Recently, a good strategy in synthesizing metal complex
with helical structure is to adopt two kinds of ligands
such as asymmetrically dicarboxylate bridging ligands
and aromatic bidentate chelate ligands [16]. This is be-
cause the nonlinear flexible or V-shaped dicarboxylate
ligands can produce the helicity or flexuosity of the
polymeric chains and aromatic bidentate chelate ligands
can prevent the forming of high dimensional expanded
structure [16,17] and provide potential supramolecular
recognition for intermolecular p–p stacking interaction
[18,19]. Based on the above synthesis strategy, we
choose V-shaped dicarboxylate ligand ipt, bidentate
chelate ligand phen and metal ion with appropriate ge-
ometry as the study system to explore potential charm-
ing helical structures. In this communication, we report
the hydrothermal synthesis and structural characteriza-
tion of 1, to our knowledge, 1 is a novel neutral cross
double-helical compound composed of two single helical
chains, left-handed and right-handed, that are cova-
lently interlinked by metal dimers and induced by the
supramolecular aromatic stacking interactions.
Compound 1 was prepared from a mixture of
FeCl2 ꢀ 4H2O (0.198 g), isophthalic acid (0.166 g), phen
(0.198 g), NaOH (0.08 g) and H2O (8.0 ml) in an 18 ml
* Corresponding author. Tel.: +86-431-5268787; fax: +86-431-
5684009.
E-mail address: wangenbo@public.cc.jl.cn (E. Wang).
1387-7003/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2003.08.015

1348
Y. Hou et al. / Inorganic Chemistry Communications 6 (2003) 1347–1349
Teflon-lined autoclave under autogenous pressure at 180
°C for six days [21].
The X-ray diffraction analysis [22] reveals that com-
pound 1 is a 3D supramolecular metal–organic coordi-
nation polymer with double-helical structure. The
fundamental unit, as shown in Fig. 1, consists of one
Fe(II) atom, one ipt ligand, and one chelating phen li-
gand. Each Fe(II) center displays a distorted octahedral
coordination geometry, being coordinated by two ni-
trogen atoms of one phen ligand and four oxygen atoms
from three different carboxylate groups of three ipt li-
ꢀ
gands. The average Fe–N bond length is 2.1891(19) A,
and the Fe–O bond lengths vary from 2.0469(15) to
ꢀ
2.3182(14) A. The ipt ligand exhibits an interesting
connection mode with metal ions. Two carboxyl groups
display two different kinds of coordination modes, that
is, the bidentate chelating and monodentate bridging
mode. Based on these connection modes, one carboxyl
group adopts the bidentate chelating mode to coordi-
nate to the Fe(II) center, and the other carboxyl group
from the same ipt ligand acts as a bridge to link other
two Fe(II) centers to form a dimer unit. Hence each ipt
ligand coordinates to three Fe(II) centers and each
Fe(II) center links to three ipt ligands. Every two dimers
are linked by two ipt ligands along two different direc-
tions alternatively to form a double-helical chain along
Fig. 2. Seeing the bc plane, phen ligands project above and below into
the interlamellar region and there exist strong p–p stacking interac-
tions between adjacent chains.
lical structure. The bond valence calculation [20]
(Fe 1.95) suggests all Fe atoms are in the +2 oxidation
state.
In this communication, we report a novel double-
helical metal–organic coordination polymer [Fe(phen)
(ipt)]n 1 which exhibits a double-helical structure con-
sisted of two helical chains which are linked together by
metal dimmers.
ꢀ
the c axis direction with a long pitch of 18.574 A, as
shown in Fig. S2. The two helical chains, left-handed
and right-handed, are interlinked together by the metal
dimer that functions as a knot (see Fig. 2).
Supplementary materials
There are two kinds of p–p interactions in compound
1, namely, within the same chain and between the ad-
jacent chains. The close contact distance between adja-
Crystal data and structure refinement, atomic coor-
dinates, bond lengths and angles, anisotropic displace-
ment parameters, and the IR spectrum of compound 1
were available from the authors on request.
ꢀ
cent aromatic rings is 3.397 A within the same chain and
ꢀ
3.338, 3.318 and 3.365 A between adjacent chains. These
supramolecular interactions together with the coordi-
nate-covalent interactions between metal and organic
ligand strengthen the stability of the double-helical
chain. Therefore, we can infer that the aromatic biden-
tate chelate ligands are crucial to the formation of he-
CCDC reference number: 208497.
Acknowledgements
This work was financially supported by the National
Natural Science Foundation of China (20171010).
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