The formation of ReS2 inorganic fullerene-like structures containing Re4 parallelogram units and metal-metal bonds

Article abstract of DOI:10.1021/ja0261630

The encapsulation of ReO_x within ReS₂ inorganic fullerene-like cages is described for the first time. The encapsulate was prepared by the sulfidization of both hand-milled and ball-milled samples of ReO₂; partial conversio

Full text of DOI:10.1021/ja0261630

Published on Web 09/11/2002
The Formation of ReS2 Inorganic Fullerene-like Structures Containing Re4
Parallelogram Units and Metal-Metal Bonds
Karl S. Coleman,*,† Jeremy Sloan,*,†,‡ Neal A. Hanson,† Gareth Brown,†,‡ Gerald P. Clancy,†
Mauricio Terrones,§ Humberto Terrones,§ and Malcolm L. H. Green†
Inorganic Chemistry Laboratory, UniVersity of Oxford, South Parks Road, Oxford, U.K., OX1 3QR, Department of
Materials, UniVersity of Oxford, Parks Road, Oxford, U.K., OX1 3PH, and IPICyT, AV. Venustiano Carranza
2425-A, Col. Bellas Lomas, San Luis Potos´ı 78210, Mexico
Received March 11, 2002
Since the discovery of C60, research into the field of carbon
fullerene chemistry has developed rapidly.1 A number of important
breakthroughs have allowed for the preparation of other carbon-
based nanostructures such as single- and multiwalled carbon
nanotubes.2a-c More recently, so-called inorganic fullerene-like
analogues (IFs) of these carbon-based materials have been discov-
ered, and their properties have been studied.3a-d Initially, these
materials were derived from layered metal chalcogens of the form
2H-MX2 with M ) Mo, W and X ) S, Se,3e-i although more
recently IFs have been formed from layered metal halides such as
NiCl2, CdCl2, and TlCl34a-c and oxides such as TiO2 and V2O5.5a,b
Additionally, IFs formed from chalcogens have been extended to
include those based on Nb6a or Ta6b and also mixed-metal
chalcogens such as W-Nb-S6c or W-Mo-S.6d
With the exception of the oxides, all of the above have in
common a six-membered ring substructural motif (Figure 1a), which
conveys smooth curvature within extended layers7a and which may
then combine with triangular or rhombohedral defects7b resulting
in three-dimensional closed or scroll-like nanostructures. We
describe here a departure from this basic template in the formation
of nanostructures derived from an ReS2 framework in which the
substructural motif consists of Re4 parallelogram units8a which
distort from the hexagonal motif (Figure 1b). With respect to the
bulk structure, this distortion results in a reduction of symmetry
from P63/mmc (Figure 1a) to P-1 (Figure 1b). With regard to the
bonding properties, the d3 Re center which forms part of the t2g
band has two electrons strongly hybridized with the p orbitals of
the sulfur with the remaining d electron residing in the delocalized
Figure 1. (a) Top-down and side-on depictions of a single layer of P63/
mmc WS2 with a W hexagonal motif indicated in blue. (b) Top-down and
side-on depiction of a single ReS2 layer derived from the triclinic P-1 bulk
form. An equivalent but distorted Re “hexagon” to that shown in (a) is
indicated in blue, while a Re4 parallelogram unit is indicated in red. Note
Re-Re metal-metal bonds.
2
2
dx -y and dxy metal orbitals. It is the overlap of these orbitals with
neighboring Re centers that form the Re4 parallelogram units
containing Re-Re metal bonds. This, in turn, results in a gap in
the middle of the bonding and antibonding t2g bands, thus giving
rise to the semiconducting nature of ReS2.8b,c
ReS2 IF nanostructures were prepared by direct sulfidization of
ReO2, formed from the decomposition of ReO3. The parent oxide
was obtained from Aldrich (99.9%) and used without further
purification. The oxide samples were ball-milled for 30 h prior to
sulfidization to produce particles in the submicron range. The ReO3
samples were decomposed to ReO2 by heating to 700 °C under a
flow of nitrogen prior to sulfidization. All sulfidizations were carried
out in a standard flow reactor at 700 °C with a flow rate of H2S of
approximately 4 mL min-1. All of the resulting products were
characterized by high-resolution transmission electron microscopy
(HRTEM) using a JEOL 3000F microscope fitted with an energy-
dispersive X-ray analysis (EDX) system and by X-ray powder
diffraction (XRD) using a Philips 1729 diffractometer equipped
with Cu KR1 radiation operated at 40 kV and 30 mA.
In general, sulfidization of commercial ReO3 produced no
complete IF ReS2 particles, although a high degree of curvature
was observed in fragments imaged by HRTEM. Therefore, ReO2
was prepared by disproportionation of ReO3, resulting in the
formation of both monoclinic and orthorhombic forms of the
reduced oxide. These reduced forms9 were found to be more
susceptible to sulfidization. Sulfidization of ReO2 formed complete
ReS2 IF-like cages encapsulating crystalline ReO2 (Figure 2a) or
amorphous ReOx particles (Figure 2b) as confirmed by HRTEM
imaging and EDX microanalysis (Figure 2c). Additionally, XRD
* To whom correspondence should be addressed. E-mail: karl.coleman@
chem.ox.ac.uk.
† Inorganic Chemistry Laboratory, University of Oxford.
‡ Department of Materials, University of Oxford.
§ IPICyT.
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J. AM. CHEM. SOC. 2002, 124, 11580-11581
10.1021/ja0261630 CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
Figure 2. (a) HRTEM micrograph showing a small ReO2 particle encapsulated by spheroidal ReS2 layers. The 0.29 nm lattice fringes (inset) correspond
to ReO2 {111} planes. (b) HRTEM micrograph showing a large amorphous or polycrystalline ReOx particle encapsulated by spheroidal ReS2 layers. (c)
EDX spectrum from (b). Inset: ReOx-ReS2 interface region. A small void is labeled (V), while the arrow depicts a layer dislocation.
such structures has been attributed to the Re4 parallelogram
structural units, which represents the first example of a nonhex-
agonal-based layer structure forming inorganic fullerenes.
Acknowledgment. K.S.C. and J.S. wish to thank the Royal
Society for University Research Fellowships and financial support.
M.T. and H.T. thank CONACyT-Mexico, Millennium Initiative
(grant 8001-W).
Supporting Information Available: XRD powder patterns calcu-
lated for idealized P63/mmc and P-1 ReS2 and observed experimental
XRD powder pattern for partially sulfidized ReO2 (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
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powder patterns obtained from partially sulfidized ReO2 particles
confirmed that this sulfide material was derived from P-1 ReS2
(see Supporting Information).
In the HRTEM, the obtained ReS2 layers are visible as dark 0.61
9
nm lattice fringes corresponding to the (100) plane of ReS2 and,
in general, displayed extremely smooth curvature with few sharp
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ReS2 layers rather than from the incorporation of defects which
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In conclusion, we have demonstrated the synthesis of the first
ReS2 inorganic fullerene structures. The ability of ReS2 to form
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