Photon Factory Activity Report 2004 #22 Part B (2005)
Chemistry

NW2/ 2003G186

Finite, Spherical Coordination Networks that Self-Organize from 36 SmallComponents
Masahide Tominaga,1 Keisuke Suzuki,1 Masaki Kawano,1 Takahiro Kusukawa,1 Tomoji Ozeki,2Shigeru Sakamoto,3 Kentaro Yamaguchi,3 and Makoto Fujita*,11
Department of Applied Chemistry, The University of Tokyo, CREST, Japan Science andTechnology Corporation (JST), Bunkyo-ku, Tokyo 113-8656, Japan2
Department of Chemistry and Materials Science. Tokyo Institute of Technology, Meguro-ku,Tokyo 152-8551, Japan
3
Chemical Analysis Center, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan)
Introduction
Highly symmetric structures often appear in nature as
revealed by, for example, the capsids of spherical viruses
that possess icosahedral symmetry consisting of 60n
identical protein subunits. The reason for the highsymmetry lies behind the principle that the increasing
symmetry elements reduce the amount of independent
structural information, which is directly related to thelength of DNA. Thus, the self-organization of tiny
subunits into a giant biological molecule can be regarded
as the process of not only the structural growth but theamplification of molecular information. We show here
that, through metal-ligand interactions, simple bananashaped organic molecules self-organize into finite,spherical coordination networks with a diameter of up to1
7 nm. The spherical coordination networks consist of 36components (12 equivalent metals and 24 equivalentligands) and possess cuboctahedron symmetry.
We expect that, if the ligand framework is slightly bent,
the coordination network will develop with a constantradius of curvature and a spherical finite network will beobtained (scheme), reminiscent of graphite vs fullerene
2formation from sp carbons. On a basis of this idea, we
designed ligands 1a and b and examined theirIIcomplexation with naked Pd ions in a square-planar
geometry.
Results
When ligand 1a (0.02 mmol) was treated withPd(NO3)2 (0.01 mmol) in dimethyl sulfoxide (DMSO)-d6(1.0 mL) at 70 °C for 4 h, the quantitative self-assembly
1of a single product was observed by H NMR
spectroscopy. Single crystals of 2b were obtained by32

Users' ReportFigure
Crystal structure of sphere 2b.
Counterions and solvent are omitted for clarity.
very slow vapor diffusion of 1,1,2-trichloroethane into aDMSO solution of 2b. With a CCD detector, Mo–Kα
radiation (55 kV, 30 mA) afforded low resolution data
(only 874 unique reflections (>2σ(I))). The poor qualityof the data was due to severe disorder of solvents andanions in the extraordinarily large void within thespherical framework of 2b. However, synchrotron X-ray
radiation with high flux and low divergence (NW2beamline) provided much higher quality of data with2717 unique reflections (>2σ(I)), from which thespherical M12L24 structure of 2b was solved with all theheavy atoms being refined anisotropically. The crystal
system is cubic (a = b = c = 47.689(4) Å) and the cell
3
volume is 108,456(16) Å . Surprisingly, the frameworkof 2b occupies only 20% of the cell volume (as estimatedby Platon program), remaining 80% being occupied bydisordered solvents and counter ions. The diameter of asphere in which 2b is inscribed is 3.4 nm. The closest
Pd–Pd distance is 1.3 nm while the furthest one is 2.6 nm.
References[1] M. Tominaga et al, Angew. Chem., Int. Ed. 43, 5621
(2004).
*mfujita@appchem.t.u-tokyo.ac.jp