Photon Factory Activity Report 2004 #22 Part B (2005)
ChemistryNW2/2003G186

Molecular weight tuning of the mixed-valence Mo spherical clusters
Tomoji OZEKI*, Takuro SAEKI
Department of Chemistry and Materials Science, Tokyo Institute of Technology,
O-okayama, Meguro-ku, Tokyo 152-8551, Japan
Introduction
Polyoxometalate chemistry finds much similarity
between the molybdates and tungstates [1]. However, thechemistry of the mixed-valence giant clusters is limited
only to those of the molybdates [2]. Aiming at exploring
the corresponding tungstate chemistry, introduction oftungsten atoms into molybdenum giant clusters wasattempted as the first step. The Mo atoms in theVIV42[Mo 72Mo 60O372(CH3COO)30(H2O)72] anion (abbreviatedas {Mo132}) [3] was proved to be partially replaceablewith W atoms. The degree of the substitution simplydepends on the ratio of the starting materials. Crystal
structures of partially substituted clusters, as well as thepure molybdate precursor, have been determined bysingle crystal X-ray diffraction experiments using the PFAR NW2 beamline [4].
Results and Discussions
Attempts to introduce the W atoms into {Mo132} werecarried out with the conditions listed in Table 1. Brown
octahedral crystals were obtained from each experiment.
Single crystal X-ray diffraction experiments wereperformed at 123K using a CCD diffractometer at the PFAR NW2 beamline. In spite of the relatively small sizes
and poor diffraction abilities of the sample crystals, highflux X-rays from NW2 provided satisfactory quality ofdata.
_ Each sample crystallized in cubic, space group
Fm3m with the unit cell dimensions listed below.
Table 1: Experimental conditions
Starting
W/M
ratio

a /Å

0.0

46.20700.1

46.1165

0.3

45.6687

0.5

45.8315

Crystal Size/ mm
0.06×0.05×
0.05
0.04×0.04×
0.04
0.12×0.12×
0.12
0.04×0.04×
0.04

R1

RefinedW/M
ratio

0.07520.0

0.07550.091

0.07350.232

0.0844

0.398

Crystals obtained from the syntheses using W sources
turned out to contain partially W-substituted sphericalVIV
42clusters, the [(WxMo1-x) 72Mo 60O372(CH3COO)30(H2O)72]
anion (abbreviated as {M132}), whose framework isidentical with that of {Mo132}. A distinct tendency of thesubstitution was unrevealed. The W atoms favor thepentagonal-bipyramidal seven-coordinate sites. To a lessextent, they also occupy the octahedral six-coordinate

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Users' Report

Figure 1. Structure of the [(WxMo1-x)VI72MoV60O372(CH3COO)30(H2O)72]42- anion.
Purple and blue
polyhedra accommodate the hexavalent W or Mo
atoms. They form the {M(M5)} pentagonal building
units. Thirty pairs of red octahedra centred by MoV
are linking twelve {M(M5)} units into a sphericalshape.
VIsites adjacent to the seven-coordinate sites.
Mooccupied these sites in the pure-molybdate precursor,{Mo132}. On the other hand, the M2 units linking the{M(M5)} pentagonal building blocks, which wereVoccupied by Mo in the precursor, never accommodate
the W atoms. Except for the distribution of the Mo/Watoms, structures of the spherical clusters are essentiallyidentical. Thus the {M132} anions can be interpreted as aseries of anions that are identical in size and charge yet
tunable in molecular weight.
References[1] M. T. Pope, Heteropoly and Isopoy Oxometalates,Springer, Berlin (1983).
[2] A. Müller, S. Roy, Coord. Chem. Rev. 245 (2003) 153.
[3] A. Müller, E. Krickemeyer, H. Bögge, M.
Schmidtmann, F. Peters, Angew. Chem. Int. Ed. 37(1998) 3360.
[4] T. Ozeki, T. Saeki, S. Adachi, T. Yamase, Photon
Factory Activity Report, PART B, (2003) 272.
* tozeki@cms.titech.ac.jp