Polyoxometalate chemistry continues to be a subject of great interest, since the wide and fascinating variety of structures and properties of these objects gives rise to numerous applications. [1] Polyoxoanions containing phosphato groups constitute the largest class of heteropolyanions, with structures ranging from molecular complexes to extended frameworks. [2] In contrast, very few polyoxometalate-containing polyphosphato groups have been structurally characterized. In 1994, Kortz and Pope reported the first X-ray structure of a polyoxomolybdate(vi) containing the pyrophosphato (P 2 O 7 ) 4À ligand. [3] Since then, only two other structures b 97.542(1), g 97.410(1)8, V 35 592(3) ä 3 , Z 1, 1 2.466 g cm À3 , m 2.907 mm À1 , F(000) 25 484, crystal size 0.35 Â 0.20 Â 0.05 mm 3 . Crystals of 1 were removed from the mother liquor and immediately cooled to 183(2) K on a Bruker AXS SMART diffractometer (threecircle goniometer with 1 K CCD detector, Mo Ka radiation, graphite monochromator; sphere data collection in w at 0.38 scan width in four runs with 606, 500, 606, and 500 frames (f 0, 88, 180 and 2688) at a detector distance of 5.00 cm). A total of 371 523 reflections (0.66 < V < 27.058) were collected of which 153 584 reflections were unique (R int 0.0511). An empirical absorption correction using equivalent reflections was performed with the program SADABS. The structure was solved with the program SHELXS-97 and refined using SHELXL-93 to R 0.0559 for 96 134 reflections with I > 2s(I), R 0.1066 for all reflections; max./min. residual electron density 3.680 and À 2.844 e ä À3 . (SHELXS/L, SADABS from G. M. Sheldrick, University of Gˆttingen 1993/97; structure graphics with DIAMOND 2.1 from K. Brandenburg, Crystal Impact GbR, 2001.) Further details on the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, ] EXAFS measurements were performed at the beamline A1 at HASYLAB (Hamburg) on samples ground together with suprapure polyethylene and subsequently pressed into pellets with a thickness of 300 mm. Spectra were obtained in the transmission mode at the Eu-L III edge covering the range from 6.75 ± 8.00 keV. The magnitude of the Fourier transform of the EXAFS after background and phase correction shows a distinct and symmetric maximum at 243 pm which is clearly a result of almost only (!) one kind of oxygen coordination to the Eu absorber. A second coordination shell at about 350 pm is assigned to Eu ¥¥¥ Mo separations.[12] Although the total number of molybdenum centers is certain, the (formal) number of Mo V centers has a slight uncertainty, though the given number of 24 is the most reasonable one according to the comparison with previous related structures, that is, parts of the well known {Mo 154 } and {Mo 176 } clusters with respect to the related BVS values of comparable protonation sites and Mo 5 O 6 -type building blocks. [1b, 6] This assignment results in a charge of À 20 per ™dimer∫ 1 a by referring to the number of abundant protons and Mo V centers (note: the rela...
