Mo2B4O9-Connecting Borate and Metal-Cluster Chemistry

摘要

We report on the first thoroughly characterized molybdenum borate, which was synthesized in a high-pressure/high-temperature experiment at 12.3 GPa/1300 degrees C using a Walker-type multianvil apparatus. Mo2B4O9 incorporates tetrahedral molybdenum clusters into an anionic borate crystal structure-a structural motif that has never been observed before in the wide field of borate crystal chemistry. The six bonding molecular orbitals of the [Mo-4] tetrahedron are completely filled with 12 electrons, which are fully delocalized over the four molybdenum atoms. This finding is in agreement with the results of the magnetic measurements, which confirmed the diamagnetic character of Mo2B4O9. The two four-coordinated boron sites can be differentiated in the B-11 MAS-NMR spectrum because of the strongly different degrees of local distortions. Experimentally obtained IR and Raman bands were assigned to vibrational modes based on DFT calculations.