Structure and Electron Configuration
With a d0 configuration, Os(VIII) is expected to form tetrahedral complexes when bound to four ligands. Tetrahedral structures are seen for the electronically related oxides MnO4– and CrO42–.
The osmium of OsO4 has a formal oxidation state of +8, the highest oxidation state known for a transition metal. The osmium atom has eight valence electrons. If one assumes that two electrons are donated by each of the four oxide ligands, the total electron count for the complex is 16, as also seen for the isoelectronic species permanganate and chromate.
The high oxidation state of osmium in this compound can be rationalized by comparison of main-group and transition-metal chemistry. Just as the elements in groups 3 through 7 form compounds analogous to those formed by elements in groups 13 through 17 (e.g. TiCl4 and GeCl4, VF5 and AsF5, CrO42− and SeO42−, etc.), we might expect the elements in group 8 to form compounds analogous to those formed by the noble gases. This is the case, as demonstrated by the existence of compounds like OsO4 and XeO4.
Read more about this topic: Osmium Tetroxide
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