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The highest oxidation states of the

transition metals


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The quest for the highest achievable oxidation states of the transition metals is of fundamental interest. Additionally, metal complexes in very high oxidation states may serve as oxidation agents in other subdisciplines. The maximum oxidation states for the early transition metals of the 5d row follow the group number up to group 8 ( OsO4). The trends for the later metals tend to be less clear-cut. In the 5d series, the trend of the experimentally suggested maximum oxidation states after osmium looks irregular (sees Figure 1).
Figure 1. The maximum experimental known oxidation states of the 5d transition metals.
In our quantum chemical calculations we provide structures and thermochemistry on high oxidation state species like OsF7[9], OsF8[9], IrF7[8], AuF7[7], AuF5·F2[12] and HgF4[2,4]. It is shown that the highest possible oxidation states with a realistic chance of experimental observation are the iridium (Ir+VII), gold (Au+V) and the mercury (Hg+IV) species.
Combining all the results of our quantum chemical predictions and of reliable experimental studies, a revised trend of the highest oxidation states of the 5d transition metal row is obtained (see open squares in Figure 2).
Figure 2. Maximum oxidation states of the 5d transition metals: Highest experimentally known values (white dots), probably incorrect experiments (orange triangle), most likely values suggested in this work (red squares).