Cerium ground state electronic configuration

Elemental lanthanum has a ground state (electronic configuration) of [Xe]5d6s. Naturally occurring lanthanum is a mixture of two stable isotopes, La and La. The element was discovered in 1839 by Carl Gustaf Mosander in the form of the lanthanum oxide, at that time called lanthana. The name is derived from the Greek lanthanein ( to fie hidden ), as the element had been overlooked due to its similarity to the earlier discovered cerium. 

Summing up, similar to cerocene the most compact description of the ground state electronic structure of Ce(CgH6)2 is by the leading 4f configuration, built from nearly pure Ce 4f and ring tt orbitals. Thus, the assignment to bis( 7 -pentalene)cerium(III) seems to be the most appropriate. 

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