tetravalency

The old dogma of the tetravalency of carbon, a cornerstone of structural organic chemistry since the days of

Press Release: The 1994 Nobel Prize in Chemistry 1994

Also since it has only one lanthanoid/cerium, which itself is usually removed due to its potential tetravalency, lanthanum is basically easy to purify.

CreationWiki - Recent changes [en] 2010

Kekule’s conclusion dating back to the 1860’s that carbon cannot bound to more than four atoms of groups, i.e. it cannot exceed tetravalency, was refuted by discoveries obtained at the Institute.

Hydrocarbons for the 21st Century - The Work of the Loker Hydrocarbon Research Institute 1999