Covalency Increase or Decrease across the Actinide Series

Does Covalency Increase or Decrease across the Actinide Series  

ThCp ), the a levels of a given irreducible representation are shown. The highest occupied orbitals are indicated by an arrow (except for ThCp. where the t, Cp Jt j-based combination is the HOMO). (From Ref. [16] (http //pubs.rsc.org/en/Content/ ArticleLanding/2010/DT/c000704h). Reproduced by permission of The Royal Society of Chemistry.) 

An(III) value for the early members of the series followed by a sharp increase to AmCpj and a dramatic reduction at CmCp3. Thus, AnCpj and An02 behave similarly, with the peak in the spin density coming one element earlier in the trivalent series, tying in with the large americium 5f contribution to the highest Cp 

These actinide examples raise an interesting, but more general question should enhanced orbital mixing be equated with enhanced covalencyPerturbation theory holds that, to first order, the mixing of molecular orbitals and cpj is governed by the mixing coefficient where 

S j is the overlap between the orbitals and the denominator is the difference in their energies. Thus, large orbital mixings can arise when (p and (pj are close in 

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