Actinide chemistry, covalent bond

The difference in the chemistry of the light and heavy actinides may be rationalized in this way. The early members beyond thorium have unpaired d and / electrons available for forming covalent bonds and hence, for example, they readily form many complex ions and intermetallic compounds. Such ions are soft acids. Beyond americium, the 5/ electrons are not competitive and the closed shell of six 5/5/2 electrons will not be readily available for bonding, so that only those / electrons with /=7/2 are available. These tend to become buried radially as the atomic number increases and hence their divalent ions become relatively hard Lewis acids. These considerations are especially helpful in the region of superactinides because these elements do not have analogs in the known periodic table, where we have deeply buried but loosely bound 5g electrons. 

In both families of elements, the eations are typical hard acids. Their outermost electronic configuration resembles that of the closed-shell systems (e.g., inert gases, alkali, and alkaline-earth cations) as the inner f orbitals are largely or completely unavailable for bond formation. There is evidence for covalent bonding in actinide chemistry in the formation of the actinyl ions, AnOj and AnO in which both f and d orbitals participate in the An-O bonds, but the extent and even the existence of covalency in the bonding of simple An" species is a subject of controversy. The presence of a slight amount of covalency in lanthanide bonds has been attributed to involvement of the lanthanide 6s orbitals rather than of the 4f orbitals (Lewis et al. 1962). Differences in interactions with soft donor atoms have been the basis of a... 

In contrast to the soft ESI ion formation technique, LA/ionization of solids as a means to produce metal cluster ions is a high-energy process that can provide various types of species, generally with strong covalent bonds, such as in oxides or carbides, as opposed to the weaker bonding exhibited in species produced by ESI. Cluster ion chemistry studies with rare earths and actinides have developed a solid history, with metallofullerenes playing an important role. 

Lucanlkova, M., Selucky, R, Rais, J., Grtiner, B., and KvfCalova, M. 2009. Cobalt bis(dicarbollide) ion deri-vates covalently bonded with diglycolyldiamide for lanthanide and actinide extractions. In Book of Abstracts, APSORC 2009-Asia-Pacific Symposium on Radio chemistry, pp. 201-201, Napa, California, U.S.A, November 29-December 4, 2009. 

In the actinide series, therefore, the energies of the 5f 6d, Is, and Ip orbitals are about comparable over a range of atomic numbers (especially U to Am), and since the orbitals also overlap spatially, bonding can involve any or all of them. In the chemistries this situation is indicated by the fact that the actinides are much more prone to complex formation than are the lanthanides, where the bonding is more ionic. The difference from lanthanide chemistry is usually attributed to the contribution of covalent hybrid bonding involving 5/ electrons. 

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