Oxidation states actinoids

The rules above gave maximum and minimum oxidation numbers, but those might not be the only oxidation numbers or even the most important oxidation numbers for an element. Elements of the last six groups of the periodic table for example may have several oxidation numbers in their compounds, most of which vary from each other in steps of 2. For example, the major oxidation states of chlorine in its compounds are -1, +1, +3, +5, and +7. The transition metals have oxidation numbers that may vary from each other in steps of 1. The inner transition elements mostly form oxidation states of + 3, but the first part of the actinoid series acts more like transition elements and the elements have... 

Table 18.1 presents the electronic structures of the actinoids along with their major aqueous oxidation states. The structures of the M" ", and M" " ... 

The members of the actinoids have a somewhat greater tendency to form complexes than those of the lanthanoids. They also show a wider variety of complexes due to their more numerous oxidation states. The cations of the actinoids display coordination numbers which are often greater than 6. Although not many data are available, M02+ and M02" " ions attach 5 or 6 HOH molecules giving the central atom a coordination number of 7 or 8, and the and ions attach 9 or 10 HOH molecules. The coordination numbers with ligands other than HOH are often of these magnitudes, but sometimes may be somewhat smaller. 

Table 24.2 shows that a wide range of oxidation states is exhibited by the earlier actinoids, but from Cm to Lr, the elements resemble the lanthanoids. This follows from the lowering in energy of the 5/ atomic orbitals on crossing the period and the stabilization of the 5/ electrons. 

Table 24.2 Oxidation states of actinium and the actinoids. The most stable states are shown in red.

The valence shell of a lanthanoid element contains 4/ orbitals and that of an actinoid, 5/ atomic orbitals. The ground state electronic configurations of the /-block elements are listed in Table 27.1. A 4/ atomic orbital has no radial node, whereas a 5/ atomic orbital has one radial node (see Section 1.6). A cmcial difference between the 4/ and 5/orbitals is the fact that the 4/ atomic orbitals are deeply buried and 4/electrons are not available for covalent bonding. Usually for a lanthanoid metal, M, ionization beyond the M ion is not energetically possible. This leads to a characteristic +3 oxidation state across the whole row from La to Lu. 

In the 5f series some of the distinctively f-subshell chemical behavior arises later, with U, leading to the term uranoid , especially for elements 92-95, which, unlike the other actinoids in the same period, have six (VI) as an important oxidation state in water. We may refer to the higher-Z actinoids, with 111 as the more characteristic oxidation state, as post-uranoids . Nature is clever in complicating our task by precluding full consistency and simplicity in any periodic chart. 

See the general references in the Introduction, and some more-speciahzed books [4, 6-58], Some articles in journals discuss actinide complexation and thermodynamics at elevated temperatures [59] classifying lanthanoids by multivariate analysis, albeit with results that seem hard to defend [60] designing sequestering agents for Pu and other actinoids [61] lanthanoid compounds with complex inorganic anions, part of a thematic issue on lanthanoid chemistry [62] Pm, discovery and chemistiy [63] recent Sc chemistiy [64] actinoid complexes [65] the transuranium elements [66] actinoid complexes with OH and [67] coordination numbers [68] the aqueous chemistiy and thermodynamics of Eu [69] photooxidation-reduction of Np and Pu [70] review of Pm [71] Rth thermochemistiy [72] unusual oxidation states of Ln and An [73] and Rth chemistiy [74]. 

In the only isolated example of actinoid NHC-ligated compounds, namely uranium complexes, the NHC-U bond lengths were in the range of lanthanoid compounds. The few reported NMR spectra exhibited extremely downfield-shifted carbene resonances. Direct comparison to NHC-lanthanoid complexes was not straightforward, due to the different oxidation states, but, for instance, compound [(NHC)2U02] 25 showed a Ccarbene resonance at 262.8 ppm and the saturated examples 45 and 46 at 281.6 ppm and 283.6 ppm (Figure 6.5). ... 

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