Interatomic distances in transition metal compounds

One property of a transition metal ion that is particularly sensitive to crystal field interactions is the ionic radius and its influence on interatomic distances in a crystal structure. Within a row of elements in the periodic table in which cations possess completely filled or efficiently screened inner orbitals, there should be a decrease of interatomic distances with increasing atomic number for cations possessing the same valence. The ionic radii of trivalent cations of the lanthanide series for example, plotted in fig. 6.1, show a relatively smooth contraction from lanthanum to lutecium. Such a trend is determined by the 

Cations of the first transition series do not conform to the smooth pattern for the lanthanide elements shown in fig. 6.1. This is illustrated in fig. 6.2a by the radii of divalent cations in oxides containing transition metal ions in high-spin states. There is an overall decrease of octahedral ionic radius from Ca2+to Zn2+, but values first decrease to V2+, then rise to Mn2+, decrease to Ni2+, and rise again to Zn2+. The characteristic double-humped curve shown in fig. 6.2a has 

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