Size of Transition 3d-Metal Ions

Variation with Z of the size of di- and trivalent 3d cations in MO oxides of an NaCl-type lattice presents a maximum for the configuration and two minimums for the d configurations (V +, Cr +), and d configurations (Ni - ). 

In a strong field, the radii of and ions decreases with Z up to the configuration t2g . At that configuration, there is an increase with stepwise occupation of Cg orbitals being more influenced by the repulsing interaction with the anionic ligands. 

Hydration enthalpy is extrapolated to infinite dilution when a metal ion coordinates only six water molecules forming hexaaquacomplexes of type [M(H20)g] +. 

FIGURE 3.10 Size of transition 3d-metal ions ( low spin A high spin). (Data from J.E. Huheey, E.A. Keiter, and R.L. Keiter, Inorganic Chemistry Principles of Structure and Reactivity, d edition [New York Harper Collins, 1993].) 

Hydration enthalpies are closely related to formation enthalpies of octahedral aqua complexes. Because the water molecule is a weak ligand, the resulting configurations are of the high-spin type. 

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