Nickel ionic radius

However, consideration in terms of the ionic radius or the LFSE shows that both factors predict that the maximum stabilities will be associated with nickel(ii) complexes, as opposed to the observed maxima at copper(ii). Can we give a satisfactory explanation for this The data presented above involve Ki values and if we consider the case of 1,2-diaminoethane, these refer to the process in Eq. (8.13). 

Derived from the German word meaning devil s copper, nickel is found predominantly in two isotopic forms, Ni (68% natural abundance) and Ni (26%). Ni exists in four oxidation states, 0, I, II, III, and IV. Ni(II), which is the most common oxidation state, has an ionic radius of —65 pm in the four-coordinate state and —80 pm in the octahedral low-spin state. The Ni(II) aqua cation exhibits a pAa of 9.9. It forms tight complexes with histidine (log Af = 15.9) and, among the first-row transition metals, is second only to Cu(II) in its ability to complex with acidic amino acids (log K( = 6-7 (7). Although Ni(II) is most common, the paramagnetic Ni(I) and Ni(III) states are also attainable. Ni(I), a (P metal, can exist only in the S = state, whereas Ni(lll), a cT ion, can be either S = or S =. ... 

The larger bite angles of the C3-bridged ligands preclude the ligand-exchange equilibrium, the ionic radius of the nickel(II) ion being too small to accommo-... 

In a similar manner, nickel(li) has the correct ionic radius for the bonding cavity of the fourteen-membered ring, tetraazamacrocycle 6.28. The reaction of 6.29 with nickel(n) acetate in the presence of base gives the nickel(n) complex of 6.28 (Fig. 6-28). This is an example of a template reaction that involves a nucleophilic displacement as the ring-formation process. 

Manganese(II) compounds are quite labile the metal shows distinct class (a) character 7 and its ionic radius (defined by the M—H20 distances in Table 1) is large compared with the other first row transition metals. These lead to distinct parallels with magnesium(II) rather than the latter, although there are also significant parallels with octahedral high spin nickel(II). 

Most trace elements have values of D< C 1, simply because they differ substantially either in ionic radius or ionic charge, or both, from the atoms of the major elements they replace in the crystal lattice. Because of this, they are called incompatible. Exceptions are trace elements such as strontium in plagioclase, ytterbium, lutetium, and scandium in garnet, nickel in olivine, and scandium in clinopyroxene. These latter elements acmally fit into their host crystal structures slightly better than the major elements they replace, and they are therefore called compatible. Thus, most chemical elements of the periodic table are trace elements, and most of them are incompatible only a handful are compatible. 

Zinc has a highly concentrated charge in comparison to its relatively small ionic radius (0.65 A) and binds modestly to anions such as carboxylates and phosphates. Its second characteristic is its high affinity for electrons, making it a strong Lewis acid, similar to copper and nickel. However, unlike the other two transition metal ions, it does not show variable valence, which might lead to it being preferred quite simply because it does not introduce the risk of free radical reactions. 

The ionic radius of divalent nickel (Ni + 0.69 A) is similar to that of divalent iron (Fe 0.77 A) and magnesium (Mg 0.71 A). Therefore the three elements substitute for one another in minerals. 

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