Nine block metal complexes

High coordination numbers are common in the f block. The didentate chelate ligand 2,4-dioxopentan-3-ido (acac ) forms six-coordinate octahedral complexes with first-row d-block metal ions (like Cr(III), shown at left), but eight or nine coordinate complexes with f-block lanthanide ions (like Eu(III), shown at right). 

The addition of five d orbitals to an s and p set, either as extra orbitals in the second period (the third row) from silicium to chlorine, or as valence orbitals for transition metal complexes is taking into account straightforwardly by raising the dimensions of the block matrices up to nine [60]. However, mixing the d functions added to the valence orbitals of non-metals, for instance sulphur, or keeping them in their primitive form, has not a great importance, because they play just a role of polarization functions in molecular structure calculations using hybridization [61]. 

Formation of these products is rationalized in terms of suprafacial addition of the elements of Pd—Cl to a ring that is opening stereospecifically in a disrotatory mode, with the breaking bond bending away from the metal (dis-out) (equation 326). The absence of rj to rj to rj interconversions between the isomeric complexes is rationalized in terms of a severe steric blocking of the anti (to metal) allylic face of the complex by the nine-membered ring. This is evident from X-ray crystal structure analysis of the mononuclear acetylaceto-nate allylic complex obtained from chloropalladation of the cw-bicyclononane ". ... 

In 1937 English chemist Nevil V. Sidgwick suggested a rule (the octet rule for first-row p-block elements) for complex formation tmder which a metal can acquire ligands until the total number of electrons around it is equal to the number surrounding the next noble gas. This rule was later expanded as the eighteen-electron rule under which a d-block transition metal atom has eighteen electrons in its nine valence orbitals [five n d one (n -I-... 

In the spirit of valence-bond theory, we must construct six hybrid orbitals that point towards the vertices of the octahedron. We must therefore combine just six of the nine valence orbitals of the metal it turns out that these are the s orbital, the three p orbitals, and two of the d orbitals (this hybridisation pattern will be written d sp, see Chapter 2, 2.1.2.3). Three d orbitals are therefore not involved in the hybridisation, and they stay unchanged (5-4). The link with MO theory is plain these are the three nonbonding orbitals of the octahedral tzg block. In a d complex, these three non-hybridized orbitals are doubly occupied. 

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