Bent ML2 complexes

ML2 complexes usually adopt a linear (or essentially linear) geometry (see 2.7). Knowledge of the orbital structure for strongly bent ML2 species is therefore useful mainly when one wishes to consider them as fragments in larger complexes. For example, the ethylene)Ni(PR3)2] complex (2-94) can be described in terms of a bent ML2 entity interacting with a molecule of ethylene. 

Starting from the butterfly ML4 fragment previously studied, a bent ML2 fragment may be obtained by removing the ligands L3 andL4 (2-95). 

A coordination number of 1 is rare for stable complexes. The examples that are known involve a very bulky ligand such as the aryl radical, 2,4,6—Ph3C6H2, which forms ML complexes with copper and silver (2-97). The M-L unit can also be considered as a fragment in a complex with a higher coordination number, such as W-CO in the complex [( l -acetylene)3W(CO)] (2-98). 

The orbitals of this fragment can be obtained in different ways, for example, by removing a ligand from a linear ML2 complex (2-99) whose orbitals have already been derived ( 2.7.1). 

The four strictly nonbonding d orbitals of the ML2 complex (Ug and Sg) remain unchanged. The orbital is stabilized by the elimination of 

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Figure 2.16. Derivation of the d-block orbitals for a bent ML2 complex from the d orbitals of a butterfly ML4 complex. The hybrid s-p orbital (2ai) and the metalp orbital (lying above the d block) are also indicated.

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