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The complexes formed by transition metals and ligands containing π electrons such as carboxyl, cyanide, alkene, etc.
often contain dp π coordination bonds (feedback bonds)
.
For example, in the carbon complex [Ni(CO) 4 ], the electronic configuration of Ni is 3d 8 4s 2 4p 0 , which is rearranged to 3d 10 4s 0 4p 0 , and the center adopts sp 3 hybridization.
The lone electrons are aligned to the sp 3 hybrid empty orbital in the center to form
.
Coordination bond, the configuration of the complex is a regular tetrahedron
The d orbital of the transition metal Ni is similar to the π* (π anti-bonding orbital) energy of CO, the symmetry is the same, and the bond can be formed
.
According to the symmetry of the overlapped orbitals, the metal d orbital overlaps the CO π* orbital to form a π bond; and when the bond is formed, the metal d orbital provides electrons and the CO π* orbital accepts electrons, so the formation is a coordination Bit key
Figure 9-6 Schematic diagram of dp-π coordination bond in [Ni(CO) 4 ]
The ligand CN- is similar to CO.
It has both a solitary electron pair that can be coordinated, and a π* orbital that is consistent with the symmetry of the d orbital to accept the coordination of d electrons
The bonding of the coordination unit [PtC1 3 (C 2 H 4 ) - ] in Zeise salt K[PtCl 3 (C 2 H 4 )]·H 2 O can be described as the bonding π electrons of ethylene to platinum The hybrid orbital coordination of Pt 2+ forms a σ coordination bond; the electrons of the d orbital of Pt 2+ coordinate to the π* orbital of ethylene to form a dp π coordination bond, as shown in Figure 9-7 .
Figure 9-7 Schematic diagram of bonding between platinum and ethylene