The dp π coordination bond in simple compounds and coordination compounds

1) dp π coordination bond in simple compounds

In the H ₂ SO ₄ molecule, the central S atom adopts sp3 hybridization
.
The sp ³ hybrid orbital of S has only 2 single electrons.

The two single-electron sp ³ hybrid orbitals of the S atom and the two OH ligands each form a σ bond, and the central S atom 2 sp ³ hybrid orbitals with electron pairs are coordinated to the two p orbitals of the terminal O Two σ coordination bonds are formed, and the H ₂ SO ₄ molecule has a tetrahedral configuration, as shown in Figure 6-34(a)
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The p orbital of the terminal O in the H ₂ SO ₄ molecule is a hybrid orbital electron pair that accepts S, and needs to be rearranged to vacate a p orbital [Figure 6-34(b)]

The electrons of the p orbital of the terminal O in the H ₂ SO ₄ molecule coordinate to the empty d orbital of the central S atom to form a π bond
.
As shown in Figure 6-34(c), the symmetry of the p orbital and the d orbital are consistent, and they can overlap effectively

Figure 6-34 (a) H ₂ SO ₄ molecular structure and bonding; (b) p-orbital electron rearrangement of end O atom; (c) overlap of p-orbital and d-orbital

H ₃ PO ₂ , H ₃ PO ₃ , H ₃ PO ₄ , P ₄ O ₁₀ , SOCl ₂ , SO ₂ Cl ₂ , HCIO ₂ , HCIO ₃ , HCIO ₄ and many other molecules have dp π coordination bonds
.
That is, the electrons of the central atom are coordinated to the terminal O to form a σ coordination bond, and the electrons of the terminal oxygen p orbital are coordinated to the empty d orbital of the central atom to form a dp π coordination bond

2) dp π coordination bond in coordination compound

In the coordination compound, if there is a double bond in the ligand, there will be a σ coordination bond formed by the coordination of the ligand's electron to the metal hybrid orbital between the center and the ligand, as well as the metal d orbital (unhybridized ) Dp π coordination bond formed by the coordination of the electron to the π* orbital of the ligand
.

In K[Pt(C ₂ H ₄ )Cl ₃ ], the π electrons of the ethylene (C ₂ H ₄ ) bond coordinate to the central Pt ²⁺ empty hybrid orbital to form a σ coordination bond, as shown in Figure 6-35( As shown in a); the d orbital electron of Pt ²⁺ is coordinated to the π* orbital of the ethylene vacancy to form a dp π coordination bond (also called feedback π bond), as shown in Figure 6-35(b)
.

Figure 6-35 Bonding of Pt and C ₂ H ₄ in K[Pt(C ₂ H ₄ )Cl ₃ ]

Similarly, K _.
3 [of Fe (the CN) _.
6 ] in both of the electron CN- of Fe ³⁺ [sigma] bonds with hybrid orbital formed by coordination, also of Fe ³⁺ electrons of the d-orbital of the CN ^- [pi] of *Dp π coordination bond formed by orbital coordination
.
The structure and bonding of Ni(CO) ₄ will be discussed in detail in the chapter "Coordination Compounds"

In the complex formed by the metal and the organic phosphine, there is a dd π coordination bond between the metal M and the P atom (the d electron of M is coordinated to the empty d orbital of the P atom)

Related link: Delocalized π bond