Ligands and Complex Formation | 配体与配合物形成

📚 Ligands and Complex Formation | 配体与配合物形成

Transition metals and many other metal ions can accept pairs of electrons from surrounding molecules or ions to form coordination compounds. These species, called complex ions, play a central role in A-Level Chemistry through precipitation, ligand substitution, redox, and colour changes. Understanding ligands and complex formation helps explain the structure, shape, colour, and stability of transition metal compounds.

过渡金属和许多其他金属离子可以接受周围分子或离子提供的电子对，形成配位化合物。这些物种称为配离子，在A-Level化学中通过沉淀、配体取代、氧化还原和颜色变化等内容占有核心地位。理解配体与配合物的形成有助于解释过渡金属化合物的结构、空间构型、颜色和稳定性。

1. What is a complex ion? | 什么是配离子？

A complex ion consists of a central metal ion surrounded by ligands that are bonded through coordinate bonds. The central ion is usually a transition metal cation such as Cu²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, or Cr³⁺. The entire species may be positive, negative, or neutral; for example, [Cu(H₂O)₆]²⁺ is a complex cation, [CuCl₄]²⁻ is a complex anion, and [Ni(CO)₄] is neutral.

配离子由一个中心金属离子和通过配位键结合的配体组成。中心离子通常是过渡金属阳离子，例如 Cu²⁺、Fe²⁺、Fe³⁺、Co²⁺、Ni²⁺ 或 Cr³⁺。整个物种可能带正电、负电或呈中性；例如 [Cu(H₂O)₆]²⁺ 是配阳离子，[CuCl₄]²⁻ 是配阴离子，[Ni(CO)₄] 是中性配合物。

The charge on a complex ion is the sum of the oxidation state of the central metal ion and the charges on all ligands. For [Cu(H₂O)₆]²⁺, Cu is in the +2 state and water ligands are neutral, giving an overall +2 charge.

配离子的电荷等于中心金属离子的氧化态与所有配体电荷之和。对于 [Cu(H₂O)₆]²⁺，Cu 为 +2 态，水配体为中性，因此总电荷为 +2。

2. What is a ligand? | 什么是配体？

A ligand is a molecule or ion that donates at least one lone pair of electrons to a central metal ion to form a coordinate bond. Ligands are Lewis bases because they donate electron pairs; metal ions are Lewis acids because they accept electron pairs.

配体是能够提供至少一对孤对电子给中心金属离子形成配位键的分子或离子。配体是路易斯碱，因为它们提供电子对；金属离子是路易斯酸，因为它们接受电子对。

The atom in the ligand that directly binds to the metal is called the donor atom. Common donor atoms are oxygen, nitrogen, chlorine, and carbon. Water uses oxygen, ammonia uses nitrogen, chloride uses chlorine, and cyanide uses carbon.

配体中直接与金属结合的原子称为供体原子。常见的供体原子有氧、氮、氯和碳。水以氧为供体，氨以氮为供体，氯离子以氯为供体，氰根以碳为供体。

3. Coordinate (dative covalent) bonding | 配位键（配位共价键）

A coordinate bond, also called a dative covalent bond, is a covalent bond in which both shared electrons come from one atom, the ligand donor atom. Once formed, a coordinate bond is identical in strength and length to an ordinary covalent bond.

配位键，也称为配位共价键，是一种共价键，其中共享的两个电子都来自同一个原子，即配体的供体原子。一旦形成，配位键的强度和键长与普通共价键相同。

For example, in [Cu(H₂O)₆]²⁺, each oxygen atom in six water molecules donates a lone pair into an empty orbital of Cu²⁺. The bond can be shown as H₂O:→Cu²⁺ or H₂O→Cu²⁺. The arrow starts at the donor atom and points to the metal ion.

例如，在 [Cu(H₂O)₆]²⁺ 中，六个水分子中的氧原子各提供一对孤对电子进入 Cu²⁺ 的空轨道。该键可表示为 H₂O:→Cu²⁺ 或 H₂O→Cu²⁺。箭头从供体原子出发指向金属离子。

4. Monodentate ligands and common examples | 单齿配体及常见例子

A monodentate ligand binds through only one donor atom. Common monodentate ligands include water (H₂O:

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