Name: metal ligand bonds in coordination complexes
Uploaded: 2020-09-24T15:06:53.000Z
Duration: 2 min 42 s
Channel: JoVE

根据参与配位共价键的金属轨道，配位络合物表现出不同的几何形状，例如八面体、四面体和 平面正方形。价键理论，或简称 VBT，根据金属 s、p、d 轨道的杂化 来解释这一现象。杂化提供了可以与已填满的配体轨道配合的 能量相等的空轨道。请考虑八面体络合物六氟钴酸盐(III)Co³⁺离子已经部分填充了 3d⁶ 轨道和空的 4s、4P 和 4d 轨道。为了形成络合物，金属的六个空轨道，4S、4p 和两个 4d，与六个 sp³d² 轨道杂交，这六个轨道指向八面体的角。杂化轨道接受来自 6 个氟化物基团的孤对电子，形成顺磁性络合物。在六氨合钴(III)中，氨基会导致钴的 3d 电子重排，产生两个空 3d 轨道。它们与 4s 和 4p 轨道结合，产生六个 d²sp³ 杂化轨道，然后与 6 个氨基团配位，形成抗磁性络合物。现在，请考虑四面体络合物-四氯镍酸盐。Ni²⁺离子具有 3d⁸ 构型。4s 和 4p 空轨道杂化，形成四个指向四面体角 的 sp³ 轨道。这里，有四对电子，每个氯化物基团一对，占据了杂化轨道，形成顺磁性络合物。最后，我们来观察正方形平面络合物，例如四氯铂酸盐。Pt²⁺离子具有 d⁸ 构型。氯化物基团迫使金属的 3d 电子重排，形成一个空轨道。这个空轨道与 4s 轨道和两个 4p 轨道结合，形成四个 dsp² 杂化轨道，指向正方形的角。当接受来自氯化物配体的电子对时，形成抗磁性络合物。尽管配位络合物的 颜色和磁行为不同，但 VBT 不能解释 它们的电子光谱以及 磁行为随温度的变化。

价键理论

Valence Bond Theory

配位化合物和复合物具有不同的颜色，几何结构和磁性行为，具体取决于它们所组成的金属原子 / 离子和配体。 为了解释键和协调波群的结构， 莱纳斯·鲍林（Linus Pauling） 使用杂化方式的概念和原子轨道的重叠，提出了价键理论，即 VBT。 根据 VBT ，中心金属原子或离子 (路易斯酸) 杂交以提供空轨道合适的能量。 这些轨道接受来自填充配体轨道 (路易斯碱) 的电子对形成配位共价金属配体键。 杂化方式的类型和杂化轨道的数量决定了复数的几何结构。 
 <table style="margin-left: auto; margin-right: auto;">
 <tbody>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">几何结构 </td>
 <td style="color: black; border: 1px solid black; text-align: center;"> 杂化方式   </td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">线性 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">SP </td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">四面体 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">SP3 </td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;"> 平面四边形  </td>
 <td style="color: black; border: 1px solid black; text-align: center;">dsp2. </td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">八面体 </td>
 <td style="color: black; border: 1px solid black; text-align: center;"> d2sp3 或 sp3d2  </td>
 </tr>
 </tbody>
 </table>
 在四面体综合体中，金属杂化上有三个空缺的 p 轨道和一个空缺的 s 轨道组成四个 SP3 杂化轨道，它们与填充的配体轨道重叠，形成共价配位键。 同样，通过混合中央金属离子 (d2sp3 或 sp3d2 杂化方式) 上的空原子轨道，为八面体络合物创建了六个杂化轨道。 对于线性复合波， 1 s 和 1 p 轨道重叠，导致形成两个 sp 杂化轨道。 
 内部和外部轨道波群 
 临近配体的强度会影响原子轨道的杂化方式对中心金属离子的影响。 考虑八面体复合物 (如 [Co (NH3) 6]3+) 的示例。 CO3+ 离子在 3D 轨道中含有六个电子，并且有四路和四路轨道空闲。 传入的 NH3 配体是强磁场配体，它可以力这些未配对的 3D 电子，以重新排列并与其他 3D 电子配对。 这将创建两个空的 3D 轨道，它与一个 4S 和三个 4p 轨道相结合，形成六个等效的 d2sp3 杂化轨道。 六个杂化轨道与氨配体的填充原子轨道重叠，形成八面体复合物。 由于金属上的内径 (3D) 轨道参与了杂化方式， [Co (NH3) 6]3+ 是一个内径轨道复合物。 由于没有未配对的电子，该复合物为二磁体，或称为低自旋复合物。 
 <img alt="Image1" src="/files/ftp_upload/11460/11460_Image_1.png" style="text-align: center; height: 100px;" />
      在另一个八面体 (如 [Co (F) 6]3+) 中，由于氟化配体是弱场配体，金属的 3d6 电子不会重新排列。 为了为杂化方式提供空轨道，两个最外空的 4D 轨道与一个 4s 和三个 4p 轨道相结合，形成六个空杂化轨道。 由于使用了最外层的轨道，杂化方式被称为 sp3d2 杂化方式，而该组合体被称为外部轨道组合体。 未配对电子的存在使复杂的准磁性，因此这些复合波也称为高自旋复合波。 
 <img alt="Image2" src="/files/ftp_upload/11460/11460_Image_2.png" style="text-align: center; height: 100px;" />
 与 低自旋或内部轨道波群相比，高自旋或外部轨道波群的稳定性更高 (由于 sp3d2 轨道的能量更高)。

配位化合物和配合物因所含金属原子/离子及配体的不同，表现出不同的颜色、几何构型和磁性行为。

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教育

JoVE Core

Chemistry

化学

Transition Metals and Coordination Complexes

过渡金属与配位化合物

transition-metals-and-coordination-complexes

KEY TERMS AND CONCEPTS

关键术语与概念

metal ligand bonds in coordination complexes

Coordination complexes form metal-ligand bonds through valence bond theory. In this model, Linus Pauling explained bonding with hybridization and overlap of atomic orbitals. The central metal atom or ion acts as a Lewis acid. It uses empty orbitals of suitable energy to accept electron pairs from ligands, which act as Lewis bases. These coordinate covalent bonds help explain the color, geometry, and magnetic behavior seen in coordination compounds.

The type of hybridization helps determine the shape of the complex. A linear complex uses sp hybridization. A tetrahedral complex uses sp3 hybridization. A square planar complex uses dsp2 hybridization. Octahedral complexes use either d2sp3 or sp3d2 hybridization. In a tetrahedral complex, three vacant p orbitals and one vacant s orbital on the metal mix to make four sp3 hybrid orbitals. These overlap with filled ligand orbitals to form the bond. In a linear complex, one s orbital and one p orbital overlap to form two sp hybrid orbitals. Octahedral complexes form six hybrid orbitals from the vacant orbitals on the metal ion.

Ligand strength can change which orbitals the metal uses. A strong field ligand can force electrons to pair up, while a weak field ligand may not. The octahedral complex [Co(NH3)6]3+ is a good example. The Co3+ ion has six electrons in the 3d orbitals and vacant 4s and 4p orbitals. The NH3 ligands are strong field ligands, so the unpaired 3d electrons rearrange and pair. This creates two vacant 3d orbitals. These join with one 4s orbital and three 4p orbitals to make six d2sp3 hybrid orbitals. The ammonia ligands then overlap with these orbitals to form the octahedral complex.

Because the inner 3d orbitals take part in hybridization, [Co(NH3)6]3+ is an inner orbital complex. It has no unpaired electrons, so it is diamagnetic. It is also called a low spin complex. A similar octahedral complex, [Co(F)6]3+, behaves differently because fluoride is a weak field ligand. In that case, the 3d6 electrons do not rearrange. Two outer 4d orbitals combine with one 4s and three 4p orbitals to form six sp3d2 hybrid orbitals. Since outer d orbitals are used, this is an outer orbital complex. The unpaired electrons make it paramagnetic, so it is a high spin complex. High spin, or outer orbital, complexes are also more labile and less stable than low spin, inner orbital complexes.

Metal Ligand Bonds in Coordination Complexes

metal-ligand-bonds-in-coordination-complexes

properties of transition metals

Transition Metals in the Periodic Table

Transition metals are the d-block elements and the inner transition metals in the f-block. They are defined by partially filled d orbitals. In the periodic table, the transition elements are in groups 3 through 11, and the inner transition metals appear in the two rows below the main body of the table. The d-block is often grouped into transition series. The first transition series runs from Sc through Cu. The second series runs from Y through Ag. The third series includes La and Hf through...

coordination compounds and nomenclature

How Transition Metal Complexes Are Named

Transition metal complexes are named by following rules for ligands, metal ions, and oxidation state. These compounds form when a central metal ion or atom, often a transition metal or inner transition metal, accepts electron pairs from ligands. A ligand is a Lewis base that can be an atom, molecule, or ion with one or more lone pairs to donate. In these complexes, the bond is a coordinate covalent bond. That means both electrons in the bond come from the donor, such as ammonia, and are...

metal-ligand bonds

Coordination Complexes and Chelation

Coordination complexes form when a metal ion bonds to ligands. These compounds appear in familiar examples such as hemoglobin in blood, chlorophyll in green plants, vitamin B-12, and the catalyst used to make polyethylene. Transition metal ions are especially likely to form these complexes. In a coordination complex, the metal acts as a Lewis acid. The ligand acts as a Lewis base and donates both electrons in the coordinate covalent bond. A ligand can be an atom, molecule, or ion, as long as...

coordination number and geometry

Transition Metal Shapes from Coordination Number

Transition metal complexes are often identified by their coordination number and the shape around the metal ion. The coordination number is the number of donor atoms bonded to the central metal. In many complexes, the most common shapes are octahedral, tetrahedral, and square planar. Coordination number and molecular geometry are linked in a clear pattern. A coordination number of 2 gives a linear shape, as in [Ag(NH3)2]+. A coordination number of 3 gives a trigonal planar shape, as in...

structural isomerism

Linkage and Ionization Isomers

Isomers are different chemical species that share the same chemical formula. In coordination compounds, structural isomerism includes linkage isomers and coordination-sphere isomers. These two forms show how the same atoms can be arranged in different ways around a metal center. Linkage isomers form when a ligand can attach to a transition metal through two different atoms. The cyanide ligand, CN−, can bind through carbon or nitrogen. The thiocyanate ligand, SCN−, can bind through sulfur or...

stereoisomerism

Isomer Shapes in Coordination Complexes

Isomer shapes in coordination complexes can change a compound’s properties even when the chemical formula stays the same. Isomers are different chemical species with the same formula. In transition metal complexes, the atoms stay connected through the same types of bonds, but their arrangement in space can differ. One common form is geometric isomerism. In these complexes, ligands (the ions or molecules attached to the metal) can sit in cis or trans positions. The octahedral [Co(NH3)4Cl2]+ ion...

valence bond theory

Coordination complexes form metal-ligand bonds through valence bond theory. In this model, Linus Pauling explained bonding with hybridization and overlap of atomic orbitals. The central metal atom or ion acts as a Lewis acid. It uses empty orbitals of suitable energy to accept electron pairs from ligands, which act as Lewis bases. These coordinate covalent bonds help explain the color, geometry, and magnetic behavior seen in coordination compounds. The type of hybridization helps determine the...

crystal field theory - octahedral complexes

crystal-field-theory-octahedral-complexes

Octahedral d-Orbital Splitting in Crystal Fields

Crystal field theory explains how ligands affect the d orbitals in transition metal complexes. This electrostatic model helps predict the colors, magnetic behavior, and some structures of coordination compounds. It focuses on the nonbonding electrons on the central metal ion, not on the metal-ligand bonds. In crystal field theory, the metal ion and ligands are treated as very small point charges. Because electrons are negative, electrons donated by the ligands repel the electrons in the...

crystal field theory - tetrahedral and square planar complexes

crystal-field-theory-tetrahedral-and-square-planar-complexes

Crystal Field Splitting in Non-Octahedral Shapes

Crystal field theory also explains d orbital splitting in tetrahedral and square planar complexes. These shapes do not follow the same pattern as an octahedral complex, so the d orbitals respond to ligand placement in different ways. In tetrahedral complexes, the four ligands sit between the axes. None of the d orbitals points directly at the ligands, but the d x2−y2 and d z2 orbitals lie along the Cartesian axes and overlap less with the ligands than the d xy, d xz, and d yz orbitals. The d...

colors and magnetism

Color and Spin in Coordination Complexes

Color in coordination complexes comes from how metal electrons absorb light. When atoms or molecules absorb light at the right frequency, electrons move to higher-energy orbitals. For many main-group atoms and molecules, the absorbed light is ultraviolet and cannot be seen. In coordination compounds, the energy gap between d orbitals often matches visible light, so the compound can absorb and emit colors that the human eye detects. Small changes in orbital energy can cause large shifts in the...

key terms and concepts

Learn how valence bond theory explains metal-ligand bonding, hybridization, complex shape, and the difference between inner and outer orbital complexes.

Metal Ligand Bonds in Coordination Complexes | JoVE K12

chemistry

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Metal Ligand Bonds in Coordination Complexes

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