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

Os complexos de coordenação exibem geometrias diferentes como o octaédrico, tetraédrico, e planar quadrado, dependendo dos orbitais metálicos participantes nas ligações covalentes coordenadas A Teoria do vínculo de valência, Ou TVV, explica isto com base na hibridização do metal das orbitais s, p e d. A hibridação proporciona orbitais livres de energias equivalentes que pode coordenar para a orbitais de ligantes preenchidos. Consideremos um complexo octaédrico, hexafluorocobalato(III)O íon Co³⁺foi parcialmente preenchido com orbitais 3d⁶ e livres 4s, 4p, e orbitais 4d.Para formar o complexo, os seis orbitais vazios do metal, 4s, 4p, e dois 4d, são hibridizados a seis orbitais sp³d², que estão a apontar para os cantos de um octaedro. Os orbitais híbridos aceitam pares solitários dos seis grupos de fluoretos para formar o complexo paramagnético. No hexamminecobalto(III)os grupos de aminoácidos levam a que os elétrons 3d de cobalto se rearranjem, criando duas orbitais 3d vagas.Estes combinam com as orbitais 4s e 4p para gerar seis orbitais híbridos d²sp³, que depois ligam de forma coordenada aos seis grupos de amoníaco para formar o complexo diamagnético. Agora, consideremos um complexo tetraédrico tetracloroníquel. O íon Ni²⁺tem uma configuração de 3d⁸.Os orbitais 4s e 4p vazios hibridizam para dar quatro orbitais sp³ que apontam para os cantos de um tetraedro. Aqui, quatro pares de elétrons, um de cada grupo de cloretos, ocupam as orbitais híbridas para formar o complexo paramagnético. Finalmente, examinemos um complexo planar quadrado como o tetracloroplatinado.O íon Pt²⁺tem um configuração d⁸. Os grupos clorados forçam os elétrons 3d do metal a se rearranjarem, criando um orbital vago. O orbital vago combina com os 4s e dois orbitais 4p para dar quatro dsp² orbitais híbridos dirigidos aos cantos de uma praça.Ao aceitar os pares de elétrons dos ligantes de cloreto, forma-se o complexo diamagnético. Embora os complexos de coordenação variem nas suas cores e comportamento magnético, TVV não explica os seus espectros eletrônicos e a variação no seu comportamento magnético com a temperatura.

teoria da ligação de valência

Valence Bond Theory

Os compostos e complexos de coordenação apresentam cores, geometrias, e comportamento magnético diferentes, dependendo do átomo/ião metálico e ligandos de que são compostos. Na tentativa de explicar a ligação e estrutura dos complexos de coordenação, Linus Pauling propôs a teoria da ligação de valência, ou TLV, usando os conceitos de hibridização e a sobreposição das orbitais atómicas. Segundo a TLV, o átomo ou ião de metal central (ácido de Lewis) hibridiza para fornecer orbitais vazias de energia adequada. Estas orbitais aceitam pares de eletrões de orbitais de ligandos preenchidas (bases de Lewis) para formar ligações covalentes metal-ligando coordenadas. O tipo de hibridização e o número de orbitais híbridas determinam a geometria do complexo.
<table style="margin-left: auto; margin-right: auto;">
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<td style="color: black; border: 1px solid black; text-align: center;">Geometria</td>
<td style="color: black; border: 1px solid black; text-align: center;"> Hibridização  </td>
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<td style="color: black; border: 1px solid black; text-align: center;">Linear</td>
<td style="color: black; border: 1px solid black; text-align: center;">sp</td>
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<td style="color: black; border: 1px solid black; text-align: center;">Tetraédrica</td>
<td style="color: black; border: 1px solid black; text-align: center;">sp3</td>
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<td style="color: black; border: 1px solid black; text-align: center;"> Quadrada plana </td>
<td style="color: black; border: 1px solid black; text-align: center;">dsp2</td>
</tr>
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<td style="color: black; border: 1px solid black; text-align: center;">Octaédrica</td>
<td style="color: black; border: 1px solid black; text-align: center;"> d2sp3 ou sp3d2 </td>
</tr>
</tbody>
</table>
Em um complexo tetraédrico, três orbitais p vazias e uma orbital s vazia no metal hibridizam para formar quatro orbitais híbridas sp3, que se sobrepõem com as orbitais preenchidas dos ligandos para formar a ligação covalente coordenada. Da mesma forma, seis orbitais híbridas são criados para os complexos octaédricos misturando as orbitais atómicas vazias no ião central de metal (hibridização d2sp3 ou sp3d2). No caso de complexos lineares, a orbital s e a p sobrepõem-se, levando à formação de duas orbitais híbridas sp.
Complexos Orbitais Interiores e Exteriores
A força dos ligandos que se aproximam influencia a hibridização das orbitais atómicas no ião metálico central. Considere o exemplo de um complexo octaédrico como [Co(NH3)6]3+. O ião Co3+ contém seis eletrões nas orbitais 3d e tem as orbitais 4s e 4p vazias. Os ligandos NH3 que chegam, que são ligandos de campo forte, forçam os eletrões 3d não emparelhados a reorganizarem-se e a emparelharem com os outros eletrões 3d. Isto cria duas orbitais 3d vazias, que se combinam com uma orbital 4s e três 4p para formar seis orbitais híbridas d2sp3 equivalentes. As seis orbitais híbridas sobrepõem-se às orbitais atómicas preenchidas dos ligandos de amoníaco para formar o complexo octaédrico. Uma vez que as orbitais interiores d (3d) no metal participam na hibridização, [Co(NH3)6]3+ é um complexo orbital interno. Devido à ausência de eletrões não emparelhados, o complexo é diamagnético, ou denominado complexo de baixo spin.
<img alt="Image1" src="/files/ftp_upload/11460/11460_Image_1.png" style="text-align: center; height: 100px;" />
      Em outro complexo octaédrico como [Co(F)6]3+, uma vez que o ligando de fluoreto é um ligando de campo fraco, os eletrões 3d6 do metal não se rearranjam. Para fornecer orbitais vazias para hibridização, duas das orbitais 4d vazias mais exteriores combinam-se com a orbital 4s e as três 4p para formar seis orbitais híbridas vazias. Uma vez que são utilizadas as orbitais d mais exteriores, a hibridização é referida como hibridização sp3d2, e o complexo é denominado complexo orbital externo. A presença de eletrões não emparelhados torna o complexo paramagnético, e, por conseguinte, estes complexos são também conhecidos como complexos de alto spin.
<img alt="Image2" src="/files/ftp_upload/11460/11460_Image_2.png" style="text-align: center; height: 100px;" />
Os complexos orbitais externos ou de alto spin são mais lábeis e menos estáveis (devido às energias mais elevadas das orbitais sp3d2) em comparação com os complexos orbitais internos ou de baixo spin.

Teoria da Ligação de Valência

Compostos e complexos de coordenação exibem diferentes cores, geometrias e comportamento magnético, dependendo do átomo/íon metálico e dos ligantes dos quais ...

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Transition Metals and Coordination Complexes

Metais de Transição e Complexos de Coordenação

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KEY TERMS AND CONCEPTS

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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

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Metal Ligand Bonds in Coordination Complexes

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