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

Coördinatiecomplexen vertonen verschillende geometrieën zoals octaëdrische, tetraëdrische en vierkante planaire, afhankelijk van de metalen orbitalen die deelnemen aan de gecoördineerde covalente bindingen. Valentiebindingstheorie, of VBT, legt dit uit op basis van de hybridisatie van s-p-en d-orbitalen door het metaal. Hybridisatie biedt lege orbitalen met gelijkwaardige energieën die kunnen coördineren met de gevulde ligand-orbitalen.Denk aan een octaëdrisch complex, hexafluorkobaltaat(III)Het Co³⁺ion heeft gedeeltelijk gevulde 3d⁶ orbitalen en lege 4s, 4p en 4d orbitalen. Om het complex te vormen, worden de zes lege orbitalen van het metaal, 4s, 4p en twee 4d, gehybridiseerd tot zes sp³d² orbitalen, die naar de hoeken van een octaëder wijzen. De hybride orbitalen accepteren vrije paren van de zes fluoridegroepen om het paramagnetische complex te vormen.In het hexamminekobalt(III)zorgen de aminogroepen ervoor dat de 3d elektronen van kobalt zich herschikken, waardoor twee lege 3d orbitalen ontstaan. Deze combineren met de 4s en 4p orbitalen om zes d²sp³ hybride orbitalen te genereren, die vervolgens gecoördineerd binden aan de zes ammoniakgroepen om het diamagnetische complex te vormen. Overweeg nu een tetraëdrisch complex tetrachloornikkelaat.Ni²⁺ion heeft een 3d⁸-configuratie. De lege 4s en 4p orbitalen hybridiseren om vier sp³ orbitalen te geven die naar de hoeken van een tetraëder wijzen. Hier bezetten vier paar elektronen, één uit elke chloridegroep, de hybride orbitalen om het paramagnetische complex te vormen.Onderzoek ten slotte een vierkant vlak complex zoals tetrachloroplatinaat. De Pt²⁺ion heeft een d⁸-configuratie. De chloridegroepen dwingen de 3d elektronen van het metaal om zich te herschikken, waardoor een lege orbitaal ontstaat.De lege orbitaal combineert met de 4s en twee 4p orbitalen om vier dsp² hybride orbitalen te geven die naar de hoeken van een vierkant zijn gericht. Bij acceptatie van de elektronenparen van de chlorideliganden wordt het diamagnetische complex gevormd. Hoewel de coördinatiecomplexen variëren in hun kleuren en magnetisch gedrag, verklaart VBT hun elektronische spectra en de variatie in hun magnetisch gedrag met temperatuur niet.

valentiebindingstheorie

Valence Bond Theory

Coördinatieverbindingen en -complexen vertonen verschillende kleuren, geometrieën en magnetisch gedrag, afhankelijk van het metaalatoom/ion en de liganden waaruit ze zijn samengesteld. In een poging de binding en structuur van coördinatiecomplexen te verklaren, stelde Linus Pauling de valentiebindingstheorie, of VBT, voor, waarbij hij de concepten van hybridisatie en de overlapping van de atomaire orbitalen gebruikte. Volgens VBT hybridiseert het centrale metaalatoom of ion (Lewiszuur) om lege orbitalen met geschikte energie te verschaffen. Deze orbitalen accepteren elektronenparen van gevulde ligand-orbitalen (Lewis-bases) om gecoördineerde covalente metaal-ligand-bindingen te vormen. Het type hybridisatie en het aantal hybride orbitalen bepalen de geometrie van het complex. 
 <table style="margin-left: auto; margin-right: auto;"> 
 	<tbody> 
 		<tr> 
 			<td style="color: black; border: 1px solid black; text-align: center;">Geometry</td> 
 			<td style="color: black; border: 1px solid black; text-align: center;"> Hybridization  </td> 
 		</tr> 
 		<tr> 
 			<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> 
 		</tr> 
 		<tr> 
 			<td style="color: black; border: 1px solid black; text-align: center;">Tetrahedral</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;"> Square planar </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;">Octahedral</td> 
 			<td style="color: black; border: 1px solid black; text-align: center;"> d2sp3 or sp3d2 </td> 
 		</tr> 
 	</tbody> 
 </table> 
 In een tetraëdrische complex hybridiseren drie lege p-orbitalen en één lege s-orbitaal op het metaal om vier sp3-hybride orbitalen te vormen, die overlappen met de gevulde ligand-orbitalen om de covalente coördinaatbinding te vormen. Op dezelfde manier worden zes hybride orbitalen gemaakt voor de octaëdrische complexen door de lege atomaire orbitalen op het centrale metaalion (d2sp3 of sp3d2 hybridisatie). In het geval van lineaire complexen overlappen de one s- en one p-orbitalen elkaar, wat leidt tot de vorming van twee sp-hybride orbitalen. 

 Binnenste en buitenste orbitale complexen 

 De sterkte van de naderende liganden beïnvloedt de hybridisatie van de atomaire orbitalen op het centrale metaalion. Beschouw het voorbeeld van een octaëdrische complex zoals [Co(NH3)6]3+. Het Co3+-ion bevat zes elektronen in de 3d-orbitalen en heeft lege 4s- en 4p-orbitalen. De binnenkomende NH3-liganden, die sterke veldliganden zijn, dwingen de ongepaarde 3D-elektronen om zich te herschikken en te paren met de andere 3D-elektronen. Hierdoor ontstaan twee lege 3D-orbitalen, die gecombineerd met één 4s- en drie 4p-orbitalen zes gelijkwaardige d2sp3-hybride orbitalen vormen. De zes hybride orbitalen overlappen met de gevulde atomaire orbitalen van de ammoniakliganden en vormen het octaëdrische complex. Omdat de binnenste d(3d)-orbitalen op het metaal deelnemen aan hybridisatie, is [Co(NH3)6]3+ een binnenste orbitaalcomplex. Door de afwezigheid van ongepaarde elektronen is het complex diamagnetisch, ook wel een low-spin-complex genoemd. 

 <img alt="Image1" src="/files/ftp_upload/11460/11460_Image_1.png" style="text-align: center; height: 100px;"> 

 In een ander octaëdrische complex zoals [Co(F)6]3+, herschikken de 3d6-elektronen van het metaal niet, omdat de fluorideligand een zwak veldligand is. Om lege orbitalen voor hybridisatie te verschaffen, combineren twee van de buitenste lege 4d-orbitalen met de ene 4s- en drie 4p-orbitalen om zes lege hybride orbitalen te vormen. Omdat de buitenste d-orbitalen worden gebruikt, wordt de hybridisatie sp3d2-hybridisatie genoemd, en wordt het complex een buitenste orbitaalcomplex genoemd. De aanwezigheid van ongepaarde elektronen maakt het complex paramagnetisch, en daarom worden deze complexen ook wel hoge-spincomplexen genoemd. 

 <img alt="Image2" src="/files/ftp_upload/11460/11460_Image_2.png" style="text-align: center; height: 100px;"> 

 Complexen met hoge spin of buitenste orbitalen zijn labieler en minder stabiel (vanwege de hogere energieën van sp3d2-orbitalen) vergeleken met complexen met lage spin of binnenste orbitalen.

Valentiebindingstheorie

Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which ...

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Transition Metals and Coordination Complexes

Overgangsmetalen en coördinatiecomplexen

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KEY TERMS AND CONCEPTS

BELANGRIJKE TERMEN EN CONCEPTEN

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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