Name: crystal field splitting in non-octahedral shapes
Uploaded: 2020-09-24T15:06:53.000Z
Duration: 2 min 46 s
Channel: JoVE

Kristal alan teorisi, bu teorinin oktahedral komplekslerde uygulanmasına benzer bir şekilde dört yüzlü ve kare düzlemsel geçiş metal komplekslerini modellemek için kullanılabilir. Örneğin, dört yüzlü tetrakloronikelat iyonunu modellemek için, her bir klorür ligandının yerini bir negatif nokta yükü alır ve bu da bir tetrahedral kristal alanı ile sonuçlanır. Bu alanın etkisinden dolayı, dxy, dyz ve dxz orbitalleri, enerji açısından dx² y² ve dz² orbitallerinden daha yüksektir.Bu, tetrahedral kristal alanı ile dxy, dyz ve dxz orbitalleri arasındaki daha güçlü etkileşime atfedilir. Daha yüksek enerjili orbitaller t₂ simetrisine sahiptir ve t₂ seti olarak anılırken, düşük enerjili orbitaller e simetrisine sahiptir ve e setini içerir. Oktahedral komplekslerdeki d orbitallerinin bölünmesine kıyasla, tetrahedral komplekslerdeki orbitallerin göreceli enerjileri tersine çevrilir ve kristal alan bölme enerjisi veya Δtet daha düşüktür.Tetrasiyanonikelat iyonu gibi kare düzlemsel komplekslerde, tüm ligandlar xy düzleminde bulunur. Burada, siyanür ligandlarının negatif nokta yükleriyle değiştirilmesiyle kare düzlemsel bir kristal alan elde edilir. Bu alanın etkisi altında, metal iyonunun d orbitalleri dört farklı enerji seviyesine ayrılır.Burada, dx² y² orbitali en yüksek enerjili orbitaldir ve lobları doğrudan ligand yüklerine dönüktür. Dxy orbital, ligand yükleriyle aynı düzlemde yatan loblarla bir sonraki enerji içindedir. Dz² orbitalinin enerjisi daha düşüktür ve xy düzlemindeki dz² orbitali ile kristal alan arasındaki küçük bir örtüşmeye atfedilir.Orbitallerin en düşük enerji kümesi olan dxz ve dyz, kristal alanla nispeten minimum etkileşime sahiptir. Kare düzlemsel komplekslerde enerji ayıran kristal alan veya Δsp, en yüksek enerjili orbital, dx² y² ve en düşük enerjili orbitaller, dyz ve dxz arasındaki enerji farkı olarak tanımlanır. Tüm kompleksler için aynı metal iyonu ve ligand molekülleri varsayıldığında, Δtet, Δsp ve Δoct oranı 0, 44:1, 7:1'dir.

kristal alan teorisi - tetrahedral ve kare düzlemsel kompleksler

Crystal Field Theory - Tetrahedral and Square Planar Complexes

Tetrahedral Kompleksler 
 
 Kristal alan teorisi (CFT), oktahedral dışındaki geometrilerdeki moleküller için geçerlidir. Oktahedral komplekslerde, dx2−y2 ve dz2 orbitallerinin lobları doğrudan ligandlara işaret eder. Tetrahedral kompleksler için, d orbitalleri yerinde kalır, ancak eksenler arasında sadece dört ligand bulunur. Orbitallerin hiçbiri doğrudan tetrahedral ligandlara işaret etmez. Bununla birlikte, dx2−y2 ve dz2 orbitalleri (Kartezyen eksenler boyunca) dxy, dxz ve dyz orbitallerinden daha az ligandlarla örtüşür. Oktahedral duruma benzer şekilde, bir tetrahedral kristal alanındaki d orbitalleri için enerji diyagramı, Şekil 1'de gösterildiği gibi tahmin edilebilir. Karışıklığı önlemek için, oktahedral eg seti bir tetrahedral e seti haline gelir ve oktahedral t2g seti bir t2 seti haline gelir.
 
 <img alt="Image1" src="/files/ftp_upload/11462/11462_Image_1.png" style="text-align: center; height: 350px;" />
 
 Şekil 1. Metal iyonunun d orbitallerinin oktahedral ve tetrahedral kristal alanları altında bölünmesi. Oktahedral kristal alanına kıyasla, tetrahedral kristal alanındaki bölme deseni ters çevrilmiştir. Oktahedral kompleksin kristal alan bölme enerjisi Δoct, tetrahedral kompleksin kristal alan bölme enerjisinden Δtet daha büyüktür.
 
 CFT elektrostatik itmeye dayandığından, ligandlara daha yakın olan orbitaller dengesizleştirilecek ve diğer orbital kümesine göre enerjide yükselecektir. Bölünme, oktahedral komplekslerden daha azdır, çünkü örtüşme daha azdır, bu nedenle kristal alan bölme enerjisi Δtet , genellikle küçüktür.
 
 Kare Düzlemsel Kompleksler 
 
 Diğer yaygın geometri kare düzlemseldir. Bir kare düzlemsel geometriyi, bir çift çıkarılmış trans ligand içeren bir oktahedral yapı olarak düşünmek mümkündür. Çıkarılan ligandların z ekseni üzerinde olduğu varsayılmaktadır. Bu, z eksenindeki veya yakınındaki orbitallerin daha kararlı hale gelmesi ve x- veya y eksenlerindeki veya yakınındaki orbitallerin daha az kararlı hale gelmesi nedeniyle d orbitallerinin dağılımını değiştirir. Bu, oktahedral t2g ve eg kümelerinin bölünmesine neden olur ve daha karmaşık bir bölme deseni verir (Şekil 2).
 
 <img alt="Image2" src="/files/ftp_upload/11462/11462_Image_2.png" style="text-align: center; height: 350px;" />
 
 Şekil 2. t2g kümesinin ve eg kümesinin kare düzlemsel bir kristal alanda bölünmesi. Kare düzlemsel komplekslerin veya Δsp'nin kristal alan bölme enerjisi Δoct'den daha büyüktür.
 
 Bu metin bu kaynaktan uyarlanmıştır: <a href="https://openstax.org/books/chemistry-2e/pages/19-3-spectroscopic-and-magnetic-properties-of-coordination-compounds">Openstax, Chemistry 2e, Section 19.3: </a><a href="https://openstax.org/books/chemistry-2e/pages/19-3-spectroscopic-and-magnetic-properties-of-coordination-compounds">S</a><a href="https://openstax.org/books/chemistry-2e/pages/19-3-spectroscopic-and-magnetic-properties-of-coordination-compounds">pectroscopic and Magnetic Properties of Coordination Compounds</a>.

Kristal Alan Teorisi - Tetrahedral ve Kare Düzlemsel Kompleksler

Tetrahedral Kompleksler 
Kristal alan teorisi (CFT), oktahedral dışındaki geometrilerdeki moleküllere uygulanabilir. Oktahedral komplekslerde, lobları ...

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

Education

JoVE Core

Chemistry

Kimya

Transition Metals and Coordination Complexes

Geçiş Metalleri ve Koordinasyon Kompleksleri

transition-metals-and-coordination-complexes

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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 orbital energy diagram is therefore split in the opposite way from the octahedral case. The octahedral e g set becomes a tetrahedral e set, and the octahedral t 2 g set becomes a t 2 set. The splitting energy, called Δ tet, is usually small because the overlap is less than in octahedral complexes.

Square planar complexes can be viewed as octahedral structures with a pair of trans ligands removed. The removed ligands are assumed to be on the z-axis. This changes d orbital stability. Orbitals on or near the z-axis become more stable, while orbitals on or near the x- or y-axes become less stable. The octahedral t 2 g and e g sets split into a more complex pattern, and the crystal field splitting energy, Δ sp, is larger than Δ oct.

Crystal Field Splitting in Non-Octahedral Shapes

crystal-field-splitting-in-non-octahedral-shapes

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

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...

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 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

Explore how crystal field theory explains d orbital splitting in tetrahedral and square planar complexes, including inverted splitting and larger square planar splitting.

Crystal Field Splitting in Non-Octahedral Shapes | JoVE K12

chemistry

JoVE Core Kimya, özlü ve kolay anlaşılır animasyon video derslerini kullanarak genel kimya kavramlarına hayat veriyor. Ek olarak, bilim insanı uygulama videolarımız ile klasik ve orijinal araştırma deneylerini dünya çapında günümüz laboratuvarlarında görselleştiriyoruz.

Crystal Field Splitting in Non-Octahedral Shapes

Description

Transcript

Tags