Unit 19: Coordination Compounds and Crystal Field Theory
Why a transition metal turns a vivid color the instant ligands surround it, and how splitting five equal d orbitals explains the color and the magnetism.
7 topics · 26 questions
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19.2 Transition Metal Complexes: Ligands and Coordination Number
- How it worksHow does a central metal ion surrounded by ligands donating electron pairs form a coordination complex?
- How it worksWalk me through counting the coordination number of a complex like [Co(NH3)6]3+.
- Common mistakeWhy isn't the bond between a metal ion and a ligand just an ordinary ionic or covalent bond formed the usual way?
- Going furtherWhat happens to a complex's coordination number when a bidentate ligand like ethylenediamine replaces two separate monodentate ligands?
Your turn1 of 2
A coordination complex has 4 monodentate ligands and 2 bidentate ligands attached to its central metal ion (each bidentate ligand occupies 2 coordination sites). Find the total coordination number.19.2 Naming Coordination Compounds
- How it worksHow do ligand names, listed alphabetically, combine with the metal's name and oxidation state to build a coordination compound's full name?
- Worked exampleFind the correct name for the coordination compound [Cr(NH3)4Cl2]Cl.
- Common mistakeWhy does a complex ion's name switch to an '-ate' ending only when the whole complex is an anion?
Your turn1 of 2
What is the correct name for the coordination compound [Cr(NH3)4Cl2]Cl?19.2 Isomerism in Coordination Compounds
- How it worksHow does swapping which side of a square planar or octahedral complex two identical ligands sit on create cis and trans geometric isomers?
- Worked exampleFind the number of geometric isomers possible for a square planar complex like [Pt(NH3)2Cl2].
- Common mistakeWhy aren't cis and trans isomers of a coordination compound just the same molecule drawn two different ways?
- Going furtherWhat happens to a complex's isomer count once a bidentate ligand chelates the metal instead of using two separate monodentate ligands?
Your turn1 of 2
How many geometric isomers are possible for a square planar complex like [Pt(NH3)2Cl2]?19.3 Crystal Field Theory and d-Orbital Splitting
- How it worksHow does repulsion between approaching ligand electrons and the metal's d electrons split the d orbitals into two energy levels in an octahedral field?
- How it worksWalk me through why the d orbitals pointing directly at the ligands end up higher in energy than the ones pointing between them.
- Common mistakeWhy isn't crystal field splitting explained by covalent bonding between the metal and its ligands the way molecular orbital theory would be?
- Going furtherWhat happens to the d-orbital splitting pattern when an octahedral complex is distorted into a tetrahedral or square planar geometry instead?
Your turn1 of 2
Crystal field theory successfully predicts how a metal's d orbitals split in energy once ligands surround it. Why isn't this splitting explained by covalent bonding between the metal and ligands, the way molecular orbital theory would explain it?19.3 High Spin versus Low Spin Complexes
- How it worksHow does the size of the crystal field splitting energy compete with the energy cost of pairing electrons to decide high spin versus low spin?
- Worked exampleFind whether a d6 octahedral complex with a strong-field ligand like CN- is high spin or low spin, and count its unpaired electrons.
- Common mistakeWhy doesn't every octahedral transition metal complex automatically fill its d orbitals following Hund's rule the same way a free atom does?
Your turn1 of 2
Is a d6 octahedral complex with the strong-field ligand CN- high spin or low spin, and how many unpaired electrons does it have?19.3 Color in Coordination Compounds
- How it worksHow does an electron jumping across the crystal field splitting gap absorb a specific wavelength of visible light, leaving the complementary color behind?
- Worked exampleFind the approximate color of a complex that absorbs orange light around 600 nm, using the color wheel of complementary colors.
- Common mistakeWhy isn't the color you see in a coordination compound the same color as the light it's actually absorbing?
- Ties togetherHow does a ligand's position on the spectrochemical series connect back to the size of the crystal field splitting energy and the color a complex displays?
Your turn1 of 2
Find the energy of a photon absorbed at a wavelength of 609 nm (E = hc / wavelength, with h = 6.626 times 10−34 J times s and c = 3.00 times 108 m/s).19.3 Magnetic Properties of Coordination Compounds
- How it worksHow does the presence of unpaired electrons in a complex's d orbitals make it paramagnetic instead of diamagnetic?
- Worked exampleFind whether a low spin d6 octahedral complex is paramagnetic or diamagnetic based on its electron configuration.
- Common mistakeWhy isn't a compound's magnetism something you can predict just by knowing which metal it contains?
- Going furtherWhat happens to a complex's measured magnetic behavior when a strong-field ligand replaces a weak-field one around the same metal ion?
Your turn1 of 2
Is a low spin d6 octahedral complex paramagnetic or diamagnetic?