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Complexes
A central metal atom bonded to a group of molecules or ions is a metal complex.If the complex bears a charge, it is a complex ion.Compounds containing complexes are coordination compounds.
The molecules or ions coordinating to the metal are the ligands.They are usually anions or polar molecules.
Complexes
Structure & isomerization
Three categories of isomerization1. Structural isomers: atoms connected in
different ways1. Coordination isomers2. Linkage isomers
2. Geometric isomers: ligands have different spatial arrangement1. Cis-trans isomers2. Octahedral complex isomers
3. Optical isomers: nonsuperimposable mirror-images (enantiomers)
Structural isomerism: coordination isomers
Coordination isomersCoordination ligand exchanges places w/uncoordinated counter-ion
Ex: [Co(NH3)5Br]Cl vs. [Co(NH3)5Cl]Br
Structural isomerism: linkage isomers
Either one of atoms in NO2- can bond to
metalWhen O, nitrito: ONO-
When N, nitro: NO2-
Different color compounds
Geometric isomerism: cis-trans isomers
Occurs in sq-planar: MA2B2
And octahedral complexes: MA4B2
8
Geometric isomerism: octahedral complex isomers
MX3Y3
Fac (facial) isomerThree identical ligands at corners of a triangular face of octahedron
Mer (meridian) isomerThree identical ligands at corners of a triangular meridian (inside octahedron)
complex Ion colorAbsorbs all colors-but- the one you see orReflects most colors but absorbs the complimentary
Complex Ion Color and Crystal Field Strength
The colors of complex ions are due to electronic transitions between the split d sublevel orbitals
The wavelength of maximum absorbance can be used to determine the size of the energy gap between the split d sublevel orbitals
Ephoton = hn = hc/l = D
Ligand and Crystal Field Strength
The strength of the crystal field depends in large part on the ligands
strong field ligands include: CN─ > NO2─ > en
> NH3
weak field ligands include: H2O > OH─ > F─ > Cl─ > Br─ > I─
crystal field strength increases as the charge on the metal cation increases
Magnetic Properties and Crystal Field Strength
The electron configuration of the metal ion with split d orbitals depends on the strength of the crystal fieldThe 4th and 5th electrons will go into the higher energy dx2-y2 and dz2 if the field is weak and the energy gap is small – leading to unpaired electrons and a paramagnetic complexThe 4th thru 6th electrons will pair the electrons in the dxy, dyz and dxz if the field is strong and the energy gap is large – leading to paired electrons and a diamagnetic complex
Low Spin & High Spin Complexes
paramagnetic
high-spin complex
diamagnetic
low-spin complex
Only electron configurations d4, d5, d6, or d7 can have low or high spin
Tetrahedral Geometry &Crystal Field Splitting
Because the ligand approach interacts more strongly with the planar orbitals in the tetrahedral geometry, their energies are raisedMost high-spin complexes
Square Planar Geometry & Crystal Field Splitting
d8 metalsThe most complex splitting patternMost are low-spin complexes
Occurs when polar molecules are attracted to each other.
Dipole interaction happens in waterpositive region of one molecule attracts the negative region of another molecule.
Dipole interactions
Dipole interactions
Occur when polar molecules are attracted to each other.Slightly stronger than dispersion forces.Opposites attract, but not completely hooked like in ionic solids.
H Fd+ d-
H Fd+ d-
The End
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