Some Coordination Compounds of Cobalt Studied by Werner Werner’s Data* Traditional Total Free Modern Charge of Formula Ions Cl- Formula Complex Ion . CoCl3 6 NH3 4 3 [Co(NH3)6]Cl3 3+ CoCl3 5 NH3 3 2 [Co(NH3)5Cl]Cl2 2+ CoCl3 4 NH3 2 1 [Co(NH3)4Cl2]Cl 1+ CoCl3 3 NH3 0 0 [Co(NH3)3Cl3] --- . . . Table 23.10 (p. 1020)

Hybrid Orbitals and Bonding in the Octahedral [Cr(NH3)6]3+ Ion Valence Bond Theory Hybrid Orbitals and Bonding in the Octahedral [Cr(NH3)6]3+ Ion Fig. 23.13

Hybrid Orbitals and Bonding in the Square Planar [Ni(CN)4]2- Ion Valence Bond Theory Hybrid Orbitals and Bonding in the Square Planar [Ni(CN)4]2- Ion Fig. 23.14

Hybrid Orbitals and Bonding in the Tetrahedral [Zn(OH)4]2- ion Valence Bond Theory Hybrid Orbitals and Bonding in the Tetrahedral [Zn(OH)4]2- ion Fig. 23.15

Isomerism

Isomerism Isomers: two compounds with the same formulas but different arrangements of atoms. Coordination-sphere isomers and linkage isomers: have different structures (i.e. different bonds). Geometrical isomers and optical isomers are stereoisomers (i.e. have the same bonds, but different spatial arrangements of atoms). Structural isomers have different connectivity of atoms. Stereoisomers have the same connectivity but different spatial arrangements of atoms.

Isomerism Diastereomers Enantiomers (Chiral: Non-superimposable Mirror Images)

Isomerism Structural Isomerism

Fig. 23.11

Stereoisomerism

Fig. 23.12

Stereoisomerism Enantiomers are chiral: I.e. They are non-superimposable mirror images. Enantiomers are “optical isomers.” eg. (+) and (-) carvone Most physical and chemical properties of enantiomers are identical. Therefore, enantiomers are very difficult to separate eg. Tartaric acid…ask Louis Pasteur. Enzymes are catalysts that are very specific, acting on only one enantiomer. Enantiomers can have very different physiological effects: eg. (+) and (-) carvone

Chirality

Optical Activity

Optical Activity (+) dextrorotatory (-) levorotatory The mirror image of an enantiomer will rotate the plane of polarized light by the same amount in the opposite direction. Eg (+) d-carvone +62o and (-) l-carvone -62o…. What about a 50:50 (racemic) mixture?

Color and Magnetism Color of a complex depends on: (i) the metal and (ii) its oxidation state. Pale blue [Cu(H2O)6]2+ can be converted into dark blue [Cu(NH3)6]2+ by adding NH3(aq). A partially filled d orbital is usually required for a complex to be colored. So, d 0 metal ions are usually colorless. Exceptions: MnO4- and CrO42-. Colored compounds absorb visible light. The color our eye perceives is the sum of the light not absorbed by the complex.

Color and Magnetism Color

An Artist’s Wheel Fig. 23.16

Relation Between Absorbed and Observed Colors Absorbed Observed Color  (nm) Color  (nm) Violet 400 Green-yellow 560 Blue 450 Yellow 600 Blue-green 490 Red 620 Yellow-green 570 Violet 410 Yellow 580 Dark blue 430 Orange 600 Blue 450 Red 650 Green 520 Table 23.11 (p. 1027)

Color & Visible Spectra

Color& Spectra The plot of absorbance versus wavelength is the absorption spectrum. For example, the absorption spectrum for [Ti(H2O)6]3+ has a maximum absorption occurs at 510 nm (green and yellow). So, the complex transmits all light except green and yellow. Therefore, the complex appears to be purple.

Color and Magnetism Magnetism Many transition metal complexes are paramagnetic (i.e. they have unpaired electrons). There are some interesting observations. Consider a d6 metal ion: [Co(NH3)6]3+ has no unpaired electrons, but [CoF6]3- has four unpaired electrons per ion. We need to develop a bonding theory to account for both color and magnetism in transition metal complexes.

Crystal-Field Theory