CHM 401

 

Transition Metal Chemistry

d block chemistry is vast, often thought of in terms of Lewis Acid/Base interactions

Metals act as Lewis acids, which react with Lewis bases

The Lewis acid/base product is generally called a coordination complex and the Lewis bases are called ligands

Wide variety of d-block chemistry to be addressed:

Structures of Coordination Complexes

CN = 2, 3

Rare, follow VSEPR rules CN =2, linear [Ag(NH3)2]+; CN = 3, trigonal planar

CN = 4

Quite common; found in two geometries-tetrahedral (Td) and square planar (D4h) some complexes are known that are between Td and D4h (D2d)

Square planar complexes can exhibit geometric isomerism: ML2L'2 cis or trans makes a difference in the chemistry: cis-Pt(NH3)2Cl2 is an anticancer drug, the trans isomer is inert

CN = 5

Not rare, not common; two geometries-trigonal bipyramid (D3h) and square-based pyramid (C4v); the two geometries are generally close in energy so ligands can scramble.

Berry pseudorotation is seen in mixed ligand complexes, this scrambles ligand positions:

CN = 6

Most common coordination number, octahedral

Often can get distortions from Oh

Extension or compression along one axis : tetragonal : D4h

Change along two axes : rhombic : D2h

Change along the diagonal (the C3 axis) : D3d

Substitutions:

disubstituted ML4L'2 : cis (C2v) or trans (D4h)

trisubstituted ML3L'3 : fac (C3v) or mer (C2v)

CN = 8

Very rare for first row (steric), found occasionally in 2nd or 3rd row complexes