The Foundations of Chemistry

Complexes of the type [MA 2 B 2 C 2 ] can exist in several isomeric forms. Consider as an
example [Cr(OH 2 ) 2 (NH 3 ) 2 Br 2 ]
. First, the members of all three pairs of like ligands may
be either transto each other (A) or cisto each other (B).

cis-diammine-cis-diaqua-cis-

dibromochromium(III) ion

B

Cr

OH 2

NH 3

Br NH 3

Br OH 2

trans-diammine-trans-diaqua-trans-

dibromochromium(III) ion

A

Cr

OH 2

OH 2

H 3 N Br

Br NH 3

A stereoview of mer–triammine-trichloroplatinum(IV) ion, mer-[Pt(NH 3 ) 3 Cl 3 ]
. The

three chloro ligands are all one meridian (in a plane), and the three ammine ligands

are all on a perpendicular meridian (a plane perpendicular to the first).

Pt

NH 3

Cl

Cl Cl

H 3 N NH 3

fac-triamminetrichloroplatinum(IV) ion,

fac-[Pt(NH 3 ) 3 Cl 3 ]

A stereoview of fac-triamminetrichloroplatinum(IV) ion, fac-[Pt(NH 3 ) 3 Cl 3 ]
. The three

chloro ligands are all on one triangular face of an octahedron, and the three ammine

ligands are all on the opposite triangular face.

Pt

NH 3

Cl

Cl NH 3

H 3 N Cl

mer-triamminetrichloroplatinum(IV) ion,

mer-[Pt(NH 3 ) 3 Cl 3 ]

Cl