How many stereoisomers of octahedral CoCl2(NH3)2(CN)2– are possible?

1 Answer
Ernest Z.
Jan 15, 2018

There are six stereoisomers of #["Co(CN)"_2("NH"_3)_2"Cl"_2]^"2-"#.

Explanation:

This is classed as an #"MA"_2"B"_2"C"_2# complex.

Let's let #"A = NH"_2, "B = Cl, C = CN"#

Then the possible combinations are

#ulbb(color(white)(ll)"A"color(white)(mml)"B"color(white)(mmll)"C"color(white)(m))#
#ciscolor(white)(mml)ciscolor(white)(mml)ciscolor(white)(mml)"pair of enantiomers"#
#ciscolor(white)(mml)ciscolor(white)(mml)trans#
#ciscolor(white)(mml)transcolor(white)(m)cis#
#transcolor(white)(m)ciscolor(white)(mml)cis#
#transcolor(white)(m)ciscolor(white)(mml)transcolor(white)(m)"impossible"#
#transcolor(white)(m)transcolor(white)(m)trans#

Here are the structures.

cis-cis-cis

CCC1
CCC2

These are a pair of enantiomers.

cis-cis-trans

CCT

cis-trans-cis

CTC

trans-cis-cis

TCC

trans-trans-trans

TTT

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