Here are all eight isomers of Ni(en)32+, including the backbone isomers.  They are shown here from least stable to most stable, and the two isomers in any row are enantiomers.  The relative energies are shown in the graph below, together with the percentage that would be in those forms at room temperature if the system was brought to thermal equilibrium.

 

Dlll 
Lddd 
Dddd
Llll
Ddll
Lddl
Dddl
Ldll