From the order the reactants are added, the formation of the [Co(en)3]3+ complex should be
a) Reaction of the hexaaquocobalt(II) ion with ethylenediamine:
[Co(H2O)6]2+ (aq) + 3en ---> [Co(en)3]2+ (aq) + 6H2O (l)
b) Oxidation of the tris(ethylenediamine)cobalt(II) ion with H2O2 in basic solution:
2[Co(en)3]2+ (aq) + H2O2 (aq) ---> 2[Co(en)3]3+ (aq) + 2OH- (aq)
A helpful site is at http://www.chemguide.co.uk/inorganic/transition/cobalt.html which mentions that the hexaamminecobalt(II) ion can be oxidized by air or H2O2 also. Although waters of hydration are common in ionic compounds, I'm not sure why your crystalline product contains NaCl, or if the NaCl would be removed by recrystallization. That is interesting in itself!
Steve
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