Re: VRD - sodium ferrocyanide, spinach and water

With apologies for the delay, the compound sodium ferricyanide is a metal
ion complex that combines with iron to give a charge transfer complex that
is deep blue in colour. To quote from Cotton & Wilkinson's "Advanced 
Inorganic Chemistry, 3rd Ed.":

It has long been known that treating a solution of iron(III) with
hexcyanoferrate(II) yields a blue precipitate called "Prussian Blue" and
that treating a solution of iron(II) with hexacyanoferrate(III) yields a
blue precipitate callled "Turnball's Blue". These substances are actually
identical, having formulas M(I)FeFe(CN)6.xH2O where M is Na, K, or Rb but
not Li or Cs.

In essence, heating the spinach breaks down the cells and releases some of
their iron content (Spinach is rich in iron which is why Popeye ate so 
much!) and it is this iron content that is forming the blue complexes.

The colour in the complex arises from the rapid exchange of an electron
between the two metal atoms, creating low lying molecular orbitals. The
colour produced is very intense - it doesn't require much iron to give a
blue solution.

And as a final note, the blue coloured compound is the basis for the paint
pigment used by artists, "Prussian Blue".