Fe Test Why Does The Complex [Fe(H2O)5NO]SO4 Form A Ring In Between Two Layers In The Brown Ring Test For Nitrates

Why does the complex [Fe(H2O)5NO]SO4 form a ring in between two layers in the brown ring test for nitrates - fe test

for anyone who could help me with an answer about the procedure, the following procedure for you:

Add the salt nitrate, freshly prepared solution of ferrous sulfate and dil.H2SO4 into a test tube and shake well. conc.H2SO4 then added slowly Innerside the test tube. appear to the brown ring ([Fe (H2O) 5NO] SO4).
PS: this also be done with the salt Na2CO3 nitrate.