Tin (II) chloride is white while tin(II) iodide is red. Why?

The answer given in my book says:

Bigger anion has higher polarizability; more polarization greater is the intensity of colour(valence shell electrons are loosely bound to the nucleus).

This answer doesn't seem to be very explanatory. Even google doesn't offer anything. It would be great if someone could explain it in a better way, focussing on the following two points:
Firstly, how does more polarization lead to greater intensity of colour?
Secondly, how is intensity anyways related to frequency of radiation?

  • 4
    $\begingroup$ (2)In molecules the intensity of electronic transitions is not primarily determined by frequency but by overlap of wavefunctions via Franck-Condon factors. (1) The polarisation does not give greater intensity of colour but shifts energy levels into visible spectrum. ('White' means solid is scattering light and probably absorbing in UV). Possibly (I'm not sure here) but the reason for this could be due to some Charge Transfer Complex formation between iodine and tin complex being stronger and hence of lower energy that that due to Cl. But it could be that the whole structure is different. $\endgroup$ – porphyrin Jan 19 '17 at 16:20
  • $\begingroup$ If I had to guess, I would say ligand to metal charge transfer. $\endgroup$ – Jan Jan 19 '17 at 19:00

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