[Ligander]

 Is there any explanation other then based of electronegativity difference?

[BluRay]

Is there any explanation other then based of electronegativity difference?

It also depend on the energy of the ionic lattice: the formation of th ionic net is favoured if  its energy is high (this, in turn, depends on the ionic radii, the ionic charges and on te coordination number):
http://en.wikipedia.org/wiki/Lattice_energy

Said in simplistic terms: if two binary compounds, let's say (two random compounds) AlF₃ and BaO, have the same electronegativity difference, but we could presume the second ionic lattice to be more stable because (...computations...) it would have greater energy, then we can be sure the second compound would be more probable ionic than the first.

[Ligander]

http://en.wikipedia.org/wiki/Fajans_rules

[BluRay]

http://en.wikipedia.org/wiki/Fajans_rules

and?