What's the rule to covalent character

[hms.tech]

What is the general rule to find out some compound is ionic or covalent?

For e.g: Tetramethyl-lead(IV) (CH3)4Pb, has lead metal in it.
Normally a metal bonded to a polyatomic molecule (or ion) is ionic, but i highly doubt it is the case here. I think (CH3)4Pb is covalent rather than ionic.

Another e.g is of Aluminium chloride (AlCl3) (in solid form) which was referred to-by my chemistry professor-as a covalent compound, together with the proof that it sublimes at about 200 Degrees C

 

[Acut]

There are no strict boundaries between covalent and ionic bonds. You may use the differences in electronegativities, Fajan's rules, dipole moment calculations as indicators, but the cases you mentioned fall right into intermediate cases.