This is a salt because there is a cation and an anion. Because lead can have multiple charges, its charge must correspond to the charge of the anion. The charge on the N is -3, so the 4 N's equal a total charge of -12. Therefore, the total charge of the 3 Pb's must be 12, so each lead should have a charge of +4. So the name of the compound is Lead (IV) Nitride.
