35Cl NQR and X-Ray Studies of Hexachloropalladates A2PdCl6 (A = Rb, Cs, NH4) and the Cl2 – Clathrates Bis(tetramethylammonium)hexachloropalladate (Me4N)2PdCl6 · Cl2 and Bis(tetramethylammonium)hexachlorostannate (Me4N)2SnCl6 · Cl2