A Novel Series of Materials Composed of Arrays of Vanadium Oxide Container Molecules, {V 18 O 42 (X)} (X = H 2 O, Cl - , Br - ): Synthesis and Characterization of [M 2 (H 2 N(CH 2 ) 2 NH 2 ) 5 ][{M(H 2 N(CH 2 ) 2 NH 2 ) 2 } 2 V 18 O 42 (X)]· 9H 2 O (M = Zn, Cd)