Macromolecular Self-Assembly of Organotin(IV) Squarates and Croconates - Preparation and Crystal Structures of [SnMe2 (H2 O)2 ]C4 O4 , [SnMe3 ]2 C4 O4 , and [SnMe3 (H2 O)]2 C5 O5 : Macromolecular Self-Assembly of Organotin(IV) Squarates and Croconates - Preparation and Crystal Structures of [SnMe2(H2O)2]C4O4, [SnMe3]2C4O4, and [S