Tetrahydroxy- p -benzoquinone as a Source of Polydentate O-Donor Ligands. Synthesis, Crystal Structure, and Magnetic Properties of the [Cu(bpy)(dhmal)] 2 Dimer and the Two-Dimensional [{SiW 12 O 40 }{Cu 2 (bpy) 2 (H 2 O)(ox)} 2 ]·16H 2 O Inorganic−Metalorganic Hybrid