Ortho-Chalcogenostannates as Ligands: Syntheses, Crystal Structures, Electronic Properties, and Magnetism of Novel Compounds Containing Ternary Anionic Substructures[M4(μ4-Se)(SnSe4)4]10− (M=Mn, Zn, Cd, Hg),{[Hg4(μ4-Se)(SnSe4)3]6−}, or{[HgSnSe4]2−}