The First Crystal Structures of Mercury(II) Complexes of Tetra‐amides (L1 and L2) and Tetramethylamides (L3 and L4) of EDTA and PDTA. Formation of Distorted Octahedral and Distorted Capped Octahedral Mercury(II) Complexes and of a Trinuclear Complex containing HgCl2‐bridged [Hg(L3)Cl]+ Moieties