Copper(II)–Mercury(II) Heterometallic Complexes Derived from a Salen-Type Ligand: A New Coordination Mode of the Old Schiff Base Ligand

Three heterometallic copper­(II)–mercury­(II) complexes,
[(CuL-CH3)­HgCl2] (1), [(CuL-CH3)2HgCl2] (2), and [(CuL-CH2-HgCl)2] (3), have been synthesized
by reacting
the “complex as ligand” [CuL-CH3] with HgCl2 by varying the reaction conditions and stoichiometry of the
reactants, where H2L-CH3 = the di-Schiff base
of 1,3-propanediamine and 2-hydroxyacetophenone. All three complexes
have been characterized by X-ray single-crystal structure, elemental,
and spectroscopic analyses. In complex 1, the Hg­(II)
ion is bonded by two phenoxido oxygen atoms of a [CuL-CH3] moiety and two terminal chloride ions to form a dinuclear species.
In the trinuclear complex 2, the central Hg­(II) ion is
coordinated by two terminal [CuL-CH3] units through one
phenoxido oxygen from each unit and two chloride ions. On the other
hand, in the tetranuclear complex 3, the Hg­(II) ion has
a distorted-tetrahedral geometry, being bonded to one chloride, two
phenoxido oxygen atoms of one [CuL–CH2]¯ unit,
and a methyl carbon atom of another [CuL–CH2]¯
unit. The structure of complex 3 reveals an unprecedented
heptadentate coordination mode (1-κ4NN′OO′:2-κ2OO′:3-κC) of the Schiff base ligand that resulted
in a unique organomercury metallamacrocycle.