Toward Rational Control of Metal Stoichiometry in Heterobimetallic Coordination Complexes:  Synthesis and Characterization of Pb(Hsal)2(Cu(salen))2, [Pb(NO3)(Cu(salen))2](NO3), Pb(OAc)2(Cu(salen)), and [Pb(OAc)(Ni(salen))2](OAc)

The ability of the transition metal complex M(salen)* (M = Ni, Cu) to form Lewis acid−base adducts with lead(II) salts has been explored. The new complexes Pb(Hsal)2(Cu(salen*))2 (1), {Pb(NO3)(Cu(salen*))2}(NO3) (2), Pb(OAc)2(Cu(salen*)) (3), and {Pb(OAc)(Ni(salen*)2}(OAc) (4) (Hsal = O2CC6H4-2-OH, salen* = bis(3-methoxy)salicylideneimine) have been synthesized and characterized spectroscopically and by single-crystal X-ray diffraction. The coordination environment of the lead in the heterobimetallic complex is sensitive both to the initial lead salt and to the transition metal salen complex that is employed in the synthesis. As a result, we have been able to access both 2:1 and 1:1 adducts by varying either the lead salt or the transition metal in the heterobimetallic coordination complex. In all cases, the salen* complex is associated with the lead center via dative interactions of the phenolic oxygen atoms. The relationship between the coordination requirements of the lead and the chemical nature of the anion is examined. In compound 1, the Pb2+ ion is chelated by two Cu(salen*) moieties, and both salicylate ligands remain attached to the lead center and bridge to the Cu2+ ions. The two Cu(salen*) groups are roughly parallel and opposed to each other as required by crystallographic inversion symmetry at lead. In contrast, the two Cu(salen*) groups present in 2 and 4 attached to the lead ion show considerable overlap. Furthermore, only one nitrate ion in 2 and one acetate ion in 4 remain bonded to the lead center. Compound 3 is unique in that only one Cu(salen*) group can bind to lead. Here, both acetate ligands remain attached, although one is chelating bidentate and the other is monodentate.