Synthesis and structure of mononuclear and binuclear zinc(II) compartmental macrocyclic complexes

The structures of four neutral binuclear Zn-II complexes of the Schiff-base macrocycles formed by the [2 + 2] template condensation of 2,6-diformyl-4-methylphenol with 1,2-diaminoethane: [H2L1], 1,3-diaminopropane: [H2L2], 1,4-diaminobutane: [H2L3] and 2,6-diacetyl-4-methylphenol with 1,2-diaminoethane: [H2L4] have been determined. The complexes [Zn-2(L-1)(OAc)(2)].2CHCl(3),[Zn-2(L-2)(OAc)(2)].2CHCl(3) and [Zn-2(L-4)Cl-2] each contain two five coordinate Zn-II centres with each metal ion bound to the N2O2 donor set of the macrocyclic ligand and to an anion molecule. Two different coordination environments are observed in [Zn-2(L-3)(mu-OAc)(OAc)].CHCl3 which contains both a five- and a six-coordinate Zn-II centre, with one acetate bridging two metal ions and a monodentate acetate bound to the six-coordinate Zn-II ion. Significantly, the reaction of pre-formed macrocyclic ligands [H4L2](PF6)(2) and [H4L4](PF6)(2) with Zn(OAc)(2).2H(2)O affords [Zn-2(L-2)(mu-OAc)](PF6).MeCN and [Zn(H2L4)(MeCN)](PF6)(2), respectively. The former shows two five-coordinate Zn-II centres in which an acetate bridges both metal ions. In the latter complex the macrocyclic ligand binds only one five-coordinate Zn-II ion with a molecule of MeCN bound at an apical position.