From monomer zinc-oxamato complexes to tetranuclear inverse 12-membered and octanuclear 12-membered metallacrowns

Interaction of ZnCl2 with Hpko (Hpko, di-2-pyridyl-ketonoxime) results in the formation of a uninuclear Zn(Hpko)Cl-2 (1) compound or in a 12-membered tetranuclear metallacrown (OH)(2)[inv12-MCZn(II)N(pko)-4]Cl-2 (2) depending on the pH of the mother solution. The addition of H(3)shi (H(3)shi, salicylhydroxamic acid) leads to the formation of the octanuclear 12-membered tetranuclear metallacrown [Zn-2]{[Zn-2(pko)(4)][12-MCZn(II)N(shi)-4](CH3OH)(2)} (3). The metallacrown core of 2 is characterized as "inverse" because the zinc atoms, rather than oxygen atoms, are oriented toward the central cavity. Two triply bridging hydroxides are accommodated in the center of the metallacrown ring. The pko(-) ligands form a propeller configuration that imposes absolute stereoisomerism with Lambda and Delta chirality. Each hydroxo oxygen bridges two octahedral zinc atoms and a tetrahedral one. The octanuclear cluster Zn-8(shi)(4)(pko)(4)(CH3OH)(2) contains a 12-membered tetranuclear metallacrown core constructed by four Zn metal atoms and four shi(3-) ligands. So, a part of the cluster can be described as having the formally anionic [12-MCZn(II)N(shi)-4](4-) core. Two of the zinc atoms are in octahedral coordination environment while for the other two the geometry is best described as distorted trigonal bipyramidal. The metallacrown core accommodates a binuclear compound with the formula [Zn-2(pko)(4)]. Two of the ring metal ions create binuclear units with two zinc ions, respectively, with two oxamato oxygens, and two phenolato oxygens, of the four interlinked shi(3-) ligands acting as bridging atoms.