Metal- and ligand-directed one-pot syntheses, crystal structures, and properties of novel oxo-centered tetra- and hexametallic clusters

摘要

Starting from closely related metal - ligand combinations, completely different oligomeric metal clusters are synthesized. Whereas, picoline-tetrazolylamide HL1 (1) and zinc or nickel acetate afforded [2 x 2] grids [M-4(L-1)(8)] (2), slightly different N-(2-methylthiazole-5-yl)-thiazole-2-carboxamide HL2 (5a) and nickel acetate yielded the monometallic complex [Ni(L-2)(2)(OH2)(2)] (6). In contrast, reaction of 5a with zinc acetate produced the tetrametallic zinc cluster [Zn4O(L-2)(4)(OAc)(2)] (7). Even more surprising, when 3-methyl-substituted HL3 (5b) instead of 2-methyl-substituted HL2 (5a) was allowed to react under identical conditions with zinc acetate, the cluster [Zn4O(L-3)(4)Cl-2] (8) crystallized from dichloromethane. Clusters 7 and 8 are isostructural. As for 7, in 8 two of the edges of the tetrahedron of zinc ions are doubly bridged, two are singly bridged, and the other two are nonbridged. On the other hand, when iron(II) acetate under aerobic conditions was allowed to react with 5a, the unprecedented complex [{Fe3O(L-2)(2)-(OAC)(4)}(2)O] (9) was isolated. Cluster 9 is composed of two trimetallic, triangular mu(3)-O2--centered [Fe3O(L-2)(2)(OAC)(4)](+) modules, linked by an almost linear mu(2)-O2- bridge. The Mossbauer spectrum together with cyclic voltammetric and square-wave voltammetric measurements of 9 are reported, and 6-9 were characterized unequivocally by single-crystal X-ray structure analyses. [References: 50]