Nonemployed Simple Carboxylate Ions in Well-Investigated Areas of Heterometallic Carboxylate Cluster Chemistry: A New Family of {Cu^II₄Ln^III₈} Complexes Bearing tert-Butylacetate Bridging Ligands

The first use of tert-butylacetate as bridging ligand in 3d/4f-metal cluster chemistry, in conjunction with the versatile chelate ligand pyridine-2,6-dimethanol, has afforded a new family of [Cu₄Ln₈(OH)₆­(NO₃)₂­(O₂CCH₂Bu^t)₁₆­(pdm)₄] clusters with unprecedented structures and slow magnetization relaxation for the {Cu^II₄Dy^III₈} member. The molecular structure of representative complex 1 consists of a {Cu^II₄Gd^III₈} cage-like cluster built from two {CuGd₃} cubanes which are linked to each other and to two {CuGd} subunits on opposite sides through two η²:η²:η²:μ₅ NO₃^– ions. The metal ions are additionally bridged by μ₃-OH^–, μ₃-OR^–, and μ-OR^– groups to give an overall [Cu₄Gd₈­(μ₅-NO₃)₂­(μ₃-OH)₆­(μ₃-OR)₂­(μ-OR)₈]¹⁴⁺ core. Peripheral ligation about the core is provided by the N,O,O-chelating part of the pdm^2– groups and, more impressively, by the oxygen atoms of 16 bridging Bu^tCH₂CO₂^– ligands; the latter are arranged into five classes, adopting a total of six different binding modes with the metal centers. The combined work demonstrates the ligating flexibility of tert-butylacetate ion and its usefulness in the synthesis of new 3d/4f-metal cluster compounds.