Tetrahedral M4(μ4‑O) Motifs Beyond Zn: Efficient One-Pot Synthesis of Oxido−Amidate Clusters via a Transmetalation/Hydrolysis Approach

Abstract

While zinc μ4-oxido-centered complexes are widely used as versatile precursors and building units of functional materials, the synthesis of their analogues based on other transition metals is highly underdeveloped. Herein, we present the first efficient systematic approach for the synthesis of homometallic [M4(μ4-O)L6]-type clusters incorporating divalent transition-metal centers, coated by bridging monoanionic organic ligands. As a proof of concept, we prepared a series of charge-neutral metal-oxido benzamidates, [M4(μ4-O) (NHCOPh)6] (M = Fe, Co, Zn), including iron(II) and cobalt(II) clusters not accessible before. The resulting complexes were characterized using elemental analysis, FTIR spectroscopy, magnetic measurements, and single-crystal X-ray diffraction. Detailed structural analysis showed interesting self-assembly of the tetrahedral clusters into 2D honeycomb-like supramolecular layers driven by hydrogen bonds in the proximal secondary coordination sphere. Moreover, we modeled the magnetic properties of new iron (II) and cobalt (II) clusters, which display a general tendency for antiferromagnetic coupling of the μ4-O/μ-benzamidate-bridged metal centers. The developed synthetic procedure is potentially easily extensible to other M(II)-oxido systems, which will likely pave the way to new oxido clusters with interesting optoelectronic and self-assembly properties and, as a result, will allow for the development of new functional materials not achievable before.