Synthesis, structure and physical properties of trinuclear M3tdt3(PEt3)3 (M = FeII, CoII) clusters containing metal–metal bonds

Trinuclear M3tdt3(PEt3)3 (M = FeII for I, CoII for II) clusters have been synthesized from the reaction between M(PEt3)2Cl2 and Na2tdt (tdt = toluene-3,4-dithiolate) in MeCN. Both complexes have been characterized by elemental analyses, FT-IR, UV–Vis, FAB-MS, 1H NMR and cyclic voltammetry. Structures of Fe3tdt3(PEt3)3 (I) and Co3tdt3(PEt3)3 (II) were determined by single crystal X-ray crystallography. The Fe3 triangular core of the 48-electron complex I, with an isosceles triangular geometry, showed very short Fe–Fe distances of 2.4014(13) and 2.4750(12) Å, which are comparable to the extensive M–M frameworks found in the FeMo-cofactor in nitrogenase. The isostructural Co3tdt3(PEt3)3 (II), with an analogous Co3 coordination geometry, showed short Co–Co distances of 2.4442(9) and 2.5551(10) Å. The slightly longer M–M distances in complex II were explained by a total valence electron counting argument. Cyclic voltammetry of Fe3tdt3(PEt3)3 (I) showed robust reduction waves compared to Co3tdt3(PEt3)3 (II). Temperature-dependent effective magnetic moment measurements of I and II showed both clusters behave similarly and the magnetic property of the M3 equilateral triangle core with extensive metal–metal interactions was characterized as degenerate frustration.

Graphical abstractTrinuclear M3tdt3(PEt3)3 (M = FeII for I, CoII for II) clusters have been synthesized and characterized. The isosceles triangular clusters with short M–M distances, comparable to the extensive M–M frameworks found in the FeMo-cofactor, show unique physical properties.Figure optionsDownload full-size imageDownload as PowerPoint slide