Synthesis, structure and physical properties of trinuclear M(3)tdt(3)(PEt3)(3) (M = Fe-II, Co-II) clusters containing metal-metal bonds

Abstract

Trinuclear M(3)tdt(3),,(PEt3)3 (M = Fe-11 for 1, Con for 11) clusters have been synthesized from the reaction between M(PEt3Cl2, and Na-2,tdt (tdt = toluene- 3 4-dithiolate) in MeCN. Both complexes have been characterized by elemental analyses, FT-IR, UV-Vis, FAB-MS, H-1 NMR and cyclic voltammetry. Structures of Fe(3)tdt(3)(PEt3)3 (1) and Co(3)tdt(3)(PEt3)3 (11) were determined by single crystal X-ray crystallography. The Fe-3 triangular core of the 48-electron complex 1, with an isosceles triangular geometry, showed very short Fe-Fe distances of 2.4014(13) and 2.4750(12) A, which are comparable to the extensive M-M frameworks found in the FeMo-cofactor in nitrogenase. The isostructurat Co(3)tdt(3)(PEt3)3 (H), with an analogous Co-3 coordination geometry, showed short Co-Co distances of 2.4442(9) and 2.5551(10) A. The slightly longer M-M distances in complex 11 were explained by a total valence electron counting argument. Cyclic voltammetry of Fe3tdt3(PEt3)3 (1) showed robust reduction waves compared to C03tdt3(PEt3)3 (11). Temperature-dependent effective magnetic moment measurements of I and 11 showed both clusters behave similarly and the magnetic property of the M-3 equilateral triangle core with extensive metal-metal interactions was characterized as degenerate frustration. (c) 2007 Elsevier Ltd. All rights reserved.