Syntheses, Structures, and Electrochemical and Magnetic Properties of Rectangular Heterobimetallic Clusters Based on Tricyanometallic Building Blocks

Three tricyanometalate precursors, (Bu 4 N)[(PhTp)Fe(CN) 3 ] · H 2 O ( 1 ), (Bu 4 N)[(MeTp)Fe(CN) 3 ] ( 2 ), and (Bu 4 N)[( i BuTp)Fe(CN) 3 ] ( 3 ) [Bu 4 N + = tetrabutylammonium cation; PhTp = tris(pyrazolyl)phenylborate; MeTp = methyltris(pyrazolyl)borate; i BuTp = 2‐methylpropyltris(pyrazolyl)borate], were successfully synthesized. By using 1 – 3 as building blocks, four rectangular clusters, [(PhTp)Fe(CN) 3 Cu(bpy)(H 2 O)(ClO 4 )] 2 · 2H 2 O ( 4 ; bpy = 2,2′‐bipyridine), [(PhTp)Fe(CN) 3 Ni(tren)] 2 (ClO 4 ) 2 [ 5 ; tren = tris(2‐amino)ethylamine], [(MeTp)Fe(CN) 3 Ni(tren)] 2 (ClO 4 ) 2 · 2H 2 O ( 6 ), and [( i BuTp)Fe(CN) 3 Ni(tren)] 2 (ClO 4 ) 2 · 2H 2 O · 2CH 3 OH ( 7 ), were prepared in parallel and structurally characterized. All clusters show similar square structures, where Fe III and M II (M = Cu II or Ni II ) ions are alternatively located on the rectangle corners. The cyclic voltammograms of Fe III 2 Ni II 2 clusters 5 – 7 reveal two quasireversible iron‐centered reduction processes and two quasireversible nickel‐centered oxidation processes. Magnetic studies show intramolecular ferromagnetic coupling and appreciable magnetic anisotropy in clusters 4 – 7 . Complexes 5 – 7 show obvious frequency dependence in the alternating current magnetic susceptibility data, which indicates single‐molecule magnet behavior with preexponential factors of τ 0 = 4.5 × 10 –8 s ( 5 ), 6.1 × 10 –8 s ( 6 ), and 5.0 × 10 –8 s ( 7 ) and the effective spin‐reversal barriers of U eff = 17.5 K ( 5 ), 20.6 K ( 6 ), and 20.8 K ( 7 ).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)