Two Heptacopper(II) Disk Complexes with a [Cu7(μ3-OH)4(μ-OR)2]8+ Core
datasetposted on 06.12.2010, 00:00 by James J. Henkelis, Leigh F. Jones, Marcelo P. de Miranda, Colin A. Kilner, Malcolm A. Halcrow
The reaction of CuX2 (X− ≠ F−) salts with 1 equiv of 3-pyridyl-5-tert-butylpyrazole (HL) in basic methanol yields blue solids, from which disk complexes of the type [Cu7(μ3-OH)4(μ-OR)2(μ-L)6]2+ and/or the cubane [Cu4(μ3-OH)4(HL)4]4+ can be isolated by recrystallization under the appropriate conditions. Two of the disk complexes have been prepared in crystalline form: [Cu7(μ3-OH)4(μ-OCH2CF3)2(μ-L)6][BF4]2 (2) and [Cu7(μ3-OH)4(μ-OCH3)2(μ-L)6]Cl2·xCH2Cl2 (3·xCH2Cl2). The molecular structures of both compounds as solvated crystals can be described as [Cu⊂Cu6(μ-OH)4(μ-OR)2(μ-L)6]2+ (R = CH2CF3 or CH3) adducts. The [Cu6(μ-OH)4(μ-OR)2(μ-L)6] ring is constructed of six square-pyramidal Cu ions, linked by 1,2-pyrazolido bridges from the L− ligands and by basal, apical-bridging hydroxy or alkoxy groups, while the central Cu ion is bound to the four metallamacrocyclic hydroxy donors in a near-regular square-planar geometry. The L− ligands project above and below the metal ion core, forming two bowl-shaped cavities that are fully (R = CH2CF3) or partially (R = CH3) occupied by the alkoxy R substituents. Variable-temperature magnetic susceptibility measurements on 2 demonstrated antiferromagnetic interactions between the Cu ions, yielding a spin-frustrated S = 1/2 magnetic ground state that is fully populated below around 15 K. Electrospray ionization mass spectrometry, UV/vis/near-IR, and electron paramagnetic resonance measurements imply that the heptacopper(II) disk motif is robust in organic solvents.