Two Heptacopper(II) Disk Complexes with a [Cu7(μ3-OH)4(μ-OR)2]8+Core

Abstract

The reaction of CuX(2) (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 [Cu(7)(μ(3)-OH)(4)(μ-OR)(2)(μ-L)(6)](2+) and/or the cubane [Cu(4)(μ(3)-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: [Cu(7)(μ(3)-OH)(4)(μ-OCH(2)CF(3))(2)(μ-L)(6)][BF(4)](2) (2) and [Cu(7)(μ(3)-OH)(4)(μ-OCH(3))(2)(μ-L)(6)]Cl(2)·xCH(2)Cl(2) (3·xCH(2)Cl(2)). The molecular structures of both compounds as solvated crystals can be described as [Cu⊂Cu(6)(μ-OH)(4)(μ-OR)(2)(μ-L)(6)](2+) (R = CH(2)CF(3) or CH(3)) adducts. The [Cu(6)(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 = CH(2)CF(3)) or partially (R = CH(3)) 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.