A tetranuclear hydroxo-bridged copper(II) cluster of the cubane type. Preparation and structural and magnetic characterization of tetrakis[(2,2′-bipyridyl)hydroxocopper(II)] hexafluorophosphate

Abstract

The title compound, C40H36N8Cu4F24O4P4, noted [Cu(bpy)(OH)]4(PF6)4, has been synthesized, and its structure has been determined by X-ray crystallographic methods. Crystal data: monoclinic system, space group C2/c, a = 24.494 (7) Å, b = 14.104 (3) Å, c = 16.336 (4) Å, β = 112.65 (2)°, Z = 4. Data up to 6 = 26° (Mo Ka radiation) were collected at room temperature on a CAD4 diffractometer. The structure was solved by direct methods and refined by full-matrix least-squares refinement to R = 0.069, including 3667 reflections with [equation omitted]. The complex may be described as two almost planar bpy-Cu-(OH)2-Cu-bpy units held together by long out-of-plane Cu-O(H) bonds (2.486 and 2.585 Å), creating a tetrameric entity with a cubane-like Cu4(OH)4 core. Within each hydroxo-bridged dinuclear unit both of the crystallographically independent copper atoms form four short equatorial bonds to two hydroxo oxygen atoms (1.947-1.962 Å) and two bipyridyl nitrogen atoms (1.981-1.997 Å). The second axial position around each copper is occupied by a fluorine atom (Cu-F = 2.64 and 2.68 Å), a hexafluorophosphate ion bridging the two copper atoms within a dinuclear unit. The two remaining hexafluorophosphate ions are uncoordinated. The magnetic properties of this compound have been studied in the 4.2-300 K temperature range. They correspond to what is expected for a ferromagnetically coupled CuCu pair with a triplet-singlet energy gap of 12 cm−1. The data may, however, also be fitted to a model that includes weak ferromagnetic interaction between dimers. Magnetization studies have confirmed such an interdinuclear interaction. © 1990, American Chemical Society. All rights reserved.