A Tetranuclear Hydroxo‐Bridged Copper( II ) Complex with PrimaryN‐Acylamidines as Ligands: Preparation, Structural, and Magnetic Characterisation

The reaction of N‐pivaloylbenzamidine (1a) and tetrakis(acetonitrile)copper(I) hexafluorophosphate in the presence of air yields a hydroxo‐bridged copper(II) complex (4). The product was characterised by X‐ray diffraction analysis and found to be a cubane‐like dimeric complex consisting of two square dimers with the formula [{(1a)2Cu2(OH)2}2](PF6)4·4 CH2Cl2 (4·4 CH2Cl2) with cupric ions and hydroxyl oxygen atoms at alternating vertices of a cube. The complex can be described as consisting of two [ligand‐Cu‐(OH)2‐Cu‐ligand] units held together by long out‐of‐plane Cu–O bonds, creating a tetrameric entity with a Cu4(OH)4 core. Each cupric ion is essentially square‐pyramidally coordinated, being bound to three OH bridges, one N atom of the amidine and one N‐acylamidine O atom. The magnetic properties of this compound have been studied in the 2–300 K temperature range. The measurements revealed that the cupric ions in the cube are antiferromagnetically coupled. This observation has been rationalised on the basis of the structural data. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)