A Tetranuclear Hydroxo‐Bridged Copper( II ) Complex with Primary N‐ 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 ) 2 Cu 2 (OH) 2 } 2 ](PF 6 ) 4 · 4 CH 2 Cl 2 ( 4· 4 CH 2 Cl 2 ) 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 Cu 4 (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)