Evidence for Hydrogen‐Bond‐Mediated Exchange Coupling in an Aqua‐Bridged Cu^II Dimer: Synthesis, Magnetic Study and Correlation with Density Functional Calculations

Abstract

Abstract A rare example of a mono‐aqua‐bridged copper( II ) dimer,namely [Cu 2 (μ 2 ‐H 2 O)L 2 (H 2 O) 2 ](ClO 4 ) 2 · 2H 2 O ( 1 ), has been synthesised and its structure determined by single‐crystal X‐ray diffraction. Each Cu II centre is in a square‐pyramidal surrounding formed by a Schiff base and a terminal H 2 O ligand; a second H 2 O ligand, which acts as a bridge, is common to two metal ions. Hydrogen bonds between the H 2 O ligand and the Schiff base of the adjacent centre complete the intra‐dimer linkages. This compound exhibits an antiferromagnetic behaviour ( J = –13.2 cm –1 , H = – J S 1 · S 2 ), and density functional calculations clearly establish that the main exchange does not proceed through the bridging H 2 O but is mediated by the intra‐dimer H‐bonds.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)