Magnetic Coupling between Copper(II) Ions Mediated by Hydrogen-Bonded (Neutral) Water Molecules

A new hydrogen-bonded dinuclear copper(II) coordination compound has been synthesized from the Schiff-base ligand 6-(pyridine-2-ylhydrazonomethyl)phenol (Hphp). The molecular structure of [Cu2(php)2(H 2O)2(CIO4)](CIO4)-(H2O) (1), determined by single-crystal X-ray diffraction, reveals the presence of two copper(II) centers held together by means of two strong hydrogen bonds, with O···O contacts of only 2.60-2.68 A. Temperature-dependent magnetic susceptibility measurements down to 3 K show that the two metal ions are antiferromagnetically coupled (J= -19.8(2) cm-1). This exchange is most likely through two hydrogen-bonding pathways, where a coordinated water on the first Cu, donates a H bond to the O atoms of the coordinated php at the other Cu. This strong O ··· H (water) bonding interaction has been clearly evidenced by theoretical calculations. In the relatively few related cases from the literature, this exchange path, mediated by a (neutral) coordinated water molecule, was not recognized