Magnetic interactions in metal complexes of pentadentate binucleating ligands. 1. Synthesis and properties of binuclear copper(II) compounds containing single-atom-bridging ligands. Crystal and molecular structure of a binuclear .mu.-hydroxo-bridged copper(II) complex of 1,5-bis[1-(pyridin-2-yl)ethylideneamino]pentan-3-ol