The synthesis and characterization of a series of bis-bidentate Schiff base ligands and their coordination complexes with silver(i), copper(i) and zinc(ii) d10 metal ionsElectronic supplementary information (ESI) available: Views of the crystal structures of ligands of 1, 2 and 3. See http://www.rsc.org/suppdata/nj/b3/b301632c/