Two new coordination complexes {[(<b>L</b>)Cu₂('-<b>L</b>)(NO₃)(CH₃OH)_0.3(H₂O)_0.7]<b>·</b>NO₃}[Cu(<b>L</b>)(NO₃)(CH₃OH)] (<b>1</b>) and [Mn₂(-<b>L</b>)₂(H₂O)(₁-N₃)₂(CH₃OH)] (<b>2</b>) derived from (<i>E</i>)-<i>N</i>-(2-hydroxy-3-methoxybenzylidene)acetohydrazide [<b>LH</b>] have been synthesized. The new potentially tetradentate ONOO donor hydrazone ligand [<b>LH</b>] has shown considerable metal ion selective phenoxo bridging in <b>1</b> and <b>2</b>. It has coordinated copper(II) ions in its tridentate as well as in tetradentate fashion whereas for manganese(II) ions it solely showed its tetradentate character. In <b>1</b> the two adjacent pentacoordinate copper(II) centers are connected by a rare single phenoxo linkage of the hydrazone ligand whereas <b>2</b> is a doubly phenoxo-bridged heptacoordinated manganese(II) dinuclear species. The 3D supramolecular networks of <b>1</b> and <b>2</b> have resulted from extensive H-bonding interactions in the respective complexes. Structural variations observed for <b>1</b> and <b>2</b> have been described by performing single-crystal X-ray analysis. The ligand and the complexes are characterized by elemental analyses, IR, UV/Vis and ¹H NMR spectroscopy. Cryomagnetic investigations, DFT studies and EPR analysis, of <b>1</b> and <b>2</b> have also been studied in detail.< Réduire