Co(II), Cu(II), Mn(II) and Ni(II) complexes of maleic hydrazide

•Crystal structures are reported for transition metal complexes of maleic hydrazide.•The ligand binds through an N atom in the octahedral Co(II) and Ni(II) complexes.•The ligand binds through an O atom in the Cu(II) and Mn(II) complexes.•The ligand and coordinated waters are involved in extensive hydrogen-bonding networks.

The binding of 3d transition metals to maleic hydrazide (3,6-dihydroxypyridazine) has been investigated. Cobalt(II), copper(II), manganese(II) and nickel(II) complexes of maleic hydrazide have been prepared, crystallized and studied by various spectroscopic techniques. X-ray crystallographic structures of ML2·nH2O complexes with all four metal ions have been obtained. In all of the complexes two maleic hydrazides bind as unidentate ligands. Water molecules occupy the remaining coordination sites. In the cobalt(II) and nickel(II) complexes, which are isomorphous, the ligand binds through a single ligand nitrogen atom whereas in the manganese(II) and copper(II) complexes the ligand binds through a ligand oxygen atom. The metal ions all have six coordinate octahedral geometries except the copper(II) complex which has a five-coordinate square pyramidal geometry.

Graphical abstractMaleic hydrazide binds as a unidentate ligand to Co(II) and Ni(II) through a ring nitrogen atom but to Cu(II) and Mn(II) through a phenolate oxygen atom. All complexes have octahedral geometries with four water ligands except the Cu(II) complex which has a square pyramidal geometry with three water ligands.Figure optionsDownload full-size imageDownload as PowerPoint slide