Copper(II) and Nickel(II) Complexes of two Nitrogen‐Functionalized N‐Salicylidene Carbonic Acid Hydrazides: Molecular and Supramolecular Architectures

Abstract

AbstractCopper(II) and nickel(II) complexes with the new Schiff‐base ligands N‐salicylidene‐3‐(2‐pyridyl)‐propionic acid hydrazide (H2salhypyp) and the newly synthesized N‐Salicylidene‐3‐(1‐benzylimidazol‐2‐yl)‐propionic acid hydrazide (H2salhyimp) have been synthesized and structurally characterized. The crystal structure analysis of the metal complexes reveals two fundamentally different structural motifs. Cationic di‐μ‐phenolate‐bridged dimers are observed for the complexes with the H2salhypyp ligand, [{Cu(H2salhypyp)(MeOH)(ClO4)}2](ClO4)2 (1) and [{Ni(H2salhypyp)Cl(MeOH)}2]Cl2(MeOH)2 (2), whereas neutral dimeric units aggregated via the side chain nitrogen donors are observed for the complexes with the H2salhyimp ligand, [{Ni(salhyimp)}2](H2O)4 (4) and [{Cu(salhyimp)}2](MeOH)4 (3). The formation of either motif depends on the charge of the ligand species and consequently on the pH‐value of the reaction solution. For the complexes 1 and 2 extensive hydrogen‐bonding networks are observed which involve the perchlorate (N–H···O–Cl) and chloride anions (N–H···Cl), respectively. The M2O2 core unit of complexes 1 and 2 facilitates the formation of intramolecular M–(Me)O–H···X–M hydrogen‐bonding interactions $\rm (X = ClO^{-}_{4}, Cl^{-})$. The copper complex 3 exhibits an unusual one‐dimensional coordination polymer which is linked through the axial coordination of phenolate oxygen atoms of adjacent dimeric units. Complex 4 exhibits a layered structure with each layer composed of hydrophobic π‐stacks of the dimeric complex units which are interlaced by hydrogen‐bonded chains of water molecules. The supramolecular structures of 3 and 4 are governed by π‐π‐stacking interactions. For 4 additional CH/π interactions are found within and between individual sheets of the layered structure.