Background The heterocyclic hydrazones constitute an important class of biologically active drug molecules. The hydrazones have also been used as herbicides, insecticides, nematocides, redenticides, and plant growth regulators as well as plasticizers and stabilizers for polymers. The importance of the phenolic quinolyl hydrazones arises from incorporating the quinoline ring with the phenolic compound; 2,4-dihydroxy benzaldehyde. Quinoline ring has therapeutic and biological activities whereas, phenols have antiseptic and disinfectants activities and are used in the preparation of dyes, bakelite and drugs. The present study is planned to check the effect of the counter anions on the type and geometry of the isolated copper(II)- complexes as well as the ligational behavior of the phenolic hydrazone; 4-[(2-(4,8-dimethylquinolin-2-yl)hydrazono)methyl] benzene-1,3-diol; (H2L). Results A phenolic quinolyl hydrazone (H2L) was allowed to react with various copper(II)- salts (Cl￣, Br￣, NO3￣, ClO4￣, AcO￣, SO42-). The reactions afforded dimeric complexes (ClO4￣, AcO￣ ), a binuclear complex (NO3￣ ) and mononuclear complexes (the others; Cl￣, Br￣, SO42-). The isolated copper(II)- complexes have octahedral, square pyramid and square planar geometries. Also, they reflect the strong coordinating ability of NO3￣, Cl￣, Br￣, AcO￣ and SO42- anions. Depending on the type of the anion, the ligand showed three different modes of bonding viz. (NN)0 for the mononuclear complexes (3, 4, 6), (NO)- with O- bridging for the dimeric complexes (1, 5) and a mixed mode [(NN)0 + (NO)- with O- bridging] for the binuclear nitrato- complex (2). Conclusion The ligational behavior of the phenolic hydrazone (H2L) is highly affected by the type of the anion. The isolated copper(II)- complexes reflect the strong coordinating power of the SO42-, AcO￣, Br￣, Cl￣ and NO3￣ anions. Also, they reflect the structural diversity (octahedral, square pyramid and square planar) depending on the type of the counter anion.
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