A series of five benzothiazolylhydrazone ligands 3a–3e and their seven novel Ru(II) polypyridine complexes 4a–4d, 5a, 5d, 5e of the type [Ru(N–N)2(L)]Cl2, where (N–N)2 is 2,2′-bipyridine (bpy)2 or 1,10-phenanthroline (phen)2 and (L) is ligands 3a–3e, have been synthesized and characterized by elemental analysis, IR, 1H NMR, electronic absorption, and emission spectral studies. The interpretation of the analytical data revealed that the ligands coordinate with the metal ion in a bidentate fashion through azomethine nitrogen and phenolic oxygen to form complexes. These ligands and complexes also exhibit absorption and luminescence properties. 1. Introduction In the last two decades, Ru(II) complexes have been widely studied in the field of inorganic chemistry [1–5]. The polypyridine complexes of Ru(II) have been studied extensively with the point of interest being their rich and well characterized photophysics [6, 7]. In recent years, transition metal complexes have been used extensively in the fore front of fields such as probes of DNA structure, DNA-dependent electron transfer, and site-specific DNA cleavage [8–10]. The area of metal complexes with hydrazones has been investigated intensively during the last years regarding their pharmacological applications such as tuberculostatic, antitumor, antibacterial, and antifungal agents [10–12]. The thiazole and benzothiazole hydrazone represent a very interesting class of ligands, due to additional donor sites: nitrogen, sulphur, or oxygen atom which introduce a wide range in their coordinative and pharmaceutical properties [10, 13–15]. In the context of this, we synthesized and characterized five ligands 2-(2′-hydroxy-3′-iodo-5′-chloro acetophenyl) benzothiazolylhydrazone 3a, 2-(2′,4′-dihydroxy acetophenyl) benzothiazolylhydrazone 3b, 2-(2′,5′-dihydroxy acetophenyl) benzothiazolylhydrazone 3c, 2-(2′-hydroxy-5′-chloro acetophenyl) benzothiazolylhydrazone 3d, 2-(2′-hydroxy-4′-methyl-5′-chloro acetophenyl) benzothialylhydrazone 3e, and their seven Ru(II) polypyridine complexes: [Ru(bpy)23a]Cl2？？4a, [Ru(bpy)23b]Cl2？？4b, [Ru(bpy)23c]Cl2？？4c, [Ru(bpy)23d]Cl2？？4d, [Ru(phen)23a]Cl25a, [Ru(phen)23d]Cl2？？5d, and [Ru(phen)23e]Cl2？？5e. 2. Experimental 2.1. Materials and Methods All reagents and solvents were purchased commercially and were used as received. 2-Mercaptobenzothiazole, hydrazine hydrate, acetophenone, and RuCl3？·？3H2O were obtained from SD Fine-chem limited (India). The compounds 3a–3e [13], [Ru(bpy)2Cl2]？·？nH2O and [Ru(phen)2Cl2]？·？nH_2 O, and the metal complexes 4a–4d, 5a, 5d, and 5e [16] were synthesized
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