1337 J. Indian Chem. Soc., Vol. 92, September 2015, pp. 1337-1347 Inorganic base assisted synthesis of sodium [tris-(acetylacetonato)nickelate(II)] complex and kinetics of its acid-dissociation Chayanika Debnath, Diptanu Debnath and Tarun Kumar Misra* Department of Chemistry, National Institute of Technology, Agartala-799 046, Tripura, India E-mail : t_k_misra@yahoo.com Manuscript received online 26 October 2014, revised 11 December 2014, accepted 15 January 2015 Abstract : Nickel(II) complexes of acetylacetone are potential materials in all disciplines notably catalysis and biology. Most of them are not easy to prepare. A synthetic method of preparation and isolation of sodium salt of tris - (acetylacetonato)nickelate(II), Na[Ni(acac) 3 ] and study of its stability in aqueous and acidic media have been reported. The complex has been characterized by conductance, elemental and metal analysis, UV-Vis and IR spectroscopy studies. Conductance measurement supported that the complex is 1 : 1 electrolyte. Elemental and metal analysis evidenced the presence of three units of acac (= acetylacetonato) per complex and one nickel atom [19.32% (Calcd. 20.03)] per acac unit, respectively. UV-Vis absorbance bands : 3 A 2g ( 3 F) 3 T 2g ( 3 F) ( 1 = 9416 cm –1 ); 3 A 2g ( 3 F) 3 T 1g ( 3 F) ( 2 = 1605 cm –1 ) of the tris-complex (azide assisted) are blue shifted in comparison with trans-[Ni(acac) 2 (H 2 O) 2 ], revealing strong Ni II - acac covalent interaction. IR spectra of tris-complex reveal that the tris-complex has no coordinated water molecules. The spectra provided (C=O) and (Ni-O) bands at 1590 and 433 cm –1 which are red and blue shifted, respectively in comparison with trans-[Ni(acac) 2 (H 2 O) 2 ], indicating strong Ni-O bonding. The tris-complex is susceptible to dissociates in aqueous medium (k obs = 4.9 × 10 –3 min –1 ) as well as in acid media (k s = 2.0 × 10 –3 min –1 ). To comprehend the potentiality of Ni II -complexes of acetylacetone, the as-synthesized tris-complex must be a futuristic material. Keywords : Nickel(II), acetylacetone, tris-complex, stability, dissociation constant. Introduction Nickel(II) complexes of acetylacetone (acacH) have been extensively studied because of their potential appli- cation in the field of catalysis : polymerization, oligo- merization, reduction, cross-coupling, oxidation, conju- gate addition to multiple bonds, rearrangements 1–6 , and so on. They are found in different forms : square planar mononuclear, Ni(acac) 2 , octahedral trinuclear, Ni 3 (acac) 6 , dinuclear, Ni 2 (acac) 2 (H 2 O) 2 and mononuclear, trans- Ni(acac) 2 (H 2 O) 2 in solid state as well as in non-coordi- nating solvents. Moreover, all complexes are solvated to mononuclear cis/trans-Ni(acac) 2 (Solv) 2 in coordinating solvents (Solv. = H 2 O, MeOH, EtOH, DMF, DMSO, etc.). Single crystal X-ray studies of some solvent adduct complexes so far isolated in the solid state are mainly trans-adducts, such as trans-Ni(acac) 2 (MeOH) 2 7 and trans- Ni(acac) 2 (EtOH) 2 8 . Crystal structures of square planar mononuclear, Ni(acac) 2 9 and octahedral trinuclear, Ni 3 (acac) 6 10 had also been studied and reported. The trinuclear species is stable in non-coordinating solvents 11,12 whereas it is converted to mononuclear and dinuclear species in coordinating solvents, such as methanol and pyridine 7,13 . Another class of compounds known as homoleptic anion coordination compounds with acetylacetone ligand have been scarcely studied 14–19 . Three nickel(II)-complexes of this class have been reported so far 14,18,19 . The first compound based on the [Ni(acac) 3 ] – anion was reported by Watson and Lin 14 with the formula Ag[Ni(acac) 3 ]· 2AgNO 3 ·H 2 O. Atencio et al. 18 reported the crystal struc- ture of K[Ni(acac) 3 ]·0.3H 2 O. Recently, Baldo et al. 19 described the crystal structure of polymeric chain com- pound, [NaNi(acac) 3 ] n . Authors of the last two compounds showed polymeric 1D array with K/Na---O interactions between the K + /Na + ions and the O atoms on opposite faces of the NiO 6 octahedron of the complex anion. Baldo et al. 19 had got the compound, Na[Ni(acac) 3 ] as a secon- dary product from the methanolic solution of a mixture :