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Hitoshi Hoshino, Takao Yotsuyanagi, Solubility and Synergistic Extraction Equilibria for [4-(2-Pyridylazo)resorcinolato] Nickel(II) Complexes, Bulletin of the Chemical Society of Japan, Volume 58, Issue 3, March 1985, Pages 1037–1040, https://doi.org/10.1246/bcsj.58.1037
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Abstract
The nickel(II) complex of 4-(2-pyridylazo)resorcinol (PAR, H2L) is known to show somewhat anomalous and complicated behavior in solution. In this regard, the solubility and the synergistic extraction equilibria of the above complex are studied in connection with acid dissociation reactions. The intrinsic solubility and the acid dissociation constants are determined to be, S0=[[Ni(HL)2]]=10−6.2±0.1 mol dm−3, Ka1=[[Ni(HL)L]−][H+][[Ni(HL)2]]−1=10−6.2±0.1, and Ka2=[[NiL2]2−][H+][[Ni(HL)L]−]−1=10−7.1×0.1, respeactively in the solution with the ionic strength of 0.10 (Na2SO4) at 298 K. Using the above constants, the extraction constant of the neutral complex with trioctylphosphine oxide (TOPO) into chloroform is evaluated as Kex=[[Ni(HL)2(TOPO)2]]o[[Ni(HL)2]]−1[TOPO]o−2=103.1±0.2, where the subscript o denotes the organic phase. An equilibrium diagram for the nickel(II)–PAR complexes is proposed.
