Spectrophotometric study of the reactions of proton and copper (II) with arsenazo I in aqueous solution

摘要: The systems of proton and/or copper(II) ion with Arsenazo I (H6L) have been characterized at 25 °C and I= 1.0 mol dm–3(KCl) using u.v.–visible spectrophotometry. cumulative mixed protonation constants the ligand L6– are log β011= 12.114(19), β021= 21.871(18), β031= 29.506(16), β041= 32.155(6), β051= 34.298(6). Complexing reactions equilibrium copper(II)–Arsenazo system given by (i)–(v) below. Both mononuclear Cu2++ H++ L6–⇌[Cu(HL)]3– β111= 23.529(29)(i), L6–⇌[CuL]4– β101= 16.797(58)(ii), 2Cu2++ 2H++ L6–⇌[Cu2(H2L)] β221= 31.878(31)(iii), HL5–⇌[Cu(HL)]3– K111011= 11.415(35)(iv), H2L4–⇌[Cu2(H2L)] K221021= 10.007(36)(v) complexes found, former includes a diprotonated dinuclear species in solutions higher metal-to-ligand ratios hydrogen concentrations, latter monoprotonated prevailing lower pH values. Data analysed two computer programs: least-squares program LETAGROPVRID, version SPEFO, SQUAD. experimental spectra compared calculated ones discussed connection those similar compounds reported literature. Accurate molar absorption coefficients computed resolved spectral bands assigned. Tentative structures proposed given.