[Pd(en)(H2O)2]2+ and [Pd(pic)(H2O)2]2+ complexation by monohydroxamic acids: A solution equilibrium and solid state approach. (4th November 2015)

• Record Type: Journal Article
• Authors: Buglyó, Péter; Lénárt, Krisztina; Kozsup, Máté; Bényei, Attila Csaba; Kováts, Éva; Sóvágó, Imre; Farkas, Etelka
• Is Part Of: Polyhedron. Volume 100(2015)
• Page Start: 392
• Page End: 399
• Publication Date: 2015-11-04
• Subjects: Palladium -- Speciation -- Hydroxamic acids -- Stability constants -- Hydroxymato-N coordination; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2015.08.036
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: While secondary hydroxamates form mononuclear [O, O] chelated complexes with [Pd(en/pic)(H2 O)2 ] 2+ primary hydroxamates are capable of binding an excess of metal ion too with the involvement of the hydroxymate-N − donor(s) yielding oligonuclear complexes with high stability. Abstract: Complex formation between [Pd(en/pic)(H2 O)2 ] 2+ (en = ethylenediamine, pic = pyridine-2-methylamine) and primary hydroxamic acids (ahaH = acetohydroxamic, bhaH = benzohydroxamic acid) or secondary hydroxamic acids (meahaH = N -methyl-acetohydroxamic, pheahaH = N -phenylacetohydroxamic and phebhaH = N -phenylbenzohydroxamic acid) was studied in aqueous solution by pH-potentiometry, 1 H NMR and ESI-TOF-MS. Secondary hydroxamates form 1:1 species with the [Pd(N, N)(H2 O)2 ] 2+ ions via the [O, O] chelating sets. Unexpectedly, in the primary ligands deprotonation and coordination of the hydroxamate-NH starts as low as pH <2, where the RC C(O)N − O − ion is capable of linking two [Pd(diamine)] 2+ units via the coordination through the [O, O] chelate to one unit and through the monodentate hydroxymato-N − atom to the another one. As a consequence, primary ligands can bind an excess of metal ion too. A trinuclear complex predominates in a wide pH-range (5–10 for en, 3–10 for pic) and the hydroxide ion starts to compete with the hydroxymato ligand only above pH 10. In the trinuclear species two [O, O] chelated Pd(II) units are bridged via a third palladium core that binds to the hydroximato-N donors of the two ligands. This binding mode was also proved by MS studies in solution and by revealing the molecular structure of [(Pd(en))3 (bhaH−1 )2 ](BF4 )2 ·2H2 O (2 ), the first reported structure with a Pd(II)-hydroxymate-N − monodentate coordination, characterized with single crystal X-ray diffraction in the solid state.