Structurally characterized luminescent lanthanide zinc carboxylate precursors for Ln–Zn–O nanomaterials

Abstract

A novel family of lanthanide zinc carboxylate compounds was synthesized, characterized (structural determination and luminescent behavior), and investigated for utility as single-source precursors to Ln–Zn–O nanoparticles. Carboxylic acids [H–ORc = H–OPc (H–O₂CCH(CH₃)₂, H–OBc (H–O₂CC(CH₃)₃, H–ONc (H–O₂CCH₂C(CH₃)₃)] were individually reacted with diethyl zinc (ZnEt₂) to yield a set of previously unidentified zinc carboxylates: (i) [Zn(μ-ORc)₃Zn(μ-ORc)]_n [ORc = OPc (1), ONc (2)], (ii) [(py)Zn]₂(μ-ORc)₄ [ORc = OBc (3), ONc (4), and py = pyridine], or (iii) Zn(ORc)₂(solv)₂ [ORc/solv = OPc/py (5), O^cNc/H₂O (6) (O^cRc = chelating)]. Introduction of lanthanide cation [Ln[N(SiMe₃)₂]₃, ZnEt₂, and HOBc in py] yielded the mixed cationic species structurally characterized as: (i) (O^cBc)Ln[(μ-OBc)₃Zn(py)]₂ [Ln = Pr (7), Nd (8), Sm (9)] or (ii) (py)₂Zn(μ-OBc)₃Ln(O^cBc)₂(py) [Ln = Tb (10), Dy (11), Er (12), Y (13), Yb (14)]. Exploration of alternative starting materials [Ln(NO₃)₃·nH₂O, Zn(O₂CCH₃)₂, HOBc in py] led to the isolation of (NO₃^c)Ln[(μ-OBc)₃Zn(py)]₂ [Ln = La (15), Ce (16), Pr (17), Nd (18), Sm (19), Eu (20), Gd (21), Tb (22) Dy (23), and Er (24); NO₃^c = chelating]. The UV-vis spectra of 7–24 revealed standard absorption spectra for the Ln cations. Representative compounds were used to generate nanoparticles from an established 1,4-butanediol-based solution precipitation route. The nanoproducts isolated adopted either a mixed zincite/lanthanum oxide (18n or 22n) or pure zincite (8n or 10n) phase dependent on NO₃ or OBc moiety. Fluorescence was not observed for any of these nanomaterials possibly due to phase separation, low crystallinity, surface traps, and/or quenching based on elevated Ln cation content.