Investigation of the zinc(ii)–benzoate–2-pyridinealdoxime reaction system

Abstract

The employment of pyridine-2-carbaldehyde oxime (paoH) in zinc(II) benzoate chemistry, in the absence or presence of azide ions, is described. The syntheses, crystal structures and spectroscopic characterization are reported for the complexes [Zn(O₂CPh)₂(paoH)₂] (1), [Zn₁₂(OH)₄(O₂CPh)₁₆(pao)₄] (2) and [Zn₄(OH)₂(pao)₄(N₃)₂] (3). The Zn^II centre in octahedral 1 is coordinated by two monodentate PhCO₂⁻ groups and two N,N′-chelating paoH ligands. The metallic skeleton of 2 describes a tetrahedron encapsulated in a distorted cube. The {Zn₁₂(μ-OH)₄(μ₃-ΟR)₄}¹⁶⁺ core of the cluster can be conveniently described as consisting of a central {Zn₄(μ₃-ΟR)₄}⁴⁺ cubane subunit (RO⁻ = pao⁻) linked to four {Zn₂(μ-OH)}³⁺ subunits via the OH⁻ group of each of the latter, which becomes μ₃. The molecule of 3 has an inverse 12-metallacrown-4 topology. Two triply bridging hydroxido groups are accommodated into the metallacrown ring. Each pao⁻ ligand adopts the η¹ : η¹ : η¹ : μ coordination mode, chelating one Zn^II atom and bridging a Zn^II₂ pair. Complexes 1 and 2 display photoluminescence with maxima at ∼355 nm and ∼375 nm, upon maximum excitation at 314 nm; the origin of the photoluminescence is discussed.