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

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), [Zn-12(OH)(4)(O2CPh)(16)(pao)(4)] (2) and [Zn-4(OH)(2)(pao)(4)(N-3)(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 {Zn-12(mu-OH)(4)(mu(3)-OR)(4)}(16+) core of the cluster can be conveniently described as consisting of a central {Zn-4(mu(3)-OR)(4)}(4+) cubane subunit (RO- = pao(-)) linked to four {Zn-2(mu-OH)}(3+) subunits via the OH- group of each of the latter, which becomes mu(3). 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 eta(1) : eta(1) : eta(1) : mu coordination mode, chelating one Zn-II atom and bridging a Zn-2(I) pair. Complexes 1 and 2 display photoluminescence with maxima at similar to 355 nm and similar to 375 nm, upon maximum excitation at 314 nm; the origin of the photoluminescence is discussed.