Dinuclear versus trinuclear complex formation in zinc(II) benzoate/pyridyl oxime chemistry depending on the position of the oxime group

Abstract

The initial employment of pyridine-3-carbaldehyde oxime, (3-py)C(H)NOH, and pyridine-4-carbaldehyde oxime, (4-py)C(H)NOH, in zinc(II) carboxylate chemistry is reported. The syntheses, crystal structures and IR characterization are described for [Zn 3(O 2CPh) 6{(3-py)C(H)NOH} 2] ( 1) and [Zn 2(O 2CPh) 4{(4-py)C(H)NOH} 2] ( 2). The trinuclear molecule of 1 has a linear structure, with one monoatomically bridging η 1:η 2:μ and two syn, syn-η 1:η 1:μ benzoate groups spanning each pair of Zn II ions; the terminal metal ions are each capped by one (3-py)C(H)NOH ligand coordinating through its pyridyl nitrogen. Complex 2 exhibits a dinuclear paddle–wheel structure with a Zn···Zn distance of 2.990(2) Å; each Zn II ion has a square pyramidal geometry with four carboxylate oxygens in the basal plane and the pyridyl nitrogen of one monodentate (4-py)C(H)NOH ligand at the apex. Both complexes form 1D architectures by virtue of hydrogen bonding interactions involving the free oxime group as donor and the oxime nitrogen ( 1) or carboxylate oxygens ( 2) as acceptors. IR data are discussed in terms of the known structures and coordination modes of the ligands.