Investigation of the zinc(II) acetylacetonate/benzotriazole reaction system in the presence of bridging N,N′-ligands: Pentanuclear, enneanuclear and polymeric complexes

The reaction of Zn(acac)₂ with btaH (1,2,3-benzotriazole) in dmf yielded the pentanuclear complex Zn₅(bta)₆(acac)₄(dmf)]·dmf (1·dmf). In the presence of pyrazine, the pentanuclear Zn₅(bta)₆(acac)₄(dmf)]·3.7dmf (2·3.7dmf) and enneanuclear Zn₉(bta)₁₂(acac)₆]·6dmf (3·6dmf) complexes were formed, whereas in the presence of 4,4′-bpy the 1D coordination polymer Zn(acac)₂(4,4′-bpy)]_n (4) was isolated. The molecular structures of 1·dmf and 2·3.7dmf reveal that the Zn₅] clusters consist of four Zn^II ions which span the corners of a tetrahedron and the fifth resides at its centre. The molecular structure of 3·6dmf reveals that the Zn₉] clusters consist of two corner sharing tetrahedra and the structure can be described as the addition of two Zn₅] clusters of 1·dmf and/or 2·3.7dmf followed by the simultaneous abstraction of Zn(acac)₂] and dmf molecules; this alternative was accomplished by recrystallization of 1·dmf from dmf which yielded 3·6dmf. Each of the μ₃-κN:κN′:κN′′ benzotriazolate ligands in 1·dmf, 2·3.7dmf and 3·6dmf spans an edge of the tetrahedron. The molecular structure of 4 reveals mononuclear Zn(acac)₂] units bridged via 4,4′-bpy molecules to 1D coordination polymer. Characteristic IR bands of the four complexes are discussed in terms of the coordination modes of the ligands and known structures.