Metal oxo cluster-based coordination polymers with rigid 1,4-naphthalenedicarboxylate and semirigid 1,3-di(4-pyridyl)propaneligands: syntheses, structural topologies, and luminescent properties

Abstract

Hydrothermal reactions of Zn(NO₃)₂ or Pb(NO₃)₂ with 1,4-naphthalenedicarboxylic acid (1,4-H₂ndc) and 1,3-di(4-pyridyl)propane (dpp) lead to two novel metal oxo cluster-based coordination polymers, namely, [Zn₅(μ₃-OH)₂(1,4-ndc)₄(dpp)₂]_n (1) and [Pb₅(μ₄-O)(1,4-ndc)₄(dpp)]_n (2). The structures exhibit different cluster motifs depending on the nature of the metal ions. Compound 1 features a 3D structure based on the pentanuclear [Zn₅(μ₃-OH)₂] secondary building unit (SBU) where the five zinc atoms are coplanar; its topological structure is an uninodal 10-connected network of (3⁶.4³⁴.5³.6²) topology. The zinc ions in 1 have a coordination number varying from 4 to 6 and are accompanied by a variety of coordination geometries such as tetrahedral, trigonal bipyramidal, and octahedral. Compound 2 has a 3D architecture containing an unusual hexanuclear [Pb₆(μ₄-O)₂] cluster unit composed of two edge-sharing oxygen-centred [Pb₄(μ₄-O)] tetrahedrons. One explanation for the presence of the centred bridging oxide ligands in 2 is that owing to steric constraints sufficient carboxylate ligands cannot coordinate to the Pb(II) centers to satisfy the positive charges of the Pb(II) cations. The Pb(II) ions in 2 exhibit diverse hemidirected coordination geometries with coordination numbers of 6 and 7. In the solid state, compounds 1 and 2 exhibit photoluminescence with emission maximum at 495 and 420 nm, respectively.