Metal directed structural diversity of two coordination polymers and their optical and magnetic properties

Two new coordination polymers [Cu(5-NIP)₂(TBPE)] (1) (where, 5-NIP = 5-nitro isophthalic acid and TBPE = trans-4,4′-bipyridylethylene) and [Zn₄(μ3-OH)₂(5-NIP)₄(TBPE)₂] (2) have been synthesized and structurally characterized. Compound 1 features a molecular ladder type structure composed of Cu₂(5-NIP)₄ as metallacyclic platforms and TBPE as building blocks. Two nearly parallel ladders are assembled through π-π interactions between benzene rings of 5-NIP molecules, whereas a supramolecular two-fold interpenetrated square grid network results from the hydrogen bonding interactions between free carboxylates and nitrates of the 5-NIP molecules. Compound 2 forms a 3D network which is constructed from tetrameric units composed of two tetrahedral and two octahedral Zn(II) centers arranged in a coplanar fashion by two triply bridging μ3-OH groups. The electronic spectra of compound 1 reflect the distorted octahedral symmetry around the copper center in corroboration with the crystal structure data. EPR measurements again reconcile the D_4h symmetry for copper in an axially elongated octahedral geometry, in agreement with the spectroscopic studies. Magnetic susceptibility measurement reveals that compound 1 behaves like a magnetically dilute system with large spin-orbit coupling and it exhibits weak antiferromagnetic coupling at lower temperatures. Furthermore, the luminescent properties of both compounds were also determined in the solid state at room temperature.