Structural diversity and properties of ZnII and CdII complexes with a flexible dicarboxylate building block 1,3-phenylenediacetate and various heterocyclic co-ligands

Abstract

A series of Zn^II and Cd^II complexes with a flexible dicarboxylate building block and various heterocyclic co-ligands, formulated as {[Zn₂(pda)₂(phen)₂]·2H₂O}_n (1), {[Zn(pda)(dpe)]·H₂O}_n (2), [Zn(pda)(bpp)]_n (3), {[Cd₂(pda)₂(2,2′-bipy)₂]·2H₂O}_n (4), {[Cd(pda)(4,4′-bipy)(H₂O)]·H₂O}_n (5) and {[Cd₂(pda)₂(bpp)₃]·14H₂O}_n (6) (pda = 1,3-phenylenediacetate, phen = 1,10-phenanthroline, dpe = 1,2-di(4-pyridyl)ethylene, bpp = 1,3-bi(4-pyridyl)propane, 2,2′-bipy = 2,2′-bipyridine, and 4,4′-bipy = 4,4′-bipyridine), have been synthesized and structurally characterized. In 1, the (H₂O)₈clusters interlink the cyclic coordination dimers to give a 3D network through hydrogen bonding. Both 2 and 3 feature 2D corrugated (4,4) layers, which are of 2-fold interpenetrating for 3. In 4, the dimeric Cd^II subunits are connected by the 1,3-pda ligands to generate a rampart-shaped 1D chain motif. As for 5, the [Cd(pda)]₂ rings are connected by the paired 4,4′-bipy ligands to afford a tube-shaped 1D motif. In contrast to 1–5, complex 6 displays a 3D diamond network and, interestingly, the T5(0)A(0)A(2) water tapes are found to locate in the channels of this 3-D array. A structural comparison of these complexes demonstrates that the characteristics of auxiliary ligands (from chelating to bridging) play a key role in governing the coordination motifs as well as the 3-D supramolecular lattices. Solid-state properties such as photoluminescence and thermal stability of 1–6 have also been studied.