Varying structural motifs in oxyanions (NO₃⁻, CO₃²⁻) and phenoxyacetate (PhOAc⁻) bridged coordination polymers derived from alkoxo-bridged dicopper building blocks with {Cu₂O₂} core

Abstract

The oxyanions (NO₃⁻, CO₃²⁻) and phenoxyacetate (PhOAc⁻) bridged three 1D-coordination polymeric chains, {[Cu₂(μ-hep)₂(μ-NO₃)]₂}_n (1), {[Cu₂(μ-hep)₂(H₂O)₂]·2H₂O(μ-CO₃)}_n (3) and {[Cu₂(μ-hep)₂(μ-PhOAc⁻)]₂}_n (2) (hep-H = 2-(2-hydroxyethyl)pyridine) have been synthesized. In 1-3 the alkoxide bridged dicopper building units, [Cu(μ-hep)]₂ with Cu₂O₂ core, are linked via the respective anions. Detailed structural analysis reveals that in 1 or 2, two units of NO₃⁻ (1) or PhOAc⁻ (2), respectively, bind with the four copper ions in two adjacent alkoxide bridged dimeric units in head-to-head and tail-to-tail fashion and the same binding mode continues along the polymeric chain. This in effect yields a 12-membered metallacyclic ring in between two dimeric core units. However, in 3 only one CO₃²⁻ group bridges the two copper centres associated with the two neighbouring alkoxide bridged dimeric units in head-to-tail mode which in turn forms a zig-zag polymeric chain. Two coordinated and two lattice water molecules from two adjacent polymeric layers in the structure of 3 form water tetramers. Furthermore, the interaction of water tetramer with the uncoordinated -C=O group of the bridging CO₃²⁻ develops an additional zig-zag chain which is being trapped between the two outer zig-zag coordination polymeric chains in 3. The polymeric chains in 1-3 further develop a 2D-network pattern via an extensive non-covalent hydrogen bonding as well as C-H···π and π···π interactions.