Self-assembly of new three-dimensional molecular architectures of Cd(II) and Ag(I)–Na(I) using croconate as a building block

Abstract

Two new coordination polymers [Cd(C₅O₅)(NH₃)₂]_n (1) and [AgNa(C₅O₅)(H₂O)₂]_n (2) (C₅O₅²⁻ = croconate dianion) have been synthesized and structurally characterized. Complex 1 is a one-dimensional coordination polymer of cadmium(II) bridging through the croconate dianion. In complex 1 each croconate chelates (O1 and O2) to a Cd centre, which is linked to another Cd centre by O1 through an oxo-bridge and the oxygen atom O5, neighbouring O1, binds to a third Cd centre and the remaining two oxygen atoms (O3 and O4) remain pendant. The 1D coordination polymer undergoes H-bonding interactions through N–H(NH₃)⋯O (pendant of C₅O₅) resulting in a 3D supramolecular network. Compound 2 is a heterometallic (Ag,Na) 3D coordination polymer. Here the croconate dianions interweave the alternately aligned and layered –Na–(μ–H₂O)₂–Na–(μ–H₂O)²⁻ and –Ag–Ag–Ag– chains. Two croconates chelate one Ag atom and two such Ag atoms from two neighbouring layers are bridged through croconate (O1, O2) and one oxygen of each croconate remains pendant (O3). The oxygen atom (O2) from every croconate binds a Na atom via an oxo-bridge. These types of tridentate and tetradentate linkage of croconate in complexes 1 and 2 are unprecedented. The thermal studies of the complexes corroborate that the ammonia molecules in 1 and the water molecules in 2 are involved in coordination together with strong H- bonding interactions.