Structural influence of the length and functionality of NN-donor spacers in Cd(II) ladder-type coordination polymers

Abstract

The understanding of the effect generated by small differences of the organic ligands on the molecular and supramolecular arrangement of coordination polymers (CPs) is a key factor to control their properties. Therefore, the study of structurally related ligands differing in some factors inter alia functional group orientation, length, or functionality is a crucial task for crystal engineers. In this contribution, the reactions between Cd(OAc)2·2H2O, α-acetamidocinnamic acid (HACA) and different N,N-donor spacers with increasing length (pyrazine, pyz; 4,4’-bipyridine, 4,4’-bipy; 1,2-bis(4-pyridyl)ethylene, 1,2-bpe), as well as additional functionalities (4,4’-azopyridine, 4,4’-azpy) have been successfully performed. Their crystal structures have been elucidated revealing a family of ladder-type 1D CPs showing molecular arrays with single pillars for {[Cd2(μ-ACA)2(ACA)2(pyz)(H2O)2]·2EtOH}n (1), and double pillars for [Cd2(μ-ACA)2(ACA)2(4,4’-bipy)2]n (2), [Cd2(μ-ACA)2(ACA)2(1,2-bpe)2]n (3) and {[Cd2(μ-ACA)2(ACA)2(4,4’-azpy)2]·4,4’-azpy·9H2O}n (4). Remarkably, the effect of the addition of the azo group in 4 compared with 2 and 3 has led to a CP with the same molecular arrangement but different crystal packing, allowing the introduction of one non-coordinated 4,4’-azpy and nine water molecules. Finally, their solid-state UV-Vis and photoluminescence have been measured observing their blue-emitting properties.