Influential Role of Geometrical Disparity of Linker and Metal Ionic Radii in Elucidating the Structural Diversity of Coordination Polymers Based on Angular Dicarboxylate and Bis-pyridyl Ligands

Abstract

As a continuation of our recent investigations on coordination polymer/metal–organic framework containing compounds, herein, four new coordination polymers, namely, {Co 2 (ADA) 2 (px2ampy)} n ( 1 ), {Cd(ADA)(px2ampy) 0.5 } n ( 2 ), {Co 2 (IPTA) 2 (px2ampy)} n ( 3 ), {Mn(IPTA)(px3ampy)} n ( 4 ) have been synthesized, based on the flexible dicarboxylate ligand H 2 ADA and rigid dicarboxylate ligand H 2 IPTA along with long flexible bis-pyridyl linkers as coligand (where H 2 ADA = 1,3-adamantanediacetic acid; H 2 IPTA = isopthalic acid; px2ampy = 1,4-bis(2-pyridylaminomethyl)benzene; px3ampy = 1,4-bis(3-pyridylaminomethyl)benzene). Compounds 1 – 4 have been characterized by routine elemental analysis, IR spectroscopy, and thermogravimetric (TG) analysis and unambiguously by single crystal X-ray diffraction analysis. The solid-state luminescent property of compound 2 has been additionally characterized. Compound 1 is a two-dimensional (2D) framework, constructed by the connectivity of Co 2 paddle-wheels as secondary building units (SBUs) and the organic linkers. The 2D sheet of compound 2 consists of Cd-dimers as SBUs and extends to a supramolecular three-dimensional (3D) framework through H-bonding interactions among the sheets. Compound 3 is a 3D coordination polymer, in which an unusual SBU is formed by two Co II centers: one in tetrahedral and the other one in octahedral coordination geometries. In the crystal structure of compound 4, the connectivity of the Mn 2 -dimers with the macrocyclic rings, formed from px3ampy coligands, results in the formation of 2D layer structures. The title compounds 1 – 4 illustrate an important structural relationship, which can be rationalized by the geometrical diversity of two different dicarboxylate ligands and the nature of different metal ions, employed in this study. The role of the metal ionic radii in assessing the formation of final architectures, thereby, influencing the dimensionality of the compounds has been discussed. The long flexible pyridyl spacers, present in all these compounds as an integral part, modulate themselves in different conformations depending on the requirement of the coordination environment.