Combining Three Different Functional Groups in One Linker: A Variety of Features of Copper(II) Aminocarboxyphosphonate

Abstract

While metal−organic frameworks (MOFs) or, more generally, coordination polymers (CPs) built using linkers possessing two different functional groups are known very well in the literature, the effect of a third functional group on the physicochemical properties of those materials is weakly recognized. To study this issue we designed an aminocarboxyphosphonic ligand, 3-amino-5-(dihydroxyphosphoryl)benzoic acid (H 3 APB), which is an amino derivative of metaphosphonobenzoic acid. By self-assembly with a copper(II) source, we obtained the three-dimensional CP {[Cu 3 (APB) 2 -(H 2 O) 6 ]•6H 2 O} n , 1, featuring rare binodal 4,5-connected tcs topology. By comparison with previously known representatives of that topology, we put forward a hypothesis that CPs of rare topologies, such as tcs, are obtained when polytopic, differentially substituted ligands are used. The structure of 1 is layered, but not in the manner typical for "traditional" metal phosphonates and carboxyphosphonates, and it was found to be flexible; structural flexibility has been demonstrated by dehydration−hydration experiments. The structural changes were probed with the use of PXRD and IR methods. We have also shown that the copper(II) aminocarboxyphosphonate 1 presented herein has moderate capability for degradation of methylene blue, rhodamine B, and acridine orange in oxidizing conditions; however, the rate of dye degradation is greatly enhanced under visible light irradiation. Analysis of magnetic properties revealed that 1 is a spin-frustrated system with a diamond-chain arrangement of copper(II) ions. The magnetic data were fitted using the isotropic Heisenberg as well as Ising models. Both models consistently indicate that magnetic exchange paths are both antiferromagnetic and ferromagnetic, with dominating participation of the former interaction.

Exploring the Isoreticular Continuum between Phosphonate- and Phosphinate-Based Metal–Organic Frameworks

“…The combination of two or more types of binding groups in one linker is an established strategy in MOF synthesis. 28 This crystal engineering approach is promising because the introduction of an additional functional group can lead to extended functionalities, novel topologies, and enhanced chemical properties. In the case of phosphonate MOFs, the most commonly used additional coordination group is the carboxylate group.…”