{CuII[N,N′-bis(2-aminoethyl)-2-(2-(4-pyridyl)ethyl)malondiamido(2-)]}: A Convenient Building Block for the Construction of Supramolecular Coordination Compounds Containing Exchangeable Peripheral CuII Cations

The ethylpyridino functionalized N,N′-bis(2-aminoethyl)-2-(2-(4-pyridil)ethyl)malondiamide ligand lb has been prepared, its protonation and complexation properties (toward CuII) have been studied in aqueous solution, and the pertinent constants have been determined. The ligand is able to coordinate one Cu” ion with the diamino-diamido binding unit, after the release of the two amido protons, thus forming complex 2, which still presents a free, outward-pointing pyridine unit, capable of coordinating a second metal center. Two 2 units have been appended, through their pyridine nitrogen atom, to the kinetically inert cis-Cl2PtII < fragment. The obtained supramolecular species 3 is able to release the peripheral CuII ions when the pH of the solution becomes acidic and to re-form the original complex when basicity is restored (the pertinent complexation constants have been determined). This system thus represents the first example of a supramolecular coordination compound which contains exchangeable peripheral transition metal cations. The crystal and molecular structure of 2 has been determined, disclosing the formation of “head to tail” dimers in the solid state, with an unusual coordination geometry of the CuII ions. Single-crystal X-ray diffraction data were collected with the use of Mo K± radiation: trigonal, space group P3 with a = b = 20.558(6) Å, c = 7.562(3) Å, V = 2768(2) Å3, and Z = 6 (R = 0.054, Rw = 0.058). Finally, electrochemical studies revealed that both in the separate component and in the assembled system the CuII centers are reversibly oxidizable to CuIII. In the supramolecular coordination compound, the two CuII centers weakly influence each other by means of electrostatic interactions. © 1995, American Chemical Society. All rights reserved.