Recyclable chemosensor for oxalate based on bimetallic complexes of a dinucleating bis(iminopyridine) ligand

Abstract

Herein we describe bimetallic di-nickel and di-copper complexes [Ni₂(L)Br₄] (1) and [Cu₂(L)Br₄(NCMe)₂] (2) (L = (1E,1′E)-N,N′-(1,4-phenylenebis(methylene))bis(1-(6-(2,4,6-triisopropylphenyl)pyridin-2-yl)methanimine)) that bind oxalate intramolecularly to form [Ni₂(L)Br₂(C₂O₄)(NCMe)] (3) and [Cu₂(L)Br₂(C₂O₄)] (4). For the di-nickel complex 1, oxalate incorporation is accompanied by a significant colour change, from red-pink (1) to deep green (3). Mass spectrometric experiments demonstrate that the compound 1 is selective for oxalate versus related mono- and di-carboxylates tested. Oxalate can be released by the addition of slight excess of calcium bromide that forms insoluble calcium oxalate and restores the original Ni₂(L)Br₄ species. The product of the oxalate release was crystallized as [Ni₂(L)Br₄]·CaBr₂(THF)₄ species.