Synthesis and coordination chemistry of tetradentate ligands containing two bidentate thioquinoline units: mononuclear complexes with Cu(I) and Cu(II), and a coordination polymer with Cu(I)

Abstract Two tetradentate ligands L 3 and L 4 have been prepared by reaction of 2 equiv. of 8-quinolinethiol with 1,2-bis(bromomethyl)benzene and 3,3′-bis(bromomethyl)biphenyl, respectively; in each case displacement of bromide by the thiolate unit affords a thioether linkage, and the two ligands accordingly have bidentate chelating quinoline/thioether units linked to a 1,2-phenyl or 3,3′-biphenyl spacer via methylene linkers. Both ligands have been structurally characterised. In L 3 the two thioquinoline units are close enough to one another for ligand to act as an N 2 S 2 -donor tetradentate chelate to a single metal ion, as shown by the structural determinations of [Cu(L 3 )][PF 6 ], a pseudo-tetrahedral, four-coordinate Cu(I) complex, and [Cu(L 3 )(MeCN)][BF 4 ] 2 , a five-coordinate Cu(II) complex with an additional MeCN ligand and a geometric τ parameter of 0.62. In contrast, reaction of L 4 with Cu(I) afforded {[Cu(L 4 )][PF 6 ]} ∞ , an infinite one-dimensional coordination polymer in which all ligands bridge two four-coordinate Cu(I) centres resulting in an MLML… alternation. Evidently, the greater separation of the bidentate termini in L 4 prevents chelation to a single metal ion. Each metal/ligand chain has a pronounced zig-zag structure; Cu⋯Cu separations between adjacent metal centres sharing a bridging ligand are approximately 12 A, but the folding of the chain is such that the separations between alternate Cu(I) centres are shorter at approximately 9 A. The chains have thioquinoline units at their periphery, and two adjacent chains interact by interleaving of these thioquinoline units to give a π-stack parallel to the direction of the chains.