In Situ Immobilization of Metalloligands: A Synthetic Route to Homometallic Mixed-Valence Coordination Polymers

This work focuses on the investigation of targeting homometallic mixed-valence copper(I/II) Schiff base coordination polymers (CPs) via a proposed synthetic strategy, namely, in situ immobilization of metalloligands. We have designed and synthesized three structurally related isomeric Schiff base ligands, all of which contain chelating and bridging sites and, accordingly, obtained two distinctly shaped metalloligands, namely, [Cu(L1)2] (1) and [Cu(L3)2] (3a) [HL = pyridinecarbaldehyde isonicotinoyl hydrazone]. By introducing cyanide-bridging spacers to the one-pot solvothermal reactions, the copper(II) Schiff base metalloligands 1 and 3a are in situ immobilized in two diverse mixed-valence copper(I/II) Schiff base CPs, namely, [Cu4(CN)3(L1)2]n (4) and {[Cu4(CN)3(L3)2]·2.5H2O}n (6). Additionally, the formation of three unexpected CPs, namely, [Cu(L3)2]n (3b), [Cu(L2)2]n (2), and [Cu2(CN)2(HL2)]n (5), indicates that the coordinating sites of the ligands and the symmetry of the metalloligands should be taken into consideration in this synthetic algorithm.