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Direct reactions between CuI and isonicotinic acid (HIN) or the corresponding esters ethyl-isonicotinate (EtIN) or methyl-isonicotinate (MeIN) give rise to the formation of the coordination polymers [CuI(L)]n with L = EtIN (1), MeIN (2) and HIN (3). 1-3 show a similar structure based on a CuI double-chain in which ethyl, methyl-isonicotinate or isonicotinic acid coordinated as terminal ligands. Albeit, their supramolecular architecture differs considerably affecting the distances and angles of the central CuI double-chains and thereby their physical properties. Hence, the photoluminescence shows remarkable differences; 1 and 2 show a strong yellow emission, whereas 3 displays a weak emission; and 1 and 2 are semiconductors with moderate room temperature conductivities, whereas 3 increases its electrical conductivity up to 3×10-3 Scm-1. Additionally, 1 and 2 present an irreversible transition to a highly conducting phase with a conductivity almost 4 orders of magnitude higher and a quasi-metallic behaviour. TGA coupled to a mass spectrometer and magnetic measurements point to a partial thermally induced oxidation of the carboxylate groups of the ligands with Cu(I) to Cu(0) reduction. DFT calculations have been carried out to rationalize these observations.