Silver and copper polyynides: A study with HPLC, FT-IR and XPS spectroscopy

The transformation of dicopper acetylide (Cu2C2) into Cu-polyynides has been studied carefully under different conditions. The conditions necessary and sufficient to produce Cu-polyynides involve the oxidation and the consequent Glaser coupling reaction of Cu2C2. The acid hydrolysis of unoxidized Cu2C2 does not yield polyynes as it happens for the oxidized derivative. Similarly, the acid hydrolysis of disilver acetylide (Ag2C2) does not produce polyynes. It is shown how to produce Ag-polyynides whose acid hydrolysis yield a mixture of polyynes. The liquid chromatographic analysis (HPLC) of the polyynes released both from Cu-polyynides and from Ag-polyynides are always dominated by the presence of C8H2 as the main product (70% by mol) followed by C10H2 in terms of abundance. The chemical structure of Cu-polyynides and Ag-polyynides has been investigated by FT-IR and XPS spectroscopy. The spectra suggest a rather complex polymeric structure for Cu-polyynides, which appear depleted in Cu content with respect to the theoretical at the XPS spectra with a C/Cu ratio of 5.7, although not far from the expected value of 4. On the other hand, for Ag-polyynides the spectral analysis suggests a more regular structure and indeed the XPS spectra suggest a C/Ag ratio of 4.5 in excellent agreement with the expected value of 4 deduced from the HPLC analysis of the hydrolysis products.