Dendritic Arrays of [Re63-Se)8]2+ Core-Containing Clusters:  Exploratory Synthesis and Electrochemical Studies

The reaction between the previously reported site-differentiated cluster solvate [Re63-Se)8(PEt3)5(MeCN)](SbF6)2 (1) with pyridyl-based ditopic ligands 4,4‘-trimethylenedipyridine (2), 1,2-bis(4-pyridyl)ethane (3), and (E)-1,2-bis(4-pyridyl)ethene (4) afforded cluster complexes of the general formula [Re63-Se)8(PEt3)5(L)](SbF6)2 (57), where L represents one of the pyridyl-based ligands. Reacting these cluster complex-based ligands with the fully solvated cluster complex [Re63-Se)8(MeCN)6](SbF6)2 (8) produced dendritic arrays of the general formula {Re63-Se)8[Re63-Se)8(PEt3)5(L)]6}(SbF6)14 (911), each featuring six circumjacent [Re63-Se)8(PEt3)5]2+ units bridged to a [Re63-Se)8]2+ core cluster by the pyridyl-based ligands. Electrochemical studies using a thin-layer electrochemical cell revealed cluster-based redox events in these cluster arrays. For 9 (L = 2), one reversible oxidation event corresponding to the removal of 7 electrons was observed, indicating noninteraction or extremely weak interactions between the clusters. For 10 (L = 3), two poorly resolved oxidation waves were found. For 11 (L = 4), two reversible oxidation events, corresponding respectively to the removal of 1 and 6 electrons, were observed with the 1-electron oxidation event occurring at a potential 150 mV more positive than the 6-electron oxidation. These electrochemical studies suggest intercluster coupling in 11 via through-bond electronic delocalization, which is consistent with electronic spectroscopic studies of this same molecule.