Electrical Conductivity of Copper Hexamers Tuned by their Ground-State Valences.

A new design concept has been realized for the construction of molecular conductors, whereby the building unit contains a core reservoir of carriers made up of metal ions with controllable valence states and shelled by flat organic ligands having an extended π-system to promote supramolecular electronic communication. Therefore, reacting the conjugated multidentate ligand 5,5'-pyridyl-3,3'-bi-1 H-pyrazole with different copper salts solvothermally led to three interesting hexameric salts having different ground-state valences, [CuII 6 (L)4 (NO3 )(CH3 OH)2 ](NO3 )3 ·4CH3 OH, [(CH3 )2 NH2 ][CuI CuII 5 (L)4 ](SO4 )2 ·4H2 O, and [CuI 2 CuII 4 (L)4 ](NO3 )2 ·2CH3 OH. The monovalent CuII 6 salt is an insulator, but the mixed-valent CuII 5 -CuI and CuII 4 -CuI 2 salts are semiconductors. Magnetic exchange interactions up to JNN = -158 cm-1 dominate the susceptibilities and lead to ground-state spin ST = 1 (CuII 6 ), 1/2 (CuII 5 -CuI ), and 0 (CuII 4 -CuI 2 ) at 40 K. Cyclic voltammetry shows the stepwise one-electron oxidation-reduction through all the possible valence states. The theoretical calculations of the electronic and band structures of the three compounds substantiate the experimentally observed physical properties.