Mono-, Di-, and Oligonuclear Complexes of Cu^II Ions and <i>p</i>-Hydroquinone Ligands: Syntheses, Electrochemical Properties, and Magnetic Behavior

Four highly soluble square-planar CuII and NiII complexes of siloxy-salens (2SiCu, 2SiNi) and hydroxy-salens (2Cu, 2Ni) have been synthesized. An X-ray crystal structure analysis was performed on 2SiCu, 2SiNi, and 2Ni. The compounds have been investigated by cyclic voltammetry, UV−vis−NIR spectroelectrochemistry, and EPR spectroscopy. According to these results, the monooxidized species [2SiCu]+ and [2SiNi]+ are to be classified as Robin−Day class II and III systems, respectively. Magnetic measurements on the dinuclear (PMDTA)CuII complex 1Cu2·(PF6)2 with deprotonated 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)-benzene (1) linker revealed antiferromagnetic coupling between the two CuII ions thereby resulting in an isolated dimer compound. Coordination polymers [1Cu]n(H2O)2n of CuII ions and bridging p-hydroquinone linkers were obtained from CuSO4·5H2O and 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)benzene. X-ray crystallography revealed linear chains running along the crystallographic a-direction and stacked along the b-axis. Within these chains, the CuII ions are coordinated by two pyrazolyl nitrogen atoms and two p-hydroquinone oxygen atoms in a square-planar fashion.