Adipate as a tetradentate bridging ligand: Synthesis, structure and properties of Cu(II) and Ni(II) compounds with 2,2′-dipyridylamine as a terminal co-ligand

Abstract

The synthesis, characterization, single crystal structures and physical properties of the compounds [Cu2(dpa)2(adp)2](H2O)2 (1) and [Ni2(dpa)2(adp)]Cl2 (2), in which dpa=2,2′-dipyridylamine; adp=adipate(2−) anion, are presented. In both dinuclear compounds the dpa is chelating bidentately, whereas adipate acts as a tetradentate bridge between the 2 metal ions, using both carboxylate oxygen atoms as a chelate. The Cu(II) compound has 2 bridging adipate dianions, whereas the Ni(II) compound has a single bridging adipate(2−); in the latter case the charge of the dinuclear unit is compensated by 2 lattice chloride anions. The N–H of the dpa donates an intermolecular H bond to neighboring molecules; i.e. to the carboxylates for the Cu compound and to the lattice chlorides for the Ni one. In both compounds the metal ions are in a distorted octahedral geometry, and diffuse reflectance spectra agree with this geometry. The Ni⋯Ni contact distance is very long (1089.3pm). The EPR spectrum of the Cu(II) compound shows a broad signal, and no hyperfine signals are resolved; also no spin=1 signals are seen, which is in agreement with the very long dinuclear Cu⋯Cu contact distance (831.7pm). Magnetic susceptibility measurements of the Cu compound down to 5K show a very weak ferromagnetic coupling with a magnetic moment (per Cu) increasing from 1.73 B.M. (room T) to 1.88 B.M. (at 5K).