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

The synthesis, characterization, single crystal structures and physical properties of the compounds [Cu-2(dpa)(2)(adp)(2)](H2O)(2) (1) and [Ni-2(dpa)(2)(adp)]Cl-2 (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 center dot center dot center dot Ni contact distance is very long (1089.3 pm). 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 center dot center dot center dot Cu contact distance (831.7 pm). Magnetic susceptibility measurements of the Cu compound down to 5 K 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 5 K). (C) 2014 Elsevier Ltd. All rights reserved.