Ru 2 M(dpa) 4 Cl 2 (M = Cu, Ni): Synthesis, Characterization, and Theoretical Analysis of Asymmetric Heterometal String Complexes of the Dipyridylamide Family

Four heterotrinuclear strings of metal atoms stabilized by dipyridylamide (dpa – ) ligands were synthesized and characterized. The metal frameworks of Ru 2 Cu(dpa) 4 Cl 2 ( 1 ), its monooxidized counterpart [Ru 2 Cu(dpa) 4 Cl 2 ]PF 6 ( 2 ), and their nickel homologues, Ru 2 Ni(dpa) 4 Cl 2 ( 3 ) and [Ru 2 Ni(dpa) 4 Cl 2 ]PF 6 ( 4 ), were shown by X‐ray diffraction to be nonsymmetric, in spite of a severe disorder affecting the metal positions. The metal string is composed of a Ru dimer with a short Ru–Ru bond that is completed with the heterometal at a longer distance from the central ruthenium atom. This nonsymmetric structure was confirmed from NMR spectroscopy. The [Ru 2 M] 6+ framework of 1 and 3 was shown from spectroelectrochemical analysis and DFT calculations to exist in the form of a mixed‐valent [Ru 2 ] 5+ moiety coupled to a formally M + heterometal. The temperature‐dependant magnetic susceptibility of these compounds is reported and interpreted by means of a model previously applied to [Ru 2 ] 5+ complexes. The redox chemistry of 1 and 3 was investigated by cyclic voltammetry, and the electronic structure of the mono‐ and dioxidized species was assigned from the observed changes in the UV/Vis spectra and from DFT calculations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)