Three oxidation states (+2, +3, +4) of an octahedral nickel center were stabilized in a newly prepared RhNiRh trinuclear complex, [Ni{Rh(apt) } ] (apt=3- aminopropanethiolate), in which the nickel center was bound by six thiolato donors sourced from two redox-inert fac-[Rh (apt) ] octahedral units. The three oxidation states of the octahedral nickel center were fully characterized by single-crystal X-ray crystallography, as well as spectroscopic, electrochemical, and magnetic measurements; all three were interconvertible, and the conversion was accompanied by changes in color, magnetism, and Jahn-Teller distortion.
The reactions of fac- [Rh(apt) Design and creation of heterometallic multinuclear complexes have long been one of the most important subjects in synthetic coordination chemistry.1 For this purpose, we have developed a metalloligand approach, in which pre-designed metal complexes with several donor sites are used as a ligand (metalloligand) instead of organic and inorganic ligands, focused on thiolato metal complexes.2 Previously, we showed that fac-[M(aminothiolato-N,S) 3 ]-type complexes act as an Sdonating metalloligand by using three thiolato groups, constructing a variety of S-bridged multinuclear structures that are largely dependent on the coordination geometries of reacting metal ions. hexanuclear complexes, respectively, the structures of which are entirely different from those derived from fac-[Rh(aet) 3 ] (Scheme 1b). To our knowledge, this is the first report that shows the drastic structural change of multinuclear structures, which is induced only by the slight change in chelate-ring sizes.A yellow powder of fac-[Rh(apt) 3 ] ([1]) was prepared from RhCl 3 ¢3H 2 O, 3-aminopropanethiol hydrochloride (Hapt¢HCl), and NaOH in water, according to a modified procedure described in the literature.8,9 Fortunately, we were able to isolate single crystals of [1] from the filtrate after removing the powder by filtration. X-ray diffraction study established that [1] has an expected mononuclear structure in fac-[Rh(apt) 3 ], in which the Rh III center is chelated by three apt ligands in an octahedral geometry, such that three thiolato donors occupy a facial position (Figure 1; av. RhN = 2.16 ¡, RhS = 2.344 ¡, N RhN = 87.2°, SRhS = 92.1°, NRhS(chelate) = 89.9°).
10Complex [1] crystallizes in a chiral space group of R3 and only the ª isomer was observed in the crystal packing. The presence of both the ¦ and ª isomers in a 1:1 ratio in the balk sample of [1] was confirmed by its silent CD spectrum.
Recently synthesized Rh-Ni trinuclear complexes hexacoordinated with sulfur ions, 3-aminopropanethiolate (apt) metalloligand [Ni{Rh(apt) 3 } 2 ](NO 3 ) n (n=2, 3, 4), are found to be chemically interconvertible between the nominal Ni 2+ and Ni 4+ states. In order to clarify the origins of their interconvertible nature and the stability of such a high oxidation state as the tetravalency from the physical point of view, we have systematically investigated the local 3d electronic structures of [Ni{Rh(apt) 3 } 2 ](NO 3 ) n by means of soft x-ray core-level absorption spectroscopy (XAS). The experimental data have been reproduced by the single-site configuration-interaction cluster-model simulations, which indicate that the charge-transferred configurations are more stable than the nominal d-electron-number configuration for n=3, 4 leading to the prominent charge-transfer effects. These are also supported by S K-edge XAS of [Ni{Rh(apt) 3 } 2 ](NO 3 ) n . Our results imply that the found charge-transfer effects have a key role to realize the interconvertible nature as well as the stability of the high oxidization state of the Ni ions.
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