A Remarkable Family of Rhodium Acetonitrile Compounds Spanning Three Oxidation States and with Nuclearities Ranging from Mononuclear and Dinuclear to One-Dimensional Chains

Abstract

A series of homoleptic cations of Rh(I,II), Rh(II), and Rh(III) have been synthesized and characterized in the solid-state and in solution. Three new dinuclear compounds of dirhodium(II,II) were prepared by treatment of Rh2(O2CCH3)4(L)2 with Et3OBF4 or Me3Si(CF3SO3) in acetonitrile or propionitrile. The cations in [Rh2 II,II(MeCN)10][BF4]4 (1), [Rh2 II,II(MeCN)10][SO3CF3]4 (2), and [Rh2 II,II(EtCN)10][BF4]4 (3) contain eight equatorial RCN groups oriented in an approximately square planar arrangement around the two Rh atoms and two axial RCN molecules. The redox properties of 1−3 were investigated by cyclic voltammetry, which revealed the presence of one or two irreversible reduction(s) but no oxidations. Although there was no electrochemical evidence for an accessible oxidation, it was found that treatment of [Rh2 II,II(MeCN)10][BF4]4 with NOBF4 occurs to yield another member of the homoleptic acetonitrile family, namely, the octahedral d6 cation [RhIII(MeCN)6][BF4]3, (4). The corresponding one-electron reduction product was isolated by a slow galvanostatic reduction of [Rh2 II,II(MeCN)10][BF4]4 (1) in MeCN at a Pt electrode. The crystals harvested from the cathode were found to be the unprecedented mixed-valence 1-D chain compound [RhI,II(MeCN)4(BF4)1.5] x (5), which result from a radical polymerization of the unstable Rh2 I,II dinuclear cation. In an effort to access the final member of this series, namely, the homoleptic RhI species, the dicarbonyl compound [RhI(CO)2(MeCN)2][BF4] (6) was prepared, but all thermal and photochemical attempts to remove the CO ligands led to the conclusion that only one CO is labile. The mixed-ligand, square planar cation [RhI(CO)2(MeCN)2]+ was found to form a 1-D stack in the solid state, unlike previously reported salts with bulky counterions. For all of the compounds under investigation, infrared spectroscopy and X-ray studies were performed. The mixed-valence product was also characterized by EPR spectroscopy and SQUID magnetometry.

A paramagnetic quasi-1D chain comprised of Pt/Rh possessing an unpaired electron

“…This tetranuclear structure is basically identical with those of the previously reported ones with other amidate ligands [19][20][21][22]. The X-ray analysis revealed that four PF 6 À ions exist per one tetranuclear unit, and therefore the platinum oxidation states of 2 are +2. with Pt(+2.25) 4 mixed-valence, and the one unpaired electron is delocalized over the four platinum cores.…”

“…Pivalonitrile and sodium hexafluorophosphate were obtained from Tokyo Kasei Industrial Co. Rhodium 6 . The details of the synthetic methods were described in the previous report [18].…”

“…For the rationally synthesis of electronconducting 1-D materials, a judicious choice of mixedvalence metal complexes (Pt, Rh, etc.) is necessary [5][6][7][8][9][10][11][12][13][14][15].…”

Synthesis and Structural and Physicochemical Characterization of {[Rh2(μ‐OOCCH3)2(dmbpy)2][BF4]}n Molecular Wire

“…If the unpaired electron were in the π* orbital one might expect g ʈ Ͼ g Ќ . The EPR spectrum of complex 3 is similar to the spectra of the chain compounds [7][8][9] and [Rh 2 (NCMe) 8 ] n -(BF 4 ) 3n [12] but different to that of the discrete dinuclear paramagnetic complex [Rh 2 (µ-OOCCH 3 ) 2 (bpy) 2 (NCCH 3 ) 2 ]-[BF 4 ]. [18] It was suggested that in the latter compound the unpaired electron is delocalized over the bpy ligand.…”

“…A 2 . In this compound, the Rh-Rh distances are longer (2.8442 and 2.9277 Å), [11,12] which suggests that rhodium MWs containing carboxylato bridging ligands are more stable. This conclusion was confirmed by formation of formato complexes [Rh 4 (µ-OOCH) 4 5+ cores, respectively.…”