A remarkable family of rhodium acetonitrile compounds spanning three oxidation states and with nuclearities ranging from mononuclear and dinuclear toone-dimensional chains

A series of homoleptic cations of Rh(I,II), Rh(II), and Rh(III) have been s ynthesized and characterized in the solid-state and in solution. Three new dinuclear compounds of dirhodium(II,II) were prepared by treatment of Rh-2( O2CCH3)(4)(L)(2) with Et3OBF4 or Me3Si(CF3SO3) in acetonitrile or propionit rile. The cations in [Rh-2(II,II)(MeCN)(10)][BF4](4) (1), [Rh-2(II,II)(MeCN )(10)][SO3CF3](4) (2), and [Rh-2(II,II)(EtCN)(10)] [BF4](4) (3) contain eig ht equatorial RCN groups oriented in an approximately square planar arrange ment around the two Rh atoms and two axial RCN molecules. The redox propert ies of 1-3 were investigated by cyclic voltammetry, which revealed the pres ence of one or two irreversible reduction(s) but no oxidations. Although th ere was no electrochemical evidence for an accessible oxidation, it was fou nd that treatment of [Rh-2(II,II)(MeCN)(10)][BF4](4) With NOBF4 occurs to y ield another member of the homoleptic acetonitrile family, namely, the octa hedral d(6) cation [Rh-III(MeCN)(6)][BF4](3) (4) The corresponding one-elec tron reduction product was isolated by a slow galvanostatic reduction of [R h-2(II,II)(MeCN)(10)][BF4](4) (1) in MeCN at a Pt electrode. The crystals h arvested from the cathode were found to be the unprecedented mixed-valence 1-D chain compound [Rh-I,Rh-II(MeCN)(4)(BF4)(1.5)](x) (5), which result fro m a radical polymerization of the unstable Rh-2(I,II) dinuclear cation. In an effort to access the final member of this series, namely, the homoleptic Rh-I species, the dicarbonyl compound [Rh-I(CO)(2)(MeCN)(2)][BF4] (6) was prepared, but all thermal and photochemical attempts to remove the CO ligan ds led to the conclusion that only one CO is labile. The mixed-ligand, squa re planar cation [Rh-I(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-r ay studies were performed. The mixed-valence product was also characterized by EPR spectroscopy and SQUID magnetometry.