Synthesis and spectroscopic characterization of [Rh(SeCN)(6)](3-) and trans-[Rh(CN)(2)(SeCN)(4)](3-), crystal structure of (Me4N)(3)[Rh(SeCN)(6)]

Abstract

Treatment of RhCl3 with KSeCN in acetone yields a mixture of selenocyanato-rhodates(III), from which [Rh(SeCN)(6)](3-) and trans-[Rh(CN)(2)(SeCN)(4)](3-) have been isolated by ion exchange chromatography on diethylaminoethyl cellulose. The X-ray structure determination on a single crystal of (Me4N)(3)[Rh(SeCN)(6)] (trigonal, space group R (3) over bar, a = 14.997(2), c = 24.437(3) Angstrom, Z = 6) reveals, that the compound crystallizes isotypically to (Me4N)(3)[Ir(SCN)(6)]. The exclusively via Se coordinated selenocyanato ligands are bonded with the average Rh-Se distance of 2.490 Angstrom and the Rh-Se-C angle of 104.6 degrees. In the low temperature IR and Raman spectra the metal ligand stretching modes nu(RhSe) of (n-Bu4N)(3)[Rh(SeCN)(6)] (1) and trans-(n-Bu4N)(3)[Rh(CN)(2) (SeCN)(4)] (2) are in the range of 170-250 cm(-1). In 2 nu(as)(CRhC) is observed at 479 cm(-1). The vibrational spectra are assigned by normal coordinate analysis based on the molecular parameters of the X-ray determination. The valence force constants are f(d)(RhSe) = 1.08 (1), 1.10 (2) and f(d)(RhC) = 3.14 mdyn/Angstrom (2). f(d)(RhS) = 1.32 mdyn/Angstrom is determined for [Rh(SCN)(6)](3-), which has not been calculated so far. The Rh-103 NMR resonances are 2287 (1), 1680 ppm (2) and the Se-77 NMR resonances are -32.7 (1) and -110.7 ppm (2). The Rh-C bonding of the cyano ligand in 2 is confirmed by a dublett in the C-13 NMR spectrum at 136.3 ppm