Linkage Isomerism: Synthesis, Vibrational Spectra, and Normal Coordinate Analysis of Bromothiocyanatoiridates(III) and Crystal Structure of trans-(n-Bu4N)3[IrBr2(SCN)4]

Abstract

By treatment of K(2)[IrBr(6)] with KSCN in aqueous solution, the linkage isomers trans[IrBr(2)(SCN)(4)](3-), trans-[IrBr(2)(NCS)(SCN)(3)](3-), and trans-[IrBr(2)(NCS)(2)(SCN)(2)](3-) are formed, which have been separated by ion-exchange chromatography on diethylaminoethyl cellulose (DEAE cellulose). The X-ray structure determination on a single crystal of trans-(n-Bu(4)N)(3)[IrBr(2)(SCN)(4)] (monoclinic, space group P2(1)/a, a = 18.143(3) angstrom, b = 15.352(3) angstrom, c = 23.381(2) angstrom, beta = 93.38(2)degrees, Z = 4) reveals the exclusive S-coordination of the thiocyanate groups with IrSC angles of 107.8 degrees-110.6 degrees. The torsion angles BrIrSC are 3.6 degrees-27.4 degrees. In the IR and Raman spectra, the metal ligand stretching modes are observed in distinguished ranges: v(IrS) = 260-300 cm(-1), v(IrN) = 250-265 cm(-1) and v(IrBr) = 190-235 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)(IrS) = 1.44-1.53, f(d)(IrN) = 2.10 and f(d)(IrBr) = 1.38-1.48 mdyn/angstrom.