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ELECTRONIC-STRUCTURE AND SPECTRA FOR SQUARE COMPLEXES CONTAINING SULFUR-DONOR LIGANDS - M(DTO)2(2+) (M = PT(II), PD(II) - DTO = 3,6-DITHIAOCTANE), M(SCN)4(2-) (M = PT(II), PD(II), AND M(ET-XAN)(2) (M = PT(II), PD(II), NI(II) - ET-XAN- = C2H5OCS2-)

1993-09-01
ISCI, HY
DAG, O
MASON, WR
Electronic absorption and magnetic circular dichroism (MCD) spectra in the UV visible region are reported for acetonitrile-solutions of [M(dto)2](ClO4)2, dto=3,6-dithiaoctane, M=Pt(II) and Pd(II); [(n-C4H9)4N]2[M(SCN)4], M = Pt(II) and Pd(II); and M(Et-Xan)2, Et-Xan =ethylxanthate, M=Pt(II), Pd(II), and Ni(II). The intense bands and the MCD B terms observed for the Pd(II) and Ni(II) complexes are generally assigned to ligand to metal charge transfer (LMCT) from orbitals of the S donor to the empty metal dsigma* orbital (nd(x2-y2)). However,the MCD in the region 3.8-5.0 mum-1 for the Pt(II) complexes is stronger and differs in pattern from the MCD associated with the LMCT bands and is attributed to the presence of Pt(II) localized 5d --> 6p(z) excitations. The most intense LMCT bands, which follow the energetic trend Pt(II) > Pd(II) > Ni(II), are ascribed to Ssigma --> dsigma*. Some internal ligand transitions are also identified in the spectra of the Et-Xan- complexes. The donor behavior of the dto, SCN-, and Et-Xan- ligands in the square MS4 complexes is discussed.