Polarisierte Absorptionsspektren von Technetium(IV) und Rhenium(IV) in trigonalen Hexahalogenostannat(IV)-Einkristallen bei tiefer Temperatur / Polarized low temperature absorption spectra of technetium(IV) and rhenium(IV) in trigonal single crystals of h

Polarized absorption spectra of technetium(IV) and rhenium(IV) in trigonal single crystals of (C2H5NH3)2 [SnCl6] and (C2H5NH3)2[SnBr6] have been measured in the range of 8000 to 2800 Å at 298 and 77 °K. The crystal point group is D3d and the metal ions occupy sites of D3d-symmetry too. The observed excited levels arise from both π24d3 and π23d4 configurations; the different temperature and polarisation dependence of d → d intra-shell and π → d metal reduction transitions is discussed. Experimental values of the parameters Dq (cubic) and υ (trigonal) are reported. The nephelauxetic ratio β55 is evaluated from the 4A2g→2T2g intrasubshell transitions. The electron transfer spectra suggest the optical electronegativity xopt = 2.3 for Tc(IV) and xopt = 2.1 for Re(IV).