SINGLE-CRYSTAL EPR, CL-35, CL-37 AND N-14, N-15 ENDOR AND ESEEM STUDIES ON (PH4AS)[TCVINCL4/TCVOCL4] .2. DETERMINATION OF THE CL-35, CL-37 AND N-14, N-15 HYPERFINE AND QUADRUPOLE TENSORS BY ENDOR AND ESEEM

Single-crystal ENDOR and ESEEM studies on 35,37Cl and 14,15N nuclei are reported for the 4d1 (S= 1 2) complex (Ph4As) [TcNCl4], a spin system consisting of four 35Cl and four 37Cl nuclei (I= 3 2), and one 14N (15N) nucleus with I = 1 (I = 1 2), respectively (I(99Tc) = 9 2). The 35,37Cl spectra are characterized by different ratios of the hyperfine, nuclear Zeeman and the nuclear quadrupole interaction depending on the B0 field orientation: HQ < Hhf+HNZ, and HQ t̃ Hhf+ HNZ and HQ≫ Hhf+ HNZ. A general description of this situation is given and the characteristics of ENDOR and ESEEM are discussed. The 14N spectra are also strongly influenced by nuclear quadrupole interaction; the isotropic 14N (15N) coupling is unexpectedly large. Molecular orbital calculations (EHMO and NDDO) are made to account for the hyperfine parameters and indicate that the 14,15N coupling is mainly determined by spin polarization. The hyperfine and nuclear quadrupole couplings are used to discuss the actual symmetry and the bonding situation of the incorporated TcNCl 4- anion. For the interpretation of the quadrupole data the Townes-Dailey model has been used. © 1990.