Hoch oder niedrig? Zur Erlaubtheit von Spinzuständen in der Übergangsmetallchemie

Square‐Planar Ruthenium(II) Complexes: Control of Spin State by Pincer Ligand Functionalization

“…In this specific case, application to the extremely rare class of compounds with 4/5d 6 ions in square-planar Figure 8. Computed versus experimental data of magnetic susceptibility (left) and magnetization at 3.5 K (right, experimental data downscaled by 12 %) [25] for complex 6.…”

“…Also, the computed structure of 1 6 exhibits considerable deviation from a squareplanar structure (NÀRuÀCl: 158.1 8) towards a sawhorse (cis-divacant octahedral) conformation, as typically observed for four-coordinate complexes of precious metal d 6 ions. [20] Hence, to probe for a possible LS/IS spin-equilibrium, the temperature dependence of the structural parameters of 6 was further examined by single-crystal X-ray diffraction at several temperatures between 30 and 200 K.…”

“…Within the square-planar coordination geometry, that is often imposed by bulky pincer ligands, complexes of ions with d 6 metal valence electron configuration are particularly interesting, because three possible spin-states have to be considered, that is, low-spin (LS, S = 0), intermediate-spin (IS, S = 1), and high-spin (HS, S = 2). All three spin-states were reported depending on the metal ion and ligand field strength ( Figure 1).…”

“…[5] However, 2 nd and 3 rd -row metal ions generally exhibit higher ligand field stabilization and smaller interelectronic repulsion. [6] Hence, HS/IS groundstate configurations are extremely rare. Caulton and co-workers reported the square-planar ruthenium(II) disilylamido PNP pincer complex [RuCl{L Si tBu}] (1, see Scheme 1) [7] and some closely related examples.…”

Reactivity of Chromium Complexes under Spin Control

“…[20] This spin state would make chromium(I) complexes spin-compatible with the commonly found chromium(III) (d 3 ) complexes with the same spin state. This leads to the interesting speculation that an important role of the ancillary ligand in catalysts for the selective olefin trimerization is the stabilization of the reduced chromium(I) center in this intermediate S = [15b] Thus, a Cr I /Cr III catalytic cycle can remain in one spin state and would be a viable alternative to the proposed Cr II /Cr IV cycle.…”