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Rational Design of a Confacial Pentaoctahedron: Anisotropic Exchange in a Linear Zn^II Fe^III Fe^III Fe^III Zn^II Complex.

ABSTRACT: The first confacial pentaoctahedron comprised of transition metal ions namely Zn^II Fe^III _A Fe^III _B Fe^III _A Zn^II has been synthesized by using a dinucleating nonadentate ligand. The face-sharing bridging mode enforces short Zn^II ⋅⋅⋅Fe^III _A and Fe^III _A ⋅⋅⋅Fe^III _B distances of 2.83 and 2.72 Å, respectively. Ab-initio CASSCF/NEVPT2 calculations provide significant negative zero-field splittings for Fe^III _A and Fe^III _B with |D_A |>|D_B | with the main component along the C₃ axis. Hence, a spin-Hamiltonian comprised of anisotropic exchange, zero-field, and Zeeman term was employed. This allowed by following the boundary conditions from the theoretical results the simulation in a theory-guided parameter determination with J^xy =+0.37, J^z =-0.32, D_A =-1.21, E_A =-0.24, D_B =-0.35, and E_B =-0.01 cm^-1 supported by simulations of high-field magnetic Mössbauer spectra recorded at 2 K. The weak but ferromagnetic Fe^III _A Fe^III _B interaction arises from the small bridging angle of 84.8° being at the switch from anti- to ferromagnetic for the face-sharing bridging mode.

SUBMITTER: Walleck S

PROVIDER: S-EPMC8596665 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The three complexes [Fe(opo)3], [Cu(opo)2], and [Zn(opo)2] containing the non-innocent anionic ligand opo- (opo- = 9-oxido-phenalenone, Hopo = 9-hydroxyphenalonone) were synthesised from the corresponding acetylacetonates. [Zn(opo)2] was characterised using 1H nuclear magnetic resonance (NMR) spectroscopy, the paramagnetic [Fe(opo)3] and [Cu(opo)2] by electron paramagnetic resonance (EPR) spectroscopy. While the EPR spectra of [Cu(opo)2] and [Cu(acac)2] in dimethylformamide (DMF) solution are very similar, a rather narrow spectrum was observed for [Fe(opo)3] in tetrahydrofuran (THF) solution in contrast to the very broad spectrum of [Fe(acac)3] in THF (Hacac = acetylacetone, 2,4-pentanedione; acac- = acetylacetonate). The narrow, completely isotropic signal of [Fe(opo)3] disagrees with a metal-centred S = 5/2 spin system that is observed in the solid state. We assume spin-delocalisation to the opo ligand in the sense of an opo- to FeIII electron transfer. All compounds show several electrochemical opo-centred reduction waves in the range of -1 to -3 V vs. the ferrocene/ferrocenium couple. However, for CuII and FeIII the very first one-electron reductions are metal-centred. Electronic absorption in the UV to vis range are due to π-π* transitions in the opo core, giving Hopo and [Zn(opo)2] a yellow to orange colour. The structured bands ranging from 400 to 500 for all compounds are assigned to the lowest energy π-π* transitions. They show markedly higher intensities and slight shifts for the CuII (brown) and FeIII (red) complexes and we assume admixing metal contributions (MLCT for CuII, LMCT for FeIII). For both complexes long-wavelength absorptions assignable to d-d transitions were detected. Detailed spectroelectrochemical experiments confirm both the electrochemical and the optical assignments. Hopo and the complexes [Cu(opo)2], [Zn(opo)2], and [Fe(opo)3] show antiproliferative activities against HT-29 (colon cancer) and MCF-7 (breast cancer) cell lines in the range of a few µM, comparable to cisplatin under the same conditions.

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Rational Design of a Confacial Pentaoctahedron: Anisotropic Exchange in a Linear Zn^II Fe^III Fe^III Fe^III Zn^II Complex.

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Rational Design of a Confacial Pentaoctahedron: Anisotropic Exchange in a Linear ZnII FeIII FeIII FeIII ZnII Complex.

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OmicsDI is part of the ELIXIR infrastructure

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Rational Design of a Confacial Pentaoctahedron: Anisotropic Exchange in a Linear Zn^II Fe^III Fe^III Fe^III Zn^II Complex.