{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T04:47:29Z","timestamp":1787028449792,"version":"build-2736575974"},"reference-count":109,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2021,4,12]],"date-time":"2021-04-12T00:00:00Z","timestamp":1618185600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>The three complexes [Fe(opo)3], [Cu(opo)2], and [Zn(opo)2] containing the non-innocent anionic ligand opo\u2212 (opo\u2212 = 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\u2212 = 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\u2212 to FeIII electron transfer. All compounds show several electrochemical opo-centred reduction waves in the range of \u22121 to \u22123 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 \u03c0\u2013\u03c0* 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 \u03c0\u2212\u03c0* 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\u2013d 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 \u00b5M, comparable to cisplatin under the same conditions.<\/jats:p>","DOI":"10.3390\/ijms22083976","type":"journal-article","created":{"date-parts":[[2021,4,12]],"date-time":"2021-04-12T11:05:06Z","timestamp":1618225506000},"page":"3976","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["FeIII, CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand\u2014Spectroscopy, Electrochemistry, and Cytotoxic Properties"],"prefix":"10.3390","volume":"22","author":[{"given":"Katharina","family":"Butsch","sequence":"first","affiliation":[{"name":"Department f\u00fcr Chemie, Institut f\u00fcr Anorganische Chemie, Universit\u00e4t zu K\u00f6ln, Greinstra\u00dfe 6, D-50939 K\u00f6ln, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0480-7568","authenticated-orcid":false,"given":"Alexander","family":"Haseloer","sequence":"additional","affiliation":[{"name":"Department f\u00fcr Chemie, Institut f\u00fcr Anorganische Chemie, Universit\u00e4t zu K\u00f6ln, Greinstra\u00dfe 6, D-50939 K\u00f6ln, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Simon","family":"Schmitz","sequence":"additional","affiliation":[{"name":"Department f\u00fcr Chemie, Institut f\u00fcr Anorganische Chemie, Universit\u00e4t zu K\u00f6ln, Greinstra\u00dfe 6, D-50939 K\u00f6ln, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ingo","family":"Ott","sequence":"additional","affiliation":[{"name":"Institute of Medicinal and Pharmaceutical Chemistry, Technische Universit\u00e4t Braunschweig, Beethovenstrasse 55, D-38106 Braunschweig, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8229-1846","authenticated-orcid":false,"given":"Julia","family":"Schur","sequence":"additional","affiliation":[{"name":"Institute of Medicinal and Pharmaceutical Chemistry, Technische Universit\u00e4t Braunschweig, Beethovenstrasse 55, D-38106 Braunschweig, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0093-9619","authenticated-orcid":false,"given":"Axel","family":"Klein","sequence":"additional","affiliation":[{"name":"Department f\u00fcr Chemie, Institut f\u00fcr Anorganische Chemie, Universit\u00e4t zu K\u00f6ln, Greinstra\u00dfe 6, D-50939 K\u00f6ln, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,4,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"558","DOI":"10.1021\/jo01204a009","article-title":"Studies in the perinaphthalene series. 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