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A thorough characterization of the title compound, (dimim)2[Fe2Cl6(µ-O)], consisting of a (µ-oxido)-bridged binuclear iron(III) complex and 1,3-dimethylimiazolium (dimim) cation, has been performed using a wide range of techniques. The room temperature disordered crystal structure of this compound transits to an incommensurately modulated crystal structure at 100 K; to our knowledge, the first one found for an imidazolium halometallate complex. The crystal structure was solved in the superspace group PĪ(/α/β/γ)0 with modulation vector q=0.1370(10) 0.0982(10) 0.326(2) at 100 K. Variable temperature synchrotron powder x-ray diffraction showed the presence of satellite peaks in addition to the main diffraction peaks up to 208 K. Furthermore, a thermal expansion study was performed with this technique from 100 to 383 K (near of its melting point) adressing questions about the nature and consequences of the ion self-assembly of this (µ-oxido)-bridged binuclear iron(III) complex, as well as the molecular motion of the imidazolium cation within the crystalline structure as a response to the temperature effect. Finally, we present a deep magnetic study based on magnetic susceptibility, magnetization and Mössbauer measurements, where the strong antiferromagnetic exchange coupling detected is due to the occurrence of a µ-oxido bridge between the Fe(III), giving rise to an intra-dimeric antiferromagnetic exchange coupling of -308 cm-1. Financial support from Universidad de Cantabria (Proyecto Puente convocatoria 2018 funded by SODERCAN_FEDER) , Universidad del País Vasco/Euskal Herriko Unibertsitatea (GIU17/50 and PPG17/37) and Ministerio de Economia y Competividad (MAT2017-89239-C2-(1,2)-P).

Although a variety of cancers are initially susceptible to chemotherapy, they eventually develop multi-drug resistance. To overcome this situation, more effective and selective treatments are necessary using anti-tumour agents that act in two or more ways and offer greater therapeutic benefits over single-mechanism entities. In this study, we report on treating cancer with Na[3,3′-57Fe(1,2-C2B9H11)2], which offers the possibility of dual action (radiation-drug combinations) to improve the clinical benefits and reduce healthy tissue toxicity. An approach to evaluating the potential of [o-57FESAN]− to treat glioblastoma using the Mössbauer effect is presented. As the therapeutic outcomes rely on the amount and distribution of [o-57FESAN]− inside the cells, several studies, using magnetization, Mössbauer spectroscopy and nuclear microscopy techniques, were performed to ascertain the uptake of [o-57FESAN]− in U87 glioblastoma cells. [o-57FESAN]− was found to be within the cells; 29% of its uptake was in the nuclear fraction, which is a particularly desirable target, because the nucleus is the cell's control centre where DNA and the transcription machinery reside. Irradiation studies with 2D and 3D cellular models of U87 cells showed that the growth inhibition effect observed was more pronounced when [o-57FESAN]− was used in combination with the Mössbauer effect in low total dose regimens, suggesting that this procedure either alone or as adjuvant may be useful for glioblastoma treatment., This work was supported by the Spanish Ministerio de Economía y Competitividad (PID2019-106832RB-100) and the Generalitat de Catalunya (2017SGR1720) and by the Fundação para a Ciência e Tecnologia (FCT/MEC) for projects UID/MULTI/04349/2020, PTDC/BTM-TEC/29256/2017, UIDB/04565/2020, UIDP/04565/2020 (iBB/IST), LA/P/0140/2020 (Associate Laboratory Institute for Health and Bioeconomy – i4HB), PTDC/QUI-QIN/32240/2017, LISBOA-01-0145-FEDER-022096 (National Infrastructure Roadmap, LTHMFL-NECL) and GCT grant to A. C. Cerdeira (BL156/2019_IST-ID). A. B. Buades was enrolled in the PhD program of the UAB. C. I. G. Pinto is enrolled in the PhD scholarship 689 DFA/BD/07119/2020. The authors thank Dr Moulay Sougrati, Charles Gerhardt Institute, ICGM UMR 5253, Montpellier, France for a kind gift of 57FeCl2. The LMRI (Metrology Laboratory of Ionizing Radiation) team is acknowledged for their support in the X-ray irradiation setup., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).