Oligonuclear homo- and mixed-valence manganese complexes based on thiophene- or aryl-carboxylate ligation: Synthesis, characterization and magnetic studies Reda F.M. Elshaarawy a,c , Yanhua Lan b,⇑ , Christoph Janiak c,⇑ a Faculty of Science, Suez Canal University, Suez, Egypt b Institute of Inorganic Chemistry, Karlsruhe Institute of Technology, Engesserstrasse 15, 76131 Karlsruhe, Germany c Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine Universität Düsseldorf, 40204 Düsseldorf, Germany article info Article history: Received 1 November 2012 Received in revised form 5 March 2013 Accepted 8 March 2013 Available online 24 March 2013 Keywords: Manganese Thiophenecarboxylate Cluster Magnetism Mixed-valence Butterfly core abstract Mixed-valence trinuclear manganese compounds [Mn 3 O(O 2 CTh) 6 (L) x (H 2 O) y ]n(solvent) (Th = thiophene, 1CH 3 CN: L = pyridine (py), x = 3, y = 0, n = 1, solvent = CH 3 CN; 1H 2 O: L = py, x = 3, y = 0, n = 1, sol- vent = H 2 O; 2: L = py, x = 2, y = 1, n = 0.25, solvent = CH 3 CN; 3: L = 3-Mepy, x = 2, y = 1, n = 0) containing a [Mn II Mn 2 III (l 3 -O)] 6+ core have been prepared. Homo-valence tetranuclear manganese complexes (NBu n 4 )[Mn 4 O 2 (O 2 CAr) 9 (L)] (4ThCO 2 HCH 2 Cl 2 : Ar = –Th, L = EtOH; 6: Ar = –Ph, L = H 2 O; 7: Ar = –Ph-p- Me, L = H 2 O; 8CH 2 Cl 2 : –Ph-3,5-Me 2 , no L) with a [Mn III 4 (l 3 -O) 2 ] 8+ core and [Mn II Mn III 3 O 2 (O 2 CTh) 7 (bpy) 2 ] (5) were synthesized, structurally and magnetically characterized. Compounds 1–3 were obtained by comproportionation of Mn II (O 2 CMe) 2 4H 2 O with (NBu n 4 )Mn VII O 4 in aprotic pyridine (1) or aprotic/protic py/EtOH (2) or Mepy/EtOH (3) solvent mixtures. Clusters 4–8 were synthesized by comproportionation of Mn II (O 2 CAr) 2 xH 2 O/ArCOOH with (NBu n 4 )Mn VII O 4 in EtOH/CH 3 CN. X-ray structural characterization of the 2-thiophenecarboxylate (ThCO 2  ) containing compounds 1CH 3 CN, 12H 2 O and 4ThCO 2 HCH 2 Cl 2 revealed a thiophene ring disorder about the (O 2 )C–C(Th) bond so that the S atom and opposite (5–)CH group are distributed over two ring positions each. The Mn II atom in the approximately isosceles triangular [Mn II Mn 2 III (l 3 -O)] 6+ cores in 1 could be clearly assigned from bond valence sum calculations and bond distances. The [Mn 4 (l 3 -O) 2 ] 8+ core in the anionic complexes in the structures of 4ThCO 2 HCH 2 Cl 2 and 8CH 2 Cl 2 has an all Mn III oxidation level and ‘‘butterfly-like’’ arrangement. The magnetic proper- ties of 4–8 were investigated by variable temperature magnetic susceptibility and magnetization mea- surements. Similar magnetic behavior was observed for the [Mn III 4 (l 3 -O) 2 ] 8+ butterfly-core compounds 4, 6–8, with antiferromagnetic interactions between pairs of manganese ions with amplitude of 14.5 cm 1 and 4.6 cm 1 for the Mn b Mn b and Mn b Mn w coupling, respectively (b = body, w = wing). Changing the Ar-ligand size in [Mn 4 O 2 (O 2 CAr) 9 (L)]  does not have a significant effect on the magnetic properties of these butterfly clusters. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The synthesis of oligonuclear manganese clusters (Mn 3–9 ) has been stimulated by their biological role and magnetochemistry. Manganese is prominent in the active sites of many metallobio- molecules [1], and the interest is, for example, to obtain molecules that can mimic the oxygen-evolving center (OEC) of photosystem II (PSII) or photosynthetic water oxidation center (WOC) which is responsible for the photosynthesis process in the green plants and cyanobacteria [2–4]. Mn clusters possess considerable high-spin (S) ground states values with a large zero-field splitting parameter (D) (compared to other 3d transition-metal clusters) which appears to be a consequence of the presence within the Mn x aggregate of (i) ferromagnetic exchange interactions between at least two of the Mn centers [5] and/or (ii) spin frustration effects (when x P 3 and Mn x alignment in certain direction) [6,7] and (iii) Jahn–Teller distorted d 4 -Mn 3+ ions. Hence, such Mn x clusters func- tion as nanoscale magnets below their critical temperature [8]. Such Single-Molecule Magnets (SMMs) do not only display magne- tization hysteresis, but also quantum tunneling of magnetization (QTM) [9] and quantum phase interference (QPI), [10] and as such they are promising new materials for data storage and quantum computing. Oxido-centered mixed-valence trinuclear systems containing a [Mn II Mn 2 III (l 3 -O)] 6+ core and homo-valence tetranuclear manganese 0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2013.03.019 ⇑ Corresponding authors. Tel.: +49 2118112286. E-mail addresses: reda_elshaarawi@science.suez.edu.eg, Reda.El-Shaarawy@uni- duesseldorf.de (R.F.M. Elshaarawy), yanhua.lan@kit.edu (Y. Lan), janiak@uni- duesseldorf.de (C. Janiak). Inorganica Chimica Acta 401 (2013) 85–94 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica