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Molecular Magnets

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Front. Chem. | doi: 10.3389/fchem.2019.00096

Giant Heterometallic [Mn36Ni4]0/2- and [Mn32Co8] ‘Loops-of-Loops-and-Supertetrahedra’ Molecular Aggregates

 Maria C. Charalambous1, Eleni E. Moushi1, 2,  Tu N. Nguyen3, Constantina Papatriantafyllopoulou1, 3, 4, Vassilios Nastopoulos5, George Christou3 and  Anastasios J. Tasiopoulos1*
  • 1Department of Chemistry, University of Cyprus, Cyprus
  • 2Department of Life Sciences, European University Cyprus, Cyprus
  • 3Department of Chemistry, University of Florida, United States
  • 4School of Chemistry, National University of Ireland Galway, Ireland
  • 5Department of Chemistry, University of Patras, Greece

We report the synthesis, crystal structures and magnetic properties of the giant heterometallic [Mn36Ni4]2-/0 (compounds 1, 2) / [Mn32Co8] (compound 3) ‘loops-of-loops-and-supertetrahedra’ molecular aggregates and of a [Mn2Ni6]2+ compound (cation of 4) that is structurally related with the cation co-crystallizing with the anion of 1. In particular, after the initial preparation and characterization of compound [Mn2Ni6(μ4-Ο)2(μ3-ΟH)3(μ3-Cl)3(O2CCH3)6(py)8]2+[Mn36Ni4(μ4-Ο)8(μ3-Ο)4(μ3-Cl)8Cl4(O2CCH3)26(pd)24(py)4]2- [1] we targeted the isolation of i) both the cationic and the anionic aggregates of 1 in a discrete form and ii) the Mn/Co analogue of [Mn36Ni4]2- aggregate. Our synthetic efforts towards these directions afforded the discrete [Mn36Ni4] ‘loops-of-loops-and-supertetrahedra’ aggregate [Mn36Ni4(μ4-Ο)8(μ3-Ο)4(μ3-Cl)8Cl2(O2CCH3)26(pd)24 (py)4(Η2Ο)2] [2], the heterometallic Mn/Co analogue [Mn32Co8(μ4-O)8(μ3-O)4(μ3-Cl)8Cl2(μ2-OCH2CH3)2(O2CCH3)28(pd)22(py)6] [3] and the discrete [Mn2Ni6]2+ cation [Mn2Ni6(μ4-Ο)2(μ3-ΟH)4(μ3-Cl)2(O2CCH3)6(py)8](ClO4)(OH) [4]. The structure of 1 consists of a mixed valence [MnIII28MnII8NiII4]2- molecular aggregate that contains two MnIII8NiII2 loops separated by two MnIII6MnII4 supertetrahedral units and a [MnIII2NiII6]2+ cation based on two [MnIIINiII3(μ4-O)(μ3-OH)1.5(μ3-Cl)1.5]4+ cubane sub-units connected through both mono- and tri-atomic bridges provided by the μ4-O2- and carboxylate anions. The structures of 2 – 4 are related to those of the compounds co-crystallized in 1 exhibiting however some differences that shall be discussed in detail in the manuscript. Magnetism studies revealed the presence of dominant ferromagnetic interactions in 1-3 that lead to large ground state spin (ST) values for the ‘loops-of-loops-and-supertetrahedra’ aggregates and antiferromagnetic exchange interactions in 4 that lead to a low (and possibly zero) ST value. In particular, dc and ac magnetic susceptibility studies revealed that the discrete [Mn36Ni4] aggregate exhibits a large ST value~ 26 but is not a new SMM. Interestingly, ac magnetic susceptibility studies of the [Mn32Co8] analogue revealed the appearance of an out-of-phase tail at low T indicating the existence of slow relaxation of the magnetization possibly due to the presence of the anisotropic Co2+ ions in this compound.

Keywords: MN, Heterometallic clusters, Diols, magnetic properties, Crystal structures

Received: 04 Aug 2018; Accepted: 04 Feb 2019.

Edited by:

Albert Escuer, University of Barcelona, Spain

Reviewed by:

Jose Ramon Galan-Mascaros, Institut Català d'Investigació Química, Spain
Belen ALBELA, École Normale Supérieure de Lyon, France  

Copyright: © 2019 Charalambous, Moushi, Nguyen, Papatriantafyllopoulou, Nastopoulos, Christou and Tasiopoulos. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Anastasios J. Tasiopoulos, University of Cyprus, Department of Chemistry, Nicosia, Cyprus, atasio@ucy.ac.cy