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Front. Chem. | doi: 10.3389/fchem.2019.00681

Conductive Self-Assembled Monolayers of Paramagnetic {CoIICoIII4} and {CoII4CoIII2} Coordination Clusters on Gold Surfaces

Sebastian Schmitz1,  Xinkai Qiu2, Maria Glöß3, Jan van Leusen4,  Natalya Izarova3, Muhammad A. Nadeem5, Jan Griebel1, Ryan Chiechi2, Paul Kögerler4 and  Kirill Monakhov1*
  • 1Leibniz Institute of Surface Modification (LG), Germany
  • 2University of Groningen, Netherlands
  • 3Julich Research Centre, Germany
  • 4RWTH Aachen University, Germany
  • 5Quaid-i-Azam University, Pakistan

Two polynuclear cobalt(II,III) complexes, [Co5(N3)4(N-n-bda)4(bza·SMe)2] (1) and [Co6(N3)4(N-n-bda)2(bza·SMe)5(MeOH)4]Cl (2), where Hbza∙SMe = 4-(methylthio)benzoic acid and N-n-H2bda = N-n-butyldiethanolamine, were synthesized and fully characterized by various techniques. Compound 1 exhibits an unusual, approx. C2-symmetric {CoIICoIII4} core of two isosceles Co3 triangles with perpendicularly oriented planes, sharing a central, high-spin CoII ion residing in a distorted tetrahedral coordination environment. This central CoII ion is connected to four outer, octahedrally coordinated low-spin CoIII ions via oxo bridges. Compound 2 comprises a semi-circular {CoII4CoIII2} motif of four non-interacting high-spin CoII and two low-spin CoIII centers in octahedral coordination environments. Self-assembled monolayers (SAMs) of 1 and 2 were physisorbed on template-stripped gold surfaces contacted by an eutectic gallium-indium (EGaIn) tip. The acquired current density–voltage (I–V) data revealed that the cobalt-based SAMs are more electrically robust than those of the previously reported dinuclear {CuIILnIII} complexes with Ln = Gd, Tb, Dy or Y (Schmitz et al., 2018). In addition, between 170 and 220 °C the neutral, mixed-valence compound 1 undergoes a redox modification, yielding a {Co5}-based coordination cluster (1-A) with five non-interacting, high-spin octahedral CoII centers as indicated by SQUID magnetometry analysis in combination with X-ray photoelectron spectroscopy and infrared spectroscopy. Solvothermal treatment of 1 results in a high-nuclearity coordination cluster, [Co10(N3)2(N-n-bda)6(bza·SMe)6] (3), containing ten virtually non-interacting high-spin CoII centers.

Keywords: Cobalt, magnetochemistry, Gold surface, Molecular conductivity, eutectic gallium-indium electrode

Received: 21 Aug 2019; Accepted: 01 Oct 2019.

Copyright: © 2019 Schmitz, Qiu, Glöß, van Leusen, Izarova, Nadeem, Griebel, Chiechi, Kögerler and Monakhov. 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. Kirill Monakhov, Leibniz Institute of Surface Modification (LG), Leipzig, D-04318, Lower Saxony, Germany,